We report the first application of a new mass spectrometry technique (gas chromatography combined to atmospheric pressure chemical ionization tandem mass spectrometry, GC/APCI-MS/MS) for fingerprinting a crude oil and environmental samples from the largest accidental marine oil spill in history (the Macondo oil spill, the Gulf of Mexico, 2010). The fingerprinting of the oil spill is based on a trace analysis of petroleum biomarkers (steranes, diasteranes, and pentacyclic triterpanes) naturally occurring in crude oil. GC/APCI enables soft ionization of petroleum compounds that form abundant molecular ions without (or little) fragmentation. The ability to operate the instrument simultaneously in several tandem mass spectrometry (MS/MS) modes (e.g., full scan, product ion scan, reaction monitoring) significantly improves structural information content and sensitivity of analysis. For fingerprinting the oil spill, we constructed diagrams and conducted correlation studies that measure the similarity between environmental samples and enable us to differentiate the Macondo oil spill from other sources.
Multiyear in situ Eulerian acoustic Doppler current profiler measurements were obtained at 5-, 10-, and 19-m depths off the Big Bend coast, and in 19 m off the Florida Peninsula to the south. Analysis on subinertial time scales, dominated by weatherband frequencies, led to the following conclusions. At the 19-m Big Bend site (K-Tower), consistent with coastally trapped wave (CTW) theory, the along-isobath flow is not proportional to the local along-isobath wind stress, but rather to the alongshore wind stress t y WFS to the south along the west Florida shelf (WFS). At the southern 19-m site, consistent with previous work, the alongisobath flow is driven by t y WFS , but is weakened by an alongshore pressure gradient brake. Via CTW dynamics this brake is due to the abrupt ''end'' of the WFS at the Florida Keys. By contrast, along-isobath flow at the shallow 5-m site is driven by the local wind in a constant stress turbulent frictional layer. Because of the freshwater flux near the coast, density usually increases seaward. This leads to a strong asymmetry in the crossisobath frictional bottom boundary layer (BBL) flow when the subinertial along-isobath flow direction changes. In one case the BBL flow is shoreward and gravitationally stable while, in the other, the BBL flow is gravitationally unstable as less dense water is forced under more dense water. Seasonal changes in the seaward horizontal density gradient also shear the seasonal along-isobath flow via thermal wind dynamics.
We report chemical characterization of natural oil seeps from the Gulf of Mexico by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and Gas Chromatography/Atmospheric Pressure Chemical Ionization Mass Spectrometry (GC/APCI-MS), to highlight how FT-ICR MS can also be employed as a means to determine petroleum connectivity, in addition to traditional GC/MS techniques. The source of petroleum is the Green Canyon (GC) 600 lease block in the Gulf of Mexico. Within GC600, two natural oil seepage zones, Mega Plume and Birthday Candles, continuously release hydrocarbons and develop persistent oil slicks at the sea surface above them. We chemically trace the petroleum from the surface oil slicks to the Mega Plume seep itself, and further to a petroleum reservoir 5 km away in lease block GC645 (Holstein Reservoir). We establish the connectivity between oil samples and confirm a common geological origin for the oil slicks, oil seep, and reservoir oil. The ratios of seven common petroleum biomarkers detected by GC/APCI-MS display clear similarity between the GC600 and GC645 samples, as well as a distinct difference from another reservoir oil collected ∼300 km away (Macondo crude oil from MC252 lease block). FT-ICR MS and principal component analysis (PCA) demonstrate further similarities between the GC600 and GC645 samples that distinctly differ from MC252. A common geographical origin is postulated for the GC600/GC645 samples, with petroleum migrating from the GC645 reservoir to the oil seeps found in GC600 and up through the water column to the sea surface as an oil slick.
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