The East Pacific Rise 8° -11° N Integrated Studies Site (ISS); Update and Opportunities

The 8° -11° N segment of the East Pacific Rise (EPR) represents a dynamic, fast-spreading type of mid-ocean ridge selected for focused interdisciplinary study within the Ridge 2000 program. Diverse fast spreading environments are encompassed by the site including a hierarchy of axial segments and discontinuities. The site "bull's- eye" is at 9° 49' - 9° 51' N where numerous high temperature vents and diffuse flow communities have been mapped and monitored over the past 10 years. Concentric circles around the bull's eye encompass ridge segments at a range of scales, from the first-order segment bounded by the Siquieros and Clipperton transform faults to the fourth-order segments which include the extent of the 1991 and 1992 volcanic eruptions. Five-year goals for the site include a working model of mantle flow and melt supply; detailed imaging of subseafloor structures and relationships to vent communities and chemistry; quantitative data about microbes and macrofauna and linkages with fluid flow, tectonics, and magmatism; quantification of the heat flux into the water column; and linkages and temporal variation in geological, chemical, and biological parameters. Field programs at the EPR site in 2004 began with a multi-program cruise lead by Schouten and colleagues that included dives for volcanological objectives, the deployment and testing of an array of in situ chemical sensors for use in monitoring vent fluids (Seyfried), and deployment of sample collection plates for a study of the role of microbes in the weathering of ocean crustal rocks (Edwards and Bach). A magnetotelluric and controlled source electromagnetic study (Constable) was carried out from 9° 30-50'N targeting mantle and crustal structure. The next cruises at this site were the time series fluid sampling program of Von Damm and biological study of Lutz and colleagues, both programs focused at the site "Bull's eye". OBSs deployed in Fall 2003 for a microseismicity monitoring study (Tolstoy and Waldhauser) were recovered and redeployed during the Lutz et al. cruise, and temperature probes were deployedduring the Von Damm cruise. Programs scheduled for 2005 include ongoing monitoring studies of seismicity and vent fauna. Recently funded studies at the EPR site include an investigation of larval dispersal (Mullineaux) and a geodetic study of seafloor motions using pressure sensors deployed along the ridge crest from roughly 9° -10° N (Cormier et al.). A three-dimensional multi-channel seismic study of subsurface structure (Mutter et al.) is scheduled for early 2006. An overview of these and other exciting on-going and upcoming studies within the EPR ISS will be presented.