PROYECTO INTERDISCIPLINARIO PATAGONIA AUSTRAL

PROYECTO
INTERDISCIPLINARIO
PATAGONIA AUSTRAL
1ª Reunión Internodos
Potrok Aike Maar Lake Sediment
Archive Drilling Project
1er Workshop Argentino
7 y 8 de octubre de 2010
Universidad Maimónides
Fundación de Historia Natural Félix de Azara
Buenos Aires, Argentina
PROGRAMA Y RESÚMENES
1
La provincia argentina de Santa Cruz resulta particularmente atractiva para la comunidad
científica internacional, no sólo por su geografía privilegiada sino también por la enorme
riqueza y variedad de ambientes que posee. A pesar de ello, y comparada con otras
regiones del mundo, ha sido relativamente poco estudiada.
En su extremo austral, desde el río Chalía (50°S) hasta el estrecho de Magallanes, aflora el
campo volcánico de Pali Aike. Sus manifestaciones eruptivas, generalmente alineadas en
dirección noroeste, forman parte de un volcanismo fisural que cubre 7500 km2. La particular
abundancia de maares, observables en superficie como cráteres de gran diámetro y escasa
altura, es responsable de la singular topografía que caracteriza a esta comarca enmarcada
por sucesivos arcos morénicos procedentes de los Andes y del estrecho de Magallanes.
El interior de los maares está ocupado generalmente por lagunas donde se acumulan los
sedimentos transportados por el agua de lluvia y de ablación nival, por lo que suelen ser de
escasa profundidad. Sin embargo, como caso excepcional, el más grande de los maares de
Pali Aike -la laguna de Potrok Aike- conserva aún un cuerpo de agua de 100 metros de
profundidad.
El Hemisferio Sur no cuenta con masas continentales emergidas más allá de los 40ºS, a
excepción de Patagonia, de modo que los sedimentos lacustres preservados en Potrok Aike
(52°S) constituyen uno de los escasos, y quizás únicos, registros capaces de revelar la
historia paleoambiental de elevadas latitudes.
Los estudios sísmicos realizados en la última década revelaron la existencia de un depósito
sedimentario de 300 o más metros de espesor en el interior de la laguna. Resultó evidente,
entonces que los sedimentos alojados en la Laguna Potrok Aike poseían una importancia
relevante, ya que ellos constituirían un archivo continuo e imperturbado de todas las
modificaciones climáticas y ambientales ocurridas desde el Pleistoceno medio hasta la
actualidad. Su estudio permitiría documentar y reconstruir cuali- y cuantitativamente los
cambios ocurridos en estas latitudes australes a lo largo de más de un ciclo glacial e
interglacial.
Esta fue la principal razón de la creación del proyecto internacional e interdisciplinario ICDPPotrok Aike Lake Sediment Archive Drilling Project (PASADO), en el que participamos como
investigadores principales (PI) algunos de los aquí presentes.
En marzo de 2005 se realizó en la ciudad de Río Gallegos, el 1er Workshop Internacional
ICDP-PASADO, al que fuimos convocados varios colegas argentinos, con especialidades
científicas muy diversas y procedentes de distintas instituciones del país y aún algunos
actualmente residentes en el exterior.
Ante la inminente aprobación de PASADO, cuyas operaciones comenzarían a desarrollarse
en 2008, nos enfrentábamos a la escasez de conocimientos publicados a nivel regional y
local que sirvieran de base para las interpretaciones de los datos obtenidos de los estudios
de un testigo de la magnitud del que se espera recuperar en la laguna Potrok Aike. Esa fue,
entonces, la oportunidad de descubrir que teníamos intereses comunes, así como la
voluntad de aunar esfuerzos para encarar un proyecto conjunto. Así fue como surgieron las
bases de lo que luego sería el Proyecto Interdisciplinario Patagonia Austral (PIPA), que
contó con el beneplácito de la Secretaría de Ciencia y Técnica de la Nación y luego fue
aprobado y financiado por la ANPCYT.
Para alcanzar los conocimientos básicos necesarios para la comprensión del problema, se
requería de un abordaje interdisciplinario en el que se combinara la información geológica
con los aspectos biológicos (incluyendo los antrópicos) tanto del presente como del pasado.
De esa manera, entonces, el objetivo principal de PIPA es reconstruir la historia natural de
esta cuenca, a partir de la recopilación de la información existente, la obtención de los datos
faltantes y la integración del conocimiento obtenido desde los distintos abordajes
disciplinarios involucrados.
2
Independientemente de los resultados que se obtengan en el marco de PASADO, es
indudable que el conocimiento generado por PIPA representará la línea de base a partir de
la cual podrá encararse cualquier otro tipo de estudios en la región.
Esta es la primera reunión de todos los integrantes de PIPA y de aquellos de nosotros que
también participamos en PASADO y esta será la ocasión de presentar nuestros primeros
resultados, compartir nuestros conocimientos, discutir distintos aspectos de nuestra tarea
científica y sentar las bases para el trabajo que aún resta.
Agradecemos el apoyo de varias instituciones, tanto las que financian nuestros proyectos
(CONICET, ANPCYT, UBA, UNPA, ICDP), el respaldo brindado por la Subsecretaría de
Medio Ambiente de la Provincia de Santa Cruz; como las que han brindado su auspicio para
la realización de este encuentro: el Museo Argentino de Ciencias Naturales “Bernardino
Rivadavia”, la Sociedad Argentina de Botánica. y muy especialmente a la Fundación Félix
de Azara.
Les damos una cordial bienvenida a los miembros de los distintos grupos de trabajo
involucrados en PIPA y a los representantes de PASADO y esperamos que esta reunión sea
tan fructífera como lo ha sido cada vez que nos hemos encontrado.
Nora Maidana
Hugo Corbella
3
Program
October 7th
13:00
13:30
Opening
Technical Report About the Potrok Aike Maar Lake Sediment Archive Drilling Project
(PASADO)
Zolitschka
13:50
Sediment core treatment in the PASADO project: On-site and Off-site core processing
procedures
Ohlendorf et al.
14:10
Charcoal Analysis: a methodology to reconstruct fires in natural landscapes at submillennial to decadal scales.
Bianchi & Quintana
14:30
Geological sketch of Potrok Aike area. Pali Aike voLcanic Field, southern Patagonia ,
Argentina.
Corbella et al.
14:50
Geomorphological characteristics of the Potrok Aike Lake area, Santa Cruz , Argentina
Coronato et al.
15:10
Distribution of diatoms in surface sediments of 33 lakes in southern Patagonia,
Argentina
Echazú &Maidana
15:30
Coffe break
16:00
Preliminary results of paleosecular variations studies on bottom sediments from Laguna
Potrok Aike ( Patagonia , Argentina )
Gogorza et al.
16:20
Magnetic characteristics of sediments from Laguna Potrok Aike
Gogorza et al.
16:40
Paleoclimatic Variations during the Holocene through magnetic proxies on sediments
from Laguna Potrok Aike (51°57’S, 70°24’W, Argentina )
Irurzun et al.
17:00
Geophysical preliminary results and new proposals for Laguna Potrok aike area Southern Patagonia - Argentina.
Gogorza et al.
17:20
Multiproxy reconstruction of hydrological changes during the late Holocene in Chaltel
Lake (Southern Patagonia, Argentina)
Maidana et al.
17:40
Planktonic microcrustacean (Cladocera and Copepoda) assemblages from inland
waters of the province of Santa Cruz , Argentina
Marinone & Menu-Marque
October 8th
9:00
The archaeology of Potrok Aike
Borrero et al.
9:20
Modern and subfossil chironomid (Insecta: Diptera: Chironomidae) studies for
quantitative paleoenvironmental reconstructions in southern Santa Cruz province,
4
Argentina
Orpella & Massaferro
9:40
Silicophytoliths in sedimentary sequences in the Laguna Potrok Aike, Santa Cruz,
Argentina
Osterrieth et al.
10:10
How to interpret pollen assemblages from the Patagonic steppe (49º-54ºS)
Paez
10:30
Fire History Reconstruction of southern South America
Quintana & Bianchi
10:50
Coffee break
11:10
Bioproxies of lacustrine sediments from Southern Patagonia: filling the gap on ostracod
biodiversity in the southernmost tip of South America
Ramon Mercau et al.
11:30
Paleoclimate reconstructions based on the pollen record from Laguna Potrok Aike
Schäbitz & Wille
11:50
The diatom record of Laguna Potrok Aike, Argentina
Recasens et al.
12:10
Phytolith analysis for the Potrok Aike Lake Drilling Project: Sample treatment protocols
for the PASADO Microfossil Manual
Zucol et al.
12:30
Lunch break
14:30
Living microbial activity in Lake Potrok-Aike sediments and its role during early
diagenesis
Vuillemin et al.
14:50
Insights into late Pleistocene environmental dynamics – Lithology and preliminary dating
of the lacustrine sediment record from the ICDP deep drilling site Laguna Potrok Aike,
Province of Santa Cruz (southern Patagonia, Argentina)
Zolitschka
15:10
Phytolith analysis for the Potrok Aike Lake Drilling Project: General methodologies for
analysis.
Zucol et al.
15:30
Phytolith analysis for the Potrok Aike Lake Drilling Project: Preliminary results and
current studies
Zucol et al.
15:50
Coffee break
16:10
Final discussions and closing remarks
5
The archaeology of Potrok Aike
Luis A. Borrero*, Ramiro Barberena*, Judith Charlin*, Patricia Campan**
* CONICET-IMHICIHU, Buenos Aires; ** Museo Manuel J. Molina, Río Gallegos
The Potrok Aike lake -the most reliable freshwater source during the last 15,000 years- is
located at the Pali Aike Volcanic Field, a region where some of the earliest south american
human occupations were recorded. Since the area is extremely dry, this lake was a magnet
for human populations. Two field seasons concentrated in the archaeological study of the
lake and its immediate catchment were conducted. This research was part of the “Proyecto
Interdisciplinario Potrok Aike” (PIPA). Previous information was limited to that provided by the
excavation of the Potrok Aike rockshelter, with a date of 740 + 180 14C years BP (Gómez
Otero 1993).
The initial surveys were concentrated near the lake, where preliminary sampling took place.
Given the Holocene pattern of predominant aeolian circulation from the W-SW quadrant
(Mayr et al. 2007), there are contrasting sedimentary and taphonomic conditions in the
different coasts of the lake. These variants are relevant for the archaeological assessment of
this locality. The E-NE coast is characterized by the presence of sand dunes, which usually
contains traces of human occupations related with both lithic provisioning and subsistence.
Archaeological sampling stations and transects were selected taking into account variation in
topography, substrate and distance to the lake. These recovery units also included
taphonomic information, particularly on guanaco remains (Lama guanicoe). This data base
will be used to expand the program of the Pali Aike regional taphonomy, which should be
useful in the comparison with other regions (v.g. Borrero 2001).
The study of the variation in the availability of lithic raw materials at Potrok Aike was an
important goal of this project. Again, this study is only part of a larger effort that includes Pali
Aike as well as other southern Patagonian regions (Charlin 2009a). Sampling stations for
lithic raw materials were selected at different locations and distances from the lake, and
variation in water energy was also taken into account (Figure 1). Abundance, size and quality
of the rocks were the main recorded properties. These analyses were combined with a
geoarchaeological assessment of the availability of rocks at the local fluvio-glacial deposits.
The study indicates that the lake is a high ranking locus, particularly given the large size of
the dark fine grain nodules (Charlin 2009a). These were the most used rocks at Pali Aike
during the late Holocene. We are evaluating eventual changes in their availability through
time. Peat samples covering some of the lithic deposits were collected and selected for
radiocarbon dating. One sample from the north margin produced a Modern age (LP-2168),
suggesting that the peat was formed during the last ca. 200 years. This is consistent with the
finding of stratified horse and guanaco remains above present lake level dated 65 ± 35 (Poz3589) and 160 ± 50 14C years BP (Poz-3590) [Haberzettl et al. 2005]. A buried soil was also
found. This soil was already recorded at several locations in the region and regionally
circumscribed within the last 500 years (Favier Dubois 2003 , Barberena and Borrero 2010).
An open-air stratified deposit was identified on the eastern coast of the lake and a test pit
produced lithic and bone archaeological remains (Figure 2). A bone sample was sent for
radiocarbon dating.
In addition to the ongoing study of the recovered artifacts, we began the study of an
unpublished collection obtained by Julieta Gómez Otero at Potrok Aike rockshelter. This
collection is deposited at the CENPAT (Puerto Madryn, Chubut). The synthesis of the
published and unpublished information from the rockshelter, together with the surface
materials, will help our understanding of the role of the Potrok Aike lake in the history of
human utilization of the Pali Aike Volcanic Field. Comparisons with Las Buitreras Cave
(Charlin 2009b), La Carlota Cave (Campan et al. 2007) and unpublished samples, like
6
Pescadores Rockshelter, stored at the Museo Manuel J. Molina (Río Gallegos), will help to
develop a cultural chronology for the area.
The description of rock art discovered by T. Haberzettl (pers. comm.) and ourselves within
the catchment of the lake was added to previous information recorded by Gómez Otero
(1993). This information was recently discussed in comparison with that from the rest of
Southern Patagonia (Charlin and Borrero 2010). Summing up, we expect that our studies will
help expanding our knowledge of the archaeology of this region (see Barberena 2008).
This study was sponsored by Proyecto Interdisciplinario Patagonia Austral (PIPA),
PICT/REDES 2006 Nº 02338.
References
BARBERENA, R. 2008 Arqueología y biogeografía humana en Patagonia meridional. Buenos Aires,
Sociedad Argentina de Antropología.
________ and L.A. BORRERO, 2010. Geoarqueología y distribuciones subsuperficiales de materiales
arqueológicos: localidad Cabo Vírgenes. Arqueología de Pali Aike y Cabo Vírgenes (Eds. L.A.
Borrero and J. Charlin), 103-122, CONICET-IMHICIHU, Buenos Aires
BORRERO, L.A., 2001. Regional Taphonomy. Background Noise and the Integrity of the
Archaeological Record. Ethnoarchaeology of Andean South America. Contributions to
Archaeological Method and Theory (Ed.L.A. Kuznar), pp. 243-254, International Monographs in
Prehistory, Ann Arbor
________ and J. CHARLIN. 2010. Arqueología del campo volcánico Pali Aike, Argentina. En:
Arqueología de Pali Aike y Cabo Vírgenes (Santa Cruz, Argentina). Editado por: L. A. Borrero and
J. Charlin, pp. 9-30. Buenos Aires, CONICET-IMHICIHU. ISBN: 978-987-02-4290-1
CAMPAN, P.A., F. CARBALLO MARINA and L.M. MANZI. 2007. Arqueología de Estancia La Carlota
(Campo Volcánico Pali Aike, Argentina). En prensa en Morello, F., A. Prieto, M. Martinic and G.
Bahamondes (eds.); Arqueología de Fuego-Patagonia. Levantando piedras, desenterrando
huesos… y develando arcanos. Punta Arenas, Ediciones CEQUA.
CHARLIN, J.E., 2009a. Estrategias de aprovisionamiento y utilización de las materias primas líticas en
el campo volcánico Pali Aike (Prov. Santa Cruz, Argentina). BAR International Series 1901,
Archaeopress, Oxford.
________ 2009b. A más de 30 años: otra mirada a la tecnología lítica de Las Buitreras 1 (cuenca del
río Gallegos, Santa Cruz). Intersecciones en Antropología 10: 237-248
________ and L.A. BORRERO. 2010 (in press). Rock art, inherited landscapes and human
populations in southern Patagonia. In A Companion to Rock Art, Blackwell, London.
FAVIER DUBOIS, C., 2003. Late Holocene climatic fluctuations and soil genesis in southern
Patagonia: effects on the archaeological record. Journal of Archaeological Science 30 (12): 16571664.
GÓMEZ OTERO, J., 1993. The Function of Small Rockshelters in the Magallanes IV Phase
Settlement System (South Patagonia). Latin American Antiquity 4 (4): 325-345.
HABERZETTL, T., M. FEY, A. LÜCKE, N. MAIDANA, C. MAYR, C.OHLENDORF, F. SCHÄBITZ, G.
H. SCHLESER, M. WILLE AND B. ZOLITSCHKA, 2005. Climatically induced lake level changes
during the last two millennia as reflected in sediments of Laguna Potrok Aike, southern Patagonia
(Santa Cruz, Argentina). Journal of Paleolimnology 33: 283–302
MAYR, C., M. WILLE, T. HABERZETTL, M. FEY, S. JANSSEN, A. LÜCKE, C. OHLENDORF, G.
OLIVA, F. SCHÄBITZ, G. SCHLESER AND B. ZOLITSCHKA, 2007. Holocene variability of the
southern Hemisphere Westerlies in Argentinean Patagonia (52ºS). Quaternary Science Reviews
26 (5-6): 579-584.
7
Figure 1
Figure 2
8
Charcoal Analysis: a methodology to reconstruct fires in natural
landscapes at sub-millennial to decadal scales.
Preliminary results in the framework of PIPA (MINCyT)-PASADO (ICDP)
María Martha Bianchi1 and Flavia Andrea Quintana2
1
CONICET- Centro Regional Universitario Bariloche (CRUB), Universidad Nacional del Comahue
2
(UNCO); CONICET-INIBIOMA-UNCO. Quintral 1250 (8400) San Carlos de Bariloche, Argentina.
[email protected]
Introduction
Fire is a critical Earth System process with broad impacts on atmospheric and
biogeochemical cycles (Bowman et al., 2009). Moreover, it is recognized as essential in most
ecosystems. In recent decades fire activity has increased dramatically in many parts of the
world, raising concerns about fire regimes with global warming. However, to fully understand
fire’s role in the earth system it is necessary to examine its causes and consequences over
multiple temporal and spatial scales Motivated by the need to understand recent large fires in
many parts of the world, as well as by projections that fire activity will soon exceed 20th
century levels, Paleofire science has experienced a considerable growth during the last two
decades (Bowman et al., 2009, Whitlock and Tinner, 2010).
High-resolution charcoal records from lake sediments offer the possibility to reconstruct fire
histories at watershed-scale, providing information about long term interactions between
climate and vegetation. New calibration methods have made possible to define fire regimes
(fire frequency, size, seasonality, intensity and severity) and their changes in the sedimentary
record (Long et al., 1998, Whitlock and Larsen, 2001, Higuera, 2008).
Multiproxy studies can greatly increase our knowledge of how ecosystems respond to fire,
providing information to preserve biodiversity, while the combination of multiple proxy,
empirical and modeling approaches are increasing our understanding of fire as a keystone
process in shaping the structure and function of ecosystems. Therefore, these insights are
most valuable for land management planning at different scales (Whitlock et al., 2010).
Previous research in Patagonia
In Patagonia fire is an important natural disturbance, shaping vegetation and landscape
structure, as well as a critical link between vegetation and climate change. The first charcoalbased fires histories in Southern South America were described by Calvin Heusser in Chile
(Heusser 1983) and Vera Markgraf in Argentina (Markgraf, 1983). Since then fire history is
been studied in many regions and most researchers suggest strong linkages between
climate and fire with human influence being more localized (Moreno et al., 2010 and
references therein). In Argentina, during the last two decades, projects nested in both
national and international research programs are making possible to study fire dynamics at
different latitudinal bands since latitude 34˚ to 52˚S (Bianchi et al., 2009 and references
therein).
Specific aims
1. To reconstruct the Holocene fire history of Patagonia.
2. To identify major interactions among fire activity, fuel conditions and vegetation at
different latitudinal bands.
3. To make paleofire reconstructions and contribute to paleoclimate model simulations.
Methods
Charcoal particles are the result of the incomplete burning of plant biomass. When a fire is
produced, charcoal fragments are dispersed into the atmosphere, transported at variable
9
distances, and deposited by gravity, rain and snow in lakes and bogs from where they can be
recovered for study. Sediment cores are collected and described. High-resolution charcoal
and pollen samples are extracted and analyzed using standard procedures (Whitlock and
Larsen, 2001). Historical records and dencdrochronological data, if available, are used for
calibration, while geochronological methods (210Pb, 237Cs,14C) allow to attach age - depth
models to the charcoal record. Fire ecologists contribute to the interpretation with information
on present fire regimes.
Results
Recent findings have been obtained in the following scientific Programs:
 PIPA: A network of 32 lakes have been sampled along a west-east transect to
obtained charcoal surface samples for calibrating recent fires (Quintana and Bianchi,
2010).
 PASADO: Analysis of core PASADO 5022-2,2. A total of 645 samples are being
analyzed. Preliminary results will be presented at the meeting.
References
BIANCHI, M. M., WHITLOCK, C., IGLESIAS, V., NAVARRO, D. AND QUINTANA, F. 2009. Firevegetation-climate linkages in Patagonia since Late Glacial times through pollen and charcoal
reocords of lake sediments. 1st South American Symposium on Fire Ecology and Management,
Fire Paradox 2009. 11- 13 June 2009. Centro Nacional Patagónico, Puerto Madryn, Chubut,
Patagonia, Argentina. Publicación en CD, Eufirelab e- Library: http://www.eufirelab.org.
BOWMAN, D. M .J .S., BALCH, J. K., ARTAXO, P., BOND, W. J., CARLSON, J. M.,. COCHRANE, M.
A., D’ANTONIO, C. M., DEFRIES, R. S., DOYLE, J. C., HARRISON, S. P., JOHNSTON, F. H.,
KEELEY, J. E., . KRAWCHUK, M. A., KULL, C. A., MARSTON, J. B., MORITZ, M. A.,
PRENTICE, C.I., ROOS, A. SCOTT, C., SWETNAM, T.W. , VAN DER WERF, G. R., PYNE, J.
2009. Fire in the Earth system. Science 324:481-484.
HIGUERA, P. 2008. Mc Age Depth 0.1: Probabilistic age depth model for continuous sediment
records. Montana State University. Available online from http:/www.montana.edu/phiguera.
HEUSSER,C. J., 1983. Quaternary pollen record from laguna de Tagua Tagua, Chile. Science, 219:
1429-1432.
LONG, C., WHITLOCK, C., BARTLEIN, P. J., AND MILSPAUGH, S., 1998. A 9000-year fire history
from the Oregon Coast Range, based on a high resolution charcoal study. Canadian Journal of
Forest Research 28: 774-787.
MARKGRAF, V. 1983. Late and Postglacial vegetational and paleoclimatic changes in subantarctic,
temperate and arid environments in Argentina. Palynology 7: 43-70.
________ 2008. Late Quaternary vegetation and fire history in the northernmost Nothofagus forest
region: Mallín Vaca Lauquen, Neuquén Province, Argentina. Journal of Quaternary Science.
DOI:10.1002/jqs. 1233.
MORENO, P., IGLESIAS, V., KITZBERGER, T. AND HOLTZ, A., 2010. Paleofires in southern South
America since the Last Glacial Maximum. PAGES News, 18 (2): 75-77.
QUINTANA F. A. AND BIANCHI, M. M., 2010. Macroscopic charcoal analysis from lacustrine
sediments as a methodology to reconstruct fire history: First results from Santa Cruz (50°-52°S).
Argentina. Potrok Aike Maar Lake Sediment Archive Drilling Project Terra Nostra, Schriften der
GeoUnion Alfred Wegener-Stiftung-2010 1: 56-57. ISSN 0946.8978
WHITLOCK, C. Y LARSEN, C. 2001. Charcoal as a fire proxy. En: Smol, J.P., H.J.B. Birks y M. Last
(Eds.). Tracking Environmental Change Using Lake Sediment. Volume 3: Terrestrial, Algal and
Siliceous Indicators: 75-97. Kluwer Academic Publishers. Dordrecht. The Netherlands.
________ BIANCHI, M. M., BARTLEIN, P., MARKGRAF, V., MARLON, J., WALSH, M., MCCOY, N.,
2006. Postglacial vegetation, climate and fire history along the east side of the Andes (lat 41-42.5
S), Argentina. Quaternary Research 66: 187-201
________ AND TINNER W., 2010. Editorial: Fire in the earth system. PAGES News 18 (2): 55-57.
________; HIGUERA, P. E., MC WETHY, D. M. AND BRILLES, C. E., 2010. Paleoperspectives on fire
ecology: revisiting the fire regime concept. The Open Ecology Journal, 3: 6-23.
10
GEOLOGICAL SKETCH OF LAGUNA POTROK AIKE AREA, PALI
AIKE VOLCANIC FIELD, SOUTHERN PATAGONIA, ARGENTINA.
Hugo Corbella1, Pedro Tiberi2, Bettina Ercolano2. Andrea Coronato3.
1 MACN-CONICET-UNPA, Avenida Angel Gallardo 470, 1405 Buenos Aires; 2 Universidad Nacional
de la Patagonia Austral, Unidad Académica Río Gallegos; 3 CADIC-CONICET-UNP San Juan
Bosco, B. Houssay 200, 9410 Ushuaia.
The Laguna Potrok Aike (LPA) area is located in the western flank of the Pali Aike volcanic
field, in the Magellan Basin, 300 kilometres East of the Andean volcanic front. Most of the
Pali Aike basaltic outcrops are part of a Pliocene-Holocene back-arc volcanic field.
In Pali Aike, the predominant fault systems have a NW direction, later followed by faults of EW and ENE strike. The NW fault system coincides with the direction of the underlying
Jurassic paleo-rift zone. The ENE and E-W structures were caused by a NW stretching due
to a new stress field in the southern flank of the Magellan Basin. Finally, N-S lineaments
seem to be younger structures in the area. The Potrok Aike maar is located in the vicinity of
alignments belonging to these three structural systems.
In the LPA area, structures with a NW direction controlled several volcanic alignments:
Cuatro Marías, Carlota, Clouds and Flamencos. NW structures seem to have also controlled
the old water way of the Bandurrias creek through the basaltic tableland, and a lineament
detected by magnetometry on the LPA.
One remarkable ENE structural feature crosses immediately North of LPA. This long
structural alignment is especially noticeable on the geological cartography when a Digital
Elevation Model is superimposed.
Other notorious structures are oriented in E-W direction. One is the E-W structure that
controlled the volcanic Rosario alignment; another is the normal fault that affected the deeply
eroded Petrus tableland basalts 3 km North of LPA.
In Potrok Aike the outcropping stratigraphic column is composed by: Santa Cruz Formation
deposits; deeply eroded Mio-Pliocene table basalts; morainic deposits; scoria cones, lava
flows and phreatomagmatic maar deposits; glacifluvial, fluvial, lacustrine and aeolian
deposits and distal Holocene tephras.
The Santa Cruz Formation (SCF) -the basal unit of the local stratigraphic column- crops out
in a wide area around LPA. It consists of a thick package of grey, yellowish grey or greenish
grey moderately to weakly lithified continental tuffaceous sandstones, micro-conglomerates
and siltstones, frequently with a tuffaceous matrix.
Analysing the logs of 58 exploratory oil drill-holes performed in an area 110 km E-W by 180
km N-S, the paleosurface of the Magallanes Fm. roof on which lies the SCF was modelled.
The thickness of the SCF was obtained subtracting the computed depth of the Magallanes
Fm. roof from the SCF outcropping heights.
The biggest thicknesses are 603 m, some kilometers NW from La Esperanza and 666 m, 6
km NE of LPA at the Petrobras X-1 drill-hole. The smallest is 126 m, occurring in the SE end
of Punta Loyola. The 3D reconstruction of the floor of the SCF allows to infer an E-W fault
~parallel to the Rio Gallegos and another ENE fault parallel to the Río Chico, this last
probably coincident with a long ENE alignment surveyed westwards.
Another unexpected feature is the sharp and steep deepening of the SCF basin towards the
West.
Fossil fragments of bones and osteoderms were found in sediments of the SCF outcropping
in the North beach of LPA or in its surroundings. Eduardo Tonni (UNLP) has identified the
following elements of the paleofauna:
11
Order Cingulata:
Family Dasypodidae, Subfamily Euphractinae, Tribe Eutatini, Stenotarus sp. (osteoderms).
Family Peltephilidae, Subfamily Peltephilidae, gen. et sp. indet (osteoderms).
Family Glyptodontidae, Subfamily Propalaeohoplophorinae, Propalaeohoplophorus sp.
(osteoderms).
Order Notoungulata:
Family Interatheriidae, Protypotherium sp.
Family Hegetotheriidae, Pachyrukhos sp.
According to E.Tonni the collected material is too fragmentary to establish an adjusted
chronology, but tentatively it is possible to consider that the Pachyrukhos and
Palaeohoplophorus presence could indicate middle or upper levels of the SCF and not the
lower one characterized by Notohippidense.
In brief, these paleontological considerations and the thicknesses found by drilling point out
that the outcropping beds around LPA belong to the upper sequence of the Santa Cruz
Formation.
Tableland Basalts are the oldest volcanic outcrops in Pali Aike. They form most of the
tableland landscapes that span to the North and West of LPA. These basaltic lavas, with a
thickness of 10 or more metres, lie on the SCF through a package of several metres of
reddish pyroclastic tuff, volcanic micro-breccias and agglomerates; products of eruptions of
mean explosive energy. Towards the North the outcrops of the Petrus tableland when free of
sedimentary coverage -usually bottom moraines- show a rugged relief caused by intense
glacial erosion.
Several age determinations of these tablelands basalts were obtained. Samples from the
basaltic scarps of the Petrus W tableland, just NE of the INTA station, dated by Ar/Ar on total
rock, yield 3.78 ± 0.12 My. K/Ar determinations done on samples coming from Bella Vista
tableland yield ages of 3.1 ± 0.1 My and later age analyses published by other authors yield
8.67 ± 0.15 and 9.16 ± 0.08 My.
Three km West of LPA, a dismantled pyroclastic edifice outcrops. It is composed by scoria,
lapilli, agglomerates and tuffs intruded by small and narrow dikes and appears to be
chemically and spatially related to the basaltic tableland lavas.
Cuatro Marías volcanic alignment. Immediately to the NW of the INTA experimental station,
over the INTA basaltic tableland rises a NW alignment of scoria cones of basanitic-tephritic
composition. They show an advanced stadium of dismantlement, probably due to an
emplacement during the Lower Pleistocene. Radiometric age determinations of these rocks
are in course.
Cerro Policía. On the SW shore of LPA, just by the Diego Rieche police station, the remnants
of an eroded scoria cone emerge. Its southern flank is covered by morainic sediments and
phreatomagmatic deposits; its northern uncovered scarp facing to the lake shore allows to
observe outcrops of scoriaceous and lavic facies and at lower levels sub-volcanic facies. This
basanitic edifice seems to have been also eroded by the waters of the primitive Bandurrias
creek. Its emplacement occurred before the deposit of the morainic sediments and the
formation of the Potrok Aike maar. A possible Lower Pleistocene age can be estimated.
Samples of this volcanic outcrop are being dated.
The dating obtained by Ar/Ar method on total rock for a considerably detached outcrop North
of the Bandurrias fall yields an age of 1.19 ± 0.02 My.
Carlota volcanic alignment. The Carlota volcanic alignment ~ 20 km NNW of LPA consists of
several basaltic edifices located along a NW structure. The complex is composed by small
scoria cones and a predominant edifice: the Carlota Maar. The volcanic products of these
outcrops lie over the Bella Vista tableland. But the phreatomagmatic deposits of the maar
cover not only the tableland terrains but also the adjacent steep basaltic scarp, testifying that
12
these eruptions occurred well after the tableland was severely eroded. The less degraded
morphology of the Carlota maar is remarkable.
Rosario volcanic alignment. This basaltic alignment appears 4 km SE of LPA. There, several
maars crop out in close succession conforming a chained string of depressions that in plan
looks like a rosary. The string of maars is considered due to the progressive migration of
lavas and eruptive ducts along an E-W fault plane. Some small and degraded scoria cones
outcrop inside and around the maars string. A lava sample from the North inside scarp of one
maar dated by Ar/Ar method on total rock yields 1.53 ± 0.11 My.
Sombrero Mejicano. Isolated from other volcanic edifices, the Sombrero Mejicano Complex
crops out 2 km SE of the LPA. The centre of a bowl shaped maar depression is occupied by
a scoria cone, hence its name. The eruption of this basanitic scoria cone, at present quite
degraded and eroded, seems to have been responsible for the oval fan of pyroclasts that to
the East cover former deposits. The peculiar morphology of this complex is considered due
to a drastic change in water availability during the eruptive events which switched an initial
phreatomagmatic activity to final strombolian eruptions.
The phreatomagmatic deposits of Potrok Aike Maar. Most of the preserved phreatomagmatic deposits crop out in the SE flank. Other smaller outcrops were found scattered
around to the South, Southwest, West and North of the lake. They lie above glacial
sediments and are covered by aeolian soils. The biggest outcrop, with a surface of ~ 3 km2
and a thickness of dozens of metres, presents a fine layering containing chilled juvenile
sideromelane clasts and minor tachilitic fragments, basanitic lapilli and abundant lithics such
as glacial or glacifluvial pebbles and silty-sand clasts.
Age determinations of a lapilli clast of this deposit by Ar/Ar method on total rock yield 0.77 ±
0.24 My.
Underlying Subvolcanics Bodies. Two intrusive bodies detected by seismic surveys are
indicated in the cartography. One of them, ~15 km2 large, extends to the NNE from the LPA
between depths that vary from 1000 to 700 m. The other one, smaller in surface and
detected between 2600 and 900 metres depth, stretches towards the W below Tetas de la
China. Both two have an irregular saucer shaped morphology, with almost horizontal
segments or sills alternating with inclined dikes that connect other horizontal segments. The
age and composition of these intrusions are still unknown, but if they were coeval with the
Plio-Pleistocene volcanism they could have provoked a relatively young local doming of the
overlying terrains.
Volcanic rocks composition. After microscopic inspection, 56 samples coming from different
volcanic outcrops were geochemically analysed. A brief result of these chemical and modal
analyses is summarized on TAS and spider diagrams. Except for the tableland basalts of
sub-alkaline nature, most volcanics erupted in the LPA area fall in the alkali-basalt and
basanitic fields of the total alkali SiO2 diagram. Some few plot in the tephrite field. Holocene
distal tephras found around the lake and in farther localities were also plotted.
Morphology of the Volcanic Edifices. The volcanic elevations in the neighbourhood of LPA
generally show weak slopes and characteristic features of having undergone a moderate to
severe dismantlement, product of gravity, weathering and erosion along a relatively extended
period of time.
The prevailing climatic characteristics of the area, the elapsed time since their eruption,
together with crioclastism and strong winds -characteristics of a periglacial area location- are
considered the dominant factors of the present geomorphic degradation.
It is possible to distinguish basaltic tablelands, representing the oldest volcanic outcrops,
associated to pyroclastics elevations deeply dismantled. Above these tablelands, several
younger volcanic alignments (Cuatro Marías, Carlota and others) rise up. Other alignments
and isolated volcanics younger than the tableland basalts: Cerro Policía, Rosario alignment,
Flamencos maars, Cerro Negro also outcrop; but most of them show a general degraded
13
morphology. The low angle slopes of the associated scoria cones point out that a relative
long period of time elapsed since their eruptive emplacement.
Potrok Aike Maar and Diatreme Morphology. The Potrok Aike maar has a broad and flat
morphology. The present lake (113 masl), inside the maar's diatreme, has an almost circular
shape 2.4-2.7 km phi. The entire depression is ~ 4-5 km wide and the altitude difference
between the lake level and the surrounding morainic plain is ~50 m.
The maar depression+diatreme ensemble has a champagne glass shape, which is
characteristic of maars erupting in soft-rock environments. The bedrock of the champagne
glass flat base is composed by tuffaceous sandstones and micro conglomerates of the SCF
usually covered by lacustrine sediments and paleoshoreline deposits, while the external
steep walls of the glass consist of till deposits crowned by phreatomagmatic sediments.
The present broad and gentle shore slopes and the widespread setback of the morainic
scarps that surround the lake could be assigned to the waves erosive action over the softer
glacial deposits along the period in which the water fluctuated dozen of metres up and down
the actual level.
The lower section of the diatreme, the long and narrow stem of the glass, is carved on the
underlying sediments. If, according to the nearby Petrobras X-1 drill-hole, the SCF floor lies
~600 m below the lake level, most of the diatreme vertical development must be housed in
rocks belonging to this formation.
Bathymetric contour curves obtained by the Salsa Team were digitalized and a 3D model of
the diatreme morphology was done. In spite of the mean resolution given by the available 5m
contour curves interval, in the more or less regular morphology of Potrok Aike diatreme's
walls it is possible to distinguish two different and contrasting features: a flat, weakly tilted
surface that partially contours the lake and a rugged surface at the NW corner. The first, the
gently dipping features at ~35 m depth were already assigned to a shoulder marking the
lowest lake level during Late Glacial to Holocene times. The NW wall abrupt ups and downs
suggest terrains affected by other phenomenon.
Six age determinations analyses of volcanic rocks are in progress and, for the next field
campaign, the survey of the aeolian deposits that cover broad areas and the paleomagnetic
studies of the morainic deposits are planned.
14
Geomorphological characteristics of the Laguna Potrok Aike area, Santa
Cruz, Argentina.
Andrea Coronato1,2, Bettina Ercolano3, Pedro Tiberi3, Hugo Corbella4.
1
2
CADIC-CONICET. B. Houssay 200, 9410 Ushuaia. Universidad Nacional de la Patagonia San Juan
3
Bosco. 9410 Ushuaia. Universidad Nacional de la Patagonia Austral, Unidad Académica Río
4
Gallegos. CONICET-MACN-UNPA. Avenida Ángel Gallardo 470, C1405 Buenos Aires.
The aim of this presentation is to indicate the spatial distribution and chrono-stratigraphic
relationships of the lake surroundings landforms according to morphogenetic criteria. This
geomorphological study was thought as to be a basic knowledge for the geologic, ecologic,
archeologic and paleoenvironmental researches to be undertaken in southernmost
Patagonia, specifically in the western section of the Pali Aike volcanic field (PAVF).
The recognition of the geomorphologic units was done by remote sensing and field control.
The mapping comprehended the analysis of air photograms, satellite images and SRTM
digital elevations models under SIG Arc-View 3.2a environment. Areas with homogeneous
textural patterns were identified, contours lines with variable intervals were drawn,
topographic profiles were done and enhancement was applied to better understanding the
morphology, structure and lithology of relative scarce relief zones and continuous vegetation
cover. The field surveys included GPS positioning and demarcation of routes, slope
measurements, topographic and sediment profiles drawings, rocks and sediments sampling.
It was assumed that the landscape morphology is the result of the combined action of
Miocene-Pleistocene volcanic activity and a variety of exogenous processes of Middle to
Recent Pleistocene age which occurred over a substratum of sub-horizontal friable
sedimentary rocks of Miocene age and exposed to semiarid climatic conditions.
Regional fault systems, transversal to the Andean cordillera axis, caused the channeling of
ancient rivers as the Río Gallegos and Pleistocene glaciers as those that flowed by the
Skyring and Otway sounds and the Magellan Strait. The origin of this faulting was attributed
to a NW stretch field still active during the Upper Tertiary.
After morphogenetic criteria the following relief components were distinguished:
Structural aggradation reliefs
Sub-horizontal surfaces are formed by Santa Cruz Fm. sedimentary rocks. Most of the times,
they are overlain by conglomerates of varied lithology coming from the Andean front (known
as “Rodados Patagonicos”). In some sectors, the conglomerates were covered by lava flows.
Erosion remnants are emplaced at the western side of Carlota (also named Robles) creek
establishing the limits for the extent of younger landforms as the Bella Vista volcanic
tableland and the Outwash Fan III. Undifferentiated debris deposits have been recognized at
the volcanic tablelands and basal moraines slopes. In the high and middle scarps of Bella
Vista tableland rotational slumps occur.
Volcanic genesis reliefs
- Volcanic plateaux. They are the highest topographic surfaces of this area (160 to 200 m).
They were formed by Mio-Pliocene lava flows. Over the Norte and INTA volcanic plateaux,
the Cuatro Marias small and severely eroded scoria cones outcrop.
- Scoria and spatter cones and associated lava flows. Conic edifices stand out from the low
terrains in the southern part of the studied area, reaching similar or even higher altitudes than
the cones on the basaltic plateau. Samples of scoria cones are: ¨Tetas de la China¨ (230 and
245 masl), the central cone of the "Sombrero Mejicano¨ Complex (247 masl) and ¨Cerro
Policía¨ (187 masl); whereas ¨Cerro Vigilante¨ (128 masl) is crowned by spatter deposits. All
of them have exogenous erosion features, well defined morphology and an average relief
15
~70 m. Cerro Policía also shows the destructive actions of the explosive volcanic processes
that formed the Potrok Aike maar. These volcanic morphologies developed from the Upper
Miocene to the Middle Pleistocene.
- Maars and phreatomagmatic deposits. The abundance of maars is one of the main
characteristics of PAVF. During the sudden eruptions generated by the explosive emanations
of water vapor generated by the contact of lava and underground water, the hyaloclastic
rings ¨Potrok Aike¨, ¨Flamencos¨, ¨Sombrero Mejicano¨ and "Carlota" were formed. Their
diameters vary between 0.8 to 3.5 km. The phreatomagmatic ring deposits originated by the
Potrok Aike maar appear discontinuously at the south, north and east coasts of the lake. This
is ascribed to later mass-wasting, aeolian and/or alluvial erosive processes.
Glacial genesis reliefs.
In nearly the whole studied area glacial features are present over the basaltic plateau or in
low terrains. They are related to old piedmont glaciations. In the basaltic plateaux the
outcropping rocks have polished surfaces and glacial striaes and grooves, especially notable
in plateau outcrops NNE of Lake Potrok Aike. Some volcanic cones present strong erosive
impact, too strong to be consequence of slumping, gravity or aeolian action. Some volcanic
cones emerging from the INTA and ¨Petrus W¨ plateaux show eroded outcrops like roches
moutonnées demonstrating the moving of ice over them.
- Sub-glacial moraines. These are the most frequent landforms in the area. They are found to
the North, South and East of the Lake Potrok Aike. On the ¨central Petrus¨ and ¨INTA¨
plateaux they appear as relative low level hills along a W-E direction, with glacial boulders
scattered on the surface; their size varies from 6 to 1 m in their longest axis. Some boulders
have a metaquartzitic lithology, thus their allochthonous character and glacial origin is
confirmed. The lowlands eastwards Lake Potrok Aike are formed by morainic hills with low
relative level, W-E oriented. Erratic boulders with quartz contents testify the glacial genesis of
these depressed zones. Large areas of elongated, subglacial hills are found at the lee-side of
the basaltic plateaux, so the sedimentary glacial load deposition must have been controlled
by the pre existent volcanic relief.
Till can be observed in few outcrops. It lies in unconformity on the Tertiary sedimentary
substratum. Of sub-glacial type, with a grey to light brown clayey sandy lime matrix it has
scarce contents of boulders but high contents of medium to fine gravel. This is the fraction
usually outcropping at the moraines surface. It is thought to be due to the incorporation of
“Rodados Patagónicos” gravels into the glacial load together with fine sediments, basalts and
allochthonous rocks, taken in the western glacial accumulation areas, in the Andean
environment. Once being part of the ice they were transported and re deposited as part of
the glacial sediments.
At the eastern margin of the Lake Potrok Aike, moraines with steep slopes towards the lake
are observed. Unlike the others and because of this erosion feature in the icewards side,
they are considered truncated by the explosive event that generated the maar depression
and associated mass-wasting processes.
Cryogenic features affect till and overlaying soils. In some outcrops sand-wedges
development and cryogenic involutions are visible. Medium sand deposits penetrate the till´s
clayey lime matrix forming wedges many centimeters long. All along an outcrop in the NE
part of the area, a number of wedges, separated 0.50-1 m, can be seen. This indicates the
presence of permafrost soils in a peri-glacial tundra environment developed during one of the
valley glaciations, sometime after the major piedmont glaciation 1 My ago took place.
-Outwash fans. Three levels of conical landforms along the Carlota creek and Gallegos river
have been recognized. They have S-N and SE-NW orientations and form very flat surfaces in
upper position related to the present valley bottoms; subsequent fluvial terrace levels have
also eroded in them. Level I is S-N, its formation was controlled by the base of the Bella Vista
and INTA plateaux. Its apex is formed at a valley narrowing between the Tetas de la China
16
cones (to the West) and the SW corner of the INTA plateau. The distal sector shows
evidences of later fluvial erosion. Level II develops from the narrowness between the Tetas
de la China basaltic cones; its distal part reaches the apex of Level I. It also developed a
prolongation to the NE towards the paleovalley where Lake Potrok Aike is presently located.
Both fans levels developed over a pre-existent subglacial morainic low relief with a gradual
general slope towards the E. The fans´ genesis is interpreted as the result of outwash
deposition during deglaciation stages. Level III outwash fan developed its apex in the valley
between INTA and Petrus central basaltic plateaux and extents first towards the NW and
then northwards, eroding the distal sector of outwash fan I. Later fluvial incision eroded it as
well. Its middle and distal sector lie on the first level of the Gallegos river terraces, the
northern front is visible eroded by later terrace-building processes by this river. From this
level emerges the Piche volcanic cone dated by previous author in ~ 2 My. Along the Rio
Gallegos valley the outwash fan stretches to the East over the basaltic lava flows up to the
outlet of the Cerro Vigilante valley. The ancient stream that formed this big outwash fan
flowed along a paleovalley where the Lake Potrok Aike stands and came from the morainic
front located further south, in Chilean territory. Nowadays the north and south Bandurrias
creeks flow along this paleo valley.
Fluvial genesis reliefs.
More than four terrace levels were recognized along Carlota creek, thus pointing to a
diminishing river condition given today by lower water flow. Also, four terrace levels were
identified along the Gallegos river. The building up of the Carlota creek's terraces is assigned
to periods of major water availability, due to increased precipitations or to glacial melting in
the southern morainic fronts, where the river sources are. This basin would have been
formed by the present Carlota creek and by another creek which we named Bandurrias
(North and South) which flowed along a paleo-valley presently partially occupied by the Lake
Potrok Aike. It is interpreted that it flowed at the foot of the INTA basaltic tableland, favored
by the lithological discontinuity between these basalts and the basal moraines. At the Diego
Rieche Police Station the paleostream had been dammed by phreatomagmatic deposits
during the Potrok Aike maar eruption and the main channel was separated. At present, this is
an elevated area in the paleovalley that gives a limit to the snow melting runoff flowing from
the south.
Headwards erosion and stream piracy occurred downstream the Police Station, thus the
main channel eroded its outlet at the Lake Potrok Aike. However, it springs northwards and
flows along its ancient paleovalley to Carlota creek, mainly during the snow melting season.
Lacustrine-aeolian genesis reliefs.
The Lake Potrok Aike (113 masl) is the most important in the region, though smaller
temporary ones also exist, located in maars and deflation basins carved in sedimentary
bedrock. Associated to the lake´s littoral dynamics different levels of beach ridges were
developed, many of them are now below the water level. It is considered that the highest
beach level reached 132 masl. The coincidence of this elevation with the bottom of the
paleovalley actually occupied by the Bandurrias Norte creek suggests that during the lake´s
highest level a river flowed northwards from the lake.
The aeolian processes are represented by sand plumes formation related to topographic
depressions and by mantle deposits. The largest aeolian plume is originated due to deflation
in a big depression located at the base of Bella Vista volcanic plateau. The plume rides up 70
m height and extents along 2,6 km over the plateau. Other aeolian features are deflation
basins formed on volcanic plateaux and over wide basal till plains where, occasionally, beach
crests were formed mainly related to ancient lacustrine activity during more humid conditions.
Final remarks
The study of the geomorphological characteristics of the Lake Potrok Aike surroundings
allows to establish some hypotheses on the evolution of the environment, although not
17
having yet sufficient age data makes it impossible to establish precise chronostratigraphy. It
can be inferred that between the Late Miocene, after the volcanic plateaux formation, and the
Middle Pleistocene (~ 1 My B.P.) glacial advances occurred in W-E direction mounting the
Bella Vista, INTA and Norte plateaux, eroding basalts, depositing erratic boulders and
forming sub glacial moraines in depressed paleosurfaces between the plateaux. As these
glacial features are located eastwards to the external moraines of the Bella Vista glaciation
(dated at 1 My B.P.) we suggest that one ore more glacial advances, not yet described, have
occurred in the Lake Potrok Aike region. Confirmation depends on radiometric ages of
basalts stratigraphically related to the till. The existence of a younger morainic front (Cabo
Vírgenes glaciation, ~780 ka B.P.) south of the studied area favoured the arrival of
glaciofluvial streams that increased the water supply of the rivers flowing northwards and
generating terrace systems and large glaciofluvial fans. The transitory Bandurrias South
creek is an example of these paleo rivers. Immediately after the glacial maximum, the
glaciers´ melting must have increased the underground water reservoirs by infiltration and
water retention along the regional faults (e.g. the faults intersection North of Lake Potrok
Aike). This situation must have contributed to generate the phreatomagmatic event that built
the maar, whose sediments were dated in ~770 ka B.P. The possibility that the Lake Potrok
Aike is emplaced in part of an old endorreic basin due to the presence of a small depression
of aeolian origin at its NE shore is not discarded. This depression is truncated in its western
site by the the lake and could be the remnant of a larger depression disposed close to the
intersection of the regional faults.
On going geomorphological and geological research will help to the comprehension of the
relations between glacial events, terraces formation and volcanic relief modelling under
different climatic conditions along the Quaternary.
18
Distribution of diatoms in surface sediments of 33 lakes in southern
Patagonia, Argentina
Echazú, D. M 1,2 and N. I. Maidana 1,3
1. Laboratorio de Diatomeas Continentales, Depto de Biodiversidad y Biología Experimental, FCEyN –
UBA; 2. Fellowship UBA; 3.CONICET; Email: [email protected]
Diatoms are valuable tools for paleoclimatic reconstructions due to their sensitivity to
climatically controlled environmental parameters, assuming that the organism- environment
relationships have not changed, at least since the late Quaternary. The development of
transfer functions, one of the numerical techniques more used for paleoenvironmental
reconstruction requires a "training set" developed from the survey of regional biodiversity.
Thus, environmental information collected from living forms can be extrapolated to the fossil
record.
Santa Cruz is one of the argentinian provinces least known in their non-marine algal
communities. Within the limited existing information for the province, the recent and fossil
diatoms are the group that has received most attention (Krasske, 1949, Luchini, 1975;
Maidana & Corbella, 1997; Maidana et al., 2005 and Espinosa, 2008, among others).
The development of a training set for water bodies located in the south of the province is an
indispensable tool to understand the ecological requirements of living species and provide
relevant information for understanding the evolution of past environments, not only for the
Laguna Potrok Aike sourrounding area (object of the ICDP-PASADO project), but also for the
entire Southpatagonic region. On the other hand, the results will increase significantly our
knowledge of diatom biodiversity at the region, which is of great importance in implementing
protection and conservation of natural resources strategies.
To achieve our objectives, water and surperficial face sediment samples were obtained from
33 permanent lakes and ponds in Southern Santa Cruz Province (50 º-52 º S, Fig 1) during
the two sampling campaigns (January/2009 and febrero/2010). In each environment we
measured in situ pH, temperature, water conductivity, dissolved solids and dissolved oxygen.
The chemical analysis of water samples were performed at the CNR-ISE (Italy). The diatom
analysis was conducted at the Laboratorio de Diatomeas Continentales (DBBE, FCEN-UBA)
and standard techniques were applied, including oxidation of the organic matter with H2O2
(Battarbee, 1986). Permanent slides were mounted with Naphrax®. For the taxonomic
identification of diatoms we have consulted the standard floras of Rumrich et al. (2000) and
Van de Vijver et al. (2002), as well as several other specific works. For the estimation of the
relative abundances, a minimum of 400 valves was counted per preparation.
Preliminary results
Diatom analysis of surface sediment samples collected in 2009 was completed and samples
collected in 2010 are still under study. 200 species of diatoms were identified so far, of which
17 taxa are new records for Argentina and 29 are new to the province of Santa Cruz. The
genera best represented in terms of number of species were Navicula (60), Nitzschia (33)
Gomphonema (25), Pinnularia (17). Species of the genera Staurosira, Staurosirella,
Pseudostaurosira and Stauroforma, grouped as "small fragilariod", were represented by
small individuals (always <15 µm long), very difficult to differentiate using only light
microscopy. Some species are still being studied, mainly those of the genera Navicula sensu
lato, Nitzschia and Fallacia, and probably those taxa are new to science. We have also been
identified some species apparently endemic to Patagonia, as Stauroneis nebulosa and
Veigaludwigia willeri, and Cyclotella ocellata could be considered as an invader species
coming from the Northern Hemisphere.
19
Preliminary statistical analysis suggests that the Oxygen availability and the electric
conductivity would be the variables that best explain the distribution of most abundant
diatoms (> 3%) in the studied environments.
Some taxa, mainly Navicula, Gomphonema and Nitzschia spp, could not be identified at
specific level and will be the subject of further study. Diatom species identification can be
often difficult due to the scarcity of literature on South America floras, and so to identify South
American species the researchers have to compare their materials with the descriptions
made in the Northern Hemisphere. This can led to misinterpretations because two species
may have morphological similarities but their ecological requirements may be different.
Our results confirm the importance of continuing stepping up surveys of the diversity of
phycoflora of Patagonia The high number of species new to the country and to the region,
found in this study confirm the need to intensify surveys of biodiversity of the phycoflora of
Patagonia.
A training set made with the information gathered from a significant number of lakes and
ponds will allow the development transfer functions for Southern Patagonia to be applied to
the paleoclimate and paleoenvironment reconstruction of the last 100,000 years, which is the
main objective of ICDP-PAST (Potrok Aike maar lake sediments archive drilling project)
which is part of this group research.
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Palaeoecology and Palaeohydrology. J Wiley & Sons Ltd. New York.
ESPINOSA, MA, 2008. Diatoms from patagonia and Tierra del Fuego. Developments in Quaternary
Sciences. 11: 382-392.
KRASSKE, J. 1949. Subfossile diatomeen aus den mooren Patagoniens und Feuerlands. Annales
Academiae Scientiarum Fennicae IV. Biologica 14:1-92.
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alimento de anfípodos lacustres (Lago Cardiel, Prov. Santa Cruz). Physis (B) 34(89):85-97.
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cuaternarias en un paleolago volcánico, Santa Cruz austral, Argentina. Pp. 336-340 en: Actas
del VI Congresso Brasileiro de Abequa. Curitiba, Brasil.
MAIDANA, NI.; I. IZAGUIRRE; G. MATALONI, A. VINOCUR; G. & H. PIZARRO. 2005. Diatomeas en
una transecta patagónico-antártica. Ecología Austral 15:159-176.
RUMRICH, U; H LANGE-BERTALOT & M RUMRICH. 2000. Iconographia Diatolmologica 9.
Diatomeen der Anden von Venezuela bis Patagonien/Tierra del Fuego. En: H Lange-Bertalot
(ed.). K G Gantner Verlag. Germany. 672 pp.
VAN DE VIJVER, B., Y. FRENOT & L. BEYENS. 2002. Freshwater diatoms from Ile de la Possession
(Crozet Archipelago, Subantartica). Bibliotheca Diatomologica 46: 1-412.
20
HUE
DE
S
VER CON
OLII
AZU II
OLI
RES
JUN MAD
HIJ
CAP
NIE
T OR
AG
U
L. Viedma
L. Argentino
SOS II
SOS I
CFII
CFI
RIN
ALT
BAN
MEL
R OC
SAR
CAC I
CAC II
SAL
ESP
PT A
AZU
8
33
25
7
15
DES
CFI
Navicula capitatoradiata
13
TOR
Navicula antonii
Cyclotella ocellata
Small fragilarioids
Fragilaria capuchina
9
12
9
7
ESP
Small fragilarioids
%
14
9
9
25
14
9
24
12
8
30
20
13
MEL
AZU
Nitzschia palea
Cyclotella ocellata
Small fragilarioids
Navicula antonii
Pequeñas fragilariodes
Taxón
Navicula vandami
Fragilaria capucina
5
15
7
7
10
PTA
13
%
33
Nitzschia linearis
Cocconeis placentula
Small fragilarioids
Navicula gregaria
Tabellaria sp 2
9
ROC
AGU
Navicula sp 59
Taxón
Small fragilarioids
Cavinula
pseudoscutiformis
Nitzschia sp 23
Ps subatomoides
Karayevia clevei
Small fragilarioids
Diploneis chilensis
Encyonema
microcephala
Small fragilarioids
Ach. minutissimum
SAR
%
18
CON
Taxón
Cyclotella meneghiniana
CFII
Fig 1: Geografical location of the sampling sites in Southern Santa Cruz province in the twe sampling
campaigns .
Campaign 2009: AGU: L. Agustín; AZU: L. Azul; BAN: L- Banderas; CFI: L. Cerro Frías I; CFII:
L. Cerro Frías II; CON: L. Cóndor; DES: L. del Desierto; ESP: L. Esperanza; HUE: L. Huemul;
MEL: L Mellizas; PTA: L. Potrok Aike; RES: L Torres; ROC: L Roca; SAL: L. Salada; SAR: L.
Sarmiento; TOR: L. El Toro.
Campaign 2010: ALT: L. Alta; AZU II: L. Azul II; CACI: L. Cachorro I; CACII: L. Cachorro II; CAP:
L. Capri; ERN: L. Ernesto; HIJ: L. Hija; JUN: L. Juncos; MAD: L. Madre; NIE: L. Nieta; OLI: L.
Las Lolas I; OLII: L. Las Lolas II; PAJ: L. Pajonales; RIN: L. Rincón; SOS I: L. Sosiego I; SOS II:
L. Sosiego II; VER: L. Verde.
Achnathes sp 16
Nitzschia sp 38
Nitzschia perminuta
Navicula sp 34
14
6
94
Table 1: Most abundant diatoms in the studied water bodies (Campaign 2009). The names of the
studied lakes are listed in Figure1
21
22
Preliminary Results of Paleosecular Variations Studies on Bottom
Sediments from Laguna Potrok Aike (Patagonia, Argentina)
Claudia S.G. Gogorza 1,2, M.A. Irurzun 1,2, A.M. Sinito 1,2, Christian Ohlendorf 3,
Bernd Zolitschka 3 and the PASADO Science Team
(1) CONICET; (2) Universidad Nacional del Centro, Argentina, (3) Institute of Geography (GEOPOLAR),
University of Bremen, Germany
Introduction
Paleosecular variation (PSV) records are presented for Laguna Potrok Aike. Paleomagnetic,
rock-magnetic and sedimentological studies were performed on a 16 m composed long
piston core from the 100 m deep centre of the Laguna, which represents the last 16,000
years.
This investigation contributes to the analysis of the sediment records recovered from the Pali
Aike Volcanic Field in the framework of the ICDP-project “Potrok Aike Maar Lake Sediment
Archive Drilling Project” (PASADO).
Site Description and sediments
This maar lake is located in the Province of Santa Cruz, Southern Patagonia (Argentina) (Fig.
1a and b). Roughly 80 km north of the Strait of Magellan; it is situated in the Pali Aike
Volcanic Field (51o 58’S, 70º 23’W) (Zolitschka et al., 2006).
Previous studies carried out at Laguna Potrok Aike by Haberzettl et al. (2005) reveal a
continuous and high-resolution sedimentary record. The sediment sequence is characterised
as minerogenic with only minor amounts of organic carbon and biogenic silica but with
varying contents of calcite.
Magnetic and Rock Magnetic Studies
In order to characterise these lake sediments the following measurements were carried out:
intensity and directions (D and I) of natural remanent magnetisation (nrm); magnetic
susceptibility at low frequency (specific, X and volumetric, k) and high frequency (470 and
4700 Hz); isothermal remanent magnetisation (IRM) in growing steps until 1.2T, reaching the
saturation (SIRM); back field, in growing steps until cancelling the magnetic remanence;
anhysteretic remanent magnetisation (ARM100mT), with a direct field of 0.1mT and an
alternating field varying between 2.5 and 100mT. Associated parameters were calculated: F%
((klow-khigh)*100/klow), S (IRM-300mT/SIRM), remanent coercitive field (BCR), SIRM/k, ARM100mT/k,
SIRM/ARM100mT, anhysteretic susceptibility (kanh) and kanh/k. As a first estimate of relative
magnetic grain-size variations the median destructive fields (MDFnrm, MDFARM, MDFSIRM) were
determined.
The detailed results of these studies are presented in other work focused on magnetic
characterisation of the sediments and paleoclimate variations along the sequence. A
summary of the main conclusions of rock magnetic studies follows:
Intensity of nrm varies between 0.33 and 50 mA/m, k values are between 17.6 and 271 x 10-5
SI; ARM100mT and SIRM oscillate between 72–520 mA/m and 4-14 A/m, respectively and F%
factors are between -1.7 and 3.9 (Fig. 2). The logs show coherence between them, with
correspondence in peaks and troughs in ARM100mT, SIRM and k.
Stepwise acquisition of isothermal remanence and the S-ratio indicate that low-coercivity
minerals are the dominant magnetic carriers in samples of this core, with BCR values that
agree with minerals like (titano-) magnetite.
23
The SIRM/k ratios are consistent with pseudo-single domain magnetite. The variation of
ARM100mT/k and ARM100mT/SIRM indicates reasonable uniformity of magnetic grain size along
the whole core. From the relationship between k and SIRM (Fig. 3), we can estimate that the
magnetic grain size varies between 4 and 8µm and a low concentration of ferrimagnetic
minerals, between 0.01% and 0.08% (Thompson and Oldfield, 1986).
Paleomagnetic Studies
Stability of the nrm was investigated by alternating-field demagnetisation (AF). Most of the
samples show no systematic changes in the direction of their remanent magnetisation during
AF demagnetisation; few of them have a viscous magnetisation, which could easily be
removed at about 10 mT (Fig. 4a and b). Directions of the stable remanent magnetisation
were derived using principle component analysis (Kirschvink, 1980) with successive
demagnetisation steps. Since the cores were not drilled orientated relative to magnetic north,
the D values for each core was centred on the average declination.
The nrm as well as declination and inclination logs of the characteristic remanent
magnetisation for all samples as function of calibrated ages were obtained.
Analysis of paleosecular variation
Comparison between inclination and declination records of Laguna Potrok Aike and results
obtained in previous studies carried out at lakes Escondido (Gogorza et al., 2002), Moreno
(Gogorza et al., 2000) and El Trébol (Irurzun et al., 2008), were performed.
Fig. 5 shows inclination profiles vs. calibrated ages for the above mentioned lakes and
correlation tie-lines among them. A general similar trend is observed (i.e. higher absolute
inclination value about 2500 years, shallower inclination between 3000 and 4100 years,
similar pattern between 8500 and 12500 years).
Conclusions
1. Preliminary high-resolution secular variation curves of geomagnetic inclination and
declination recorded in the lacustrine sediment from Laguna Potrok Aike for the last
16000 years were obtained. The new PSV record can be used to assess the general
characteristics of geomagnetic field variability during the studied period and to complete
the records obtained previously for these latitudes.
2. The main magnetic carriers are (titano)magnetite minerals with a grain size between 4 to 8
µm, while the mineral concentration varies between 0.01 and 0.08%.
3. The observed consistency of the PSV records from south-western Argentina confirms, in a
preliminary way, that PSV dating may be valuable on a regional scale.
References
GOGORZA, C.S.G., SINITO, A.M., DI TOMASSO, I., VILAS, J.F., CREER, K.M. NUÑEZ, H., 2000.
Geomagnetic secular variations 0-12000 year as recorded by sediments from Moreno Lake
(South Argentina). J. South Am. Earth Sci. 13, 627-645.
GOGORZA, C.S.G., SINITO, A.M., LIRIO, J.M., NUÑEZ, H., CHAPARRO, M.A.E., VILAS, J.F., 2002.
Paleosecular variations 0–19,000 years recorded by sediments from Escondido Lake
(Argentina). Phys. Earth Planet. Inter. 133, 35–55.
HABERZETTL, T., WILLE, M., FEY, M., JANSSEN, S., LÜCKE, A., MAYR, C., OHLENDORF, C.,
SCHÄBITZ, F., SCHLESER, G.H., ZOLITSCHKA, B., 2006: Environmental change and fire
history of southern Patagonia (Argentina) during the last five centuries. Quart. Int. 158, 72-82.
IRURZUN, M.A., GOGORZA, C.S.G., SINITO, A.M., CHAPARRO, M.A.E., NÚÑEZ, H., LIRIO, J.M.,
2008. Paleosecular variations 12-20 kyr. as recorded by sediments from Lake Moreno (southern
Argentina). Stud. Geophys. Geod. 52, 157–172.
KIRSCHVINK, J.L., 1980. The least-square line and plane and the analysis of paleomagnetic data.
Geophys. J. Roy. astr. Soc. 62, 699–718.
THOMPSON, R., OLDFIELD, F., 1986. Environmental Magnetism. Allen & Unwin Ltd, 225pp.
24
ZOLITSCHKA, B., SCHÄBITZ, F., LÜCKE, A., CLIFTON, G., CORBELLA, H., ERCOLANO, B.,
HABERZETTL, T., MAIDANA, N., MAYR, C., OHLENDORF, C., OLIVA, G., PAEZ, M.M.,
SCHLESER, G.H., SOTO, J., TIBERI, P., WILLE, M., 2006. Crater lakes of the Pali Aike
Volcanic Field as key sites of paleoclimatic and paleoecological reconstructions in southern
Patagonia, Argentina. J. South Am. Earth Sci. 21, 294-309.
Fig.1: (a) Geographical Location of Laguna Potrok Aike in southern Argentina; (b) Aerial photograph and bathymetric map of Laguna
Potrok Aike with locations of analysed core.
25
Fig. 2: k, nrm and F - factor logs from Laguna Potrok Aike vs. calibrated ages.
Fig. 3: k vs. SIRM plot, (Thompson and Oldfield, 1986).
26
Fig. 4: Demagnetisation plot; (a) Sample 400; (b) Sample 530
Fig. 5: Comparison of inclination records from lakes of SW of Argentina.
27
Magnetic characteristics of sediments from Laguna Potrok Aike
C.S.G. Gogorza1 C. Ohlendorf2 B. Zolitschka2
1
IFAS, Universidad Nacional Del Centro, Pinto 399, 7000 Tandil, Argentina; CONICET.
2
Institute of Geography (Geopolar), University of Bremen, Bremen, Germany
Objectives
Three composite sediment cores collected from the centre of Laguna Potrok Aike (Fig.1),
which represent a total of approximately 105 m of sediment, will be used to obtain a
continuous and well-dated record of paleomagnetic and paleoenvironmental changes for the
last ca. 50,000 years. The coring activities were carried out from August 31 to December 1,
2008 in the framework of the ICDP-project PASADO (expedition 5022). The core sections
are 74.67 m, 64.25 m, 62.09 m (Hole A, Hole B and Hole C, respectively) long with a
diameter of 60 mm collected in PVC tubes. The cores were cut into 1-2 m segments and split
into halves, they were then sealed in a vacuum process and stored at 4°C. One half of each
core was described, and then subsampled using cubic plastic boxes of 2 cm x 2 cm x 2 cm at
regular intervals, sealed and weighed for rock and paleomagnetic studies. In total, 5320
subsamples were taken and a group of 1440 was used for these studies.
In detail, the objectives for this study are:
a) To extend the paleosecular variation record into the period of the last glaciation. Creer et
al. (1983) carried out first paleomagnetic studies of sediments from Argentina. Gogorza et
al. (1999; 2000a,b; 2002) presented paleomagnetic results of sediments from Lakes
Escondido, Moreno and El Trébol of southwestern Argentina (41°S; 72°W) (Irurzun et al.,
2006) and established a regional paleosecular variation (PSV) type curve (Gogorza et al.,
2000a).
b) To reconstruct hydrological variations. Understanding the rock magnetic properties in a
sedimentary sequence and the processes involved in formation, transport, and preservation
of these magnetic minerals will lead to the identification of magnetic parameters with the
best performance as environmental proxies.
c) To investigate sources (e.g. fluvial vs. aeolian) of magnetic minerals.
d) To determine post-depositional changes in magnetic minerals caused by
diagenesis/authigenesis and by biological processes. Magnetic mineral assemblages
(combined with geochemical data) in a relatively small lake are helpful to analyze
diagenetic dissolution as a result of changing redox conditions associated with e.g.
eutrophication (Anderson and Rippey, 1988).
Methods
In order to characterise these lake sediments the following measurements were performed:
(1) intensity and directions (declination, inclination) of natural remanent magnetisation (NRM)
using a 2G high-resolution cryogenic magnetometer with RF SQUID sensors. Stability of
the magnetisation was analysed by alternating-field (AF) demagnetisation. The directions
of the stable remanent magnetisation were determined by vector analysis of the
demagnetisation results. The value of the MDFNRM, the field that is necessary to reduce
the remanent magnetisation to 50% of the NRM, was calculated;
(2) low-field susceptibility (specific, X and volumetric, k), using a Kappabridge KLY-2 (Agico)
with operating frequency of 920 Hz, and a magnetic induction of 0.4 mT;
(3) isothermal remanent magnetisation (IRM) acquisition in fields up to 0.7 T using a 2G highresolution cryogenic magnetometer with RF SQUID sensors;
28
(4) anhysteric remanent magnetisation (ARM100mT) using a 2G high-resolution cryogenic
magnetometer with RF SQUID sensors, in a peak 100 mT AF and 0.1 mT bias field.
For a set of pilot samples the hysteresis properties (such as saturation magnetisation MS,
saturation remanence MRS, coercitivity HC, coercitivity of remanence HCR and high-field
susceptibility (kh)) using a MicroMag™ Model 2900 (AGM) Alternating Gradient
Magnetometer were obtained.
The ratios ARM100mT/k, SIRM/ARM100mT and BCR (remanent coercitive field), kanh and the Sratio
were calculated. Assuming a uniform ferromagnetic mineralogy dominated by magnetite,
grain size variations can be deduced from the inter-parametric ratios kARM/k, kARM/ MRS and
MRS/k (Maher and Thompson, 1999). However, these ratios should be used as grain size
indicators with caution due to influence of dia- or paramagnetic minerals and non-linear
behaviour with concentration (Stockhausen and Zolitschka, 1999).
The magnetometer that was used in the measurements is equipped with a pneumatic autosampler which had been developed by the Marine Geophysics Section (Prof. Dr. Tilo von
Dobeneck and Dr. Thomas Frederichs, University of Bremen). The 'robot' takes sets of up to
eight samples at a time from the tray and inserts them into the magnetometer. After
completing the measurement, the 'robot' takes the sample set out again, stores it back on the
tray and continues with the next set. The exact sample sets and the type(s) of measurement
are defined by a script file that can manage up to 96 samples. This equipment is essential for
carrying out the proposed tasks due to the number of samples and measurements involved.
Preliminary Results
Magnetic and rock magnetic studies
Fig. 2 shows MDFNRM, k, NRM intensity, ARM100mT and SIRM logs of the 5022-1A. These
parameters and k were measured for the three sequences and all show similar
characteristics. There is a good consistency between k, ARM100mT and SIRM logs for each
sequence, implying that the behaviour of these parameters is mainly controlled by changes in
the concentration of the magnetic minerals. NRM intensity varies between 5 and 240 mA/m,
k varies between 195 and 7016×10−6 SI. ARM100mT and SIRM vary between 15-490 mA/m
and 2-60 A/m, respectively.
Stepwise acquisition of isothermal remanence in fields up to 2.5 T shows that about 90% of
the SIRM is obtained between 150 and 250 mT. These results indicate that low-coercitivity
minerals are the dominant magnetic carriers in samples of these cores. Progressive removal
of this SIRM by back-field demagnetisation indicates BCR between 20 and 75 mT. The values
of BCR, a little higher than the characteristic average value of pure magnetite (between 8 and
60 mT; Peters and Dekkers, 2003), may be explained by the presence of oxidised
titanomagnetite (Kruiver et al., 2001; Roberts and Turner, 1993; Reynolds et al., 1994) and/or
antiferromagnetic minerals in low concentrations, or by the relative decrease in the grain
size. Sratio, which reflects the variations in the coercivities of the magnetic carrier minerals
(Meynadier et al., 1992), varies between 0.9 and 1.
Changes in the ratios ARM100mT/k and ARM100mT/SIRM imply changes in grain size, higher
ratios indicating smaller grain size and a higher proportion of single-domain (SD) grains
(Hunt et al., 1995). Fig. 3 shows that the variation of ARM100mT/k and ARM100mT/SIRM is about
a factor 3. This finding also indicates reasonable uniformity of magnetic grain size along the
whole core. The SIRM/k (Fig. 3) ratios are between 5 and 15 kA/m (average 8.01±0.09
kA/m), these SIRM/k ratios are consistent with predominance of pseudo-single (PSD)/multi
domain (MD) magnetite (Thompson and Oldfield, 1986).
From Fig. 3, which shows k versus SIRM for samples of 5022-1A we can estimate that the
magnetic grain size varies approximately between 4 and 16 µm and the concentration is
between 0.01 and 0.5% (Thompson and Oldfield, 1986).
29
Hysteresis parameters are useful for determining grain size and domain state of magnetite
particle (Day et al., 1977). The hysteresis ratios are consistent with a dominant low-coercivity
ferrimagnetic component (most likely magnetite) that is of PSD/MD range magnetic grain
size.
Paleomagnetic Studies
In order to test the stability of the NRM and to remove any viscous overprints, progressive
alternating field (AF) demagnetisation was carried out. Pilot samples were demagnetised
successively at 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 and 100 mT peak field. A
representative example of a demagnetisation plot is shown in Fig. 4. The MDFNRM varies from
4 to 47 mT (average 14.1±0.2 mT in 5022-1A; average 14.2±0.2 mT in 5022-1B and average
14.3±0.2 mT in 5022-1C).
The orthogonal demagnetisation (Zijderveld) diagrams are shown in Fig. 4. In general, we
observe straight lines that passed through the origin of the demagnetisation diagram,
indicating a single component, stable characteristic remanent magnetisation (e.g. sample
5022-1A - 408). A limited number of samples show a small viscous remanent magnetisation
(VRM) that is progressively destroyed at 10–15 mT. Further steps revealed a high stability of
the directions of magnetisation. Taking these results into account, all samples were
demagnetised at 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 70 and 100 mT.
The directions of the characteristic remanent magnetisation were obtained, using principle
component analysis (Kirschvink, 1980), from the results of successive demagnetisation
steps. To avoid influence of VRM, the results of NRM and the first three demagnetisation
steps (5, 10 and 15 mT), on the other hand, the last two to three steps (70-100 mT) were not
used for the vector analysis if they represented spurious data. A preliminar plot of inclination
vs. number of sample for the three holes is shown.
References
ANDERSON, N.J. & RIPPEY, B. Diagenesis of magnetic minerals in the recent sediments of
a eutrophic lake. Limnology and Oceanography 33 (6): 1476-1492, 1988.
CREER, K. M., VALENCIO, D. A., SINITO, A. M., TUCHOLKA, P. & VILAS, J. F.
Geomagnetic Secular Variations 0-14000 yr. BP as recorder by lake sediments from
Argentina 74(1): 109-222, 1983.
DAY, R.M., FULLER, D. & SCHMIDT, V.A. Hysteresis properties of titanomagnetite: Grain
size and composition dependence. Physical of the Earth and Planetary Interiors 13: 260–
266, 1977.
GOGORZA, C.S.G., SINITO, A.M., DI TOMMASO, I., VILAS, J.F., CREER, K.M. & NUÑEZ,
H. Holocene geomagnetic secular variations recorded by sediments from Escondido Lake
(South Argentina). Earth, Planets and Space 51(2): 93-106, 1999.
GOGORZA, C.S.G., SINITO, A.M., VILAS, J.F., CREER, K.M., NUÑEZ, H. Geomagnetic
secular variations 0-6500 yr. as recorded by sediments from lakes of South Argentina.
Geophysical Journal International 143(3): 787-798, 2000a.
GOGORZA, C.S.G., SINITO, A.M., Di Tommaso, I., Vilas, J.F., Creer, K.M., Nuñez, H.
Geomagnetic secular variations 0-12000 yr. as recorded by sediments from Moreno Lake
(South Argentina). Journal of South American Earth Sciences 13(7): 627-645, 2000b.
Gogorza, C.S.G., Sinito, A.M., Lirio, J.M., Nuñez, H., Chaparro, M.A.E., Vilas, J.F.
Paleosecular variations 0-19,000 years recorded by sediments from Escondido lake
(Argentina). Physical of the Earth and Planetary Interiors 133(1-4): 35-55, 2002.
IRURZUN, M.A., GOGORZA, C.S.G., SINITO, A.M., LIRIO, J.M., NUÑEZ, H., CHAPARRO,
M.A.E. Paleosecular variations recorded by Holocene-Pleistocene sediments from lake El
Trébol (Patagonia, Argentina). Physical of the Earth and Planetary Interiors 154: 1-17,
2006.
KIRSCHVINK, J.L. The least-square line and plane and the analysis of paleomagnetic data.
Geophysical Journal of the Royal Astronomical Society 62: 699–718, 1980.
30
KRUIVER, P.P., DEKKERS, M.J., HESLOP, D. Quantification of magnetic coercivity
components by the analysis of acquisition curves of isothermal remanent magnetisation.
Earth and Planetary Science Letters 189: 269–276, 2001.
MAHER, B.A. AND THOMPSON, R. (Eds.). Quaternary climates, environments and
magnetism. Cambridge University Press. Cambridge, 390 pp., 1999.
MEYNADIER, L., VALET, J.P., WEEKS, R., SHAKLETON, N.J., HAGEE, V.L. Relative
geomagnetic intensity of the field during the last 140 ka. Earth and Planetary Science
Letters 114: 39–57, 1992.
PETERS, C., DEKKERS, M.J. Selected room temperature magnetic parameters as a
function of mineralogy, concentration and grain size. Physics and Chemistry of the Earth
28: 659–667, 2003.
REYNOLDS, R.L., TUTTLE, M.L., RICE, C.A., FISHMAN, N.S., KARACHEWSKI, J.A.,
SHERMAN, D.M. Magnetization and geochemistry of greigite-bearing Cretaceous strata,
North Slope Basin, Alaska. American Journal of Science 294: 485–528, 1994.
ROBERTS, A.P., TURNER, G.M. Diagenetic formation of ferrimagnetic iron sulphide
minerals in rapidly deposited marine sediments, New Zealand. Earth and Planetary
Science Letters 115: 257–273, 1993.
STOCKHAUSEN, H., ZOLITSCHKA, B. 1999. Environmental changes since 13,000 cal. BP
reflected in magnetic and sedimentological properties of sediments from Lake Holzmaar
(Germany). Quaternary Science Reviews 18: 913-925, 1999.
THOMPSON, R., OLDFIELD, F. Environmental Magnetism. Allen & Unwin Ltd, p. 225, 1986.
Figure 1
31
Figure 2
Figure 3
32
Paleoclimatic Variations During the Holocene Through Magnetic
Proxies on Sediments from Laguna Potrok Aike (51°57’S, 70°24’W,
Argentina).
María A. Irurzun1,4, Claudia S. G. Gogorza1,4, Ana M. Sinito1,4, Daniel Aguilar1,
Christian Ohlendorf2, Bernd Zolitschka2, PASADO Science Team3
1. Universidad Nacional del Centro de la Provincia de Buenos Aires. Contacting person:
[email protected]. 2. Institute of Geography (GEOPOLAR), University of Bremen,
Germany. 3. http://www.icdp-online.org/front_content.php?idcat=1494
4. CONICET, Argentina.
Introduction
Lake sediments are excellent sources for many different paleoenvironmental and
paleoclimatic information as they provide continuous and high-resolution records. They are
also first class recorders of magnetic parameters widely used around the world as proxies for
paleoenvironmental variations, because every change in the catchment area (rainfall and
drought periods, temperature changes, differences in sedimentation rates) is likewise
reflected in variations of the magnetic parameters.
Relationships between magnetic parameters, total organic carbon, total inorganic carbon,
different elements, gastropods (Haberzettl et al., 2007), pollen (Wille et al., 2007) and diatom
frustules (Mayr et al., 2009) were analysed to infer lake level changes and to suggest related
hydrological and climate fluctuations. The results from these previous studies suggest a dry
period around 11600 cal BP and periods of moister environment at the beginning of the
Holocene followed by drier conditions between 8700 and 6000 cal BP, and then an increase
of available moisture. A lower lake level event was recognized around 7000 cal BP and
periodic changes among low and high lake levels were identified for the last 1500 cal BP with
a particular high lake level between 500 and 150 cal BP which is attributed to the “Little Ice
Age (LIA)”.
Site description
Laguna Potrok Aike is located in southern Santa Cruz, Argentina (51°37’S, 69°10’W, Fig. 1).
Is a maar lake, permanently water-filled lacustrine system in the Patagonian steppe, with a
current water depth of around 100 m. Precipitation (200 mm/yr) is equally distributed around
the wind rose. There is no stratification of the lake because of the strong winds (50% from
the west) that enforce polymictic conditions in summer and inhibit freezing in winter.
Temperatures during summer time reach 10–12°C. Currently, the 3470 m wide circular lake
has no surface outflow. This lake responds very sensitively to changes in the
precipitation/evaporation ratio, with rising/falling lake levels in times of wetter/drier climatic
conditions (Haberzettl et al., 2007).
Materials and methods
This work was carried out on three piston cores collected from the centre of Laguna Potrok
Aike (Fig. 1). The cores (PTA02/3, PTA03/12 and PTA03/13) form a composite core for the
past 16000 cal BP, but only the Holocene period is studied in this work.
The following measurements were performed on sub-samples from 11700 cal. BP to the
present: magnetic susceptibility (specific χ, and volumetric, k); isothermal remanent
magnetisation reaching the saturation (SIRM); back-field in growing steps until cancelling the
magnetic remanence; anhysteretic remanent magnetisation (ARM100mT), with a direct field of
0.1 mT and a peak alternating field of 100 mT. Associated parameters also were calculated:
S-ratio (IRM-300mT/SIRM), %soft IRM ((SIRM-IRM-40mT)/SIRM), frequency-dependence
magnetic susceptibility (F-factor=(klow frecuency-khigh frecuency)*100/klow frecuency), coercivity
remanence (BCR), anhysteretic susceptibility (kanh) and interparametric ratios (ARM/SIRM,
kanh/k, ARM/k).
33
Rock Magnetic Studies
The IRM curves (Fig. 2A) show that the saturation of the isothermal magnetization is
obtained with an applied field of about 300 mT and the BCR are between 30 and 50 mT,
suggesting the presence of magnetite as a magnetic carrier of the samples. BCR (Fig. 2B)
depends on the composition of the sample and the magnetic grain size. This parameter show
more conspicuous variations during the late Holocene and a trend to lower values since 4500
cal BP. According to Peters and Dekkers (2003) all the samples are located in the region for
(titano) magnetite (Fig. 2C). To determine magnetic grain size, the interparametric ratios
were calculated. Higher/lower ratio indicates finer/coarser magnetic grain size. Fig. 2D shows
an stable behaviour from 11700 to 5000 cal BP and a tendency to finer magnetic grain size
since 5000 cal BP, in both cases there is a superimposed oscillatory behaviour more evident
in kanh/k.
Fig. 3 show all the results obtained from magnetic studies and a summary of the results from
previous works. F-factor has values from 0 to 4% indicating no presence of
superparamagnetic particles (around 0.03 μm). From 11700 to 8000 cal BP: SIRM, , kanh
and %soft IRM show a decreasing trend, S-ratio show oscillations around 0.96. BCR has an
increasing trend in that period and considering that the interparametric ratios do not show
notorious changes, the presence of hard materials in low percentages is suggested. From
8000 to 5000 cal BP: all the parameters do not show variations, but the records are scattered
and more data are needed. log show maxima at 4700 cal BP, coincident with a high lake
level and more humid conditions. Since 5000 cal BP until our days there is high presence of
magnetite-type minerals inferred from the %soft IRM, S-ratio and BCR logs. During the LIA the
magnetic parameters show a maximum in , kanh, BCR, SIRM and a minimum in %soft IRM
indicating the presence of a low percentage of hematite-like minerals.
Conclusion
•
According with the rock magnetic studies (Fig. 2), the main magnetic carrier in the
sediments is magnetite. The magnetic grain size is between 4 and 16 m, with strong
variations in the first 2000 yrs. The general behaviour indicates a change from
coarser to finer magnetic grain size.
•
The comparison with previous results shows a good agreement between  and the
lake level changes (direct relationship).
•
During dry periods BCR show higher values while %soft IRM show lower values,
indicating the presence of a low percentage of antiferromagnetic minerals, suggesting
an eolian sediment source in these periods.
Referentes
HABERZETTL, T., CORBELLA, H., FEY, M., JANSSEN, S., LÜCKE, A., MAYR, C., OHLENDORF, C.,
SCHÄBITZ, F., SCHLESER, G.H., WILLE, M., WULF, S. AND ZOLITSCHKA, B. 2007. The
Holocene 17: 297-310.
MAYR, C., LÜCKE, A., MAIDANA, N.I., WILLE, M., HABERZETTL, T., CORBELLA, H., OHLENDORF,
C., SCHÄBITZ, F., FEY, M., JANSSEN AND S., ZOLITSCHKA, B. 2009. J Paleolimnol 42: 81–
102.
PETERS, C. AND DEKKERS, M. J., 2003. Physics and Chemistry of the Earth, 28, 659–667.
WILLE, M., MAIDANA, N.I., SCHÄBITZ, F., FEY, M., HABERZETTL, T., JANSSEN, S., LÜCKE, A.,
MAYR, C., OHLENDORF, C., SCHLESER, G.H. AND ZOLITSCHKA, B. 2007. Review of
Palaeobotany and Palynology 146: 234–246.
34
Fig. 1: Study site and location of the cores. (Modified from Haberzettl et al., 2007)
15000
A
B
48
10000
SIRM
44
176
57
0
-5000
-10000
BCR [mT]
IRM [mA/m]
5000
-15000
0
200
36
32
BCR
-200
40
400
600
800
1000
28
1200
0
1500
3000
Applied field [mT]
4500
6000
7500
9000
10500
Age [cal yrs. BP]
0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000 11000
6000
7000
8000
9000 10000 11000
8
C
Kanh/k
10
Magnetite region
(Peters and Dekkers, 2003)
4
2
0
D
6
ARM/SIRM
SIRM/k [kA/m]
6
1
10
4
2
0
100
0
BCR [mT]
1000
2000
3000
4000
5000
Age [cal yrs. BP]
Fig. 2: Magnetic characterization of the bottom lake sediments from Laguna Potrok Aike. A) IRM
acquisition curves with main characteristic shown in the figure. B) BCR vs. applied field. C) SIRM/k vs.
BCR. D) Interparametric ratios: kanh/k and ARM/SIRM vs. age in calibrated years BP.
35
Dry
Lake level
Humid
0
LIA
MWP
2000
Age [cal BP]
4000
6000
Thermal optimum
8000
10000
1
low
2
middle
3
high
0
15000
30000
0.95
1.00
1.05
30
S-ratio
SIRM [mA/m]
0
50
0
1000
1000
2000
2000
3000
3000
4000
4000
5000
5000
6000
6000
7000
7000
8000
8000
9000
9000
10000
10000
11000
11000
0
40
80
-5
120 160
 [10 SI]
0
300
-8
600
3
KAnh [10 m /kg]
0
2
4
F-factor [%]
90
120
%soft IRM [%]
0
3
-2
Age [cal BP]
Age [cal yrs. BP]
40
BCR [mT]
6
ARM/k [10 A/m]
Fig. 3: Lake level and humid/dry conditions obtained from previous studies: Haberzettl et al. (2007),
Wille et al. (2001) and Mayr et al. (2009), specific susceptibility (), kanh, F-factor, SIRM, S-ratio, BCR,
%soft IRM and ARM/k vs. age in calibrated years BP. LIA (Little Ice Age), MWP (Medieval Warm
Period).
36
Geophysical preliminary results and new proposals for Laguna Potrok
aike area - Southern Patagonia - Argentina.
1
José Kostadinoff, 1Ariel Raniolo, 2,3 Pedro Tiberi, 2Javier Szewczuk,
3
Eduardo Rodas, 3,4Hugo Corbella.
1
Universidad Nacional del Sur, Depto. de Geología. Bahía Blanca (8000). 2 Subsecretaría de Medio
Ambiente, Provincia de Santa Cruz. 3Universidad Nacional de la Patagonia Austral - Unidad
Académica Rio Gallegos. 4 CONICET–Museo Argentino de Ciencias Naturales.
Laguna Potrok Aike (LPA) (51°58' S, 70°23' W), the largest and deepest phreatomagmatic
maar-lake in the Pali Aike Volcanic Field in Southern Patagonia, has a diameter of ~3 km and
a 100 m depth. A broad depression was carved in Miocene tuffaceous sandstones and
micro-conglomerates of the Santa Cruz Formation, till deposits and 1.2 My old basaltic lavas.
Phreatomagmatic deposits dated 0.7 My and aeolian deposits followed on top.
Gravimetric and magnetic field measurements in LPA area started in autumn 2010.
For total magnetic field determinations the instrument employed was a Geometric G-826
protonic precession magnetometer. To determine the gravimetric values a LaCoste &
Romberg 418 geodetic gravimeter was used.
On the field, benchmarks and surveying points were established by GPS positioning. Two
concentric polygons with sites at 250 m intervals; one near the lake´s shore and the other
separated ~500 m from the first, and also two E-W traverses with a 500 m interval between
sites were established; totalizing a measured distance of 25 km.
In geologically representative sites the magnetic susceptibility of the outcropping rocks was
measured. The obtained magnetic susceptibilities values indicate the existence of two
dominant types of basaltic rocks included between 46350 x10-6 to 15100 x10-6 SI and
between 6890 x10-6 to 3660 x10-6 SI; while the sedimentary rocks have much lower magnetic
susceptibility values, in the order of 4410 x10-6 to 2650 x10-6 SI.
The obtained magnetometric values were processed and measurements corrected with
diurnal variation values given by the Trelew Geomagnetic Station. And to filter the deep crust
effects, IGFR (International Geomagnetic Referent Field) values were subtracted.
The magnetic anomalies of the total component of the geomagnetic field were used to trace
a contour map showing the zones that could be related with the outcrops and structures
around LPA. These anomalies suggest the existence of NW-SE and SW-NE alignments.
Precision leveling of the surveying points employed during the geophysical survey are now
being carried out by differential GPS measurements.
Then, the Bouguer gravimetric anomalies map will be compared with the magnetic map in
order to establish a geological structural model based on geophysic anomalies.
During the spring and summer of the present year we are planning to enlarge the area of the
magnetic survey and also to perform an underwater geophysical study. We will explore the
lake with a Geometric G877 marine magnetometer and a pneumatic boat to tow the sensor
at 4 meters depths in a regular grid in order to establish magnetic anomalies.
With this, we endeavor to survey the underwater magnetic features of the lake and to verify
the existence of intrusive bodies into the lower levels of the Potrok Aike diatreme.
37
Figure 1. Magnetic contour map over a satellite image of the Potrok Aike Lake Area
38
Multiproxy reconstruction of hydrological changes during the late
Holocene in Chaltel Lake (Southern Patagonia, Argentina)
Maidana, N. 1,3, Laprida, C. 2,3,, Ramón Mercau, J. 1,4, Fey, M. 5, Massaferro, J. 3,6,
and SALSA Science team
1
Depto. de Biodiversidad y Biología Experimental. Facultad de Ciencias Exactas y Naturales,
Universidad de Buenos Aires, Buenos Aires, Argentina; 2 Depto. de Ciencias Geológicas. Facultad de
Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; 3 CONICET; 4.
FONCyT fellowship; 5 Universität Bremen, Institut für Geographie, Bremen, Germany; 6 CENAC, APN,
Bariloche, Argentina
Lakes are excellent sponsors of environmental change, including climatic change.
Diatoms and ostracods are among the most useful biological indicators for
paleoenvironmental reconstruction found in lake sediments, due to their
sensitiveness to abiotic variables (Lotter et al., 1999; De Deckker & Forester, 1988).
However, the use of these microfosils in quaternary studies for Southern Patagonia is
still limited and poorly understood because of the paucity of regional taxonomic and
paleoenvironmental knowledge. The multiproxy study of lacustrine sediments from
Chaltel presented here aims to partially fill this gap.
Chaltel (49° 57’ S- 71° 06’ W) is a crater lake located in the semiarid steppe of
Patagonia (Fig. 1). Several cores obtained in the framework of the South Argentinean
Lake Sediment Archives and Modelling (SALSA) international research project were
analyzed using a multi-proxy approach to reconstruct the paleoenvironmental history
of the lake. Changes in diatom, ostracod, and chironomid assemblages and detailed
geochemical analysis provided information about past lake water level fluctuations
and hydrological changes in the watershed.
For diatom analysis, a subsample of each sample was processed following estándar
procedures (Battarbee, 1986) and permanent slides were mounted with Naphrax®.
Identifications were based on Rumrich et al. (2000) and others. For ostracods
studies, samples were washes and dried. Specimens were picked onto special
slides.
To explore the relations between species and environmental variables, a Canonic
Correspondence Analysis (CCA) was performed considering the most abundant
species frequencies (>3%) (CANOCO program; ter Braak, 1988) The significance of
the canonical axes was tested using Monte Carlo’s permutation of samples.
Ostracods were present in both studied cores CHA04/4 (60 cm, center of the lake)
and CHA04/5 (100 cm, more litoral) while diatoms were present only in the
uppermost 30 cm of CHA04/4 but they were found all along CHA04/5. The results of
the combination of the information coming from both cores show several interesting
changes.
Coniss diagram (Tilia program, Grimm 1999) allowed us to recognize four zones in
the sedimentary record of core CHA04/4 (Fig. 2).
Zone A (4500 - 3150 cal BP). Relatively moist conditions can be inferred from
ostracods. Notably, diatoms were not present at this zone, probably due to diagenetic
dissolution. The ostracod Limnocythere rionegroensis was by far the dominant form.
Other species were present but in lower numbers, and only in the subzone A1-older
than 4000 cal BP. In subzone A2, geochemical data point to allochthonous input of
39
organic matter to the lake while ostracods assemblages composition suggest a shift
to saline conditions probably higher than 2-3 mg/l and Na-dominated waters being L.
rionegroensis the only species recovered. Both biotic and abiotic proxies indicate low
water level and increased littoral erosion by that time.
Zone B (3150 - 2400 cal. BP). Conditions became moister with a concurrent lake
level rise. Moderate salinities and the presence of abundant marginal vegetation are
inferred from ostracods (mainly the contribution of L. patagonica) and the increased
abundance of planktonic and epiphytic diatoms (Thalassiosira patagonica and
Cocconeis placentula, respectively).
Zone C (2400 - 1300 cal. BP). Changes in diatom and ostracod assemblages
suggests lower salinities, and probably higher productivity. The progressive decrease
in the abundance of L. rionegroensis agrees with that of the heavily silicified
“Hyalodiscus” sp A noticeable increase in diatom abundances may have been
enhanced by expansion of littoral habitats. These less saline conditions could be
related to an increase in the lake level.
Zone D (younger than 1300 cal. BP). A new shift to moister conditions took place at
around 1400 cal. BP, when modern lake conditions were established. The cooccurrence of L. patagonica and Kapcypridopsis megapodus allow us to infer
salinities lower than ca. 2 ‰ and Ca-dominated waters. The absolute dominance of a
true planktonic diatom species support the idea of an increased water level.
The present work, which was partially financed by the Southern Patagonia
Interdisciplinary Project (PIPA, PICT/R 2006 – 2338) and includes neolimnological
information obtained by its members, enhances the understanding of spatial patterns
of past hydrological changes in Southern Patagonia steppe, indicating further
hydrological variations during the late Holocene.
References
BATTARBEE, RW., 1986. Diatom Analysis. en: BE Berglund (ed.). Handbook of Holocene
Paleoecolgy and Paleohidrology. John Wiley & Sons Ltd, New York, 527-570.
DE DECKKER, P. & R. M. FORESTER, 1988. The use of ostracods to reconstruct
palaeoenvironmental records. En De Deckker, P., J.-P Colin & J.-P. Peypouquet (eds.)
Ostracoda in the Earth Sciences. Elsevier, Amsterdam: 175–199.
GRIMM, E. 1992. TILIA Program versión 2.0. TILIA Graph 1.28. Illinois State Museum, Springfield.
LOTTER, AF, PIENITZ, R. & SCHMIDT, R. 1999. Diatoms as indicators of environmental change near
arctic and alpine treeline. En: Stoermer, E. F. & Smol, J. P. (eds), The diatoms: Applications
for the Environmental and Earth Sciences, Cambridge University Press, Cambridge, 205-226.
RUMRICH, U; H LANGE-BERTALOT & M RUMRICH. 2000. Iconographia Diatolmologica 9.
Diatomeen der Anden von Venezuela bis Patagonien/Tierra del Fuego. En: H Lange-Bertalot
(ed.). K G Gantner Verlag. Germany. 672 pp.
TER BRAAK, CJF., 1988. CANOCO: a FORTRAN program for canonical community ordination by
correspondence analysis, principle components analysis and redundancy analysis (version
2.1). Report LWA-88-02. Agricultural Mathematical Group, Wageningen, The Netherlands, 95
pp.
40
Figure 1
41
Planktonic microcrustacean (Cladocera and Copepoda)
assemblages from inland waters of the province of Santa Cruz,
Argentina
Marinone, M.C. and Menu Marque, S.A.
Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales,
UBA, Argentina – e-mail: [email protected] / [email protected]
The Argentine province of Santa Cruz has a remarkable biogeographical interest, both owing
to its location at the southern end of the American continent and to its geological history. This
region was explored at the end of the XIXth century, by several European scientific
expeditions (Lubbock, 1855; Mrázek, 1901; Daday, 1902; Ekman, S. 1900), which collected
abundant material, mostly from areas close to seaports. These early investigations lead to
the description of numerous species of endemic zooplanktonic microcrustaceans and some
rotifers. Although most of these species are still valid, recent taxonomical revisions are
introducing important nomenclatorial changes. Our research is aimed at elaborating a wide
provincial updated database, in order to describe the distribution of zooplankton species,
which can be utilized as paleoenvironmental proxies due to their ecological fidelity.
Particularly, the fossil and subfossil remains of Cladocera (ephippia and exosqueleton parts)
are valuable proxy indicators of different types of aquatic habitats and zooplanktivory
(Amsinck et al., 2007).
The present study synthesizes the microfaunistic data from 152 samples collected by the
authors and collaborators from 1987 to 2007, and more recently, by the PIPA project. We
also considered published information on plateau lakes and ponds (Reissig et al., 2006).
Samples were taken from the shore, with zooplankton nets (55 to 300 µm mesh size), mostly
during the warm season. Since most of the province is either arid or semiarid, our data set
comprises only 12% of permanent lakes, whereas the remaining 88% are temporary
unknown water bodies that represent the actual proportion of this kind of habitat in Santa
Cruz (localities will published elsewhere). Determinations are based on detailed
morphological grounds, which in some cases were corroborated by molecular techniques
(DNA sequencing and allozyme variation).
All the copepod species found are common representatives in inland waters of the Andean
Biogeographic Region that includes the territory of Santa Cruz. The copepods belonging to
the Order Calanoida of inland Patagonia belong to the family Centropagidae, represented by
the genera Boeckella and Parabroteas. Seven endemic species of Boeckella are usually
found in Santa Cruz, being B. brasiliensis, B. gracilipes and B. michaelseni the most
frequently occurring ones (Table 1). In coincidence with the observations by Reissig et al.
(2006), we found that the species of Boeckella span a relatively wide range of body sizes and
often two or three species of different size coexist in the same water body, indicating a
partitioning of the trophic spectrum.
The Order Cyclopoida was represented by eight species of the family Cyclopidae. The most
frequent species was Microcyclops anceps s.l., followed by Mesocyclops annulatus and
Metacyclops mendocinus each (Table 1).
The Order Harpacticoida embraces a set of mostly benthic species, although some can be
found in open waters. This group was scarce and in many cases only represented by
immature stages that cannot be determined.
Only 7% of the habitats had cyclopoids exclusively, which in most cases where undetermined
copepodites. Conversely, and showing their preponderance in this region, calanoids were the
only copepods present in half of the samples.
42
Order CALANOIDA
Order ANOMOPODA (CLADOCERA)
%
Boeckella spp. (robust copepodites)
%
9
Alona (6 spp.)
19
Boeckella spp. (slender copepodites)
7
Bosmina chilensis
6
5
Bosmina longirostris
1
24
Camptocercus aloniceps
2
Boeckella gracilipes
20
Ceriodaphnia cf. dubia
23
Boeckella meteoris
14
Chydorus (3 spp.)
24
Boeckella michaelseni
20
Daphnia commutata
24
3
Daphnia dadayana
27
Boeckella bergi
Boeckella brasiliensis
Boeckella poopoensis
Boeckella poppei
13
Daphnia menucoensis
5
Parabroteas sarsi
30
Daphnia (Ctenodaphnia) n.sp.
2
Daphnia (Ctenodaphnia) sp. (ephippia)
Order CYCLOPOIDA
Cyclopoida spp. (copedites)
%
19
4
Daphnia obtusa group sp. 1
11
Daphnia obtusa group sp. 2
4
Acanthocyclops or Diacyclops
3
Daphnia cf. pulex
2
Eucyclops chilensis
3
Daphnia pulicaria
8
Mesocyclops annulatus
7
Daphnia sp. (data from the literature)
5
Mesocyclops sp.
1
Leydigia leydigi
3
Metacyclops mendocinus
6
Macrothrix oviformis
4
Microcyclops anceps sensu lato
Macrothrix spp.
11
Paracyclops chiltoni
3
Moina sp.
Tropocyclops prasinus meridionalis
1
Pleuroxus scopuliferus
Order HARPACTICOIDA
Family Canthocamptidae
%
9
19
1
14
Pleuroxus spp.
3
Scapholeberis armata freyi
1
Simocephalus sp.
8
Table 1: List of microcrustacean species found in inland waters of Santa Cruz Province, over
a 20-year period (1987-2009). Percentages represent the frequency of occurrence of
each taxon.
The rest of the lakes (37%) exhibit several assemblages of different Boeckella species with
various cyclopoids. Copepod species richness can attain values as high as five or six,
particularly in water bodies connected with flowing waters.
All the species of Boeckella included in the present database have been recorded since the
first expeditions to Santa Cruz. Ringuelet (1958) also found B. meteoris in Ghio Lake and B.
michaelseni in a pond close to Lake San Martín. Menu-Marque and Locascio de Mitrovich
(1998) added the findings of B. brasiliensis and B. meteoris coexisting in Cardiel Lake and
the presence of B. michaelseni in lakes Posadas and Roca. In a review of the distribution of
the species of Boeckella in South America, Menu-Marque et al (2000) also confirmed the
presence in Santa Cruz of B. bergi, B. gracilipes, B. gracilis (not reported in this database)
and B. poppei. Although B. longicauda Daday 1901 and B. silvestrii (Daday, 1901) have been
mentioned for Santa Cruz province, they have never been found since Daday´s description.
The citation by Ringuelet (1958) cannot be confirmed, since there is a certain degree of
overlap with the description of B. poppei (Mrázek, 1901), these two nominal species should
not be taken into account until more material can be studied.
Among the Cyclopoida, Metacyclops mendocinus is considered a Neotropical species and
the present one is the first mention of this taxon for Santa Cruz. Mesocyclops annulatus
(Wierzejski, 1892) was one of the earliest mentions of the group for Santa Cruz (Daday,
1902). Microcyclops anceps was found by Ringuelet (1958), but detailed studies (Rocha,
1998) have shown that this might be a complex of species widespread all over the American
continent, thus deserving a more detailed taxonomic study. Eucyclops chilensis was
originally described by Löffler as a subspecies of Eucyclops serrulatus. Menu-Marque and
Locascio de Mitrovich (in press) have redescribed this taxon and validated its specific rank.
Thus, most probably, the citations of E. serrulatus for Patagonian localities, including
43
Daday´s (1902) should be ascribed to this taxon. Eucyclops ensifer Kiefer, 1936, found by
Ringuelet (1958) in Santa Cruz, was not detected in any of the samples here studied. Both
this taxa were originally described from Chilean localities at Patagonian latitudes. Although
ours is the first citation of Paracyclops chiltoni for Santa Cruz, most of the previous citations
of P. fimbriatus for this province (Ringuelet, 1958) must be assigned to P. chiltoni, since P.
fimbriatus (Fischer 1853) is not a South American species (Karaytug & Boxshall, 1998) and
P. chiltoni is the only truly cosmopolitan species of the fimbriatus-group. Tropocyclops
prasinus meridionalis (Kiefer, 1931) has a widespread distribution in South America and was
already known from Santa Cruz (Daday, 1902; Ringuelet, 1958). As for the Harpacticoida,
the family Canthocamptidae, which is most probably polyphyletic, clumps together a huge
variety of freshwater taxa that are in need of revision. Cletocamptus deitersi was mentioned
from Santa Cruz by Daday (1902) but a recent revision of the deitersi-complex (Gómez &
Gee, 2009) has shown that other species are also present in Patagonia. Although several
species of Attheyella are cited for Santa Cruz by Ringuelet (1958), the degree of taxonomical
confusion of this group makes it difficult to identify the species of this genus.
Concerning cladocerans, all of the studied representatives belong to the order Anomopoda.
Daphniidae, the most frequently occurring family, includes two dominating genera: Daphnia
(present in 61% of the sites) and Ceriodaphnia (23%) (Table 1). In spite of being typically
benthic or littoral, Chydoridae (Alona, Camptocercus, Chydorus, and Pleuroxus) are
frequently overepresented in samples taken from shallow habitats or collected near the lake
shore, like in our case. The members of the Macrothricidae family are well represented for
the same reason.
Most of the species herein reported have either being described from this region
(Camptocercus aloniceps Ekman, 1900; Chydorus patagonicus Ekman, 1900; Pleuroxus
scopuliferus Ekman 1900, etc.) or identified as cosmopolitan species (e.g. Chydorus
sphaericus O.F. Müller or Ceriodaphnia dubia Richard, 1895, which in fact belong to cryptic
species complexes). Other species still deserve recognition as new endemic taxa
(Adamowicz et al. 2004) or require the aid of molecular techniques to unravel their condition
of cryptic colonizers, such as D. pulicaria (Adamowicz et al. 2002).
The two most frequently occurring species in this lake set were Daphnia dadayana Paggi,
1999 (best represented in the plateau) and D. commutata Ekman, 1900 (dominant in Andean
and foothill lakes). Both endemic species co-occur in many Extra-Andean locations also
sharing their habitat with different Boeckella species. However, judging from the number of
co-occurrences, the larger D. dadayana (18 cases) seems to be much better adapted to
coexist with the predator Parabroteas sarsi (< 5 mm) than D. commutata (4 cases). Except D.
pulicaria, the endemic Daphnia of Santa Cruz are well adapted to prosper in very turbid
environments, where they found refuge from visual predators as well as from UV radiation. D.
commutata also is provided with the extra protection of a melanic pigmentation on the dorsal
part of its carapace. Exosqueletal characters together with the frequent production of resting
eggs enclosed in a melanized and hardened ephippia, make cladocerans excellent
candidates to be proxy indicators (Amsinck et al., 2007). At present the ephippia of the
seven species of Daphnia so far known from Santa Cruz have been characterized and can
be recognized (Marinone & Adamowicz, 2008). However, a couple of species mentioned in
the literature have not been found or cannot be assigned to any of the valid species, namely:
D. silvestrii, Daday 1902 and D. hastata Daday, 1902, while the resurrected and carefully
redescribed D. cavicervix Ekman, 1900 (Kotov & Gololobovab, 2005) has been not
recognized yet among the specimens collected in Santa Cruz.
The taxonomic status of some species is controverted and its elucidation still deserves a
great deal of systematic research. Although the present contribution includes an substantial
proportion of plateau environments, from a microfaunistic view point, the central zone of
Santa Cruz remains as a vast terra incognita, which most probably serves as a refuge for
unknown endemic species.
44
References
ADAMOWICZ, S.J., GREGORY, T.R., MARINONE, M.C. & HEBERT, P.D.N. 2002. New insights into
the distribution of polyploid Daphnia: the Holarctic revisited and Argentina explored. Molecular
Ecology 11: 1209-1217.
ADAMOWICZ, S.J., HEBERT, P.D.N. & MARINONE, M.C. 2004. Species diversity and endemism in
the Daphnia of Argentina: a genetic investigation Zoological Journal of the Linnean Society
140: 171-205.
AMSINCK, S.L. JEPPESEN, E. & VERSCHUREN, D. 2007. Use of cladoceran resting eggs to trace
Climate-driven and anthropogenic changes. In: V. R. Alekseev et al. (eds.), Diapause in
Aquatic Invertebrates, Springer, pp.: 135-157.
DADAY, E. 1901. Diagnoses Precursoriae Copepodorum Novorum E Patagonia. Thermészetrajzu
Füzetek 24: 345-350.
_____ 1902. Mikroskopische Süsswassertiere aus Patagonien, gesammelt von Dr. Filippo Silvestri in
Jahre 1889-1900. Thermészetrajzu Füzetek 25: 201-310.
EKMAN, S. 1900. Cladoceren aus Patagonien , gesammelt von der Schwedischen Expedition nach
Patagonien 1899. Zool. Jahr. Syst. 14: 62-84.
GÓMEZ, S. & GEE, J.M. 2009. On four new species of Cletocamptus Shmankevich, 1875 (Copepoda:
Harpacticoida) from inland waters of Argentina. Journal of Natural History 43 (45): 2853- 2910.
KARAYTUG, S. & BOXSHALL, G. 1998. The Paracyclops fimbriatus-complex (Copepoda,
Cyclopoida): a revision. Zoosystema 20 (4): 563-602.
KOTOV, A.A. & GOLOLOBOVAB, M.A. 2005. Types of cladoceran species described by Sven Ekman
in the Swedish Museum of Natural History, with redescription of Daphnia cavicervix Ekman,
1900 (Daphniidae, Anomopoda, Cladocera). Journal of Natural History 39 (33): 3059-3074.
LUBBOCK, J. 1855. On the freshwater Entomostraca of South America. Transactions of the
Entomological Society London (N.S.) 3: 232-240.
MARINONE, M.C. & ADAMOWICZ, S.J. 2008. El género Daphnia en la provincia de Santa Cruz,
Argentina. IV Congreso Argentino de Limnología, Bariloche, 26-30/10/08. Resumen: pag. 100.
MENU-MARQUE, S. & LOCASCIO DE MITROVICH, C. 1998. Distribución de las especies del género
Boeckella (Copepoda: Calanoida: Centropagidae) en la Argentina. Physis, Secc. B 56
(130/131): 1-10.
_____ . & LOCASCIO DE MITROVICH, C. (in press). Löffler´s Chilean Eucyclops (Copepoda,
Cyclopoida, Cyclopidae) revisited. Crustaceana.
_____ MORRONE, J.J. & LOCASCIO DE MITROVICH, C. 2000. Distributional patterns of the South
American species of Boeckella (Copepoda: Centropagidae): a track analysis. Journal of
Crustacean Biology 20 (2): 54-64.
MRÁZEK, A. 1901. Süsswasser - Copepoden. Ergebnisse der Hamburger Magalhaensischen
Sammelreise 6 (2): 1-29.
RINGUELET, R.A. 1958. Los Crustáceos Copépodos de las aguas continentales de la República
Argentina. Sinopsis sistemática. Contribuciones Científicas de la Facultad de Ciencias
Exactas y Naturales, Universidad de Buenos Aires, Serie Zoología 1: 35-126.
ROCHA, C. E. F. 1998. New morphological characters useful for the taxonomy of the genus
Microcyclops (Copepoda, Cyclopoida). Journal of Marine Systems 15: 425-431.
REISSIG, M., TROCHINE, C., QUEIMALIÑOS, C., BALSEIRO, E. Y MODENUTTI, B. 2006. Impact of
fish introduction on planktonic food webs in lakes of the Patagonian Plateau. Biological
Conservation 132: 437-447.
45
Sediment core treatment in the PASADO project: On-site and Offsite core processing procedures
C. Ohlendorf 1, C. Gebhardt 2, A. Hahn 1, P. Kliem 1, B. Zolitschka 1 and the PASADO
Science Team 3
(1) Geopolar, Institute of Geography, University of Bremen, Germany ([email protected]) (2)
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany 3) PASADO
Science Team as cited at: http://www.icdp-nline.org/front_content.php?idcat=1494
Lake drilling in the framework of the ICDP project PASADO (Potrok Aike Maar Lake
Sediment Archive Drilling Project) was carried out between September and late November
2008. From the maar lake Laguna Potrok Aike (52°S, 70°W; 116 m asl.; diameter: 3.5 km;
water depth: 100 m) in southern Patagonia, Argentina, in total 510 m of lacustrine sediments
have been recovered using the GLAD800 platform equipped with a CS-1500 drill rig. At two
drillsites quadruplicate (site 1) and triplicate (site 2) cores down to a maximum depth of 101.5
m below lake floor have been recovered using mainly the hydraulic piston coring tool.
Recovered core sections and core catcher samples were transferred to the shore-based
fieldlab where first on-site measurements were done.
Owing to the great diversity of continental drilling projects, workflow in an ICDP deep drilling
project seems to be much less standardised then is the case for IODP projects. For instance,
according to our knowledge, PASADO was the first ICDP project where continuous
subsamples were taken for the entire sediment sequence (106 m). Such an approach
requires logistical preparations different from sub-sampling campaigns of cores drilled in the
framework of most other projects. We therefore take this as an opportunity to present field
and lab protocols that were applied during the PASADO drilling and subsampling campaigns.
Sample handling begins already on-site as soon as the core is handed over from the drilling
crew to the onboard scientists with cutting the core runs into sections and packaging the core
catcher samples. For the latter, analysis in the on-site field lab included sample description,
photography, smear slide preparation and the determination of water content, as well as
producing a suspension and a HCl-extract in which conductivity, Ca2+- and Cl- concentration
were measured. Core sections were weighted and magnetic susceptibility was logged.
For the off-site lab procedures it was important to design a workflow that accounts for the
needs of all involved research groups. In 2009 all cores from Site 2 (southern part of the
deep, central basin) and all except one core from Site 1 (central deep basin) were opened,
described, documented by digital high resolution photography and scanned with different
non-destructive techniques. Core scanning was performed at 5 mm resolution for all
parameters and involved the following techniques: 1) color scanning with a handheld X-rite
spectrometer, 2) magnetic susceptibility scanning with a Bartington MS2F-sensor, 3) XRF
scanning and X-radiography with an ITRAX core scanner (COX analytical systems) and 4) pwave velocity/transmission seismograms and gamma ray absorption with a modified Geotek
MSCL tool. Immediately after non-destructive scanning anaylses were finished, core halfs
were covered with cling-film, vacuum sealed in tubular film and stored at 4°C to prevent
drying and surface oxidation of sediments until sampling begun.
An essential task was to amalgamate all cores from one site to establish a composite profile
that then could be sampled in consecutive steps. For Site 2, a 106.08 m long composite
profile was composed based on visual core correlation and core scanning data. The working
half of this composite profile was then sampled completely in consecutive 2 cm thick
intervalls. Using an especially designed sampling device each sample was divided into 6
volumetric and one non-volumtric sub-samples during the sampling process, whereas
smeared sediment close to the liner wall was discarded simultaneously. Subsamples were
stored and processed according to the needs of the respective research groups. From the
archive half a U-channel was taken, which is regarded as the archive sediment for the
46
PASADO project, since only non-destructive rock- and paleomagnetic analyses will be
performed on it. In the trench that was left behind from U-channel trepanning, samples for
thin section preparation, grainsize analysis and micro magnetic properties were taken. Based
on the core description and a detailed inspection during sampling 1) 18 samples of aquatic
moss remains were sieved out for AMS 14C dating, 2) 16 samples of tephra layers were taken
for geochemical fingerprinting and 3) a first identification of redeposited sediment sections
was accomplished. According to first results from these samples, the sedimentary record
from Laguna Potrok Aike reaches back to approx. 50 ky BP and exhibits contrasting
lithologies downcore especially in the Pleistocene part of the record. First estimates indicate
that up to 50% of the record consist of redeposited sediments.
Core series 1A, 1B and 1C from Site 1 were opened and sampled for rock- and
paleomagnetic studies whereas core series 1D was reserved for OSL-dating. From the latter
core series selected sections were split and sampled under red light. The sampled halves as
well as the non-sampled archive halves were photographed digitally to assure 1) the exact
positions of OSL samples and 2) the exact correlation with parallel cores from Site 1 and with
the composite profile of Site 2. All not sampled core sections from 1D were then opened
under red light. The archive half was immedeately sealed in black tubular film to conserve the
possibility of later OSL sampling, whereas the working half was photographed digitally,
vacuum sealed in tubular film and stored at 4°C. Through a thorough correlation of Site 1
cores with the Site 2 composite profile the OSL chronology will then be available for both
sites.
47
Modern and subfossil chironomid (Insecta: Diptera: Chironomidae)
studies for quantitative paleoenvironmental reconstructions in
southern Santa Cruz province, Argentina
Orpella German1 y Julieta Massaferrro1,2
1
2
CENAC APN, Bariloche, Rio Negro, Argentina.; CONICET
Introduction
In the last 20 years, Patagonia has become increasingly important in paleoclimate research
due to its exceptional geographic location and the abundance of lakes, ponds and bogs. Inlake paleo indicators are subfossil and fossil remains of aquatic organisms that lived in that
environment. The different species of those organisims have specific ecological preferences
and tolerances which make them useful paleoenvironmental indicators and an invaluable tool
for reconstructing past lake conditions. One of the most promising biological proxies for
paleoenvironmental reconstructions are the chironomids (Insecta: Diptera: Chironomidae).
Their remains are of special interest in paleolimnology because their strongly sclerotized
larval head capsules preserved in sediment deposits. Chironomids are recordedin almost all
aquatic environments, including marine one and thepotential of this groupas paleoindicators,
is that they are ver sensitive to key environmental variables, are widely distributed with a high
abundance and diversity and especially valuable, offering a continuous record of climate
change. Chironomids are stenothermal species (i.e., able to adapt only to a narrow range of
temperature conditions) and respond rapidly to environmental change. Therefore, they are
used in quantitative climate reconstructions. The study of these fossil records, combined with
physical and chemical parameters measured in situ, can provide accurate information for
climate change studies.
Quantitative palaeoenvironmental reconstructions involving the modeling of modern
analogous and the development of transfer functions. In order to develop these functions it is
necessary a compilation of extensive datasets involving species abundance, distribution and
ecological data, physical- chemical parameters, and obtaining a large number of modern
environmental samples containing a large number of taxa to build what is called a "training
set" from which those functions are developed. (Warwick, 1980). The potencial of the
quantitative method technique arises from the fact that utilize multivariate ordination and
classification to the bioproxies (palaeoenvironmental biological indicators) and climate data
modeling. Thus, environmental data gathered from modern forms can be used as analogues
and extrapolated to the fossil record.
The transfer function (Fig. 1) is a calibration method that expresses the environmental
variable value as a function of biological data. There are several methods for creating a
transfer function, the most commonly used with chironomid are WA (weighted average), PLS
(partial least squares) and WA-PLS (weighted average partial least squares) (Juggins, 2003)
and it is used one another according to: the size of the training set, linear or unimodal
species distribution, etc.
The work presented here exhibits the first approaches of my doctoral thesis. In this context,
the main specific objectives of this research to be achieved are: 1) Developing a modern
chironomids biodiversity database and its current geographical distribution in aquatic
environments from southern Santa Cruz province, between 50 and 52 degrees south,
representing a gradient of lentic ecosystems from the Andes mountains to the Atlantic. 2) To
relate the modern chironomids distribution to physical, chemical and climatic data from the
habitats they occupy to better understand the ecological ranges of species. 3) Subfossil
chironomid analysis from short sediment cores. 4) Reconstruction of the
environmental/climate history using the application of transfer functions to the fossil record.
5) Comparison of the results with those from other paleoenvironmental biological indicators
48
(ostracods, diatoms, pollen, etc.). The multiproxy comparison will add strength and
robustness to the obtained results.
Preliminary results
Proyecto Interdisciplinario Patagonia Austral (PIPA, PICT/REDES Nº 2338) is currently
undertaking a compilation and analysis of datasets needed to develop an aquatic
organisms biodiversity database potentially useful as palaeoenvironmental indicators
(proxies). This research shows the first steps in the development of a transfer function to
quantitatively reconstruct climate from chironomids preserved in lacustrine surface sediments
of 31 lakes for southern Santa Cruz province (50-52°S)(Fig.2).
Preliminary results from 15 permanent lakes in the study area (Echazú et al., 2009; Ramon
Mercau et al., 2010) suggested that biodiversity and distribution of the taxa, were associated
with some physical-chemical parameters measured in the respective environments. The
chironomid assemblage consisted of a total of 31 different sub-fossil taxa (Sub-families
Chironominae, Tanypodinae, Orthocladiinae, and Diamesinae). Orthocladiinae was the most
diverse and abundant (72.8%). The second sub-family in importance was Chironominae
(25.3 %), followed by Tanypodinae (1.5 %). The sub-family Diamesinae had a very low
relative abundance (0.4 %) (Fig.3). Some of the most representative quironomids found in
the study area were Cricotopus sp, Limnophyes sp, Smittia sp, Labrundinia sp, Polypedilum
sp. and Parachironomus sp (Fig. 4).
A third fieldwork will be carried out next year to accomplishthe goals proposed in this
research. A last field work is particularly important, to improve the model. It is necessary to
strengthen the size of the "training set” (from which transfer functions will be developed), by
adding new samples to provide a better taxonomic resolution of modern and fossil
chironomids, an increasing number of fossils and sediment surface samples from modern
environments, extending the sampling area in Santa Cruz province to a total of 50 set of
lakes, adding extra strength and robustness to the model to resemble as closely as possible
to European models, developing related topics for over a decade (Brooks, 2006).
During this two years project, a 60-cm short sediment core from Laguna El Chaltel (49° 57'S71° 06' W) has been analysed in order to obtain information about the paleoenvironmental
evolution of the lake during the last ca. 5000 yr BP. The 210Pb / 237C dating gave an age of
4685 cal yr BP for the base of the core. According previous work (Fey et al., 2005 and
PASADO Team) and the first results from these samples (Massaferro et al, 2010), the lake
has experienced a highly variable hydro-geochemical changes. Between the 3900 and 3150
cal. BP, the climate was dry, establishing the modern lake wet conditions from 1400 cal. BP.
The presence of littoral and semiterrestrial chironomid species, suggests oscillations in the
lake level during the timespan of the core and confirms expansion of littoral habitats. Some
geochemical and physical parameters such as, TIC (Total Inorganic Carbon), TOC (Total
Organic Carbon), Ca, Sr, and magnetic susceptibility (K (10-6 SI)), exhibit similar patterns
evidencing important variations in lake dynamics during the late Holocene (Fig. 5).
Future work
Next year a 80 cm core from Laguna Vizcacha (50 ° 42 'S-71 ° 59' W) which is s currently
being analysed, will be finished in order to obtain information about the paleoenvironmental
evolution of the lake.
Applying transfer function for Laguna EL Chaltel, Laguna Vizcacha and other sediments
cores, that will be taken in a third fieldwork next year, in order to quantitatively reconstruct
environmental/climate past conditions.
Continue to improve taxonomical resolution of modern and fossil chironomids adding extra
strength and robustness to the model.
On the other hand, regarding to modern chironomid material, there has been an original
important advancement on the genus Alotanypus (Chironomidae: Tanypodinae).
49
Redescription of imagines, description of immatures and phylogenetic analysis of the genus
(Siri, et al., submitted).
References:
BROOKS, S. 2006. Fossil midges (Diptera: Chironomidae) as palaeoclimatic indicators for the
Eurasian region. Quaternary Science Reviews 25: 1894–1910.
ECHAZÚ, D.M., M.J.RAMÓN MERCAU, & G. ORPELLA, 2009. Diatomeas, Ostrácodos y
Quironómidos en lagos y lagunas permanentes del sur de Santa Cruz, Arg.XXXII Jornadas
Argentinas de Botánica(Sociedad Argentina de Botánica).Córdoba, Arg. Octubre 2009.
FEY, M., H.CORBELLA.,H. HABERZETTL., S. JANSSEN.,B.KUCK.,A. LUCKE., N. MAIDANA., C.
MAYR., C. OHLENDORF., F. SCHABITZ., G.H. SCHLESER., M. WILLE & B. ZOLITSCHKA.
2005. The maar lake Laguna Chaltel (Southern Patagonia Argentina)-first results of a mutyproxy sediment study. Terra Nostra,5,1, 43-44.
JUGGINS.S. 2003. C2. User guide. Software for ecological and paleoecological data analysis and
visualisation. University of Newcastle. Newcastle upon Tyne. 69 pp.
HALL, R.I. & J.P. SMOL. 1999. Diatoms as Indicators of Lake Eutrophication. En E.F.
Stoermer&j.pSmol (eds).The Diatoms: Applications for the environmental and earth
Sciences.Cambridge Univ Press. Pp 128-168.
MASAFERRO, J., C.LAPRIDA., G. ORPELLA., & J. RAMÓN MERCAU. 2010. Fossil chironomids
and ostracods from a 5000 years- sediment sequence of Laguna El Chaltel, Southern
Patagonia, Argentina. X Congreso Argentino de Paleontología Y Bioestratigrafía Y VII
Congreso Latinoamericano de Paleontología (APA, Asociación Paleontológica Argentina). La
Plata, Buenos Aires, Argentina. Septiembre 2010.
RAMÓN MERCAU, M.J., D.M. ECHAZÚ, G. ORPELLA, C. LAPRIDA, J. MASSAFERRO, & N.I.
MAIDANA. 2010. Proyecto Interdisciplinario Patagonia Austral (PIPA) – Goals and work in
progress. VI Southern Connection Congress. Bariloche, Rio Negro, Argentina. Febrero 2010.
SIRI, A., M. DONATO, G. ORPELLA & J. MASSAFERRO. Alotanypus vittigera (Edwards) comb. nov.:
redescription of imagines, description of immatures and a phylogenetic analysis of the genus
(Chironomidae: Tanypodinae) Zootaxa (enviado).
WARWICK, W.F. 1980. Palaeolimnology of the Bay of Quinte, Lake Ontario: 2800years of cultural
influence.Canadian Bulletin of Fisheries and Aquatic Sciences 206:1-118.
Fig. 1: Steps in the development of a tranfer function, and its use in paleoenvironmental
reconstructions.
50
Fig. 2: Distribution of transfer-functions lakes in Southern Patagonia, Argentina.
Fig. 3: Percentage of relative abundance sub-fossil chironomid taxa, grouped by sub-families,
collected from 15 lake sediment samples in Southern Santa Cruz province (50- 52ºS)
51
Fig. 4: Some of the most representative quironomids found in Southern Santa Cruz province (5052ºS). a) Cricotopus sp, b) Limnophyes sp, c)Smittia sp, d) Labrundinia sp, e)Polipedilum sp.
y f) Parachironomus sp
Fig. 5: Chironomid stratigraphy at Laguna El Chaltel (Santa Cruz, Argentina). Geochemical and
physical data.TOC:Total Organic Carbon. TIC: Total Inorganic Carbon. Ca, Sr and Magnetic
sucseptibility: K(10-6 IS).
52
Silicophytoliths in sedimentary sequences in the Laguna Potrok Aike, Santa
Cruz, Argentina
Osterrieth, M 1; Alvarez, MF 1,2; Buezas, G 1; Rojo, J 1; Borrelli, N 1,2; Fernández
Honaine, M 1,2 and L Benvenuto 1 and PASADO and SALSA Science Teams
1
Instituto de Geología de Costas y del Cuaternario, FCEyN, UNMdP, Dean Funes 3350, CC 722, Mar del Plata
(7600). 2 Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET). [email protected]
The biomineralization process is the precipitation of a mineral or mineraloids as a result of
the metabolic activity of organism (Jahren, 1996; Osterrieth, 2004). Phytoliths are
biomineralizations deposited in plant tissues, most of them compounded by hydrated SiO2
(Parry and Smithson, 1964; Blackman, 1971; Piperno, 1988). Following degradation of the
tissue, phytoliths are incorporated into the soil, where they can be preserved for thousands of
years in depositional environments that do not have high alkalinity. Thus, it is possible to use
these microfossils as indicators of the plant communities of the past, in palaeoenvironmental,
palaeobotanical or archaeological studies (Twiss et al., 1969; Rovner, 1971; Piperno, 1988;
Fredlund and Tieszen, 1994; Alexandre et al., 1997; Barboni et al., 1999; Carter, 2000;
Osterrieth, 2008; 2009).
The aim of this study is to analyze the silica biomineralizations, particularly the phytolith
morphotypes present in sedimentary sequences of the Laguna Potrok Aike (PTA) located in
southern Santa Cruz, Argentina. PTA is one of the very few locations that are suited to
reconstruct the paleoenvironmental and climatic history of southern Patagonia. In the
framework of the multinational ICDP deep drilling project PASADO several long sediment
cores to a composite depth of more than 100 m were obtained. According to Roig et al.
(1985) and León et al. (1998), the vegetation surrounding the PTA is the xeric grass steppe.
In this first stage to the subsequent sampling of PASADO, we worked with surface sediment
samples of PTA. These samples were selected for pollen studies (Quintana, 2008). These
samples also were included in the SALSA project (South Argentinean Lake Sediment
Archives and modeling). In addition, we worked with some of the treated samples for the
study of diatoms provided by Dr. Maidana, all they included in the ASADO project (Analysis
of Sediment Distribution in Laguna Potrok Areal Aike).
In the sediment samples of SALSA, organic matter was oxidized with 30% hydrogen
peroxide at 70 °C. Biomineralizations were extracted by repeated centrifugation at 1000 rpm
for 3 min (Alvarez et al. 2008). Sediment samples of ASADO (sequences of 0-1m depth)
were analyzed along four transects in N, S, E and W directions (Figure 1).
The samples (SALSA. ASADO and PASADO) were mounted with immersion oil and 400
minerals grains were counted in each slide under optical microscope for the quali-quantitative
analysis. The phytolith morphotypes were described according to ICPN descriptors (Madella
et al. 2005).
Preliminary results of SALSA showed a predominance of phytoliths with respect to other
biomineralizations in the Laguna Potrok Aike samples (Figure 2). These were mostly
represented by rondel and elongated morphotypes, other phytolith morphologies (unciform
and cuneiform), chrysophytes and zooliths were also observed.
The results of ASADO showed a predominance of diatoms (entire and broken) with respect
to other biomineralizations in the four transects (Figure 3). Phytoliths were observed in low
percentages, and were mostly represented by rondel and elongated morphotypes, all
corresponding to the Pooide. A few bilobates phytoliths were observed and they were more
weathered. Due to the presence of vegetation around the wetland, phytoliths percentage was
higher in lower depths of it. In relation with phytolith distribution within the lagoon, higher
values were detected in the northern sector (transect 1) while the lower ones were in the
53
southern sector (transect 3) (Figure 3).The preliminary exporation of PASADO samples( 9
samples provided by Dr. Maidana), showed: two levels steriles, low contents of rondels and
elongates, largely altered and broken, associated with diatoms degraded, too.
Nowadays, wetland samples are still being collected in order to obtain a better understanding
of the phytolithic assemblage in relation to the vegetation of the area. These studies are
relevant and, through phytolith study, it is possible to make inferences about taphonomic,
environmental and paleoenvironmental processes in the core samples of PASADO project.
Ackowledgements. To Drs Marta Paez and Flavia Quintana for providing the studied
samples and to UNMDPfor the financial support (EXA 465/09)
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ROVNER I. 1971. Potential of opal phytolith for use in paleoecological reconstruction. Quaternary
Research 1: 343–359.
TWISS PC, SUESS E, SMITH RM. 1969. Morphological classification of grass phytoliths. Soil Science
Society of America Proceedings 33: 109–115.
54
Figure 1. Map location of the simples in the transects (ASADO)
Figure 2. Percentage of biomineralizations in some SALSA samples.
55
Figure 3. Percentage of biomineralizations in the ASADO samples.
56
How to interpret pollen assemblages from the Patagonic steppe
(49º-54ºS)
Paez, Marta Mercedes
Laboratorio de Paleoecología y Palinología. Facultad de Ciencias Exactas y Naturales. Universidad
Nacional de Mar del Plata. Funes 3250 (7600) Mar del Plata, Argentina. [email protected]
The interpretations on modern pollen assemblages (Quintana, 2009; Tonello et al., 2009;
Karsten et al., 2010) and pollen records of the Holocene (McCulloch and Davies, 2001;
Huber and Markgraf, 2003; Markgraf et al., 2003; Mancini et al., 2005; Villa-Martínez and
Moreno, 2007; Wille et al., 2007; Moreno et al., 2009; Quintana, 2009; Tonello et al., 2009;
Wille and Schäbitz, 2009) carried out in southern Patagonia call attention to some interesting
topics on climate and environmental inferences. This communication intends to analyze the
critical influence of these interpretations to the understanding of the structure and functioning
of the southern end of the Patagonic steppe ecosystem (49°-54°S), chiefly through its impact
on water dynamics (sensu Paruelo et al., 1998). This approach aims to reach a consensus
on the theoretical and methodological frameworks to be applied to future interpretations of
the PASADO lacustrine records.
Antecedents
In the nineties, the palynological studies were focused on the corroboration of
correspondence hypotheses among pollen associations, vegetation and climate
characteristics of Patagonia. The sampling design of modern samples consisted in the
recollection of surface soil samples from the main physonomical - floristic types developing
along west-east gradients. In their qualitative and quantitative analysis of pollen assemblages
and annual precipitation from arid and semiarid formations located between 38° - 46°S, Paez
et al. (2001) and Schäbitz (2003) put forward a series of features intrinsic to those pollen
assemblages (dispersion types, pollen deposition and plant cover, among others) to be used
as analogues in the palaeoclimatic reconstruction from pollen records.
In recent years, new theoretical and methodological frameworks emphasize the useful
approach of quantifying past climate parameters from pollen data by means of regional
pollen – climate calibrations (Seppä and Bennett, 2003; among others). Within the SALSA
project framework Quintana (2009) developed pollen – climate calibrations (annual and
monthly precipitation and temperature) from surface pollen samples in the 50°-54°S, 67°74°W range. Tonello and collaborators (2009) have worked out a modern pollen – climate
(annual precipitation) calibration set from surface pollen samples in the 46°-52°S, 67°-73°W
range.
Twenty five years from the beginning of the development of pollen data bases from
Patagonia, this newest pollen – climate calibration opens new questions for obtaining a
greater precision on pollen-based climate reconstructions.
a. Location of pollen records
For those records located in the Nothofagus forest and in the ecotone forest – steppe, the
available moisture (sensu Wille et al., 2007; Wille and Schäbitz, 2009) and precipitation or
moisture availability (sensu Tonello et al., 2009) explain changes in pollen assemblages of
plant formations: Nothofagus forests in contrast with Poaceae steppes. This interpretation is
consistent with studies that point out that at the continental scale the total amount of
precipitation is the main control of the differences between Patagonia and the Subantarctic
forests (Paruelo et al.,1998). The grass steppes from the ecotone forest - grass steppe are
characterized by the predominance of Festuca pallescens and they exhibit a series of
particular features (distribution, cover, species associations) with regard to the rest of the
Patagonian grass steppes. The pollen assemblages, still scarce, represent this structure with
57
high values of Poaceae, associated to low values of cushions and/or dwarf shrubs taxa. The
interpretations derived from these pollen assemblages are not extrapolative to those of other
Patagonian grass steppes.
b. Vegetation and climate in pollen assemblages of the steppe
The interpretation of pollen assemblages is much more complex when they represent a
diversity of vegetation types (physiognomies) and/or a greater diversity of communities or
plant associations which can be assigned to the Patagonian steppe. Seppä and Bennett
(2003) assert that “in plant ecological research the basic units of classification are plant
communities. The corresponding units of classification in pollen analysis are pollen
assemblage zones and temporal entities of pollen samples with relatively uniform pollen
composition (Ritchie, 1995)”. Since this proposition also fits at the spatial scale, the
interpretation of modern pollen assemblages from grass and shrub steppes requires an
evaluation of the ecological and palaeoecological theoretical framework.
The studies on Patagonian vegetation remark the intricacy of the influences of environmental
variables on plant water availability and water dynamics (sensu Paruelo et al., 1998) at
different spatial scales and in different sectors of Patagonia. Shrub species increase as mean
annual precipitation decreases and the percentage of winter precipitation increases. By
contrast, grass species increase as precipitation increases. Climate variables affect not only
the relative abundance of functional types (shrubs and grasses) but the species distribution,
plant cover changes and net primary production as well. Local factors (soil texture,
percentage of stones, appearance and slope, among others) also exert a major influence on
water dynamics (Fig. 1).
c. Modern pollen samples and multi - proxy data
With reference to the numerous contributions presented to the 1st International ICP-Worshop
PASADO the need arose to devote a greater attention to the pollen – climate training set
designs and to the selection of the site to be reconstructed. This proposal concluded with the
elaboration of the PIPA project (Proyecto Interdisciplinario Patagonia Austral), in which it is
assumed that every proxy takes its own unique place in the ecosystem network and can be
used to reconstruct different facets of the ecosystem (sensu Birks and Birks, 2006). In
particular, the need to evaluate whether a bias in pollen assemblages coming from surface
soil samples exist, since these samples become from depositional environments different
from those of lake stratigraphic records.
In this Project, modern pollen samples have been collected from sites representing similar
taphonomic (?) and sedimentary environments. Thirty five samples (17-800 m a.s.l.) from
permanent lagoon tops located between 49° - 51°S and 69° - 72°W are available. This range
comprises the Nothofagus pumilio and N. antarctica forests, the forest-steppe ecotone, the
grass -shrub steppe, and the Festuca gracillima and F. pallescens grass steppes. The
analysis of this data set will allow a better understanding of the relationships between
modern vegetation changes, the magnitude of compositional change, their causal factors and
related pollen-analytical implications. The development of multi – proxy (pollen, diatoms,
ostracods, chironomids) transfer functions will permit an increasing precision of
environmental and palaeoclimatic reconstructions. An immediate question to be solved,
related to these reconstructions in multi – proxy studies, will be to discriminate ‘signal’ from
‘noise’ (sensu Birks 1998). Will these interpretations facilitate the testing of problems or
hypotheses derived from modern ecology and vegetation as well as problems of insensitivity
that could arise from Holocene inferences?.
References
BIRKS, H.J.B., 1998. Numerical tools in palaeolimnology — progress, potentialities, and problems.
Journal of Paleolimnology 20, 307–332.
BIRKS, H. H. AND H.J.B. BIRKS. 2006. Multi-proxy studies in palaeolimnology. Vegetation History
and Archaeobotany 15, 235-251.
58
GONZALEZ, L., P. RIAL (Eds.). 2004. Guía geográfica interactiva de Santa Cruz. INTA.
HUBER, U.M., V. MARKGRAF. 2003. Holocene fire frequency and climate change at Rio Rubens Bog,
southern Patagonia. In: Veblen, T.T., Baker, W.L., Montenegro, G., Swetnam, T.W. (Eds.), Fire
and Climatic Change in Temperate Ecosystems of the Western Americas. Springer Verlag, New
York, pp. 357–380.
KARSTEN, S., C. OHLENDORF, T. HABERZETTL, A. LÜCKE, N.I. MAIDANA, C. MAYR, F.
SCHÄBITZ AND B. ZOLITSCHKA. 2010. Spatiel sediment distribution al laguna Potrok Aike,
southern Patagonia, Argentina – An areal survey to analyse the influence of late Holoecene
climate variability on sediment characteristics. 2nd International ICDP-Workshop PASADO. Vienna,
Austria, 31-39.
MARKGRAF, V, J.P. BRADBURY, A. SCHWALB, S.J. BURNS, C. STERN, D. ARIZTEGUI, A.
GILLI,F.S. ANSELMETTI, S. STINE, N. MAIDANA. 2003. Holocene palaeoclimates of southern
Patagonia: limnological and environmental history of Lago Cardiel, Argentina. The Holocene 13
(3), 597–607.
MCCULLOCH, R.D., S.J. DAVIES. 2001. Late-glacial and Holocene palaeoenvironmental change in
the central Strait of Magellan, southern Patagonia. Palaeogeography, Palaeoclimatology,
Palaeoecology 173, 143–173.
MORENO, P.I., FRANÇOIS, J.P., VILLA-MARTINEZ, R.P., MOY, C.M., 2009. Millenial-scale variability
in Southern Hemisphere westerly wind activity over the last 5000 years in SW Patagonia.
Quaternary Science Reviews 28, 25–38.
PAEZ M.M., F. SCHÄBITZ AND S. STUTZ. 2001. Modern pollen-vegetation and isopoll maps in
southern Argentina. Journal of Biogeography 28, 997–1021.
PARUELO, J.M., BELTRÁN, A., JOBBÁGY, E., SALA, O., GOLLUSCIO, R., 1998. The climate of
Patagonia: general patterns and controls on biotic process. Ecologia Austral 8, 85–101.
QUINTANA, F.A. 2009. Paleoambientes del extremo sur de Santa Cruz: análisis polínico de
sedimentos lacustres del Cuaternario tardío. Doctoral Thesis. Universidad Nacional de Mar del
Plata. 146 pp.
RITCHIE, J.C. 1995. Current trends in studies of long-term plant community dynamics. New
Phytologist 130, 469–494.
SCHÄBITZ, F., 2003. Estudios polínicos del Cuaternario en las regiones áridas del sur de Argentina.
Revista del Museo de Ciencias Naturales Bernardino Rivadavia Nueva Serie 5 (2), 291–300.
SEPPÄ, H., BENNETT, K.D., 2003. Quaternary pollen analysis: recent progress in palaeoecology and
palaeoclimatology. Progress in Physical Geography 27, 548–579.
TONELLO, M.S., M.V. MANCINI AND H. SEPPÄ. 2009. Quantitative reconstruction of Holocene
precipitation changes in southern Patagonia. Quaternary Research 72, 410–420.
VILLA-MARTÍNEZ, R., P. I. MORENO. 2007. Pollen evidence for variations in the southern margin of
the westerly winds in SW Patagonia over the last 12,600 years. Quaternary Research 68, 400–
409.
WILLE M., N.I. MAIDANA, F. SCHÄBITZ, M. FEY, T. HABERZETTL, S. JANSSEN, A. LÜCKE, C.
MAYR, C. OHLENDORF, G.H. SCHLESER, B. ZOLITSCHKA 2007. Vegetation and climate
dynamics in southern South America: the microfossil record of Laguna Potrok Aike, Santa Cruz,
Argentina. Review of Palaeobotany and Palynology 146.234–246
WILLE, M., F. SCHÄBITZ. 2009. Late-glacial and Holocene climate dynamics at the steppe/forest
ecotone in southernmost Patagonia, Argentina: the pollen record from a fen near Brazo Sur, Lago
Argentino. Vegetation History and Archaeobotany 18:3, 225-234
59
Figure 1: Influences of environmental variables on plant water availability (modified from Paruelo et al.,
1998). Distribution of pollen records in vegetation units (modified from González &
Rial,2004).
60
Fire History Reconstruction of southern South America
Preliminary results in the framework of PIPA (MINCyT)-PASADO (ICDP)
Flavia Andrea Quintana1 and María Martha Bianchi 2
1
CONICET-INIBIOMA-UNCO. Quintral 1250 (8400) San Carlos de Bariloche, Argentina; 2CONICETCentro Regional Universitario Bariloche (CRUB), Universidad Nacional del Comahue (UNCO).
[email protected]
Introduction
The Southern tip of South America constitutes an interesting area to study long-term trends
of fire regime in relation to past changes of vegetation and climate revealed by earlier studies
(Heusser, 2003; Markgraf et al., 2003; Wille et al., 2007).
Fire is considered as an important disturbance agent affecting directly the vegetation
structure and dynamics (Dentoni, 2001; Veblen et al., 2003; Witlock et al., 2007). Fire
frequency, intensity and seasonality fluctuate as a response to lightening frequency, wind
intensity and precipitation seasonality as well as fuel characteristics such as vegetation
structure, accumulation and desiccation (Dentoni, 2001; Veblen at al., 2003; Huber y
Markgraf, 2003).
Past fire activity can be reconstructed based on charcoal and pollen records recovered from
lakes. The combined analysis of pollen and macroscopic charcoal records is relevant to gain
a better understanding about vegetation, climate and natural/anthropogenic disturbances
relationships in temporal scales further than instrumental records. The reliability of such
reconstructions depends on the knowledge about what these proxies are representing today.
Very little is known about modern fire events taking place in forest and steppe ecosystems
placed between 50°-52°S, and how these events are reflected by lacustrine charcoal records.
A method to reconstruct local fire events analyzing contiguous macroscopic charcoal content
(>125µ) instead of microscopic charcoal is proposed. Microscopic charcoal counting on
pollen slides is a common method applied in many studies performed in southern South
America. However, it is dependent on the resolution of the pollen analysis which is nonadequate for calculating fire frequency. Besides, the source area is somehow unclear
(Whitlock and Larsen, 2001). In contrast, macroscopic charcoal analysis allows identifying
several characteristics of fires regimes such as frequency, intensity and severity.
The specific aims of this study were:
- Analyzing the macroscopic charcoal content of surface lakes sediments and short cores
along an east-west gradient between 50°-52°S.
- Surveying and mapping known fire events records occurred between 50°-52°S.
- Determining the charcoal particles >125µ content in the 16cm resolution (645 samples
involved) composite profile PASADO (5022-2).
- To determine periods of major interest in of the composite profile PASADO (5022-2) for
future high resolution analyses (every centimeter) in order to reconstruct the local fire
regime’s history (fire frequency, intensity and severity).
Method
Significant fire events were reconstructed indentifying intervals with great abundance of
charcoal particles. The fire source area was estimated from the predominant size of charcoal
particles, and the fuel composition analysis offered information about the type of vegetation
that has been burnt. Charcoal concentration by sample was determined.
Surface lakes sediments treatment:
61
A total of 32 lakes placed between 50-52°S in forest, forest-steppe transition and steppe
environments were sampled during January 2009 and April 2010. An amount of 5cc of
sediment per sample was treated with potassium hydroxide (10%) overnight. Samples were
filtered using mesh sieves of 250µ, 125µ and 63µ for obtaining different charcoal particle
sizes and counting was performed under stereomicroscope. Grass charcoal particles were
differentiated from the woody or other herbaceous types when possible.
Composite profile PASADO (5022-2) samples treatment:
A total of 115 samples were selected for starting the analysis of the PASADO site 2 core,
covering the average depth range of 3-1802cm (last ~15500 average Cal yr BP). An amount
of 1cc of sediment per sample was soaked in sodium hexametaphosphate (5%) overnight.
Samples were washed through a 125µ mesh sieve. A 125µ mesh size was selected because
it is assumed that particles greater than this size are not dispersed distant from the source
area, providing information about local fire history (Whitlock and Millspaugh, 1996; Whitlock
and Larsen, 2001). Counting was performed under stereoscopic microscope (Nikon E200,
fiber optic illuminator NI-30). Grass particles were differentiated from the other types of
charcoal particles. Chronology is based on the correlation of the pre-existing SALSA core
(Haberzettl et al. 2007) with the uppermost section of the PASADO site 2 core (uppermost
18,25m).
Results
Modern fire records were provided by CAP (Consejo Agrario Provincial) and PN (Parques
Nacionales), Seccional El Calafate, Santa Cruz province, Argentina. The records provided by
the CAP covered the periods 1995-1998 and 2000-2007, whereas the PN records enlarged
the discontinuous period 1989-2007. These records indicated that most of fires occurred due
to human intervention and natural causes like lightening were quite scarce.
Surface lakes sediments:
Macroscopic charcoal particles were found in 31 of the 32 lakes prospected. Concentration of
particles, indicative of local fire events, was low in every environment sampled (forest, foreststeppe transition and steppe) and fluctuated between 1-3part/cm3 (>250µ) and 6-11 (>125µ).
Concentration of particles indicative of regional fire events (>63µ) was high in the steppe
(76,5part/cm3) probable due to direction and intensity of the predominant westerly winds.
Concentration of this particle-size was lower in the
forest-steppe transition (~20part/cm3)
3
and the forest (~27part/cm ).
Composite profile PASADO (5022-2)
The preliminary charcoal analysis with a 16cm of resolution has shown the presence of
macroscopic particles >125µ in almost the whole record. The charcoal content in some
intervals with no signals of re-deposition was sometimes higher than those found in the
surface lake sediment.
Future steps
- Calibrating the relationship between the characteristics of modern fire events (location,
seasonality, size, frequency, intensity and severity) and macroscopic charcoal particles
deposition in lakes of Southern Santa Cruz (50°-52°S) in the line of Proyecto
Interdisciplinario Patagonia Austral (PIPA).
- Analyzing the macroscopic charcoal content of short cores from lakes located between 50°52°S in the forest, forest-steppe transition and steppe environments to calibrate intervals
with great abundance of charcoal particles with historical fires records.
- Reconstructing the fire history of the Southern tip of South America based on macroscopic
charcoal data obtained from cores within PASADO project.
- Comparing macroscopic charcoal data with the pollen trends of the same periods to
perform a complete reconstruction of past fire regimes.
62
References
DENTONI, M. 2001. Fire Situation in Argentina. In FAO (Ed.), Global Forest Fire Assesment 1990 –
2000. Forest Resources Assesment Programme, Working Paper 55. FAO. Rome. pp. 457 – 462.
HABERZETTL, T., CORBELLA, C., FEY, M., JANSSEN, S., LÜCKE, A., MAYR, C., OHLENDORF, C.,
SCHÄBITZ, F., SCHLESER, G.H., WILLE, M., WULF, S., ZOLITSCHKA, B., 2007. Lateglacial
and Holocene wet-dry cycles in southern Patagonia: chronology, sedimentology and
geochemistry of a lacustrine sediment record from Laguna Potrok Aike, Argentina. The Holocene
17, 297–310.
HEUSSER, C.J., 2003. Ice Age southern Andes: a chronicle of paleoecological events. Developments
in Quaternary Science 3. Elsevier. Amsterdam.
HUBER, U.M. AND MARKGRAF, V. 2003. Holocene fire frequency and climate change at Rio Rubens
Bog, southern Patagonia. In Veblen T.T., Baker, W.L., Montenegro, G. and Swetnam., editors.
Fire and climatic change in temperate ecosystems of the western Americas. Ecological Studies
160. New York. Springer: 357 – 380.
MARKGRAF, V., BRADBURY, J. P., SCHWALB, A., BURNS, S. J., STERN, C., ARIZTEGUI, D.,
GILLI, A., ANSELMETTI, F. S., STINE, S., MAIDANA, N., 2003. Holocene palaeoclimates of
southern Patagonia: limnological and environmental history of Lago Cardiel, Argentina. The
Holocene. 13, 581-591.
VEBLEN, T.T., KITZBERGER, T., RAFFAELE, E. AND LORENZ, D.C. 2003. Fire history and
vegetation change in northern Patagonia, Argentina. In Veblen T.T., Baker, W.L., Montenegro, G.
and Swetnam., editors. Fire and climatic change in temperate ecosystems of the western
Americas. Ecological Studies 160. New York. Springer: 357 – 380.
WHITLOCK C., MORENO, P.I. AND BARTLEIN, P. 2007. Climatic controls of Holocene fire patterns in
southern South America. Quaternary Research 68, 28-36.
__________; and LARSEN, C.. 2001. Charcoal as a fire proxy. En: Smol, J.P., H.J.B. Birks y M. Last
(Eds.). Tracking Environmental Change Using Lake Sediment. Volume 3: Terrestrial, Algal and
Siliceous Indicators: 75-97. Kluwer Academic Publishers. Dordrecht. The Netherlands.
__________; AND MILLSPAUGH, S.H. 1996. Testing the assumptions of fire - history studies: an
examination of modern charcoal accumulation in Yellowstone National Park, USA. The Holocene
6: 7 – 15.
WILLE, M., MAIDANA, N.I., SCHÄBITZ, F., FEY, M., HABERZETTL, T., JANSSEN, S., LÜCKE, A.,
MAYR, C., OHLENDORF, C., SCHLESER, G.H., ZOLITSCHKA, B., 2007. Vegetation and
climate dynamics in southern South America: the microfossil record of Laguna Potrok Aike, Santa
Cruz, Argentina. Review of Palaeobotany and Palynology 146, 234–246.
63
Bioproxies of lacustrine sediments from Southern Patagonia: filling
the gap on ostracod biodiversity in the southernmost tip of
South America
Josefina Ramón Mercau1,3 & Cecilia Laprida2,4
1
Depto de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales,
Universidad de Buenos Aires, Buenos Aires, Argentina [email protected]; 2 Depto de Ciencias
Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires,
Argentina. [email protected], 3 FONCYT Fellowship, 4 CONICET.
Introduction
Ostracods (Arthropoda, Crustacea) constitute a diverse group which can be found in
a wide range of both marine and non-marine habitats, from the poles to the equator.
They secrete a calcite bivalve carapace of high potential of preservation, thanks to
which they have left an excellent fossil record extended as deep as the Ordovician. In
addition to their wide geographical and geological range, the marked preferences of
some species to particular environmental conditions render ostracods good proxies
of environmental change (Horne, 2002).
As with other biological proxies, use of ostracods for paleoenvironmental
reconstructions requires a deep knowledge of their taxonomy and ecology, a
requisite usually not met especially in remote areas. One of such poorly studied
areas is Southern Patagonia, a region of particular interest for Quaternary
paleoclimatic research as the sole emerged landmass in high latitudes in the
Southern hemisphere besides Antarctica (Zolitschka et al, 2006). During the last few
years, a number of multiproxy paleolimnological studies have been carried out in the
region (Schäbitz et al, 2003; Zolitschka et al, 2004; Haberzettl et al, 2005; Mayr et al,
2005; Haberzettl et al, 2005; Haberzettl et al, 2006; Haberzettl et al, 2007 a;
Haberzettl et al, 2007 b; Mayr et al, 2007; Wille et al, 2007; Fey et al, 2009), but none
of them including ostracods. In Patagonia, the southernmost studies in which modern
and fossil ostracods are considered are from Lakes Cardiel and Cari-Laufquen,
situated in Eastern Central Patagonia (Cusminsky & Whatley, 1996; Whatley &
Cusminsky, 2000; Schwalb et al, 2002; Cusminsky et al, 2005). The use of ostracods
in Southern Patagonia could be extended if more precise taxonomical and ecological
information was available. The Southern Patagonia Interdisciplinary Project (PIPA,
by its Spanish abbreviation) aims to partially fill this gap with regards to selected
bioproxies –ostracods, chironomids and diatoms- in order to provide the basic
foundations for future paleoclimatic research in the region. The Project contemplates
both the generation of new knowledge and the compilation of existing information. In
particular, the research of Cusminsky & Whatley (1996), Whatley & Cusminsky
(2000), Schwalb et al (2002) and Cusminsky et al (2005) among others constitute the
fundamental precedent for the study of Patagonian ostracods and as such were
carefully considered in our studies.
Materials and Methods
Two fieldtrips were carried out in January, 2009 and April, 2010. Superficial
sediments and water were sampled from 33 water bodies located between 49° - 52°
S and 69° - 73° W in Southern Santa Cruz (Table 1).
64
Site
Lat. (S)
Long. (W)
Site
Lat. (S)
Long. (W)
Site
Lat. (S)
Long. (W)
L. Agustín
L. Alta
L. Azul
L. Azul II
L. Banderas
L. Cachorro I
L. Cachorro II
L. Capri
L. Cerro Frías I
L. Cerro Frías II
L. Cóndor
49º 36’ 50’’
50º 25' 31''
52º 04’ 29’’
49º 12' 57''
50º 17’ 92’’
50º 28' 58''
50º 29' 34''
49º 18' 13''
50º 19’ 10’’
50º 19’ 07’’
49º 11’ 15’’
72º 10’ 55’’
71º 51' 52''
69º 34’ 52’’
72º 58' 32''
72º 46’ 77’’
72º 26' 46''
72º 27' 44''
72º 55' 42''
72º 47’ 45’’
72º 47’ 32’’
72º 56’ 58’’
L. del Desierto
L. El Toro
L. Ernesto
L. Esperanza
L. Hija
L. Huemul
L. Las Lolas I
L. Las Lolas II
L. Madre
L. Mellizas
L. Nieta
49º 04’ 45’’
49º 34’ 52’’
50º 10' 38''
51º 12’ 04’’
49º 18' 09''
49º 04’ 23’’
49º 13' 33''
49º 13' 19''
49º 17' 25''
50º 31’ 29’’
49º 18' 30''
72º 53’ 15’’
72º 21’ 00’’
72º 50' 00''
72º 05’ 04’’
72º 57' 08''
72º 54’ 06’’
72º 57' 54''
72º 58' 00''
72º 56' 40''
72º 47’ 43’’
72º 57' 04''
L. Pajonales
L. Potrok Aike
L. Rincón
L. Roca
L. Salada
L. Sarmiento
L. Torres
L. Verde
L. Sosiego I
L. Sosiego II
49º 23' 07''
51º 37’ 27’’
50º 13' 38''
50º 26’ 28’’
51º 07’ 08’’
50º 28’ 30’’
49º 19’ 49’’
49º 12' 34''
50º 10' 49''
50º 11' 05''
72º 54' 13''
69º 13’ 24’’
71º 45' 43''
72º 37’ 34’’
71º 52’ 55’’
71º 47’ 41’’
72º 59’ 21’’
72º 58' 25''
72º 46' 03''
72º 45' 45''
Table 1. Name and location of the waterbodies sampled in the present study.
The sediment samples were washed under tap water on a 75 µm pore diameter sieve
and dried by thermostatic stove at 40 ºC. Five grams of sediment from each sample
were examined under stereomicroscope and any ostracods found were picked out
with a brush and placed in a micropaleontological slide. For the time being, 23
samples have been entirely analysed, while another four have been preliminary
screened for ostracods. Ostracods were determined at specific level based on
specialized bibliography (Cusminsky & Whatley, 1996; Cusminsky et al, 2005;
Meisch, 2000; Martens & Behen, 1994; Rossetti & Martens, 1998).
Water temperature, pH, conductivity, dissolved oxygen and Total Dissolved Solids
(TDS) were measured in situ with a Hanna HI 9828 Multiparameter Portable Meter.
The water samples obtained simultaneously with the sediment samples from all the
sites were cold stored and analyzed for elemental analyses, TN, TP and TC at the
CNR – ISE (Istituto per lo Studio degli Ecosistemi, Verbania Pallanza, Italy). Water
type of both the sites sampled in this study and those presented in the works of
Schwalb et al (2002) and Cusminsky et al (2005) was determined with the use of the
AquaChem© software.
Results and Discussion
Waterbodies characterization
The sampled sites are quite variable with respect to most chemical parameters
measured. Two of the lakes are one (Laguna Potrok Aike) or two (Laguna Salada)
orders of magnitude more saline than the rest, so they are considered outliers with
regards to ionic composition considerations. Likewise, Laguna Salada and Lago Las
Mellizas -both with total phosphorus (TP) content an order of magnitude greater than
the highest TP values of the rest of the dataset- are excluded from the analysis of the
variability of trophic status. Even with the exclusion of outliers from the dataset, the
measurements obtained are very variable (coefficients of variation range between
approximately 1 and 3) so median values and ranges are informed, rather than
means and standard deviations.
Conductivity varies between 14 and 550 µS/cm, with a median value of 78 µS/cm.
For its part, pH ranges between 6.49 and 8.35, with a median value of 7.33. The
majority of the lakes within the set have alkaline –that is, calcium and bicarbonate
dominated- waters (Figure 1). Median total alkalinity (TA) is 0.71 meq/l (0.117 –
4.100 meq/l), while median Ca+2 content is 13.05 mg/l (1.59 – 94 mg/l). As for more
saline waters, five lakes are chlorine or sulfate dominated, four are sodium
dominated and seven have similar proportions of Na+, Ca+2 and Mg+2. Median Clconcentration is 0.85 mg/l (0.11 – 25.60 mg/l) and median SO4-2 concentration is 4.84
mg/l (0 – 221.7 mg/l). Na+ content varies between 0.21 and 88.60 mg/l (median
65
value: 3.01 mg/l); median K+ content is 0.59 mg/l (0.06 – 7.94 mg/l) and median Mg+2
concentration is 1.46 mg/l (0.08 – 15.30 mg/l).
With regards to the trophic status, most of the lakes can be classified as oligotrophic
or mesotrophic, with a median value of 7 µg/l of total phosphorus (TP) content,
although the dataset covers a wide range of conditions, including some eutrophic and
hypertrophic lakes (range: 1 – 398 µg/l TP). Variability of total nitrogen (TN) content
and total organic carbon (TOC) content is much less pronounced; the former varies
between 0.06 and 2.34 mg/l (median concentration: 0.25 mg/l) and the latter between
0.22 and 20.34 mg/l (median concentration: 3.26 mg/l). The latter values are
calculated excluding Laguna Salada.
Modern Southern Patagonia Ostracod assemblages: qualitative approach
Of the 23 samples examined so far, ten were fertile (Table 2), although only sporadic
occurrences (1 to 5 individuals) were registered in six of those samples. The most
diverse assemblage was recovered from Lago Cerro Frías I, were 9 species were
present.
Ostracod
assemblages
Environmental characteristics
Site type
Water type
Conductivity
Trophic status
(µS/cm)
(TP content, µg/l)
pH
S
Diversity
(H)
L. Cerro Frías I
P.L
Ca-Na-Mg-HCO3
7.78
390
Mesotrophic (16)
9
1.616
L. El Toro
P. L
Na-Ca-Mg-HCO3
8.11
500
Oligotrophic (7)
7
1.483
L. Sosiego I
P. Po
Ca-HCO3
8.69
327
Eutrophic (35)
2
0.3768
L. Pajonales
P. Po
Ca-Na- HCO3
8.85
35
Oligotrophic (1)
1
0
L. Las Lolas II
P. Po
Ca-HCO3
7.00
43
Hypereutrophic (116)
*
*
L. Hija
P.L
Ca-HCO3
7.74
82
Oligotrophic (4)
*
*
L. Mellizas
P.L
Ca-Na-Mg-HCO3
8.14
298
Hypereutrophic (1475)
*
*
L. Verde
P.L
Ca-Na-HCO3-SO4
8.06
17
Oligotrophic (5)
*
*
L. Desierto
P.L
Ca-Mg-HCO3
7.35
5
Hypereutrophic (136)
*
*
L. Ernesto
P.L
Ca-SO4-HCO3
8.71
624
Mesotrophic (13)
*
*
Table 2. Characterization of the sites were ostracods were found. Sites marked with an (*)
with reference to ostracod assemblages are those were only sporadical occurrences were
registered. P= Permanent; L= Lake; Po = Pond
Abundance and diversity of assemblages are unexpectedly low; a total of eleven
species (Table 3) were found. Those species which had already been cited for
Northern Patagonian settings are discussed below.
The sites were L. patagonica was found in the present study and those of Schwalb et
al (2002) and Cusminsky et al (2005) are permanent lakes with Na-Ca-Mg,
bicarbonate-dominated waters. On the contrary, L. rionegroensis inhabits mainly
ephemeral waterbodies with Cl / SO4-HCO3-Cl, sodium-dominated waters (Schwalb
et al, 2002; Cusminsky et al, 2005). This evaluation of the information gathered so far
on these species strengthens their proposed use as indicators of opposed prevailing
environmental conditions.
A similar consideration of the eucyprids E. virgata, E. cecryphalium and E. fontana
allows to characterize them as inhabitants of Na-Ca-Mg, bicarbonate-dominated
66
waters; the latter species can also be found in Na-HCO3 waters. While E. virgata and
E. fontana have been found both in permanent and ephemeral habitats, E.
cecryphalium has been found so far only in permanent lakes and - with very low
abundance - in a stream (Schwalb et al, 2002; Cusminsky et al, 2005).
Another noteworthy constituent of the ostracod assemblages is I. ramirezi, which is
by far the dominant species in Lago Cerro Frías I. Schwalb et al (2002) and
Cusminsky et al (2005) have found this species in Na-Ca-Mg-HCO3 waters, which is
in accordance with our findings, as well as in one site with NA-HCO3 waters. These
authors have proposed this species as an indicator of running waters. However, both
of the sites were it was found –alive- in this study are permanent lakes and there
were no creeks or seeps in the vicinity of the sampling point. Therefore, some
considerations on the ecological preferences of I. ramirezi might need to be revisited.
The last species from our dataset already mentioned by Schwalb et al (2002) and
Cusminsky et al (2005) for Northern Patagonia is K. megapodus, found by these
authors with very low abundances (≤ 2%) in chlorurated and/or sulphated, sodium
dominated waters. In this study K. megapodus was found with somewhat higher
abundances (≈ 8%) in Na-Ca-Mg, bicarbonate dominated waters. This species might
therefore be considered as (slightly) tolerant of saline waters, but more characteristic
of alkaline waters.
As for other species, it is noteworthy that this work is, to our knowledge, the first
report of Isocypris beauchampi in the Argentinean Patagonia, and the southernmost
report of the darwinulid Penthesilenula incae. The latter species has been cited for
Peru, Bolivia and thermal waters in the Argentinean Altiplano (Laprida et al, 2006)
and, as discussed by Rossetti and Martens (1998), it is probably a junior synonym of
P. setosa, described by Daday (1902) from Santa Cruz Province, Argentina.
However, the poor descriptions and illustrations do not allow for comparison between
the two. In our study, the four samples where darwinulids were present bore
individuals with two to five (usually three) larvae retained within the caparace. As far
as we know, this constitutes the first report on the reproductive biology of P. incae.
Conclusions
More basic research is needed in order to shift from qualitative to quantitative use of
ostracods for environmental reconstruction in the area. In view of the useful but
relatively poor ostracod data obtained, the sampling strategy needs to be redefined.
Due to operational reasons, sampling was concentrated on littoral zones, often with
little or no aquatic vegetation, to which ostracods are associated. A more thorough
sampling of different habitats within each waterbody should yield better results; the
occasional individuals found in six lakes are evidence that ostracods are present in
some of the sampled sites, but were inadequately looked for.
Acknowledgments
The authors wish to thank the Istituto per lo Studio degli Ecosistemi (CNR – ISE) for
the chemical analysis of the water samples.
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Ostracods from Patagonia, Argentina. Revista Española de Micropaleontología. 37(3): 431 – 450
_________ & WHATLEY, R. C. 1996. Quaternary non-marine ostracods from lake beds in northern
Patagonia. Revista Española de Paleontología. 11(2): 143 – 154
67
DADAY, E. 1902. Mikroskopische süsswaserthiere aus Patagonien, gesammelt von Dr. Filippo
Silvestri. Természetrajzi futzetek. 25: 201 - 310
FEY, M.; KORR, C.; MAIDANA, N.; CARREVEDO, M. L.; DIETRICH, S.; CORBELLA, H.;
HABERZETTL, T.; KUHN, G.; LÜCKE, A.; MAYR, C.; OHLENDORF, C.; SCHÄBITZ, F. &
ZOLITSCHKA, B. 2009. Palaeoenvironmental changes during the last 1600 years inferred from
the sediment record of a cirque lake in southern Patagonia (Laguna Las Vizcachas, Argentina).
Palaeogeography, Palaeoclimatology, Palaeoecology. 281: 363 – 375
HABERZETTL, T.; FEY, M.; LÜCKE, A.; MAIDANA, N.; MAYR, C.; OHLENDORF, C.; SCHÄBITZ, F.;
SCHLESER, G.H.; WILLE, M. & B. ZOLITSCHKA. 2005. Climatically induced lake level changes
during the last two millennia as reflected in sediments of Laguna Potrok Aike, southern Patagonia
(Santa Cruz, Argentina). Journal of Paleolimnology. 33: 283 – 302
_________; WILLE, M.; FEY, M.; JANSSEN, S.; LÜCKE, A.; MAYR, C.; OHLENDORF, C.;
SCHÄBITZ, F.; SCHLESER, G.H. & ZOLITSCHKA, B. 2006. Environmental change and fire
history of southern Patagonia (Argentina) during the last five centuries. Quaternary International.
158: 72 – 82
_________; CORBELLA, H.; FEY, M.; JANSSEN, S.; LÜCKE, A.; MAYR, C.; OHLENDORF, C.;
SCHÄBITZ, F.; SCHLESER, G. H.; WESSEL, E.; WILLE, M.; WULF, S. & ZOLITSCHKA, B. 2007.
A continuous 16,000 year sediment record from Laguna Potrok Aike, southern Patagonia
(Argentina): Sedimentology, chronology, geochemistry. The Holocene. 17: 297 – 310
_________; MAYR, C.; WILLE, M. & ZOLITSCHKA, B. 2007. Linkages between southern hemisphere
westerlies and hydrological changes in semi-arid Patagonia during the last 16,000 years. PAGES
News 15 (2): 22 – 23
HORNE, D. J., COHEN, A. & MARTENS, K. 2002. Taxonomy, Morphology and Biology of Quaternary
and Living Ostracoda. In: J. Holmes and A. R. Chivas (eds.), The Ostracoda: Applications in
Quaternary Research. AGU Geophysical Monograph Series. 131: 5 – 36
LAPRIDA, C.; DÍAZ, A. & RATTO, N. 2006. Ostracods (Crustacea) from thermal waters, southern
Altiplano, Argentina. Micropaleontology. 52 (2): 177 – 188
MARTENS, K. Y BEHEN, F. 1994. A checklist of the Recent non-marine ostracods (Crustacea,
Ostracoda) from the Inland waters of South America and adjacent islands. Travaux scientifiques
du Musée National d'Historie Naturelle de Luxembourg. 22: 84 pp.
MAYR, C.; FEY, M.; HABERZETTL, T.; JANSSEN, S.; LÜCKE, A.; MAIDANA, N.I.; OHLENDORF, C.;
SCHÄBITZ, F.; SCHLESER, G.H.; WILLE, M. & ZOLITSCHKA, B. 2005. Palaeoenvironmental
changes in southern Patagonia during the last millennium recorded in lake sediments from Laguna
Azul (Argentina). Palaeogeography, Palaeoclimatology, Palaeoecology. 228: 203 - 227
_________; WILLE, M.; HABERZETTL, T.; FEY, M.; JANSSEN, S.; LÜCKE, A.; OHLENDORF, C.;
OLIVA, G.; SCHÄBITZ, F.; SCHLESER, G. H. & ZOLITSCHKA, B. 2007. Holocene variability of
the Southern Hemisphere westerlies in Argentinean Patagonia (52°S). Quaternary Science
Reviews. 26: 579 - 584
MEISCH, C. 2000. Freshwater Ostracoda of Western and Central Europe. En J. Schwoerbel and P.
Zwick (Eds): Suesswasserfauna von Mitteleuropa 8/3. Spektrum Akademischer Verlag,
Heidelberg, Berlin. 522 pp
ROSSETTI, G. & MARTENS, K. 1998. Taxonomic revision of the Recent and Holocene
representatives of the Family Darwinulidae (Crustacea, Ostracoda), with a description of three
new genera. Biologie. 68: 55 - 110
SCHÄBITZ, F.; PÁEZ, M.M.; MANCINI, M.V.; QUINTANA, F.A.; WILLE, M.; CORBELLA, H.;
HABERZETTL, T.; LÜCKE, A.; PRIETO, A.R.; MAIDANA, N.; MAYR, C.; OHLENDORF, C.;
SCHLESER, G.H. & ZOLITSCHKA, B. 2003. Estudios paleoambientales en lagos volcánicos en la
Región Volcánica de Pali Aike, sur de Patagonia (Argentina): palinología. Revista del Museo
Argentino de Ciencias Naturales, Nueva Serie. 5: 301 - 316
SCHWALB, A.; BURNS, S. J.; CUSMINSKY, G. C.; KELTS, K. AND MARKGRAF, V. 2002.
Assemblage diversity and isotopic signals of modern ostracodes and host waters from Patagonia,
Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology. 187(3-4): 323 – 339
WHATLEY, R. C. AND CUSMINSKY, G. C. 2000. Quaternary lacustrine ostracoda from Northern
Patagonia: a review. In: E.H. Gierlowski-Kordesch and K.R. Kelts (eds.), Lake Basins Through
Space and Time. AAPG Special Volumes. 46: 581 – 590
WILLE, M.; MAIDANA, N.; SCHÄBITZ, F.; FEY, M.; HABERZETTL, T.; JANSSEN, S.; LÜCKE, A.;
MAYR, C.; OHLENDORF, C.; SCHLESER, G. H. AND ZOLITSCHKA, B. 2007. Vegetation and
climate dynamics in southern South America: The microfossil record of Laguna Potrok Aike, Santa
Cruz, Argentina. Review of Palaeobotany and Palynology. 146: 234 – 246
68
ZOLITSCHKA, B.; SCHÄBITZ, F.; LÜCKE, A.; WILLE, M.; MAYR, C.; OHLENDORF, C.;
ANSELMETTI, F.; ARIZTEGUI, D.; CORBELLA, H.; ERCOLANO, B.; FEY, M.; HABERZETTL, T.;
MAIDANA, N.I.; PÁEZ, M.M. AND SCHLESER, G.H. 2004. Climate changes in Santa Cruz
(southern Patagonia, Argentina ) inferred from crater lake sediments – The multi-proxy approach
of SALSA. PAGES Newsletter. 12: 9 - 11
_________; SCHÄBITZ, F.; LÜCKE, A.; CLIFTON, G.; CORBELLA, H.; ERCOLANO, B.;
HABERZETTL, T.; MAIDANA, N.; MAYR, C.; OHLENDORF, C.; OLIVA, G.; PÁEZ, M.M.;
SCHLESER, G.H.; SOTO, J.; TIBERI, P.; WILLE, M. 2006. Crater lakes of the Pali Aike Volcanic
Field as key sites of paleoclimatic and paleoecological reconstructions in southern Patagonia,
Argentina. Journal of South American Earth Sciences. 21: 294 - 309
Species / Site
L. Cerro Frías
I
L. El Toro
L. Sosiego I
L.
Pajonales
Darwinula cf. D. stevensoni
Potamocypris smaragdina
0
0
87.5
100
0
0.4
12.5
0
Ilyocypris ramirezi
50.9
2.8
0
0
Penthesilenula incae
8
13.9
0
0
Limnocythere patagonica
9.1
52.8
0
0
Eucypris virgata
3.3
0
0
0
Eucypris fontana
12.7
5.6
0
0
Eucypris cecryphalium
4
11.1
0
0
Kapcypridopsis megapodum
6.9
8.3
0
0
Isocypris beauchampi
4.7
0
0
0
Candoninae sp
5.6
0
0
0
Table 3. Ostracod assemblage composition of the sites.
Figure 1. Piper plot depicting water ionic composition of the 32 waterbodies sampled in the present
study. Open circles represent lakes and ponds where no or scarce ostracods were found, while filled
symbols represent the lakes which yielded fertile samples.
69
The diatom record of Laguna Potrok Aike, Argentina
Cristina Recasens1, Daniel Ariztegui1, Nora Irene Maidana2,3 and the PASADO
Scientific Team
1
Section of Earth and environmental Sciences, University of Geneva, Switzerland; 2 Departamento de
Biodiversidad y Biología Experimental, FCEyN-UBA, Argentina; 3 CONICET
Diatom analysis of the sediment record from Laguna Potrok Aike, obtained in the
framework of the ICDP-sponsored project PASADO (Potrok Aike Maar Lake
Sediment Archive Drilling Program), provides a continuous record of hydrological and
climatic changes since the Late Pleistocene. Previous multi-proxy studies in the area
have characterized the environmental history of the drylands in the Patagonian
Steppe for the last 16,000 cal BP (Wille et al. 2007).
Diatoms are widely used to characterize and often quantify the impact of past
environmental changes in aquatic systems. Diatomological analysis was performed
on a set of 94 samples from PTA-1D (Fig.1), a 97.3 m long sedimentary core from the
central part of the lake that spans approximately the last 50 kyrs (ongoing
radiocarbon datings will better constrain the age model). We use variations in diatom
concentration and in their taxonomical assemblages, blended with other proxies, to
track changes in lake conditions and tackle the most interesting sections to carry out
higher resolution analyses (in composite core 2, see location map).
Diatom concentrations fluctuate between 0 and 7x108 valves/gr along the core and so
far more than 200 different taxa have been identified in the sediment (including
several endemic species and most probably some new species). The results for the
main taxa are reprensented in figure 1. While Cyclotella agassizensis dominates in
the top part of the core together with Thalassiosira patagonica, as previously seen in
earlier studies on this lake, these indicators of more brackish conditions are rare or
not found at all in deeper sediments. The first occurrence of certain species and the
correlation of the record with the previous short core studied allows us to
approximately locate an age of 15’560 cal yr BP corresponding with the appearance
of Cyclostephanos patagonicus (between 12 and 15m sediment depth) and an age of
approximatively 8’600 cal yr BP corresponding to a peak in Thalassiosira patagonica
at about 8-10m depth. Variations in the planktonic/non-planktonic species ratio, with
a particularly high amount of non-planktonic taxa between 12 and 17m sediment
depth, could point toward lower lake-level stands or periods of ice-cover in the lake.
Nevertheless, a correlation with other proxies is necessary to further develop these
hypotheses.
The multi-proxy approach of the PASADO project, and its combination with the
modern training set for Patagonia that will be produced within the framework of the
ongoing PIPA argentine project, will provide unique paleoecological information for
the Southern Hemisphere.
References:
WILLE, M., MAIDANA, N.I., SCHABITZ, F., FEY, M., HABERZETTL, T., JANSSEN, S., LUCKE, A.,
MAYR, C., OHLENDORF, C., SCHLESER, G.H., AND ZOLITSCHKA, B., 2007. Vegetation and
climate dynamics in southern South America: the microfossil record of Laguna Potrok Aike, Santa
Cruz, Argentina. Rev. Palaeobot. Palynol.
70
Fig.1: Drilling sites. Core PTA-1D is located in drilling site 1. The composite core were higher
resolution multiproxy analyses will be carried out is located in site 2.
Fig.2: Diatom diagram of core PTA-1D (only dominant taxa are shown)
71
Paleoclimate reconstructions based on the pollen record from
Laguna Potrok Aike
Frank Schäbitz, Michael Wille and the PASADO Science Team
Laguna Potrok Aike located in southern Argentina is one of the very few locations
that are suited to reconstruct the paleoenvironmental and climatic history of southern
Patagonia. In the framework of the multinational ICDP deep drilling project PASADO
several long sediment cores to a composite depth of more than 100 m were obtained.
Here we present first results of pollen analyses from sediment material of the core
catcher and lower parts of the composite profile on the base of the first age model
covering roughly the last 50 ka BP. Pollen spectra with a spatial resolution of three
meters show that Laguna Potrok Aike was always surrounded by Patagonian Steppe
vegetation. However, the species composition underwent some marked proportional
changes through time. The uppermost pollen spectra show changing but high
contribution of Andean forest and charcoal particles as it can be expected for
Holocene times and the ending last glacial. The middle part shows no or very low
forest signals and relatively high amounts of pollen from steppe plants indicating cold
and dry full glacial conditions. The lowermost samples are characterized by a
significantly different species composition as steppe plants like Asteraceae,
Caryophyllaceae, Ericaceae and Ephedra became more frequent. In combination
with higher charcoal amounts and an algal species composition comparable to
Holocene times we suggest that conditions during the formation of sediments at the
base of the PASADO record were more humid and/or warmer causing a higher fuel
availability for charcoal production compared to full glacial times. Furthermore,
reconstructed precipitation amounts based on a transfer function between pollen and
climate values are presented for the first analyzed PASADO-pollen samples.
72
Living microbial activity in Lake Potrok-Aike sediments and its role
during early diagenesis
A. Vuillemin1, D. Ariztegui1, J. Pawlowski2, C. Vasconcelos 3, F.S. Anselmetti 4 and
the PASADO Science Team
1
Section of Earth and Environmental Sciences, University of Geneva, Switzerland; 2 Department of
Zoology, University of Geneva, Switzerland; 3 Geological Institute, ETH-Zürich, Switzerland; 4 Eawag,
Dübendorf, Switzerland.
At present microbial activity in sediments is fully recognized as a major player in early
diagenetic processes (Nealson and Stahl, 1997; Frankel and Bazylinski, 2003).
Results from cores retrieved during ODP and IODP -sponsored drilling campaigns
have shown that these organisms are active even in extreme environments such as
basaltic subseafloor, and capable of catalyzing and enhancing diagenetic reactions.
The distribution and diversity of microbes in marine sediments have been already
studied for several years but there is a lack of these investigations in their lacustrine
counterparts (Parkes et al., 1994; D’Hondt et al., 2004; Teske, 2005). In lake basins
these studies are focusing mainly on the water column and/or very recent sediments
(Humayoun et al., 2003; Spring et al., 2000; Zhao et al., 2007). Modern lakes are
ideal systems to study early diagenetic processes, combining physical, chemical and
biological aspects on subrecent sediments. Geomicrobiology studies allow to
determine the role played by microbes in this late process, as microbial biomass,
although ruling a substantial part of the organic matter record, is still difficult to
distinguish from terrestrial or algal inputs. Other factors such as grain size and/or
nutrient availability are instrumental on the colonization of lacustrine substrates by
microbes. These two factors are highly dependent on the hydrological regime and,
therefore, directly related to lake levels.
A seismic study of Laguna Potrok Aike in the Santa Cruz province, Argentina,
showed a thick sedimentary sequence (Anselmetti et al., 2009) that was the target of
the PASADO project. This international research initiative had a key objective:
quantitative climatic and environmental reconstruction of this remote area through
time (Zolitschka et al., 2009). The multiproxy investigation of these lacustrine
sediments provides unique material to initiate – for the first time in an ICDP project –
a systematic study of the living lacustrine subsurface environment. From a total of
533 m of sediment cores recovered at 100 m water depth a 1 m long gravity core
PTA-1I and the 97 m long hydraulic piston core PTA-1D were sampled following a
newly established strategy to obtain semi-aseptic samples for geomicrobiological
studies. A sampling strategy was specially defined to track microbial activity enabling
the inspection of undisturbed lacustrine sediments through depth (Vuillemin et al., in
press). Special windows were cut in the liners for direct sampling under the most
sterile conditions possible immediately after core recovery. Samples from sixty
windows were immediately chemically fixed and/or frozen, optimizing the
preservation of their initial conditions for further analyses such as methane
determination, cell counting, DGGE (molecular fingerprinting technique) and cell
cultivation. In situ ATP measurements were taken as indication of living organisms
within the sediments. The presence of ATP is a marker molecule for living cells since
it is not known to form abiotically.
73
ATP can be easily detected with high sensitivity and high specificity using an
enzymatic assay
ATP + Luciferin + O2 –> AMP + Oxyluciferin + PPi + CO2 + Light
Light is emitted as a result of the reaction, which is detected by a photomultiplier. We
used the Uni-Lite NG Luminometer (Biotrace International Plc., Bridgend, UK), in
combination with the “Clean-Trace” and “Aqua-Trace” swab kits, which measure ATP
concentrations by a firefly enzyme-based test. The sensitivity of the test is on the
order of 20-40 microbes, as expressed in RLU (relative light units) or 0.01
attomoles/ml water, corresponding to about 5 cells of Escherichia coli. This handheld
device was previously tested at the Geomicrobiology Laboratory, ETH Zurich
(Switzerland) indicating that this method could be applied on geological material,
such as rock surfaces and other environmental biofilms. It was successfully used for
fast and accurate measurement of life activity for freshly retrieved cores in lithified
sediments of the IODP Expedition 310 in Tahiti (Camoin et al. 2007). The
performance of this instrument in fresh sediments was however uncertain and, in our
knowledge, this is the first time that it was successfully applied to lacustrine
sediments. Additionally, the application of this test to water samples can aid in the
evaluation of the degree of contamination of the drilling water, which percolated along
the inside of the core liner.
The 97 m long sediment core retrieved from Laguna Potrok Aike provided us the
opportunity to identify a transition from a weak but active to a dwelling state of
microbial communities as reflected by in situ ATP measurements. These results were
further compared with those from DAPI counting on the fixed samples carried out
several months later in the laboratory. The DAPI fluorochrome dyes DNA without
distinction: active, dormant and dead cells, either eukaryote or prokaryote, and it is
considered as a semi-quantitative index. Both data sets, however, show an
increasing trend from the sediment surface to ca. 6 m depth within sediments mainly
composed of black mud and subject to gas expansion. The DAPI and ATP trends
throughout depth suggest an exponential decrease in microbial activity that is most
probably linked to a progressive compaction and gradual nutrient depletion within the
sediments. There is, however, detectable microbial activity down to 40 to 50 m and
recoverable DNA down to 60 m sediment depth. The presence of nutrients as energy
sources is critical, promoting an active behavior of the inner microbial communities
within sediments. When certain nutrient concentrations are below a threshold, these
microbial communities become oligotroph and enter in a dwelling state. Thus,
microbial communities installed in deep sediments can be considered as mainly
oligotroph and dwell.
The statistical analyses of DGGE (approach based on 16S rDNA) gels permit the
identification of a broad and constant diversity pattern in the older sediments, while
the diversity is subject to variations and decrease in the upper section. Results of
bulk sediment elemental analyses (H, C, N) suggest that the observed negative
correlation between activity and diversity could be the result of a systematic depletion
of nutrients through bacterial activity cycles. The latter is forcing microbial
communities to adapt to a decreasing trophic state, although sediment compaction
may be another important factor. Methane headspace (gas chromatography
technique) data show a regular increase of the organic matter decomposition process
from the sediment surface to 2-meter depth. The entire record, however, shows a
quite constant trend with peaks at 65, 38, and 10 meters indicating that methane is
best preserved in fine sediments.
74
The sediments recovered from Laguna Potrok Aike are dominantly argillaceous, but
are occasionally interrupted by coarser sandy layers associated to slumps triggered
by erosional and/or volcanic activities (Zolitschka et al., 2009). The latter is very
important since allochthonous organic matter is harder to degrade and microbial
preservation is highly dependent on grain size. Different sediment features are further
constraining microbial activity as they provide colonization niches. Although microbial
communities may adapt to trophic changes by shifting either their activity and/or
dominant species, they are still highly representative of the lake catchment and their
dominating climate. These preliminary results suggest that microbial communities are
tightly related to distinctive sediment types representative of changing lake levels.
Ongoing multiproxy analyses of these cores will allow characterizing the sedimentary
sequence and provide the critical grounds to interpret the results of the observed
microbial behavior.
Acknowledgements
We thank the PASADO Scientific Drilling Party for fruitful discussions and help during
drilling operations. We are particularly indebted to S. Templer (MIT, Boston, USA) for
productive discussions and introducing us into geomicrobiological sampling
techniques. C. Recasens, R. Farah (University of Geneva, Switzerland) and C. Mayr
(University of Erlangen, Germany) are kindly acknowledged for their help during field
sampling.
Funding for drilling was provided by the ICDP, the German Science Foundation
(DFG), the Swiss National Funds (SNF), the Natural Sciences and Engineering
Research Council of Canada (NSERC), the Swedish Vetenskapsradet (VR) and the
University of Bremen. We are also grateful to the Swiss National Science Foundation
(Grant 200020-119931/2 to D. Ariztegui); and the University of Geneva, Switzerland.
References
ANSELMETTI, F.S., ARIZTEGUI, D., DE BATIST, M., GEBHARDT, C., HABERZETTL, T., NIESSEN,
F., OHLENDORF, C., AND ZOLITSCHKA, B., 2009. Environmental history of southern
Patagonia unraveled by the seismic stratigraphy of Laguna Potrok Aike. Sedimentology
56/4:873–892, doi:10.1111/j.1365-3091.2008.01002.x.
CAMOIN, G.F., IRYU, Y., MCINROY, D.B., and Expedition 310 Scientists, 2007. IODP Expedition
#310: Proceeding IODP, 310. College Station TX (Integrated Ocean Drilling Program
Management Iternational, Inc.).
D’HONDT S., JORGENSEN B.B., MILLET D. J., BATZKE A., BLAKE R., CRAGG B.A., CYPIONKA
H., DICKENS G.R., FERDELMAN T., HINRICHS K.-U., HOLM N.G., MITTERER R., SPIVACK
A., WANG G., BEKINS B., ENGELEN B., FORD K., GETTEMY G., RUTHERFORD S.D., SASS
H., SKILBECK C.G., AIELLO I.W., GUÈRIN G., HOUSE C.H., INAGAKI F., MEISTER P.,
NAEHR T., NIITSUMA S., PARKES R.J., SCHIPPERS A., SMITH D.C., TESKE A., WIEGEL J.,
PADILLA C.N., AND ACOSTA J.L.S., 2004. Distributions of microbial activities in deep
subseafloor sediments. Science, 306: 2216–2221, doi:10.1126/science.1101155.
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in Mono Lake, a meromictic soda lake in California. Applied and Environmental Microbiology,
69:1030–1042, doi:10.1128/AEM.69.2.1030–1042.2003.
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and distribution in the Holocene sediments of a northern temperate lake. Microbial Ecology,
54:252–263, doi:10.1007/s00248-006-9195-9.
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characterization of ecologically significant prokaryotes in the sediment of freshwater lakes:
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13/9:402–404, doi:10.1016/j.tim.2005.07.004.
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press, Establishing sampling procedures in lake cores for subsurface biosphere studies:
Assessing
in
situ
microbial
activity.
Scientific
Drilling
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doi:10.1016/S1001-0742(08)60035-2.
ZOLITSCHKA B., ANSELMETTI F., ARIZTEGUI D., CORBELLA H., FRANCUS P., OHLENDORF C.,
SCHÄBITZ F., and the PASADO Scientific Drilling Team, 2009. The Laguna Potrok Aike
Scientific Drilling Project PASADO (ICDP Expedition
76
Insights into late Pleistocene environmental dynamics – Lithology
and preliminary dating of the lacustrine sediment record from the
ICDP deep drilling site Laguna Potrok Aike, Province of Santa Cruz
(southern Patagonia, Argentina)
Bernd Zolitschka1 & PASADO Science Team2
1
Geopolar, Institute of Geography, University of Bremen, Bremen, Germany
2
http://www.icdp-online.org/front_content.php?idcat=1494
Laguna Potrok Aike, located in the southern Patagonian Province of Santa Cruz (52°58’S,
70°23’W, 112 m a.s.l.), was formed by a volcanic maar eruption during the mid Pleistocene in
the Pali Aike Volcanic Field. This archive holds a unique record of paleoclimatic and
paleoecological variability from a region sensitive to variations in southern hemispheric wind
and pressure systems, which provide a significant cornerstone for the understanding of the
global climate system. Moreover, Laguna Potrok Aike is close to many active volcanoes
allowing a better understanding of the history of regional volcanism. Patagonia also is the
source region of eolian dust blown from the South American continent into the South Atlantic
Ocean and onto the Antarctic ice sheet. Ongoing global climate change, the thread of
volcanic hazards as well as of regional dust storms are of increasing socio-economic
relevance and thus challenging scientific themes that are tackled for southernmost South
America with an interdisciplinary research approach in the framework of the “Potrok Aike
Maar Lake Sediment Archive Drilling Project” (PASADO) which is a contribution to the
“International Continental Scientific Drilling Program” (ICDP).
Using the hydraulic piston coring system from the GLAD800 drilling platform, a total of 510 m
of overlapping sediment cores from two sites in the central 100 m deep basin of Laguna
Potrok Aike was recovered between September and November 2008. The excellent core
recovery rate of 94.4% enables to develop an almost complete reference profile with a
composite length of 106 m (Zolitschka et al., 2009). This record consists of undisturbed
laminated and sand-layered lacustrine silts at top with an increasing number of coarse gravel
layers, turbidites and homogenites at depth. Below 80 m composite depth two massmovement deposits (10 m and 5 m in thickness) are recorded with tilted and distorted layers
as well as nodules of fine-grained sediments and randomly distributed gravel. Such features
either indicate an increased seismicity that cannot be completely excluded for this late
Quaternary backarc volcanic field or they are the result of hydrologically induced lake level
variations and hence relate to changes in hydrological conditions in the catchment area.
Intercalated throughout the record are 24 macroscopically visible volcanic ash layers that
document the regional volcanic history. Moreover, these isochrones potentially act as links to
southern hemispheric marine sediment and ice core records.
For the upper part of the profile the chronology published by Haberzettl et al. (2007) was
adapted and assigns a Holocene to Lateglacial age. It consists of 19 AMS radiocarbon and 3
tephra dates. 18 additional radiocarbon ages obtained from aquatic plant macrofossils
provide ages back to 55,000 cal. BP for the lower glacial part of the record indicating a mean
sedimentation rate of 0.9 mm/a. To obtain this age/depth relationship it was indispensable to
subtract all volcanic ashes and re-deposited sediment units (ca. 50% of the entire record) as
they are linked to instant events contributing to sediment thickness but not to sediment age.
Re-deposition also leads to one third of radiocarbon ages being out of sequence. The highly
dynamic environmental conditions during the last glacial thus caused chronological
complications that we envisage to overcome with 33 samples analysed for optically
stimulated luminescence (OSL) dating, 15 additional radiocarbon dates in progress of
analysis and in combination with stratigraphic correlation techniques (e.g. paleomagnetism).
This approach will provide a robust time frame for ongoing interdisciplinary
paleoenvironmental and climatic reconstructions.
77
Reference
HABERZETTL, T., CORBELLA, H., M. FEY, S. JANSSEN, A. LÜCKE, C. MAYR, C.
OHLENDORF, F. SCHÄBITZ, G.-H. SCHLESER, E. WESSEL, M. WILLE, S. WULF, B.
ZOLITSCHKA, 2007. A continuous 16,000 year sediment record from Laguna Potrok
Aike, southern Patagonia (Argentina): Sedimentology, chronology, geochemistry. The
Holocene 17: 297-310.
ZOLITSCHKA, B., F. ANSELMETTI, D. ARIZTEGUI, H. CORBELLA, P. FRANCUS, C.
OHLENDORF, F. SCHÄBITZ And the PASADO Scientific Drilling Team, 2009. The
Laguna Potrok Aike Scientific Drilling Project PASADO (ICDP Expedition 50
78
Technical Report About the Potrok Aike Maar Lake Sediment
Archive Drilling Project (PASADO)
Bernd Zolitschka1 and the PASADO Science Team2
1
Geopolar, Institute of Geography, University of Bremen, Celsiusstr. FVG-M, 28359 Bremen,
Germany 2 http://www.icdp-online.org/contenido/icdp/front_content.php?idcat=960
The Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO) is a deep lake
drilling project under the umbrella of the „International Continental Scientific Drilling Program“
(ICDP). Based on international cooperation and after seven years with detailed
limnogeological studies, pre-site surveys, on-site monitoring, climatic and hydrologic
modelling an international team of scientists from Argentina, Canada, Germany, Sweden,
Switzerland and the United States representing a wide array of research fields was excited to
obtain long sediment cores from Laguna Potrok Aike. This crater (maar) lake is located in the
late Quaternary Pali Aike Volcanic Field of southern Patagonia (Province of Santa Cruz,
Argentina). Seismic surveys demonstrated that ~400 m of pelagic sediments were deposited
in the lake centre underlain by an unknown thickness of volcaniclastic breccias. Based on
this seismic data, three primary and three alternative drilling sites were selected:
(1) From the deepest part to obtain a continuous and high-resolution record of climatic and
environmental changes (0-400 m – in triplicate) and to unveil the phreatomagmatic history
including more precise age constrains for the maar-diatreme formation from the volcaniclastic
sediments below (400-600 m),
(2) From a subaquatic lake level terrace at 35 m water depth to constrain the range of lake
level variations (0-50 m – in triplicate) and
(3) From an angle hole passing through lacustrine sediments and the crater wall into the
molasse-type basement rocks (0-400 m) to study the impact of explosive volcanism in this
relatively young maar-diatreme structure.
The proposed drilling operation plan had the objective to achieve all necessary technical
needs in close cooperation with DOSECC, which provides the technical infrastructure and
the know-how to carry out the drilling at water depths of almost 100 m.
During the entire drilling operation, including mobilisation and demobilisation, a total of 42
people (26 scientists, 10 DOSECC staff, 4 Argentinean support personnel, 2 technicians)
were present. In total, 1986 man days were used for this operation. In the following list of
drilling statistics, applied and realised times and hole depths for drilling are summarised:
applied
14 days
60 days
Drilling statistics:
Time for mobilisation:
Time for Drilling:
Downtime related to weather conditions:
Downtime related to technical conditions:
Total hole depth:
Average core recovery per drilling day:
Time for demobilisation:
1850 m
14 days
realised
45 days
12 days
16 days
6 days
533 m
44 m
10 days
Drilling was carried out from the platform R/V “Kerry Kelts” with the GLAD800 drill rig. The
drill pipe was stabilised with a casing that was run down from the deck of the platform to a
few meters above sediment surface. The drilling tool almost exclusively used was the
Hydraulic Piston Corer (HPC). Core liners had a total length of 3.3 m and were, under ideal
circumstances, cut into two sections each 1.5 m long.
79
Drilling operations in the framework of PASADO have been successful in obtaining more
than 500 m of sediments but dramatically failed to attain the drilling objectives as described
in the ICDP Full Proposal. From three targets only the central deep was partly realised. Out
of the 1850 m of cores initially planned for recovery, only 533 m have been obtained from 7
holes, just two of them reaching a depth of more than 100 m. One reason was that fieldwork
has been marked by extended periods of strong winds. In addition to wind-related down-time
of drilling, we noted numerous defaults from DOSECC and believe these are similarly
responsible for not attaining the objectives of the PASADO drilling campaign.
Having lost 30 days due to the extended mobilisation, we had to change the proposed
sequence of drill sites. The near shore site at 35 m water depth was cancelled and we
started with the central deep site 1 at 98 m water depth. After the first site had to be
abandoned (lost pipe and casing did not allow to continue drilling at this site) without
reaching volcaniclastic deposits underneath of the lacustrine sediments, we moved 700 m to
the south remaining in the central deep basin (ca. 95 m water depth) but shifting towards an
area, where the Sparker seismic survey revealed a region with deeper penetration. The
second and last site 2 confirmed our assumptions and we recovered finer grained lacustrine
deposits. Downhole logging was intended to be carried out at least for one (the deepest) hole
of every site. All equipment was ready to be deployed, except for the radioactive source
needed for one of the logging tools which was not allowed to be imported into Argentina.
However, due to strong winds and problems with safely anchoring the platform, there was not
one option for logging down a complete hole during the entire period of operation.
For site 1 a total of 295 m of cores were obtained with a core recovery rate of 92%. For site 2
there are 208 m with a recovery rate of 99%. The better recovery rate for site 2 seems to be
linked to the generally finer grained lacustrine deposits. More sandy sections mainly caused
problems for site 1 with imploded or deformed liners stuck in the core barrel. A total number
of 178 core catcher samples were taken. Before being stored away, parts of the core catcher
samples were processed and subsampled in the field laboratory.
Several parameters were measured immediately after core recovery onshore at the campsite laboratory. This field laboratory was especially designed prior to the field period to fulfil
our requirements. It was purpose-built based on a standard 40-foot working container split
into two sections. One section was used for first physical and chemical analyses of the core
catcher samples such as pH, Cl-, Ca2+, electrical conductivity, water content and dry density
measurements as well as for an initial lithologic description (digital photographies,
macroscopic description, smear slide preparation with microscopic description).
The second section of the field laboratory was designed to hold the 5.5 m long Geotek Multi
Sensor Core Logger (MSCL) and a small office to process the MSCL data. The MSCL used
for PASADO was provided by the ICDP-OSG and equipped to measure temperature, core
diameter, p-wave velocity, magnetic susceptibility and GRAPE density. Unfortunately, it was
not possible to import the 137Cs radioactive source to Argentina, thus GRAPE density was not
measured on-site. In addition, the gas content in the liner did not allow to reliably measure pwave velocities. Therefore, magnetic susceptibility was the only parameter measured on-site
with the MSCL. For this reason all other petrophysical parameters will be measured in the
home laboratory at the Alfred Wegener Institute Bremerhaven prior to core opening.
Magnetic susceptibility was measured on all core sections with a loop sensor (80 mm
diameter) in 2 cm measuring intervals. Data were processed after acquisition and turned out
to be a highly reliable data set for core correlation from the different holes of one site as well
as between the two drilled sites. Using magnetic susceptibility data as a reference, cores
were correlated to composite profiles for site 1 and site 2.
The 178 core catcher samples (site 1: 107; site 2: 71) have been archived and described
following a certain protocol. In addition to the mentioned on-site analyses, core catcher
samples were subsampled for further and more detailed investigations to be carried out in
the respective home laboratories. Scheduled investigations for which samples have been
80
taken include: pollen, diatoms, stable isotopes and bulk geochemistry. Moreover, analyses to
determine the microbial activity in sediments (deep biosphere) have been carried out for the
first time within an ICDP-sponsored deep lake drilling project. For lakes a new sampling
strategy was designed and adapted from those existing for marine sediments. On-site
samples for microbial activity were measured by fluorescence using an ATP device.
Adenosine-tri-phosphate or ATP is only produced when living bacteria exist and thus gives
immediate information about microbial activity. Samples were also taken for sequencing DNA
and for cell counting in the home laboratory.
Although the total catch of cores was less than one third of the proposed amount, PASADO
recovered the so far longest environmental and climatic record of South America south of the
tropics, which will be analysed soon with the highest possible temporal resolution. Moreover,
lacustrine deposits have not been penetrated completely. Thus there is a potential for future
coring activities if a drilling platform can be anchored securely and all the other problems that
occurred with this remote Patagonian maar lake can be overcome.
More information about PASADO is available from the ICDP homepage (http://www.icdponline.org)
that
includes
a
general
description
(http://www.icdponline.org/contenido/icdp/front_content.php?idcat=722) and pictures from the drilling
operations (http://www.icdp-online.org/contenido/icdp/front_content.php?idart=2185).
Another source of information is the PASADO homepage located at (http://www.pasado.unibremen.de).
A report about the drilling campaign is published as
ZOLITSCHKA, B., F. ANSELMETTI, D. ARIZTEGUI, H. CORBELLA, P. FRANCUS, C.
OHLENDORF, F. SCHÄBITZ AND THE PASADO Scientific Drilling Team, 2009. The
Laguna Potrok Aike Scientific Drilling Project PASADO (ICDP Expedition 5022).
Scientific Drilling, 8: 29-33; doi:10.2204/iodp.sd.8.04.2009.
81
Phytolith analysis for the Potrok Aike Lake Drilling Project: Sample
treatment protocols for the PASADO Microfossil Manual
Alejandro F. Zucol*, Esteban Passeggi*, Mariana Brea*, Noelia I. Patterer*, María G.
Fernández Pepi** and María de los Milagros Colobig*
* Laboratorio de Paleobotánica, CICYTTP-Diamante (CONICET) Materi y España sn. (E3105BWA),
Diamante, Entre Ríos, Argentina. ** Laboratorio de Anatomía Vegetal, Museo Argentino de Ciencias
Naturales “Bernardino Rivadavia”. Buenos Aires, Argentina.
Based upon the results of meetings and previous microfossil research conducted as part of
the Drilling Projects serie (SALSA and PASADO), some of the researchers from the various
disciplines involved are coordinating their protocols, in order to help standardize the various
methodologies used to achieve their research objectives (Schäbitz and Wille, Unpub.). This
document has therefore been created to inform the PASADO microfossil community of the
methodologies that are being applied in the phytolith analyses, as well as to discuss the
potential types of paleobotanical and paleoenvironmental reconstructions being focused
upon as objectives.
The phytoliths from the Potrok Aike Lake sedimentary sequence are being studied jointly by
two research groups: Diamante and Mar del Plata. This presentation is focused on
communicating the details of the protocol that the Diamante group is implementing for the
treatment and study of these samples, with the eventual goal of coordinating these
methodologies to develop one common protocol used by both groups.
Sample treatment for phytolith analysis
1.-Sample storage.
Dried samples of undisturbed sediments are taken from the core sequence, and are stored in
hermetic plastic tubes until the time of processing.
2.-Sample treatment and classification.
The set of samples are classified according to the different sections that are to be studied by
each research group. Each sample consists of approximately 5g of dry sediment. Sets of
samples are prepared and classified, then packaged to be sent to the various laboratories
where the treatment will take place.
Laboratory procedures can be summarized as involving two stages: 1) sample pre-treatment,
including removal of soluble salts, carbonate material, and organic matter, as well as
deflocculation of the clastic material; and 2) sample treatment to separate the various
granometric components and to concentrate the biomorphic particles using heavy liquid
flotation.
3.-Sample pre-treatment.
a. Elimination of carbonates, humic components and concretions. The sediment sample
aliquot (5g) is placed in a Pyrex beaker and dilute hydrochloric acid (10 %) is added, with
moderate warming in a water bath. Reaction with carbonate and calcium cements is evident
in the release of gasses that produces bubbling in the sample, with this release being
increasingly intense in accordance with the abundance of these compounds. The presence
of humic components and iron oxides is demonstrated by yellowish coloration of the solution.
This treatment is repeated until gaseous release is no longer observed and the solution
becomes translucent.
This solution is then left to settle for 30 minutes to prepare for decanting. The upper column
of the solution is removed by pipette or siphoning and the presence of chloride ions in the
wash water is tested using silver nitrate solution (1%).
Additional stages
82
1: If it is necessary to preserve all particles sizes, the sample wash should be performed
using a porous filter, or instead the sample can be centrifuged, in order to avoid loss of
material.
2: If iron oxides persist in the sample, the treatment can be intensified by adding stannous
chloride crystals to the hydrochloric acid solution, being careful to maintain the pH level
between 4.5 and 8.5.
b. Elimination of soluble salts. The remaining sediment from the previous stage is put in a
new Pyrex beaker and 200 ml of distilled water is added, stirring with a glass rod. When the
content becomes uniform the solution is allowed to settle for 30 minutes to allow decanting.
The clean liquid above the deposit is eliminated. These steps are repeated two to three times
with cold water and once more with immersion in a warm water bath (60-70ºC), in order to
eliminate all of the soluble sales that may be present.
Additional stages 1: To test for the presence of chloride ions, transfer an aliquot of the
solution to a glass test tube. Add a few drops of concentrated nitric acid and 4 drops of 4%
silver nitrate. If the solution becomes white, it will be necessary to repeat the above
elimination steps. To test for the presence of sulphate ions, transfer an aliquot of the solution
to a glass test tube and first add a few drops of concentrated hydrochloric acid, then 5 drops
of saturated barium chloride solution. If a precipitate forms then washing of the sample will
have to be continued.
c. Elimination of organic matter. The sediment remaining after the previous stage is put in a
Pyrex beaker and 30% hydrogen peroxide is added for a period of 24 hours, stirring
periodically with a glass rod. The solution is then warmed in a water bath (60–70ºC) with
further addition of hydrogen peroxide until gaseous release is no longer observed. At this
point the solution is allowed to evaporate until the sample has become dry.
Additional stages
1: If the organic content is especially high, the hydrogen peroxide reaction may cause the
level of liquid to rise to the point of overflowing. In this case the reaction can be diminished
by adding a few drops of common alcohol. The reaction produced by the organic matter is
different than the one that is produced by the presence of manganese, which is indicated
by violent bubbling with release of a dense white steam.
2: If the presence of organic matter persists, it is possible to try an alternative, more volatile
oxidation treatment of the sample using 5% permanganate of potassium (KMnO4) and
addition of some drops of sulphuric acid. This reaction is allowed to continue for 24 hours
without heating and with periodic agitation, and then with warming to 100ºC until all free
oxygen has been released.
d. Dispersion. Sample dispersion is performed using a 1N solution of sodium
hexametaphosphate (a.k.a. Calgon or Sodium Beta), diluted in the sample to 0.1N. The
sample is placed in this solution and is stirred with a mixer for 5 minutes, then left to settle for
24 hours.
4.-Granometric class separation.
The granometric separation procedures will have to be adapted to the specific purposes and
material types, although in all cases the various granometric classes are separated by
sieving and/or by use of their differential sedimentation rates, with the steps adjusted
according to which particle sizes need to be obtained. In our case, three main fractions will
be first be separated: fine (particles with diameter from 5–53 m), medium (from 53–250 µm),
and coarse (greater than 250 µm). These three fractions can first be separated from each
other by sieving using a #60 sieve (250 µm mesh) and a #270 sieve (53 µm mesh).
Separation of the fine fraction, which passes through both sieves, into fine and medium-fine
sub-fractions can be performed using differential sedimentation if required. Separation using
differential sedimentation is based upon the application of Stokes' Law, which states that at a
given temperature, the sedimentation velocity of a particle depends upon its size. After
83
particular lengths of settling time, it is possible to calculate the particle sizes that will remain
suspended in the solution, as well as those that will have settled to the bottom of the burette.
5.-Heavy-liquid flotation.
After separation into different size classes, the size fractions from 5 – 250 µm in diameter
(this includes the fine and medium fractions) are used for flotation.
Phytoliths have a specific gravity ranging from 1.5 to 2.3 g/cm3 (Piperno, 2006 and
references therein). There are numerous heavy liquids that can be used for densimetric
separation, but we prefer sodium polytungstate, since densimetric adjustments can be made
using distilled water, the solution can be recycled, and this chemical possesses minimal
environmental toxicity. The phytolith flotation is performed by adding sodium polytungstate
solution (with its specific gravity adjusted to 2.345 g/cm3) to the processed sample, followed
by centrifugation at 1200 rpm for 5–10 minutes.
Monitoring of solution density is performed using a densimeter for precise measurement (a
Westphal balance or picnometer can also be used), or by means of Kranz indicators that also
provide a measurement of density ranges.
The supernatant liquid containing the floating material is removed with a pipette and
recovered by filtering in a funnel with a paper filter, then the material is washed with distilled
water. In a separate funnel, the same process is performed for the fraction of heavier
material that sinks during centrifugation. Both filters are washed with an abundance of
distilled water until traces of the heavy liquid can no longer be observed in the wash water.
The different subsamples obtained during these two steps (4 and 5) are then labeled and
added to the collection of sediment samples.
6.-Microscope slide mounting.
Two types of slide mounting can be used for the phytolith microscope observation: liquid and
solid, and both have their advantages. Liquid mounting can preserve mobility of the material
to be observed, while solid mounting is more durable and allows better preservation in
reference collections.
Both types of slides are made following standard procedures, but with specific types of
mounting media used that are most appropriate for the refractive index possessed by
phytoliths (see Zucol and Osterrieth, 2002). Thus for the liquid slides, immersion oil is used,
while the solid slides are made using Canada balsam.
At least one slide is made from each of the granometric fractions created in step 4 (more
than one if needed for counting purposes), and these are stored in the microscopic slide
collection of the Paleobotanical Laboratory for later reference.
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ROVNER I. 1972. Note on the safer procedure for opal phytolith extraction. Quaternary Research 2(4):
591.
SCHÄBITZ, F. AND M. WILLE. Unpublished. The PASADO Microfossil Manual. Version 1.0. University
of Cologne, Seminar for Geography and Education, Gronewaldstr. 2, 50931 Cologne,
Germany. 40 pp.
ZUCOL, A. F. AND M. OSTERRIETH. 2002. Técnicas de preparación de muestras sedimentarias para
la extracción de fitolitos. Ameghiniana 39 (3): 379-382.
85
Phytolith analysis for the Potrok Aike Lake Drilling Project: General
methodologies for analysis
Alejandro F. Zucol*, María de los Milagros Colobig*, Noelia I. Patterer*, María G.
Fernández Pepi**, Esteban Passeggi* and Mariana Brea*
* Laboratorio de Paleobotánica, CICYTTP-Diamante (CONICET) Materi y España sn. (E3105BWA),
Diamante, Entre Ríos, Argentina. ** Laboratorio de Anatomía Vegetal, Museo Argentino de Ciencias
Naturales “Bernardino Rivadavia”. Buenos Aires, Argentina.
The principal rules or methodological topics to consider for the Potrok Aike Lake sedimentary
sequence must be addressed for each of the three areas involved in the characterization and
analysis of phytolith assemblages: (1) phytolith identification; (2) phytolith morphotype
quantification; and (3) data analysis.
1.-Identification of phytolith morphotypes.
The processed sample with the concentrated phytolith material is slide mounted for
microscopic observation. The microscopic slides are given a preliminary check for the
purpose of establishing the different morphotypes present in the set of samples.
Phytolith morphotypes are classified according to previous morphological classifications such
Twiss et al. (1969), Bertoldi de Pomar (1971), Twiss (1992), Kondo et al. (1994), Runge
(1999), Zucol (1996, 1999), Wallis (2003), Zucol and Brea (2005) and the descriptors
proposed by the IPCNWG (2005). Recently these classifications and their taxonomic
correlations have been summarized by Zucol et al. (2010) with the aim of contributing to the
creation of a common classificatory scheme.
2.-Quantification of phytolith morphotypes.
The presence of particular microfossils can be described by direct quantification (number of
each element present in a sample) or by means of relative frequencies of the different
elements, using their overall frequencies as indicators of their relative abundances.
The frequencies can thus be recorded by relative or absolute methods. Relative abundances
are expressed as a percentage of each morphotype in the total number of elements found in
a sample, while the absolute abundances relate to the concentration of individual types in
terms of volume or weight within the sample in which they have been counted.
For the Potrok Aike Lake sediment samples, we have been planning to use quantification by
absolute frequencies, using a methodology similar to one commonly used in
paleopalynology. In this method, a known quantity of Lycopodium sp. spores is added to the
sample, which permits absolute quantification of the phytolith material observed on the
microscopic slides.
The phytolith variability found in each sample is not uniform, so it is necessary to first perform
an analysis to define the phytolith variability in the analyzed set of samples, and by means of
these studies to also define the minimum number of specimens that must be counted in order
to obtain a properly representative sample. It is then necessary to meet this minimum sample
requirement during counting in order to be able to consider the results reliable in terms of
numerical analysis.
To obtain the minimal representative sample count for a set of samples of equivalent origin, a
random selection of samples is taken. Counting of the number of elements present proceeds
progressively in each of them (for example every 30 elements)(Fig. 1).
The number of taxa represented tends to increase progressively with the total number of
specimens counted, until a point is reached where a substantial increase in counting no
longer produces significant changes in the Taxa value, which then stays more or less
86
constant. This is then considered to be the size of counting sample that allows the
variability of elements in the assemblage to be properly accounted for. Generally, for
chosen set of samples tested, the sample with the highest minimal value will be used for
study of the entire profile, and samples where counting cannot reach this value are
considered in the subsequent numerical analyses.
full
the
the
not
Other way of describing the abundance of morphotypes is by using abundance categories,
such as using a method where 5 categories are established, listed here in order of lesser to
greater frequencies of morphotypes: Absent, Rare, Scarce, Frequent, and Very frequent
(Zucol 1996, 1998, 2000). For the delimitation of these categories in this particular case, and
to obtain suitable proportions for every category, the following specifications have been used:
1. The maximum value of the scale (D) is equal to the value of the morphotype class with the
greatest frequency in the assemblage.
2. Absence is represented by a 0% frequency.
3. Phytolith types are considered Rare when they possess frequency values greater than 0%
but less then the limit A, where A = 0.1 x D.
4. Phytolith types are considered Scarce when they possess frequency values that are equal
to or greater than A but less than the limit B, where B = 0.3 x D.
5. Phytolith types are considered frequent when they possess frequency values that are
equal to or greater than B but less than the limit C, where C = 0.6 x D.
6. Phytolith types are considered Very frequent when they possess frequency values
between C and D.
3.-Data analysis.
Once counting has been performed for every sample in order to establish the different
frequencies found in the phytolith assemblage, these values are organized to obtain the
volumetric abundance information (these calculations can be made automatically using Tilia
software (Grimm, 1991) or with a spreadsheet). A Data Matrix (DM) is also generated with
these values (in terms of counts and/or percentages) for the various samples, which will
allow implementation of various types of data analysis.
The first step of data organization is the presentation of the information in phytolith diagrams,
a graphic representation of the abundance of each morphotype in all samples from the
sedimentary sequence. This diagram also includes additional information such as sample
name, depth, ages, lithology, etc. Next, an analysis of the data is performed by applying
constrained incremental sum of squares cluster analysis, using the DM, in order to define
zones along the sequence. This can be done using the computer program CONISS or
COSLINK. The TILIA/TILIAGRAPH programs (Grimm, 1991) and POLPAL Numerical
Analysis Program (Walanus and Nalepka 1999a, b; Nalepka and Walanus 2003) can also be
used to create phytolith diagrams and perform square cluster analysis. POLPAL also allows
calculation of the rarefaction of the taxa in each sample.
On the other hand, implementation of non-constrained numerical analysis may also be
desirable or necessary, especially as a means by which to establish relationships between
samples independent of their place of origin in the profile. For this, cluster analysis using
distance or correlation indices can be used, which allows evaluation of the links between
samples. However, if it is necessary to determine the role of individual morphotypes in the
relations between samples, principal components analysis (PCA or PCO) or correlation
analysis (CA) will have to be performed. These analyses can be carried out using various
different statistical programs such as PAST - PAlaeontological STatistics (Hammer et al.
2007).
87
References
BERTOLDI DE POMAR, H. 1971. Ensayo de clasificación morfológica de los silicofitolitos.
Ameghiniana 8 (3-4): 317-328.
GRIMM, E.C. 1991. TILIA Software. Illinois State Museum. Research and Collection Center,
Springfield, IL, USA.
IPCNWG, 2005. International Code for Phytolith Nomenclature 1.0. Annals of Botany 96(2): 253-260;
doi:10.1093/aob/mci172.
HAMMER O., HARPER D.A.T. AND P.D. RYAN. 2007. PAST - PAlaeontological STatistics, ver. 1.75.
86 pp. http://folk.uio.no/ohammer/past
KONDO, R., CHILDS, C. AND I. ATKINSON. 1994. Opal phytoliths of New Zealand. Maanaki Whenua
Press. 85 pp.
NALEPKA, D. AND A. WALANUS. 2003. Data processing in pollen analysis. Acta Paleobotanica 43
(1): 125-134.
RUNGE, F. 1999. The opal phytolith inventory of soils in central Africa- quantities, shapes,
classification, and spectra. Review of Palaeobotany and Palynology 107: 23-53.
TWISS, P.C. 1992. Predicted world distribution of C3 and C4 grass phytoliths. In: Rapp, G. Jr and S.C.
Mulholland (eds.), Phytoliths Systematics.Emerging Issues Advances in Archaelogical and
Museum Science 1: 113-128.
______, SUESS, E. AND R. SMITH. 1969. Morphological classification of grass phytoliths. Soil
Science Society of America, Proceedings 33(1): 109-115.
WALANUS A. AND D. NALEPKA. 1999a. POLPAL. Program for counting pollen grains, diagrams
plotting and numerical analysis. Acta Palaeobotanica Suppl. 2: 659-661.
______ 1999b. POLPAL. Numerical analysis. W. Szafer Institute of Botany. Polish Academy of
Sciences. Poland. 10. pp.
WALLIS, L. 2003. An overview of leaf phytolith production patterns in selected northwest Australian
flora. Review of Palaeobotany and Palynology, 125: 201-248.
ZUCOL, A. F. 1996. Microfitolitos de las Poaceae argentinas: I. Microfitolitos foliares de algunas
especies del género Stipa (Stipeae: Arundinoideae), de la Provincia de Entre Ríos.
Darwiniana 34: 151-172.
______. 1998. Microfitolitos de las Poaceae argentinas: II. Microfitolitos foliares de algunas especies
del género Panicum (Paniceae: Panicoideae: Poaceae), de la Provincia de Entre Ríos.
Darwiniana 36: 29-50.
______ 1999. Fitolitos de Poaceae argentinas: IV. Asociación fitolítica de Cortaderia selloana
(Danthonieae: Arundinoideae) de la Provincia de Entre Ríos. Natura Neotropicalis 30: 25-33.
______ 2000. Fitolitos de Poaceae de Argentina: III. Fitolitos foliares de especies del género
Paspalum (Paniceae), en la Provincia de Entre Ríos. Darwiniana 38: 11-32.
______ AND M. BREA. 2005. Sistemática de fitolitos, pautas para un sistema clasificatorio. Un caso
en estudio en la Formación Alvear (Pleistoceno inferior). Ameghiniana 42 (4): 685-704.
______, BREA M. AND E. BELLOSI. 2010. Phytolith studies in Gran Barranca (Central Patagonia,
Argentina) focused in the Middle Eocene. In: The Paleontology of Gran Barranca: Evolution
and Environmental Change through the Middle Cenozoic of Patagonia. Eds: R. Kay et al.
Cambridge University Press. Chapter 22: 313- 336.
88
Figure 1. Hypothetical plot showing variability vs. sample count size, with the number of specimens
counted (Specimens) and number of taxa represented (Taxa). In gray: standard deviation.
89
Phytolith analysis for the Potrok Aike Lake Drilling Project:
Preliminary results and current studies
Alejandro F. Zucol*, Mariana Brea*, Esteban Passeggi*, María G. Fernández Pepi**,
María de los Milagros Colobig* and Noelia I. Patterer*
* Laboratorio de Paleobotánica, CICYTTP-Diamante (CONICET) Materi y España sn. (E3105BWA),
Diamante, Entre Ríos, Argentina. ** Laboratorio de Anatomía Vegetal, Museo Argentino de Ciencias
Naturales Bernardino Rivadavia. Buenos Aires, Argentina.
The preliminary phytolith studies from the Potrok Aike Lake sedimentary sequence were
made with SALSA core samples (Zolitschka and Schäbitz, 2007), which included 9 samples
from across this drilling section (Table 1). These samples were sent for analysis by Dr. Nora
Maidana (PI of the PASADO project) for the purpose of verifying the presence of siliceous
microremains and particularly phytoliths, in order to evaluate the potential information that
might be obtained using this approach in the analysis of the Potrok Aike Lake sedimentary
sequence. In these preliminary analyses, the phytoliths became the main emphasis and
therefore the study of other types of microremains (Maidana et al., 2005; Wille et al., 2007)
was not included.
The samples had been processed previously in the Laboratorio de Diatomeas Continentales
(FCEyN, UBA), according the diatom protocol (Schäbitz and Wille, unpublished) of this
research group, with warm hydrogen peroxide treatment followed by washes with distilled
water. No separation of the components or concentration of any type took place (Maidana
com. pers.), and because of this these samples contained both microremains and clastic
materials.
Although counting levels in these preliminary analyses did not reach those of the minimal
representative sample, a variety of phytolith types could nevertheless be observed and
identified in the sequence.
The results of the preliminary analysis show the presence of various types of silica
microremains in all of the analyzed samples (Fig.1). Phytolith distributions show a marked
abundance of non-diagnostic elements such elongate prismatic, fan-shaped, and pointshaped phytoliths, as well as a clear abundance of diagnostic elements linked to the
microthermic grass lineages (such as pooids, festucoids, stipoids, and danthonioids). These
were represented mainly by festucoid boats, crescents, truncated cones, and stipa-type
morphotypes. The majority of these grass groups are typical of the Patagonian steppe.
For other types of grasses, diagnostic phytolith morphotypes such dumbbell shapes are
found in these samples, with highest abundances in the upper samples of the sequence.
Panicoid elements are not characteristic of the region's floral composition, and the presence
of these megathermic grasses can perhaps be related to an antropical factor. Other
diagnostic grass types such as collapsed saddle phytoliths, which can be related to the
bambusoid groups, are considered as Andean forest elements, as are some nothofagoid and
gymnosperm morphotypes.
These distributions, although not considered securely comparable because of the insufficient
counting levels applied during this preliminary analysis, do create a pattern that resembles
the pattern seen in the paleopalynological records (Wille et al., 2007), with Patagonian
steppe in the lower core section and Andean forest in the upper section.
Current studies
As part of the PASADO project, the study of phytoliths from samples from the most recent
drilling has begun, and this work is now being carried out by the Diamante and Mar del Plata
research groups in a coordinated manner. However, the newer PASADO drilling sequence
contains a more extensive record than the previously analyzed SALSA sequence. For this
90
reason, as well as the fact that there are both undisturbed and redeposited sediments in the
sequence, two research approaches have been initially planned: 1) a detailed analysis of the
upper 2500 cm section (Fig. 2), which includes the material equivalent to the sequence
already analyzed for the SALSA project; and 2) a low-resolution analysis of the middle and
lower sections. The preliminary analysis of these samples will allow evaluation of the future
potential for performing high-resolution studies of both sections, which are characterized by
the presence of many redeposited samples. Also included in this approach will sections
expected to reflect a low level of biotic activity corresponding to glacial periods.
In addition to these low- and high-resolution studies that are now being implemented,
members of the Diamante research group in particular are also carrying out complementary
analyses with the goal of establishing modern reference patterns of phytolith production/
incorporation system. These are focused on the main ecological communities found in the
region: Patagonian steppe, Patagonian ecotone, and Andean forest.
These studies are being developed in part as the subject of a doctoral thesis by one of the
present authors (MGFP), who is now performing analyses of phytolith production and
incorporation in various plant communities from the ecotonal region of Tierra del Fuego.
These studies have been designed to complement the phytolith analysis of various species
of the Andean forest that have also been carried out, specifically in the case of some
Bambusoideae, Nothofagaceae, Asteraceae and Gymnosperm species.
References
MAIDANA, N., IZAGUIRRE I., VINOCUR A., MATALONI G. AND H. PIZARRO. 2005. Diatomeas en
una transecta patagónico-antártica. Ecología Austral 15: 159-176.
SCHÄBITZ, F. AND M. WILLE. Unpublished. The PASADO Microfossil Manual. Version 1.0. University
of Cologne, Seminar for Geography and Education, Gronewaldstr. 2, 50931 Cologne,
Germany. 40 pp.
WILLE M., MAIDANA N.I., SCHÄBITZ F., FEY M., HABERZETTL T., JANSSEN S., LÜCKE A., MAYR
C., OHLENDORF C., SCHLESER G.H. AND B. ZOLITSCHKA. 2007. Vegetation and climate
dynamics in southern South America: The microfossil record of Laguna Potrok Aike, Santa
Cruz, Argentina. Review of Palaeobotany and Palynology 146: 234–246.
ZOLITSCHKA B. AND F. SCHÄBITZ. 2007. Südargentinische Seesediment Archive und Modellierung
(SALSA) Sedimentologie und Datierung (SALSA I). Paläobiologie und Klimarekonstruktion
(SALSA II). http://www.salsa.uni-bremen.de/ 57 pp.
Table 1.
Sample ID
Depth (cm)
Age (cal
BP)
2227
96
1362
2228
104
1439
2229
112
1508
2230
409
4107
2231
417
4154
2232
1047
8305
2233
1055
8315
2234
1579
13145
2235
1585
13246
Samples analyzed. Sample ID: number recorded in the Laboratorio de Paleobotánica
(CICYTTP-Diamante) sediment sample collection. Depth and age of each sample according
to Wille et al., 2007.
91
Figure 1.
Silica microremains diagram with relative abundance of phytoliths, stomatocysts, and
fragmented sponge spicules. Details of the phytolith morphotypes assigned to each class
are found in the text.
Figure 2. Schematic profile of the sedimentary sequence, with the distribution of the undisturbed
samples in black (332 total undisturbed samples).
92
Authors Index
Aguilar .............................................................................................................................................32
Alvarez .............................................................................................................................................52
Anselmetti.........................................................................................................................................72
Ariztegui...................................................................................................................................... 69, 72
Barberena...........................................................................................................................................5
Benvenuto ........................................................................................................................................52
Bianchi..........................................................................................................................................8, 60
Borrelli ..............................................................................................................................................52
Borrero ...............................................................................................................................................5
Brea...................................................................................................................................... 81, 85, 89
Buezas .............................................................................................................................................52
Campan..............................................................................................................................................5
Charlin ................................................................................................................................................5
Colobig ................................................................................................................................. 81, 85, 89
Corbella ................................................................................................................................ 10, 14, 36
Coronato.................................................................................................................................... 10, 14,
Echazú …………………………………………………………………………………………………………..18
Ercolano .................................................................................................................................... 10, 14,
Fernández Honaine...........................................................................................................................44
Fernández Pepi..................................................................................................................... 81, 85, 89
Fey ...................................................................................................................................................38
Gebhardt...........................................................................................................................................45
Gogorza................................................................................................................................ 22, 27, 32
Hahn.................................................................................................................................................45
Irurzun ........................................................................................................................................ 22, 32
Kliem ................................................................................................................................................45
Kostadinoff........................................................................................................................................36
Laprida ....................................................................................................................................... 38, 63
Maidana................................................................................................................................ 18, 38, 69
Marinone...........................................................................................................................................41
Massaferro.................................................................................................................................. 38, 47
Menu Marque....................................................................................................................................41
Ohlendorf.............................................................................................................................. 22, 32, 45
Orpella..............................................................................................................................................47
Osterrieth..........................................................................................................................................52
Paez .................................................................................................................................................56
Passeggi............................................................................................................................... 81, 85, 89
Patterer................................................................................................................................. 81, 85, 89
Pawlowski .........................................................................................................................................72
Quintana.......................................................................................................................................8, 60
Ramón Mercau ........................................................................................................................... 38, 63
Raniolo .............................................................................................................................................36
Recasens..........................................................................................................................................69
Rodas ...............................................................................................................................................36
Rojo..................................................................................................................................................52
Schäbitz............................................................................................................................................71
Sinito .......................................................................................................................................... 22, 32
Szewczuk .........................................................................................................................................36
Tiberi .................................................................................................................................... 10, 14, 36
Vasconcelos .....................................................................................................................................72
Vuillemin...........................................................................................................................................72
Wille..................................................................................................................................................71
Zolitschka ............................................................................................................22, 27, 32, 45, 76, 78
Zucol..................................................................................................................................... 81, 85, 89
93
94