Oman coral δ¹⁸O seawater record suggests that Western Indian Ocean upwelling uncouples from the Indian Ocean Dipole during the global-warming hiatus.

ABSTRACT: The Indian Ocean Dipole (IOD) is an interannual mode of climate variability in the Indian Ocean that has intensified with 20^th century global-warming. However, instrumental data shows a global-warming hiatus between the late-1990s and 2015. It is presently not clear how the global-warming hiatus affects 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 δ¹⁸O from a Porites coral drilled in the Gulf of Oman. Sea surface temperature (SST_anom) is calculated from Sr/Ca ratios, and seawater δ¹⁸O (δ¹⁸O_sw-anom) is estimated by subtracting the temperature component from coral δ¹⁸O. Our δ¹⁸O_sw-anom record reveals a significant regime shift in 1999, towards lower mean δ¹⁸O_sw values, reflecting intensified upwelling in the western Indian Ocean. Prior to the 1999 regime shift, our SST_anom and δ¹⁸O_sw-anom show a clear IOD signature, with higher values in the summer of positive-IOD years due to weakened upwelling. The IOD signature in SST_anom and δ¹⁸O_sw-anom disappears with the overall intensification of upwelling after the 1999 regime shift. The inferred increase in upwelling is likely driven by an intensified Walker circulation during the global-warming hiatus. Upwelling in the Western Indian Ocean uncouples from the IOD.

SUBMITTER: Watanabe TK 

PROVIDER: S-EPMC6374511 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature