TOPOGRAPHIC CONTROL OF A DISPERSING HYDROTHERMAL PLUME

Deep-sea hydrothermal vents represent a major source of heat and chemi cals to the oceans and support endemic chemosynthetic biological commu nities. To fully understand the impact of hydrothermal activity upon t he oceans, however, requires investigation of both the physical and th e biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans. We have recently conducted a detailed multidisciplinary study of the late ral dispersion of the hydrothermal plume emitted from the Rainbow vent site near 36 degrees 15'N, Mid-Atlantic Ridge. Combining velocity mea surements from a lowered ADCP, optical back scatter measurements from a deep-tow CTD and methane measurements from bottle samples we are abl e, for the first time in the Atlantic, to trace a neutrally buoyant pl ume for a distance of over 50 km. The path of the plume is seen to be heavily controlled by the local topography with a general northeast mo vement of water. Both particle and methane concentrations decrease dow nstream over the length of the observed plume, The dataset provides an excellent opportunity to study the mixing and biogeochemical processe s active in a hydrothermal plume and estimate fluxes of biogeochemical constituents. (C) 1998 Elsevier Science B.V. All rights reserved.