U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications
Seafloor hydrothermal circulation is the principal agent of energy and mass exchange between the ocean and the earth's crust. Discharging fluids cool hot rock, construct mineral deposits, nurture biological communities, alter deep-sea mixing and circulation patterns, and profoundly influence ocean chemistry and biology. Although the active discharge orifices themselves cover only a minuscule percentage of the ridge-axis seafloor, the investigation and quantification of their effects is enhanced as a consequence of the mixing process that forms hydrothermal plumes. Hydrothermal fluids discharged from vents are rapidly diluted with ambient seawater by factors of 104-105 [Lupton et al., 1985]. During dilution, the mixture rises tens to hundreds of meters to a level of neutral buoyancy, eventually spreading laterally as a distinct hydrographic and chemical layer with a spatial scale of tens to thousands of kilometers [e.g., Lupton and Craig, 1981; Baker and Massoth, 1987; Speer and Rona, 1989].
Early investigations focused on plumes simply as indicators of nearby discharge sources. More comprehensive studies, however, quickly demonstrated that plumes integrate hydrothermal heat and mass flux [Baker and Massoth, 1987; Rosenberg et al., 1988; Rudnicki and Elderfield, 1992], provide natural laboratories for measuring the chemical reactions that control the ultimate dispersal of various hydrothermal species [Klinkhammer et al., 1983; Mottl and McConachy, 1990; Feely et al., 1991; German et al., 1991; Metz and Trefry, 1993; Rudnicki and Elderfield, 1993; Kadko, 1994], disperse vent-specific biological populations [Mullineaux et al., 1995], track deep-ocean circulation patterns [Lupton and Craig, 1981; Reid, 1982], and, in general, provide opportunities for identifying and quantifying the effects of hydrothermal activity. In this paper we focus narrowly on the use of plumes as a tool for hydrothermal exploration and geological interpretation. We begin by outlining commonly used techniques for producing detailed maps of the hydrographic and chemical anomalies produced by plumes along oceanic spreading centers. We then review those ridge-crest areas in the Pacific (including the western Pacific marginal basins), Atlantic, and Indian Oceans where sufficient data exist to map, or at least detect, plumes at vent-field, segment, or multisegment scales. Many of these data are new or formerly available only in fragmented form. Finally, we offer some geological interpretations of the data, using as an example the emerging coherence between hydrothermal discharge patterns and ridge-crest spreading rate.
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