FY 1987

Evidence for high-temperature hydrothermal venting on the Gorda Ridge, northeast Pacific Ocean

Baker, E.T., G.J. Massoth, R.W. Collier, J.H. Trefry, D. Kadko, T.A. Nelsen, P.A. Rona, and J.E. Lupton

Deep-Sea Res., 34(8), 1461–1476 (1987)

The first water-column survey of the axial valley of the Gorda Ridge, a slow- to medium-rate spreading center within 300 km of the coast of Oregon and California, found strong evidence for ongoing hydrothermal venting. At the northern end of the ridge, anomalously high concentrations of helium-3, dissolved manganese, particulate iron, and methane confirmed the hydrothermal origin of above-bottom plumes identifiable as maxima in light-attenuation profiles. The presence of excess radon-222 and the highly soluble hydrothermal precipitate anhydrite in the plumes require a local vent source; the precipitation of anhydrite requires fluid temperatures of at least 130°C. Indications of hydrothermal activity elsewhere in the axial valley were inconclusive.