Methane, manganese, and helium in hydrothermal plumes following volcanic eruptions on the East Pacific Rise near 9 degree 50'N

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2008-06, Vol.9 (6), p.np-np
• Main Authors: Love, Brooke A, Resing, Joseph A, Cowen, James P, Lupton, John E, nari, Daniel J, Shank, Timothy M, Biller, Dondra
• Format: Article
• Language: English
• Subjects: Carbon; Fractionation; Hydrothermal plumes; Manganese; Marine; Methane; Microorganisms; Plumes; Sea beds
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2008GC002104

As part of a rapid response cruise in May 2006, we surveyed water column hydrothermal plumes and bottom conditions on the East Pacific Rise between 9 degree 46.0'N and 9 degree 57.6'N, where recent seafloor volcanic activity was suspected. Real-time measurements included temperature, light transmission, and salinity. Samples of the plume waters were analyzed for methane, manganese, helium concentrations, and the [delta] super(13)C of methane. These data allow us to examine the effects of the 2005-2006 volcanic eruption(s) on plume chemistry. Methane and manganese are sensitive tracers of hydrothermal plumes, and both were present in high concentrations. Methane reached 347 nM in upper plume samples (250 m above seafloor) and exceeded 1085 nM in a near-bottom sample. Mn reached 54 nM in the upper plume and 98 nM in near-bottom samples. The concentrations of methane and Mn were higher than measurements made after a volcanic eruption in the same area in 1991, but the ratio of CH sub(4)/Mn, at 6.7, is slightly lower, though still well above the ratios measured in chronic plumes. High concentrations of methane in near-bottom samples were associated with areas of microbial mats and diffuse venting documented in seafloor imagery. The isotopic composition of the methane carbon shows evidence of active microbial oxidation; however, neither the fractionation factor nor the source of the eruption-associated methane can be determined with any certainty. Considerable scatter in the isotopic data is due to diverse sources for the methane as well as fractionation as methane is consumed. One sample at +21ppt versus Peedee belemnite standard is among the most enriched methane carbon values reported in a hydrothermal plume to date.