资源环境科技发展态势分析平台

Modern observations from Bay of Bengal (BOB) head have shown that precipitation delta O-18 value reaches the lowest stage during late postmonsoon when the summer monsoon has weakened or retreated, complicating the traditional interpretation of low delta O-18 value as strong monsoon. We show that this postmonsoon O-18 depletion phenomenon exists from BOB periphery to the southeast and south Tibetan Plateau. Accumulative precipitation along back-trajectory still explains daily precipitation delta O-18 variability during both the monsoon and nonmonsoon, thus indicating that longer-term weighted-mean delta O-18 is biased toward synoptic conditions during precipitation events. Further, we propose that transport of moisture from the east (west) of the India-Burma Trough leads to depleted (enriched) delta O-18 during the postmonsoon (premonsoon). Our results reconcile the apparent contradiction but beg the consideration of potential bias and influence of different precipitation regimes in paleo archives.