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Undercover Arctic algae impact ocean ecosystems


By David Smith

“Take a look around,” my dad would say on our hikes in the woods. “What do you see?” It was Northern Ontario. I saw rocks, trees, moss, and lakes. Dad would then lean down and lift up a stone or peel back a chunk of moss, revealing the damp soil. “Don’t let your eyes fool you,” he’d exclaim, handing me a fistful of wet dirt. “Look there,” he’d say, nodding towards my muddied hands. “You’re holding more than a million microbes.”

My father was bang on. No matter where you go on this planet, much of the action isa taking place beneath the surface — on a microbial scale. Recently, this point was proven in fine fashion when an international team of scientists on the U.S. Coast Guard icebreaker Healy discovered a massive algal bloom under the Arctic sea ice.

Algae are sun-loving creatures and tend to do best in open water where they can bask in the daylight, uninhibited. Thus, as the Healy crunched through vast expanses of metre thick ice in the Chukchi Sea, north of the Bering Strait, the researchers weren’t expecting to uncover a thriving mass of algae. They were wrong.

The ship was deep within the Arctic ice pack when one of its instruments used to measure ocean fluorescence lit up, essentially saying: “Ladies and gentlemen, we have algae.” The crew stopped the boat and sampled the ice-ridden water. It was the colour of pea soup and dense with unicellular diatom algae — a common type of phytoplankton. When the Healy cut further into the frozen sea, the algal bloom got even denser, much denser than what was observed in the open water. The scientists estimate that the under-ice bloom extended for more than 100 kilometres, and in some places was greater than 50 metres in depth.

How could these algae flourish beneath the ice, ostensibly veiled from the sun’s nourishing rays? In an article published in the journal Science, researchers from the Healy explain how in the Arctic Ocean “light transmission has increased in recent decades because of thinning ice cover and the proliferation of melt ponds.” Melt ponds — pools of water on top of sea ice — are a big deal because they thin the underlying ice, creating portholes that allow sunlight to sneak through, while also filtering harmful UV rays. “Although the under-ice light field was less intense than in ice-free waters,” write the researchers, “it was sufficient to support the blooms… which grew twice as fast at low light as their open ocean counterparts.” Sub-ice algal blooms have been spotted in other polar regions, including the Canadian Arctic Archipelago and the Barents Sea, suggesting that they are more widespread than previously thought. Scientists will need to reassess their view of Arctic Ocean ecosystems, taking in account the potential for a teeming under-ice algal world, and one that might grow larger and larger as Arctic ice packs continue to thin.

But this isn’t the only tale of under – cover Arctic algae. In a separate expedition, European and Russian scientists on the icebreaker Polarstern visited the Eastern Central basins of the High Arctic and discovered that forests of algae anchored to the underside of sea ice are falling to the ocean floor in alarming numbers.

Researchers aboard the Polarstern used state-of-the-art equipment to photograph and collect samples from the seafloor, three to four kilometres beneath the water’s surface. The bottom of the Arctic Ocean is typically barren and bleak, so the scientists were surprised when they stumbled upon mounds of fresh algae scattered across the seabed. Many of these algae were Melosira arctica — a species that grows underneath ice floes, forming metre-long filaments, which extend into the water column. If the sea ice thins, cracks, or melts, these filamentous algae can lose their grip and sink to the ocean floor where they are gobbled up by sea cucumbers and other types of deep-sea creepy crawlers. Arctic warming and the record loss of sea ice may explain why Melosira and other types of ice algae are falling to the seabed earlier in the season and in greater numbers than ever before.

What does all this mean? If I’ve learned one thing from the wilderness walks with my father, it’s that if you meddle with the microbes, including the algae, you can bet your winter boots that you’ll be meddling with everything. As Arctic temperatures rise and ice packs thin and recede, some of the algae will blossom, others will fall to the floor, but all of the ocean’s ecosystems will feel the impact.

David Smith is an assistant professor in the biology department at Western University in London, Ontario.

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