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Posted by on August 31, 2006, 1:24 pm
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Aug. 31, 2006
Erica Hupp/Dwayne Brown
Headquarters, Washington
202-358-1237/1726
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
301-286-4044
RELEASE: 06-306
NASA STUDY SOLVES OCEAN PLANT MYSTERY
A NASA-sponsored study shows that by using a new technique, scientists
can determine what limits the growth of ocean algae, or
phytoplankton, and how this affects Earth's climate.
Phytoplankton is a microscopic ocean plant and an important part of
the ocean food chain. By knowing what limits its growth scientists
can better understand how ecosystems respond to climate change.
The study focused on phytoplankton in the tropical Pacific Ocean. It
is an area of the ocean that plays a particularly important role in
regulating atmospheric carbon dioxide and the world's climate. This
area of the ocean is the largest natural source of carbon dioxide to
the atmosphere.
"We concluded that nitrogen is the primary element missing for algae
growth and photosynthesis in the northern portion of the tropical
Pacific, while it was iron that was most lacking everywhere else,"
said Michael J. Behrenfeld, an ocean plant ecologist from Oregon
State University, Corvallis, Ore.
Scientists determined when phytoplankton is stressed from lack of
iron; it appears greener, or healthier than they really are.
Normally, greener plants are growing faster than less green plants.
When iron is lacking, enhanced greenness does not mean phytoplankton
are growing better. They are actually under stress and unhealthy.
These conclusions solved the mystery why healthy looking
phytoplankton are actually not so healthy.
"Because we didn't know about this effect of iron stress on the
greenness of algae or phytoplankton before, we have always assumed
that equally green waters were equally productive," Behrenfeld said.
"We now know this is not the case, and that we have to treat areas
lacking iron differently."
For the tropical Pacific, correction for this "iron-effect" decreases
scientists' estimates of how much carbon ocean plants photosynthesize
for the region by roughly two billion tons. This figure represents a
tremendous amount of carbon that remains in the atmosphere that
scientists previously thought were being removed.
The results about the false health of phytoplankton allow scientists
using computer models to re-create the movement of carbon around the
world much more accurately. Resource managers will become more
knowledgeable about where carbon is going and the impact of
recreational, industrial or commercial processes that use or produce
carbon. Researchers better understand the Earth as an ecosystem, and
can incorporate these findings in future modeling, analysis and
predictions.
While satellite data from NASA's Sea-viewing Wide Field-of-view Sensor
played an important part in the study, the real cornerstone of the
discovery was ship-based measurements of fluorescence.
Fluorescence occurs when plants absorb sunlight and some of that
energy is given back off again as red light. Scientists looked at
approximately 140,000 measurements of fluorescence made from 1994 to
2006 along 36,040 miles of ship tracks. They found that phytoplankton
give off much more fluorescence when the plants do not have
sufficient iron. It is this signal they used to fingerprint what
parts of the ocean are iron-stressed and what parts are
nitrogen-stressed.
It is important that scientists understand how ocean plants behave
because all plants play a critical role in maintaining a healthy
planet. Plants annually take up billions of tons of carbon dioxide
from the atmosphere through photosynthesis and use this carbon to
create the food that nearly all other organisms on Earth depend on
for life.
Nutrients that make ocean plants thrive, such as nitrogen and
phosphate, mostly come from the deep parts of the ocean, when water
is mixed by the wind. Iron also can come from dust blowing in the
air.
Approximately half of the photosynthesis on Earth occurs in the
oceans, and the remainder on land. Ocean and land plants share the
same basic requirements for photosynthesis and growth. These
requirements include water, light and nutrients. When these three are
abundant, plants are abundant. When any one of them is missing,
plants suffer.
An article on this technique appears in a recent issue of Nature. For
images related to this research, visit:
http://www.nasa.gov/centers/goddard/news/topstory/2006/mystery_plants.html
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