LAUSR

Abstract Stable isotope composition of syngenetic and epigenetic ice wedges, radiocarbon age, and pollen spectra of the surrounding deposits were studied during long term investigations at the “Belyi Klyuch” site on the first (6–8 m height) terrace of the Chara River (720 m.a.s.l.) in northern Transbaikalia to assess climatic conditions during ice-wedge formation. It was revealed that Holocene ice wedges had been formed from 10 to 7.5 ka 14C BP. The isotope composition (δ18О, δ2H) of relict ice wedges is the lightest and amounts −23‰ and −185‰, correspondingly. The isotopic compositions of ice lenses from sandy loam above ice wedges are −15.7‰ and −133‰; of small ice wedge in peat and sand are −15.3‰ and −117.9‰, accordingly. Interpretation of the ice wedge isotope composition has yielded that mean winter temperatures during cold stages of Holocene optimum were lower than today, during warm stages they were close to modern ones. During the coldest stages of Holocene optimum the total annual freezing index varied from −5100 to −5700 °C degree days, i.e. 300–600 °C degree days colder than during extremely severe modern winters. The total annual thawing index varied from 1300 to 1800 °C degree days, which was slightly higher than modern ones.