Лëд и снег (Mar 2019)
Winter air temperature in Holocene reconstructed from the ice wedges stable water isotopes near Anadyr town
Abstract
The object of research is syncryogenic Holocene strata on the coast of the Onemen Bay, 2 km from the town of Anadyr. In July 2017, the outcrop of the first marine terrace uncovered by strong storms was examined. The stratigraphy of the outcrop was represented mainly by sandy loam (5–7 m thick) covered by peat (1–1.5 m) and underlain by sand. Numerous ice wedges were opened in the upper part of this outcrop. Along with that another outcropping of transect of a lakemarsh basin represented by a peat bog of 2–2.5 m thick underlain by sandy loam was also investigated. Ice wedges occur below the polygonal trenches. The present-day narrow ice wedges were found in the upper part of the peat bog. Two representative fragments of both the above outcrops were thoroughly examined. Radiocarbon dating had shown that accumulation of peat on surface of the first marine terrace started in early Holocene (about 8 ka BP). Accumulation of peatland within the lake-marsh basin was also dated to the beginning of the Holocene (about 9 ka BP). In the middle of the Holocene, it was most likely interrupted as a result of thermokarst processes and bogging of the surface. Formation of peatlands in Chukotka during the Holocene is known to be accompanied by active growth of the ice wedges inside them, so the age of the wedges studied by us was estimated as the beginning of the Holocene. The analysis of stable oxygen and hydrogen isotopes in the Holocene and the modern ice wedges had allowed establishing mainly the atmospheric type of moisture feeding of the wedges (due to melted snow) and lack of noticeable isotope fractionation during the ice formation. It has been found that δ18О and δ2Н values in the Holocene ice wedges were lower than in the modern wedges and snow by an average 2–3 and 7–12 ‰, respectively. Paleotemperature reconstructions performed on the basis of isotopeoxygen data showed that the air temperature of the coldest winter month in the first half of the Holocene in the Onemen Bay area was lower than the present-day ones by an average 2–3 °C, which is in a good agreement with the trend of rising winter temperatures throughout the Chukotka Peninsula, as well as in other areas of Eastern Siberia and Alaska.
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