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Change in loop current could give Florida a break from oil spill

By Pat Farnan and Katie Sanders, Times Staff Writers
In Print: Friday, May 21, 2010

* Maps: See how the current will change where the oil goes next.

Scientists are tracking a potential shift in the Gulf of Mexico loop current that could dramatically reduce the amount of oil carried to Florida or the East Coast over the next several months.

Essentially, the loop current would reroute itself, no longer sweeping up oil from the massive spill in the central gulf and carrying it south to the Keys and beyond.

Instead, the current would remain well to the south, with surface oil out of reach.

"This could be great news for Florida, at least for now,'' said Frank Muller-Karger, biological oceanographer at the University of South Florida.

The loop current is constantly reshaping itself. But this latest change could last several months, giving much of Florida a reprieve from the tendrils of oil now making their way south in the loop current.

It may be days or weeks before scientists can say with certainty that the loop current's path has changed. It is known for unpredictability, and many scenarios are still possible. Moreover, the rerouting may not affect what is happening beneath the surface, which ultimately could be a bigger problem.

For now, however, many scientists are hopeful.

"The bottom line of all this happening is that it would slow down the path of the oil to the Keys and Florida's coast," said Mitch Roffer, president of Roffer's Ocean Fishing Forecasting Service, who briefed the White House on Wednesday about the oil spill. "It would buy us a lot of time."

• • •

The loop current probably has received more attention recently than at any time in its history.

Scientists, environmentalists and the public want to know if it is going to transport oil from the central gulf to the Florida shoreline, the Keys or the Atlantic coast.

Here's what's happening:

The loop current is part of the Gulf Stream system, a strong current in the western Atlantic Ocean. Easterly tradewinds push water from the Atlantic into the Caribbean Sea, where it is funneled into the narrow Yucatán Channel between Mexico and Cuba.

The pressure caused by the wind and the narrowness of the channel speeds the loop current along at about 5 mph, pushing it north into the central Gulf of Mexico. Eventually, the land mass to the north and the Earth's rotation cause the current to loop back to the south and flow to the Florida Straits.

From there the water heads north as the Gulf Stream moves parallel to the Atlantic coast until it begins to head east off the Carolina shoreline.

But this flow changes dramatically from time to time. The transition can take anywhere from six months to more than a year.

Imagine the loop current in the shape of a horseshoe. Eddies, created by the complex system of currents and topography interacting with one another, develop along the outer wall of the horseshoe.

One of these, known as the Tortugas Eddy, periodically expands and moves westward, rotating counter-clockwise. If it continues long enough, usually a few weeks, it can literally clip the north end of the loop current from the south.

The top of the loop current then becomes its own system. Up to 300 miles across, it wanders off in a westward direction, eventually crashing into Texas or Mexico and dissipating.

As this happens, the bottom of the loop current changes direction. Instead of shooting north into the central gulf, it takes a more easterly course, traveling from the Yucatán Channel to the Florida Straits, then up the East Coast.

If the north end of the loop current is clipped off in the next few hours, days or even weeks, scientists say, it would be far less likely to carry huge amounts of oil from the spill to the Florida shoreline, the Keys or even the Atlantic Coast.

It simply wouldn't be far enough north to pick up the oil from the spill.

That's good news for Florida — at least temporarily — but perhaps not for Texas, Louisiana and Mexico.

Eventually, the loop current would push its way north and reform in the north central gulf. But that usually takes several months.

Nothing is certain of course. Every year for the past three years, the northern part of the loop current appeared to separate itself from the south, but somehow it reattached and then detached again.

"We just don't know for sure if this time it will have a clean break or if it will reattach itself,'' Muller-Karger said.

• • •

In one respect, Florida already has gotten a break.

Under the current scenario, it is unlikely that oil in the loop current will make its way to the west Florida coast. It would take sustained winds, probably a tropical storm or more for several days, to push oil from the loop current, across the relatively shallow Florida shelf to the state's west-central coast.

If the north end of loop current separates — known among scientists as the '"shedding of an eddy'' — that also would bode well for Florida.

But other problems remain.

The Keys, for example, may still see some form of contamination within a few days because of the tendrils of oil already in the loop current. If the top of the loop current separates, however, that oil may never get to the Keys.

The greater danger, some scientists say, is the oil below the surface.

The loop current affects water from the surface to depths of about 3,000 feet. Because the leak is at a depth of about 5,000 feet, it raises questions about oil moving around beneath the loop current.

"We don't know what's happening with that oil,'' said Muller-Karger, who testified Wednesday before a House Energy and Commerce subcommittee hearing in Washington, D.C. "It's much easier to track oil on the surface than it is to track oil well beneath the surface.''

What's more, the oil is still pouring into the gulf.

"If they don't get this thing plugged," said Muller-Karger, "everything could change."

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