FY 2005
CO2 and 3He in hydrothermal plumes: Implications for mid-ocean ridge CO2 flux
Resing, J.A., J.E. Lupton, R.A. Feely, and M.D. Lilley
Earth Planet. Sci. Lett., 226(3–4), 449–464 (2004) |
Measurements of pH and total carbon dioxide ( CO ) from Axial Volcano in the 2 years following its eruption and from the Southern East Pacific Rise from 27°S to 32°S are used to demonstrate that decreases in pH in hydrothermal plumes at mid-ocean ridges are primarily caused by the emission of CO-rich hydrothermal fluids. As a result, changes in pH can be directly related to the amount of CO added to the hydrothermal plumes. Because hydrothermal plumes integrate the hydrothermal output and chemical signatures from multiple sources in a vent field area, the chemistry in plumes reflects that in fluids being emitted from vent field areas as a whole. We use directly measured CO, CO inferred from changes in pH, and  He data to constrain the ratio of CO/He in hydrothermal plumes along extensive segments of the mid-ocean ridge and over time following a volcanic eruption. There are a limited number of CO/He values reported for mid-ocean ridge basalts and hydrothermal fluids, and thus the CO/He ratios determined here greatly increase their geographic and temporal distribution and demonstrate that this ratio is fairly constant along the mid-ocean ridges (MORs), having a value of ~2 × 10 . These data suggest that a large degree of fractionation between He and CO does not occur during magmatic degassing, eruption, and hydrothermal circulation.
If a CO/He ratio of 2 × 10 is representative of the ratio found in the mantle beneath the MOR, then hydrothermal fluxes of CO can be estimated for the global oceans based on the flux of He from the mantle and MORs. These results suggest a MOR CO flux of 0.5-2 ×10 mol year , which is consistent with other estimates. |
