Natural Science Forum / Earth Science / Oceanography / March 2006

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.

Tracey Bryant (302) 831-8185
University of Delaware, Newark

News Release: 2006-040                          March 20, 2006

Scientists Use Satellites to Help Detect Deep-Ocean Whirlpools

Move over, Superman, with your X-ray vision. Marine scientists
have figured out a way to see through the ocean's surface and
detect what's below, with the help of satellites.

Using sensor data from several U.S. and European satellites,
researchers from NASA's Jet Propulsion Laboratory, Pasadena,
Calif.; the University of Delaware, Newark; and Ocean
University of China, Qingdao; have developed a method to
detect salty, submerged eddies called "Meddies" that occur
in the Atlantic Ocean off Spain and Portugal at depths of
more than 1,000 meters (one-half mile).

These warm, deep-water whirlpools, part of the ocean's complex
circulatory system, help drive the ocean currents that moderate
Earth's climate. The research marks the first time scientists
have detected this phenomenon from space, and the first use of
a new multi-sensor technique that can track changes in ocean
salinity. Results are reported in the April issue of the
American Meteorological Society's Journal of Physical
Oceanography.

"Since Meddies play a significant role in carrying salty water
from the Mediterranean into the Atlantic, new knowledge about
their trajectories, transport and life histories is important
to understanding their mixing and interaction with North
Atlantic water," said Professor Xiao-Hai Yan of the University
of Delaware, lead author of the study and co-director of the
university's Center for Remote Sensing. "Ultimately, we hope
this will lead to a better understanding of their impact on
global ocean circulation and global climate change."

First identified in 1978, Meddies are so named because they
flow out of the Mediterranean Sea. A typical Meddy averages
about 600 meters (2,000 feet) deep and 100 kilometers (60
miles) in diameter, and contains more than 900 billion
kilograms (a billion tons) of salt.

While warm water ordinarily resides at the ocean's surface,
the warm water flowing out of the Mediterranean Sea has such
a high salt concentration that when it enters the Atlantic
Ocean at the Strait of Gibraltar, it sinks to depths of more
than 1,000 meters (one-half mile) along the continental shelf.
This underwater river then separates into clockwise-flowing
Meddies that may continue to spin westward for more than two
years, often coalescing with other Meddies to form giant,
salty whirlpools that may stretch for hundreds of miles.

"Since the Mediterranean Sea is much saltier than the Atlantic
Ocean, the Meddies constantly add salt to the Atlantic," Yan
said. Without this steady salt-shaker effect, he notes, the
conveyor belt of ocean currents that help distribute heat
from the tropics toward the North Pole might be diminished,
resulting in colder temperatures in regions such as New England
and northwestern Europe that currently experience more
temperate climates.

"There is concern about global climate change shutting down
the ocean currents that warm the Atlantic Ocean," Yan saids.
"The melting of sea ice at the North Pole could add enormous
amounts of fresh water to the Atlantic, reducing its salinity
enough to slow the sinking of cooler water, which would shut
down the conveyor belt of ocean currents that help warm major
regions of the planet."

Yan and his team drew on data from several satellite sensors
that can read an important signal of a Meddy's presence.
Altimeters flying aboard NASA's Topex/Poseidon and Jason
satellites and the European Space Agency's European Remote
Sensing and Environment (Envisat) satellites measured the
height of the sea surface compared to average sea level,
revealing the difference in altitude where a Meddy entered
the Atlantic.

Specialized microwave radars called scatterometers, including
the former NASA Scatterometer (Nscat) on Japan's Midori-1
spacecraft and the current SeaWinds instrument on NASA's
QuikScat spacecraft, measured the surface wind over the ocean,
providing data needed to remove the surface variability
"noise" caused by the wind blowing over the ocean's surface.

"By carefully removing the stronger surface signatures of
upper ocean processes, we were able to unveil the surface
signatures of deeper ocean processes, such as the Meddies, to
these space-based sensors," said Dr. W. Timothy Liu, QuikScat
project scientist at JPL.

The scientists also analyzed data provided by an infrared
spectrometer known as the Advanced Very High Resolution
Radiometer, which flies aboard National Oceanic and
Atmospheric Administration satellites. This instrument maps
heat emitted by the ocean's top layer and showed the increase
in temperature from a warm Meddy before it began sinking.

While the technique is not yet 100 percent accurate, Yan and
his colleagues are continuing to refine it, and are exploring
its application to other coastal regions of the world. They
are currently examining salinity variations in the East China
Sea before and after the building of the Three Gorges Dam,
the largest dam in the world. The data will help researchers
assess the dam's impacts on the ecosystem and on water
circulation patterns.

For more information, visit:

http://sealevel.jpl.nasa.gov ; and

http://winds.jpl.nasa.gov

JPL is managed for NASA by the California Institute of
Technology in Pasadena.

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