Chronologies of active growth of ice wedges and Middle Holocene palaeoclimate at Lorino site, Chukchi Peninsula, easternmost Siberia

Abstract AMS radiocarbon ages of organic matter from ice wedges and enclosing peat were determined for the polygonal peatland at the Lorino site on the eastern coast of the Chukchi Peninsula. The study’s goal was to fill a knowledge gap about the dynamics of polygonal peatlands with ice wedges and winter climate conditions during the Holocene in this easternmost region of the Russian Arctic. It has been found that peatland accumulated during the Younger Dryas and early Holocene, mostly between 14 and 9.9 cal ka BP, while ice wedges were dated from 7.7 to 6.6 cal ka BP. Since ice wedges have features of syngenetic growth, the discrepancy in the age of ice wedges and enclosing peatland may result from the significant presence of early and pre-Holocene peat. It is assumed that the older polygonal peatland deeply thawed during the Holocene optimum, and subsequently, when the permafrost aggraded, a new generation of ice wedges was formed. The AMS 14 C age (18.1 cal ka BP) of the ice wedge exposed below the peat indicates the presence of a Late Pleistocene generation of ice wedges at the study site. Paleotemperature reconstructions based on the stable isotope composition of ice wedges show that the mean January air temperature during the Northgrippian stage of the Holocene varied from –27 to –23°C, and at the end of the Late Pleistocene, from –32 to –26°C.