INTRO: Some very tiny plants play a very big role in the world's oceans, but there aren't as many of these plants as there used to be. As Doug Schneider reports in this week's Arctic Science Journeys Radio, global warming is reducing the levels of phytoplankton in the world's oceans, and that includes the North Pacific Ocean off Alaska.

STORY: Phytoplankton are single-celled plants that float on the surface of the ocean. They're important because they form the foundation of the marine food chain. Watson Gregg is an oceanographer with NASA, and he uses satellite images to study these tiny plants.

GREGG: "They're the basis of the food chain. All the rest of life in the oceans is derived from the food source that's provided by phytoplankton. Just like on land, eventually everything is based upon the plant life. Phytoplankton is the fundamental plant life of the oceans."

Gregg uses satellite data to measure the amount of phytoplankton at sea. He says chlorophyll inside the plants appears as reflected green light on satellite images. Gregg and his colleague recently compared satellite images of phytoplankton from the early 1980s with those taken in the late 1990s.

Gregg says global phytoplankton levels fell six percent on average during this time. And he says parts of the oceans that are most affected by global warming have lost the most phytoplankton.

GREGG: "What we found out is that the largest changes occurred in the high latitudes, the North Atlantic and North Pacific. And those were associated with some of the most severe temperature increases."

In the North Atlantic Ocean, phytoplankton levels fell 14 percent, while closer to Alaska, in the North Pacific Ocean, levels dropped 30 percent. In some parts of the world where no temperature change occurred, researchers said phytoplankton levels either went up slightly or stayed about the same.

Watson Gregg says phytoplankton live near the surface, but to grow they need nutrients that well up from the ocean depths. Warm temperatures and calm winds tended to keep the ocean layers from mixing. In the North Pacific, for example, average summer sea surface temperatures were .7 degrees Fahrenheit (.4 degrees Celsius) warmer from the early 1980s to 2000, while average spring winds decreased by about eight percent. These factors combined to cause significant declines in summer plankton levels in the region. Researchers say fewer phytoplankton means less food for fish, birds and mammals farther up the food chain.

If you'd like to learn more about plankton changes in the world's oceans, just come to our website at www.asjnews.org. Help this week comes from Earthwatch Radio at the University of Wisconsin Sea Grant Program. This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. I'm Doug Schneider.

Thanks to Earthwatch Radio for help preparing this script.

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