Cryostratigraphy, Radiocarbon dates of surrounding sediments, Stable isotope values for Holocene ice wedges and modern ice veinlets of the northwestern Siberia

Stable isotope composition of ice wedges has been widely used for reconstruction winter climatic conditions in the Arctic regions. In this study, stable isotope composition of Holocene syngenetic ice wedges and modern ice veinlets of northwestern Siberia is investigated. Radiocarbon dating of enclosing sediments and organic material data obtained for ice wedges, demonstrate that ice wedges grew constantly within the study area during the Holocene though early–mid-Holocene in northwestern Siberia is often considered as a thermal optimum. Many proxy records indicate an increase of summer air temperatures followed by thermokarst activity, peatland formation, and northward advance of the treeline. According to our data, winter climate conditions in terms of mean air temperature of the coldest winter month (January) did not change significantly during the key Holocene stages, and during the Greenlandian and most of the Northgrippian stages (between 11.4 and 6 cal ka BP) mean January air temperature (TmJ) varied between –21 and –30℃, and from the end of the Northgrippian, during the Meghalayan stages of Holocene (5.2–0.9 cal ka BP), TmJ varied between –24 to –28℃. Mean January air temperature during the Holocene was generally 1–2℃ lower than the modern one, meanwhile the submeridional direction of TmJ isotherms and eastward decrease of TmJ values in Holocene are similar to the modern pattern.