Hydrological and geochemical anomalies associated with hydrothermal activity in SW Pacific marginal and back-arc basins

Hydrological and geochemical anomalies were investigated in the Woodlark, Lau and Manus basins, all regions of active spreading associated with island arcs of the southwest Pacific. The water column in all areas provides clear indications of hydrothermal activity. In the Woodlark Basin hydrothermal materials behave diffusely, with dissolved Mn concentrations 2-4 x background and slightly elevated temperatures somewhat above the seabed, and also near-bottom plumes with dissolved Mn 4-6 x background and no changes in turbidity, derived from weak low-temperature vents. In the eastern Lau Basin a plume with high turbidity and very high dissolved Mn (up to 2000 ng/l, about 50 x background) was discovered. Strong plumes from high-temperature vents were encountered in the eastern Manus Basin, and from grey smokers in the central Manus Basin, distinguished by turbidity, concentrations of dissolved Mn and suspended micro-elements. All plumes show positive temperature and salinity anomalies. (C) 1997 Elsevier Science B.V.