Estimation of atmospheric CO₂ uptake by silicate weathering in the Himalayas and the Tibetan Plateau: a review of existing fluvial geochemical data

The fluvial geochemical data of major rivers draining the Himalayas and the Tibetan Plateau (HTP) are compiled from literature and supplemented with data from the author's group to explore the spatial variability in the major element and strontium isotopic compositions and in rates of silicate weathering and concomitant drawdown of atmospheric CO₂. The results indicate that carbonate weathering dominates the major element composition of these rivers, and when the silicate contributions are carefully separated, there is spatial variability within the HTP system. Silicate contributions are highest in the rivers of the Himalayan syntaxes and in the Yamuna, Alaknanda-Bhaghirathi and Kosi tributaries of the Ganges. The ⁸⁷Sr/⁸⁶Sr ratios are especially radiogenic in the Ganges tributaries but the values do not necessarily correlate with the relative input from silicate weathering. Even in the Yamuna tributary of the Ganges where rates of CO₂ consumption by silicate weathering are several times those of the rivers of the eastern Tibetan Plateau, the rates are comparable to the rivers draining the Andes. Thus, the Ganges tributaries supply uniquely radiogenic ⁸⁷Sr to the ocean but cannot be considered anomalous in terms of silicate weathering rates in comparison to other major rivers draining orogenic zones.