ИСТИНА

We have obtained 14C ages of polygonal peat and isotope composition of syngenetic ice wedges nearby Vorkuta town, north of East European Plain. It makes possible to reconstruct winter temperatures during ice wedge formation and deduce the temporal trend of the temperature. To establish the timing of ice wedge formation, a detailed sampling of various organic materials (peat and wood) from the ice wedges, surrounding peat and from the ground wedges was carried out. According to 14C ages from the peat the timing of the ice-wedge, can be estimated at 9-5.5 ka BP. The ice wedges began to form within a drier part of the bog whereas ground wedges began to form in the more frequently flooded part. Under conditions of frequent changes in flooding environment, peat and twigs entered the thawing elementary ice wedges in the ground wedge. The subsequent drainage of this part of the swamp resulted in the formation of a new elementary ice wedge. Two or three such cycles produced the peat ice wedges. Later, this part of the swamp was substantially flooded. Consequently, ice began to thaw and replaced by loam, which now overlies the peat layer with the peat-loam wedge. The oxygen isotope and deuterium diagrams show stable winter conditions. In wedges, δD values varies from –119.1 to –111.6‰; δ18O values varies from –16.35 to –15.45‰; and the deuterium excess, from 13.8 to 9.0‰. In the lens ice, δD values vary from –128.4 to –97.8‰; δ18O values varies from –17.48 to –12.79‰; and the deuterium excess, from 11.4 to 4.5‰. In snow of an old snowfield, δD value is –134.4‰, δ18O is –18.91‰, and the deuterium excess is 16.9‰. In water of a small interpolygonal pond, δD value is equal to –87.4‰, δ18O is –11.31‰, and the deuterium excess is 3.1‰. The upper part of the wedge shows a sharper change at isotope plots: relatively sharp replacement of the positive shift of δD and δ18O values by negative ones. A very perceptible increase of deuterium excess up to 13.8‰ (against the common value of 11-12‰). These data indicate relatively more contrast changes in winter climatic and, probably, geocryological conditions near the middle of the Holocene Optimum. For comparison, snow samples taken from fresh snow near stations Seida and Eletskaya near Vorkuta on December 24 yielded the following values: δD values varies from –203.6 to –189.4‰, δ18O values varies from –27.22 to –25.93‰, and the deuterium excess from 14.2 to 18.0‰. Previously, δ18O values were determined for ice wedges in recent sediments from Amderma (-15.2‰). It is evident that the oxygen-isotope ratio in ice wedges of the Vorkuta peat bog does not differ much from that of the Recent and Holocene varieties (usually 0.5-1‰ lighter than their Amderma counterparts). Judging from the isotopic composition of ice wedge, which is mainly characterized by its proximity to present-day isotope characteristics of Holocene ice wedges in this region, we can infer that winter conditions in the first half of the Holocene Optimum were similar in severity to current conditions (in any case, the Holocene winter was not warmer than the current one).