Wind, currents keep Gulf slick from shore

Favourable winds and currents have kept most of the massive Gulf of Mexico oil slick from reaching the fragile wetlands and sandy beaches of the US Coast for more than three weeks, experts say.

But landfall is inevitable given the sheer volume of crude gushing out of the wreckage of a BP-leased rig, as is damage to marine life and the subsea ecosystem.

"It's going to be bad," said biologist Dennis Takahashi-Kelso, who was Alaska's commissioner of environmental conservation at the time of the Exxon Valdez disaster in 1989.

A big fear is that the oil will get into the fast-moving "loop current" which carries water from the Gulf of Mexico through the Florida Keys and up to North Carolina before heading out into the Atlantic.

The winds that have kept the oil away from the current are forecast to shift on Wednesday or Thursday, said Steven Morey, who is tracking the spill.

If the oil gets into the loop current it will reach Florida in days, but it is not yet clear how much will get onto the beaches.

"It brings back the classic argument of decades ago that the solution of pollution is dilution," said Morey, of the University of Florida's Center for Ocean-Atmospheric Prediction Studies.

Some oil will simply evaporate. Some will be skimmed or burned off the surface by cleanup crews. Some is being broken down by chemical dispersants. Some will be eaten by microbes. Some will sink to the bottom.

"We don't expect the oil to stay as concentrated," Morey told AFP.

"It would be broken up and diffused and dispersed. I'm sure it would be detectable and there would be isolated blobs, but it's not clear to me that there would be huge quantities... unless it keeps going."

The real question is how much oil there is in the Gulf, and when it will stop gushing out of a broken pipe 5,000 feet (1,500 metres) under the surface and 52 miles (83 kilometers) from the Louisiana coast.

BP succeeded Sunday in capturing some oil and gas by inserting a one mile (1.6 kilometer) long tube into the main Gulf of Mexico leak, but did not say what percentage of the gusher was being contained.

Researchers analyzing the rate of flow on a video released last week say it could be anywhere from 20,000 to 100,000 barrels a day, drastically higher than initial estimates of 5,000 barrels a day.

The undulating slick -- estimated to stretch across an area roughly 60-miles long and 100-miles wide -- has now broken up into smaller patches separated by open water.

Most of the oil on the surface will elude some booms and skimmers even in good weather, warned Dec Doran, an oil spill consultant who worked for Exxon during the Exxon Valdez spill.

"If you can contain and recover 20 percent of this oil, you've reached the maximum efficiency of booms and skimmers," said Doran, who has worked on more than 2,000 spills.

It is also forming giant plumes underwater - "perhaps due to the deep injection of dispersants which BP has stated that they are conducting," said researchers from the National Institute for Undersea Science and Technology.

"There's a shocking amount of oil in the deep water, relative to what you see in the surface water," Samantha Joye, a researcher at the University of Georgia who is coordinating the mission told the New York Times.

The plumes - one as large as 10 miles (16km) long, three miles (5km) wide and 300 feet (100 metres) thick in spots - have depleted the oxygen in the nearby water by as much as 30 percent, she said.

"If you keep those kinds of rates up, you could draw the oxygen down to very low levels that are dangerous to animals in a couple of months," she told the paper.

"That is alarming."

Another concern is that the dispersed oil is more easily able to penetrate the tissue of marine animals, marine biologist Thomas Shirley said in a telephone interview.

"We don't know if this oil will make it through food webs," said Shirley, of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi.

"There's the potential for lots of ecological problems."

The Gulf already absorbs about 48 million gallons of oil seeping every year from natural leeks in its seabed, Shirley said.

Marine life has learned to evade a massive dead-zone created by agricultural runoff that breeds algae which suck the oxygen out of the water.

And it has even recovered from the 1979 blow-out of the Ixtoc I rig in Mexico's Bay, which emptied 140 million gallons of crude into the Gulf before it was finally capped nine months later.

Some 71,500 barrels of oil eventually washed 600 miles north where it coated 162 miles of US beaches.

Populations of the small crustaceans and worms that shorebirds and small fish relied upon plummeted by 80 percent in the intertidal zone and 55 percent in the surf zone, said John "Wes" Tunnell, who studied the effects of the Ixtoc I spill on the South Texas coast.

"The good news is that it recovered fairly quickly," said Tunnell, also of the Harte Research Institute for Gulf of Mexico Studies.

"The Gulf of Mexico is a very resilient place to have an oil spill."