Holocene Palsa Evolution near the Eletsky village using Stable Isotope Tracers and Radiocarbon Dating (Part 2. Isotope-geochronological scenario of ice core formation)

The main purpose of this study is to assess the features of the large palsa massif located in the Bolshezemelskaya Tundra near Eletsky village during the Holocene. This assessment relies on a detailed examination of the radiocarbon ages of peat, the isotopic composition of oxygen and hydrogen (δ¹⁸O and δ²H) in ice from the frozen core of the palsa, the identification of water sources responsible for ice core formation, and the compilation of an isotope-geochronological scenario for ice core development throughout the Holocene, using data from isotopic tracers and radiocarbon dating. The analysis of 44 radiocarbon dates from eight palsas of varying heights and ages has led to the formulation of a geochronological scenario for the evolution of the palsa within the Eletsky peatland. It has been established that peat accumulation commenced in the Early Holocene, specifically between 11 and 8 cal. ka BP and again between 8 and 5 cal. ka BP. During this period, frost heaving and palsa growth were particularly pronounced, with the largest palsa achieving heights of 3 to 5 meters. Subsequently, some palsas partially thawed from the surface, while others completely collapsed and sagged. A new stage of heaving occurred around 2 cal. ka BP, characterized by the emergence of new mounds and the ongoing growth of older palsas. The investigation into the isotopic composition of oxygen and hydrogen in the ice of the frozen core, combined with an analysis of potential water sources for its accumulation, has concluded that precipitation, with an isotopic composition similar to modern annual averages, served as the primary source of water for ice core formation. Ice core formation mainly took place in an open system due to the migration of moisture to the freezing front. However, in certain instances—such as at the tops of some mounds—conditions indicative of a closed system were observed, involving late summer and autumn precipitation that froze at the boundary of the active layer. Based on the analysis of isotope tracers, we propose a model in which the deeper sections of the cores formed during the rapid freezing of thawed snow and autumn waters, while the upper layers underwent repeated thawing during warmer periods of the Holocene, accompanied by precipitation infiltration and subsequent freezing in a closed system.