Acidifying ocean may stifle phytoplankton

Chemical changes in seawater make a key nutrient less available to these organisms

Depending on nature — or at least phytoplankton in the ocean — to absorb humans’ ever-increasing emissions of planet-warming carbon dioxide probably won’t solve the problem, new research suggests.

A few scientists have long argued that increasing CO2 levels will stimulate long-term carbon-sopping plant growth, but the idea hasn’t proven true for land plants (SN: 12/16/00, p. 396). Now, new findings suggest that the notion won’t hold for tiny ocean plants either, thanks to one of the nagging side effects of carbon dioxide emissions — the gradual acidification of the ocean’s surface waters. Research by oceanographer Dalin Shi and his colleagues at Princeton University hints that rising CO2, instead of providing extra nutrients for phytoplankton, may actually curb the growth of these organisms, which form the base of the ocean’s food chain. The team reports these findings online January 14 and in an upcoming Science.

In their tests, the researchers studied how acidification, a decline in ocean pH, affects the ability of phytoplankton to take up dissolved iron, another nutrient required for growth. The scientists measured growth rates of four species of the marine microorganisms — including two that Shi described as “the lab rats of phytoplankton” — in ocean water with pH values that ranged from 8.8 to 7.7. On average, the pH of ocean surface waters today is about 8.08, says Shi.

Sid Perkins, ScienceNews, 14 January 2010. Full article.

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