| Summary: | Main processes of the ice core isotopic composition formation are overviewed. Theory of isotope-temperature relationship is discussed and confirmed by a number of experimental data. The factors related to wind-driven spatial snow redistribution and post-depositional isotopic changes that may alter or weaken this relationship, are also considered. For high-resolution isotopic time-series obtained at sites with low accumulation of snow, the signal-to-noise ratio is shown to be as low as 0.25, which means that noise accounts for about 80 % of the total variance. It is demonstrated that "classical isotopic method" (based on the present-day geographical isotope-temperature slope) underestimates the amplitude of past temperature changes in Antarctica. The most likely reason for the discrepancy is the change in the moisture source conditions. After correction for the latter, the paleo-temperature reconstructions produced by the isotopic method become consistent with those obtained from borehole temperature measurements. We show that in the case of the Vostok ice core, both approaches lead to the same temperature shift of 10℃ between LGM and the present time. The isotopic composition of the basal part of the Vostok ice core, comprising frozen subglacial Lake Vostok water, is also discussed. IV. Chemical properties and isotopes
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