Early Holocene climate signals from stable isotope composition of ice wedges in the Chara Basin, northern Transbaikalia, Russia

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 C-14 BP. The isotope composition (delta O-18, delta H-2) of relict ice wedges is the lightest and amounts -23 parts per thousand and -185 parts per thousand, correspondingly. The isotopic compositions of ice lenses from sandy loam above ice wedges are -15.7 parts per thousand and -133 parts per thousand; of small ice wedge in peat and sand are -15.3 parts per thousand and -117.9 parts per thousand, 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 degrees C degree days, i.e. 300-600 degrees C degree days colder than during extremely severe modern winters. The total annual thawing index varied from 1300 to 1800 degrees C degree days, which was slightly higher than modern ones. (C) 2017, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.