A reconstruction of Antarctic Sea ice extent since the 1950s from a snowpit methanesulfonate (MSA) record in East Antarctic inland

Abstract

Antarctic sea ice plays a crucial role in regulating regional and global climate, as well as ecosystem productivity of the Southern Ocean. Since sea ice data were rare before 1978C.E., reconstruction of past sea ice conditions is of vital importance for understanding their impact on past climate change. Methanesulfonate (MSA) in Antarctic ice cores is considered a potential proxy of sea ice extent (SIE). In this study, we tested this approach by measuring the variations of MSA flux (1950–2016C.E.) in samples collected from a snowpit at Dome A, the summit of Eastern Antarctic ice sheet, and investigating its relationship with the SIE in the Southern Ocean. The result shows a significant and positive correlation between the MSA flux and the observed mean SIE in the Indian Ocean sector of the Southern Ocean from 1979 to 2016C.E. In addition, our study shows that the MSA is mainly influenced by Southern Hemisphere westerly winds (zonal winds) and katabatic winds (flowing from inland to the coast). Enhanced winds in both systems promote sea ice production in the Southern Ocean. These wind systems significantly influence the MSA cycle, stronger westerlies and katabatic winds increase MSA production, whereas meridional winds facilitate the transport and subsequent deposition of MSA at Dome A. Our findings suggest that MSA recorded in snow from Dome A could serve as a reliable proxy or reconstruction for mean SIE. Consequently, MSA in deep ice cores from Dome A offers a valuable archive for investigating past sea ice conditions in the Indian Ocean sector of the Southern Ocean, biogenic sulfur, and their climatic impacts.