Regional controls on daily to interannual variations of precipitation isotope ratios in Southeast China: Implications for paleomonsoon reconstruction

Abstract

Many key paleomonsoon records in East Asia rely on past precipitation isotope ratios (δ18Op) as proxies for hydroclimate, however, the relationship between climate variability and δ18Op remains an ongoing debate. Here we investigate dominant climatic drivers and test actively-discussed hypotheses of Southeast China δ18Op variability over multiple timescales, using an 8-yr-long daily δ18Op record from Guangzhou and updated GNIP dataset from Hong Kong. Our moisture source diagnostic analyses suggest that the primary moisture of Guangzhou precipitation essentially comes from the proximal northern South China Sea (SCS). Convective activities over the primary moisture source regions, measured by cumulative precipitation along back-trajectory, regional precipitation and outgoing longwave radiation, play a key role in regulating δ18Op variability across different timescales. These effects can be related to the direct changes of convection intensity over the SCS or the indirect changes associated with the shift of moisture source. In consequence, δ18Op records seasonal monsoon dynamics associated with the intertropical convergence zone migration and the El Niño-Southern Oscillation (ENSO). Further tests of different hypotheses and their links to the ENSO via the 2015 strong El Niño event support the above conclusions. Taken together, these results demonstrate that Southeast China δ18Op represents a spatial-temporally integrated measure of precipitation and convection tracing from the measured site to moisture sources, shedding light on the interpretation of paleo-isotope data in the monsoon domain.