NASA Study Finds Atlantic 'Conveyor Belt' Not Slowing

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.
Alan.buis@jpl.nasa.gov

News release: 2010-101 March 25, 2010

NASA Study Finds Atlantic 'Conveyor Belt' Not Slowing

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-101&cid=release_2010-101

PASADENA, Calif. – New NASA measurements of the Atlantic Meridional Overturning
Circulation, part of the global ocean conveyor belt that helps regulate climate around the North
Atlantic, show no significant slowing over the past 15 years. The data suggest the circulation may
have even sped up slightly in the recent past.

The findings are the result of a new monitoring technique, developed by oceanographer Josh Willis of
NASA's Jet Propulsion Laboratory in Pasadena, Calif., using measurements from ocean-observing
satellites and profiling floats. The findings are reported in the March 25 issue of Geophysical
Research Letters.

The Atlantic overturning circulation is a system of currents, including the Gulf Stream, that bring
warm surface waters from the tropics northward into the North Atlantic. There, in the seas
surrounding Greenland, the water cools, sinks to great depths and changes direction. What was once
warm surface water heading north turns into cold deep water going south. This overturning is one part
of the vast conveyor belt of ocean currents that move heat around the globe.

Without the heat carried by this circulation system, the climate around the North Atlantic -- in
Europe, North America and North Africa -- would likely be much colder. Scientists hypothesize that
rapid cooling 12,000 years ago at the end of the last ice age was triggered when freshwater from
melting glaciers altered the ocean's salinity and slowed the overturning rate. That reduced the amount
of heat carried northward as a result.

Until recently, the only direct measurements of the circulation's strength have been from ship-based
surveys and a set of moorings anchored to the ocean floor in the mid-latitudes. Willis' new technique
is based on data from NASA satellite altimeters, which measure changes in the height of the sea
surface, as well as data from Argo profiling floats. The international Argo array, supported in part by
the National Oceanic and Atmospheric Administration, includes approximately 3,000 robotic floats
that measure temperature, salinity and velocity across the world's ocean.

With this new technique, Willis was able to calculate changes in the northward-flowing part of the
circulation at about 41 degrees latitude, roughly between New York and northern Portugal.
Combining satellite and float measurements, he found no change in the strength of the circulation
overturning from 2002 to 2009. Looking further back with satellite altimeter data alone before the
float data were available, Willis found evidence that the circulation had sped up about 20 percent
from 1993 to 2009. This is the longest direct record of variability in the Atlantic overturning to date
and the only one at high latitudes.

The latest climate models predict the overturning circulation will slow down as greenhouse gases
warm the planet and melting ice adds freshwater to the ocean. "Warm, freshwater is lighter and sinks
less readily than cold, salty water," Willis explained.

For now, however, there are no signs of a slowdown in the circulation. "The changes we're seeing in
overturning strength are probably part of a natural cycle," said Willis. "The slight increase in
overturning since 1993 coincides with a decades-long natural pattern of Atlantic heating and
cooling."

If or when the overturning circulation slows, the results are unlikely to be dramatic. "No one is
predicting another ice age as a result of changes in the Atlantic overturning," said Willis. "Even if the
overturning was the Godzilla of climate 12,000 years ago, the climate was much colder then. Models
of today's warmer conditions suggest that a slowdown would have a much smaller impact now.

"But the Atlantic overturning circulation is still an important player in today's climate," Willis added.
"Some have suggested cyclic changes in the overturning may be warming and cooling the whole
North Atlantic over the course of several decades and affecting rainfall patterns across the United
States and Africa, and even the number of hurricanes in the Atlantic."

With their ability to observe the Atlantic overturning at high latitudes, Willis said, satellite altimeters
and the Argo array are an important complement to the mooring and ship-based measurements
currently being used to monitor the overturning at lower latitudes. "Nobody imagined that this large-
scale circulation could be captured by these global observing systems," said Willis. "Their amazing
precision allows us to detect subtle changes in the ocean that could have big impacts on climate."

For more information about NASA and agency programs, visit: http://www.nasa.gov .

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

-end-

To remove yourself from this mailing, please go to http://www.kintera.org/TR.asp?a=dqLIIUNwHdIUKcJ&s=eoLQLPOpEaJCKOMvHoH&m=kpJRI2OBKbLSF

To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=ilKSK9PQJjIWLiK&s=eoLQLPOpEaJCKOMvHoH&m=kpJRI2OBKbLSF