The very essence of a hydrothermal system is transfer of heat by a convecting fluid. Despite this central role played by heat transfer, there exists a woefully poor knowledge of the flux of heat from seafloor hydrothermal systems and its variation through time. For the well-studied Main Endeavour Field (MEF) on the Juan de Fuca Ridge, existing estimates vary widely (from -100 to -10000 MW) and have large uncertainties (often spanning an order of magnitude). The Autonomous Benthic Explorer (ABE) will be equipped with sensors to measure the velocity, temperature and salinity of rising hydrothermal plumes. Data from a series of ABE dives will provide precise, replicate measurements of the heat flux, achieving uncertainty better than 20%. These dives will be complemented with a program of hydrographic work conducted at comparable spatial scales.
