Reconstructing ice conditions in the southern Chukchi Sea during the last millennium based on chemical composition of sediments and diatom assemblages

Abstract

Using transfer functions, this study reconstructed the ice-free period (IFP) that occurred 4.7 kya in the southern Chukchi Sea, based on the comparison between the observed data and the chemical composition of sediments accumulated during the observation period. During the analysis, a double normalization of the chemical element contenton rubidium and minimax - was implemented for the first time. It was established that the duration of the IFP varied between 90 and 140 days/year. The highest values are observed in the 21st century and 4–5 kya, coinciding with Pacific water inflow through the Bering Strait. The reconstruction of water masses based on diatom thanatocoenosis has revealed the considerable impact of the Alaskan coastal current on the duration of the IFP. The penetration of its waters to the west during the following time periods - 2750-2550, 1450–800, 350–0 cal yr BP - led to an increase in the duration of the IFP in the central part of the sea by 10–15 days, relative to background values. As a result, the identified variations in the duration of the IFP in the southern Chukchi Sea do not coincide with global climate events of the last millennium, but are clearly demonstrated by an increase in the IFP during the Little Ice Age. Currently, the influence of the Alaskan coastal water is summed up by the effect of increasing global temperatures and Pacific water inflow, which has led to a sharp increase in the IFP in the last few decades.