Intellectual Merit: The Deepwater Horizon oil spill in the Gulf of Mexico requires a rapid response by the oceanographic community to measure subsurface oil and where it is going. The proposal is to deploy a Spray glider equipped with a CTD, CDOM fluorometer, and ADP in an effort to observe subsurface oil and general oceanographic conditions. The combination of CDOM fluorometer measurements and acoustic backscatter intensity will be used to sense oil in water. Work will be in collaboration with Breck Owens of Woods Hole Oceanographic Institution, who will take an important role in glider piloting. The glider will be deployed from Cocodrie, Louisiana aboard the vessel Acadiana during the first week of June. The glider will be sent south of the spill site, and away from surface slicks, with the goal of observing the offshore extent of subsurface oil. The data will be widely disseminated in real time for the purpose of establishing oceanic conditions and initializing predictive models.
Broader Impacts: As the oil spill is of extreme societal importance, this work proposed here has potentially huge broader impacts. Public interest in the oil spill is extremely high, with intense media coverage. A successful demonstration of the observation of subsurface oil will influence the response to oil spills for years. The collaboration of ocean scientists to address this problem of national scope may prove to be a model for the future. The data generated by gliders may lead to improved prediction of ocean currents in the region, which is essential for knowing how the oil will disperse. This use of gliders is an excellent example of their utility as a tool for rapid response.
The Deepwater Horizon oil spill in the Gulf of Mexico presented an immediate challenge for ocean scientists in the country. This project aimed to use an underwater glider to measure subsurface hydrocarbons and currents. In addition, the glider measured a suite of oceanographic variables to be sent in real time to analysis and modeling centers for use in establishing and predicting ocean state. We used a Spray glider, similarly equipped to those we use routinely in the California Current. In this application, Spray cycled from the surface to 500 m over a period of 3 h, during which time Spray traveled 3 km horizontally relative to the water. Position was measured by GPS at the beginning and end of each dive, allowing a dead reckoning estimation of depth-mean current. Spray carried a pumped Sea-Bird CTD to measure pressure, temperature, and salinity, and a Seapoint fluorometer in the pumped stream. A 750-kHz SonTek acoustic Doppler profiler (ADP) measured depth-dependent currents. Data were transferred by the Iridium satellite system once per dive, when commands to the glider were also be sent. In an effort to detect hydrocarbons in water, we used two approaches. First, we installed a Color Dissolved Organic Matter (CDOM) fluorometer on the glider. Second, we used acoustic backscatter from the ADP in an effort to measure oil droplets. The ADP transducers are limited to pressures less than 500 dbar, so we never sensed hydrocarbons in the main plume observed at depths of 1100-1300 m in ship surveys. The glider was deployed June 7 and recovered on September 20, 2010 after a 105-day deployment, covering 3180 km in 929 dives. During the first part of the deployment, we flew the glider close to the wellhead in an effort to observe the subsurface plume. Our closest approach to the wellhead was 22 km. During this time we coordinated operations with the Naval Oceanographic Office (NAVO), who had two gliders in the water. The glider fleet in the Gulf had a maximum of eight gliders in the water at one time, from various institutions. Our deployment was the longest, and Spray was the last glider to be recovered after the response. Most of the deployment, from about June 28 on, was spent surveying the Loop Current Eddy. The glider made one complete trip around the eddy, while repeated crossing the strong currents on the eddy edge. Ours was the only glider piloted extensively in the eddy during the response to the oil spill. We were committed to rapid dissemination of the Spray glider data to anyone involved in the response to the oil spill. All data was made available on our server to Rutgers, who maintained a map showing all gliders. We continued a partnership with the NAVO, who assimilates our Spray glider data in their model of the California coastal region. We provided the data to NAVO by email of standard KKYY files on a four-hourly interval. We sent these same KKYY files to the National Data Buoy Center of NOAA by ftp. In turn NOAA made the data available on Global Telecommunication System, and has archived the data at the National Ocean Data Center. We displayed our data to the public on two websites: spray.ucsd.edu, our lab site, and sccoos.org, the site of the Southern California Coastal Ocean Observing System. The fundamental results of the Spray glider deployment involved the physical oceanography of the Loop Current and Eddy. Depth-average currents in the Loop Current Eddy approached 1 m s-1, about 4 times the 0.25 m s-1 speed of Spray. While this makes piloting challenging, we have learned how to take advantage of the currents to navigate in the Gulf. The ADP on Spray allowed measurement of depth-dependent velocity. Near-surface currents at the eddy’s edge approached 2 m s-1. Isopycnals tilted upward toward the edge of the anticylonic eddy. Velocity shear was consistent with thermal wind. The center of the eddy was marked by high salinity, indicating water from the subtropical gyre. This water from the oligotrophic gyre had low acoustic backscatter, suggesting relatively little zooplankton. Diel migration of zooplankton was apparent as vertical banding in acoustic backscatter, especially early in the deployment to the north. Particularly relevant to the spread of oil was the fact that the Loop Current Eddy was separated during the spill. Any oil that might have been entrained in the current would have been trapped in the eddy, without a direct path to travel out of the Gulf.
