CONVECTIVE HYDROTHERMAL CO2 EMISSION FROM HIGH HEAT-FLOW REGIONS

In addition to volatiles released from volcanoes, the flux of CO2 to t he atmosphere from other sources (e.g., metamorphism and subsurface ma gmatism) represents an important aspect of the global carbon cycle. We have obtained a direct estimate of the present-day atmospheric CO2 fl ux from convective hydrothermal systems within subaerial, seismically- active, high heat flow regions. Geothermal systems of the Salton Troug h (California, U.S.A.) and the Taupo Volcanic Zone (New Zealand) provi de benchmarks for quantifying convective hydrothermal CO2 fluxes from such regions. CO2 fluxes from the Salton Trough (similar to 10(9) mol yr(-1)) and the Taupo Volcanic Zone (similar to 8.10(9) mol yr(-1)) we re computed using data on convective heat flow and the temperatures an d CO2 concentrations of reservoir fluids, The similarity in specific C O2 flux (similar to 10(6) mol km(-2) yr(-1)) from these two disparate geologic/tectonic settings implies that this flux may be used as a bas eline to compute convective hydrothermal CO2 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 CO2 flux could equal or exceed 10(12) mol yr(-1). Adding this flux to a present-day volcanic CO2 flux of similar to 4.10(12) mol yr(-1), the total present-day Earth degassing flux could balance the amount of CO 2 consumed by chemical weathering (similar to 7.10(12) mol yr(-1)).