Contrasting Impacts of ENSO Evolution on the Interannual Variation of Precipitation Isotopes Over the Tibetan Plateau

The interannual variability in the stable oxygen isotopes in precipitation (δ¹⁸O_p) in the Tibetan Plateau (TP) has been linked to the El Niño-Southern Oscillation (ENSO) dynamics, yet the specific mechanisms driving this variability remain unclear. Here, we use an isotope-enabled climate model with water-tagging capability to show that the developing and decaying phases of ENSO are associated with distinct patterns of interannual δ¹⁸O_p variability in the northern and southern TP. To explore the underlying mechanisms, we conducted modeling experiments to investigate three potential processes through which ENSO may affect the interannual variation of δ¹⁸O_p in the TP, including (a) the initial vapor isotopic signal in the ocean sources, (b) the relative moisture contribution from different sources, and (c) atmospheric processes along the moisture transport path. We find that δ¹⁸O_p is dominantly influenced by upstream processes along the moisture transport, in response to ENSO-driven changes in atmospheric activities. Specifically, during the summer and fall of the developing El Niño (La Niña) phases, δ¹⁸O_p in the southern TP is affected by convective activities in the Indian Peninsula, Bay of Bengal, Indochina Peninsula, and South China Sea, leading to enrichment (depletion) in δ¹⁸O_p. In contrast, atmospheric activities over the Eurasian landmass and the local TP during the mature winter and the decaying spring phases of El Niño (La Niña) result in depletion (enrichment) of δ¹⁸O_p in the northern TP. Our study suggests the possibility of improving the reconstruction of past ENSO-related interannual variations at a seasonal scale by integrating isotopic proxies from TP.