Mesoscale biogeophysical characterization of Woolsey Mound (northern Gulf of Mexico), a new attribute of natural marine hydrocarbon seeps architecture

Located on the continental slope in 900 m of water, Woolsey Mound dominates seafloor morphology at Mississippi Canyon 118. The carbonate-hydrate mound is the site of the Gulf of Mexico Hydrates Research Consortium's seafloor observatory to investigate and monitor hydrographic, geophysical, geological, geochemical and biological processes of the hydrocarbon system, northern Gulf of Mexico. Innovative survey and monitoring systems, sensors, and tools have been developed to extract samples and data to unravel the history, character and composition of the site. Many hours of visual data have been collected to investigate benthic communities thriving at the cold seep site associated with the mound. These communities' habitats are described here, for the first time, in terms of faunal assemblage, substrate nature, and presence/absence of chemosynthetic species. Based on these factors, we grouped them into four benthic meso-habitats. We speculate that the spatial distribution of these meso-habitats is large enough to make this characteristic comparable to the geophysical response of the seismo-acoustic systems. We have tested this hypothesis carefully analyzing the relationship between benthic habitats zonation and the geophysical response of Side Scan Sonar, Chirp Subbottom, Surface Source Deep Receiver (SSDR) vertical incidence profiler and 3-D oil industry multichannel data. We observe that the geophysical response is not unique, a single habitat may correlate with many geophysical attributes, or a single geophysical attribute may span many habitats. However, we find that geophysical data can predict seep locations. They can also convey some information concerning community composition and complexity that function as proxies for seep duration/age while specific community components are believed to reflect composition of seep fluids. Although preliminary, this approach represents a novel classification/characterization for seafloor hydrocarbon seeps, one that reflects a historical component.