Ask any good meteorologist what "normal" is, and you'll likely hear that there's no such thing.
The weather is always changing, and "normal" is just a label we humans like to attach to some arbitrary average, or midpoint, in a world of extremes.
So it goes on a grander scale -- what scientists consider to be a climatological time frame -- with the waxing and waning of the ever-present El Niño/La Niña cycle. Depending on where you live, these two ends of the surface temperature continuum in the tropical Pacific Ocean bring either more or less moisture to your neighborhood for months at a time.
Now, a unique view from space has helped researchers watch an intense biological seesaw. This previously unobserved swing in the oceanic food chain, extending across a huge swath of the Pacific, produced wild changes in the amount of carbon dioxide being released into the atmosphere.
El Niño and La Niña once again get the blame for our planetary extremes.
Using NASA's Sea-viewing Wide Field-of-View Sensor (SeaWiFS) satellite, researchers watched chlorophyll levels plunge in December 1997 to the lowest ever recorded during a strong El Niño. During El Niño, normal west-blowing trade winds relax in the central and western Pacific. The surface water off the coast of Central and South America warms up as these winds slacken.
La Nina is currently the dominant weather variable, and will remain so through the winter.
When the warm-water surface layer extended to its greatest depths and the upwelling of nutrients necessary for phytoplankton growth virtually ceased, chlorophyll values plummeted. Phytoplankton or microscopic algae, form the base of the oceanic food chain.
The following summer, when El Niño's cooler little sister La Niña took over, observations revealed the largest bloom of microscopic algae ever seen in the region. La Niña is caused when winds blow westward across the water of the eastern Pacific Ocean near the equator. Cool water is pulled up from below in a process scientists call "upwelling."
La Nina is currently the dominant weather variable, and will remain so through the winter.
Researchers suppose that elevated iron concentrations stimulated the intense bloom, a result of the increased upwelling associated with La Niña.
"With SeaWiFS in orbit, we were able to see for the first time not only the vast size and intensity of the ocean's biological rebound from El Niño, but also the unbelievable speed of that recovery," said Gene Feldman, an oceanographer at Goddard Space Flight Center. Feldman is co-author of the weather/climate study appearing in the December 10 issue of the journal Science.
Researchers also calculated how these swings in biological activity caused massive changes carbon dioxide releases. Deep ocean waters normally release large amounts of carbon dioxide, scientists say, but during El Niño, the carbon dioxide-rich waters are held below the surface.
Unlike most parts of the worlds oceans, the equatorial Pacific is a major contributor of atmospheric carbon dioxide because of the carbon-dioxide-rich deep ocean waters brought to the surface, and because of the relatively low levels of biological activity.
The researchers calculate that 700 million metric tons of carbon normally released to the atmosphere as carbon dioxide were kept in the ocean during the roughly one year that El Niño conditions dominated. This is equivalent to half of the United States' total annual carbon dioxide emissions from fossil fuel burning, according to researchers involved in the study.
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