Spatial variability of stable isotopes in river water over the Tibetan Plateau

Estimating isotopic changes of river water on the Tibetan Plateau (TP) remains highly uncertain due to variable water sources related with seasonality of atmospheric circulations and local kinetic fractionation. The in-depth understanding of such changes is crucial for accurate palaeoaltimetry reconstruction and for river budget evaluation which related with surviving of one-fifth of the world's population under accelerated warming. Here, we present a comprehensive river water isotopic composition dataset (delta 18O, delta D and d-excess, 1852 samples) over the TP to systematically describe spatial distribution and explore possible controlling factors of isotopic data in theses rivers. Results showed that delta 18O in river water range from -20.8 parts per thousand to -5.2 parts per thousand (latitudinally, 0.92 parts per thousand per degree), enriching northwardly in the seven exorheic river basins. The d-excess values range from -19.7 parts per thousand to 20.5 parts per thousand with the pronounced low values in endorheic rivers basins. We identified that moisture sources and atmospheric transports leave significant signals in isotopic compositions of river water in the Upper Brahmaputra (UB), Upper Mekong (UM) and Upper Yangtze (UYA) basins, and local processes modify the isotopic signals mainly in the Upper Salween (US), Upper Indus (UI), Upper Yellow (UYE) and Endorheic Rivers (ER) basins. The delta 18O-elevation relationships are only established in the UB, UI and UYE with lapse rates of -4.4 parts per thousand/km, -3.4 parts per thousand/km and -3.5 parts per thousand/km, respectively. We suggest that as changes of moisture sources and lapse rates in different basins, it is cautious to apply delta 18O-elevation lapse rates for palaeoaltimetry reconstruction. Our dataset will benefit regional studies of hydrological, biogeochemistry, palaeoaltimetry reconstruction and palaeoclimate. We found gradual increasing of river water delta 18O northwardly and uneven variability of river water d-excess over the Tibetan Plateau. Spatial variabilities of river water isotopes were primarily shaped by distinct moisture sources related with large-scale moisture transport and local processes. The delta 18O-elevation relationships were only established in the Upper Brahmaputra, Upper Indus and Upper Yellow basins.image