Studying Coastal Eddies: Restaurants and Nurseries of the Sea
Two NASA oceanographers have found and described numerous coastal ocean
eddies off the southern California coast that are smaller and more abundant than
previously reported.
The results of the study by Benjamin Holt and Paul DiGiacomo of NASA’s Jet
Propulsion Laboratory, Pasadena Calif., also emphasize the potential importance of the
eddies to local marine flora and fauna.
“Eddies can serve as mini-restaurants and nurseries in the coastal ocean,”
DiGiacomo said. “Many organisms spend time within them feeding and developing.”
Eddies, which are whirlpool-like occurrences in the ocean, can foster plant growth
by supplying nutrients. They can also concentrate and transport organisms, particularly
planktonic larvae and juvenile fish, carrying them to fertile coastal environments critical
for survival and growth.
This is the most comprehensive study to date of small coastal ocean eddies in the
Southern California Bight, or the coastal ocean from Point Conception to just south of
San Diego. The results of their study were published in the Oct. 15 issue of the Journal
of Geophysical Research — Oceans.
Although eddies are related to the ocean water around them, they have distinct
biological and physical personalities. Visual clues to the existence of some eddies are
circular slicks, or glassy water, on the ocean’s surface. Deceptively tranquil, these ocean
phenomena may dramatically affect the local ecosystem.
The dispersal of pollutants, a significant environmental concern, can also be
affected by coastal ocean eddies. Knowing the characteristics of these eddies can help
authorities monitor and control oil spills and coastal runoff.
“Pollutants do not necessarily just get flushed out and then diluted in the ocean,”
DiGiacomo said. “They can even be brought back to shore depending on conditions.”
The study analyzed satellite radar images of the Southern California Bight
acquired between 1992 and 1998. Holt and DiGiacomo took advantage of the high
resolution of the radar images to map the seasonal and spatial distributions of these
previously under-sampled ocean features. Field measurements acquired in the ocean with
buoys, both moored and drifting, were also used to complement the satellite research. All
the coastal eddies found were less than 50 kilometers (about 31 miles) in diameter, and
70 percent of them were less than 10 kilometers (about 6.2 miles) in diameter, considered
small in the world of eddies.
Synthetic aperture radar satellite images used in the study were obtained from the
European Space Agency’s first and second European Remote Sensing Satellite missions.
Advanced Very High Resolution Radiometer satellite imagery data were obtained from
the National Oceanic and Atmospheric Administration’s CoastWatch Program.
Representative images are available online at
http://www.jpl.nasa.gov/images/earth/pacificocean .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
