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 and rhenium 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
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.