MIAMI — Starved of its daily dose of crude and under assault by wind, waves, sun, oil-eating bacteria and the largest fleet of oil skimmers ever assembled, the massive oil slick that has stalked the Gulf of Mexico for three months has been shrinking for the past week.
Now, a blustery tropical system expected to hit the main spill area Saturday could literally blow much of the slick's remnants away, whipping the countless drifting streamers of ooze, mats and balls so far and wide that the surface slick could virtually vanish overnight.
That sounds like good news, but Bonnie, now a tropical depression, also could drive a toxic tide deeper into the rich and fragile estuaries of coastal Louisiana or propel tar balls onto the beaches in Florida and Mississippi. It could even draw oil suspended thousands of feet down up to the surface to form new slicks.
"What we have learned completely changes the idea of what an oil spill is," said David Hollander, a chemical oceanographer at the University of South Florida, where researchers on Friday announced that they'd definitively traced oil found suspended in the Gulf to BP's blown-out well through chemical fingerprinting.
Never miss a local story.
"It has gone from a two-dimensional disaster to a three-dimensional catastrophe."
Experts said they can't predict with certainty whether Bonnie will help or hurt as it races across the Gulf.
"In some areas,it may disperse oil. In other zones, it may shove it inland," said Ron Kendall, director of the Institute of Environmental and Human Health at Texas Tech University.
Coast Guard Admiral Thad Allen, the Obama administration's point man on the spill, said that he'd flown over the area the previous day and "there's not a lot of oil out there."
He acknowledged, however, that the storm could drive much is still out there onto beaches or into wetlands yet untouched by the spill. He said crews were "prepared to move out and aggressively attack this once the threat is passed through."
With seas up to 10 feet likely to swamp miles of boom set to protect coastal areas, there was little question that portions of low-lying coastal marshes would be inundated.
The federal government's daily shoreline report showed heavy oiling already in some spots at the tip and both sides of the Louisiana's Mississippi delta, from Barataria Bay to the Chandeleur Islands.
Hurricane Alex, which passed far south of the spill site in June, managed to push oil as far north as Lake Pontchartrain. Bonnie, though less powerful, was tracking dead center toward the Deepwater Horizon site some 50 miles off the delta's tip and pushing an expected storm surge of 2 to 5 feet.
In 1979, Hurricane Frederic actually removed tons of oil hardened with sand that had piled on Texas beaches three months after the Ixtoc well blowout in Mexico's Bay of Campeche.
Experts are divided by what will happen with this storm.
Kendall argues that the consistency of the vast volume of oil now in the Gulf, much of it suspected to lie below the surface, bodes badly for wetlands in Louisiana that already had suffered the brunt of the oil exposure.
Much of it, he said, had congealed into a pudding-like ooze that, once the tide falls out, could suffocate plants or tiny wetlands denizens or act as pockets of slow-release poison.
Jerry Galt, a physical oceanographer with the National Ocean and Atmospheric Administration, said the intense sloshing most likely would dilute the oil's impact, reducing its concentration and breaking it into smaller pieces more easily consumed by oil-hungry microbes common in the Gulf.
Just how much oil remains in the Gulf is uncertain, but the surface slick has visibly shriveled in the eight days since BP finally corralled its raging well.
The day before BP closed the last valve to seal the flow, skimmers slurped up 25,000 barrels, most of it oil. By late last week, daily volume skimmed had plunged to 56 barrels, half of it water. NOAA's trajectory maps also showed a dramatic reduction in both the size of the slick and the density.
It remains undetermined how much oil lies beneath the surface in "plumes" that BP initially denied existed.
In a report issued Friday, NOAA confirmed that clouds of oil now stretch throughout the Gulf at depths of 3,300 to 4,300 feet, carried through the Gulf by its natural currents.
Those plumes are probably too deep to be churned to the surface by a storm the size of Bonnie, said Nick Shay, a physical oceanographer at the University of Miami Rosenstiel School of Marine and Atmospheric Science.
Hollander's USF's study, however, also found a 100-foot thick plume much closer to the surface, one-quarter of a mile deep, 45 miles north-northeast of the well.
.A storm of Bonnie's strength might churn the ocean with enough force to force an "upwelling'' that draws cool water closer toward the surface from as deep as 300 to 600 feet.
"If there are shallow subsurface plumes, we should see them after this," Shay said.
(Morgan reports for The Miami Herald.)
MORE FROM MCCLATCHY
Follow McClatchy on Twitter.