Convective hydrothermal CO2 emissions from high heat flow regions
D.M. Kerrick, M.A. McKibbon, T.M. Seward & K. Caldeira
In the natural carbon cycle, there is a delicate balance between input and uptake of CO2. Uptake is generally controlled by weathering while input is controlled by processes such as volcanism and metamorphism. However, the amount of CO2 derived from non volcanic sources had not been directly estimated prior to this paper's publication. It focuses on estimating CO2 flux from convective hydrothermal circulation on the Earth's surface in high heat areas.
In addition to volatiles released from volcanoes, the flux of CO2 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 CO2 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 CO2 fluxes from such regions. CO2 fluxes from the Salton Trough ( ~ 109 mol yr-1) and Taupo Volcanic Zone ( ~ 8•109 mol yr-1) were computed using data on convective heat flow and the temperatures and CO2 concentrations of reservoir fluids. The similarity in specific CO2 flux ( ~ 106 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 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 1012 mol yr-1. Adding this flux to a present-day volcanic CO2 flux of ~ 4 • 1012 mol yr-1, the total present-day Earth degassing flux could balance the amount of CO2 consumed by chemical weathering ( ~ 7 • 1012 mol yr-1).