U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications
Hydrothermal plumes, formed by the turbulent mixing of hot vent fluids and ambient
seawater, are potent tools for locating, characterizing, and quantifying seafloor
hydrothermal discharge. Hydrographic, optical, and chemical tracers have all been used
successfully to identify plumes. Observational techniques have progressed from discrete
samples collected on vertical casts to continuous, in situ physical and chemical analyses
that produce two- and three-dimensional plume maps. We present here a synthesis of
available data from spreading centers throughout the world ocean wherever plumes have been
mapped on a vent-field, segment, or multisegment scale. About 3% of the global divergent
plate margin has been scrutinized for hydrothermal plumes; close to twice that distance
has been sampled at least cursorily. Along medium- to superfast-spreading ridges in the
eastern Pacific, where the most detailed work has been done, venting is common and plumes
overlie 20-60% of the ridge crest length. Plumes are found also wherever careful surveys
have been conducted in western Pacific marginal basins. Slow-spreading ridges in the North
Atlantic, sampled over greater length scales but in less detail than in the Pacific,
appear to have a comparatively low incidence of venting. Little is known of plume
distributions over ridges in other oceans. These studies confirm that hydrothermal venting
is present across the entire range of spreading rates and that continuous, underway plume
surveys are the most efficient means available for locating seafloor discharge sites.
Moreover, plume surveys are the only practical approach to mapping hydrothermal discharge
patterns over multisegment spatial scales, and to integrating hydrothermal fluxes on a
vent-field or larger scale. The plume surveys conducted to date indicate that the
incidence of hydrothermal plumes over the ridge axis increases directly with increasing
spreading rate. This observation supports models of crustal evolution that predict a
direct relationship between the axial hydrothermal heat flux and spreading rate. This
conclusion must be tempered, however, by the recognition that most of the global spreading
center system remains unexplored for hydrothermal activity.