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Measuring Phytoplankton

worldplank.jpgPhytoplankton -- microscopic plant forms floating in the oceans -- are the closest thing on the planet to the underlying fuel for life. Phytoplankton are at the base of the marine food chain, and produce around half of the oxygen in our atmosphere. We know that they bloom and are consumed quickly; phytoplankton have an annual production comparable to all terrestrial plants on Earth. Up until now, however, nobody had figured out a way to determine precise phytoplankton growth rates.

Researchers at UC Santa Barbara and NASA have done just that, using satellite observations of phytoplankton color.

The new approach is based on the premise that the "greenness" in phytoplankton, its level of pigmentation per cell, is a reflection of its growth rate, said David Siegel, professor of geography and director of the Institute for Computational Earth System Science at UCSB. The researchers have discovered a means, by satellite, to measure the biomass of phytoplankton from ocean light-scattering properties, and to infer growth rates from simultaneous measurements of the greenness of the individual phytoplankton cells.

It's hard to overestimate the importance of phytoplankton in the global ecosystem -- or how tricky it is to get a handle on measuring their production.

They produce about 50-65 billion tons of organic matter each year, and in the process absorb carbon dioxide and pour oxygen into the atmosphere.

Their abundance dictates the location and health of most marine fisheries. They play a critical role in marine water quality issues, can help regulate climate, and their productivity is in turn affected by climate. The very basis of sustainable ecological systems is almost impossible to understand without a good grasp of phytoplankton productivity, and its implications for global climate change, according to the scientists.

[...] [Phytoplankton] production can be enormous, and highly variable. Phytoplankton biomass can double in as little as one day, and it's routine for the entire mass of phytoplankton in an area to either be consumed by other life forms or die and sink to the ocean bottom in less than a week.

The next step will be getting satellites up to undertake the measurement. Current ocean observing satellites, like Aqua (part of NASA's Earth Observing System satellite program), focus on chlorophyll concentrations as a proxy for phytoplankton (the image accompanying this post is a NASA map of chlorophyll concentrations from July 1, 2002 through December 31, 2004). The UCSB/NASA team is now working on a satellite module to do just that -- ORCA, or Ocean Radiometer for Carbon Assessment.

(Via Biology News)


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