RECENT ADVANCES IN UNDERSTANDING OF THE ROLE OF FLUID FLOW THROUGH CONTINENTAL MARGINS IN EARTH SYSTEM PROCESSES

Advective fluid flow into, across, and out of continent-ocean interfaces has been known to occur for years, but its significance to the larger earth system is only beginning to be appreciated. Margin fluids transport heat and solutes, and are linked with sediment compaction, diagenesis, and erosion at many scales. The relative contributions, however, of meteoric, oceanic, and lithospheric fluid sources in margin settings are poorly constrained, and pathways and timescales of fluid migration are equally mysterious. Mechanisms that affect these fluids are generally difficult to measure and study except in the shallowest sediments. New instruments and methods that are advancing understanding of these systems include: electrical resistivity techniques for characterizing fluid properties and flow pathways, geochemical methods for dating fluids and determining their recharge histories from dissolved gases, radioisotopic tracers of water-sediment interaction on grain to margin scales, novel drilling techniques and downhole tools for logging in situ properties and collecting samples of margin fluids, innovative seepage meter designs that permit collection of time series of discharge and water quality variation, and high-resolution analysis of submarine tufas and other authigenic and biogenic deposits to reconstruct margin flow histories. Using these and other novel techniques, active fluid flow research includes: 1) localized studies of impacts of nearshore submarine ground-water discharge on coastal ecosystems; 2) examination of specific venting features in deeper water such as mud volcanoes, brine seeps associated with salt domes, and cold seeps supporting chemosynthetic communities; 3) regional and shelf-scale investigations of spring sapping and submarine canyon formation, variable cross-shelf flow driven by glacial-interglacial sea-level change, and hydrogeology and thermodynamics of modern glaciated and permafrost-bearing shelves; 4) development of dynamic models of gas hydrate occurrence and stability explicitly incorporating fluid flow; and 5) quantification of contributions from margin fluid cycles to elemental budgets for the global ocean. A general overview of recent research and important milestones in margin fluid flow will be presented.