Oman coral δ 18 O seawater record suggests that Western Indian Ocean upwelling uncouples from the Indian Ocean Dipole during the global-warming hiatus

The Indian Ocean Dipole(IOD) is an interannual mode of climate variability in the Indian Ocean that has intensifiedwith 20th century global-warming. However, instrumental data shows a global-warming hiatusbetween the late-1990s and 2015. It is presently not clear how the global-warming hiatusaffects modes of climate variability such as the IOD, and their basin-wide ocean-atmosphere teleconnections. Here, we present a 26-year long, biweekly record of Sr/Ca and δ18Ofrom a Poritescoral drilled in the Gulf of Oman. Sea surface temperature (SSTanom) is calculated from Sr/Ca ratios, and seawater δ18O(δ18Osw- anom) is estimated by subtracting the temperature component from coral δ18O. Our δ18Osw- anomrecord reveals a significant regime shiftin 1999, towards lower mean δ18Osw values, reflecting intensified upwellingin the western Indian Ocean. Prior to the 1999 regime shift, our SSTanom and δ18Osw- anomshow a clear IOD signature, with higher values in the summer of positive-IOD years due to weakened upwelling. The IOD signature in SSTanom and δ18Osw- anomdisappears with the overall intensification of upwellingafter the 1999 regime shift. The inferred increase in upwellingis likely driven by an intensified Walker circulationduring the global-warming hiatus. Upwellingin the Western Indian Ocean uncouples from the IOD.