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The Deep Horizon oil spill in the Gulf of Mexico has raised concerns about the possibility of some of that oil reaching Georgia’s coastal waters and ecosystems. According to scientists from the Skidaway Institute of Oceanography, the concern is not far-fetched, but the Georgia coast is not under any immediate threat.
The concern centers on the possibility of oil becoming entrained in the Gulf of Mexico’s Loop Current. The Loop Current is a continuous feature that exits the Gulf south of Florida and passes through the Florida Straits where it becomes known as the Florida Current or the Gulf Stream. Along the east coast the flow strengthens somewhat from contributions from the Antilles Current and recirculations on the offshore side. All the named portions are known collectively as the Gulf Stream System.
“As of May 24th, the position of the Loop Current was southward of the Deep Horizon well, so that most of the spilled oil has not been entrained into this strong current,” said Skidaway Institute professor Jay Brandes.
However, according to Brandes, there are indications  that some oil has begun traveling southwards on a section of the Loop current. Any oil that is entrained may eventually pass offshore of Florida, Georgia, and the Carolinas.
The average velocity experienced by oil entrained in the edge of the Gulf Stream should be about one mile per hour, or about a half a degree of latitude per day, so it would be two to three weeks from the earliest known entrainment on May 17 before that first surface oil gets to the ocean off Georgia.
Oil is degraded by sunlight and consumed by microorganisms. With the warm waters and intense sunshine of the Gulf of Mexico and the nearby Atlantic Ocean, those processes should be much more effective than they were during the Exxon Valdez spill.
“The oil will also be transformed by dilution and mixing with saltwater to become tar balls and denser oil-saltwater mixtures, which may not all be at the surface”, said Brandes. “Where and when that deeper part goes is harder to predict.”
Light and microbial degradation may not be as effective down deeper, and tar balls are more impervious to microbial degradation than surface oil slicks. The lifetime of the impervious tar balls in the ocean is estimated at about one year.
When the oil does make it into the Gulf Stream, one factor that will help protect the Georgia coast is that the Gulf Stream runs roughly 75 miles off the coast.
“The Gulf Stream is a much deeper current -- about a half mile deep -- than the shallow continental shelf,” said Skidaway Institute scientist Dana Savidge. “Since the shelf is only about a tenth as deep, the Gulf Stream does not flow near shore, but tends to hug the edge of Georgia’s broad shelf.
“Florida and North Carolina are at higher risk because their shelves are much narrower so the Gulf Stream is closer to beaches, marshes, mangroves, and sounds.
Once off the Georgia coast in the Gulf Stream, any surviving entrained oil, mixtures, and tar balls would have to get across our broad shelf somehow before it could affect the beaches and marshes.
“Unfortunately, the processes that might do that are poorly quantified or understood, so it could happen,” Savidge said.
An extreme event, like a hurricane, could potentially push oil in the Gulf Stream onto the shelf perhaps even as far as the Georgia coast. Other avenues may exist that can potentially move oil onshore as well.
There was a previous similar incident in 1979 when the IXTOC I oil spill occurred, pumping about 20,000 barrels of oil per day for eight months from a well west of the Yucatan Peninsula. Some of that oil was also eventually entrained in the Loop Current. Skidaway researchers sampled ten months after the blowout off Savannah, Ga. and New Smyrna Beach Fla. They found tar balls in the Gulf Stream and on outer shelf, but no evidence of tar balls within 40 miles of the coast. Ultimately about 200 miles of Texas coastline was significantly affected.
Skidaway Institute will be able to monitor the surface ocean currents on the Georgia shelf with its coastal radar system. This system measures surface currents out into the Gulf Stream and from the Georgia-Florida state line north into South Carolina. With it, scientists can better gauge the potential threat to the Georgia coast from any oil that manages to get onto our continental shelf. Unfortunately, while the entire west coast and the northeast coast of the U.S are monitored by similar radars, coverage in the southeast and the Gulf is very sparse. You can see the coverage in the southeast at http://www.secoora.org/, and in the entire country at: http://hfradar.ndbc.noaa.gov/.
Skidaway Institute is part of a consortium of research institutions called SECOORA (Southeast Costal Ocean Observation Regional Association). Skidaway Institute’s fellow SECOORA partners are also monitoring the progress of any oil in the Loop Current and Gulf Stream.
One of the SECOORA partners, the University of South Florida, has an excellent video of the projections based on several models. You can see it at: http://ocgweb.marine.usf.edu/~liu/oil_spill_ensemble_forecast.html
“Notice that the models don't all predict the same paths,” said Savidge. “Modeling is difficult in areas of the ocean where there are few real world observations to improve the model's performance with.”
Forecasters look at several models, and use their experience and good sense to predict which is most correct under different circumstances.
Current updates can be found at: www.skio.usg.edu or http://oceanscience.wordpress.com
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