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Benthic processes

Continental margin processes
Project Manager: Bill Ussler
Lead Scientists: Charlie Paull, Gary Greene, Keith Kvenvolden

The seagoing and laboratory efforts of this group of MBARI scientists to study the processes associated with continental margin development address two themes: 1) The significance of the movement of fluids and gases from their source, through the seafloor, and into the ocean; 2) The structural and tectonic controls on and the sedimentary processes associated with the development of the offshore central California Margin with emphasis on the formation of submarine canyons.

We plan to complete our analysis of archived remotely operated vehicle (ROV) data to obtain an unbiased understanding of seep distribution within Monterey Bay. These activities are being conducted with the assistance of MBARI's Information Application Group and involve the cleaning up of the ROV navigation, and combining it with the EM-300 bathymetry and video information databases to obtain statistics on the distribution of seepage-related features.

We plan to collect hydrocast samples to measure dissolved methane concentrations in the water column along systematic transects north of Point Conception. The objective of this effort is to define where along the central California Coast there is the greatest likelihood of active gas venting. Systematic measurements from south of Point Conception show that large quantities of methane occur in the water column of the Santa Barbara area. However, no published data exist further to the north along the central California Coast. We have made some spot measurements which show that there is little methane in the water column in lower Monterey Canyon and significant quantities to the north off Ascension Canyon. The proposed surveys will further constrain the distribution and importance of gas seepage along the central California coast and its relationship to continental margin morphology and development. In subsequent years, we will propose to use the R/V Zephyr to expand the spatial coverage and sampling density.

We plan to improve our ability to collect radium from seawater for the detection of fluid seepage from the seafloor.  The proposed radium measurements will be an extension of the surveys conducted by Peter Brewer’s group in the past in the shallow water of Monterey Bay. Transects will be located along the axis of Monterey and Carmel Canyons, and the unnamed canyon that extends to the north of the San Gregorio Fault, and across the few areas associated with known seepage to establish where fluid seepage is most active in Monterey Bay. Additional transects will be located where our video-archive-based seep search shows the largest data gaps. 

We propose to conduct a cruise to outer Monterey Bay and the Monterey Fan. This expedition will involve diving in three areas: the axis of the lower canyon, the sinuous channel on the fan, and in the heads of Lucia Canyon. Sampling the sediments in the axis of the lower canyon and out onto the Monterey Fan will focus on determining the timing and patterns sediment transport through Monterey Canyon. To date, our sampling work has indicated that pesticide concentrations (DDT) define a trail of recent sediment transport through the axis of upper Monterey Canyon. However, we have no idea how far out onto the fan the trail of pesticide-bearing sediment extends. At the same time we are interested in establishing when the last major, high-energy canyon-scouring event occurred. The dives in Lucia Canyon are to compare the processes with Monterey Canyon and other canyons. Lucia Canyon is unique in that its head is directly connected to a large supply of coarse sediments that are currently being transported down the very steep flanks of the Coast Ranges.