Stable isotope evidence for moisture sources in the Asian summer monsoon under present and past climate regimes -: art. no. L08203

Stable isotope compositions of present day precipitation in the 70 degreesE - 160 degreesW longitude range reveal a strong correlation with moisture source and transport patterns and are not correlated with the amount of precipitation, contrary to existing interpretations. Spatially and temporally variable moisture sources and cyclonic circulation result in more depleted isotope values (delta(18)O similar to - 5 to - 7parts per thousand) in the 100 degreesE - 170 degreesE range. Oceanic moisture with minimal continental loss or input results in comparatively enriched delta(18)O values (similar to - 2 to - 4parts per thousand) in the 70 degreesE - 100 degreesE range and east of 170 degreesE. Isotope compositions of dated groundwater archives from the Philippines, Vietnam, Thailand and Bangladesh, reflecting past isotopic composition of precipitation, indicate that this distinction in moisture regimes was preserved during the last glacial period and strongly suggest that there was no significant shift in the summer Inter-Tropical Convergence Zone (ITCZ) in this region.