Climate-driven redox changes in the Antarctic region: New insights from sedimentary sulfur isotopes

Reconstruction of the history of bottom-water redox conditions in the climatically sensitive Southern Ocean can provide comprehensive information regarding oceanic circulation, global carbon cycling, and global climate changes. Here we present high-resolution sedimentary redox records over the last ~35 ka in the deep Protector Basin (~4,100 m water depth) of the southern Scotia Sea. Sedimentary δ³⁴S and redox-sensitive trace metals were comprehensively analyzed and compared with ²³⁰Th-normalized Ba- and opal-based export fluxes to constrain bottom-water or sedimentary redox and bottom-water oxygenation conditions. The results demonstrate tight coupling of redox state proxies (sulfur isotopes and trace metals) over the glacial–interglacial cycle; the presence of oxidizing conditions during glacial periods rapidly transitions to reducing conditions during interglacial periods. Our findings indicate that absolute control of sedimentary redox variability in the study area involves climate-forced primary production, rather than the deep circulation and ventilation dynamics previously highlighted in the Antarctic Zone. Signs of climate-driven redox changes are also evident in two episodic cold events superimposed on the warm Holocene climate. The glacial–interglacial pattern of redox changes observed in this study contrasts with previous observations in the Southern Ocean, including the Antarctic Zone, suggesting spatial heterogeneity of bottom-water and sediment conditions during orbital-scale climate cycles. This study may help to elucidate paleoenvironmental changes in the Southern Ocean, such as changes in the dynamics of Antarctic Bottom Water production and Holocene climate instability.