A new, close look at what's growing in seawater suggests that a species of extra-large plankton is more abundant than was previously known. And it may be extracting so much carbon dioxide from the air that global warming will be less than predicted, scientists report.
"It's possible that this organism plays a major role in fixing carbon in the world's oceans," said biologist Edward J. Carpenter.
If so, he said, it may tell scientists why the sea soaks up more carbon dioxide than calculations say it should.
Carbon dioxide, and a few other compounds such as methane, are called "greenhouse gases" because they tend to trap heat. It is feared that as they increase because of fossil-fuel burning, global temperatures will also increase with a severe environmental impact.
Mr. Carpenter, at the State University of New York at Stony Brook Marine Sciences Center, reported this month in Science magazine that the organism, trichodesmium, also extracts nitrogen from the air, providing a larger-than-expected source of "fixed nitrogen" in the sea.
Scientists generally think of the seas as "nitrogen-poor," so the new findings may alter another fundamental idea.
Nitrogen is vital for life as a crucial ingredient in proteins.
In collaboration with Kristen Romans, from the Sea Education Association in Massachusetts, Mr. Carpenter measured the abundance of the organisms, a form of algae, afloat in the top layers of North Atlantic. They found a much higher population of trichodesmium than had been recorded before.
Earlier measurements of trichodesmium were probably misleading, Mr. Carpenter said, because of sampling and counting errors.
The new results suggest that unanticipated amounts of carbon dioxide are absorbed by the plankton, with the carbon eventually being deposited in seafloor sediment.
In the past, most studies have focused on plankton that are much, much smaller, about the size of bacteria. Mr. Carpenter and Ms. Romans studied organisms more than one-tenth of an inch in diameter.
Most plankton, like plants with leaves, absorb solar energy and convert carbon dioxide and nitrogen into the cells they need to live and grow. This process, photosynthesis, is the basic source of almost all food.