Unraveling 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. 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 δ 18 O 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.

Climatic Drivers of Deglacial SST Variability in the Eastern Pacific

“…The significant correlation between EEP SSTs and PC1 is therefore consistent with GHG‐induced weakening of the Pacific Walker cell over the deglacial interval. Again, while we cannot rule out that ice sheet‐albedo forcing played a role in shaping the deglacial evolution of SSTs in this region, there is some evidence that ice sheet forcing is less influential on the Pacific Walker cell compared to GHG forcing (Windler et al., 2020).…”

Glacial‐Interglacial Shifts Dominate Tropical Indo‐Pacific Hydroclimate During the Late Pleistocene

“…Specifically, it resulted in a decoupling of the Indian and Pacific Walker Circulation cells during the LGM leading to widespread drying across the exposed area and a spatially distinct precipitation isotope response with increased low-level moisture convergence (divergence) causing a lighter (heavier) isotope signal over the Pacific (Indian) Ocean side of the IPWP (Windler et al, 2020). Notably, the South China Sea  D wax becomes isotopically lighter during glacial periods (Figure 4c), which is consistent with the simulated precipitation isotope response to sea level and ice sheet albedo in Windler et al (2020). Similarly, the secondary precession modes appear to influence the South China Sea and Sumatra/Bay of Bengal in opposite ways (Figure 4), following regional patterns of seasonal precipitation changes driven by insolation reported in Tierney et al (2012).…”

“…The distinct spectral configurations between these regions (Figures 3e and 3f) contradicts the theory that eastern China  18 O speleo reflects upstream moisture sources from the Indian monsoon region (Pausata et al, 2011;Battisti et al, 2014). In addition to ice volume, McGrath et al (2021) find that Bay of Bengal  D precip is in phase with greenhouse gas concentration maxima during the late Pleistocene; however, isotope-enabled simulations have shown that greenhouse gas forcing is expected to cause lighter precipitation isotope values across the entire IPWP and Bay of Bengal during glacial periods, whereas ice sheets/sea level result in the glacial enrichment visible in the Bay of Bengal, Borneo, and Sumatra (Windler et al, 2020).…”

“…C values in the same core to account for vegetation shifts over time, following the methodology of Windler et al (2020). WINDLER ET AL.…”

Termination 1 Millennial‐Scale Rainfall Events Over the Sunda Shelf

“…Fully-coupled general circulation model simulations with enabled water isotopes is a tool that can be utilized to assist with IPWP stalagmite δ 18 O interpretations (e.g. Windler et al, 2020;Du et al, 2021).…”