Precipitation Oxygen Isotope Changes Over East Asia Driven by Sea Surface Conditions During the Last Glacial Maximum

The seasonal changes in East Asian monsoon precipitation during the Last Glacial Maximum (LGM, 23,000-19,000 years B.P.) and its isotopic expression remain ambiguous. This study investigates changes in the seasonal precipitation delta O-18 (delta O-18(p)) over East Asia during the LGM relative to the preindustrial (PI) and the underlying mechanisms using an isotope-enabled atmospheric general circulation model. We show more depleted delta O-18(p) in summer and a meridional tripolar delta O-18(p) pattern in winter during the LGM compared to the PI. The depletion of summer delta O-18(p) resulted from stronger upstream convective rainout due to the intensification of the Intertropical Convergence Zone. In contrast, the mechanisms for winter delta O-18(p) changes were more complicated. With a series of sensitivity tests, we demonstrate that sea surface temperature controlled delta O-18(p) changes across the whole of East Asia in summer and in the southern part of East Asia in winter. The depletion of winter delta O-18(p) in central China arose largely from the suppression of droplet evaporation due to higher snow fraction. Our work provides important insights into the aspect of seasonal isotope changes during the LGM and may help facilitate an improved level of paleoclimatic interpretation of speleothem delta O-18 records from East Asia.