NANFA-- Fish Research from Space

Shireen Gonzaga (
Tue, 15 Feb 2000 08:58:49 -0800 (PST)

PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011

Contact: Diane Ainsworth
February 14, 2000


Some of the largest ocean eddies to form in
recent years along the west coast of Alaska and
Canada, bringing with them nutrients to feed a
dwindling population of salmon and other marine life,
are being tracked with satellite data from the joint
NASA-French space agency TOPEX/Poseidon.

An eddy is a water current that runs contrary to
the main current. The large "Sitka" and "Haida"
eddies, named for the town of Sitka, Alaska, and the
native name for the Queen Charlotte Islands, British
Columbia, Canada, form along the Alaskan Panhandle and
Canadian west coast each year and drift into deeper
waters to the west. The TOPEX/Poseidon satellite has
tracked these and other eddies since the 1992-93
winter. Years with heavy El Niņo winds appear to
produce particularly large eddies that can last for
several years and replenish nutrient-starved regions
of the ocean. Observations of the Haida Eddy by the
Canadian research vessel J.P. Tully show that the
eddies move fresh water, iron and nitrates from land
to sea.

"Our concern over the depletion of fish in this
region makes altimeter measurements such as
TOPEX/Poseidon data particularly important to
understanding the formation and movement of these
nutrient-rich eddies and how they influence salmon
growth and other fisheries," said William Crawford of
Fisheries and Oceans Canada at the Institute of Ocean
Sciences. He and colleague Frank Whitney have been
using TOPEX/Poseidon images produced by the University
of Colorado to track large-scale eddies along the
Pacific Northwest. They observed unusually high Sitka
and Haida eddies in the ocean during the severe El
Niņo of 1998. Both eddies were 30 centimeters (12
inches) higher than surrounding waters.

"These eddies, which brought higher nutrient
levels and a local resurgence of phytoplankton, became
two of the largest observed," Crawford said.
Phytoplankton is the minute plant life found in bodies
of water. "With the subsidence of the Haida Eddy over
the next year, we began to observe in the eddy a
steady depletion of nutrients that are important to
the food chain."

The eddies usually drift westward and disappear
within two years in deep waters off the Gulf of
Alaska. These rotating masses of water can average up
to a few hundred kilometers in diameter, forming along
the coast within the northbound coastal current,
Crawford said, and a large eddy can contain up to
5,000 cubic kilometers of water, which is about the
volume of Lake

New measurements taken by TOPEX/Poseidon are
available online at

Salinity and temperature measurements from the
Canadian ship J.P. Tully have indicated that the
subsurface water is fresher and warmer in this region
than surrounding waters. Plans are under way to
augment that data and to combine topographic
measurements from space with new data on nutrient
levels and fish abundance from ships to help
fisheries predict annual food production. Crawford and
Whitney will use TOPEX/Poseidon observations in the
Gulf of Alaska to determine the average seasonal
height of the sea surface and help determine the
northward flow of surface currents along the Pacific

The U.S./French mission, launched in 1992, is
managed by the Jet Propulsion Laboratory for NASA's
Earth Sciences Enterprise, Washington, D.C. JPL is a
division of the California Institute of Technology in

02/14/2000 DEA

Shireen Gonzaga
Baltimore, MD
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