GEOLOGICAL, BIOLOGICAL, AND CHEMICAL LINKAGES WITHIN THE ENDEAVOUR HYDROTHERMAL SYSTEM

The Endeavour Segment of the Juan de Fuca Ridge is one of the most vigorously venting hydrothermal systems along the global mid-ocean ridge spreading network. In part because of its spectacular attributes it is now a Canadian Marine Protected Area, and it has been designated by the US RIDGE Program as one of three Integrated Studies Sites. Along a 15 km long portion of the segment, there are at least five black smoker fields, spaced ~ 2-3 km apart. The most active field, the Main Endeavour Field MEF), hosts over 100 black smoker chimneys, many of which in 2000 were venting 380C fluids. In contrast, the most northerly field (Sasquatch), ~ 6 km to the north appears to be in a waning stage of activity with very few smokers and a continuous array of extinct sulfide pinnacles that can be followed for >500 m. Both boiling and condensation in the subsurface influence the chemistry of the vent fluids, and perhaps the microbial communities as well. In all fields, lower temperature, diffusely venting fluids are associated with high temperature flow, forming discontinuous aureoles of tubeworm patches around the fields. There are also localized areas of diffuse flow distal to sites of high temperature outflow. A continuum of venting styles and edifice morphology are present within this system, in addition to well-defined gradients in temperature and fluid chemistry (e.g salinity) along axis. This along axis variability is also expressed at depth as shown by seismic imaging that defines a very strong reflector beneath the MEF (Detrick et al., 2002). However, to the north, beneath Sasquatch it is significantly weaker, and to the far south (beneath Mothra) it deepens dramatically. That magmatic processes dramatically influence these systems is shown by perturbations associated with magmatic intrusion in 1999-2000. This resulted in increased venting temperatures of 15C, CO2 concentrations five times higher than those measured in 1998, a corresponding increase in H2, and He/heat ratios that increased significantly (Lilley et al., 2003). Macro- and microbiological communities were also significantly influenced. A very significant increase in floculant material in diffuse venting systems was observed for several months following this event and there has been a dramatic increase in macrofaunal growth during the subsequent three years.