FY 1989

The geochemistry of submarine venting fluids at Axial Volcano, Juan de Fuca Ridge: New sampling methods and a VENTS Program rationale

Massoth, G.J., H.B. Milburn, S.R. Hammond, D.A. Butterfield, R.E. McDuff, and J.E. Lupton

In Global Venting, Midwater, and Benthic Ecological Processes, National Undersea Research Program Report 88-4, M.P. De Luca and I. Babb (eds.), 29–59 (1989)

Observations of vent fluids collected in 1986 with the submersible Pisces IV from the ASHES vent field at Axial Volcano, Juan de Fuca Ridge suggest that hydrothermal fluids similar to those vented at other sediment-starved ridgecrest sites are being discharged along with unprecedented Cl-poor, gas-enriched fluids that are likely the result of phase separation. Anomalously low concentrations of silica, calcium, manganese and iron were also observed in the Cl-poor vent fluids. New sampling tools and protocols conceived to overcome the interpretive limitations inherent to conventional vent fluid data were tested during 1987 using the Deep Submersible Alvin. A Submersible-coupled In situ Sensing and Sampling System (SIS) enabled a more efficient collection of high quality vent fluid samples coincident with the sensing of temperature. An In Situ Chemical Analyzer (ISCA), based on the technology of flow injection analysis and configured to monitor the chemical output of a warm spring vent for HS, Fe, pH, and temperature, was deployed with partial success for 3 days at the ASHES vent field. The integral role of vent fluid studies in testing the hypothesis that hydrothermal venting along the Juan de Fuca/Explorer/Gorda Ridge system plays a major role in controlling the chemistry of the northeastern Pacific Ocean is identified and supported.