Mountain respiration: Oxidation of sedimentary organic carbon in mountain river catchments revealed using the trace element rhenium Seminar

Oxidation of fossil organic carbon (OCfossil) during weathering of sedimentary rocks is a major source of carbon dioxide (CO2) to the atmosphere. The oxidation rate is thought to be enhanced by physical erosion, suggesting that mountain belts could release large amounts of CO2 which could counter the CO2 sequestration achieved by transfer and burial of recent OC from the terrestrial biosphere. However, this geological respiration by OCfossil oxidation has not been quantified in mountain belts. Here we use Rhenium (Re) as a proxy to track OCfossil oxidation and quantify the CO2 release in the mountain belt of Taiwan, where erosion rates and recent OC transfers have been quantified. Re is associated with OCfossil in rocks and following oxidation forms a soluble anion which contributes to the dissolved load of rivers. The dissolved Re flux can provide a first order estimate of the corresponding release of CO2 by OCfossil weathering in mountain river catchments. Re-derived OCfossil oxidation rates from Taiwanese rivers confirm that physical erosion rate is a major control on this CO2 release. Nevertheless, the estimated CO2 release from this mountain belt by OCfossil oxidation does not negate estimates of recent OC sequestration, suggesting that mountain building in the tropics can result in a net sink of OC which sequesters atmospheric CO2.