Effect of precipitation seasonality on annual oxygen isotopic composition in the area of spring persistent rain in southeastern China and its paleoclimatic implication

Abstract

This study examines the seasonality of precipitation amount and δ18O over the monsoon region of China (MRC). We found that the precipitation amount associated with the East Asian summer monsoon (EASM) in the spring persistent rain (SPR) region is equivalent to that of the nonsummer monsoon (NSM). The latter contributes ∼50 % to amount-weighted annual δ18O values, in contrast with other areas in the MRC, where the δ18O of annual precipitation is dominated by EASM precipitation. Interannual relationships between the El Niño–Southern Oscillation (ENSO) index, simulated δ18O data from IsoGSM, and seasonal precipitation amount in the SPR region were also examined. We found that on interannual timescales, the seasonality of precipitation amount (EASM ∕ NSM ratio) was modulated by ENSO and primarily influences the variability of amount-weighted annual precipitation δ18O values in the SPR region, although integrated regional convection and moisture source and transport distance may also play subordinate roles. During El Niño (La Niña) phases, less (more) EASM and more (less) NSM precipitation leading to lower (higher) EASM ∕ NSM precipitation amount ratios results in higher (lower) amount-weighted annual precipitation δ18O values and, consequently, in higher (lower) speleothem δ18O values. Characterizing spatial differences in seasonal precipitation is, therefore, key to correctly interpreting speleothem δ18O records from the MRC.