Entrainment and vertical transport of deep-ocean water by buoyant hydrothermal plumes

Submarine hydrothermal vents produce effluent plumes in the water column which can be easily detected with tracers such as ³He, manganese and methane^1-3. Comparison of the tracer concentrations and temperature anomalies in such plumes with direct measurements of the pure vent waters shows that the plumes are typically mixtures of 1 part vent water with 10⁴ parts ambient sea water¹. However, the extent to which hydrothermal plumes entrain and transport sea water and contribute to deep-ocean mixing is not known. We present here hydrographie data collected in the vicinity of an active hydrothermal field on the Endeavour segment of the Juan de Fuca Ridge where a well-defined effluent layer resides in the water column ~200 m above the depth of the vent field. The temperature and salinity signature of this layer indicates that a small volume of hot vent water can be very efficient at entraining ambient sea water. Directly above the Endeavour vent field, the effluent layer is composed of 0.01% vent water, 30% ambient water normally found at that depth, and ~70% entrained water which has been transported from deeper in the water column.