PEATLANDS OF THE WESTERN SIBERIAN LOWLANDS: CURRENT KNOWLEDGE ON ZONATION, CARBON CONTENT AND LATE QUATERNARY HISTORY

The Western Siberian Lowlands (WSL) are the world's largest high-latitude wetland, and possess over 900,000 km2 of peatlands. The peatlands of the WSL are of major importance to high latitude hydrology, carbon storage and environmental history. According to the Russian classification system, the modern peatlands can be subdivided on the basis of morphology, hydrology, permafrost conditions and vegetation cover into six latitudinal zones. From north to south these are comprised of: 1. Polygonal Bog Zone, 2. Flat Hill-Bog Zone, 3. Large Hill-Bog Zone, 4. Oligotrophic (Sphagnum) Bog Zone, 5. Flat Eutrophic and Mesotrophic (Carex-Hypnum and forest) Bog Zone, and 6. Eutrophic (Phragmites) and Brackish Bog Zone. Analysis of the existing Russian data suggests that the mean depth of peat accumulation in the WSL is 256 cm and the total amount of carbon stored there may exceed 53,836 million metric tons. A synthesis of published and unpublished radiocarbon dates indicates that the peatlands first developed at the end of the last glacial, with a rapid phase of initiation between 11,000 and 10,000 Cal yr BP (14C years before present calibrated to calendar years). Initiation slowed after 8000 Cal yr BP and reached a nadir at 4000 Cal yr BP. There has been renewed initiation, particularly south of 62o N, following 4000 Cal yr BP. The initial development of peatlands in the WSL corresponds with the warming at the close of the Pleistocene that led to the development of taiga forest across northern Eurasia. The subsequent decline in initiation, particularly in the south, corresponds with warm conditions in the mid Holocene. Cooling after 4000 Cal yr BP has likely led to increased permafrost and increased peatland development particularly in central and southern regions. Cold and dry conditions in the far north may have inhibited peatland formation in the late Holocene. Despite the general conclusions outlined above, interpretation of the existing Russian data on peatland carbon storage and history remains problematic due to the relative scarcity of sampling sites for peat depths and ages, and the concentration of most such sites in and near major river valleys.