– JESSICA RESNICK-AULT

Bloomberg News

The millions of gallons of oil leaking from a broken well a mile under the Gulf of Mexico may create oxygen-depleting dead zones below the ocean, killing sea life and upsetting the region’s ecology for decades, scientists say.

BP’s oil spill, the biggest in U.S. history, has been sprayed with 950,000 gallons of chemicals on the surface and near the seabed to dissolve the oil into water. The amount of dispersants used is unprecedented and the behavior of the dissolved oil unknown, Environmental Protection Agency Administrator Lisa Jackson has said.

“There is great, great concern of the subsurface nature of this event, of the amount of dispersants and what this means to the entire ecosystem,” Roger Helm, Chief of the Fish and Wildlife Service’s Division of Environmental Quality, said at a press conference. “This is going to be groundbreaking science.”

A government team appointed by the Coast Guard estimates oil has been spilling from the well at a rate of 12,000 to 19,000 barrels a day. That could increase as much as 20 percent when BP makes its next attempt to control the leak by sawing off a damaged pipe. Within the week, BP plans to reconnect the pipe and funnel oil to a ship on the surface.

Even if BP succeeds, long-term damage to the Gulf ecosystem is unavoidable, said Rick Steiner, a marine biologist and consultant who has worked with governments and the United Nations on oil spills.

“This much oil in a productive marine environment will cause substantial environmental damage,” he said.

Marine biologists are worried the oil will kill off fragile organisms, such as shrimp and fish larvae and plankton, a critical part of the offshore food chain, Steiner said. Fish can also suffocate if their gills are coated with crude.

Microbes in the sea that feed on oil seeping from the seabed are expected to consume most of the underwater oil from the leak, said Frank Muller-Karger, professor of biological oceanography at the University of South Florida.

With such a big oil spill, that may bring its own problems, he said. Populations of oil-gorged microbes could expand rapidly, consuming oxygen needed by other sea life and creating “dead zones.”

“You end up with a transformation of the chemistry of the water, and we are not clear on what that is,” Muller-Karger said.

Universities and federal agencies are dispatching boats to search for oil deep within the sea, where it remains unseen and more difficult to measure than the oil floating atop the water or washing ashore.

Oil from the spill may have spread underwater for 22 miles toward Mobile, Ala., researchers aboard a University of South Florida vessel reported Thursday. Initial tests aboard the Weatherbird II show the highest concentrations of “dissolved hydrocarbons” were 1,312 feet below the surface.

Research crews dispatched to study the spill include expeditions funded by the Louisiana Universities Marine Consortium, the National Oceanic and Atmospheric Administration, and the National Science Foundation.

Coastal marshlands, which are breeding grounds for a rich variety of sea life, will take years to recover from the toxic effects of crude, scientists say.

The environmental effects of oil spreading beneath the sea are less certain.

Clouds of oil-contaminated water may threaten fish that are migrating through the area. As the Northern Gulf of Mexico warms, bluefin tuna, kingfish, and marlin swim from the Atlantic into the Gulf, said Muller-Karger, of the University of South Florida. Sea turtles, whale sharks, and others follow the same migratory path.

“Animals are reproducing at this time of the year,” he said.

Oil will kill shrimp larvae hatched from eggs laid in the open sea, said John Williams, executive director of the Southern Shrimp Alliance in an interview.

“Once you break that cycle, there is no telling how long it will take to build the cycle back up,” Williams said. “Until the oil is stopped, we can’t begin to determine the immediate or long-term impacts.”