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Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32 – 45
www.elsevier.com/locate/palaeo
Nitrogen isotope analyses of reindeer (Rangifer tarandus), 45,000 BP to
9,000 BP: Palaeoenvironmental reconstructions
Rhiannon E. Stevens a,⁎, Roger Jacobi b , Martin Street c , Mietje Germonpré d , Nicholas J. Conard e ,
Susanne C. Münzel e , Robert E.M. Hedges f
a
McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, CB2 3ER, UK
The British Museum, 38-46 Orsman Road, London, N1 5QJ, and Department of Palaeontology, Natural History Museum, London SW1 5BD, England, UK
c
Römisch-Germanisches Zentralmuseum, Forschungsbereich Altsteinzeit, Schloss Monrepos, 56567 Neuwied, Germany
d
Department of Palaeontology, Royal Belgian Institute for Natural Sciences, Vautierstraat 29, 1000 Brussels, Belgium
e
Institut für Ur und Frühgeschichte und Archäologie des Mittelalters, Eberhard-Karls-Universität Tübingen, Schloss Hohentübingen,
Burgsteige 11, D-72010 Tübingen, Germany
Research Laboratory for Archaeology and the History of Art (RLAHA), University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, UK
b
f
Received 2 September 2006; received in revised form 14 January 2008; accepted 25 January 2008
Abstract
Pleistocene faunal δ15N variations are thought to reflect changes in climatic and environmental conditions. Researchers are still unclear,
however, which climatic/environmental parameter is the primary control on Pleistocene faunal δ15N values. Through extensive nitrogen isotope
analysis of Late Pleistocene reindeer (Rangifer tarandus) collagen we investigated whether permafrost development during the Late Pleistocene
coincided with changes in δ15N values. After 45 ka BP reindeer δ15N declined, with lowest δ15N values observed after the Last Glacial Maximum
(LGM), between 15 and 11 ka BP. The decline in δ15N appears to be of a greater magnitude in more northern regions than in the South of France,
a pattern similar to that previously observed for horse. On a global scale, ecosystem δ15N is controlled by the relative openness of the nitrogen
cycle, which in turn is controlled by climate. Low soil and plant δ15N are observed in cold and/or wet regions and high δ15N are seen in hot and/or
arid areas. The regional pattern in reindeer δ15N decline mimics the pattern of climatic deterioration in Europe culminating at the LGM, with
climate cooling being more intense in northern Europe than in southern Europe. However, the lowest reindeer δ15N values are observed after
temperatures started to rise. This may have been due to a lag in the response of the nitrogen cycle to increasing temperatures. Alternatively it may
have been linked to the influence of permafrost degradation on soil and plant δ15N and thus faunal δ15N. The renewed climatic cooling during the
Younger Dryas did not see a fall in reindeer δ15N. Limited data does, however, suggest a post Younger Dryas depletion in reindeer δ15N values.
© 2008 Elsevier B.V. All rights reserved.
Keywords: Isotope; Nitrogen; Palaeoclimate; Palaeoenvironment; Reindeer; Bone
1. Introduction
Palaeodietary reconstructions using isotope techniques are
based on the principle that food sources contain different
isotope signatures, which are passed along the food chain to
their consumers (Schoeninger and DeNiro, 1984; Ambrose and
⁎ Corresponding author. Fax: +44 1223 333503.
E-mail address: [email protected] (R.E. Stevens).
0031-0182/$ - see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.palaeo.2008.01.019
DeNiro, 1986; Bocherens et al., 1999; Richards and Hedges,
1999; Privat et al., 2002). Although diet is the principal control
determining bone collagen isotope values, climate and local
environment can also create small-scale isotopic variability (van
Klinken et al., 1994; Cormie and Schwarcz, 1996; Gröcke et al.,
1997; Schwarcz et al., 1999). From small-scale variability in
bone collagen nitrogen isotope signatures researchers have in
recent years attempted to reconstruct palaeoenvironmental
conditions at specific sites, over time and across regions (e.g.
Gröcke et al., 1997; Iacumin et al., 1997, 2000; Drucker et al.,
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
2000; Richards and Hedges, 2003; Drucker et al., 2003; Stevens
and Hedges, 2004). A number of studies have focused on the
Late Pleistocene, with a lowering of faunal nitrogen isotope
values roughly coinciding with the widespread climatic cooling
culminating at the Last Glacial Maximum (LGM, 22,000–
18,000 BP) (Drucker et al., 2003; Stevens and Hedges, 2003;
Stevens, 2004). However, in studies to date, the magnitude and
timing of the variation in faunal δ15N over the last 45,000 years
is still fairly unclear due to a lack of continuity of data from any
single species, both temporally and spatially. Furthermore, the
environmental controls directly influencing faunal δ15N during
the Late Pleistocene are unknown. Permafrost development has,
however, been suggested as a parameter that could possibly
cause variation in Late Pleistocene herbivore δ15N values
(Stevens and Hedges, 2003; Drucker et al., 2003; Stevens and
Hedges, 2004). The aim of this study was to determine whether
permafrost development during the Late Pleistocene coincided
with changes in faunal δ15N values and thus whether it could be
the primary environmental control influencing Late Pleistocene
faunal δ15N values.
To improve the continuity of Late Pleistocene faunal δ15N
data we selected a single species, reindeer (Rangifer tarandus),
for investigation. Reindeer are adapted to temperate and cold
environments. They have large feet which facilitate walking on
snow and digging through snow for winter forage, long thick
winter pelage with hollow guards hairs and a close underfur for
extra insulation, valvular nostrils, broad short furry ears and
short fury tails (Banfield, 1977; Leader-Williams, 1988;
Weinstock, 2000). Today reindeer inhabit arctic tundra,
subarctic taiga, mountainous areas – where they occupy the
alpine tundra and subalpine forest zones – and boreal
coniferous forest, which they only visit in winter (Heptner et
al., 1966; Banfield, 1977; Weinstock, 2000). Reindeer typically
occupy habitats with between 300 mm and 700 mm of rainfall
per year, average January temperatures of − 70 °C to − 10 °C
and average July temperatures of 0 °C to 17 °C (Delpech, 1983).
Snow cover correlates with habitat suitability, with a maximum
depth of 60 cm being acceptable to the reindeer (Baker, 1978;
Boyle, 1990). Reindeer are mixed feeders. In summer months
they mainly consume a wide range of vascular plants and to a
lesser extent lichen, whereas in winter months their diet is much
less varied, with lichen of greater importance in lower latitudes
and graminoids and moss of greater importance in the high
arctic (Weinstock, 2000). During the Late Pleistocene in
Northern Eurasia reindeer was the most abundant large
herbivore occupying regions subject to permafrost development
and regions proximal to the ice sheets. Thus reindeer is a good
species to investigate potential correlations between permafrost
development and faunal δ15N values.
Reindeer obtain their nitrogen from their food, i.e. plants. Thus
their nitrogen isotope signatures reflect those of the plants they
consume. In modern ecosystems plant δ15N is dependent on
multiple factors including soil δ15N, soil development, nutrient
availability (nitrogen and phosphorus), mycorrhizal associations,
soil acidity and nitrogen cycling. However, the predominant
mechanism determining soil and plant δ15N is the extent to which
the nitrogen cycle is an open or closed system. The “openness” of
33
the nitrogen cycling system can be determined by the relative
importance of within-ecosystem nitrogen cycling versus the
relative importance of inputs and outputs (Handley et al., 1999).
In cold and/or wet ecosystem inputs and outputs are limited and
within-ecosystem cycling of nitrogen between live organic and
dead organic pools is dominant. As little nitrogen is lost from the
system, soil and plant δ15N remain low (Handley et al., 1999).
This is particularly true in permafrost regions where low soil
temperatures lead to low mineralization rates and limited
availability of inorganic nitrogen. In hot and/or arid ecosystems
this cycle is interrupted, with proportionally more nitrogen
flowing from organic to mineral nitrogen pools, which are subject
to preferential loss of 14N through processes such as leaching,
denitrification and ammonia volatilisation, resulting in enrichment of soil and plant δ15N (Austin and Vitousek, 1998; Handley
et al., 1999). Thus, on a global scale, ecosystem δ15N is controlled
by the relative openness of the nitrogen cycle which in turn is
controlled by climate, resulting in low δ15N observed in cold and/
or wet areas and high δ15N seen in hot and/or arid areas
(Amundson et al., 2003). Although some of the lowest plant δ15N
values are observed in arctic and tundra regions we are not aware
of any study that has directly look at the influence of permafrost
development or degradation on soil or plant δ15N values.
2. Materials and methods
2.1. Sample selection
The continuity of Late Pleistocene reindeer data was improved by collecting and analysing the isotopes of reindeer
bones from a number of European Late Pleistocene sites and
through collation of published reindeer δ15N results. Nitrogen
isotope values from 294 reindeer are included in this study. 121
samples were collected, prepared and analysed by R. Stevens at
the Research Laboratory for Archaeology and the History of
Art, Oxford (RLAHA) as part of a NERC D.Phil studentship
(NER/S/A/2000/03522). 32 results were extracted from the
Oxford Radiocarbon Database. A further 141 results were taken
from the published literature (Drucker et al., 2000 (n = 39);
Iacumin et al., 2000 (n = 22); Drucker et al., 2003 (n = 80)). The
reindeer samples were sourced from 52 sites – in the UK and
Ireland (21 sites, 60 samples, from here on grouped as UK),
Belgium (4 sites, 11 samples), Germany (11 sites, 74 samples),
southern France (13 sites, 127 samples) and Siberia (3 sites, 22
samples) (Fig. 1). The majority of these sites contained archaeological as well as palaeontological material. A full provenance for each sample can be found in the online supplementary
dataset. Only 55 of the samples were directly radiocarbon dated.
However, other samples collected and analysed in this study were
indirectly dated through radiocarbon dates of associated material
(see online supplementary dataset). Results collated from
published literature were assigned to a time block based on the
chronology available from the published literature (established
either via radiocarbon dating or via radiocarbon dates from
associated material). Data was separated into archaeological time
blocks as many of the samples have not been radiocarbon dated.
The duration of time blocks used in this study is based on those
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35
used by Huijzer and Vandenberghe (1998) in their reconstruction
of Late Pleistocene permafrost development and degradation.
Although employing time periods of varying duration (and thus
number of samples) can affect the chronological analysis of the
data, we selected this method in order to test for isotope differences
between periods with known permafrost histories. Unless
otherwise stated dates quoted in the text are in uncalibrated 14C
Years BP. This takes into consideration controversies regarding the
feasibility of radiocarbon calibration beyond 26,000 calibrated
years BP (the limit of IntCal04) and ongoing efforts to extend this
(discussion e.g. van Andel, 1998, 2005; van der Plicht, 1999).
Dates younger than 26,000 BP were also not calibrated in order to
maintain a single chronological scale throughout the discussed
dataset. However, all dates were calibrated with CalPal Online
(which uses the CalPal_2007_HULU calibration curve) and can be
found in the supplementary dataset.
2.2. Stable isotope methods
Samples were prepared according to the procedure used by
the Oxford Radiocarbon Accelerator Unit (ORAU) (with some
modifications) (Bronk Ramsey et al., 1999). Bone samples were
obtained using a drill. The surface of the bone was drilled away
to remove any surface contamination and then a second aliquot
of powder (approximately 300–500 mg) was drilled out and
collected. For samples that had been (or were suspected to have
been) conserved with PVA glue, a solvent extraction pretreatment was used to remove the adhesive. Pre-treatment
involved heating the sample at 40 °C for an hour in distilled
water, then repeating the heating process using acetone, distilled
water, methanol and distilled water respectively. Collagen was
extracted by a modified Longin method (Longin, 1971; Brown
et al., 1988): samples were demineralised in 0.5 M aq. HCl at
4 °C until all the mineral had dissolved. Samples were then
rinsed with distilled water and 0.1 M Sodium hydroxide was
added for 30 minutes to remove humic acids. Samples were then
rinsed with distilled water and gelatinised in a pH 3 solution for
48 h at 75 °C. Then the filtered supernatant containing the
soluble collagen was collected, frozen and lyophilized. Between
2.5 and 3.5 mg of collagen was loaded into a tin capsule for
continuous flow combustion and isotopic analysis.
Samples were analysed using an automated Carlo Erba carbon
and nitrogen elemental analyser coupled with a continuous flow
isotope ratio-monitoring mass spectrometer (PDZ Europa Geo
20/20 mass spectrometer). Results are reported in units per mil
(‰) and δ15N values were measured relative to the AIR
(atmospheric nitrogen) standards. Where possible each sample
was run in duplicate or triplicate. Replicate measurement errors on
laboratory standards (comprising in-house standards of nylon and
Fig. 2. Boxplot of 294 reindeer δ15N plotted over time.
alanine calibrated against IAEA standards and modern bovine
bone collagen as a standard “unknown”) were less than 0.2‰ over
the period of analysis. For 14C dated samples the analytical errors
are larger, potentially as large as ±0.3‰ (Peter Ditchfield pers.
Comm.). Radiocarbon dating of three bones (A/VC/B/7, A/GON/
B/45, A/DMC/B/13) was conducted on the collagen extracted for
isotope analysis. Prior to radiocarbon dating samples were rehydrolyzed and ultra-filtered by the use of a Vivaspin 15,
Sartorius ultra filter (30-kDa molecular-mass cutoff) prior to
lyophilization so that molecules over 30 kDa were retained. The
C/N ratios calculated for all of the samples in this study were
between 2.9 and 3.6, a range considered to be indicative of good
collagen preservation (DeNiro, 1985; Ambrose, 1990). Data from
the ORAU database include analyses of bone, antler and a single
tooth. Antler is a type of bone that grows rapidly. The relationship
between bone and antler collagen δ15N values has not been
investigated. For this study they are assumed to be equivalent;
however, they should been considered with caution in absence of
such a systematic investigation. Reindeer adult dentine δ15N is
systematically 15N enriched relative to bone, even in late growing
teeth which form post-weaning (Drucker et al., 2001). Thus the
single reindeer tooth δ15N result must be considered with caution.
3. Results
The δ15N values of 294 reindeer can be seen in Fig. 2 and in
the online supplementary dataset. Collectively the reindeer
δ15N values range from 0.4 to 6.3‰ with a mean δ15N value of
3.3‰ (± 1.2‰). The change in reindeer δ15N over time is
considerable (Fig. 2). Pre 20 ka BP reindeer mean δ15N (4.2‰
Fig. 1. Site locations in British Isles, Germany, France, and Belgium. 1 = Kents Cavern, 2 = Pixie's Hole, 3 = Chelm's Combe, 4 = Gough's Old Cave 5 = Badgerhole,
6 = Hyena Den, 7 = Wolf Den, 8 = Aveline's Hole, 9 = Paviland, 10 = Fox Hole Cave, 11 = Castlepook Cave, 12 = Lynx Cave, 13 = Ossom's Cave, 14 = Mother Grundy's
Parlour, 15 = Pinhole Cave, 15 = Dead Man's Cave, 17 = Kinsey Cave, 18 = Sewell's Cave, 19 = Victoria Cave, 20 = Bart's Shelter, 21 = Shelter Cave, 22 = Chaleux,
23 = Goyet Cave, 24 = Trou da Somme, 25 = Trou de Nutons, 26 = Karstein rockshelter, 27 = Andernach, 29 = Gönnersdorf, 30 = Wildscheuer Cave, 31 = Abri Stendel,
32 = Breitenbach, 33 = Wiesbaden-Igstadt, 34 = Geissenklösterle, 35 = Hohlefels, 36 = Buttentalhöhle, 37 = Kastelhohle, 38 = Le Bois Ragot, 39 = Ferme de la
Bouvière, 40 = Vergisson, Saint Romans, 41 = Grotte du Tai, 42 = Les Peyrugues, 43 = Laugerie-Haute est, 44 = Le Flageolet, 45 = Les Jamblanc, 46 = Moulin-neuf,
47 = St-Germain la Rivière, 48 = Combe Sauniere, 49 = Le Brassot. 50 = Afontova Gora II, 51 = Kashtanka, 52 = Listvenka. Map generated from ESRI map data using
ArcGIS v.9.1.
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Table 1
Statistical assessment of differences between the mean δ15N of each time block (results of one way ANOVA with post hoc Bonferroni correction)
9–10
9–10
10–11
11–13
13–15
15–30
20–27
27–32
32–36
36–45
10–11
11–13
13–15
N/A
p ≤ 0.001
p = 0.003
p ≤ 0.001
N/A
p = 0.003
p ≤ 0.001
p ≤ 0.001
p = 0.001
p ≤ 0.001
p = 0.001
N/A
p = 0.006
p ≤ 0.001
p = 0.010
p ≤ 0.001
p = 0.008
15–20
20–27
p ≤ 0.001
p = 0.006
N/A
p ≤ 0.001
p = 0.003
p ≤ 0.001
p ≤ 0.001
p ≤ 0.001
N/A
27–32
32–36
36–45
p = 0.001
p = 0.010
p ≤ 0.001
p ≤ 0.001
p = 0.004
p = 0.001
p = 0.008
N/A
p = 0.003
s.d. 1.0‰ (n = 77)) is significantly higher than that of post 20 ka
BP reindeer (2.9‰ s.d. 1.1‰ (n = 217)) (Independent Student's
t-test, p ≤ 0.001). The lowest δ15N values are observed during
the Late Glacial interstadial (13–11 ka BP) (Table 1, Fig. 2).
The mean reindeer δ15N values for the majority of time blocks
are statistically significantly different (one-way anova with post
hoc bonferroni correction, see Table 1 for further details). The
standard deviations within each time block are relatively similar
(Table 2), with substantial variability in δ15N observed.
The observed pattern of δ15N over time appears to vary
between geographic regions, however, this pattern is less
statistically robust than the chronological trend observed for
the reindeer collectively. Fig. 3 shows the reindeer δ15N plotted
by country. Within each time block the range in δ15N values can
be as much as 6‰ (Fig. 3A), however, only nine of the results are
statistically considered to be outliers (Fig. 3B). Within a time
block reindeer δ15N can differ between countries, e.g. at 13–
11 ka BP Siberian reindeer δ15N range from 1.3‰ to 2.3‰,
whereas the δ15N of reindeer from the south of France range
from 2.6‰ to 4.4‰. Mean reindeer δ15N significantly differed
between the following countries within the following time
blocks: 32–27 ka BP Germany and the UK (p = 0.036); 27–20 ka
BP Siberia and France (p = 0.002); 15–13 ka BP France and
Germany (p ≤ 0.001) and France and Siberia (p ≤ 0.001); 13–
11 ka BP Belgium and Siberia (p = 0.014), France and Germany,
France and the UK and France and Siberia (p = 0.004, p = 0.003,
p = 0.001, respectively). Within the 45–36 ka, 36–32 ka, 20–
15 ka, 11–10 ka, 10–9 ka BP time blocks mean reindeer δ15N
did not significantly differ between countries. In addition, the
δ15N of reindeer from a single country can differ between time
blocks, e.g. reindeer from Germany have δ15N values that range
from 1.4‰ to 2.9‰ at 13–11 ka BP, whereas at 33–32 ka BP
they range from 4.1‰ to 5.6‰. Mean reindeer δ15N in Germany
significantly differs between 11–10 kaBP and both 36–32 ka
and 32–27 ka BP (p = 0.040 and p = 0.001, respectively);
between 13–11 ka BP and 45–36 ka BP, 36–32 ka BP and
32–27 ka BP (p ≤ 0.001, p ≤ 0.001, p = 0.001, respectively);
between 15–13 ka BP and 45–36 ka BP, 36–32 ka BP and 32–
27 ka BP(p ≤ 0.001, p ≤ 0.001, p ≤ 0.001, respectively); and
between 20–15 ka BP and 36–32 ka BP (p ≤ 0.001) (one-way
anova with post hoc bonferroni correction).
The trends in reindeer δ15N for different geographic regions
are shown most clearly in Fig. 3C (Outliers were not removed
during calculation of means and standard deviations). At 45–
36 ka BP, reindeer δ15N values in the UK are similar to those in
N/A
p = 0.004
N/A
N/A
Germany. UK reindeer δ15N values then gradually decline,
ranging from approximately 2‰ to 3.5‰ at 32–27 ka BP.
Between 27 ka BP and 13 ka BP, only one sample was analysed
from the UK mainly due to lack of animals present in the UK
because of harsh climatic conditions. UK reindeer δ15N values
during the Late Glacial interstadial (13–11 ka BP) are similar to
those at 32–27 ka BP, although the number of samples is
considerably different. UK reindeer δ15N values are higher by
around 1.5‰ in the Younger Dryas (11–10 ka BP) and early
Holocene (10–9 ka BP) relative to values in the Late Glacial
interstadial. Within the UK only the 13–11 ka BP and 11–10 ka
BP time blocks, however, have mean δ15N values that differ
significantly (p = 0.002, one-way anova with post hoc bonferroni correction). In certain time blocks, UK reindeer δ15N
values are similar to those from Germany (e.g.13–11 ka BP),
whereas in other time blocks (e.g. 32–27 ka BP), they are lower
by around 1‰ to 2‰. Sufficient data from the south of France
are only available after 27 ka BP. At 27–20 ka BP reindeer δ15N
values in the south of France are relatively high, ranging from
around 3‰ to 6‰. In the subsequent time block (20–15 ka and
15–13 ka BP) reindeer δ15N in the south of France is
significantly lower (p ≤ 0.001 and p ≤ 0.001 respectively) by
approximately 1‰. Although reindeer data from the south of
France are limited in number during the Late Glacial interstadial
(13–11 ka BP), their δ15N values appear to be higher than
during the preceding time block (15–13 ka BP). Throughout the
time periods covered, reindeer from the south of France have
δ15N values that are generally higher than those from Germany
and the UK by around 1‰ to 2‰. Belgian reindeer δ15N results
are concentrated at 13–11 ka BP and are slightly higher than
Table 2
Statistical summary of reindeer δ15N values according to time block
Time period Number of Mean Standard
in ka BP
individual
deviation
Minimum Maximum Median
9–10
10–11
11–13
13–15
15–20
20–27
27–32
32–36
36–45
1.9
1.5
0.4
0.6
1.1
2.7
1.8
1.7
2.9
8
33
47
61
68
39
15
14
9
3.2
3.4
2.4
2.6
3.3
4.4
3.7
4.4
3.9
1.0
1.2
1.1
1.0
0.7
0.9
1.2
1.0
1.0
4.6
5.8
6.2
4.8
5.2
6.3
5.7
6.0
5.8
3.3
3.4
2.3
2.7
3.2
4.2
3.6
4.5
3.7
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37
Fig. 3. A: Reindeer δ15N plotted by country and time block. B: Box plots of Reindeer δ15N by country and time block. Box plots show the median, minimum, and maximum
values, the inter-quartile range, and outliers. C: Mean reindeer δ15N and standard deviation Grey square = Siberia, white circle= Germany, grey diamond = UK, white
square = Belgium, black circle= south of France. Country that box plot applies to can be seen by referring to samples directly above and below in A and C.
those in the UK and Germany at this time. Siberian reindeer
δ15N results are available from three time blocks, with those at
27–20 ka BP being significantly higher by around 2‰ than
those between at 15–13 ka BP and 13–11 ka BP (p ≤ 0.001 and
p ≤ 0.001 respectively). This shows that the variation in
reindeer δ15N values is not just a phenomenon of North West
Europe. German reindeer δ15N values initially rise from
approximately 3‰ to 5‰ at 45–36 ka BP to around 4‰ to
6‰ at 36–32 ka BP. From 32 ka BP to 11 ka BP German
reindeer δ15N values fall, with typical values of 1‰ to 3‰
observed during the Late Glacial interstadial. Mean reindeer
δ15N in Germany is slightly higher (by approximately 0.5‰)
during the Younger Dryas than during the Late Glacial
interstadial.
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Fig. 4. δ15N of radiocarbon dated reindeer from Germany between 45 ka and
9 ka BP.
Of the radiocarbon-dated samples analysed, only those from
Germany are present throughout most of the time period
covered in this study and are relatively evenly distributed
chronologically. The results of these samples alone (n = 21)
show very clearly the gradual decline in reindeer δ15N values
over the Late Pleistocene. (R2 = 0.4807) (Fig. 4).
4. Discussion
During the Late Pleistocene, reindeer δ15N declined, with
lowest δ15N values being seen after the LGM, between 18 ka BP
and 11 ka BP. When time blocks are used to chronologically
divide results this decline appears to be gradual, however, the use
of time blocks could potentially mask the real chronological trend
in δ15N (Fig. 2). δ15N of radiocarbon-dated reindeer from
Germany also suggest that this decline was gradual (Fig. 4). δ15N
values were higher during the Younger Dryas and early Holocene
than during the Late Glacial interstadial. However, the timing and
the magnitude of the changes in reindeer δ15N vary between
different geographic regions. Although data are not available for
each time period from all regions, a general geographical pattern
can be seen. At 45–32 ka BP δ15N in the UK and Germany were
similar. After 32 ka BP reindeer δ15N values were lower, although
the depletion was greater in the UK than in Germany. In the south
of France, δ15N values became lower after c.20 ka BP, however,
data are limited prior to 27 ka BP. Thus the onset of the decline in
reindeer δ15N appears to be earlier and of a greater magnitude in
more northern regions than in the South of France.
4.1. Species comparisons
Geographical variations in faunal δ15N have only been
previously reported for horses and bovids (Stevens and Hedges,
2003; Drucker et al., 2003; Stevens and Hedges, 2004; Stevens,
2004). Although the δ15N of reindeer, horse and bovid collagen
are not directly comparable due to their differing diets and
physiologies, the pattern of δ15N variation over time can be
compared. Even though data are limited, geographical variations
in Bos/bovine δ15N values appear to be comparable to reindeer
with relatively high values in both northern and southern Europe
at 33–26 ka BP and divergent δ15N values at 18–11 ka BP, with
lowest values being seen in northern Europe, higher values in
southern France and highest values in Italy (Iacumin et al., 1997;
Drucker et al., 2003; Stevens, 2004). In contrast to large bovines,
horse δ15N data are more plentiful. European horse δ15N values
between 40 ka BP and 25 ka BP were relatively constant, in
contrast to the gradually declining reindeer δ15N values.
However, data from each country (UK, Germany, Belgium and
south of France) during this time period are limited which may
prevent recognitions of trends. Between 27 ka BP and 20 ka BP
horse δ15N in the UK, Belgium (extremely limited data) and in
the south of France were lower than pre-27 ka BP values. A rise
in horse δ15N in the south of France after the LGM (c. 20–18 ka
BP) is mirrored in the reindeer δ15N results. During the early part
of the Late Glacial interstadial the pattern of horse δ15N values
was very similar to that of reindeer, with particularly low horse
δ15N being seen in the UK, Germany and Belgium, whereas in
the South of France δ15N was slightly higher. However, as the
Late Glacial interstadial progressed and subsequently during the
Younger Dryas (11–10 ka BP) horse δ15N in the UK, Germany
and Belgium rose dramatically. Due to the limited number of
radiocarbon dated reindeer at this time it is impossible to tell if
reindeer δ15N values rise through the Late Glacial interstadial,
however, it is clear that reindeer δ15N was higher during the
Younger Dryas in the UK and Germany than in the Late Glacial
interstadial. Where data are available, horse δ15N in Italy remains
relatively high and constant during periods where δ15N in more
northern regions declined. Thus a lowering and subsequent rise
in δ15N is observed during the Late Pleistocene for both reindeer
and horse. This regional pattern in δ15N decline mimics the
general pattern of climatic deterioration in Europe culminating at
the LGM, with climate cooling beginning earlier and being more
intense in northern Europe than in southern Europe (Huijzer and
Vandenberghe, 1998).
4.2. Comparison with climatic record
Although temperatures generally declined between 45 ka BP
and the LGM, the climate is thought to have been extremely
variable and the decline in temperature was interrupted by
multiple short lived warm episodes (Table 3). At 45–36 ka BP
temperature had already started to decline, with plant and insect
data suggesting the mean temperature of the warmest month
was between 10 °C and 11 °C and periglacial data suggesting
the mean temperature of the coldest month was between − 27 °C
and − 20 °C (Huijzer and Vandenberghe, 1998). Permafrost was
not present in Northwest Europe during the early part of this
time window. However, by 38 ka BP discontinuous permafrost
had developed (Fig. 5A), suggesting mean annual air
temperature were between − 8 °C and − 4 °C (Huijzer and
Vandenberghe, 1998). Most of France was permafrost free at
this time (Huijzer and Vandenberghe, 1998). Conditions were
relatively arid although a slight precipitation increase occurred
between 38 and 36 ka BP. A short-lived period of climatic
warming at around 38–36 ka BP may have resulted in some
permafrost degradation (Kasse et al., 1995). At 45–36 ka BP
reindeer δ15N in the UK and Germany (both subject to
discontinuous permafrost) was relatively high compared to
those from same countries in subsequent periods.
Author's personal copy
Table 3
Summary of climatic conditions between 45 ka and 9 ka BP (data summarized from Coope and Brophy, 1972; Vandenberghe and Pissart, 1993; Kasse et al., 1995; Walker, 1995; Isarin, 1997; Huijzer and Vandenberghe,
1998; Lowe et al., 1999; Renssen and Vandenberghe, 2003; Vandenberghe et al., 2004)
Temperature
Precipitation
Permafrost
9–10
Early Holocene
• Wetter
• No Permafrost
10–11
• Younger Dryas
• Relatively arid in the
British Isles, Germany
and Belgium
• Continuous permafrost in north Britain
• Discontinuous permafrost in southern
Britain, Belgium, and northern Germany
• No permafrost in most of France
11–13
• Late Glacial
• Wetter
• No Permafrost in N.W. or S.W. Europe
13–15
• Late Pleniglacial
• Extremely Arid
• Permafrost boundaries continued to migrate further north
15–20
• Late Pleniglacial
• Warm interglacial climatic conditions
• Temperatures similar to today
• Mean temperature of warmest month = 15 °C to 17 °C
• Climatic cooling
• Re-advance of ice sheets
• Mean annual temperature in northern Britain = b−8 °C
• Mean annual temperature in southern Britain,
Belgium, and northern Germany = − 4 °C to − 8 °C
• Mean annual temperature in France = N− 4 °C
• Rapid warming in British Isles & Germany,
• Thermal maximum in British Isles, Germany and S.W. Europe
• Mean temperature of the warmest month = 16 °C and 18 °C
• First sustained warming in S.W Europe at 15 ka BP
• Rapid warming in N Europe after 13.5 ka BP
• Mean annual temperature in Uk and Belgium = − 9 °C to 1 °C
• Mean temperature of coldest month = −21 °C to − 9 °C
• Polar desert over most of Europe
Mean temperature of warmest month = 8 °C to 11 °C
• Mean temperature of coldest month = −21 °C to − 9 °C
• Mean annual temperature in N.W. Europe = −8 °C
• Low biological productivity
• Mean temperature of warmest month = 8 °C
• Mean temperature of coldest month = −25 °C to − 20 °C
• Mean annual temperature in N.W. Europe =b − 8 °C
• Significant climatic cooling
• Ice sheet advance
• Mean temperature of warmest month = 10 °C
• Mean temperature of coldest month = −12 °C to−20 °C
• Mean annual temperature in N.W. Europe − 8 °C to −2 °C
• Mean temperature of warmest month = 10 °C to 11 °C
• Mean temperature of coldest month = −27 °C to − 20 °C
• Mean annual temperature in N.W. Europe = −8 °C to− 4 °C
• Mean annual temperature in S.W. Europe =N − 4 °C
• Extremely arid
• Continuous permafrost marginal to thawing ice sheet
20–27
• Late Pleniglacial
27–32
• Mid Pleniglacial
32–36
• Mid Pleniglacial
36–45
• Mid Pleniglacial
• Slightly wetter but moisture
locked up in ice sheets.
• A Slightly wetter but moisture
locked up in ice sheets
• Slightly Wetter
• Discontinuous permafrost extended north from
northern France and Germany
• Continuous Permafrost in British Isles,
most of Germany and Belgium
• Discontinuous permafrost extended down to the
South of France
• Permafrost development and advancement
• No Permafrost in France and Germany or
• ?? Discontinuous permafrost in British Isles??
• Arid although a slight precipitation • No permafrost at start of interval
increase occurred between 38 and
• Permafrost developed by 38 ka BP in N.W. Europe
36 ka BP
• Slight warming and permafrost degradation
between 38 ka BP and 36 ka BP
• No Permafrost in France
R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
Time Interval ka BP (uncal) Time period
39
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
Fig. 5. Change in the distribution of Permafrost during the late Pleistocene. A = 41–38 ka BP, B = 36–32 ka BP, C = 27–20 ka BP, D = 20–14 ka BP, E = 13–11 ka BP
(Late Glacial), F = 11–10 ka BP (Younger Dryas). Map redrawn from Huijzer and Vandenberghe (1998), and Renssen and Vandenberghe (2003). Map generated from
ESRI map data using ArcGIS v.9.1.
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
At 36–32 ka BP the climate was very similar to, but slightly
warmer than the previous time interval, with botanical and
coleopteran data suggesting the mean temperature of the warmest
month was around 10 °C (Huijzer and Vandenberghe, 1998).
Periglacial and botanical evidence suggest the mean annual air
temperature was between −8 °C and −2 °C and mean temperature
of the coldest month was between −12 °C and −20 °C (Huijzer
and Vandenberghe, 1998). The discontinuous permafrost boundary shifted through the Netherlands several times during this time
block (Fig. 2B) (Huijzer and Vandenberghe, 1998). Reindeer
δ15N in Germany (permafrost free in central and southern
Germany from which samples were obtained) was slightly higher
than during the previous time interval, whereas in the UK
(discontinuous permafrost possibly present) it was slightly lower.
Between 32 and 27 ka BP climate cooled significantly and
by 27 ka full glacial conditions were present. Biological
productivity of the whole ecosystem was extremely low.
Coinciding with this climatic cooling reindeer δ15N in Britain
and Germany declined. The extent of the depletion was greater
in the British Isles than in Germany.
At 27–20 ka BP the mean temperature of the warmest month
in northwest Europe was around 8 °C according to botanical and
coleopteran evidence (Vandenberghe et al., 2004). However,
there was a strong north-south thermal gradient (much stronger
than today) and mean annual temperature in more northern
regions was probably no more than 4 °C (Vandenberghe et al.,
2004). Mean temperature of the coldest months was between
− 25 °C and − 20 °C, thus the annual temperature range was
large. Although annual precipitation rates were relatively high
toward the start of this time interval (Huijzer and Vandenberghe,
1998) water became locked up in ice sheets, glaciers and
permafrost, thus water availability was limited. Continuous
permafrost was present throughout the UK (with the exception
of areas covered by ice sheet), most of Germany and Belgium.
Discontinuous permafrost extended from northern to southern
France (Huijzer and Vandenberghe, 1998) (Fig. 5). Reindeer
δ15N values in the south of France at this time interval were
relatively high in comparison to subsequent periods. δ15N data
from northern Europe are extremely limited during this time
interval as the greater part of northern Europe was a barren cold
desert with almost no biota present (Walker, 1995).
During the time interval 20–13 ka BP the ice sheet decayed
and progressively retreated to the north, resulting in permafrost
formation in areas previously covered by ice (Huijzer and
Vandenberghe, 1998). Precipitation rates during this time period
were low and widespread loess accumulation suggests a high
degree of aridity (Huijzer and Vandenberghe, 1998). However,
ice sheet and permafrost melting would potentially increase
water availability in certain areas. During the early part of this
time interval (20–15 ka BP) conditions were still arctic. Sparse
palaeobotanical and coleopteran data suggest mean temperatures of the warmest month were between 8 °C and 11 °C. The
mean annual temperature in northern regions was around
− 8 °C. The southern limit of continuous permafrost was
marginal to the thawing ice sheet and discontinuous permafrost
extended from across northern France into northern Germany
(Huijzer and Vandenberghe, 1998) (Fig. 5D). Reindeer δ15N
41
values in both Germany and the south of France were lower than
in earlier time intervals, however, values in the south of France
were higher than those in Germany. During the later part of this
time interval (15–13 ka BP) periglacial evidence suggests that
as the permafrost boundaries migrated northwards, the zones of
continuous and discontinuous permafrost became very narrow.
Between 20 ka BP and 13 ka BP coleopteran data suggest mean
annual temperatures in the UK and Belgium ranged from
around − 9 °C to 1 °C. By 13 ka BP coleopteran evidence
suggests that temperatures could have been rising as fast as 1 °C
per decade (Coope and Brophy, 1972). By 15 ka BP to 13 ka BP
reindeer δ15N values in Germany had declined further, whereas
in France they rose very slightly. During this time interval
Belgian reindeer δ15N values were similar to those of German
reindeer.
During the Late Glacial interstadial (13–11 ka BP), sustained
widespread warming became established (Walker, 1995; Lowe
et al., 1999). Temperatures rose very rapidly and between 13ka
BP and 12.5 ka BP present-day temperatures were exceeded in
Southern Europe and the British Isles (Walker, 1995). During
the thermal maximum the mean temperature of the warmest
month was between 16 °C and 18 °C (Walker, 1995).
Permafrost was absent from Western Europe during the Late
Glacial interstadial (Fig. 5E). Reindeer δ15N values in the UK,
Belgium, Germany and Siberia were very low. Similarly horse
δ15N values in the UK, Germany and Belgium were very low at
the start of this time interval, however, they rose rapidly during
this time interval (Stevens and Hedges, 2004). Only improving
the chronology of reindeer δ15N through radiocarbon dating
will allow us to determine if the rise in horse δ15N is mirrored in
reindeer.
An abrupt cooling occurred during the Younger Dryas (11–
10 ka BP) and alpine glaciers and ice sheets re-advanced
(Vandenberghe and Pissart, 1993). Coleopteran data suggests
mean temperatures of the warmest month were around 10 °C
(Walker, 1995). In northern Britain continuous permafrost
developed (suggesting mean annual temperatures of b − 8 °C),
whereas discontinuous permafrost extended across southern
Britain, Belgium and northern Germany (suggesting mean
annual temperatures between − 8 °C and −4 °C) (Fig. 2F)
(Isarin, 1997). Most of France was permafrost free at this time
with mean annual temperature exceeding − 4 °C (Isarin, 1997).
Younger Dryas reindeer δ15N values were higher in both the
UK and Germany than during the Late Glacial interstadial. The
rise in δ15N values appears to have been greater in the UK than
in Germany, however, this may be a function of limited data
from Germany.
During the early Holocene (10 ka BP to 9 ka BP) temperatures
rose rapidly, with conditions comparable to today being
established by 9 ka BP. In northwest Europe Betula, Pinus and
Corylus woodland replaced steppe tundra communities and in
southern Europe Pinus, Corylus and Quercus woodland rapidly
succeeded Artemesia dominated steppe vegetation (Walker,
1995). Mean temperatures of the warmest month were between
15 °C and 17 °C in the British Isles (Walker, 1995). Early
Holocene reindeer δ15N values in the UK were slightly lower than
those in the Younger Dryas.
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
4.3. Potential parameters influencing reindeer δ15N
With diet as the primary control on animal collagen δ15N, it
might be suggested that the variation in Late Pleistocene
reindeer δ15N was caused by dietary adaptation (to include
more plants with low δ15N signatures) and physiological
adaptations in response to changing climatic conditions.
Reindeer eat relatively large amounts of lichen, particularly
when the availability of other plants is limited. Consequently
reindeer are typically nutritionally deficient as lichen is poor in
protein (Drucker et al., 2001). When lichen is the predominant
dietary intake, reindeer recycle their body protein into urea in
order to cope with the low protein diet (Soveri, 1992). Elevated
δ15N values have been reported in nutritionally stressed
animals, which potentially may be caused by additional isotopic
fractionation due to body protein mobilisation for the metabolic
nitrogen pool (Hobson et al., 1993; Drucker et al., 2001). As
climatic conditions became colder and drier towards the LGM,
the availability of plant foods became more limited and thus the
amount of lichen consumed by reindeers is likely to have
increased. The physiological response to the increased nutritional stress as a result of dietary change should theoretically
have resulted in a rise in reindeer δ15N coinciding with climatic
deterioration. However, our results show the opposite of this,
with δ15N falling as climatic conditions declined, suggesting
dietary change is not the primary mechanism controlling Late
Pleistocene reindeer δ15N. Furthermore, the gradual lowering of
faunal δ15N during the Late Pleistocene is relatively consistent
across species. Reindeer, horse, red deer and large bovines can
all live within the same ecosystem, however, they exploit
different ecological niches and are thus unlikely to all change
their diets and physiologies at the same time and in the same
way. Thus, we agree with previous studies (Richards and
Hedges, 2003; Drucker et al., 2003; Stevens and Hedges, 2003,
2004) that dietary change is unlikely to be a primary mechanism
causing the changes in Pleistocene faunal δ15N.
The variations in reindeer δ15N are more likely to be due to a
change in the isotopic composition of the plants they consume
rather than the species of plants they select. Plant δ15N is
dependent on soil δ15N, soil development, nutrient availability
(nitrogen and phosphorus), mycorrhizal associations, soil
acidity and nitrogen cycling (see Stevens and Hedges, 2004
for further details). However, the predominant mechanism
determining soil and plant δ15N is the extent to which the
nitrogen cycle is an open or closed system. i.e. the relative
importance of within-ecosystem nitrogen cycling versus the
relative importance of inputs and outputs (Handley et al., 1999).
This in turn is controlled by climate, resulting in low δ15N
observed in cold and/or wet areas and high δ15N seen in hot
and/or arid areas (Amundson et al., 2003). If water availability
was controlling nitrogen cycling during the Late Pleistocene,
we would expect to see a rise in reindeer δ15N values when
conditions became more arid and water availability became
limited as water became locked up in ice sheets and permafrost.
The reindeer δ15N results at 20–15 ka and 15–13 Ka BP show
the opposite of this and, furthermore, declined at 13–11 ka BP
when conditions became wetter. Thus it appears that water
availability is not the primary control on nitrogen cycling in the
Late Pleistocene.
Permafrost development has previously been suggested to
coincide with faunal δ15N declines (Drucker et al., 2003;
Stevens and Hedges, 2003, 2004). Although this may be the
case for horse and bovids in the south of France (Drucker et al.,
2003), it is not true of horse and reindeer δ15N in more northern
regions. Moreover permafrost degradation occurred relatively
rapidly after the LGM, when faunal δ15N in northern regions
noticeably declined. By the Late Glacial interstadial, permafrost
was absent from Western Europe. However, the lowest faunal
δ15N values in northern regions are observed at the start of the
Late Glacial interstadial. We suggest that the variations in
reindeer δ15N during the late Pleistocene are linked to the
influence of temperature and permafrost degradation on soil and
plant δ15N.
The gradual decline in reindeer δ15N values between 45 ka
BP and the LGM could be a record of the nitrogen cycle's
response to falling temperatures. Although reindeer δ15N values
were relatively high at 45 ka BP to 36 ka BP compared to later
reindeer δ15N values, they were significantly lower than those
from oxygen isotope stage 5A, when warm temperate
conditions were present in the UK (Stevens unpublished
data). The lowering temperatures would have resulted in
gradual changes in nitrogen cycles, moving them from open
to closed systems, thus resulting in a decline in ecosystem δ15N.
The most noticeable drop in reindeer δ15N occurs between 27–
20 ka BP and 13–11 ka BP. In Southern and Central France the
decline in reindeer δ15N values coincides with permafrost
degradation, with higher values observed at 27–20 ka BP when
discontinuous permafrost was present and lower values at 20–
15 ka BP during permafrost degradation. The first sustained
warming occurred in southern Europe around 15 ka BP. The
slight rise in reindeer and horse δ15N in the south of France at
this time suggests initial climate warming had influenced
ecosystem δ15N. The more limited magnitude of the depletion
in reindeer δ15N in Southern France may relate to the fact that
the permafrost in this region was discontinuous rather than
continuous.
In more northern regions the lowest reindeer δ15N values
occur later at 15–13 ka BP in Germany and at 13–11 ka BP in
the UK (although no results are available from the UK during
the 15–13 ka BP). Permafrost boundaries migrated northwards
between 15 ka and 13 ka BP and extensive permafrost
degradation occurred. The greater magnitude of the depletion
in reindeer δ15N in northern regions may relate to the previous
presence of continuous permafrost. Widespread climatic
warming in northwest Europe occurred after 13.5 ka BP
(Walker, 1995), yet reindeer and horse δ15N values in the UK,
Germany and Belgium were very low at the start of the Late
Glacial interstadial. This suggests there was a delay in the
response of ecosystem δ15N to the rising temperatures which
may be linked to permafrost degradation and soil development.
Evidence from modern ecosystems support this possibility, with
exceptionally low soil δ15N values of around − 1‰ and plant
δ15N values of around−11‰ being reported in the forefront of
the retreating Lynmann Glacier (Hobbie et al., 2005). These low
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
soil and plant δ15N values are likely to occur because initial N
inputs to the soil (e.g. via weathering from primary minerals,
atmospheric N deposition, biological fixation) are 15N depleted.
The plants in such nutrient-poor environments are likely to have
relied on mycorrhizal associations to aid their uptake of
nitrogen, as plants do in the present day arctic (Smith and
Read, 1997; Hobbie and Hobbie, 2006). Plants with these
ericoid and ecto-mycorrhizal association often have very
depleted δ 15 N values as low as − 12‰ (Handley and
Scrimgeour, 1997). Moreover, in areas proximal to the ice
sheets nitrogen cycling had essentially stopped during the LGM
and it may have taken some time for the system to re-start.
Although temperatures started to rise after the LGM, plant δ15N
(and thus reindeer δ15N) remained low. Limited directly
radiocarbon dated reindeer δ15N during the Late Glacial
interstadial makes it impossible to establish how quickly they
responded to increasing temperature, however, horse δ15N rose
rapidly during this time interval (Stevens and Hedges, 2004).
The Younger Dryas cooling appears not to have been long or
severe enough to effect ecosystem δ15N even though discontinuous permafrost extended across the UK. The dates for the
Younger Dryas Chronozone used in this study are those defined
by Mangerud et al. (1974): 1000 uncalibrated radiocarbon years
starting from 11,000 BP and ending at 10,000 BP. However,
establishing the duration of Younger Dryas is not straightforward. Firstly the radiocarbon plateau at 10,000 BP affects
calculations of the duration and secondly the duration varies
regionally (Lotter, 1991). Evidence from the Grip Ice Core
suggest the Young Dryas lasted for 1240 Years from 12,890 to
11,650 ice core years BP (Stuiver et al., 1995), whereas
laminated varve sediments from Soppensee (Switzerland)
suggests a duration of 680 to 720 years (Lotter, 1991). Thus
using Mangerud et al's Younger Dryas definition may have
resulted in grouping reindeer from regions where the Younger
Dryas was short, with those where it was more persistent and
may have had a greater affect on the reindeer δ15N values. The
few available radiocarbon dated horse δ15N values from the
Younger Dryas are however, substantially higher than those
from the Late Glacial interstadial (Stevens and Hedges, 2004).
Renewed climate warming during the early Holocene (10–9 ka
BP) saw reindeer δ15N values in the UK slightly decline. As
with the post LGM low reindeer δ15N values, this decline might
relate to permafrost degradation, as during the Younger Dryas
discontinuous permafrost was present across the UK. Further
investigation of the Younger Dryas and early Holocene reindeer
δ15N may help elucidate links between permafrost degradation
and faunal δ15N.
It is clear that the relationship between climate and faunal
δ15N is not a direct one to one correlation. The lack of radiocarbon dates for many of the samples forces the grouping of
data based on associated dates. With stratigraphic mixing often
occurring at archaeological sites several of the non-radiocarbon
dated samples could potentially be assigned to the wrong time
block. The extensive scatter observed within each time block
could be due the grouping of samples. This scatter may relate to
rapid climate variation and further radiocarbon dating may help
elucidate further chronological trends within this dataset.
43
However, several radiocarbon plateaux have occurred during
the last 50,000 years potentially causing errors in the radiocarbon dates. Although calibrating some of the dates is possible,
some of the significant changes in faunal δ15N values occur
during these plateaux, making it extremely hard to determine
the rate of change in faunal δ15N. Disparities in the timing of
variations in faunal δ15N and climate may also be because the
nitrogen cycle is a complex system, which is likely to take time
to respond to climate change and that initial responses may not
be detected in the isotope record.
5. Conclusions
Reindeer δ15N data confirms temporal and geographical
trends previously observed in horse and bovid δ15N values, with
the onset of the decline being earlier and of a greater magnitude
in northern Europe compared to Southern Europe. No correlation
was observed between reindeer δ15N and permafrost development. Correlations between reindeer δ15N and permafrost
degradation during the Late Pleistocene suggest this parameter
may have influenced ecosystem δ15N. A lag in the response of
the nitrogen cycle to increasing temperatures is observed which
may relate to the influence of permafrost degradation on soil and
plant δ15N and thus faunal δ15N. The renewed climatic cooling
during the Younger Dryas did not see a fall in reindeer δ15N,
however, the limited reindeer data from the UK for the early
Holocene suggest permafrost degradation may also influence the
post Younger Dryas reindeer δ15N values. The link between
climate and faunal δ15N values is complex. Further Pleistocene
data and modern studies are required to establish relationships
between the two. However, faunal nitrogen isotopes provide
insights into past biogeochemical cycles that cannot be currently
gained from other palaeoenvironmental proxies. Further isotopic
investigations and radiocarbon dating will provide us with a
better understanding of how the nitrogen cycle responded during
periods of rapid climate transition.
Acknowledgements
We would like to thank Peter Ditchfield for technical assistance
with isotopic analysis. This project was funded by a NERC
studentship to R.E.Stevens (NER/S/A/2000/03522) and Europeanfunded “Improving Human potential program: Access to Belgium
Collections (ABC)” and “Synthesis” grants to R.E. Stevens. Our
thanks go to Jef Vandeberghe of Vrije University Amsterdam and
Erik Hobbie of the University of New Hampshire for communications on permafrost histories and mycorrhiza, respectively.
Cameron Petrie is thanked for his assistance with graphics. We
would like to thank the following institutions and people for
providing samples for analysis: Andy Currant at the Natural
History Museum London, Generaldirektion Kulturelles Erbe,
Rheinland-Pfalz, Tom Lord, The Royal Belgian Institute for
Natural Sciences, Wells Museum, The University of Bristol
Speleological Society Museum, Torquay Museum, Creswell Crags
Museum and Education Centre, University of Cambridge Museum
of Archaeology and Anthropology, Buxton Museum, Stoke-OnTrent Potteries Museum & Art Gallery, Lancaster Museum.
Author's personal copy
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R.E. Stevens et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 262 (2008) 32–45
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.palaeo.2008.01.019.
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