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Seabed Fluid Dynamics and Gas HydratesSediments scraped from subducting plates form large accretionary wedges attached to the continental landmass. Fluids moving within these sediments transport chemical compounds that assist in sediment diagenesis, hydrocarbon concentration and clathrate formation. Long-term time-series observations at deep-ocean sites could directly measure rates of transfer of these compounds into the water column. The Juan de Fuca plate exhibits a range of sea floor characteristics, from rock near the ridge to thick sediment near the continental margin. Instrumented boreholes connected to the NEPTUNE array could provide long-term measurements of crustal responses to events and cyclic perturbations, while sea floor instruments could measure episodic and seasonal variations in nutrient fluxes, and other physical, chemical and biological parameters. Benthic 'rovers' based at NEPTUNE observatories could conduct periodic surveys of nearby areas. The margins of the continents are shaped by sediment transported across the continental shelves and down over the shelf edge. This process carries organic and inorganic material into the deep ocean, including carbon and anthropogenic pollutants. It often involves episodic, violent phenomena like turbidity currents and slumps. The NEPTUNE area includes the largest source of sediment to the Pacific between Alaska and South America, the Eel River in Northern California. Cabled observatories with ample electrical power and control from shore could provide real time observations of particulate fluxes and related water movements and permit quick response to events, independent of weather. Science Themes
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