14C Dating of Peat and δ18O-δd in Ground Ice From Northwest Siberia

We present new radiocarbon dates from a number of Holocene peat deposits along a north-south transect across the Yamal Peninsula. The samples were collected from frozen peat deposits with large ice wedges in: the northern tundra near Seyaha Settlement, in the Central Yamal Peninsula, the southern tundra in Shchuch'ya River valley at the Edem'yaha mouth, the southern part of the Yamal Peninsula, and the southern forest tundra near Labytnangi Town. 14C dates of wood remains from the tundra in the Yamal Peninsula could be used to reconstruct a northern limit of forest during the Holocene Optimum. The wood layers at the bottom of the peat give evidence for immigration of trees further north beyond the present boundary. The first forest appearance in the Seyaha River valley area is dated about 9 ka BP according to the oldest peat date in the Seyaha cross section. This suggests that summer temperatures were higher than at present. Very fast accumulation of peat (around 5 m/ka: about 9–8 ka BP at Seyaha and about 7–6 ka BP at Shchuch'ya) also supports this observation.In contrast, oxygen isotope composition of Holocene syngenetic ice wedges from the area (δ18O= −19.1 to −20.3‰ in the Seyaha cross-section and −17.3 to −20.3‰ in the Shchuch'ya River) show that winter temperatures were significantly lower than presently, i.e. the climate during the Holocene Optimum was slightly more continental. The frozen peat near Labytnangi has thawed during the last 20 years, indicating global warming.