The Deepwater Horizon disaster has released more than 20 million gallons of oil into the Gulf of Mexico. Due to the extreme depth and broad area of impacted region, it is critical that the presence and structures of oil plumes be determined for accurate mass balance calculations, estimating damage, and understanding the overall chemical/physical behavior of individual hydrocarbons comprising the oil. There exists considerable uncertainty on the presence of subsurface plumes reported by other researchers. The latter is due, in part, because the findings are based on in situ fluorescence typically used to measure dissolved organic matter. In addition, these findings only provide an estimate of total oil.
To provide a robust and higher resolution dataset on the hydrocarbon distribution and structure in the Gulf of Mexico, researchers at the Woods Hole Oceanographic Institution will deploy the TETHYS in-situ mass spectrometer. TETHYS compliments conventional sampling by providing near-continuous records and by providing far greater spatial resolution. Additionally, real time feedback from TETHYS can be used to guide conventional sampling.
The TETHYS in-situ mass spectrometer is optimized for long-term unattended environmental monitoring of low molecular weight (2-200 amu) gases and volatile chemicals in a variety of hostile environments. TETHYS is also unique among field-portable or underwater mass spectrometers in that it retains high mass resolution in the low-mass range (1-25 amu), allowing it to quantify hydrogen, helium, and methane. In this study of the Deepwater Horizon spill, TETHYS will be deployed on two different subsea platforms: an enhanced CTD rosette and the autonomous underwater vehicle (AUV) Sentry.
The research team will work collaboratively with a number of other investigators from Woods Hole, Texas A & M University, and the University of California at Santa Barbara who have separately received RAPID funding to study various aspects of this historic oil spill. All of these investigators have prior experience with the TETHYS/CTD/Sentry technology.
Broader Impacts: Results from this research are expected to contribute to a deeper understanding of petroleum fate and carbon cycling in the Earth system. Knowledge gained from this research will also be translated and transmitted directly to state and federal agencies involved in the spill damage assessment and restoration. The project will provide the concepts, processes, and parameters necessary for existing industry oil spill models to be adapted to the unparalleled situation of a major oil release on the deep sea floor. The continued expansion of offshore drilling operations into deeper waters may lead inevitably to the risk of more spills in the future.
NSF Award ID: 1045025 PI: Richard Camilli Findings: This research program focused on characterizing subsurface hydrocarbon plumes resulting from the Deepwater Horizon blowout, the largest offshore oil spill in history. Our methods involved subsurface water column surveys using Sentry, an autonomous underwater vehicle (AUV) and a ship-cabled sampler; both of which were equipped with TETHYS in-situ mass spectrometers. These findings indicate the presence of a continuous plume of hydrocarbons, more than 35 kilometers in length, at approximately 1,100 meters depth. Samples collected from within the plume reveal monoaromatic hydrocarbon concentrations in excess of 50 micrograms per liter. These data indicate that monoaromatic input to this plume was at least 5,500 kilograms per day, which is more than double the total source rate for monoaromatic petroleum hydrocarbons from all the natural seeps in the northern Gulf of Mexico. The composition and concentrations of these hydrocarbons within the plume are indicative of originating from the Macondo well. Dissolved oxygen concentrations suggest that microbial respiration rates within the plume were not appreciably more than 1 micromolar oxygen per day. Research and Education Activities: A series of AUV and Conductivity, Temperature, and Depth (CTD) water column surveys were completed in the area surrounding the Deepwater Horizon site. These surveys were used to inform water sample collection for the Natural Resource Damage Assessment. Contributions within Discipline: The findings have provided new insights in oil spill research and, more broadly, environmental chemical contamination research. The robotic techniques implemented have advanced the research areas of field robotics and extended autonomy. Contributions to Other Disciplines: The results and findings of this RAPID project are now being used to improve understanding the dynamics of deep sea hydrocarbon releases and their impact on marine ecosystems, particularly Gulf of Mexico fisheries. Contributions to Human Resource Development: The work has contributed to improving the capability of the NSF-supported National Deep Submergence Facility at Woods Hole Oceanographic Institution. The Sentry vehicle operations team has been able to transfer new techniques (e.g., real-time chemical mapping and acoustic data communication) for use in other basic earth science programs. Contributions to Resources for Research and Education: The research program has provided a case study for teaching secondary school students about environmental and robotics research. Several hundred news articles appeared worldwide featuring the findings of the research as well as the robotic technologies used, improving science and technology literacy. Contributions Beyond Science and Engineering: Data and analysis from the EN-478 cruise were provided to Federal officials as part of the ongoing Deepwater Horizon response efforts. Water samples were collected during the EN-478 cruise operations for the Natural Resource Damage Assessment effort based on georeferenced plume mapping. Findings from this research have been used to inform policy relating to offshore oil production and marine pollution. The PI (Camilli) testified before the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling about this work. The National Commission subsequently used published findings from this RAPID program in its final report. The ongoing Natural Resource Damage Assessment effort continues to use samples and data collected as part of this RAPID program.
