Abstract
The Indian Ocean Dipole (IOD) is an interannual mode of climate variability in the Indian Ocean that has intensified with 20th 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 (SSTanom) is calculated from Sr/Ca ratios, and seawater δ18O (δ18Osw-anom) is estimated by subtracting the temperature component from coral δ18O. Our δ18Osw-anom record reveals a significant regime shift in 1999, towards lower mean δ18Osw values, reflecting intensified upwelling in the western Indian Ocean. Prior to the 1999 regime shift, our SSTanom and δ18Osw-anom show 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-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.
Highlights
The Indian Ocean Dipole (IOD) is an interannual, aperiodic oscillation of sea-surface temperatures in the equatorial Indian Ocean, with positive, neutral and negative phases[1]
Satellite-based sea surface temperature (SST) data suggest that the main cause of the global-warming hiatus is the Interdecadal Pacific Oscillation (IPO), which is the dominant mode of atmosphere-ocean interactions in the subtropical Pacific
In order to investigate the impact of the global-warming hiatus on the stability of the IOD teleconnection in the western Indian Ocean, we developed biweekly-resolved records (0.5 mm sampling interval) of seawater oxygen isotopes (δ18Osw) and strontium/calcium ratios (Sr/Ca) from a 26-year long coral core drilled in the Gulf of Oman, Arabian Sea (Fig. 1)
Summary
Received: 5 April 2018 Accepted: 27 December 2018 Published: xx xx xxxx the Indian Ocean Dipole during the global-warming hiatus. Previous studies have observed that global surface air-temperatures remained relatively constant between the late-1990s and 2015 (Fig. 2a), climate models predicted continued anthropogenic warming This so-called global-warming hiatus has received considerable attention[7]. Satellite-based wind stress data suggest that the Indo-Pacific Walker circulation intensified during the global-warming hiatus[11] At present, it is poorly understood how the regime shift of the IPO in 1999 and the global-warming hiatus influence the variability and the basin-wide teleconnections of the IOD. In order to investigate the impact of the global-warming hiatus on the stability of the IOD teleconnection in the western Indian Ocean, we developed biweekly-resolved records (0.5 mm sampling interval) of seawater oxygen isotopes (δ18Osw) and strontium/calcium ratios (Sr/Ca) from a 26-year long coral core drilled in the Gulf of Oman, Arabian Sea (Fig. 1). A previous study of the Oman coral proxy records has demonstrated that they record boreal summer upwelling driven by the Indian/Arabian monsoon from June to September (Indian summer monsoon: ISM)[16]
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