Asian monsoon hydrometeorology from TES and SCIAMACHY water vapor isotope measurements and LMDZ simulations: Implications for speleothem climate record interpretation

摘要

Observations show that heavy oxygen isotope composition in precipitation (δ ~(18)O _p) increases from coastal southeastern (SE) China to interior northwestern (NW) China during the wet season, contradicting expectations from simple Rayleigh distillation theory. Here we employ stable isotopes of precipitation and vapor from satellite measurements and climate model simulations to characterize the moisture processes that control Asian monsoon precipitation and relate these processes to speleothem paleoclimate records. We find that δ ~(18)O _p is low over SE China as a result of local and upstream condensation and that δ ~(18)O _p is high over NW China because of evaporative enrichment of ~(18)O as raindrops fall through dry air. We show that δ ~(18)O _p at cave sites over southern China is weakly correlated with upstream precipitation in the core of the Indian monsoon region rather than local precipitation, but it is well-correlated with the δ ~(18)O _p over large areas of southern and central China, consistent with coherent speleothem δ ~(18)O _p variations over different parts of China. Previous studies have documented high correlations between speleothem δ ~(18)O _p and millennial timescale climate forcings, and we suggest that the high correlation between insolation and speleothem δ ~(18)O _p in southern China reflects the variations of hydrologic processes over the Indian monsoon region on millennial and orbital timescales. The δ ~(18)O _p in the drier part (north of ～30N) of China, on the other hand, has consistently negative correlations with local precipitation and may capture local hydrologic processes related to changes in the extent of the Hadley circulation.