NASA/Goddard Space Flight Center
 NASA
has collected the first continuous global observations of the biological engine
that drives life on Earth. Researchers expect this new detailed record of the
countless forms of plant life that cover land and oceans may reveal as much about
how our living planet functions today as fossil and geologic records reveal about
Earth's past.
"This is a period of exploration for us," said lead author
Michael Behrenfeld, an oceanographer at NASA's Goddard Space Flight Center, Greenbelt,
MD. "We've never been able to see the Earth this way before."
The study,
which appears this week in the journal Science, is based on the first three years
of daily observations of ocean algae and land plants from the Sea-viewing Wide
Field-of-View Sensor (SeaWiFS) mission, creating the most comprehensive global
biological record ever assembled. Scientists will use the new record of the Earth's
surface to study the fate of carbon in the atmosphere, the length of terrestrial
growing seasons and the vitality of the ocean's food web.
"With this record
we have more biological data today than has been collected by all previous field
surveys and ship cruises," added Gene Carl Feldman, SeaWiFS project manager at
Goddard. "It would take a ship steaming at 6 knots over 4,000 years to provide
the same coverage as a single global SeaWiFS image."
The new study presents
a global assessment of the fundamental work that plants perform to make life possible
Ð producing food, fiber, and oxygen Ð and how their productivity changes from
season to season and year to year in response to our changing environment.
The
biological record from SeaWiFS indicates that global plant photosynthesis increased
between September 1997 and August 2000. Photosynthesis by land plants and algae
absorbs carbon dioxide from the atmosphere and ocean, which plays a critical role
in regulating atmospheric carbon levels. The initial increase in carbon fixation
was largely due to the response of marine plants to a strong El Ni–o to La Ni–a
transition, but the cause of the continued increase during the later portion of
the record is not yet clear.
"With three years of observations we can
see seasonal changes in plant and algae chlorophyll levels very well, but we don't
yet have a long enough record to distinguish multi-year cycles like El Ni–o from
fundamental long-term changes caused by such things as higher carbon dioxide levels
in the atmosphere," Behrenfeld concluded.
"The SeaWiFS record provides
a baseline against which future estimates of Earth system carbon cycling can be
compared," said Feldman.
NASA plans to produce a five-year record using
SeaWiFS observations and extend the continuous biological record with two Earth
Observing System (EOS) spacecraft, Terra, launched in December 1999, and Aqua,
scheduled for launch later this year. This constellation of EOS satellites allows
U.S. scientists to examine practically every aspect of Earth's atmosphere, oceans
and continents from space in an unprecedented way.
The new biological
record benefits ongoing studies of desertification and changes in growing-season
lengths by joining an existing 20-year record of land plant productivity based
on observations from meteorological satellites with the new generation of spacecraft
instruments. These records will compliment ongoing observations obtained on land
and at sea.
"SeaWiFS not only adds finer detail to our observing capability,
it supplies essential continuity between data records that is critical to long-term
monitoring of changes in the biosphere," says biogeochemist James Randerson of
the California Institute of Technology, a co-author on the study.
This
research was conducted by NASA's Earth Science Enterprise, a long-term research
effort dedicated to studying how human-induced and natural change affects our
global environment.
Scientists also are using the biological record from
SeaWiFS to monitor the health of coral reefs, track harmful "red tides" and algae
blooms, and improve global climate models.
Additional information is available
on the Internet at:
http://www.gsfc.nasa.gov/gsfc/earth/environ/carbon/carbon.htm
More information about the SeaWiFs program is available on the Internet
at:
http://seawifs.gsfc.nasa.gov/seawifs.html |
