Distribution of dissolved sulfide, methane, and manganese near the seafloor at the Lucky Strike (37°17′N) and Menez Gwen (37°50′N) hydrothermal vent sites on the mid-Atlantic Ridge

During the 1994 DIVA-1 cruise, the distribution of sulfide, methane and total dissolvable manganese (TDM) in the water column was examined near the seafloor at two locations on the mid-Atlantic ridge (MAR) affected by hydrothermal venting. Samples for this study were obtained using a miniature rosette mounted on the Nautile submersible and hydrographic data was collected using a CTD probe. Water samples were analyzed on board ship (sulfide and methane) or at the shore laboratory (TDM). The results presented here show that nanomolar level sulfide measurements can be used to describe hydrothermal plumes. In the first study area, called the Lucky Strike hydrothermal field (MAR at 37°17′N), the distribution of hydrothermal tracers (<5 m above the seafloor) was strongly influenced by the location of known hydrothermal vents. A study of water samples collected above the Tour Eiffel smoker shows that for the buoyant plume, sulfide is rapidly removed, while TDM and methane behave similarly (conservatively) upon mixing with ambient seawater. At the Menez Gwen hydrothermal field, which was the second site and which was discovered during the DIVA-1 cruise, a distribution map (3 km×4 km) of sulfide, TDM, and methane concentrations was completed. The highest tracer concentrations were found in close proximity to the vent field and ca. 1 km to the west of the venting site. These and other data are evidence for possibly additional venting on the western wall of the axial graben of the Menez Gwen segment.