An undersea conveyor belt to Florida is approaching the Gulf Coast oil spill, and should it stretch past its typical bounds, oil from the BP PLC accident, blobbing placidly off the Louisiana coast, could soon stream into the Florida Keys and up the United States' Eastern Seaboard.
Or the current could miss the spill entirely.
Government officials and scientists from Mississippi to Florida are holding their collective breath to see whether a strong but unpredictable current in the Gulf of Mexico, known as the Loop Current, will continue to expand north toward Louisiana. Two days ago -- the latest time for which satellite data are available -- the current sat 125 miles south of the spill, its rotating tendrils licking at the slick's eastern edge.
"It is a very important concern," said Bob Weisberg, an oceanographer at the University of South Florida, who has long warned of the flow's potential impact on his state. "The Loop Current is actually moving toward the oil."
For the current to begin conveying the oil at any volume, it would still have to surge much farther north, which some computer models like Weisberg's are predicting. However, as Weisberg confesses, many of these models are deeply flawed, and the behavior of the Loop Current -- when it will decide to surge or instead break apart -- is prohibitively complex to forecast.
In other words, "no one has really been able to predict with much accuracy what the Loop Current will do," said Nan Walker, the director of the Earth Scan Laboratory at Louisiana State University, who is monitoring the oil and current with several sets of satellite data.
The worst-case scenarios have been concerning enough for communities in Florida ranging from Tampa Bay to Key West to begin mobilizing contingency plans. Should the current reach the spill, oil would begin to flow down past Florida's western coast, which would be largely spared due to its wide coastal shelf, and into the Florida Strait. There, the chemical dispersants used to break up the oil could turn on vulnerable wildlife.
"The dispersants could kill corals," Walker said. "Obviously, oil is not going to be good for corals. That is probably one of the biggest concerns if [the oil] was entrained."
But this devastation is far from a sure bet, scientists say.
The Loop Current runs from the Yucatan Peninsula to the Florida Strait, where it eventually feeds the Gulf Stream. Often, the current lies low in the latitudes, barely extending into the Gulf of Mexico. But then, in erratic but frequent intervals, the current plunges deep up into the Gulf's eastern waters, like a sharp elbow extending from Cuba into the gut of Louisiana.
Without fail, however, the current cannot sustain this intrusion, and the current's northernmost reaches break apart. Small currents, known as eddies or ring separations, begin rotating toward the west, against the current's flow. And eventually, the whole top of the current breaks apart and floats west toward Texas.
The current "usually grows and eventually runs out of room," said Villy Kourafalou, a Gulf of Mexico modeler at the University of Miami's Rosenstiel School. "The whole top of the Loop Current gets disconnected."
When this will happen to the present iteration of the current is nearly impossible to say, though scientists hope it will shed its top before approaching the oil spill. The current's lifetime can run from a half-year to almost 18 months, showing little seasonal variability. When and why the separation occurs is an area of very active research, Kourafalou said.
Even satellite imagery of the current, which can run up to 1,000 meters deep, is difficult to compile. It takes a week of data to get an accurate picture, said Tony Sturges, an oceanographer at Florida State University. Sturges, one of the foremost experts on the current, is concerned that oil could sluice down to Miami.
But "do I have any idea whether it will come to pass?" he said. "Not a clue."
No prediction system
Weisberg has been using several models to attempt to predict the Loop Current, hoping their various flaws will average out, much as is done with hurricane prediction. Those models indicate the current is moving toward the oil, but Weisberg can't say for certain when or if the current will hit.
More likely, but still uncertain, is that small eddies could swirl off the current and entrain at least a small amount of oil, Walker said. These currents are generally weak; some are already helping to both push the oil toward the shore and draw some of it toward the east. How much oil could circulate this way is difficult to say.
The prevailing winds on the Gulf Coast, which typically run from east to west, are likely to begin blowing instead toward Florida. Some of the oil will go toward Louisiana beaches and marshes, and some will push farther east, though with all the complex currents running in the area, long-term predictions are tough, Walker said, though there is one certainty.
"This oil spill is going to be around for a while, I'm afraid," she said.
There is some precedence for the conveyor belt action of the Loop Current. In the 1990s, the current transported floodwaters flush with nutrients out of the Mississippi Delta all the way to eastern Florida. But instances when the current comes so close are rare, Walker said.
It is also far from certain that the current would provide a straight shot to the Florida Keys. In particular, Kourafalou is eyeing a large vortex down the current's path east that could delay the oil or even pitch it off. Or, she added, the oil could miss it entirely and flow like a "flume" eastward.
If the worst comes to pass, Florida's eastern shores would be particularly vulnerable, she added. The narrow shelf of the Florida Keys could cause the current to break apart, delivering oil and dispersants to the shore. Unlike the state's west, the Atlantic shore lies close to deep water and the Florida Current, which the Loop Current feeds.
Everglades researchers are already expressing fear that the oil could run into Florida Bay and potentially devastate its fisheries, sea grasses and shallows. More water evaporates from the bay than flows into it from the Everglades this time of year, creating a sink-like effect that leaves the delicate ecosystem at some risk of attracting oil flows, said James Fourqurean, a sea-grass ecologist at Florida International University.
"That means, then, that if a surface slick runs down very close to shore along the southern tip of the peninsula, that slick could be pulled into Florida Bay and remain resident there for a number of years," he said.
While the fate of the Everglades remains to be seen, Kourafalou finds it shameful that the government and oil companies have not been better prepared and committed the money to get a full-fledged, accurate prediction system operating for the Gulf, she said.
"It's amazing that there's no prediction system in place for the Gulf of Mexico," she said. "It should be in real time. It should be ready."
Reporter Paul Quinlan contributed.
Source: http://www.nytimes.com/gwire/2010/05/05/05greenwire-unpredictable-current-is-wild-card-in-gulf-dis-51911.html
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