A segment-scale survey of the Broken Spur hydrothermal plume

We conducted a segment-scale hydrothermal plume survey of the Broken Spur segment, 29 degrees 00-20'N, Mid-Atlantic Ridge (MAR). The purpose of the study was to identify the distribution of sources of venting throughout the segment as part of a larger study of hydrothermal fluxes. Evidence from plume particle concentrations las deduced from in situ nephelometer data) and total dissolvable Mn (TDMn) analyses (from discrete water samples) indicated a restricted source of venting close to the segment centre, coincident with the previously known vent-site. No other pronounced plume signals were observed outside an area bounded by 29 degrees 07.5-12.5'N and 43 degrees 10-12'W, representing less than 10% of the >300 km(2) of deep water (>2500 m) within the segment. In addition, however, low-level (<2 nmol l(-1)) deepwater TDMn concentrations reveal a pervasive enrichment throughout the segment of greater than or equal to 0.15 nmol l(-1). For the 4 x 10(11) m(3) of deepwater within the Broken Spur segment, this corresponds to a standing crop of 6 x 10(4) mol of hydrothermal Mn. Future studies of long-term current flow will allow the flux of dissolved Mn out of the segment to be established and will investigate the partitioning of its source, between high temperature and axial diffuse flow. (C) 1999 Elsevier Science B.V. All rights reserved.