A.-R. Diercks

Marine snow formation in the aftermath of the Deepwater Horizon oil spill in the Gulf of Mexico

The large marine snow formation event observed in oil-contaminated surface waters of the Gulf of Mexico (GoM) after the Deepwater Horizon accident possibly played a key role in the fate of the surface oil. We characterized the unusually large and mucus-rich marine snow that formed and conducted roller table experiments to investigate their formation mechanisms. Once marine snow lost its buoyancy, its sinking velocity, porosity and excess density were then similar to those of diatom or miscellaneous aggregates. The hydrated density of the component particles of the marine snow from the GoM was remarkably variable, suggesting a wide variety of component types. Our experiments suggest that the marine snow appearing at the surface after the oil spill was formed through the interaction of three mechanisms: (1) production of mucous webs through the activities of bacterial oil-degraders associated with the floating oil layer; (2) production of oily particulate matter through interactions of oil components with suspended matter and their coagulation; and (3) coagulation of phytoplankton with oil droplets incorporated into aggregates. Marine snow formed in some, but not all, experiments with water from the subsurface plume of dissolved hydrocarbons, emphasizing the complexity of the conditions leading to the formation of marine snow in oil-contaminated seawater at depth.

In situ settling speeds of marine snow aggregates below the mixed layer: Black Sea and Gulf of Mexico

Abstnct-Zn situ settling speeds of marine snow aggregates were determined with the Marine Aggregate Settling Collector and Observation Tower (MASCOT) in the central Black Sea and in the northern Gulf of Mexico. The Black Sea data showed a wide distribution in size and settling speeds of marine snow aggregates (0.5-55 mm diameter and 1.3-280 m/d) with an average settling speed of 11.7 m/d over all size classes. However, these settling speeds might have been inlhtenced by the addition of salt (0.9% above the background seawater) plus formalin to the water in one side of the acrylic chamber of the MASCOT. Data from the Gulf of Mexico had a smaller range in terms of size and speed (0.5-3.5 mm diameter and IO-89 m/d). The average settling speed over all size classes was approximately three times higher (33.8 m/d) than for aggregates measured in the Black Sea. Stokes’ Law predicts that settling speeds are determined by both density and volume of an aggregate. For both study sites no statistically significant correlation of settling speed with the equivalent spherical diameter (ESD) of the aggregates was found. It was therefore concluded that variations in density controlled the aggregate settling speeds measured in these two study areas. 0 1997 Elsevier Science Ltd

Geochemical and Structural Aspects of the Pycnocline in the Black Sea (R/V KNORR 134-8 LEG 1, 1988)

During leg 1 of the R/V KNORR 1988 Black Sea cruise a variety of investigations was carried out to study the vertical and lateral structure of the upper water column in the Black Sea. Insitu TV inspection allowed us to discern - from top to bottom - three macrofauna zones in the oxygenated layer above the pycnocline: the Aurelia zone, the Pleurobranchia zone and (existing only in coastal waters) the Sagitta zone. At a density of 16.1 to 16.4 ∑Θ a layer is present consisting of very fine particles. The fine particle layer (FPL) follows the doming of the Black Sea pycnocline but it’s intensity and thickness declines quickly from the coast towards the center. Particulate material collected by in-situ pumping in or near the FPL was inspected by EDX. Manganese is always present in dominant quantities in the form of finely dispersed (ca. 0.5 µm diameter) microspherules and probably is the main compound responsible for the transmissometer peaks. These observations could be explained by mobilization of Mn from shallow coastal sediments, a process which may greatly be enhanced by internal waves warping the pycnocline near the coast and operating a “manganese pump”. Macroflocs, present at concentrations between 0.8 to 4.6 per liter carry Mn particles back into the anoxic zone. The large Aurelia and Pleurobranchia populations observed may be producers of the organic matter necessary to assemble macroflocs.

Enhancing NIUST's SeaBED class AUV, Mola Mola

Mola is a seafloor mapping AUV owned and operated by the National Institute for Undersea Science and Technology (NIUST). Since its initial sea trials in May of 2009, effort has been applied to enhancing the navigation and imaging systems for high-resolution surveys of specific targets in depths up to 2000 meters. These surveys require accurate positioning during the initial dive to the seafloor, and smooth navigation once the survey begins. To work toward this goal, an inertial navigation system with position and velocity aiding has been integrated with the vehicle software, and it is currently being field tested. The imaging system has also been modified by adding LED arrays to provide more consistent lighting and by merging navigation data with the images for georeferencing. The above system enhancements have forced changes in the vehicles layout, and operational experiences have led to improvements in the vehicles mechanical systems.

NIUST - Deepwater horizon oil spill response cruise

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. NIUSTs AUVs 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.

Expanding the capabilities of the NIUST AUVs

The seafloor mapping AUVs Eagle Ray and Mola Mola have vastly different capabilities and operational requirements, yet they perform complementary tasks. These AUVs are operated by the National Institute for Undersea Science and Technology (NIUST), which is a NOAA sponsored partnership between the University of Mississippi and the University of Southern Mississippi. Eagle Ray collects Multibeam sonar bathymetry and CTD data, as well as data from guest payloads. Mola Mola collects color images of the seafloor along with multibeam bathymetry. In back-to-back dives, Mola Mola can conduct focused studies over targets determined from broad surveys carried out by Eagle Ray, but the two vehicles have also had successful cruises independently.

NIUST AUVs - Expanding possibilities

The National Institute of Undersea Science and Technology (NIUST)s Underwater Vehicle Technology Center (UVTC) expanded their operational capabilities by acquiring a SeaBED class AUV in early 2009. This vehicle dubbed, Mola Mola after the Ocean Sunfish, is a superb addition to the UVTC, as it adds photographic capabilities at very slow moving speeds to the centers repertoire. The vehicle is designed to fly at speeds of 0.2 ms-1 about 3m above the seafloor, snapping high resolution digital images of the seafloor at preset intervals of 4 to 5 seconds. Normal mission behavior, programmed prior to launch of the vehicle, is to cover a certain area on the seafloor in a lawn mowing track, with parallel lines covering the entire area. At the end of the mission, geo-referenced photo mosaic maps of the target of interest on the sea floor are computed. The vehicle was deployed for several missions on the NASA vessel Liberty Star in the Bahamas. High resolution imagery of the bottom fauna and flora from depths too deep for deep divers to reach, provided insight into the distribution of Lion Fish in the coral reefs of the Bahamas. At the end of the field season engineering efforts were started to reorganize and replace certain hardware components to allow for improved navigation and data handling within the vehicles software architecture. They vehicle itself has since been modified from its original design, adding guided inertial navigation and improvements in its image acquisition process. Changes further include obstacle avoidance, GPS positioning and addition of a VHF radio beacon. In October 2009 combined efforts of both AUVs, the Mola Mola and the Explorer class Eagle Ray were needed in the Gulf of Mexico aboard the NOAA ship Nancy Foster, to locate and retrieve information about sunken ships of historic interest, some of which may have disappeared below the water surface of the northern Gulf of Mexico, almost 200 years ago. In a collaboration between NIUST, MMS and NOAA Office of Ocean Exploration and Research, targets identified in side scan sonar images, were selected and investigated by the AUVs. Eagle Ray, due to its large size and design features, performed initial multibeam surveys of the target areas, producing high-resolution maps of the seafloor. These maps were used to determine safe working areas for the Mola Mola, which was subsequently launched to take a continuous series of photographs in close proximity to the seafloor, producing a photo-mosaic map of the target area. Eagle Ray served as a platform for a mass spectrometer mapping of the Mississippi Canyon Block 118 Hydrate Mount as a part of the Gas Hydrate Observatory efforts. Results o this dive produced a high resolution spatial map of methane gas distribution 6m above the seafloor, discovering three new methane seeps in the area Continued mapping efforts in the Hudson Canyon together with the National Marine Fisheries Service and Rutgers University. High resolution multibeam data from the canyon revealed interesting never before seen detail and bottom features in this area. Enough data to spark new and diverse interest about sub bottom composition and marine live within the canyon.

NIUST AUV's study shipwrecks in the northern Gulf of Mexico

In October 2009 two autonomous underwater vehicles (AUVs), the explorer class Eagle Ray and the seabed class Mola Mola, were launched from the NOAA ship Nancy Foster to locate and retrieve information about sunken ships of historic interest, some of which had disappeared below the water surface of the northern Gulf of Mexico, almost 200 years ago. In a collaboration between the National Institute for Undersea Science and Technology (NIUST,) the US Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) and the US NOAA Office of Ocean Exploration and Research (OER), targets identified in side scan sonar images, were selected and investigated by the AUVs. Eagle Ray, due to its large size and design features, performed initial multibeam surveys of the target areas, producing high-resolution maps of the seafloor. These maps were used to determine safe working areas for the Mola Mola, which was subsequently launched to take a continuous series of photographs in close proximity to the seafloor, producing a photo-mosaic map of the target area. Operational procedures and results from these dives will be presented, showing the complementing features of these two very different AUVs in operation.

New developments for the NIUST AUVs

The National Institute for Undersea Science and Technology operates two AUVs, Eagle Ray and Mola Mola that are primarily tasked with performing seafloor surveys. Upcoming missions will require surveys at 1200 to 1600 meters depth, so the vehicles are being prepared with new and updated systems and software. Recently, Eagle Ray was equipped with new batteries and a subbottom profiler. A descent weight system was added to Mola Mola, along with a revised power system and new mission capabilities.

Mola Mola, NIUST's low-altitude photo and multibeam AUV

Mola Mola is a seafloor mapping AUV owned and operated by the National Institute for Undersea Science and Technology (NIUST). Its primary sensor is a downward-facing camera producing color-corrected seafloor imagery which, with proper navigation and post processing, can be converted to a photo mosaic. It also uses a multibeam sonar to gather bathymetry encompassing the photo coverage. Since its delivery in May of 2009 Mola Mola has been modified in the areas of its imaging and navigation systems as well as several mechanical systems.