ISOSCAPES AND PALEOISOTHERMS OF THE HOLOCENE MEAN JANUARY AIR TEMPERATURE IN THE NORTHWESTERN SIBERIA (BASED ON STABLE OXYGEN ISOTOPE COMPOSITION OF ICE WEDGES)

Holocene ice wedges at 16 sites in the Northwestern Siberia were studied, the age of ice wedges was determined, and stable isotope data ( 18O and 2Н values) for all studied ice wedges have been summarized. The δ2H-δ18O ratio and the dexc values for ice wedge ice indicate good preservation of the isotope signal of winter precipitation in ice, which allows to use the obtained δ18O values for paleotemperature reconstructions. The isoscapes (lines of equal 18O values) created for the Holocene ice wedges and modern ice veinlets are generally submeridional; the 18O values decrease from west to east of the study area. Taking into account a new Holocene tripartite division scheme it was shown that the mean January air temperature (TmJ) in the Northwestern Siberia ranged approximately from -21 to -30°С during Greenlandian and the first half of the Northgrippian stage of the Holocene (11,4 to 6 cal ka BP) and approximately from -24 to -27°С from the end of the Northgrippian - to the Meghalayan stage of the Holocene (5,2 to 0,9 cal ka BP). The Holocene isotherms are close to the modern sub-meridional position and show an eastward decrease in TmJ values. Winter climatic conditions in the Northwestern Siberia were generally stable during the Holocene, meanwhile TmJ was on average 1-2°C lower than modern ones.