1999 Projects: Benthic processes
Fluid flow, diagenesis, and chemical fluxes in the oceanic crust
There are many examples of fluid flowing from the seafloor in addition to the spectacular hydrothermal vents on mid-ocean ridges. Seawater also circulates through the oceanic crust due to the intrusion of basaltic magma at hotspots and differential cooling of the lithosphere on mid-ocean ridges and flanks. And, fluid is expelled from the seafloor due to compression along zones of subduction and differences in pore pressure in the sediments on continental shelves and margins. In each of these diverse settings, the crust and fluid are both altered as they react with each other. These temporal and spatial interactions lead to chemical fluxes to and from the ocean that are potentially important to global geochemical cycles within the ocean. Unfortunately, these reactions and fluxes are poorly understood due to the lack of instrumentation capable of collecting data at the needed resolution.
Under this project we will expand our understanding of these chemical processes by continuously sampling and analyzing fluids from the seafloor in several diverse settings: Monterey Bay, Juan de Fuca Ridge, and the Axial and Loihi seamounts. In Monterey Bay we will deploy OsmoSamplers, OsmoAnalyzers, and pore-water equilibrators ("peepers") to measure chemical profiles of sediment pore-waters at cold seeps. These measurements will help determine geochemical conditions at depth and the sources and chemical compositions of the fluids.
Outside Monterey Bay at several hydrothermal sites, two types of continuous sampling devices recently developed at MBARIAcid Addition OsmoSamplers and Iron OsmoAnalyzershave been deployed. On the eastern flank of the Juan de Fuca Ridge, data from these samplers will allow us to bridge the gaps between the sporadic sampling of seafloor chemistry previously done only when personnel and submersibles visited the area. From these data we will derive a better understanding of the nature of the subseafloor "plumbing" and associated chemical transformations there. Long-term, continuous samplers also will be deployed at deep-sea volcanic settings (Loihi and Axial Seamounts) to monitor chemical changes over time in the chemical fluxes following tectonic or volcanic activity. These investigations over a range of settings will allow us to study the processes of evolution of the crust along a continuum, from the point of origin at the mid-ocean ridge axis, to the ridge flanks, to subduction zones, where it is ultimately recycled.
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Last updated: 07 October 2004