Unraveling Glacial Hydroclimate in the Indo‐Pacific Warm Pool: Perspectives From Water Isotopes

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. Here, we present a 450,000‐year record of precipitation δD from southern Sumatra that records a consistent pattern of glacial isotopic enrichment and interglacial depletion. We 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). 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. We conclude that reorganization of regional circulation under glacial conditions controls precipitation isotope variability in the IPWP: Low‐level tropospheric convergence dominates the signal in the north/east, whereas divergence controls the response in the south/west. Additional sensitivity simulations suggest that the LGM ice sheets and the associated lowering in sea level, rather than decreased greenhouse gases, are responsible for the distinctive spatial pattern in glacial changes of precipitation isotopes and hydroclimate across the IPWP.Key PointsA new precipitation isotope record from southern Sumatra shows consistent enrichment during the five most recent glacial periodsGlacial‐interglacial changes in proxy precipitation isotope data from the Indo‐Pacific Warm Pool agree well with isotope‐enabled simulationsSpatial heterogeneity of Warm Pool hydroclimate is linked to regional moisture convergence/divergence over the Pacific and Indian OceansPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163613/3/palo20944_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163613/2/palo20944-2020PA003985-sup-0001-SI.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163613/1/palo20944.pd