Examining long-term hydroclimate variability in the southern Indo-Pacific Warm Pool using paleo-indicators of water isotopes

The Indo-Pacific Warm Pool (IPWP) is home to the warmest sea surface temperatures in the tropics, favoring strong convective motion and heavy rainfall; however, the amount of rainfall varies spatially within the region. The Intertropical Convergence Zone (ITCZ) sits over the southern edge of the area during boreal winter when heavy rainfall is widespread. The ITCZ shifts to the north during boreal summer, thus leading to a relative dry season in much of the southern sector of the IPWP, including southern Sumatra, Java, and the Lesser Sunda Islands. To understand rainfall variability in the IPWP through time, we are analyzing the δD of n-alkanoic acids from terrestrial leaf waxes in marine core MD98-2152, located in the tropical eastern Indian Ocean (6.33S, 103.88E), for the last 450ky. We examine modern water-isotope data from a GNIP station in Jakarta in conjunction with HYSPLIT trajectories to inspect the modern moisture sources to our study site and their isotopic contributions. We compare our δD record from southern Sumatra with other paleo water isotope data from across the IPWP, as well as iCESM simulation results for the Last Glacial Maximum for a proxy-model comparison. HYSPLIT trajectory analyses demonstrate that modern sources of moisture to southern Sumatra during the rainy season are coming from the Indian Ocean and the South China Sea, which contribute rainfall that is depleted in deuterium relative to dry season precipitation, which primarily comes from the Timor Sea. These moisture sources and their δD values may have changed through time, thus affecting the δD of precipitation at our site. Our data suggest that changing moisture source contributions and their water isotope values likely play a more prominent role than the amount effect in controlling the isotopic composition of precipitation in the southern sector of the IPWP.