Tabatha Thompson/Dwayne Brown
Headquarters, Washington
202-358-3895/1726
RELEASE: 07-119
NASA SATELLITES BOLSTER RESEARCH ON BARREN MID-OCEAN REGIONS
WASHINGTON - NASA satellite data have helped scientists solve a
decades-old puzzle about how vast blooms of microscopic plants can
form in the middle of otherwise barren mid-ocean regions. A research
team led by the Woods Hole Oceanographic Institution, Woods Hole,
Mass., has used the data in its work to show that episodic, swirling
current systems known as eddies act to pump nutrients up from the
deep ocean to fuel such blooms.
Dennis McGillicuddy, a Woods Hole oceanographer and leader of the
Eddies Dynamics, Mixing, Export, and Species composition (EDDIES)
project, found that ocean productivity was surprisingly high when
stirred by certain types of mid-ocean eddies. These huge parcels of
water were teeming with diatoms - a type of phytoplankton - in
concentrations 10,000 to 100,000 times the norm, among the highest
ever observed in the Sargasso Sea.
"Past research has shown that the open ocean is far more productive
than we could explain based on what we knew about nutrients in the
surface water," said McGillicuddy. "Scientists have been trying to
figure out where the nutrients come from to make these oases in the
oceanic desert, and some of us hypothesized that eddies were part of
the answer. The EDDIES project has validated that suspicion."
McGillicuddy and colleagues published their work in the May 18 issue
of the journal Science. The National Science Foundation primarily
funded the work, while NASA satellite measurements helped guide
shipboard sampling. Data sets came from NASA's TOPEX/Poseidon, Jason,
Aqua and QuikSCAT satellites with additional contributions from the
Navy's Geosat Follow-on mission and the European Space Agency's ERS-2
satellite.
The Sargasso Sea, like other mid-ocean regions of the world, is
warmer, saltier, bluer and clearer than most other parts of the North
Atlantic. The prevailing oceanographic wisdom has suggested that such
open waters were mostly desert-like, unproductive regions populated
by smaller plant species. Yet observations showed oxygen and other
biologically important elements being consumed at a higher rate than
the theories and models could account for. Scientists believed there
had to be some natural nutrient source.
McGillicuddy and his colleagues found that eddy-driven nutrient
transport actually primes the ocean's "biological pump," fertilizing
the waters with nutrients from the deep. Fed by this unusual
upwelling, the phytoplankton population greatly increases and, in
turn, attracts more zooplankton and other animals higher up the food
chain. The fate of all of that biomass also is important, as plankton
blooms can remove substantial amounts of carbon dioxide from surface
waters and sink it to the deep ocean. The plants in the bloom either
die and sink when the bloom runs its course or are consumed by
animals, which then make fecal pellets that drop to the sea floor.
The EDDIES project team included chemists, biologists, and physical
oceanographers from Woods Hole; the Bermuda Institute of Ocean
Sciences, Ferry Reach, Bermuda; Rutgers University, New Brunswick,
N.J.; the University of Southampton, Southampton, U.K.; the
University of California, Santa Barbara, the Virginia Institute of
Marine Science, Gloucester Point, Va.; Humboldt State University,
Arcata, Calif.; and the University of Miami, Fla.
"Eddies are the internal weather of the sea," said McGillicuddy, "the
oceanic equivalent of storms in the atmosphere." The largest eddies
can contain up to 1,200 cubic miles of water and can last from months
to a year.
These distinct parcels of water are formed by differences in ocean
temperature and salinity that give water different densities. On a
rotating planet, these different water masses tend to dance around
one another rather than mix. The density inside an eddy can be higher
or lower than the surrounding water, like high and low-pressure
systems in the atmosphere. The balance pressure differences and
Earth's rotation give eddy currents their distinctive clockwise or
counterclockwise spin. The direction of the spin depends on whether
the eddy contains a cooler or a warmer core.
Working from a long-debated but mostly untested hypothesis, EDDIES
investigators measured how these swirling currents can perturb the
layers of the ocean and cause an upwelling of nutrient-rich water
into the sunlit "euphotic" zone - the top 330 feet that light
penetrates.
In nearly six months of ship-based work in the summers of 2004 and
2005, the researchers employed a combination of remote sensing, video
plankton recorders, ocean drifters, tracers and traditional
measurements of water properties and current speeds.
The team started with NASA satellite measurements of sea surface
height to locate eddies in the Sargasso Sea, south and east of the
Gulf Stream in the North Atlantic.
For more information about the EDDIES project, visit:
http://science.whoi.edu/users/olga/eddies/EDDIES_Project.html
For more information about NASA and agency programs, visit:
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