Categorizing Submarine Cold Seeps by Geomorphology and Acoustic Response Utilizing Publicly Available Multibeam Echo Sounder and Remotely Operated Vehicle Datasets
Abstract
The use of multibeam echo sounders (MBES) for the remote detection of natural hydrocarbon seeps has been well established. Seeps are associated with geologic features identified by MBES bathymetry, such as faults, salt, and pockmarks. The hardness and/or roughness of the seafloor associated with these seep-related geomorphic features can also be recognized acoustically as MBES backscatter anomalies: high intensities may represent the formation of authigenic carbonates or chemosymbiotic mussel beds at seep locations and low intensities can be characteristic of brine pools or seep vents. Gas bubble plumes from the release of hydrocarbon-rich fluids into the water column can be interpreted using MBES mid-water backscatter data. Although thousands of seeps have been identified, little is known about how different seep seafloor morphologies can be differentiated by their acoustic signal.
In the Gulf of Mexico and along the Atlantic margin MBES and ROV video data were collected aboard the Okeanos Explorer (EX1304; EX1711) using the same Kongsberg EM302 (30 kHz) MBES system. Because different MBES frequencies can produce very different bathymetric images and backscatter intensities, these publicly-available datasets provide a unique opportunity to compare the geomorphology of submarine cold seeps in different geologic settings to the unique acoustic responses of the same sonars. We observed that upper-slope seeps related to methane hydrate disassociation had different seafloor morphologies and benthic communities than seeps associated with geologic structures where a potential mixture of hydrocarbon-rich fluids could use fractures as pathways to the seafloor. These morphological differences also yielded different acoustic signatures. Here we will show seep morphologies and associated geologic features imaged with ROV videos, compared to their MBES responses (bathymetry, backscatter and water column), and classified into seep "types" at locations in the Gulf of Mexico and along the Atlantic Margin. This approach to characterization of cold seep habitats can help constrain global methane budgets, and lead to a greater understanding of the distribution of deep benthic communities associated with hydrocarbon expulsion.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS24C..05B
- Keywords:
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- 3002 Continental shelf and slope processes;
- MARINE GEOLOGY AND GEOPHYSICSDE: 3004 Gas and hydrate systems;
- MARINE GEOLOGY AND GEOPHYSICSDE: 3045 Seafloor morphology;
- geology;
- and geophysics;
- MARINE GEOLOGY AND GEOPHYSICSDE: 3050 Ocean observatories and experiments;
- MARINE GEOLOGY AND GEOPHYSICS