On the Pacific coast of New Zealand, the advance of austral spring returns sunlight to spur phytoplankton blooms. This 2005 image shows a plume extending from the coast near Castlepoint in the southern North Island, and rotating in an offshore eddy. Another broader swath of less-intensely colored plankton appears in the lower part of the image.
Large areas of plankton occur at 40° South latitude along the convergence zone known as the Subtropical Front, between the Antarctic Circumpolar Current and subtropical waters. The converging water masses mix and disperse nutrients with plankton blooms when spring lighting becomes strong enough. The zone extends east-west at the latitude of Cook Strait, and plankton in this image went east, past the Chatham Islands.
Image courtesy ISS Crew Earth Observations & Image Science & Analysis Group, Johnson Space Center, NASA
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Less phytoplankton growth reduces carbon dioxide absorption from the atmosphere, causing increased climate change ... a vicious cycle
"Rising levels of carbon dioxide in the atmosphere play a big part in global warming," said lead author Michael Behrenfeld of Oregon State University. "This study shows that as the climate warms, phytoplankton growth rates go down and along with them the amount of carbon dioxide these ocean plants consume. That allows carbon dioxide to accumulate more rapidly in the atmosphere, which would produce more warming."
An uninterrupted nine-year record shows in detail the ups and downs of marine biological activity or productivity from month to month and year to year. Captured at the start of this data record was a major, rapid rebound in ocean biological activity after a major El Nino event.
El Nino and La Nina are major warming or cooling events respectively, that occur about every 3-7 years in the eastern Pacific Ocean and are known to change weather patterns around the world.
Scientists made their discovery by comparing the SeaWiFS record of the rise and fall of global ocean plant life to different measures of recent global climate change. The climate records included several factors that directly effect ocean conditions, such as changes in sea surface temperature and surface winds.
The results support computer model predictions of what could happen to the world's oceans as the result of prolonged future climate warming.
Ocean plant growth increased from 1997 to 1999 as the climate cooled during one of the strongest El Niņo to La Niņa transitions on record. Since 1999, the climate has been in a period of warming that has seen the health of ocean plants diminish.
The new study also explains why a change in climate produces this effect on ocean plant life. When the climate warms, the temperature of the upper ocean also increases, making it "lighter" than the denser cold water beneath it. This results in a layering or "stratification" of ocean waters that creates an effective barrier between the surface layer and the nutrients below, cutting off phytoplankton's food supply. The scientists confirmed this effect by comparing records of ocean surface water density with the SeaWiFS biological data.