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NASA Solves Plankton MysteryWhy healthy looking plankton have a slow growth |
By Vlad Tarko, Senior Editor, Sci-Tech News
5th of September 2006, 15:01 GMT
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What are the limits of the growth of ocean algae, or phytoplankton, and how does this affect Earth's climate? And why aren't the healthy looking plankton really healthy? A NASA-sponsored study pioneered a new technique that helped answer these questions. Scientists studied the tropical Pacific Ocean, which is the largest natural source of carbon dioxide to the atmosphere and which plays a particularly important role in regulating atmospheric carbon dioxide and the world's climate.
"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 found that iron was the key for solving the mystery of the healthy looking plankton.
When plankton is stressed from lack of iron, it appears greener. Normally, greener plants are growing faster than less green plants but when iron is lacking the enhanced greenness, it does not mean phytoplankton are healthier. Actually, it's just the opposite.
"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."
Learning about this "iron effect" researchers managed to correct their estimates about how much carbon dioxide ocean plants photosynthesize for the region. The result is two billion tons less than previous estimates. This is a huge amount of carbon dioxide that future climate models will have to take into consideration.
Scientists used satellite data from NASA's Sea-viewing Wide Field-of-view Sensor, but the real cornerstone of the discovery was ship-based measurements of fluorescence. When plants absorb sunlight, some of the energy is re-released again as red light. When phytoplankton have insufficient iron they are more fluorescent (release more light). This is how scientists took into account the iron-effect.
They studied approximately 140,000 measurements of fluorescence made from 1994 to 2006 along 58 kilometers of ship tracks. This allowed them to determine what parts of the ocean are iron-stressed and what parts are nitrogen-stressed.
| Click to see animation of where there is more or less plant life on our planet. The animation is a series of monthly images of where phytoplankton are from August 1997 through March 2003, as seen by NASA and ORBIMAGE's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on the SeaStar satellite. On land, the dark greens show where there is abundant vegetation and the tan colors show relatively sparse plant cover. In the ocean, red, yellow, and green areas show higher levels of phytoplankton, and these are regions of the ocean that are the most productive over time, while blue and purple areas show where there is very little of the microscopic marine plants called phytoplankton. Click on image to view animation. Click on image to view animation. Credit: NASA/ORBIMAGE/G. Feldman, NASA GSFC |
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