Scientists Find Seafloor Storms in Ocean

W A S H I N G T O N, Nov. 2, 2000 -- Thousands of feet below the ocean’s surface, sudden powerful currents stir up sediments and sweep fish andshrimp along as though they were in a river, scientists havediscovered.

Past sonar readings and furrows on parts of the seafloor havehinted at these currents, called storms by some researchers.

Now they have finally been experienced, off the edge of thecontinental shelf in the Gulf of Mexico, some 8,000 to 10,000 feetdeep.

Witnessing the Storm

“Abyssal storms arise suddenly and sweep along the base of theescarpment. We got to witness that first hand,” Ian MacDonald ofTexas A&M University said Wednesday.

The powerful currents — seen by researchers during a two-weekexpedition involving several dives in the deep-sea submersibleAlvin — have carved furrows into the seafloor.

Scientists now are working to determine what causes the stormsand what implications they might have, particularly for deep seagas and oil wells now being developed in this region.

MacDonald said the storms are massive currents nearly 2,000 feetthick, moving at 1 to 1.5 knots. A knot is 1.15 miles per hour.

While that “doesn’t sound like much,” MacDonald said, normalwater movement in the deep oceans is less than one-tenth knot. Therelatively fast-moving water presses against anything in its pathwith a great force.

William R. Bryant, a Texas A&M geologic oceanographer, wasaboard Alvin during one dive into one of the powerful currents.

“It was first time anyone had ever been in” one of theseevents, he said.

A Concern for Pipelines

Currents had been detected by instruments before and powerfulones were suspected because of the shape of the seafloor, saidBryant, who was swept along in a 1.5 knot current. He believes somereach more than 2.5 knots.

“Those are exceptional, high currents,” he said. “We seelarge geological features, furrows, that are the result of thesecurrents.”

Bryant said the currents are a “constraint” rather than ahazard to oil and gas rigs. The current is sufficient to underminepipelines on the seafloor, he said, so oil and gas developers willhave to determine the maximum speed of likely currents and createdesigns to cope with them.

The area in which the storms were found has not produced gas andoil in the past but is currently undergoing development, he said.

MacDonald discussed the results of the cruise in a telephoneinterview from Key West, Fla., while Bryant spoke by telephone fromhis office at the university.

Other findings from the expedition included:

Large amounts of gas hydrates, ice-like forms of methane, onthe sea floor. Hydrates have attracted a lot of interest recentlyas a possible energy source.

New and unusual samples of plants and animals living near gasseeps.

Deep sea mats of bacteria.

Extensive flows of brine on the sea floor where saltconcentrations have increased through the formation of gashydrates.

But it was the deep storms that seemed to most surprise thescientists, who had suspected their existence but not encounteredthem, MacDonald said.

Like a Desert Landscape

The water movement had channeled the seafloor into miles-longgullies. The gullies “reminded me of the buttes and mesas in theSouthwest,” MacDonald said.

When researchers descended into a region about 180 miles southof the Louisiana coast, the submersible was caught in the current.

“The sediments were stirred up by it. They saw fish and shrimpbeing whipped along like in a river ... animal life was being sweptaway,” MacDonald said.

Unlike storms in the air, the water movement was horizontal, notup and down, he said. But the mass of moving water was 2,000 feetthick.

“That’s an enormous force,” he said.

The cause of the storms remains a mystery and, he added, “wedon’t know if they occur elsewhere ... this is the firstsighting.”

But the current isn’t continuous, he said. A storm lastedthroughout a six-hour dive, but when they went back the next day,the storm was over.

The expedition, which departed from Galveston, Texas, on Oct.16, was Alvin’s first to the Gulf in eight years. The submersibleis operated by Woods Hole Oceanographic Institution.

The National Oceanic and Atmospheric Administration sponsoredthe expedition through its National Undersea Research ProgramCenter at the University of North Carolina at Wilmington.

Besides Texas A&M, other organizations participating includedLouisiana State University, University of South Carolina, Collegeof William and Mary and the Department of Energy.