Diagnosis of atmospheric circulation shifts in the central Tibetan Plateau: Evidence from stable isotopes

The productivity of the alpine meadows in the central Tibetan Plateau (TP) is usually linked to atmospheric circulation shifts between the westerlies and Indian monsoon. Hence, it is critical to identify the dates of these circulation shifts, i.e., the Indian monsoon onset and retreat. However, the exact timing of the Indian monsoon onset in the central TP is highly uncertain. Here, we diagnose the atmospheric circulation shifts in the central TP during 2016-2018 using hydrogen and oxygen stable isotopes. Our results show that the Indian monsoon onset was marked by sharp decreases of the stable isotopes in both water vapor and precipitation (delta H-2(v) and delta H-2(p)) in mid-late June, which is approximately one month later than previous findings. In the subsequent period, the Indian monsoon replaced the westerlies across the central TP, where water vapor and precipitation were characterized by persistently lower stable isotope values. Substantial increases of the delta H-2(v) and delta H-2(p) values in late September denoted the Indian monsoon retreat. The delta H-2(v) and delta H-2(p) values also record fluctuations of the Indian monsoon intensity and the occasional intrusions of the westerlies even during the monsoon season. Our findings propose that stable isotopes can be used as indicators of atmospheric circulation shifts and may act as potential indices to monitor the vegetation growth in the central TP.

Automated summary

By analyzing hydrogen and oxygen stable isotopes, we found that the atmospheric circulation in the central Tibetan Plateau underwent a significant shift in mid-late June during 2016-2018, marking the onset of the Indian monsoon approximately one month later than previous findings. The Indian monsoon replaced the westerlies across the central TP, with persistently lower stable isotope values in water vapor and precipitation. The retreat of the Indian monsoon was denoted by substantial increases in stable isotopes values in late September. Our study suggests that stable isotopes can serve as indicators of atmospheric circulation shifts and potential indices for monitoring vegetation growth in the central TP.