Boats spray water onto the Deepwater Horizon oil rig April 21, 2010, in the Gulf of Mexico off the coast of Louisiana. The rig exploded the previous day, and 11 people were killed.
Deep beneath the Gulf of Mexico's surface, oil droplets the size of marbles, peas and BBs speckle more than 1,235 square miles of seafloor, a new study finds. The globules are a toxic and permanent legacy of 2010's deadly Deepwater Horizon explosion and oil spill that spans an area larger than Rhode Island or Yosemite National Park.
'It really brings it home,' says study co-author Sarah Bagby, an environmental microbiologist at the University of California-Santa Barbara. 'We just don't know what the impacts are going to be.'
As lead author David Valentine describes: 'It's a lot of oil.' And, he suspects, researchers likely found only up to 16 percent of the Deepwater oil that's out there.
'I was surprised,' he says. 'It would have been so much cleaner if that were a higher number.'
The findings also point to perhaps the most controversial aspect of the post-explosion cleanup: whether the millions of gallons of chemical dispersants that were sprayed on and injected into the Gulf to break up the oil are to blame.
'That's the $1 million question,' Bagby says.
BP, which had leased the Deepwater Horizon rig, last month was found guilty in federal court of gross negligence and willful misconduct for its role in the disaster.
On Monday, the company issued a statement disputing the Valentine study's findings, arguing that the research team's methods led them 'to grossly overstate the amount of residual Macondo oil on the seafloor and the geographic area in which it is found.'
'Instead of using rigorous chemical fingerprinting to identify the oil, the authors used a single compound that is also found in every natural oil seep in the Gulf of Mexico, causing them to find false positives all over the seafloor,' the statement says. 'In addition, while the authors acknowledge the scattered nature of the impact to sediments, their mapping technique connects the sample locations as if the oiling were continuous between the sampling points. This dramatically overestimates the impacted area.'
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Eleven workers died and 16 were injured in the Deepwater Horizon explosion and ensuing fire, which were sparked by a blowout while BP drilled the Macondo well. Roughly 5 million barrels of oil spewed into the Gulf, making the incident the worst marine oil spill in history.
Much of that oil coagulated into slicks, washing up on Gulf Coast beaches. But plenty never reached the surface, instead clouding into a plume and settling farther down. Valentine, an expert in marine geochemistry at UC-Santa Barbara, set out to find out where it all went.
He and his team explored hundreds of kilometers of the Gulf, finding 'patterns in all those areas that pointed us right back to the Deepwater Horizon source.'
'At a small scale, it's like a splatter: It landed in small drops, bigger drops, and there may even be some giant drops out there,' Valentine says. 'It splattered on the seafloor in such a way that if you took five samples within a few feet of each other, you might see a hundredfold difference in the amount of oil between each other.'
The oil droplets, he and his team found, sank about a centimeter or two into the seabed. On deep sea coral in particular, they settled in 'a very large area of very high concentration.'
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'These are communities that lived for hundreds of years in the deep oceans - home for ecosystems. These are corals that are fixed to rocks on the seafloor and eat things that happen by,' Valentine says. 'It's rich in life, and the oil has the impact to affect that life, and in this case it did.'
What's unclear is why the oil dispersed into particles, and even why it sank in the first place: 'We know that a fresh oil droplet, one that just leaked out of the well, shouldn't be dense enough to sink,' Bagby explains
And that leads back to the question of chemical dispersants.
In the weeks and months after the disaster, nearly 2 million gallons of toxic dispersant was dumped and pumped into the Gulf to break up oil slicks. Critics alleged that BP and its supporters in government were merely trying to hide the oil from sight as quickly as possible. Others, however, argued that breaking up the slicks helped avoid far worse damage from oil washing onto the beach.
'The dispersant certainly contributed to the oil that got stuck in the water of the deep ocean,' Valentine says. 'But dispersant is not going to make something sink to the seafloor, nor is it going to make it rise. Something acted on that oil that made at least some of it sink to the seafloor below.'
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That something could be bacteria. Some amount of oil naturally seeps from the Gulf floor, and microbes there have developed the ability to eat it. As bacteria glommed on to oil droplets, they may have gained enough density to sink.
'At least some of the small droplets were coalescing into bigger particles,' Bagby says. 'We don't know whether that happened without dispersants interacting, or whether the dispersants were still there but bacteria still interacted with the droplets - we have no idea how that works.
'This doesn't close the case by any stretch,' Bagby says. 'A spill this big and this deep has never been seen before, so there was a big question about what happens when you use dispersants deep in the water column and when you have a spill deep in the water column. And we're as a community still trying to figure that out.'
Posted by Unknown on Monday, October 27, 2014 - Rating: 4.5
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