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An active methane vent in Mississippi Canyon Block 118 (MC118), Gulf of Mexico, has been the focus of persistent research. This vent area contains both active and dormant vents as well as blocks of methane hydrate outcropping on the seafloor. It is proposed that methane hydrate blocks also form within the Hydrate Stability Zone (HSZ) beneath the vent. Through collaborative work done by the Gulf of Mexico-Hydrate Research Consortium (GOM-HRC), surficial characteristics and mound chemistry is understood, but quantifiable distributions of hydrate with the HSZ is unknown. Highfrequency seismic imaging of the mound is hindered by the presence of free gas, hydrate, and biogenic carbonate blocks on the surface.

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Geophysical investigations of the first 100 m below the seafloor in deep-marine environments are done to assess drilling hazards, to plan routes for pipelines and cables, and to study benthic organism communities. The tool of choice for these investigations is subbottom profiling, which uses acoustic signals in the range of 1 to 25 kHz to image near-bottom stratigraphy. An existing engineering-scale, direct-current resistivity (DCR) system for use in deep-marine, near-bottom environments has been adapted. It is potentially useful in settings in which the presence of free gas, gas hydrates, coarse sediment, cemented carbonate, or highly deformed sediment limits the effectiveness of the subbottom-profiling method. The adapted DCR system was used to survey Woolsey Mound, Mississippi Canyon Block 118 (MC118), Gulf of Mexico, to characterize the shallow gashydrate system. Three conventional modes of DCR data acquisition -continuous-resistivity profiling (CRP), static array, and time lapse with a fixed array -were evaluated on the deep seafloor. High-resistivity anomalies likely associated with high concentration of hydrate deposits were imaged with all three modes of acquisition.