Abstract

Corals are important marine archives for high-resolution reconstructions of low-latitude climate variability in preinstrumental and historical periods. Herein, we present monthly-resolved records of δ18O and Sr/Ca for the 20th century (1917–2007) from a Porites lutea colony from the Maldives (northwestern Indian Ocean). Previous studies of annual mean extension rates of this coral revealed a distinct dependency of coral growth on variations of sea surface temperature (SST) and hydraulic energy, driven by El Niño-Southern Oscillation (ENSO) and southwestern Indian monsoon forcing. This enables the investigation of coral δ18O and Sr/Ca ratios from the Maldives as archives of historical ENSO and Indian monsoon variability. Unlike other locations in the Indian Ocean, correlation of δ18O and SST is weak (r  =  −0.42; p < 0.001), suggesting interferences of SST and seawater δ18O at the location. These interferences probably caused significantly weaker interannual ENSO signatures in δ18O as evident in the extension rates of our coral and in geochemical proxies measured at other sites in the northwestern Indian Ocean. Sr/Ca ratios show bias by nontemperature effects, and were not used to estimate seawater δ18O and salinity. Strong decadal variability (10–14 years) in δ18O, indicative of a Pacific ENSO signal, is not found in instrumental SST, and could be explained by variations in salinity. Interannual and decadal monsoon variability (6–7 yrs and 18–19 yrs), found in the extension rates, was not found in δ18O, suggesting, in agreement with other studies, that geochemical coral proxy records from the northwestern Indian Ocean do not capture temporal variations of the Indian monsoon strength.

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