THE GEOCHEMISTRY OF SUBMARINE VENTING FLUIDS 



AT AXIAL VOLCANO, JUAN DE FUCA RIDGE: 



NEW SAMPLING METHODS AND A VENTS PROGRAM RATIONALE 



Gary J. Massoth 1 , Hugh B. Milburn 1 , Stephen R. Hammond 2 , 

 David A. Butterf ield 3 , Russell E. McDuff 3 , and 

 John E. Lupton^ 



l-NOAA/PMEL, Seattle, WA 98115 



2 Mark 0. Hatfield Marine Science Center, Newport, OR 98195 



°School of Oceanography, University of Washington, 



Seattle, WA 98195 



^Marine Science Institute, University of California, 



Santa Barbara, CA 93106 



ABSTRACT 



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 I_n situ Sensing and Sampling System (SIS 3 ) 

 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 H2S, Fe 2+ , 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. 



INTRODUCTION 



The operating hypothesis of the NOAA VENTS Program as formu- 

 lated within its Implementation Plan is: Hydrothermal venting 

 along the Juan de Fuca/Explorer/Gorda Ridge system plays a major 

 role in controlling the chemistry of the northeastern Pacific 

 Ocean. Fundamental to the testing of this hypothesis are 

 determinations of the chemical source strengths of hydrothermal 



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