The undersea plumes that BP and the feds denied are still there.
Is most of the oil gone or not? At the beginning of the month the government released its assessment of where the 4.9 million barrels of oil from the Deepwater Horizon had gone. Its rose-colored-glasses conclusion: about one quarter of the oil that gushed up from the Macondo well was physically removed (skimming, booming, piping to surface), one quarter was dissolved in the gulf waters, and one quarter was busted up by chemical dispersants or natural weathering into microscopic droplets. That left “only” 26 percent to foul shores and surface waters. That has triggered the predictable “Ha! I told you those crazy enviros were exaggerating how bad this was” chorus in the blogosphere.
Not so fast. As NEWSWEEK reported in June, the biggest long-term environmental threat from BP’s oil comes from vast undersea hydrocarbon plumes, not the stuff on the surface. Now a team of scientists has concluded that those plumes are even bigger than initially feared, that the flow rate that produced them swamps the natural “seeps” of hydrocarbons from vents on the seafloor, and that microbial decomposition is so slow the plumes aren’t going to dissipate for some time.
Oceanographic Institution used the autonomous robot sub Sentry (which took 3,500 measurements over 140 miles as it moved in a zigzag pattern at different depths) and a cable-tethered mass spectrometer (2,300 measurements) to sample water from the gulf from June 19 to 28 and analyze it for the presence of oil and methane. What they found was like dipping a drinking cup repeatedly into Loch Ness and coming up with enough body parts to infer the existence of a monster: there is a continuous, unbroken plume of hydrocarbons about 3,300 feet down, stretching southwest from the well for some 22 miles. The scientists suspect it is even longer, but they had to stop sampling when Hurricane Alex blew in. Still, said Camilli, “we’ve shown conclusively not only that a plume exists, but also defined its origin and ... structure. Until now, these have been treated as a theoretical matter”—especially by BP and even the government, which for weeks denied the existence of the plumes. (In late June and again in late July, however, the National Ocean and Atmospheric Administration released results of subsurface monitoring by several of its research vessels, finding a “cloud of diffuse oil at depths of 3,300 to 4,600 feet near the wellhead.”)
The plume has “persisted for months without substantial biodegradation,” the scientists report in an account of their discovery in tomorrow’s issue of the journal Science. The plume measured 650 feet high and, in certain places, more than 1.2 miles wide. It maintained its structural integrity—that is, it didn’t dissipate—more than 21 miles from its source at the wellhead. For as long as the scientists sampled the plume, it seemed to be holding at a constant depth. “But we do not know what its fate now is,” Camilli said at a press conference in Washington this afternoon. It was traveling at about four miles per day, and so would be far from where the scientists detected it in June.
The density of hydrocarbons (benzene, toluene, ethylbenzene, and xylenes—all toxic and some carcinogenic) in the plume was about 50 micrograms per liter, which is equal to about half a cup in an Olympic-size swimming pool. (The government estimated four to seven, and if you include all the components of petroleum, the density would be greater.) That implies the hydrocarbons that formed this plume were gushing out of the well at a rate of at least 40 barrels per day, which is more than twice the total rate of 14 barrels a day at which all the natural seeps in the northern gulf release these hydrocarbons. (The overall rate—including oil that made it to the surface and onto coasts—was as much as 60,000 barrels per day. Only the tiniest fraction of the overall gusher was therefore sufficient to form this massive plume.) So much for the contention that since the gulf is used to petroleum leaks because of its natural hydrocarbon-venting seeps, BP’s oil wouldn’t be much of a problem. That’s like saying that because having one bottle of wine won’t make you drunk, neither will drinking three.
So much, too, for the argument that natural oil-chomping microbes would take care of the undersea plume. They seem to be degrading the plume only slowly, at least when and where the Woods Hole scientists did their sampling. Further evidence of that: the scientists found no “dead zones” in the plume—that is, regions so depleted of oxygen that fish and other animals would have trouble surviving. That supports the idea that microbes, which consume oxygen, are not present in the quantities needed to quickly degrade the plume. If so, says Woods Hole geochemist Benjamin Van Mooy, “the hydrocarbons could persist for some time. So it is possible that [the plumes of] oil could be transported considerable distances from the well before being degraded.” Camilli adds: “Many people speculated that subsurface oil droplets were being easily biodegraded. Well, we didn’t find that. We found it was still there.”
The Woods Hole study was not the only one this week suggesting that the government has low-balled estimates of the remaining oil. On Tuesday five marine scientists at the University of Georgia announced their own calculation of how much of BP’s oil remains: up to 79 percent has not been recovered and remains a threat to the ecosystem, they said.
Why the difference from the government’s claim that only one quarter of the oil remains? The government, in a debatable choice of categorization that was widely echoed in the media, counted “dissolved oil” as, basically, gone. But that’s like saying if you dissolve two packets of sugar in your coffee it’s gone. Only oil at the surface of the ocean can evaporate into the atmosphere—and as the Woods Hole study shows, large plumes of oil are trapped in deep water, going nowhere fast.