Phytoplankton distribution changing as climate warms

Posted: March 13, 2009 in environment
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A large floating ice mass is seen in the gateway of the Antarctic Peninsula March 9, 2008.
Photo: Enrique Marcarian

WASHINGTON – You just don’t want to make phytoplankton mad.

These microscopic sea plants are at the bottom of the food chain in the waters that surround the Antarctic peninsula, and when they’re unhappy, everything that depends on them suffers, including fish, penguins and possibly, eventually, people.

A new study published on Thursday in the journal Science indicates that some of these Antarctic phytoplankton have become increasingly grumpy over the last 30 years.

Like most plants, phytoplankton need food and sunlight to survive. For some that live off the west coast of the Antarctic peninsula, getting these essentials has been an increasing challenge, with a 12 percent decrease in phytoplankton populations seen in the last three decades.

U.S. researchers figured this out by looking at satellite data and tracking the amount of chlorophyll — a sign of phytoplankton photosynthesis — in the Southern Ocean off the Antarctic peninsula, a long tail of land that juts out from the main body of the continent and points toward South America.

This area is a good place to look for signs of climate change, because it is warming faster than any other place on Earth in the winter.

Phytoplankton are excellent markers for climate change because they respond quickly, sometimes in as little as a day, to varying environmental conditions, and because so much of the food chain relies on their survival.


Because atmospheric circulation patterns are shifting over the peninsula — probably due to climate change — there are now cloudy skies where there used to be sunshine and vice versa, said study co-author Martin Montes-Hugo of Rutgers University.

In the southern part of the peninsula, the clouds are decreasing and sunlight is melting the sea ice, freeing up more open water that sunlight can shine through, Montes-Hugo said by telephone.

“You have more open water and so you have light penetration, so the phytoplankton is happy in the south,” he said, because like most plants, phytoplankton need sunlight for photosynthesis.

In the northern part of the peninsula closer to the warm equator there are more clouds, and sea ice is even more reduced than in the south. Changing atmospheric patterns are whipping up increasing winds in the area, churning the ocean water, which enables the phytoplankton to go deeper. At these deeper levels, the little plants can catch less sunshine.

“This makes phytoplankton mad,” Montes-Hugo said. “It’s not good for phytoplankton because you have less light.”

Phytoplankton, like other plants, absorb the climate-warming greenhouse gas carbon dioxide; less phytoplankton means less of this gas will be absorbed.

A decrease in phytoplankton along the Antarctic peninsula results in less food for krill, the tiny crustaceans that small fish eat, and on up the food chain to Adelie penguins and other creatures.

Adelie penguins are moving southward because the extreme Antarctic climate they require is no longer present in parts of the peninsula; Chin-strap penguins that can tolerate warmer temperatures are moving into the area, Montes-Hugo said.

(Planet Ark, editing by Philip Barbara)

© Thomson Reuters 2009 All rights reserved

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