A multi-proxy approach to decipher global sea-level and ice-volume dynamics during late Cenozoic “snapshot” intervals based on benthic foraminiferal cal-cite from ODP site 849

The response of ice sheets and sea level to a warming climate is of global concern, with significant implications for human populations. To better understand these dynamics, especially during climates warmer than today, this project reconstructs sea-level and ice-sheet variability across six glacial-interglacial (G-IG) cycles of the late Cenozoic (~5 Ma), spanning the transition from the Pliocene greenhouse to the Pleistocene icehouse.

We use paired measurements of benthic foraminiferal δ¹⁸O and Mg/Ca ratios to reconstruct bottom-water temperature (BWT) and derive seawater δ¹⁸O (δ¹⁸Oₛw), a proxy for global ice volume. While effective for interglacials, the Mg/Ca proxy likely overestimates glacial lowstands due to non-thermal effects. To improve reconstructions, we integrate carbonate clumped isotope (Δ₄₇) thermometry, a seawater chemistry-independent BWT proxy, using material from Eastern Equatorial Pacific ODP Site 849. Though analytically demanding, Δ₄₇ offers a critical calibration check for Mg/Ca-derived BWTs.

Preliminary paired δ¹⁸O-Mg/Ca data from Oridorsalis umbonatus (3.35–2.0 Ma) at sub-millennial resolution reveal G-IG sea-level cycles with glacial lowstands lower than previous estimates. Δ₄₇-BWTs, available at lower resolution, broadly support the Mg/Ca-based reconstructions, reinforcing their validity despite limited precision and resolution.

Future work will refine the understanding of discrepancies between Mg/Ca- and Δ₄₇-derived BWTs, improving glacial sea-level estimates. This study aims to constrain sea-level variability rates and assess existing reconstructions, offering a more robust understanding of past ice-volume dynamics and informing projections of future sea-level rise.