SGER: Changes in vent fluid chloride and volatile content as a result of the 2006 eruption at 9N, EPR

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Intellectual Merit: This proposal requests funding to cover the costs incurred in participating in two cruises to establish a baseline data set for understanding the changing chemistry associated with the recent volcanic eruption at the 9 N East Pacific Rise Ridge 2000 Integrated Studies Site hydrothermal system. The initial cruise took place in June 2006 and resulted in initial volatile data that indicated significant changes in gas concentrations since the latest prior visit to the site in November, 2004. In addition, a resistivity instrument capable of measuring chloride concentrations on a 30 sec interval was placed in a 375 C vent during the June 2006 cruise. By monitoring changes in chlorinity of vent fluids, constraints are placed on time-changes in the degree and nature of phase separation that occurs within the water-rock reaction system. This provides important controls on hydrothermal alteration, since chloride has an important role in determining mieral solubility. This instrument will be recovered in November 2006 and two additional instruments will be deployed for one year duration. On the order of fifty fluid samples will also be collected in November 2006, the gas contents extracted and returned to the laboratory for concentration and isotopic analyses. These data collected as soon as possible after the eruption will be of great use in helping to understand the overall behavior of the hydrothermal system to a magmatic perturbation. Broader Impacts: This research is part of a multi-disciplinary inter-institutional collaboration. This project will directly address key questions from the NSF Ridge 2000 program concerning the relationship of magmatism to ocean chemistry and to the geochemical environment that supports an extremophilic biosphere of chemosynthetic primary producers.