Climate-driven redox changes in the southern Scotia Sea over the last 35 kyr: Insights from sedimentary sulfur isotope

Abstract

Reconstructing sedimentary redox history provides valuable insights into for understanding of paleoceanographic/paleoclimatic changes in the climatically sensitive Southern Ocean. However, our comprehension of the spatial variations in historical redox changes and the driving forces in the Southern Ocean, especially the Antarctic Zone, remains incomplete. Here, we present detailed sedimentary records of the redox state (i.e., sulfur isotopes), bottom-water oxygenation conditions (i.e., redox-sensitive metals), export production (i.e., 230Th-normalized biogenic opal and barium), and carbon burial flux over the last ∼35 kyr in the Protector Basin, the deepest basin of the southern Scotia Sea. The studied sediment record in this basin reveals significant variations in geochemical redox proxies throughout the glacial (MIS 2)–interglacial (MIS 1) period, featuring a significant 34S depletion of up to ∼40‰ relative to seawater sulfate and a noticeable increase in ERMo/ERU ratio in interglacial sediments. These findings highlight a significant shift in bottom-water and/or sediment oxygenation from glacial oxic to interglacial anoxic/euxinic conditions, primarily driven by climate-induced changes in biogenic productivity, rather than the deep circulation and ventilation dynamics previously emphasized in the Antarctic Zone. Signs of the climate-driven redox change are also evident in two millennial-scale cold events (∼9–8 ka and ∼3–2 ka), marked by sudden shifts toward oxic conditions. Importantly, our results reveal a contrasting scenario to previous observations in the glacial–interglacial redox history within the Antarctic Zone, signifying spatial disparity in bottom-water and sediment redox chemistry.