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	Manifestations of fluid flow and biogeochemical turnover at cold seeps of the Aleutian subduction zone Peter Linke, Klaus Wallmann, Erwin Suess, Gerhard Bohrmann, Heiko Sahling, Anke Dahlmann GEOMAR, Research Center for Marine Geosciences Dept. of Marine Environmental Geology Wischhofstr. 1-3 Kiel, 24148 Germany Along 3 sectors of the eastern Aleutian Trench characteristic manifestations of fluid flow were observed and sampled. In one area, in situ oxygen fluxes were measured at a water depth of 5000 m using a TV-guided benthic flux chamber. The obtained fluxes were two orders of magnitude greater than the normal benthic consumption on the continental margin off Alaska. Pore water profiles obtained from sediments below a seep site indicated high concentrations of sulphide, methane, and ammonia. These reduced inorganic compounds were transported to the seep site by fluids expelled from deeper anoxic sediment layers by the force of plate convergence. The tectonically driven Darcy flow of these fluids was determined from the biogeochemical turnover in vent communities and found to be 3.4 ± 0.5 m y-1. A model was used to quantify the transport of silica, Ca2+ , and sulfate via diffusion, advection, and bioirrigation through the surface sediments of a seep site. By fitting the model curves to the measured pore water profiles a nonlocal mixing coefficient of 20-30 y-1 was determined which demonstrates that the transport of solutes within the surface sediment and across the sediment-water interface is dominated by the activity of the seep fauna. From these data it becomes evident that the seep biota shape their immediate environment, control the sediment-water exchange, and the benthic flux at seep sites.
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