The section of the southern East Pacific Rise (S EPR) between the Garrett Transform and the Easter Microplate has one of the fastest spreading rates on the global ridge system and is the locus of the most intense hydrothermal activity, reflected in the density of venting sites and in the water column plumes, of all mid-ocean ridge (MOR) systems studied to date. Recent submersible and surface ship visits to this region by the French and Japanese/American (PMEL NOAA) have revealed that hydrothermal plumes overlay over 60% of the ridge crest between 14Ã50' and 18Ã40' S. Furthermore, dramatically variable vent fluid chemistries result in distinct, and unusual signatures in the plume waters. The intense, nearly continuous, and dynamic nature of the hydrothermal system over this section of the S EPR provides for the most focused impact anywhere of the global ridge system on the ocean geochemistry and biosphere. Research efforts focused on the hydrothermal venting and plumes of this system will continue with two NSF funded collaborative projects. M. Lilley, K.Von Damm, and J. Lupton have been funded to perform a 25 dive submersible program on the S EPR, focusing on the collection of vent fluds from several regions of documented venting south of 17ÃS. R. Collier has been funded to extend the submersible observations of the hydrothermal vent characteristics to the water column hydrothermal plume at the local (vent field) to segment scale. In addition, the Japanese/PMEL NOAA are continuing their joint, interdisciplinary investigation of the distribution and composition of hydrothermal venting/plumes along the EPR axis south of the Garrett. A study of the geomicrobiology of the intense S EPR hydrothermal plumes will be made in collaboration with the above funded programs. The goals of the present proposal are highly complementary to and will extend the primary goals of the funded Lilley/Collier programs; these studies will assess the rate of change of microbial populations and biogeochemical processes in an evolving plume. Collaboration with the Japanese/PMEL- NOAA (RIDGE Flux) S EPR project will allow the determination of representative hydrothermal mineral and organic C vertical fluxes at some of the same sites and to relate these fluxes to biogeochemical transformation rates of hydrothermal constituents and metalliferous sediment distributions and accumulation rates. Analyses and interpretation of transformation processes and flux rates will be completed in close collaboration with M. Lilley (UW) (and K.Von Damm and J. Lupton), R. Collier (OSU), Japanese (T.Urabe, J. Ishibashi, H. Kawahata, K. Marumo, A. Marnyarna, and colleagues) and PMEL /NOAA (E. Baker, R. Feely, G. Massoth, D. Butterfield and colleagues) scientists.
