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Benthic processes

Continental margin fluids and gases
Lead Scientist: Charles Paull
Project Manager: Bill Ussler

We propose a multi-year study of the processes associated with movement of fluids and gases from their source, through the seafloor, and into the ocean. Our efforts are similar to previous MBARI projects associated with the investigation of seafloor seepage phenomena.

We intend to focus on the following specific themes:

(1) Biogeochemistry of Sub-Seafloor Fluids. We intend to focus on the processes that affect fluid and microbial conditions where redox states change at and near the seafloor. Where chemically reduced fluids discharge onto the seafloor, focused seep communities occur.

However, similar horizons of rapid organic and inorganic change will occur wherever there are sharp geochemical boundaries or accumulations of microbial substrates in the subsurface. We will focus investigations on (a) the sulfate-methane interface, and (b) hydrogen production and consumption within continental margin sediments.

(2) Geomorphologic Significance of Fluid and Gas Venting. The escape of fluids and gas through the seafloor are purported to influence the local geomorphology. A number of geomorphic features are commonly considered to be associated with fluid processes (including the development of pockmarks, slumps, rills, and box canyon heads). Moreover, the role of geologic structures (faults, canyon heads, slide scars, and laterally truncated aquifers) in focusing fluid flow and the role of gas and gas hydrates are poorly understood. Thus, we will conduct studies of the sub-surface fluid chemistry in selected geomorphic regimes. This project will be integrated with the companion canyon and continental margin process project.

(3) Isotopes as Tracers of Mass Transport at Seafloor Seepage Sites. Wherever exotic fluids discharge onto the seafloor, organic and diagenetic reactions will occur which include chemosynthetic primary production and formation of authigenic minerals (e.g. carbonates, barite, and sulfides). To understand the processes that occur at these sites, we intend to conduct selected detailed sampling, geochemical and isotopic measurements on all significant fluid, gaseous and solid phases that contain carbon, sulfur, and nitrogen at selected sites.

(4) Mass Flux at Seafloor Seepage Sites. The overall significance of seafloor seepage is related to the total flux of fluids. The rates of flow, the composition of the fluids and the surface area that is affected determine the total flux. While in the long term we are interested in all of these factors, we believe that the percent of the sea floor that is affected by seepage is currently the least known factor within the Monterey Bay region. Thus, we will initially try to determine the area that is affected by studying the existing dive observations in the MBARI video archives and combining them with other data to generate statistics on the extent seepage affects this area.