ENSO variability reflected in precipitation oxygen isotopes across the Asian Summer Monsoon region

摘要

Oxygen isotope signals (delta O-18) from paleo-archives are important proxies for past Asian Summer Monsoon (ASM) climate reconstruction. However, causes of interannual variation in the. delta O-18 values of modern precipitation across the ASM region remain in argument. We report interannual delta O-18 variation in southern Tibetan Plateau precipitation based on long-term observations at Lhasa. These data, together with precipitation delta O-18 records from five Global Network of Isotopes in Precipitation (GNIP) stations and two ice core delta O-18 records, were used to define a regional metric of ASM precipitation delta O-18 (ASMOI). Back-trajectory analyses for rainy season precipitation events indicate that moisture sources vary little between years with relatively high and low delta O-18 values, a result that is consistent for the south (Lhasa), southeast (Bangkok), and east ASM regions (Hong Kong). In contrast, delta O-18 values at these three locations are significantly correlated with convection in the estimated source regions and along transport paths. These results suggest that upstream convection, rather than moisture source change, causes interannual variation in ASM precipitation delta O-18 values. Contrasting values of the ASMOI in El Nino and La Nina years reveal a positive isotope-El Nino Southern Oscillation (ENSO) response (e.g., high values corresponding to warm phases), which we interpret as a response, to changes in regional convection. We show that the isotope-ENSO response is amplified at high elevation sites and during La Nifia years. These findings should improve interpretations of paleo-delta O-18 data as a proxy for past ASM variation and provide new opportunities to use data from this region to study paleo-ENSO activity. (C) 2017 Elsevier B.V. All rights reserved.