labs_title

Caldeira Lab Research:Paleoclimate and geochemical cycles

Was the Himalayan orogen a climatically significant coupled source and sink for atmospheric CO2 during the Cenozoic?

D.M. Kerrick & Ken Caldeira

A study of the Himalayan orogen's role in CO2 production and as a CO2 sink in the Cenozoic. A previous paper suggested that the CO2 produced during the Himalayan orogen was cancelled out by later chemical weathering in the same area. Here it is shown that the magnitude of CO2 produced by the creation of the Himalayas would be far too much for the same area to act as a sink for it several million years later.


Kerrick, D.M., and Caldeira, K., Was the Himalayan orogen a climatically-significant coupled source and sink for atmospheric CO2 during the Cenozoic? Earth and Planetary Science Letters 173, 195–203, 1999.

Amount of time required for carbon dioxide concentration to reach 10,000 ppm: The amount of time in millions of years that it would take for the atmosphere to reach 10,000 ppm at various carbon flux rates. At a flux rate of .2 x 1012 (the rate calculated for the Himalayan Orogen), it would take around 5 Myr to reach 1000ppm, the assumed maximum concentration at the time.

Amount of time required to remove the excess carbon from the atmosphere: The amount of carbon dioxide in the atmosphere is graphed as a function of time for various rates of excess drawdown caused by weathering. The graph for .064 is based on what is estimated to have been the rate of drawdown during the Himalayan weathering. This implies that for Himalayan weathering to cancel out the carbon input caused by its orogen, it would have to take place for 35 million years, an unlikely feat.

Abstract

The hypothesis that the Himalayan orogen was a climatically significant coupled source and sink for atmospheric CO2 during the Cenozoic is evaluated in light of the timing, duration and CO2 fluxes associated with Himalayan metamorphism and chemical weathering. We suggest that diachronous Eohimalayan metamorphism occurred over a ~20 Myr time span (Middle Eocene to Early Oligocene) with total metamorphic CO2 production of ~4–10 • 1018 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 Myr after the peak of metamorphism, we conclude that it is implausible that CO2 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 CO2 degassing from the Himalayan orogen would have produced a warming of <0.5ºC, and enhanced weathering in this orogen would have produced a cooling of <0.2ºC; thus, direct climate effects of this degassing and weathering were likely to have been minor.