Articles | Volume 21, issue 6
https://doi.org/10.5194/cp-21-973-2025
https://doi.org/10.5194/cp-21-973-2025
Research article
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03 Jun 2025
Research article | Highlight paper |  | 03 Jun 2025

Mean ocean temperature change and decomposition of the benthic δ18O record over the past 4.5 million years

Peter U. Clark, Jeremy D. Shakun, Yair Rosenthal, Chenyu Zhu, Patrick J. Bartlein, Jonathan M. Gregory, Peter Köhler, Zhengyu Liu, and Daniel P. Schrag

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Cited articles

Ahn, S., Khider, D., Lisiecki, L. E., and Lawrence, C. E.: A probabilistic Pliocene–Pleistocene stack of benthic δ18O using a profile hidden Markov model, Dynamics and Statistics of the Climate System, 2, 1–16, 2017. 
Alder, J. R. and Hostetler, S. W.: Global climate simulations at 3000-year intervals for the last 21 000 years with the GENMOM coupled atmosphere–ocean model, Clim. Past, 11, 449–471, https://doi.org/10.5194/cp-11-449-2015, 2015. 
Baggenstos, D., Haberli, M., Schmitt, J., Shackleton, S. A., Birner, B., Severinghaus, J. P., Kellerhals, T., and Fischer, H.: Earth's radiative imbalance from the Last Glacial Maximum to the present, P. Natl. Acad. Sci. USA, 116, 14881–14886, https://doi.org/10.1073/pnas.1905447116, 2019. 
Barrientos, N., Lear, C. H., Jakobsson, M., Stranne, C., O'Regan, M., Cronin, T. M., Gukov, A. Y., and Coxall, H. K.: Arctic Ocean benthic foraminifera Mg / Ca ratios and global Mg / Ca-temperature calibrations: New constraints at low temperatures, Geochim. Cosmochim. Ac., 236, 240–259, https://doi.org/10.1016/j.gca.2018.02.036, 2018. 
Bartlein, P.: pjbartlein/MOTvsSST: MOT vs SST regressions (v0.1), Zenodo [code], https://doi.org/10.5281/zenodo.14759006, 2025. 
Co-editor-in-chief
This Milankovic Medalist paper represents a tour de force, addressing a complex yet crucial question: the evolution of global climate over the past 4.5 million years. This paper makes a significant contribution to the geoscience community by providing a self-consistent decomposition of global mean benthic δ18O into its temperature and seawater (ice volume) components. This approach is consistent with independent estimates of global mean sea surface temperature (GMSST) and sea level constraints.The analysis incorporates numerous high-resolution records spanning this period and highlights two distinct climatic regimes: • Before 1.5 million years ago, a warm period characterized by smaller-amplitude ice sheet and sea level cycles, primarily driven by obliquity timescales. • Following the Mid-Pleistocene Transition (MPT), i.e. after 1 million years, a well-documented increase in the amplitude of glacial cycles became evident. The central finding of the study is that, during the MPT, there was a shift in ocean heat storage efficiency (HSE). Prior to this transition, HSE remained low and constant, whereas after the MPT, it doubled and stabilized at a higher value. This finding is supported by the observation of subtle differential changes in global mean SST and mean ocean temperature (MOT), which appear to be time-dependent. These observations suggest a potential fundamental shift in oceanic heat storage dynamics.
Short summary
We reconstruct changes in mean ocean temperature (ΔMOT) over the last 4.5 Myr. We find that the ratio of ΔMOT to changes in global mean sea surface temperature was around 0.5 before the Middle Pleistocene transition but was 1 thereafter. We subtract our ΔMOT reconstruction from the global δ18O record to derive the δ18O of seawater. Finally, we develop a theoretical understanding of why the ratio of ΔMOT / ΔGMSST changed over the Plio-Pleistocene.
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