Variations in hydrothermal methane and hydrogen concentrations following the 1998 eruption at Axial Volcano

Abstract

During the February response cruise to Axial Volcano, methane and hydrogen concentrations within the plume were significantly elevated above background. CH4/3He ratios were found to be 5-10 times greater than previously reported values for unsedimented ridges. An average δ13C value of -32.7 ± 0.8 ‰ was determined for CH4 concentrations > 10 nM and CH4/Mn ratios were determined to be 2.2. Hydrogen concentrations as high as 183 nM were measured; however most were < 10nM. Microbial oxidation of methane was negligible (<0.001 day-1) during this sampling period. However, microbial hydrogen oxidation was sufficient to explain decreased H2 concentrations measured at 'older' downstream stations. Copyright 1999 by the American Geophysical Union.