By Stephen Leahy

[Originally published Jul 31, 2010 for the Inter Press Service (IPS)]

The oceans are the lifeblood of our planet and plankton its red blood cells. Those vital “red blood cells” have declined more than 40 percent since 1950 and the rate of decline is increasing due to climate change, scientists reported this week. (Update Dec 2016: New analysis show this is an overestimate. See my comment below.)

“Phytoplankton are a critical part of our planetary life support system. They produce half of the oxygen we breathe, draw down surface CO2, and ultimately support all of our fisheries,” said

Boris Worm of Canadas Dalhousie University and one of the worlds leading experts on the global oceans.

“An ocean with less phytoplankton will function differently,” said Worm, the co-author of a new study on plankton published this week in Nature. Plankton are the equivalent of grass, trees and other plants that make land green, says study co-author Marlon Lewis, an oceanographer at Dalhousie.

“It is frightening to realise we have lost nearly half of the oceans’ green plants,” Lewis told IPS.

“It looks like the rate of decline is increasing,” he said.

[See also my series of articles on ocean acidification]

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Climate change is warming the oceans about 0.2C per decade on average. This warmer water tends to stay on top because it is lighter and essentially sits on top of a layer of colder water. This layering, or stratification, is a problem for light-loving plankton because they can only live in the top 100 to 200 meters.

Eventually they run out of nutrients to feed on unless the cold, deeper waters mix with those near the surface. Ocean stratification has been widely observed in the past decade and is occurring in more and larger areas of the world’s oceans. Continue reading →