Stable-isotopic composition of precipitation over the northern slope of the central Himalaya

Stable-water-isotope data (δD and δ 18O) from three groups of samples (fresh-snow and snow-pit samples collected on Qomolangma (Mount Everest) and Xixa-bangma during field seasons 1997, 1998 and 2001, and precipitation samples collected at Tingri station during summer 2000) are presented and used to survey the isotopic composition of precipitation over the northern slope of the central Himalaya. Multi-year snow-pit samples on Qomolangma have a local meteoric water-line (slope = 8) close to the global value. Deuterium excess (d = δD – 8δ 18O) values at Tingri are much lower than those in fresh snow from Qomolangma, probably due to differences in moisture source and air-mass trajectories as well as local weather conditions. There is no obvious seasonal trend for d values in the Qomolangma region. A negative relationship exists between δ 18O and d values in both fresh snow on Qomolangma and precipitation at Tingri. Fresh-snow samples collected from different altitudes on Xixabangma allow us to investigate the altitude effect on δ 18O values in snow. Of four storm events, only one has an obvious altitude effect on δ 18O variation and a very low gradient of −0.1 % per 100 m elevation.