Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils.

Lithospheric organic carbon ("petrogenic"; OC) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OC initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OC remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO emission fluxes that increase with erosion rate, thereby counteracting CO drawdown by silicate weathering and biospheric OC burial.