Oxygen-18 in present-day precipitation on the Tibetan Plateau

Abstract

The temporal and spatial variations of the δ18O in precipitation on the Tibetan Plateau are analyzed. There is no temperature effect in the southern Tibetan Plateau. Amount effect has been observed at Lhasa station. However, the seasonal variations of the δ18 in precipitation are different from that of precipitation intensity, showing that the precipitation intensity is not a main controlling factor on the stable isotopic compositions in precipitation in the southern Tibetan Plateau. There is notable temperature effect in the middle and northern Tibetan Plateau. The seasonal variations of the δ18O in precipitation are almost consistent with those of air temperature there, indicating that temperature is a main factor controlling the stable isotopic variations in precipitation. A meridional cross-section shows that a notable depletion of the stable isotopic ratio in precipitation takes place in the Himalayas due to very strong rainout of vapor as it rises over the Himalayas, then the δ18O remains basically unchanged although a big temperature fluctuation appears from Tingri to Amdo, and the δ18O in precipitation increases rather than decreases from Tanggula to the northern Tibetan Plateau. Such a spatial distribution is related to the replenishment of vapor with the relatively heavy stable isotopic compositions originated from the inner Plateau.