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.
Marine Isotope Stage 11 from ~424 to 374 ka experienced peak interglacial warmth and highest global sea level ~410–400 ka. MIS 11 has received extensive study on the causes of its long duration and warmer than Holocene climate, which is anomalous in the last half million years. However, a major geographic gap in MIS 11 proxy records exists in the Arctic Ocean where fragmentary evidence exists for a seasonally sea ice‐free summers and high sea‐surface temperatures (SST; ~8–10 °C near the Mendeleev Ridge). We investigated MIS 11 in the western and central Arctic Ocean using 12 piston cores and several shorter cores using proxies for surface productivity (microfossil density), bottom water temperature (magnesium/calcium ratios), the proportion of Arctic Ocean Deep Water versus Arctic Intermediate Water (key ostracode species), sea ice (epipelagic sea ice dwelling ostracode abundance), and SST (planktic foraminifers). We produced a new benthic foraminiferal δ18O curve, which signifies changes in global ice volume, Arctic Ocean bottom temperature, and perhaps local oceanographic changes. Results indicate that peak warmth occurred in the Amerasian Basin during the middle of MIS 11 roughly from 410 to 400 ka. SST were as high as 8–10 °C for peak interglacial warmth, and sea ice was absent in summers. Evidence also exists for abrupt suborbital events punctuating the MIS 12‐MIS 11‐MIS 10 interval. These fluctuations in productivity, bottom water temperature, and deep and intermediate water masses (Arctic Ocean Deep Water and Arctic Intermediate Water) may represent Heinrich‐like events possibly involving extensive ice shelves extending off Laurentide and Fennoscandian Ice Sheets bordering the Arctic.
more » « less- NSF-PAR ID:
- 10373052
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 34
- Issue:
- 12
- ISSN:
- 2572-4517
- Page Range / eLocation ID:
- p. 1959-1979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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