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EMBARGOED FOR 6 P.M., EDT
NSF PR 96-55 - October 9, 1996
Media contact: |
Cheryl Dybas |
(703) 306-1070 |
cdybas@nsf.gov |
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Don Rice |
(703) 306-1589 |
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Iron 'Fertilization' Causes Plankton Bloom
Scientists Link Iron to Climate
Change
For farmers and gardeners it would be revolutionary:
a novel fertilizer with a cheap and widely available
ingredient, iron, that produces more than two thousand
times its weight of plant growth -- within a week.
Iron has that effect on parts of the ocean.
Despite being the fourth most abundant element in
soil and rock (and the most common on Earth as a whole),
iron is in short supply in much of the sea.
Scientists have long suspected that iron deficiencies
might affect some 20 percent of the global ocean,
yet this idea has only recently been tested. New results
by National Science Foundation (NSF)-funded researchers,
published in this week's science journal Nature,
confirm earlier experiments that indicated a strong
biological response to added iron. But this time the
effects lasted longer, and large changes were observed
in the air-sea transfer of gases involved in climate
processes.
On an oceanographic research cruise called "IronEx
II," led by scientists from Moss Landing Marine Laboratories
(MLML) in California, 37 scientists from 13 institutions
in the U.S., England, and Mexico "fertilized" with
iron a patch of ocean waters some 800 miles west of
the Galapagos Islands. Nearly one-half of one ton
of iron was added to the experimental patch, increasing
surface water iron concentrations by 100 parts per
trillion. The experiment was tracked for 18 days.
Iron-starved plant plankton, called phytoplankton,
native to the region responded rapidly; the amount
of plankton began to nearly double each day. Working
around the clock, scientists performed continuous
measurements and over-the-side sampling operations.
"Within one week, about two million pounds of phytoplankton
had grown, representing a thirty-fold increase," says
scientist Kenneth Coale of MLML. "At the same time,
the rapid growth of these plankton began to 'draw
down' carbon dioxide in surface waters. After 10 days,
the concentration of carbon dioxide had dropped 20
percent over the initial values."
The waters in which this experiment were conducted
are representative of about 20 percent of the ocean's
surface area. They are called High Nitrate, Low Chlorophyll
(HNLC) waters. "The experiment strongly supports the
hypothesis that these waters do not grow more plant
plankton because they lack iron," says Don Rice, director
of NSF's chemical oceanography program, which funded
the research along with the Office of Naval Research.
Tiny additions of this nutrient to HNLC waters have
the potential to cause rapid plant growth and a "draw-down"
in the concentration of atmospheric carbon dioxide.
This experiment may have pulled more than 2,500 tons
of carbon dioxide from area waters before the patch
was broken up by ocean currents, according to Coale.
"It demonstrates that changes in iron supply to HNLC
ocean regions play an important role in regulating
atmospheric carbon dioxide and climate."
Could we slow future climate change resulting from
human activities by adding iron to under-productive
oceans? Calculations for the equatorial Pacific, reported
in the Nature papers, indicate that iron fertilization
there would not significantly counteract the projected
future increase of atmospheric carbon dioxide.
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