Glacial Hydroclimate in the Indo-Pacific Warm Pool: Perspectives from Water Isotopes

Abstract:

The Indo-Pacific Warm Pool (IPWP) is home to the warmest sea surface temperatures in the world oceans, favoring strong tropospheric convection and heavy rainfall. The mechanisms controlling long-term change in the region’s hydroclimate are still uncertain. We present a leaf wax-derived record of precipitation δD from southern Sumatra, spanning the last 450,000 years, which shows a consistent pattern of glacial isotopic enrichment and interglacial depletion. We also synthesize existing paleo-indicators of precipitation δD and δ¹⁸O in the IPWP and compare results with water isotope-enabled climate simulations of the Last Glacial Maximum (LGM), using the Community Earth System Model (iCESM). The simulations show glacial isotopic enrichment over the eastern Indian Ocean extending into the southern IPWP and isotopic depletion over southeast Asia, the west Pacific, and Australia. The pattern of simulated LGM isotopic change agrees generally well with our proxy synthesis and suggests that the mechanisms controlling precipitation isotope variability under glacial conditions vary spatially in the IPWP: regional convergence dominates the signal in the north/east, whereas divergence and reduced rainfall controls the response in the south/west. Additionally, sensitivity simulations suggest that the LGM ice sheets and associated lowering in sea level, rather than greenhouse gases, are responsible for the distinctive spatial pattern in glacial changes of precipitation isotopes and hydroclimate across the IPWP.