More sunlight penetrates thinning sea ice, enabling algal growth

By Erin Wayman

Web edition: February 14, 2013
Print edition: March 23, 2013; Vol.183 #6 (p. 14)

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Researchers aboard the research vessel Polarstern (shown) in summer 2012 found large clumps of fresh algae whose growth was probably enabled by thinning Arctic sea ice.

Credit: Courtesy of Sea Ice Physics Group/Alfred Wegener Institute Helmholtz Center for Polar and Marine Research

By letting sunlight through, thinning Arctic sea ice may be promoting the growth of algae, researchers suggest online February 14 in Science.

The alga Melosira arctica grows in long strands on the underside of sea ice. In summer 2012, scientists found large clumps of fresh algae, up to 50 centimeters across, that had fallen to the seafloor across the Central Arctic.

The researchers, led by Antje Boetius of the Alfred Wegener Institute for Polar and Marine Research in Germany, inferred that the algae must have grown rapidly because more than 95 percent of the region’s sea ice was less than a year old. The ice, averaging less than a meter thick, was much thinner than the multiyear, meters-thick ice that has melted away. The researchers also estimated that M. arctica was responsible for 45 percent of the region’s primary production, a measure of the organic matter created during photosynthesis.

But the thinning also speeds the algae’s death: As the ice melts, algae break free and sink to the ocean bottom, where hungry invertebrates await.