Authigenic Be Isotopes Record Circumpolar Deep Water Inflow and Subglacial Outflow in Antarctic Shelf Sediments

Abstract

The Antarctic Ice Sheet (AIS) has recently undergone accelerating mass loss driven primarily by basal melting associated with Circumpolar Deep Water (CDW) inflow onto the continental shelf. However, temporal variability in CDW inflow and its role in mass loss from the AIS over longer timescales remain uncertain because the duration of the observational record is too short to refine future projections. Robust proxies are therefore needed to reconstruct past CDW inflow and AIS variability. Although beryllium (Be) isotopes in marine sediments have been used to trace meltwater input, recent studies have challenged this interpretation, suggesting that ¹⁰ Be may instead reflect deep‐ocean currents, such as CDW. Here, we investigate the spatial distribution of authigenic Be isotopes in surface marine sediments from two fast‐flowing ice stream regions of East Antarctica and combine satellite with in situ oceanographic observations to evaluate Be isotope sources. Our results indicate that ¹⁰ Be concentrations and ¹⁰ Be/ ⁹ Be ratios increase along the CDW pathway and decrease from offshore to the ice shelf front. Notably, the spatial distribution of ¹⁰ Be is not correlated with the extent of seasonal sea ice. These findings suggest that CDW inflow is the dominant control on ¹⁰ Be distributions. In contrast, ⁹ Be concentrations are higher near the ice shelf front, likely reflecting sediment delivery from beneath the AIS, and may serve as indicators of subglacial meltwater. These findings highlight the potential of authigenic Be isotopes in Antarctic marine sediments to serve as proxies for reconstructing past variability in both CDW and AIS dynamics.