Monsoon-induced cooling of the western equatorial Indian Ocean as recorded in coral oxygen isotope records from the Seychelles covering the period of 1840–1994 AD

We have developed a new, bimonthly resolved coral δ18O time series from the Seychelles (55°E, 4°S). Our coral time series covers the period of 1840–1994 AD and shows stable correlations with regional sea surface temperatures over the past 50 years. The strength of the proxy-climate relationship depends on the annual cycle of the Asian monsoon. Seasonal correlation patterns suggest that the coral primarily records the boreal summer cooling in the western Indian Ocean and Arabian Sea, which results from wind-induced mixing and evaporation during the SW monsoon season. We have combined our coral time series with an existing 150-year long coral record from the Seychelles to strengthen the climatic signals recorded in the two cores. This new coral index shows a strong correlation with historical surface temperatures from the Arabian Sea and India, suggesting that the corals can be used to reconstruct regional temperature trends in pre-instrumental times. The coral index also shows a significant correlation with the Niño 3.4 index, which captures the ENSO phenomenon centred in the tropical Pacific. Cross-spectral analysis confirms that the coral index and Niño 3.4 are coherent at decadal periods, supporting the notion that decadal El Niño-like variability influences the Indian Ocean.