The Indo-Pacific Warm Pool, the warmest expanse of ocean on Earth, drives the Walker circulation—a key engine of tropical rainfall and global heat distribution. Because of its outsized role in climate, scientists need to know how the Warm Pool changed in the past. Yet, reconstructions often disagree. Foraminifera-based proxies commonly yield different temperature signals than biomarker proxies, leading to contrasting interpretations of past climate dynamics.
A new study from the IONTU Paleoproxy Lab, led by postdoctoral researcher Maria Makarova and Associate Professor Sze Ling Ho, tackled this puzzle. Unlike most work, the team combined fossil data obtained from long sediment cores with modern observations from plankton nets, sediment traps, and surface sediments to clarify what each proxy actually records.
Their foraminiferal clumped isotope (Δ47) results show that during the Last Glacial Maximum (LGM, ~20,000 years ago) surface-dwelling foraminifera experienced strong cooling of about 6.1°C, while thermocline dwellers cooled only 1.6°C. This implies a weaker vertical temperature gradient and deeper thermocline than today. These findings are broadly consistent with foraminiferal Mg/Ca data, though dissolution effects likely underestimated thermocline temperatures in Mg/Ca records. In contrast, biomarker proxies (UK′37 and TEX86) suggest either a stronger or unchanged thermal gradient during the LGM. The team’s analyses indicate these discrepancies reflect differences in proxy depth and sensitivity to upwelling, rather than contradictions.
By integrating modern and fossil data, this work reconciles long-standing proxy conflicts and advances our understanding of how the Indo-Pacific Warm Pool—and the global climate it drives—responded to past climate change.
This study was published in AGU journal Paleoceanography and Paleoclimatology.
Further reading:
Makarova, M., Tapia, R., Mohtadi, M., Hou, A., Groeneveld, J., Meckler, A. N., Huang, K.-F., Tung, R.-Y., Iizuka, Y., Ho, S. L.. (2025). Contrasting scenarios for upper ocean temperature changes at the Last Glacial Maximum inferred from inorganic and organic paleothermometers: A case study from the eastern tropical Indian Ocean. Paleoceanography and Paleoclimatology, 40, e2024PA004908. https://doi.org/10.1029/2024PA004908
