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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.
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Changes in Antarctic Bottom Water Formation During Interglacial Periods
Abstract In the modern Southern Ocean and during the last interglacial period, Marine Isotope Stage 5e, there are observations that point to reduced Antarctic Bottom Water (AABW) formation. These reductions are believed to be driven by an increase in the strength of the Southern Ocean density stratification due to Antarctic ice melt‐induced surface water freshening. Any reduction in AABW formation has important implications for global climate as AABW plays a vital role in the cycling of carbon in the world's ocean. The primary question this study seeks to answer is do these AABW reductions occur during any of the other interglacials of the past 470,000 years? To study AABW changes in the paleoceanographic record, we look at changes in the redox record. Newly formed AABW is oxygen‐rich, so any reduction should lead to a decrease in oxygen concentrations in the deep Southern Ocean. The trace element uranium is useful for studying these redox changes as it is enriched in marine sediments under low‐oxygen conditions. When accounting for other factors, such as paleoproductivity, that can also decrease the oxygen concentrations in sedimentary porewater, it is possible to identify changes in AABW using authigenic uranium. The survey conducted by this study found a possible AABW reduction during late Marine Isotope Stage 11 (~397 ka). The cause of this event is less clear than others studied, and we explore the possibilities of ice melt‐induced freshening or a change in the position or strength of the Southern Hemisphere westerly winds.
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- Award ID(s):
- 1658445
- PAR ID:
- 10456494
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 35
- Issue:
- 8
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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