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), doi: 10.1016/j.epsl.2004.07.028, 449–464 (2004) |
| Measurements of pH and total carbon dioxide (ΣCO2) 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 CO2-rich hydrothermal fluids. As a result, changes in pH can be directly related to the amount of CO2 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 CO2, CO2 inferred from changes in pH, and 3He data to constrain the ratio of CO2/3He in hydrothermal plumes along extensive segments of the mid-ocean ridge and over time following a volcanic eruption. There are a limited number of CO2/3He values reported for mid-ocean ridge basalts and hydrothermal fluids, and thus the CO2/3He 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 × 109. These data suggest that a large degree of fractionation between 3He and CO2 does not occur during magmatic degassing, eruption, and hydrothermal circulation.
If a CO2/3He ratio of 2 × 109 is representative of the ratio found in the mantle beneath the MOR, then hydrothermal fluxes of CO2 can be estimated for the global oceans based on the flux of 3He from the mantle and MORs. These results suggest a MOR CO2 flux of 0.5-2 ×1012 mol year−1, which is consistent with other estimates. |
