An El Nino Mode in the Glacial Indian Ocean?

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 Nino and is currently not active in the Indian Ocean.