Interannual modulation of the East and South Asian summer precipitation 618O by the Indian and western North Pacific summer monsoon strength

The understanding of the relationship between the variation of precipitation stable oxygen isotope ratio (618Op) and monsoon activity in the Asian monsoon region is crucial for an in-depth comprehension of the regional hydrological cycle processes and for reconstructing the history of Asian paleomonsoon changes. Based on the 1979-2017 summer 618Op output by two isotope-enabled atmospheric general circulation models nudged to climate reanalysis data, this study explores the associations of the Indian summer monsoon (IM) and western North Pacific summer monsoon (WNPM) intensities with the interannual variations of the regional 618Op and their possible physical mechanisms. Statistical analyses demonstrate that the East Asian 618Op is negatively correlated with the IM intensity while the Indian 618Op is positively correlated with the WNPM intensity. Moreover, the underlying mechanisms linking the monsoon and 618Op vary in different regions. In strong IM years, with the intensified convection and increased precipitation near the Indian peninsula, the water vapor isotope ratio (618Ov) transported to East Asia has lower values, resulting in the depletion of 618Op there. The opposite is true for weak IM years. In years of strong WNPM, the intensified convection over the tropical western Pacific and the suppressed convection over the western Indian Ocean may be linked to a Walker-type circulation anomaly, accompanied by the enlarging of the vertical wind shear between the western Pacific and the western Indian Ocean. Accordingly, the decreasing of convection and precipitation over the Arabian Sea results in higher 618Ovvalues in the upstream area of India, which ultimately increases 618Op values in the Indian peninsula through the monsoonal moisture transport; and vice versa.