Transport and settling of organic material in a deep-sea hydrothermal plume: evidence from particle flux measurements

Abstract

Results of time-series experiments using moored sediment traps to quantify the settling hydrothermal particle flux above Endeavour Ridge suggest that the oceanic effects of carbon production associated with mid-ocean ridge hydrothermal systems are not limited to the area immediately surrounding seafloor vents. We hypothesize that particulate organic material is entrained, possibly generated in, and removed from the hydrothermal plume at least 2 km from a site of active venting. More than 95% of the organic carbon collected 21 m directly above a site of hydrothermal fluid discharge has a near-bottom, chemosynthetic source. Up to 62% of the total organic carbon flux measured 100–200 m above bottom and ≈2 km northeast of the vent field (47°57.05′N, 129°06.30′W, depth ≈ 2200 m) is chemosynthetic. Despite injectionof organic carbon at plume depths, perplexing minima in the fluxes of biogenic and inorganic detrital particles are observed at plume-depth 1900 m traps. Possible explanations for the attenuated particle fluxes include removal of material from the laterally advecting plume by zooplankton feeding, biologically mediated particle breakdown, and the effect of currents on particle collection. Patterns of particle flux we observed indicate simultaneous addition and removal of organic material at plume depths (i.e. nutrient cycling), and support the hypothesis that laterally dispersing hydrothermal plumes are three-dimensional, biologically active zones in the deep sea.