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 – producing food, fiber, and oxygen – 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 Niño to La Niña 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 Niño 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.
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More information about the SeaWiFs program is available on the Internet at:
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HIGHLIGHTS OF THE MARCH 30TH SCIENCE PAPER
* The annual rate of carbon consumed by the Earth’s land plants and ocean algae fluctuated between 111 billion metric tons during the peak of the 1997-98 El Nino event and 117 billion metric tons during the strong La Nina that followed.
* This result is important for global carbon cycle research because it sets a new baseline measurement for global photosynthesis, the primary pathway through which carbon enters the Earth’s biosphere.
* The SeaWiFS record marks the first time that the abundance of plants and algae have been measured globally by a single instrument, making this the most complete and consistent data set available. Previous estimates of carbon uptake by the biosphere combined sporadic observations over many years from different instruments to produce an annual average.
* The “greenness,” or productivity, of the world’s oceans increased on a global scale during the three years of this study. No such multi-year trend was seen in land plants on a global scale, although certain regions experienced pronounced changes.
* The extent of summer phytoplankton blooms in the Northern Hemisphere exceeded those in the Southern Hemisphere.
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QUICK FACTS ABOUT SEAWIFS
* The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was launched on Aug. 1, 1997, and has continuously collected data since Sept. 18, 1997. The sensor is carried on the OrbView-2 spacecraft, which is operated by Orbital Imaging Corporation (ORBIMAGE) of Dulles, Va.
* The SeaWiFS mission is the first NASA Earth Science “data buy,” and industry/government partnership in which industry led the development of the mission.
* SeaWiFS orbits the Earth from pole to pole 14 times a day providing a complete global view every two days.
* SeaWiFS can pick out features as small as 1 kilometer (.6 miles) across.
* Every month SeaWiFS provides greater global coverage of the biosphere than its predecessor, NASA’s Coastal Zone Color Scanner (CZCS), collected during the entire lifetime of that mission (1978-1986).
* NASA leads an international scientific collaboration using SeaWiFS data. More than 1600 scientists representing 35 countries have registered to use the data. There are over 78 ground stations around the world that receive SeaWiFS data and provide it to NASA.
Materials provided by NASA/Goddard Space Flight Center--EOS Project Science Office. Note: Content may be edited for style and length.
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