Linking Natural Oil Seeps from the Gulf of Mexico to Their Origin by Use of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

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.

Comment on "A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico".

Kessler et al. (Reports, 21 January 2011, p. 312) reported that methane released from the 2010 Deepwater Horizon blowout, approximately 40% of the total hydrocarbon discharge, was consumed quantitatively by methanotrophic bacteria in Gulf of Mexico deep waters over a 4-month period. We find the evidence explicitly linking observed oxygen anomalies to methane consumption ambiguous and extension of these observations to hydrate-derived methane climate forcing premature.

Microbial diversity in sediments associated with surface-breaching gas hydrate mounds in the Gulf of Mexico.

Abstract A molecular phylogenetic approach was used to characterize the composition of microbial communities from two gas hydrate sedimentary systems in the Gulf of Mexico. Nucleic acids, extracted from sediments directly overlying surface-breaching gas hydrate mounds collected from a research submersible (water depth 550-575 m), were amplified with nine different 16S rDNA gene primer sets. The polymerase chain reaction primers targeted microorganisms at the domain-specific (Bacteria and Archaea) and group-specific (sulfate-reducing bacteria (SRB) and putative anaerobic methane-oxidizing (ANME) archaea) level. Amplicons were obtained with five of the nine primer sets including two of the six SRB Groups (SRB Group 5 and Group 6) and used to generate five different clone libraries. Analysis of 126 clones from the Archaea library revealed that the sediments associated with naturally occurring gas hydrate harbored a low diversity. Sequence analysis indicated the majority of archaeal clones were most closely related to Methanosarcinales, Methanomicrobiales and distinct phylogenetic lineages within the ANME groups. The most frequently recovered phylotypes in the ANME library were related to either ANME-2 or Methanomicrobiales. In contrast to the two archaeal libraries, bacterial diversity was higher with the majority of the 126 bacterial clones most closely related to uncultured clones dominated by the delta- and epsilon-Proteobacteria. Interestingly, while 82% of the clones in the SRB Group 5 library were affiliated with delta-Proteobacteria, the vast majority (83%) of clones in the SRB Group 6 library was affiliated with the Firmicutes. This is the first phylogenetic-based description of microbial communities extant in methane-rich hydrate-associated sediments from a hydrocarbon seep region in the Gulf of Mexico.