Ascending and descending particle flux from hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge

Bio-acoustic surveys and associated zooplankton net tows have documented an omalously high concentrations of zooplankton within a 100 m layer above the hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge. These and ot her data suggest that congregating epi-plume zooplankton are exploiting a f ood substrate associated with the hydrothermal plume. Ascending, organic-ri ch particles could provide a connection, Consequently, two paired sequentia lly sampling ascending and descending particle flux traps and a current met er were deployed on each of three moorings from July 1994 to May 1995. Moor ing sites included an on-axis site (OAS; 47 degrees 57.0'N, 129 degrees 05. 7'W) near the main Endeavour vent field, a "down-current" site 3 km west of the main vent field (WS), and a third background station 43 km northeast o f the vent field (ES). Significant ascending and descending particle fluxes were measured at all sites and depths. Lipid analyses indicated that ascen ding POC was derived from mid-depth and deep zooplankton whereas descending POC also contained a component of photosynthetically derived products from the sea surface. Highest ascending POC fluxes were found at the hydrotherm al plume-swept sites (OAS and WS). The limited data available, however, pre cludes an unequivocal conclusion that hydrothermal processes contribute to the ascending flux of organic carbon at each site. Highest ascending to des cending POC flux ratios were also found at WS. Observed trends in POC, PMn/ PTi, and PFe/PTi clearly support a hydrothermal component to the descending flux at the plume-swept WS site (no descending data was recovered at OAS) but not at the background ES site. Alternative explanations for ascending p article data are discussed. First-order calculations for the organic carbon input (5-22 mg C m(-2) d(-1)) required to sustain observed epi-plume zoopl ankton anomalies at Endeavour are comparable both to measured total POC flu x to epi-plume depths (2-5 mg C m(-2) d(-1): combined hydrothermal and surf ace derived organic carbon) and to estimates of the total potential in situ organic carbon production (2-9 mg C m(-2) d(-1)) from microbial oxidation of hydrothermal plume H-2. CH4 and NH4+. (C) 2001 Published by Elsevier Sci ence Ltd. All rights reserved.