Was the Himalayan orogen a climatically significant coupled source and sink for atmospheric CO 2 during the Cenozoic?

Abstract

The hypothesis that the Himalayan orogen was a climatically significant coupled source and sink for atmospheric CO 2 during the Cenozoic is evaluated in light of the timing, duration and CO 2 fluxes associated with Himalayan metamorphism and chemical weathering. We suggest that diachronous Eohimalayan metamorphism occurred over a ∼20 m.y. time span (Middle Eocene to Early Oligocene) with total metamorphic CO 2 production of ∼4–10×10 18 mol. Because this is much greater than the amount of carbon stored in the atmosphere and oceans, and because uplift and accelerated erosion began at least ∼5 m.y. after the peak of metamorphism, we conclude that it is implausible that CO 2 produced by metamorphism in the Himalayan orogen was consumed millions of years later by erosion-enhanced weathering in this orogen. Assuming a global climate/silicate-weathering feedback, we estimate that metamorphic CO 2 degassing from the Himalayan orogen would have produced a warming of <0.5°C, and enhanced weathering in this orogen would have produced a cooling of <0.2°C; thus, direct climate effects of this degassing and weathering were likely to have been minor.