We studied the structure and composition of Late Pleistocene cyclic ice wedge complexes in the Mayn River Valley and syngenetic ice wedges in adjacent areas of the Southern Chukchi Peninsula. Analysis of stable isotopes (δ18O and δD) and major ion chemistry of ice, as well as radiocarbon ages and pollen spectra of the host sediments, allowed detailed quantitative evaluation of changes in Late Pleistocene permafrost and climate conditions of the area, between 38 and 12 Kyr BP. The study has confirmed the previous inference that winters were much colder than now in the latest Pleistocene and rather severe during the Holocene optimum. The sediments have been dated by the radiocarbon (14C) method (Kotov and Ryabchun, 1986) in Magadan (North East Science Center, Far East Branch, Russian Academy) , which places exact time constraints on the yedoma history. Winter mean (twint.mean) and January (tJ) air temperature means for the Southern Chukchi Peninsula were inferred by comparing the oxygen isotope composition of present growing ice wedges (δ18Opiw) and winter temperatures for the period of their growth, were calculated using equation: tJ = 1.5 δ18Opiw (±3 °C), twint.mean = δ18Opiw (±2 °C). Mean annual ground temperatures were calculated using reconstructions of mean summer temperature by the technique of A. Vasil'chuk (2007) and of mean winter temperature by the technique of Yu. Vasil'chuk (1989). Analysis of major ion chemistry of ice - titration methods (titrimetric methods) are based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte. Isotopic analyses were made in the isotope laboratory of the Institute of Geology of Estonia (Prof. R. Vaikmäe) using mass-spectrometer Finnigan Delta-E and in the Hannover Isotope Laboratory, Geological Survey of Lower Saxony (Prof. M.A. Geyh).

Data was submitted and proofread by Yurij K Vasil'chuk and Lyubov Bludushkina at the faculty of Geography, department of Geochemistry of Landscapes and Geography of Soils, Lomonosov Moscow State University.