ROV Deep Discoverer investigates the geomorphology of Block Canyon. Image courtesy of the NOAA Office of Ocean Exploration and Research, Northeast U.S. Canyons Expedition 2013. Download larger version (jpg, 1.1 MB).
Dive 15 focused on exploring the geomorphology and biological communities of Block Canyon starting at a depth of 1,134 meters. Remotely operated vehicle Deep Discoverer (D2) descended onto a soft sedimented seafloor composed of silt and clay mixed with scattered rocks and boulders of various sizes. Numerous fishes were evident, including cutthroat eels, red crabs, blue cod, witch flounder, and grenadier. Rocks were colonized sparsely by small bamboo corals accompanied by mysid shrimp hovering around the colonies. As D2 transited to the base of a vertical rock wall, octopus and coral colonies, including one hosting a ring anemone and a brittle star, were observed. At 1,111 meters D2 reached the base of the vertical wall, which was horizontally stratified with layers of carbonate and porcellanite, a hard, dense sedimentary rock somewhat similar in appearance to unglazed porcelain, which here appeared stronger and less bio-eroded compared with the carbonate layers. Continuing upslope, bamboo coral, limid bivalves, and two species of stony corals were observed before reaching a promontory feature near 1,030 meters – the most extensive area of concentrated colonization. The most abundant fauna were bivalves, occurring in linear arrays along the wall. Octocorals, bamboo corals, and a few black coral colonies with brittle stars, polychaetes, and mysid shrimp associates were observed. D2 moved downslope until reaching the base at a depth of 1,116 meters, and then returned upslope, noting the same patterns of faunal colonization along this traverse. During the last 30 minutes of the dive, D2 approached a flat sedimented area and then a relatively barren second wall, with a few bivalves and sponges. D2 left bottom from a depth of 995 meters.