ИСТИНА

Ice wedges develop as a result of infilling of frost cracks with snow and snowmelt water. This means that the composition of stable isotopes of oxygen and hydrogen in syngenetic ice wedges allows reconstructing winter paleo-temperatures. The key problem of paleo-climatic studies related to stability of the atmospheric circulation in the entire Arctic during the alternating cycles of warming and cooling in the late Pleistocene-Holocene still remains unsolved. For our analysis, only the data on the isotope composition of syngenetic ice wedges, which have the same age as the adjacent sediments with reliable dates, were used. The data base on the isotope composition (δ18O, δD и d-excess) of syngenetic ice wedges and elementary ice veins was developed. Besides our own data, all available published data on the isotope composition of syngenetic ice wedges of known age were analyzed. The data base comprise information on 30 segments of the Eurasian Arctic with available data on δ18O, δD and d-excess obtained from ice wedges of different ages – from modern and MIS 1 to MIS 4. MIS 1 and MIS 3 correspond to the periods of global warming (thermochrones) and MIS 2 and MIS 4 – to those of global cooling (cryochrones). Sampling sites locations cover the area of the Eurasian Arctic from 66 to 78о N and from 15 to 171о E. All sampling sites are located at the sea coasts or close to the coastal area. Spatial distribution of δ 18O values of the ice wedges in the Eurasian Arctic is shown separately for ice wedges of MIS 1 – MIS 4 and modern elementary ice veins. The pattern of this distribution has remained stable during the last 50,000 years, which indicates a stable trend in atmospheric circulation from 50,000 yr BP to the present. Probably, dimensions of the ice sheet were not big enough to change directions of atmospheric transfer from west to east. This is confirmed by the new data on boundaries of glaciers during the Last Glacial Maximum (LGM) based on studies of till distribution at the bottom of Barents and Kara Seas and composition of erratic material in Scandinavia. Differences in winter temperatures indicated by the isotope composition of ice wedges during MIS 3 (thermochrone) and MIS 2 (cryochrone) were relatively small. This confirms a recent hypothesis about relatively cold winters during MIS 3. Thus, based on the trends of spatial distribution of the isotope composition of ice wedges, we suggest a hypothesis about a stable character of atmospheric circulation in the Eurasian Arctic during the last 50,000 years. Stable isotope analyses of wedge ice were performed by Dr. Hanno Meyer in the Laboratory of Isotope Research (Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany).