A little more than six months after the Deepwater Horizon oil platform caught fire and ultimately sank, signs of that accident continue to appear along the shores of the Gulf of Mexico.
Louisiana fishermen found "massive stretches" of oil floating toward marshes in the Mississippi Delta on Friday. According to the New Orleans Times-Picayune newspaper, boat captains working the BP clean-up effort said they have been reporting large areas of surface oil off the delta for more than a week.
It is hardly the only observation of surface, or near-surface, oil since the Obama administration gleefully declared in August that 75 percent of the Deepwater Horizon spill had been magically cleaned up. For much of this past summer, for example, I helped coordinate a Greenpeace tour of the Gulf, members of which found tarballs on Horn Island off Mississippi last month.
That Greenpeace expedition primarily sought to provide an opportunity for independent researchers to use the organization's vessel Arctic Sunrise as a platform from which to look beneath the surface and begin to answer the questions of where most of the oil has gone and what the possible impacts of the spill might be. That tour ended this past weekend in New Orleans.
The crew of the Sunrise hauled plankton nets off the stern so that a team from Tulane University could examine the possible impacts of the oil on blue crab larvae, a key component of the Gulf ecosystem. A consortium of researchers deployed passive acoustic buoys to listen for sperm and beaked whales.
Equipped with several years of baseline studies that have enabled them to establish distributional patterns of those species in the Gulf, the researchers will be able, once they complete analysis of the recordings on the buoys' hard drives, to get a sense of whether any of those patterns have changed since the spill.
The Sunrise crew also worked with a team from Texas A&M University to search for undersea plumes of oil:
And it even deployed a submersible -- kindly donated by the Waitt Institute for Discovery -- to search for possible impacts of oil on deep sea coral systems in the Gulf:
And yet, still unresolved is perhaps the most contentious issue of all: Where did all the oil go?
Even allowing for the skimming and burning of much of the surface oil, the bulk of what entered the Gulf as a result of the Deepwater Horizon disaster should still be somewhere beneath the waves. The Texas A&M team on board the Sunrise found evidence of oil in the water column far beneath the surface, approximately 300 miles (500 km) from the site of the accident, by analysing the water for low oxygen levels -- a sign that oil-consuming bacteria were in the area.
Interestingly, however, the scientists didn't find quite as strong a low-oxygen signal as they anticipated. This doesn't mean that the oil isn't there, but rather that bacteria aren't consuming as much of it as they might have predicted.
It could be that some of those undersea plumes have, as time has passed, become more diffuse and thus harder to detect. Increasingly, however, researchers are looking to the bottom.
In September, the Texas A&M team pulled up several samples of sediment from the sea floor that contained visible amounts of smellable oil. That echoed findings by Samantha Joye of the University of Georgia, and also more recently by Kevin Yeager of the University of Southern Mississippi, who just completed a research voyage on board the National Science Foundation-owned vessel Cape Hatteras.
"Clearly, there appears to be vast volumes of oil present on the seafloor," Yeager said. "We saw considerable evidence of it."
Precisely how much oil that is, and what its effects are on the ecosystem, are for now matters of great uncertainty. For Gulf researchers, this is merely the end of the beginning. The Macondo well spilled oil into the Gulf for over two months. Establishing the full consequences of that spill will take scientists much longer than that.
Tags: Oceanography, Water
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