Glacial to Holocene Hydroclimate of the western Indo-Pacific Warm Pool

Abstract:

The Indo-Pacific Warm Pool (IPWP) is of utmost importance for the global hydrologic cycle nowadays and characterized by a complex interplay between ocean currents and different oscillations operating at different timescales such as the Australasian monsoon systems, ENSO, the Indian Ocean Dipole, and the Madden-Julian Oscillation. On longer timescales, changes in sea level, insolation, the intensity of the Atlantic Meridional Overturning Circulation, and land-sea, zonal and meridional temperature gradients are thought to influence the IPWP climate. Despite the limited temporal and spatial coverage of the hitherto applied proxies/model simulations, the response of the IPWP to forcing changes appears nonlinear and nonuniform, and precludes a simplistic view of forcing and feedback mechanisms. A growing body of evidence from marine and terrestrial archives within the ever-wet part of the IPWP suggests that changes in regional hydroclimate on millennial timescales was substantially greater than that on glacial-interglacial timescales. This finding is interpreted as a response of the IPWP to climate change at high northern latitudes through changes in the interhemispheric temperature gradient and/or through upper tropospheric circulation anomalies, ultimately leading to changes in the Hadley Circulation and the associated position of the Intertropical Convergence Zone. In contrast, hydroclimate archives from the monsoon domain of the IPWP are equivocal. Some indicate drier and cooler glacials compared to the interglacials and have been interpreted to reflect changes in sea level and/or monsoon intensity, whereas others show patterns similar to those from the ever-wet part of the IPWP and imply locally different responses to the same forcing. Lastly, high-resolution hydroclimate data from both the ever-wet and the monsoonal IPWP are reminiscent of solar irradiance, ENSO, and the Indian Ocean Dipole patterns/reconstructions during the Holocene. Overall, it appears that the sensitivity of the IPWP hydrclimate is modulated by background climate conditions.