Лëд и снег (Aug 2020)
Use of stable water isotopes to identify water as a source for palsa ice core formation
Abstract
Isotopic characteristics of ice cores of peat mounds (palsa) are considered. The distribution of the values of δ18O, δ2H, dexc and ratios δ18O–δ2H within the palza ice lense is associated with freezing in a closed or open system, and this allows finding the source of water for the ice formation. The use of computational modeling of the distribution of the values of δ18О and δ2Н during the ice formation in a closed system and the selection of the calculated parameters, performed in such a way that the actual values in the ice are described, show the initial isotopic characteristics of the moisture from which the ice was formed. The subject of investigation is the isotopic composition of segregated ice in the upper part of the ice core of a palsa near the Yeletsky settlement. Ice samples were obtained by drilling with a hand-held electric drill. In its upper part, the core is composed of frozen peat and loam. The source of water for the formation of segregated ice from this palsa was the atmospheric moisture with isotopic characteristics equal, on average, to: δ2Н = −106.7, δ18О = −15.3 and dexc = 15.7 ‰. These values correspond to the current atmospheric precipitation in the vicinity of the Amderma settlement. The water of the nearest bog did not serve as a source of water for the ice formation. The same conclusion, fully confirmed by the application of the calculated approach, was obtained for the hummocky massif of the Yukon (Canada). The calculation did show that the water from which the ice of the Canadian palsa was formed was a mixture of local atmospheric precipitation (80%) and the boggy waters of the peat plateau (20%). The presence of the last water is a possible indication to re-formation of mounds, when evaporated water from bog could participate in ice core formation.
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