Silicon isotopes in an EMIC’s ocean: sensitivity to runoff, iron supply and climate
• +3
• Heiner Dietze,
• Ulrike Löptien,
• Robinson Hordoir,
• Malte Heinemann,
• Willem Huiskamp,
• Birgit Schneider
Heiner Dietze
Institute of Geosciences, Christian-Albrechts-University of Kiel

Corresponding Author:heiner.dietze@ifg.uni-kiel.de

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Ulrike Löptien
Institute of Geosciences, Christian-Albrechts-University of Kiel
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Robinson Hordoir
Bjerknes Centre for Climate Research
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Malte Heinemann
Kiel University
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Willem Huiskamp
Potsdam Institute for Climate Impact Research (PIK)
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Birgit Schneider
Institute of Geosciences, Christian-Albrechts-University of Kiel
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## Abstract

The isotopic composition of Si in biogenic silica (BSi), such as opal buried in the oceans’ sediments, has changed over time. Paleo records suggest that the isotopic composition, described in terms of $\delta^{30}$Si, was generally much lower during glacial times than today. There is consensus that this variability is attributable to differing environmental conditions at the respective time of BSi production and sedimentation. The detailed links between environmental conditions and the isotopic composition of BSi in the sediments are, however, controversially discussed in the literature. In this study, we explore the effects of a suite of offset boundary conditions during the LGM on the isotopic composition of BSi archived in sediments in an Earth System Model of intermediate complexity. Our model results suggest that a change in the isotopic composition of Si supply to the glacial ocean is sufficient to explain the observed overall low(er) glacial $\delta^{30}$Si in BSi. All other processes explored triggered model responses of either wrong sign or magnitude, or are inconsistent with a recent estimate of bottom water oxygenation in the Atlantic Sector of the Southern Ocean. Caveats, mainly associated with generic uncertainties in today’s pelagic biogeochemical modules, remain.
Oct 2020Published in Paleoceanography and Paleoclimatology volume 35 issue 10. 10.1029/2020PA003960