A previously unidentified plume of hydrocarbons approximately 200 meters deep has been discovered by scientists on the R/V Cape Hatteras. The new plume appears to run south and east of the Deepwater Horizon site.
Earlier in the week, the Cape Hatteras collected samples to the west of the main plume, which runs southwest from the well site at about 1,200 meters. A number of research cruises have been collecting data on this plume, which the US National Oceanic and Atmospheric Administration (NOAA) is aggregating onto one grid. But on Thursday last week, the R/V Oceanus, conducting research under the same National Science Foundation (NSF) grant as the Hatteras, reported lower beam transmission, a data signal indicative of increased methane levels and the presence of hydrocarbons, between 200 and 300 meters. The Hatteras steamed more than 10 hours back to where these readings were taken, in the vicinity of the well site, to investigate further. “While I would like to have found the western edge of the main plume we’ve all been mapping,” chief scientist Tracy Villareal said, "this new development was way too exciting not to pursue.”
Indeed, data collected by the Hatteras all day on 10 September along a transect some 40 nautical miles long, provided strong evidence of a new, shallower plume. Those data include real-time high beam attenuation measurements, says Villareal, and elevated levels of methane in lab tests of water samples. Antje Vossmeyer, a scientist with the University of Georgia, Athens, working on board the Hatteras (see picture), reports measuring consistently elevated methane on the order of as much as 100 times background levels along this transect.
By end of the day on Friday, the Hatteras had completed the transect, which ran south and east of the well. Villareal notes that while some earlier models indicated a plume to the southeast of the well, the model placed it at much great depths. “This is not the plume shown on the model,” he said. “This is an entirely new one.” The final station on Friday recorded smaller anomalies, indicating that the eastern edge of the plume might be near. On Saturday 11 September, the ship ran a transect northward, on the east side of the well, hoping to locate the northern edge of the plume.
Last week, the Oceanus also discovered oiled sediment on the bottom of the Gulf, reported in a previous ‘oil spill science’ post and on the University of Georgia marine science department Gulf Oil Blog.
This search for oil faces many challenges, not least of which is the sheer size of the Gulf of Mexico. The Hatteras can steam for hours and cover mere inches on the map. So much water, often thousands of meters deep, offers so many places oil could be, or could go. It would take months, even years, of the methodical, careful sampling these scientists are carrying out to say with any confidence that all the oil has been found.
It will take even more work, back in labs as well as at sea, to say what effect that oil has had on the Gulf’s ecosystems. But those on the Hatteras, working diligently through station after station on this 27-day cruise, believe it is important to try. They clearly get excited about discoveries such as the new plume, which warranted a posting on the lab whiteboard, “We are documenting a new hydrocarbon plume. Very cool!”
UPDATE
The distribution of these newly-identified layers showing elevated concentrations of methane and particles present an unusual pattern, but scientists involved in the sampling mission are emphasising that their origin is not yet clear. “We cannot with any level of confidence whatsoever link this methane or other data to the Deepwater Horizon wellhead,” cautioned Samantha Joye, a University of Georgia Athens scientist on board the R/VOceanus, which is working in tandem with the Hatteras. (Two scientists on the Hatteras, including Vossmeyer, collect data specifically for Joye’s studies.) “At this time, use of the word plume is even inappropriate.”
The northern Gulf of Mexico contains many natural seeps, and there is, as yet, no clear linkage between these latest data and the well blow-out. This contrasts with the plume found earlier in the summer, where it was possible to track an increasing intensity of hydrocarbons along transect lines running southwest from the wellhead, clearly connecting that deep plume to the well.
To determine whether this new feature derives from Deepwater Horizon, Joye says, will require “fingerprinting” the samples in the lab after the cruise ends this Thursday. Throughout Sunday and Monday, the Hatteras continued running transects in shallower waters to the north of the well site, collecting data to map the extent and intensity of these new layers.
Posted on behalf of Melissa Gaskill
Photo credit: Melissa Gaskill