Totally Unexpected: Massive Under-Ice Bloom

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Don’t you just love it when nature dishes out something scientists have never seen before?

Take phytoplankton, for example. Satellite images tell us that these microscopic marine plants (which, by the way, produce half the oxygen we breath) absolutely love icy coastlines. Spring blooms in the Ross Sea are among the largest in the world (note the bright green swirls in the photograph above).

But no one ever thought these microscopic cornucopias could appear under the ice—until now.

During an icebreaker mission north of the Arctic circle in July 2011, a team of ecologists stumbled across a massive bloom of phytoplankton beneath ice pack one meter thick.

Today in the journal Science, the team reports that the amount of phytoplankton growing in this under-ice bloom was four times greater than the amount found in neighboring ice-free waters. What is more, the bloom extended laterally more than 100 kilometers (62 miles) underneath the ice pack.

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Before this serendipitous discovery, scientists fully expected sea ice would block sunlight and limit the growth of microscopic marine plants living under it. Something was happening that no one had ever considered before.

That special something turned out to be the sky-blue pools of melt water that were accumulating atop the ice as the Arctic summer progressed. These summer pools served as transient skylights that magnified and focused sunlight through the ice and into waters above the continental shelf, where currents steer nutrient-rich deep waters up toward the surface.

Phytoplankton must have been primed to take advantage of this narrow window of light and nutrients, explained biologist Sam Laney of the Woods Hole Oceanographic Institution in a press release. Laney is part of the multi-institutional team, led by Kevin Arrigo of Stanford University, that made the discovery.

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Just as a rainstorm in the desert can cause the landscape to explode with wildflowers, this study shows that short-lived events can have major effects on the ecosystem, even in the Arctic. Indeed, calculations based on satellite images, which don’t account for under-ice blooms, may be underestimating phytoplankton production 10-fold, the team concluded.

Laney says: “If you don’t catch these ephemeral events, you’re missing a big part of the picture.”

Photo:

True-color satellite image of a phytoplankton bloom in the Ross Sea on January 22, 2011. Bright greens are plant life, deep blues are open ocean water; bright white are glaciers and snow. (NASA image courtesy Norman Kuring, Ocean Color Team at NASA Goddard Space Flight Center)