DISTRIBUTION OF DISSOLVED SULFIDE, METHANE, AND MANGANESE NEAR THE SEA-FLOOR AT THE LUCKY-STRIKE (37-DEGREES-17'N) AND MENEZ-GWEN (37-DEGREES-50'N) HYDROTHERMAL VENT SITES ON THE MID-ATLANTIC RIDGE

During the 1994 DIVA-1 cruise, the distribution of sulfide, methane an d total dissolvable manganese (TDM) in the water column was examined n ear the seafloor at two locations on the mid-Atlantic ridge (MAR) affe cted by hydrothermal venting. Samples for this study were obtained usi ng a miniature rosette mounted on the Nautile submersible and hydrogra phic 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 measurem ents can be used to describe hydrothermal plumes. In the first study a rea, called the Lucky Strike hydrothermal field (MAR at 37 degrees 17' N), the distribution of hydrothermal tracers ( < 5 m above the seafloo r) was strongly influenced by the location of known hydrothermal vents . A study of water samples collected above the Tour Eiffel smoker show s that for the buoyant plume, sulfide is rapidly removed, while TDM an d methane behave similarly (conservatively) upon mixing with ambient s eawater. At the Menez Gwen hydrothermal field, which was the second si te and which was discovered during the DIVA-1 cruise, a distribution m ap (3 km x 4 km) of sulfide, TDM, and methane concentrations was compl eted. 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 wes tern wall of the axial graben of the Menez Gwen segment. (C) 1998 Else vier Science Ltd. All rights reserved.