Another One......
Hidden Storms
Bottom of the Ocean Experiences Fierce ‘Weather’
By Randolph E. Schmid
The Associated Press
W A S H I N G T O N, Nov. 2 — Thousands of feet below
the ocean’s surface, sudden powerful currents stir
up sediments and sweep fish and shrimp along
as though they were in a river, scientists have
discovered.
Past sonar readings and furrows on parts of the seafloor
have hinted at these currents, called storms by some
researchers.
Now they have finally been experienced, off the edge of
the continental shelf in the Gulf of Mexico, some 8,000 to
10,000 feet deep.
Witnessing the Storm
“Abyssal storms arise suddenly and sweep along the base of
the escarpment. We got to witness that first hand,” Ian
MacDonald of Texas A&M University said Wednesday.
The powerful currents — seen by researchers during a
two-week expedition involving several dives in the deep-sea
submersible Alvin — have carved furrows into the seafloor.
Scientists now are working to determine what causes the
storms and what implications they might have, particularly
for deep sea gas and oil wells now being developed in this
region.
MacDonald said the storms are massive currents nearly
2,000 feet thick, moving at 1 to 1.5 knots. A knot is 1.15
miles per hour.
While that “doesn’t sound like much,” MacDonald said,
normal water movement in the deep oceans is less than
one-tenth knot. The relatively fast-moving water presses
against anything in its path with a great force.
William R. Bryant, a Texas A&M geologic oceanographer,
was aboard Alvin during one dive into one of the powerful
currents.
“It was first time anyone had ever been in” one of these
events, he said.
A Concern for Pipelines
Currents had been detected by instruments before and
powerful ones were suspected because of the shape of the
seafloor, said Bryant, who was swept along in a 1.5 knot
current. He believes some reach more than 2.5 knots.
“Those are exceptional, high currents,” he said. “We see
large geological features, furrows, that are the result of
these currents.”
Bryant said the currents are a “constraint” rather than a
hazard to oil and gas rigs. The current is sufficient to
undermine pipelines on the seafloor, he said, so oil and gas
developers will have to determine the maximum speed of
likely currents and create designs to cope with them.
The area in which the storms were found has not
produced gas and oil in the past but is currently undergoing
development, he said.
MacDonald discussed the results of the cruise in a
telephone interview from Key West, Fla., while Bryant spoke
by telephone from his office at the university.
Other findings from the expedition included:
Large amounts of gas hydrates, ice-like forms of
methane, on the sea floor. Hydrates have attracted a lot of
interest recently as a possible energy source.
New and unusual samples of plants and animals living
near gas seeps.
Deep sea mats of bacteria.
Extensive flows of brine on the sea floor where salt
concentrations have increased through the formation of gas
hydrates.
But it was the deep storms that seemed to most surprise
the scientists, who had suspected their existence but not
encountered them, MacDonald said.
Like a Desert Landscape
The water movement had channeled the seafloor into
miles-long gullies. The gullies “reminded me of the buttes
and mesas in the Southwest,” MacDonald said.
When researchers descended into a region about 180
miles south of the Louisiana coast, the submersible was
caught in the current.
“The sediments were stirred up by it. They saw fish and
shrimp being whipped along like in a river ... animal life was
being swept away,” MacDonald said.
Unlike storms in the air, the water movement was
horizontal, not up and down, he said. But the mass of
moving water was 2,000 feet thick.
“That’s an enormous force,” he said.
The cause of the storms remains a mystery and, he
added, “we don’t know if they occur elsewhere ... this is the
first sighting.”
But the current isn’t continuous, he said. A storm lasted
throughout 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
submersible is operated by Woods Hole Oceanographic
Institution.
The National Oceanic and Atmospheric Administration
sponsored the expedition through its National Undersea
Research Program Center at the University of North Carolina
at Wilmington.
Besides Texas A&M, other organizations participating
included Louisiana State University, University of South
Carolina, College of William and Mary and the Department of
Energy. |
