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Contact: Diane Ainsworth


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 Niño 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 Niño of 1998. Both
eddies were 30 centimeters (12 inches) higher than surrounding

“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 coasts.

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 Pasadena.