DISSOLVED AND PARTICULATE TRACE-METALS IN HYDROTHERMAL PLUMES AT THE MID-ATLANTIC RIDGE

Seawater samples from the non-buoyant plume have been collected at the TAG (26 degrees N) and Snakepit (23 degrees N) hydrothermal sites on the Mid-Atlantic Ridge (MAR), and analysed for dissolved (<0.4 mu m) a nd particulate (>0.4 mu m) trace metals. Up to 50% of vent fluid Fe is present in the <0.4 mu m fraction in the non-buoyant plume. Increases in particulate concentrations of Cd are accompanied by a reduction in dissolved Cd to levels below ambient seawater. We show that dissolved Cd is scavenged from seawater in the buoyant section of the plume whi le Cd re-dissolves from the particles in the non-buoyant plume. Up to 43% of hydrothermally injected Cu is found in the <0.4 mu m fraction i n the nonbuoyant plume.