Location of natural oil seep and chemical fingerprinting suggest alternative explanation for deep sea coral observations

Exponent, Inc., Maynard MA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2012; 109(40):E2647. DOI: 10.1073/pnas.1209658109
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Available from: Paul D Boehm, Feb 09, 2014
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    ABSTRACT: Our original study (1) used visual inspection as well as biological and geochemical analyses of corals and the surrounding sediment to provide complementary and compelling evidence linking the Deep-water Horizon (DWH) oil spill to the presence of damaged deep-water corals and brittle stars 11 km from the site of the leaking oil. The probability that the impact to this coral community oc-curred independently of the DWH spill can be estimated on the basis of three facts. (i) This is the only site among 20 deep-water coral communities associated with authigenic seep carbonates in the northern Gulf of Mexico where visual inspection over the past decade has revealed evidence of notable damage to corals. (ii) The presence of dead and dying tissue and the attachment of living ophiuroids to the corals indicate that the impact was recent (Fig. 1). (iii) The average age of four coral colonies sampled from the site is 460 ± 35 y [according to radio carbon dating as in Prouty et al. (2)]. Assuming that an independent event had an equal chance of occurring at any of the other seep-related coral sites (1 in 20) and during any of the past 460 y at this site (1 in 460), this yields a probability of this happening coincidently at this place and time of approximately 0.0001. In addition, there is no evidence from Bureau of Ocean and Energy Management seismic data, National Oceanic and Atmo-spheric Administration multibeam data, or high-resolution AUV Q:6 multibeam data to indicate slope failure and the underwater landslide suggested by Boehm and Carragher (3) as an alternate explanation for the damage to this site. It is also noteworthy that this community is on top of a discrete ridge where no known mechanism would gather material from such an event and not also be apparent in the surrounding area. The coral community examined in our original article is 11 km to the southwest of the Macondo well at a depth of 1,370 m (1), placing it in the path of a documented deep-water plume enriched with petroleum hydrocarbons. A maximum of oil constituents centered at ∼1,400 m was observed within 2 km of these corals between June 23 and 27, 2010 (4), and levels of polycyclic aro-matic hydrocarbons considered to be toxic to marine organisms were measured up to a distance of 13 km to the southwest of the Macondo well, at depths between 1,000 and 1,400 m between May 9 and 16, 2010 (5). Both of these studies support our findings (1) and describe discrete measurements that reflect a minimum of petroleum hydrocarbons that may have impacted coral commu-nities over the 86 d of the DWH spill. The consistent biomarker ratios between coral samples and the oil from the DWH spill were determined using comprehen-sive 2D gas chromatography coupled to a time-of-flight mass spectrometer (GC×GC-TOF-MS). Although oil samples in the area are indeed difficult to distinguish, GC×GC-TOF-MS is capable of separating, identifying, and quantifying compounds that may not be resolved by the 1D chromatographic techniques (6) referred to by Boehm and Carragher (3). ACKNOWLEDGMENTS. We thank James Rosenberger, PSU
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    Proceedings of the National Academy of Sciences 10/2012; 109(40):2648-E2648. DOI:10.1073/pnas.1210413109 · 9.67 Impact Factor
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    ABSTRACT: On April 20, 2010, the Deepwater Horizon (DWH) blowout occurred, releasing more oil than any accidental spill in history. Oil release continued for 87 d and much of the oil and gas remained in, or returned to, the deep sea. A coral community significantly impacted by the spill was discovered in late 2010 at 1,370 m depth. Here we describe the discovery of five previously unknown coral communities near the Macondo wellhead and show that at least two additional coral communities were impacted by the spill. Although the oil-containing flocullent material that was present on corals when the first impacted community was discovered was largely gone, a characteristic patchy covering of hydrozoans on dead portions of the skeleton allowed recognition of impacted colonies at the more recently discovered sites. One of these communities was 6 km south of the Macondo wellhead and over 90% of the corals present showed the characteristic signs of recent impact. The other community, 22 km southeast of the wellhead between 1,850 and 1,950 m depth, was more lightly impacted. However, the discovery of this site considerably extends the distance from Macondo and depth range of significant impact to benthic macrofaunal communities. We also show that most known deep-water coral communities in the Gulf of Mexico do not appear to have been acutely impacted by the spill, although two of the newly discovered communities near the wellhead apparently not impacted by the spill have been impacted by deep-sea fishing operations.
    Proceedings of the National Academy of Sciences 07/2014; 111(32). DOI:10.1073/pnas.1403492111 · 9.67 Impact Factor
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