Interannual controls on oxygen isotope variability in Asian monsoon precipitation and implications for paleoclimate reconstructions

Abstract

AbstractOrbital to millennial‐scale variations in Asian monsoon speleothem δ18O have been widely interpreted as records of monsoon intensity and/or rainfall amount. To assess the influence of these and other mechanisms on higher‐frequency δ18O variability, we utilize simulations from a spectrally nudged isotope‐enabled general circulation model coupled with instrumental climate data to investigate the climatic controls on interannual precipitation δ18O (δ18Op) variability at four key cave locations affected by the Asian monsoon: Qunf Cave, Oman; Mawmluh Cave, India; Tham Mai Cave, Laos; and Dongge Cave, China. Comparison with instrumental climate data shows that interannual δ18Op variations are only weakly related to local precipitation amount at the four sites and are instead controlled primarily by large‐scale monsoon intensity and upstream precipitation over the tropical Indo‐Pacific region, which influence the δ18O of incoming moisture. Spatial correlations with sea surface temperature and precipitation, composite analyses, and time series analyses show that the El Niño–Southern Oscillation (ENSO) also plays a key role in modulating interannual precipitation δ18Op variability in the region, especially in northern India and Southeast Asia, with positive δ18Op anomalies during El Niño years reflecting increased contribution of high δ18O moisture from the nearby Bay of Bengal. Coherent interannual to decadal δ18O variations seen in high‐resolution proxy records from across the Asian monsoon region, likely record monsoon intensity and upstream rainout, whereas ENSO related variability is likely to be strongest in records from northern India and Southeast Asia, with the largest anomalies expected when weak monsoons and El Niño occur together.