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

We used a high-resolution oxygen isotope (δ(18)O(coral)), carbon isotope (δ(13)C(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 δ(13)C(coral) record shows sharp negative excursions in the summer, which correlate with known upwelling events. Using δ(13)C(coral) anomalies as a proxy for upwelling, we found 17 summer upwelling events occurred in the last 26 years. These anomalous negative excursions of δ(13)C(coral) result from upwelled water depleted in (13)C (dissolved inorganic carbon) and decreased water-column transparency. We reconstructed biweekly SSTs from coral Sr/Ca ratios and the oxygen isotopic composition of seawater (δ(18)O(SW)) by subtracting the reconstructed Sr/Ca-SST from δ(18)O(coral). Significant δ(18)O(SW) anomalies occur during major upwelling events. Our results suggest δ(13)C(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.