Gulf Oil Spill: Brace for Hurricane Season

As if people along the Gulf of Mexico didn't have enough to worry about, researchers at the U.S. Naval Research Laboratory in Mississippi have crunched some numbers and warn that passing hurricanes — the season begins next week, and NOAA predicted today it will be “active to extremely active”  — could snap undersea oil pipelines in ways never before estimated.

Most of us think of hurricanes as violent storms in the atmosphere.  But Hemantha Wijesekera and her colleagues looked at data from Hurricane Ivan in 2004 — a category-4 storm, the tenth most intense on record — and found it was scouring the gulf floor as much as 90 meters (300 feet) beneath the surface.

This matters because of the network of pipes and cables that connect offshore rigs in the gulf to the mainland.  There are 31,000 miles of pipelines snaking across the floor of the gulf, according the American Geophysical Union.

Wijeskera et al, writing in Geophysical Research Letters for publication on June 10, say the undersea force of the storm was considerable.

"During the passage of Ivan, the bottom stress was highly correlated with the wind with a maximum of about 40 percent of the wind stress," they say. "The bottom stress was dominated by the wave-induced stresses, and exceeded critical levels at depths as large as 90 m. Surprisingly, the bottom damaging stress persisted after the passage of Ivan for about a week, and was modulated by near-Inertial waves."

The paper was submitted for publication in March, well before the Deepwater Horizon crisis began on April 20, but it will become one more factor to consider in the debate over offshore drilling.

I traded e-mails a couple of weeks ago with Mark Bourassa, a meteorologist at Florida State University who studies the transfer of energy between the ocean and atmosphere, and he said a hurricane in the gulf could make a mess of cleanup efforts.

"It would generate lots of relatively large waves, which will make booms less effective even far away from the storm — how far depends on the strength of the storm," he wrote. "It will also spread the oil over a much larger area.

"However, rougher seas will also mix the oil, taking some of it off the surface and increasing the surface area of the oil," he said.

Would the presence of a large oil slick have an effect on a hurricane's strength or path?  Not likely, said Bourassa, but it's a complicated issue.  It is possible, he said, that a slick could trap heat — the fuel of a tropical cyclone — in the water beneath it.

"If the oil does trap a lot of heat, and if a very slow-moving storm enters the Gulf and generates lots of waves to mix up the oil, then we could have a very bad situation!"
(Satellite image of Hurricane Ivan in 2004. Courtesy NOAA.)