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 methane1–3. 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.