Sea Technology

MAY 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Natural hydrocarbon seep being monitored by AquaPix autonomous video camera deployed from ROV Global Explorer MK3. (Photo Credit: Schmidt Ocean Institute) Clearly Superior imaging SONAR SYSTEMS SiDe SCan SonarS was that it occurred at 1,500 meters depth. Hydrocarbons discharged from the well were transported as diffuse plumes a few-hundred meters above the seafoor and in surface layers that ranged from microns to centimeters in thickness. The deepwater plumes moved primarily to the southwest, while the surface layers were carried by wind and current to the coasts of Louisiana, Mississippi, Alabama and northern Florida. In both directions, impact assessments have been complicated by incomplete prior knowledge. Nowhere was this more apparent than in the DeSoto Canyon. This prominent submarine canyon extends northnortheast from the Macondo well almost to the Florida Panhandle. At the time of the blowout, the bathymetry for most of the canyon was only mapped to a resolution coarser than 500 meters in the horizontal and 100 meters in the vertical. This limited responders' ability to anticipate how bottom features could affect oil deposition and shape biological habitats. Results from the University of South Florida indicate that some of the surface oil settled out in what they dubbed "a dirty blizzard." DeSoto Canyon is potentially a topographic vector connecting the deep to the coastal zone. When the Gulf of Mexico Research Initiative put out a call for research consortia to investigate potential and actual oil spill impacts in the Gulf of Mexico, 10 major institutions joined under the leadership of Florida State University to form Deep-C with the goal of conducting basic and applied science focused on the canyon's oceanographic features. Deep-C got an early assist from NOAA's Ocean Exploration program when, in the fall of 2011, the RV Okeanos Explorer was brought into the Gulf. During expeditions lasting several weeks, Okeanos Explorer completed bathymetric charting of DeSoto Canyon and other areas of interest using its onboard Kongsberg (Kongsberg, Norway) EM 302 multibeam echosounder. The effort clearly delineated features like salt domes, erosion channels and natural-gas seeps. This allowed DeepC investigators to establish the benthic array of study sites at localities in the canyon that represent depth gradients and signifcant anomalies. The role of MILET and USBL telemetry is to determine the seafoor characteristics and ecological diversity at the Deep-C study sites. By sampling along kilometer-long transects at sites with depths from 500 to 2,500 meters while logging geotagged images and readings from the instrument suite, MILET provides a repeatable sample of sediment characteristics, mobile fauna and water chemistry. Biannual repeat sampling will make it possible to test for seasonal effects on the biological community and particle fallout. MILET was initially deployed with a 13-megapixel digital camera—AquaPix's (Tallahassee, Florida) AquaSLR— and low-light video camera. However, the modular fexibility of the MacArtney NEXUS telemetry interface is readily upgradable, with multiple ports for RS232, RS485, analog video, and 1000BASE-T network connections. The team behind MILET has been fnalizing the addition of an EdgeTech www.sea-technology.com SuB-BoTTom proFilerS BaTHymeTry SySTemS The Leader in Underwater Technology info@edgetech.com uSa 1.508.291.0057 May 2013 / st 25

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