Abstract
In May 2010, the National Institute for Undersea Science and Technology (NIUST) had a 17-day research cruise aboard the UNOLS vessel R/V Pelican scheduled. NIUST is a partnership of the University of Mississippi, the University of Southern Mississippi and NOAA. Before sailing, the Deepwater Horizon oil platform burned and sank, resulting in an uncontrolled oil spill at a depth of 5000 ft at Mississippi Canyon Block 252. Subsequently, the decision was made to abort the planned hydrate and ship wreck research in favor of an oil spill response. The primary goals of the redefined cruise were to acquire baseline and early impact data for seafloor sediments and subsurface distribution of oil and gas hydrates as close as possible in time and space to the origin of the oil spill. Investigating an oil spill nearly a mile deep in the ocean presents special benthic sampling and subsurface oil detection challenges. NIUST's AUV's were unloaded from the ship and a larger main winch installed to allow operation of a large box corer for collecting sediment samples in water depths up to 2000 m. During the first five-day leg of the cruise, a total of 28 box cores were collected. The Pelican returned to port (Cocodrie, LA) to drop off sediment and water samples for immediate analyses, and to take on more sampling gear and supplies for the second leg of the cruise, including an Acrobat, a CDOM fluorometer, a Video Ray ROV, and a C02 sensor in addition to the already installed CTD Rosette with 02 sensor and light transmissometer. During Leg 2, box core samples were collected until weather prohibited safe operations. CTD stations were plotted to cover the area surrounding the wreck site and at various depths to cover the water column in order to map the subsurface water column structure and chemistry as baseline values for future investigations and especially to look for submerged oil and/or gas hydrates. Early in the water column sampling, a subsurface feature was discovered at 1200 to 1400 m depth. This layer was detected by three independent sensors, CDOM (colored dissolved organic matter) fluorometer, light transmissometer, and oxygen sensor. All three instruments responded in unison with greater fluorescence and beam attenuation and decreased 02 concentration. These signals were first observed at a station 5 miles from the accident site. Second and third station measurements, exactly half the distance to the spill site from the previous one, at 2.5 miles, and at 1.25 miles, showed the same signal but with significantly greater magnitude. Following this discovery, the sampling plan for the remaining days of the cruise was changed to map the newly discovered feature. This paper will discuss methods, pursuit of leads, gear and instrumentation utilized, resulting in the initial discovery of deep hydrocarbon plume features resulting from the uniquely deep oil spill.