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Once thought impossible, the bloom was discovered by the 2011 NASA-sponsored ICESCAPE expedition led by Kevin Arrigo, professor of environmental Earth System science at Stanford University.

The paper announcing the find is published online June 7 in Science.

Unlike most Arctic research teams, ICESCAPE headed deep into the Chukchi Sea ice pack north of the Bering Strait. The research cruise, consisting of prominent scientists in the fields of oceanography, biology, chemistry, and optics, was intended to improve NASA’s remote monitoring of the Arctic’s changing conditions.

“Suddenly, the fluorometer”—the fluorescence-measuring device used to estimate the algal content of water—”went nuts,” Arrigo says. “We thought there was something wrong with the instrument.”

Most models of biological production in the Arctic Ocean assume a value of zero below pack ice. Sea ice and snow cover have historically reflected incoming solar radiation, leaving no sunlight for plankton in the water below.

“Not only was the value not zero,” says Arrigo, “production was higher there than it was in open water.”

Based on samples from surrounding water and on the species of algae in the bloom, the scientists confirmed that the phytoplankton had not drifted under the ice from elsewhere.

Instead, changing ice conditions now allow light to penetrate large swaths of Arctic sea ice. Thick “multi-year” ice, which requires several seasons to accumulate, is on the decline, while warming temperatures favor thinner “first-year ice.” Additionally, the melt pools that now commonly form on top of Arctic sea ice decrease the ice pack’s ability to reflect light.

The resulting under-ice environment is ideal for Arctic phytoplankton. The thin ice lets in light while protecting the algae from ultraviolet radiation.

“Grow rates under the ice are higher than I thought was possible for Arctic phytoplankton,” Arrigo says. Algal cells that would normally take three days to divide were doubling more than once a day.

A shifting Arctic

While the discovery marks the first direct observation of an under-ice bloom, the conditions that allow for it in the Chukchi Sea exist over a large area of the Arctic.

“We suspect that this is a lot more widespread than we realize,” says Arrigo.

The appearance of under-ice blooms may presage wholesale shifts in the ecosystem of the Arctic. Colder-water phytoplankton production, as with under-ice algae, may cause organic matter to drop to the ocean floor sooner. The effect would benefit bottom-feeding species, to the detriment of species that feed in the water column.

And, as algal blooms are able to occur earlier in the year, animals that depend on timing their behavior to “pulses” in algal productivity may be left out in the cold.

One piece of seemingly good news is an increase in the Arctic’s ability to sequester carbon. As the Arctic Ocean’s productivity increases, so should its carbon capture rate. But, Arrigo says, the effect is unlikely to make much difference, Arrigo says.

“Even if the amount of CO2 going into the Arctic Ocean doubled, it’s a blip on a global scale.”

More news from Stanford University: http://news.stanford.edu/