| Summary: | International audience Assessing the response of interannual climate variability in the tropical Pacific Ocean to future greenhouse warming is of paramount importance. However, the dominant mode of Pacific atmosphere-ocean variability on interannual timescales, the El Niño-Southern Oscillation (ENSO), is poorly understood with respect to its behaviour under boundary conditions different from today. For last glacial conditions, model simulations and rare proxy records of interannual climate variability in the Pacific are contradictory. Here we present a monthly resolved reconstruction of tropical South Pacific climate from 15,000 years ago at the end of the last glacial. This period was characterised by substantial cooling in the North Atlantic Ocean and a reduction in the strength of the Atlantic Meridional Overturning Circulation (AMOC) in response to massive iceberg discharge associated with Heinrich stadial 1 (H1). Our Sr/Ca palaeotemperature record constructed from a fossil coral recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 to Tahiti indicates pronounced interannual ENSO variability, even though the site is only weakly influenced by ENSO today. From our coral record and simulations with a comprehensive climate model (CCSM3) we conclude that interannual ENSO variability in the tropical Pacific was strong during H1. Our results suggest that enhanced interannual variability in tropical Pacific temperatures is the ENSO response to a reduced AMOC under glacial boundary conditions.
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