FY 2000

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

McLaughlin-West, E.A., E.J. Olson, M.D. Lilley, J.A. Resing, J.E. Lupton, E.T. Baker, and J.P. Cowen

Geophys. Res. Lett., 26(23), doi: 10.1029/1999GL002336, 3453–3456 (1999)

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 <10 nM. 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.