HYDROGRAPHY AND GEOCHEMISTRY OF SEA-SURFACE HYDROTHERMAL PLUMES RESULTING FROM HAWAIIAN COASTAL VOLCANISM

The entry of lava into the ocean at Kilauea Volcano, Hawaii has produc ed extensive sea surface hydrothermal plumes. Studies at this site ove r 1989-1991 showed that particle-rich, chemically altered thermal plum es of 1-3 m thickness can be mapped for distances up to 2 lan from the entries using an array of physical and chemical tracers. Particle con centrations in the plumes were as high as 65 mg L(-1), and produced li ght attenuation anomalies exceeding 11 m(-1); the maximum observed sea water temperature was 69 degrees C. The following extremes in plume ch emical markers were measured: H-2, 2.1 mu M; dissolved Mn, 320 nM; dis solved Si, 55 mu M; Sigma CO2, 1.6 mM; alkalinity, 1.5 meg L(-1); and pH, 7.1. Dissolved H-2 linearly increased, and Sigma CO2, pH, and tota l alkalinity decreased with increasing seawater temperature. Dissolved Mn and Si also increased with increasing temperature but were better correlated with each other, indicating that heat is not conserved in t he surface plumes. Heat and mass inputs to the ocean are comparable to those from mid-ocean ridge crest vent fields.