The PI requests MRI RAPID funding to acquire a spectrofluorometer to measure the multi-spectral fluorescence properties of subsurface oil and a Volatile Organic Carbon Analyzer to measure VOCs in the subsurface plume during upcoming oceanographic cruises. Both instruments are essential for properly calibrating and ground truthing other fluorescence-based instruments used to research the oil spill. A key benefit of these instruments is the ability to provide rapid and detailed analyses of oil properties and composition on board ship in near real-time. In addition, the PI?s request a dedicated APEX profiler with UV fluorescence, particle backscattering, and oxygen sensors to monitor subsurface plumes autonomously during and after the cruises.
The instruments in this request will be deployed in an upcoming RAPID funded research cruise to study the biomass, photosynthetic capacity and population composition of photosynthesizing organisms with regard to the potential effects of the oil spill using the Advanced Laser Fluorometer (ALF). They will detect subsurface plumes of oil using APEX floats and study vertical and horizontal velocities in the water column using LADCPs. The spectrofluorometric and VOC measurements will be essential for rapid, on-site confirmation and calibration of fluorescence-based measurements from the other equipment used on this cruise. The output from these two instruments will also be critical for identifying the source signature of any underwater hydrocarbons found. The APEX float will provide a continuous presence in the Gulf of Mexico following the cruise. The excitation/emission spectra obtained on this cruise will be made available to all the investigators working in the Gulf of Mexico to help them interpret their results.
Broader Impacts
The requested instruments will aid in investigating some of the most fundamental questions about the oil spill ? with this data the PI?s will try to estimate the location and magnitude of the subsurface plumes, to map the spatial extent of the near surface plume, and to understand the effect of the plume on subsurface oxygen concentrations. In addition, the work will complement and inform other interdisciplinary investigations including high-resolution modeling work currently being carried out in the Gulf.
The Deepwater Horizon accident in the Gulf of Mexico released an estimated 4.4 million barrels of oil and 500,000 t of gaseous hydrocarbons into the Gulf over 87 days. This release was unprecedented in U.S. waters in the magnitude of total hydrocarbons introduced into the marine environment. The accident was also unprecedented in the depth of the hydrocarbon release. While most marine oil spills result in release of oil near the surface of the ocean, here oil and gas gushed out of the ocean floor from a depth of approximately 1500 m. This resulted in atomization of the hydrocarbons into fine particles that formed deepwater hydrocarbon plumes (as deep as 1100 m). Among the most pressing issues raised during and after this accident, that largely remain open questions, were to understand the physical distribution of the subsurface hydrocarbon plumes, understand the chemical and biological degradation processes, and to understand the impact of these hydrocarbon plumes and associated dispersants on the ecosystem of the Gulf of Mexico. At the time of writing of the MRI RAPID proposal in June 2010, the Deepwater Horizon wellhead had not been capped and there was no indication when this might happen. Fresh hydrocarbons were still being released and there were on-going controversies about the amount of hydrocarbons released, and the dispersion and fate of these hydrocarbons, with claims and counter claims by the academic and federal research communities. We therefore proposed an MRI RAPID grant from the NSF to obtain three instruments: 1) a Webb Teledyne APEX Profiler with CTD, oxygen, UV-stimulated (CDOM) fluorescence, chlorophyll fluorescence, and particle backscattering sensors; 2) a Horiba Jobin Yvon Fluoromax-4 spectrofluorometer; and 3) an Infinicon CM5000 Volatile Organic Carbon (VOC) monitoring system. Each of these instruments is manufactured in the US. Together, these three instruments were to be used to identify and characterize the dispersal of surface and underwater hydrocarbon plumes in the Gulf of Mexico near the Deepwater Horizon site. We proposed deploying these instruments on a research cruise to the Gulf of Mexico on the R/V Oceanus from 21st August to 16th September 2010. The wellhead was eventually capped successfully on July 15, 2010, so our sampling occurred after hydrocarbon release from the wellhead ceased. Oxygen profiles measured from the RV Oceanus, and more extensively by our APEX profilers, POGO and BOBO, revealed several regions in the Gulf of Mexico with small, though readily detectable, oxygen anomalies during the summer and fall following the explosion of the Deepwater Horizon oil rig. Over a period of several months, dissolved oxygen anomalies of up to 0.59 mL*L-1 were discovered at sites as close as 12 km, and as far as 300 km, from the wellhead. These dissolved oxygen anomalies provided a means of identifying portions of the deep water hydrocarbon plume that originated from the Deepwater Horizon site. Together, these oxygen profiles should inform the validation of computer models of the plume’s trajectory, allowing us to develop a better picture of the transport and fate of the hydrocarbon plumes released during the disaster at BP’s Deepwater Horizon oil rig. All data from the APEX floats are now publically available through the Biological and Chemical Oceanography Data Management Office (BCO-DMO). Spectrofluorometric and VOC analyses of water collected from depths coinciding with oxygen anomalies did not show the characteristics of fresh oil. These data therefore provide an important constraint on estimates of hydrocarbon dispersion and degradation within the deepwater plume. In the time since the MRI RAPID grant ended, the principal investigators have secured additional funding through the Gulf of Mexico Research Initiative to continue research on the effects of deep water hydrocarbon releases on the Gulf of Mexico. Thus, the instrumentation acquired through the MRI RAPID will continue to be used for studying Gulf of Mexico oceanography, as well as other research projects.
