Hydrothermal exploration by AUV: Progress to-date with ABE in the Pacific, Atlantic & Indian Oceans

During 2004-08 we have conducted a series of five expeditions mobilizing the ABE autonomous underwater vehicle aboard various research ships of opportunity to prospect for and locate sites of hydrothermal activity along sections of back-arc basin and/or mid-ocean ridge where mid-water hydrothermal plumes had previously been detected. In all circumstances, to date, these expeditions have led to discovery of at least one new hydrothermal field at the seafloor - in the Lau Basin and on the equatorial East Pacific Rise, southern Mid-Atlantic Ridge and SW Indian Ridge, on very fast-, fast-, slow- and ultraslow-spreading ridges, respectively. Our method requires three stages of deployment which, to date, have always been conducted with the aid of combined LBL/DVL navigation. First: in situ sensor mapping of the water column is carried out in plan-view (along constant depth surfaces) to locate the core of a dispersing hydrothermal plume; Second: high-resolution bathymetric mapping of the underlying seafloor is carried out along grid-lines sufficiently close-spaced to ensure interception of rising buoyant plumes (also detected by in situ sensors); Third: photo-reconnaissance, 5 m above the seafloor, over areas of active venting and associated biological communities. This approach has already proven effective for first order exploration for (e.g.) the Census of Marine Life but improvements sought for the future include vehicle endurance and survey speed, improved in situ sensor payloads, ldquodecision-makingrdquo autonomy at the seafloor and introduction of sampling capability (e.g. via the Nereus H-ROV).