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CIRCUMARCTIC PEATLAND HISTORY AND GLOBAL ATMOSPHERIC METHANE

MACDONALD, GLEN M  UCLA.
Smith, Larry C  UCLA.
Kremenetski, Konstantine V  UCLA.
Sheng, Yongwei  UCLA.
Beilman, Dave W  UCLA.
Andrei, Velichko A  RAS.

Holocene concentrations of atmospheric methane reconstructed from the Greenland and Antarctic ice cores present puzzling patterns. First, there is a rapid increase of Northern Hemisphere derived methane at 12,000 Cal yrs BP (years before present) followed by a general decline between 10,000 and 5000 Cal yrs BP. The causes of the rapid increase to Holocene maximum levels is debated with some speculating this reflects the rapid release of marine methane by marine clathrates while others suggesting it reflects the establishment of methane producing peatlands in the high latitudes as these regions warmed at the close of the Pleistocene. Following 5000 Cal yrs BP there is another increase in methane that has persisted to present. The causes of this late Holocene increase in methane are again debated. Some have argued that it represents a new expansion of northern peatlands as high latitude summer insolation decreased and climate cooled from a thermal maximum. In contrast, it has also been suggested that anthropogenic activities, namely rice cultivation, drove much of the increase. We have sought to solve these puzzles by obtaining radiocarbon dates to document the history of the world’s largest high latitude peatland complex in west Siberia and combine these dates with a data base of over 1000 peat initiation dates from around the Northern Hemisphere. Peatland initiation in areas such as western Siberia coincides with the initaition of widespread warming in the early Holocene coincidental with boreal forest development and extension of treeline north of modern limits. There is evidence of limited new peatland development at the southern edges of the modern boreal zone in concert with neoglacial cooling. The preliminary results suggest caution in attributing all of the early and late Holocene increases in methane to high latitude peatlands and their response to Holocene warming and cooling.

REFERENCES
Kremenetski, K.V., Velichko, A.A., Borisova, O.K., MacDonald, G.M., Smith, L.C., Frey, K.E. and Orlova, L.A. 2003. Peatlands of the Western Siberian lowlands: current knowledge on zonation, carbon content and Late Quaternary History. Quaternary Science Reviews 22: 703-723.



MacDonald, G.M., Velichko, A.A., Kremenetski, C.V., Borisova, O.K., Goleva, A.A., Andreev, A.A., Cwynar, L.C., Riding, R.T., Forman, S.L., Edwards, T.W.D., Aravena, R., Hammarlund, D., Szeicz, J.M., Gattaulin, V.N. 2000. Holocene treeline history and climate change across northern Eurasia, Quaternary Research 53: 302-311.



Smith, L.C., MacDonald, G.M., Velichko, A.A., Beilman, D.W., Borisova, O.K., Frey, K.A., Kremenetski, K.V., and Sheng, Y. 2004. Siberian peatlands a net carbon sink and global methane sourse since the early Holocene. Science 303: 353-356.



Figure 1. Atmospheric methane and peatland history in west Siberia (from Smith et al. 2004)


Figure 2. Warming of northern Eurasia (after MacDonald et al. 2000)


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