Biogeochemistry of Himalayan rivers as an agent of climate change

Abstract

Uplift of the Himalaya, intensification of the Asian monsoon and increased erosion from the Himalayan orogen are all intimately coupled and reflected in the transport of weathering products to the ocean by the large rivers, namely the Indus, Ganga, Brahmaputra, Mekong, Chang Jiang and Irrawady^1-6. In recent years, several studies have focused on the coupling between continental weathering rates and changes in atmospheric CO₂ budget. Because the atmospheric CO₂ reservoir is relatively small and CO₂ gets converted to bicarbonate anion (HCO₃^-) and is balanced by dissolved cations from the silicate/carbonate rocks; it is likely that this reservoir is sensitive to changes induced by chemical weathering rates. In such a scenario, increased chemical weathering and associated CO₂ consumption rates in the Himalayan rivers could alter the atmospheric CO₂ levels and hence the global climate. Both oceanic and terrestrial evidence points to a marked, progressive period of intense cooling of global climate over the geologic past. Existing-models of the global CO₂ cycle do not include detailed consideration of such tectonically-driven enhanced chemical weathering. The purpose of this paper is to evaluate the present-day CO₂ consumption rates by chemical weathering processes in the Himalaya, based on newer data⁶, and their implications to long-term climate change.