Arctic Birds Carry Signs of an “Atlantifying” Ocean
Regime change comes to Arctic Ocean food webs as temperatures rise and waters respond.
Article body copy
Clouds of white kittiwakes drift like summer snow flurries around the Svalbard islands high in the European Arctic, searching for fish in the ice-studded fjords of the Barents Sea. The prey these small polar gulls ferry back to their cliff-side colonies are a sign of an abrupt and alarming shift—instead of cold-loving Arctic fish, new research shows that the seabirds are capturing creatures more at home in the warmer Atlantic. Scientists say it’s a clear sign of “Atlantification,” a sea change now underway as warm Atlantic waters muscle their way into the Arctic Ocean.
“This area used to be polar-influenced, cold water,” says Geir Wing Gabrielsen, a scientist with the Norwegian Polar Institute and a coauthor of the new study. “Now it is the Atlantic system which is really dominating.”
Black-legged kittiwakes, which spend most of their lives at sea, are effective messengers of this change, Gabrielsen says. He and his colleagues have monitored colonies on the island of Spitsbergen in Svalbard, a Norwegian archipelago some 1,000 kilometers north of the mainland, since 1982, providing valuable long-term data on this rapidly changing region. The foraging seabirds, which spew their stomach contents when handled, tell researchers what’s swimming in areas they can’t otherwise observe. For decades, the birds were catching almost entirely Arctic species like polar cod. But in 2007, capelin, an Atlantic fish, suddenly took over. Atlantic cod, herring, and other warmer-water denizens soon followed. Today, Atlantic species all but rule the kittiwakes’ diet.
This abrupt shift was triggered by a flush of warm water moving from the adjoining Atlantic Ocean deep into the coastal fjords, Gabrielsen says. “Immediately, you started to see Atlantic species getting into the food samples.” A decade on, this polar marine ecosystem appears more Atlantic than Arctic.
The Atlantification underway around Svalbard is now spreading eastward across the Arctic Ocean, another recent report finds. This shows that the eastern Arctic’s distinct layering of seawater—which provides a physical buffer against the Atlantic—is losing its strength, says lead author Igor Polyakov, a University of Alaska Fairbanks oceanographer. Normally, Arctic waters are highly stratified, with cold bands of lighter, fresher water atop heavier, saltier water. These layers cap the warm, dense Atlantic water and keep it from reaching the surface. As the climate changes, the new study shows that the barrier in the eastern Eurasian Arctic basin (north of Scandinavia to Russia) is breaking down, allowing Atlantic water to mix with the Arctic layers.
Scientists are trying to understand the environmental impacts of this momentous shift. One of the biggest, already underway, is the toll on sea ice—which a new report shows is at a record low for this time of year, when it should be near its peak. Increased fluxes of Atlantic water in winter prevent new ice from forming, opening the door to solar heat and expanded algal blooms. And the more the ice cover shrinks, the more Atlantic water can move in.
Polyakov says the phenomenon is accelerating and may continue to spread eastward toward Siberia. And though ocean physics are very different on the Pacific side of the globe, he says parts of the Canadian Arctic show signs of “Pacification.”
“This is a new polar ocean for us, a new polar ocean from many perspectives,” says Polyakov. “It’s just a completely new environment.”
Back in Svalbard, some seabirds are thriving on their new diet. Kittiwake populations, plummeting throughout much of their range, are actually increasing here. Atlantic puffins—endangered in Europe—are also flourishing in the archipelago. But for Svalbard’s little auks, the Atlantic influx has swapped the small, rich polar crustaceans, Calanus hyperboreus, for the less-nutritious Atlantic species, Calanus finmarchicus, leaving these seabirds critically short on fuel.
“So it really shows that there are winners and losers in this new system,” says Gabrielsen.