From: Editor, Science Daily
Published October 17, 2011 09:15 AM

Plankton's Shifting Role in Deep Sea Carbon Storage Explored

ScienceDaily (Oct. 17, 2011) — The tiny phytoplankton Emiliania huxleyi, invisible to the naked eye, plays an outsized role in drawing carbon from the atmosphere and sequestering it deep in the seas. But this role may change as ocean water becomes warmer and more acidic, according to a San Francisco State University research team.

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In a study published this week in the journal Global Change Biology, SF State Assistant Professor of Biology Jonathon Stillman and colleagues show how climate-driven changes in nitrogen sources and carbon dioxide levels in seawater could work together to make Emiliania huxleyi a less effective agent of carbon storage in the deep ocean, the world's largest carbon sink.

Changes to this massive carbon sink could have a critical effect on the planet's future climate, Stillman said, especially as atmospheric carbon dioxide levels continue to rise sharply as a result of fossil fuel burning and other human activities.

While floating free in the sunny top layers of the oceans, the phytoplankton develop elaborate plates of calcified armor called coccoliths. The coccoliths form a hard and heavy shell that eventually sinks to the ocean depths. "About 80 percent of inorganic carbon trapped down there is from coccoliths like these," said Stillman.

Stillman and his colleagues wanted to discover how ocean acidification and changes in the ocean's nitrogen cycle -- both hallmarks of climate warming -- might effect coccolith development. So they raised more than 200 generations of Emiliania huxleyi in the lab, adjusting carbon dioxide levels and the type of nitrogen in the phytoplankton's seawater bath.

They found that high levels of carbon dioxide -- which make the water more acidic -- along with a shift in the prevailing nitrogen type from nitrates to ammonium -- "had a synergistic effect" on the phytoplankton's biology and growth.

In particular, coccoliths formed under conditions of high carbon dioxide and high ammonium levels were incomplete or hollow, and contained less than the usual amount of inorganic carbon, the researchers noted.

Article continues: http://www.sciencedaily.com/releases/2011/10/111013162934.htm

Image Credit: The University of Liverpool

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