Study: Oil will not create ‘dead zones’

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.”

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.