Climate Warming Reduces Ocean Food Supply
In a NASA study, scientists have concluded that when Earth's climate warms, there is a reduction in the ocean's primary food supply. This poses a potential threat to fisheries and ecosystems.
Image right: Satellite data reveals the ebb and flow of microscopic plant life in the world's ocean. In this image of the Pacific from the late 1990s, robust plant growth is represented in green; areas of low "productivity" are in blue. NASA research has now shown how these marine plants are linked to changes in climate. Credit: NASA
By comparing nearly a decade of global ocean satellite data with several records of Earth's changing climate, scientists found that whenever climate temperatures warmed, marine plant life in the form of microscopic phytoplankton declined. Whenever climate temperatures cooled, marine plant life became more vigorous or productive.
The results provide a preview of what could happen to ocean biology in the future if Earth's climate warms as the result of increasing levels of greenhouse gases in the atmosphere.
Image left: A close-up view of phytoplankton, the tiny plants that live in the sunlit upper layer of the ocean. Changes in phytoplankton growth influence fishery yields and marine bird populations. Credit: NASA
"The evidence is pretty clear that the Earth's climate is changing dramatically, and in this NASA research we see a specific consequence of that change," said oceanographer Gene Carl Feldman of NASA's Goddard Space Flight Center, Greenbelt. Md. "It is only by understanding how climate and life on Earth are linked that we can realistically hope to predict how the Earth will be able to support life in the future." Feldman is a co-author on the study, which was published this week in Nature.
Phytoplankton are microscopic plants living in the upper sunlit layer of the ocean. They are responsible for approximately the same amount of photosynthesis each year as all land plants combined. Changes in phytoplankton growth and photosynthesis influence fishery yields, marine bird populations and the amount of carbon dioxide the oceans remove from the atmosphere.
Image right: The Sea-viewing Wide Field-of-view Sensor launched in 1997 supports pioneering global environmental research. By providing a regular picture of plant activity on land and in the ocean, researchers are able to learn about the world's interconnected ecosystems. Credit: NASA
"Rising levels of carbon dioxide in the atmosphere play a big part in global warming," said lead author Michael Behrenfeld of Oregon State University, Corvallis. "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."
The findings are from a NASA-funded analysis of data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) instrument on the OrbView-2 spacecraft, launched in 1997.
Image left: Changes in phytoplankton change how much carbon dioxide the oceans remove from the atmosphere. The life cycle of phytoplankton in the ocean involves absorbing carbon dioxide from the atmosphere and nutrient-rich waters. That carbon is then passed on to higher life forms that feed on the plants. Some also sinks to the ocean floor. Click image to play movie. Credit: NASA
The uninterrupted nine-year record shows in great 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 Niño event. El Niño and La Niña are major warming or cooling events, respectively, that occur approximately every 3-7 years in the eastern Pacific Ocean and are known to change weather patterns around the world.
Ocean plant growth increased from 1997 to 1999 as the climate cooled during one of the strongest El Niño to La Niña transitions on record. Since 1999, the climate has been in a period of warming that has seen the health of ocean plants diminish.
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