Peat as an organic record

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Peat as an organic record
Peat as an organic record Peat Society Clip Peat Descrip,on • 
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Peat accumulates at a rate of about 0.5 -­‐ 1 mm per year (or 5-­‐10 mover 10,000 years) with strong local variaAons. Peat can be formed from mosses, lichens, sedges, grasses, shrubs (heather) or trees. In northern regions, mosses are the main peat-­‐forming plants while trees are the main ones in the tropics. Most peatlands that exist today formed in the last 15,000 years since the last Ice Age. Peat consists of accumulated dead plant material of which at least 50% is carbon. Water saturaAon means that plant remains decompose slowly and form peat Peat moss Sphagnum flexuosum Lichen in peat Sphagnum spp. Moss peat with sedges of Carex spp. Peat Distribu,on of the record •  Peat has been forming in the planet during the last 360 Million yr and nowadays holds 550 Gt of carbon (1015g). •  Worldwide peatlands cover about 500 million hectares of land, some 5-­‐8% of the world's surface. •  They are most extensive in North America, Asia and Europe. •  The remainder are found in tropical areas the most extensive in south-­‐east Asia. •  Overall, hold 10% of freshwater world’s resources. In Europe there are 515,000 km2, around 15% In Spain around 300 km2 ( 0.05% !!) Peat (=turf, e.g, in Ireland) Peat types Elevated Bog Peatland an area with a naturally accumulated peat layer at the surface Mire a peatland where peat is currently forming and accumulaAng Fen Bog, pH 3.2 to 4.2; Ash 3% a peatland which receives water solely from rain and/or snow falling on its surface. Poor trophic status. Up to 12 m thick!! Blanket Bog Fen pH 7 to 8; Ash 10% a peatland which receives water and abundant nutrients from the soil, rock and groundwater as well as rain and/or snow. Up to 2 m. Fen Peat Structure •  Bogs: 98% water! Only 2% solids. •  Fens: 85% / 15% •  A bog consists of two layers: •  the upper, very thin layer, known as the acrotelm, is only some 30cm deep, and consists of upright stems of the Sphagnum mosses, largely sAll alive and colourful with their red, yellows and ochre. Water can move rapidly through this layer. •  Below this is a very much thicker bulk of peat, known as the catotelm, where individual plant stems have collapsed under the weight of mosses above them to produce an amorphous, chocolate-­‐coloured mass of Sphagnum fragments. here the water slowly seeps down through the bog over several weeks or even months. Peat Peat forma,on Peatlands are composed of deep layers of waterlogged peat and a surface layer of living vegetaAon. Peat consists of the dead remains of plants (and to a lesser extent of animals) that have accumulated over thousands of years. Peat accumulates in areas where the rate of plant produc,on exceeds the rate of plant decomposi,on. Complete plant decomposiAon is prevented in areas where waterlogging occurs. Peat Proxies Water table oscilla,ons throuhg the fossil record Testate amoeba Testate amoebae are rouAnely used as indicators of past changes in peatland hydrology. These single-­‐
celled organisms respond quickly to environmental change, produce decay-­‐resistant and taxonomically disAncAve shells and are generally well preserved and abundant in Holocene peat deposits. In oligotrophic peatlands, testate amoeba community composi,on is primarily controlled by the moisture content of the surface peat, allowing the development of transfer funcAons to bdepths. Peat Applica,on examples Peat as an archive of atmospheric pollu,on •  Some bogs are uniquely suited to natural and anthropogenic airborne parAcles because their surface layers are only fed by atmospheric inputs (rain, snow, fog, dust). •  Pb is well retained by bogs (adequate pH). •  Stable isotopes allow discriminaAng between natural and anthropogenic metal abundance, and its origin. •  Metal/Titanium (conservaAve metal), allows such discriminaAon. De Vleeschouwer et al 2010 Peat Applica,on examples Peat pollen record as a paleothermometer •  Pollen-­‐based warm season temperature reconstrucAon •  Upper panel is detrended to remove human effects (de-­‐ or re-­‐forestaAon). •  Reconstructed detrended series are compared to instrumentally measured temperatures. •  CorrelaAon begins to be good in 1900 at a decadal resoluAon. Lamentowicz et al 2010 Peat Applica,on examples Peat proxies record solar ac,vity •  Proxies: •  Normalized testate amoebae water table reconstrucAon (blue) •  Plant macrofossil Dupont wetness index (green) •  Normalized 14C relaAve producAon rate (accreAon) (gray) •  Historical solar minima are indicated, and arrows show significant raises in water table. •  Low solar acAvity results in weier seasons/periods, increasing the water table and consequently, bog accreAon (producAon). Chambers et al 2010 • 
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Water table changes (WTC) of several bogs in North America during the last 3000 years (a) Microcharcoal par,cles reveal fire destroying the bog in Michigan (blue) and allows establishing recovery Ame (resilience; paleo-­‐
ecology). StaAAcal removal of long term paierns allows building a composite record of all three bogs (b). WTC Aghtly matches the severe drought periods (yellow). Tree rings and dune ac,vity (aeolian transport) match drought periods too. ReconstrucAons of anomalous SST both in the Pacific and in the AtlanAc, and of the NAO (Niño) using tree-­‐reings, support all previous proxies and records.
Peat serve to cross-­‐test global climate hypotheses (Booth et al 2010) Peat Applica,on examples MCA: Medieval Climate Anomaly; PDO: Pacific Decadal OscillaAon Peat Applica,on examples Hg as pollu,on and temperature proxy •  Galician peat records net accumulaAon of atmospheric Hg during the last 4000 years. •  Differences in thermal lability of Hg allowed to a quanAtaAve paleotemperature reconstrucAon during that period. •  Natural Hg can be disAnguished from anthropogenic Hg, allowing to establish background levels and record mining acAviAes. •  Discriminant analysis allowed to build a relaAve scale of temperature (Temperature index) Marjnez-­‐CorAzas et al. 1999 Peat as a paleo-­‐record Literature and web sites • 
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Dise, N.B, 2009: Peatland responses to global change, Science, 326: 810-­‐811. Booth, R.K., 2008: Testate amoebae as proxies of mean annual water-­‐table depth in Sphagnum-­‐dominated peatlands of North America, Journal of Quaternary Science, 23: 43-­‐57. Booth, R.K., 2010: TesAng the climate sensiAvity of peat-­‐based paleoclimate reconstrucAons in mid-­‐
conAnental North America, Quaternary Science Reviews, 29: 720-­‐731. doi: 10.1016/j.quascirev.
2009.11.018 Barber, K.E., 1981: Peat Stra>graphy and Clima>c Change—a Palaeoecological Test of the Theory of Cyclic Peat Bog Regenera>on, A A Balkema, Roierdam. Vleeschouwer et al., 2010: Peat as an archive of atmospheric polluAon and environmental change: a case study of lead in Europe. PAGES, 18: 20-­‐22. The Holocene 2001, volume 11, number 5, includes various arAcles using peat as a paleorecord. hip://www.lehigh.edu/~rkb205/ (Robert K. Booth web site). hip://www.peat-­‐portal.net/index.cfm?&menuid=115&parenAd=113 hip://www.ipcc.ie/wptourhome1.html (peatlands around de world) hip://www.doeni.gov.uk/niea/biodiversity/habitats-­‐2/peatlands/about_peatlands.htm (‘about peatlands’) hip://www.landforms.eu/Caithness/Peat%20formaAon.htm (peat structure) hip://www.imcg.net/pages/publicaAons/papers.php?lang=EN (Int. Mire Cons. Group; bibliography) Peat as a paleo-­‐record Literature and web sites Antonio MarZnez-­‐Cor,zas: Spanish specialist in the use of peat as a paleorecord. Universidad de SanAago de Compostela, Depto. Edafología y Química Agrícola [email protected] • 
Marjnez CorAzas A, Pontevedra-­‐Pombal X, García-­‐Rodeja E, Nóvoa-­‐Muñoz JC, Shotyk, W (1999) Mercury in a Spanish peat bog: archive of climate change and atmospheric metal deposiAon. Science 284:939–42. • 
Marjnez CorAzas A, Pontevedra-­‐Pombal X, Nóvoa-­‐Muñoz JC, García-­‐Rodeja E. Four thousand years of atmospheric Pb, Cd and Zn deposiAon recorded by the ombrotrophic peat bog of Penido Vello (Northwestern Spain) (1997). Water Air Soil Poll, 100:387–403. • 
Marjnez CorAzas A, García-­‐Rodeja E, Pontevedra-­‐Pombal X, Nóvoa-­‐Muñoz JC, Weis D, Cheburkin A (2002) Atmospheric Pb deposiAon in Spain during the last 4600 years recorded by two ombrotrophic peat bogs and implicaAons for the use of peat as archive. Sci Total Environ, 292:33–44. • 
Marjnez CorAzas A, Pontevedra X, Nóvoa JC, Peiteado E, Piñeiro R (2005) Linking changes in atmospheric dust deposiAon, vegetaAon change and human acAviAes in north-­‐western Spain during the last 5300 years. The Holocene, 15:698–706. 

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