May 22, 2007
NASA SATELLITES BOLSTER RESEARCH ON BARREN MID-OCEAN REGIONS
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,
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
"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
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
For more information on the EDDIES
project, visit:
http://science.whoi.edu/users/olga/eddies/EDDIES_Project.html
##
Contact:
Tabatha Thompson
NASA Headquarters
202-358-3895
This text is
derived from:
http://www.nasa.gov/home/hqnews/2007/may/HQ_07119_Barren_Oceans.html