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Abstract Reconstructing past oxygen fluctuations in oxygen minimum zones (OMZs) is crucial for understanding their response to climate change. Numerous studies suggest better oxygenation in the Arabian Sea OMZ during the Last Glacial Maximum (LGM) compared to the Holocene. However, bottom water oxygen (BWO) variability during the Penultimate Glacial Cycle (Marine Isotope Stage [MIS] 6 to MIS 5e, ∼140–115 ka B.P.) remains poorly constrained. This study reconstructs BWO variations during this period from sediment core TN041‐8JPC in the western Arabian Sea OMZ, utilizing proxies including benthic foraminiferal surface porosity, redox‐sensitive trace metal enrichment factors (e.g., UEF), and U/Ba ratios. Bottom water oxygen concentrations were 24.4 ± 5.9 μmol/kg during MIS 6 and 16.8 ± 6.5 μmol/kg during MIS 5e, with all proxies indicating higher BWO in MIS 6 than in MIS 5e. However, these proxies show different patterns within MIS 5e, indicating that UEFand U/Ba ratios may be limited to recording average BWO in glacial and interglacial (quasi)steady states. We propose that the intensified OMZ during MIS 5e, relative to MIS 6, was driven by higher productivity, temperature‐induced reductions in oxygen solubility, and reduced delivery of Southern‐sourced intermediate waters. In contrast, the intensified OMZ during the Holocene, compared to the LGM, was likely influenced by lower oxygen solubility, reduced Southern water delivery, and winter convective mixing rather than productivity. This study highlights a general trend of weaker OMZs in glacial than interglacial periods, though the mechanisms may not be identical, offering insights into OMZ dynamics under climate change in the past.
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Southern Ocean Oxygenation Changes Inferred From Redox‐Sensitive Trace Metals Across Marine Isotope Stage 11
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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- Award ID(s):
- 1658445
- PAR ID:
- 10367037
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 22
- Issue:
- 8
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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