Southern Ocean Oxygenation Changes Inferred From Redox‐Sensitive Trace Metals Across Marine Isotope Stage 11

Abstract

Abstract Changes in the circulation of the Southern Ocean are known to have impacted global nutrient, heat, and carbon cycles during the glacial and interglacial periods of the late Pleistocene. Proxy‐based records of these changes deserve continued scrutiny as the implications may be important for constraining future change. A record of authigenic uranium from the South Atlantic has been used to infer changes in deep‐sea oxygenation and organic matter export over the past 0.5 million years. Since sedimentary uranium has the possible complication of remobilization, it is prudent to investigate the behavior of other redox‐sensitive trace metals to confidently interpret temporal changes in oxygenation. Focusing here on the exceptionally long interglacial warm period, Marine Isotope Stage (MIS) 11, we found concurrent authigenic enrichments of uranium (U) and rhenium (Re) throughout MIS 12 to 10, overall supporting prior interpretations of low‐oxygen periods. However, there are differential responses of Re and U to oxygen changes and some evidence of small‐scale Re remobilization, which may involve differences in molecular‐level reduction mechanisms. Peaks in authigenic manganese (Mn) intervening with peaks in Re and U indicate increases in porewater oxygenation which likely relate to increased Antarctic Bottom Water circulation at the onset of MIS11c and during the peak warmth of the interglacial around 400 ka.

Keywords

• ocean circulation
• interglacial
• manganese
• Antarctic Bottom Water
• rhenium