Atmospheric Controls on Seasonal and Interannual Variations in the Precipitation Isotope in the East Asian Monsoon Region

Abstract

ABSTRACT Understanding variations in isotopic composition of precipitation from monsoon regions is crucial for its utilization in paleoclimate studies. This study explores the relationship between precipitation δ18O data for the East Asian monsoon (EAM) region archived in Global Network for Isotopes in Precipitation (GNIP) and the cloud data archived in ISCCP and their linkage with large-scale atmospheric circulation patterns. Results show that precipitation δ18O are significantly and positively correlated with cloud-top pressure (CTP) on both local and regional scales. Mechanically speaking, the stronger the monsoon convection precipitation, the higher the cloud and the lower the condensation temperature and thus the lower the precipitation δ18O. This result implies that the sharp drop in precipitation δ18O in the early summer in monsoonal Asia is related to the atmospheric circulation pattern rather than the different moisture sources, as was previously assumed. This result helps explain the processes leading to the observed “amount effect.” A comparison of atmospheric circulation patterns with precipitation δ18O on an interannual scale shows that the positive CTP anomalies in the central Indo-Pacific within the weak Walker circulation (El Niño) can be associated with positive δ18O anomalies, while negative CTP anomalies in the central Indo-Pacific within the strong Walker circulation (La Niña) can be linked to negative δ18O anomalies. This result further confirms the aforementioned conclusion. This is important for understanding paleoclimatic change in monsoonal Asia, as interannual variations in stable isotopes in that region have received less attention in the past.