Convective hydrothermal C02 emission from high heat flow regions

Abstract In addition to volatiles released from volcanoes, the flux of CO 2 to the atmosphere from other sources (e.g., metamorphism and subsurface magmatism) represents an important aspect of the global carbon cycle. We have obtained a direct estimate of the present-day atmospheric CO 2 flux from convective hydrothermal systems within subaerial, seismically-active, high heat flow regions. Geothermal systems of the Salton Trough (California, U.S.A.) and the Taupo Volcanic Zone (New Zealand) provide benchmarks for quantifying convective hydrothermal CO 2 fluxes from such regions. CO 2 fluxes from the Salton Trough ( ∼ 10 9 mol yr −1 ) and the Taupo Volcanic Zone (∼ 8·109 mol yr −1 ) were computed using data on convective heat flow and the temperatures and CO 2 concentrations of reservoir fluids. The similarity in specific CO 2 flux ( ∼ 10 6 mol km −2 yr −1 ) from these two disparate geologic/tectonic settings implies that this flux may be used as a baseline to compute convective hydrothermal CO 2 emission from other areas of high heat flow. If this specific flux is integrated over high heat flow areas of the circum-Pacific and Tethyan belts, the total global CO 2 flux could equal or exceed 10 12 mol yr −1 Adding this flux to a present-day volcanic CO 2 flux of ∼ 4·10 12 mol yr −1 the total present-day Earth degassing flux could balance the amount of CO 2 consumed by chemical weathering ( ∼ 7·10 12 mol yr −1 ).