An El Niño Mode in the Glacial Indian Ocean?


Thirumalai, Kaustubh
DiNezio, Pedro N.
Tierney, Jessica E.
Puy, Martin
Mohtadi, Mahyar


Despite minor variations in sea surface temperature (SST) compared to other tropical regions, coupled ocean‐atmosphere dynamics in the Indian Ocean cause widespread drought, wildfires, and flooding. It is unclear whether changes in the Indian Ocean mean state can support stronger SST variability and climatic extremes. Here we focus on the Last Glacial Maximum (19,000–21,000 years before present) when background oceanic conditions could have been favorable for stronger variability. Using individual foraminiferal analyses and climate model simulations, we find that seasonal and interannual SST variations in the eastern equatorial Indian Ocean were much larger during this glacial period relative to modern conditions. The increase in year‐to‐year variance is consistent with the emergence of an equatorial mode of climate variability, which strongly resembles the Pacific El Niño and is currently not active in the Indian Ocean.

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Fig. 2c: Percent changes in reconstructed and simulated standard deviation of individual foraminiferal-δ¹⁸O (%) at each site. Reconstructed changes are from IFA-δ¹⁸O between the late Holocene and LGM samples whereas simulated changes are calculated from forward-modeled IFA-δ¹⁸O between the preindustrial and LGM simulations from Community Earth System Model Version 1.2. Solid fills indicate significant changes in variance (F-test; p < 0.01).

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