Past summer upwelling events in the Gulf of Oman derived from a coral geochemical record

We used a high-resolution oxygen isotope (delta O-18(coral)), carbon isotope (delta O-18(coral)) and Sr/Ca ratios measured in the skeleton of a reef-building coral, Porites sp., to reveal seasonal-scale upwelling events and their interannual variability in the Gulf of Oman. Our delta C-13(coral) record shows sharp negative excursions in the summer, which correlate with known upwelling events. Using delta C-13(coral) anomalies as a proxy for upwelling, we found 17 summer upwelling events occurred in the last 26 years. These anomalous negative excursions of delta C-13(coral) result from upwelled water depleted in C-13 (dissolved inorganic carbon) and decreased water-column transparency. We reconstructed biweekly SSTs from coral Sr/Ca ratios and the oxygen isotopic composition of seawater (delta O-18(SW)) by subtracting the reconstructed Sr/Ca-SST from delta O-18(coral). Significant delta O-18(SW) anomalies occur during major upwelling events. Our results suggest delta C-13(coral) anomalies can be used as a proxy for seasonal upwelling intensity in the Gulf of Oman, which, driven by the Indian/Arabian Summer Monsoon, is subject to interannual variability.