The weathering of petroleum hydrocarbons in the coastal ocean is a phenomenon that marine chemists and environmental chemists have been interested in for more than three decades. While there have been countless studies on this topic, advances have stalled due to the narrow analytical windows provided by traditional analytical techniques, leaving fundamental questions unanswered.
In this project, researchers at the University of California at Santa Barbara and the Woods Hole Oceanographic Institution will look at this problem in a new way through a concerted application of two advanced approaches: comprehensive, two-dimensional gas chromatography and Fourier transform ion cyclotron resonance mass spectrometry, to provide an unprecedented level of detail on the weathering of hundreds to thousands of petroleum hydrocarbons. Specifically, this research will identify and apportion the role of photolysis, evaporation, dissolution, and biodegradation associated with oil weathering at the natural oil seeps off Santa Barbara, CA, where more than 5 million liters of oil seep annually into the ocean. This effort directly addresses recommendations by the US National Research Council's 2003 report Oil in the Sea III, and will be driven by two overarching hypotheses: (1) Hydrocarbon mass loss in chronic oil slicks is dominated by evaporation > biodegradation > dissolution > photo-oxidation; and (2) High-molecular-weight and polar compounds in petroleum are transformed primarily in shallow sediments by microbiological processes, yielding high molecular weight dissolved organic molecules and a residual tar. These hypotheses will be addressed by collecting and analyzing oil samples from the Santa Barbara seeps. Changes in the distribution of molecules within each sample will be assessed as a function of environmental exposure to provide tests of the hypotheses. New data analysis tools will also be developed and validated.
Broader Impacts: Results from this research will contribute broadly to an understanding of petroleum weathering and carbon cycling in the Earth system, and will be broadly disseminated through popular outlets. Knowledge gained from this research will also be translated directly to federal agencies including the National Oceanic and Atmospheric Administration's Assessment and Restoration Division where such information is critical for short and long-term decision making following oil spills. Direct educational impacts of this research include the training and education of undergraduate and graduate students.
This study provided numerous key insights on how oil behaves once released into the environment. The initial goal was to focus on the natural seeps off the coast of Santa Barbara, CA, but we took advantage to study seeps near the Deepwater Horizon disaster. The most noteworthy breakthrough at Santa Barbara was using comprehensive two-dimensional gas chromatography (GC×GC) and Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR-MS) to study an asphalt sample collected by the DSV Alvin from the seafloor. This sample was estimated to be 35,000 years old from an ancient eruption of oil. We believe that using these two analytical techniques was the first ever and revealed how powerful this combination can lead to new insights into the weathering of hydrocarbons. We found that although GC×GC provided limited information, FT-ICR-MS produced vast amounts of previously unknown insights on the hydrocarbons present in the asphalt. These results mean that after 35,000 years of weathering, gas chromatography, the workhorse of oil spill science for decades, no longer yielded significant information, but FT-ICR-MS did. This is a major breakthrough and will revolutionize how oil seeps and oil spills are studied. That is, we need to expand our analytical windows to characterize all of the carbon released during a spill. This also led us to consider Deepwater Horizon samples, and we saw similar trends. The most unique outcome from studying at the Deepwater Horizon site was that we used alkenes commonly found in synthetic drilling fluids to identify possible sources of oil sheens that were first observed in September 2012 in close proximity to the Deepwater Horizon (DWH) disaster site, more than two years after the Macondo well was sealed. While exploration of the sea floor by BP confirmed that the Macondo well was sound, they identified the likely source as leakage from an 80-ton cofferdam, abandoned during the operation to control the well in May 2010. We acquired and analyzed sheen samples and cofferdam oil using GC×GC. This allowed for identification of a suite of alkenes in sheen samples that were absent in cofferdam oil. Furthermore, the spatial pattern of weathering, mainly evaporation, in the sheen samples indicated that the oil surfaced closer to the Deepwater Horizon wreckage than the cofferdam site. These lines of evidence led us to state that the observed sheens were sourced from tanks or pits from the Deepwater Horizon wreckage and therefore represented a finite oil volume for leakage. It is key that we communicated the results of this study within days to BP and other government stakeholders aiding them on responding to this issue. My knowledge about natural oil seeps and the behavior of oil in the ocean have been incredibly useful during and following the Deepwater Horizon disaster. I have discussed natural oil seeps during briefings to Capitol Hill staffers, Congressman, and members of the executive branch. I have given numerous talks about oil spills with a goal of being an honest broker of information to the public and policymakers. This may be the most important outcome of this project. Providing novel and useful science that can be used to make informed decisions about pressing issues.
