Carbon sources in arc volcanism, with implications for the carbon cycle

Abstract

ABSTRACT New CO 2 / 3 He data from the East Sunda Arc (Indonesia) confirm earlier observations that arc volcanic gases have higher CO 2 / 3 He ratios than MOR environments.On average, > 80% of arc volcanic CO 2 is recycled, exogene carbon. Addition of a few percent of carbonate‐bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases, but can not explain the He isotope observations. The CO 2 / 3 He in arc volcanoes is not strongly dependent on the composition of modem trough sediments (e.g. deep sea clays vs carbonate‐rich sequences), and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of, arcs. The sum of globally deep‐subducted sediment and slab carbon exceeds the estimated arc CO 2 flux, and approximately 3.5 teramole of carbon may return annually to the mantle in convergent zones. The modem combined processes of MOR volcanism, slab alteration, and subduction volcanism do not produce a substantial carbon flux into the exosphere, and rate‐changes in ocean floor spreading are unlikely to cause major changes in atmospheric CO 2 as a result of changes in the volcanic CO 2 fluxes. Intense pulses of flood basalt volcanism, however, may alter the CO 2 contents of the atmosphere over the course of a millenium or so, and influence global climate.