A closeup of the primary tool used to map hydrothermal plumes. A ring of plastic sampling bottles surrounds the CTD, an electronic package that monitors seawater Conductivity, Temperature, and Depth. The bottles are closed on command from the ship, usually when a scientist monitoring the sensors sees strong evidence of a plume. The CTD carries other sensors that measure optical light backscattering, seawater pH and Eh, and other chemical species. Pictured here are Ed Baker (left) and Cornel deRonde (right).