Millions of barrels of crude spewed by BP’s blown-out well have reduced deep-sea oxygen levels — but nowhere near enough to create another of the “dead zones” that periodically plague the Gulf of Mexico, a federal study said Tuesday.
The report is the latest to suggest chemically dispersed oil suspended near the sea floor did not become the drifting cloud of death some doomsayers had predicted. Instead, currents and oil-eating microbes appear to have steadily dissipated and degraded the crude in the two months since BP capped its well, said Steven Murawski, leader of a team of scientists that produced the report.
Plumes once stretching miles from the belching well have broken into disconnected pieces that are “harder and harder” to find, he said, as the concentrations fade to levels barely detectable by the most sophisticated instruments.
The oil, Murawski said, has become “like a shadow out there.”
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Though the “sag” in levels of life-giving oxygen, created by an explosion of bacteria feasting on the surge in food, posed no problem for marine life, Murawski cautioned it will take much more data and time before scientists can pronounce the threats over for the Gulf’s fragile food web.
Oil-eating bacteria, for instance, eat the lightest of the dozens of compounds comprising crude oil, leaving behind the heaviest and most toxic pollutants, including dozens of PAHs (poly-aromatic hydrocarbons) that can cause cancer or genetic mutations. Even minute amounts could potentially damage tiny plankton and fish larvae, the vulnerable base of the food web, said Murawski, chief fisheries scientists for the National Oceanic and Atmospheric Administration.
“Are we going to skip a generation on things like bluefin tuna?” he asked. “That’s another question we will try to answer.”
Still, the data offered the latest evidence that the Gulf was showing considerable natural resilience to the effects of the largest oil spill in U.S. history.
When the plumes were first detected between 3,300 and 4,300 feet below the surface in May by scientists from the University of Georgia and then confirmed by researchers from the University of South Florida, the unprecedented discovery raised concerns that a mistlike mass of oil combined with chemical dispersant could be worse for marine life than crude by itself — either proving outright toxic or triggering a frenzy of blooming bacteria that would consume all the oxygen from the deep zone.
A subsequent series of reports produced largely by government agencies have been far more upbeat. The latest report on oxygen data, based on May-to-August sampling from 419 spots as far as 60 miles from BP’s well, found average levels down only about 20 percent. Murawski said levels would have to drop another 70 percent to reach the oxygen-starved hypoxic range that defines a dead zone.
The Gulf is already peppered with them, including one of the largest in the world that forms every summer from pesticides, fertilizers and other chemicals pouring out of the Mississippi River.
The 95-page report, produced by the Joint Analysis Group, which is comprised mainly of government scientists with some academic input, also appeared to validate the unprecedented and controversial use of dispersants on the leak some 5,000 feet down.
In a move opposed by many environmental groups and scientists, the federal government allowed BP to pump nearly 800,000 gallons of chemical dispersants into the flowing oil. The tactic may have contributed to the plumes, producing fine droplets that remained suspended deep beneath the sea, but it also did what it was intended to do, Murawski said.
“The whole theory of using dispersants was, you would make the droplets small enough so that they would be rapidly consumed by bacteria,” he said. “That is what is happening.”
The report follows a study published by another team of federal scientists in the journal Science late last month that described a newly identified microbe doing much of the cleanup work underwater.
Lead author Terry Hazen, a microbiologist at the Lawrence Berkeley National Laboratory in California, had predicted bacteria would make quick work of the spill and continued monitoring has confirmed that, he said. Hazen goes further than the joint group’s study, pronouncing the plume “gone.”
“If there is anything there, it is in very low concentrations,” he said during an interview last month.
Other recent studies by academic groups, however, suggest the potential for continuing impacts. Tests last month by a University of South Florida team, which returned from the Gulf this week, produced preliminary results showing water samples collected far from the well caused damage to exposed plankton. The group also found oil in bottom sediments. In a blog post Sunday, University of Georgia marine scientist Samantha Joye, leader of the team that first discovered the plumes, reported finding oil in bottom sediments 16 miles from the well during an ongoing voyage.
Richard Camilli, an associate scientist of ocean physics and engineering at Woods Hole Oceanographic Institute in Massachusetts, said there was little question that time, ocean currents and the Gulf’s microbes would render much of the remaining oil undetectable.