Marine carbon cycle dynamics in the southern high latitudes during the Mid-Pleistocene transition: new insights from the central South Pacific Ocean

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• Julia Gottschalk, Kiel University
• Wednesday 19 November 2025, 17:30-19:00
• Latimer Room, Clare College.

If you have a question about this talk, please contact sr632.

The mid-Pleistocene transition (MPT) is arguably the most enigmatic long-term climate shift of the Quaternary and is characterized by increasingly severe glacial conditions about 1.2 to 0.6 million years ago. Although the MPT was suggested to be linked with a continuous lowering of glacial atmospheric CO2 (CO2,atm) levels, the processes underlying this CO2 ,atm decline are incompletely understood. Here we compare two new benthic foraminiferal (Cibicidoides/Cibicides sp.) d13C records reflecting Circumpolar Deep Water (CDW), from central South Pacific International Ocean Discovery Program Site U1541 (54.2°S, 125.4°W, 3606 m water depth) and Southeast Atlantic Ocean Drilling Program Site 1094 (53.2°S, 05.1°E, 2807 m water depth), with similar records from the global ocean to identify possible reorganizations in the oceanic respired carbon pool over the past 2 million years that may explain CO2 ,atm changes across the MPT . We show a good agreement between lower CDW d13C signatures in the central South Pacific and in the Southeast Atlantic, and a wide-spread glacial decline in CDW d13C signatures across five Southern Ocean sites during the MPT . This points at a contribution from reduced glacial CDW ventilation and increased glacial respired carbon storage in the Southern Ocean to the glacial CO2 ,atm decline across the MPT . We also highlight an Atlantic-Pacific Southern Ocean-wide increase in the magnitude of deglacial CDW δ13C shifts during the MPT , which coincides with an amplitude increase in glacial-interglacial Antarctic Circumpolar Current flow strength variations (Lamy et al., 2024). This highlights that not only an increased Southern Ocean respired carbon storage might have driven CO2 ,atm variations across the MPT but also more efficient outgassing of that carbon during deglacial phases post-MPT. We will address potential linkages of glacial respired carbon storage and deglacial outgassing to changes in Antarctic ice sheet dynamics and southern hemisphere westerlies across the MPT .

References:

Lamy, F., Winckler, G., Arz, H., Farmer, J., Gottschalk, J., Lembke-Jene, L., Middleton, J.L., et al., 2024. Five million years of Antarctic Circumpolar Current strength variability. Nature 627, 789–796. doi: 10.1038/s41586-024-07143-3

This talk is part of the Quaternary Discussion Group (QDG) series.

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