Originally this story appeared in Hakai magazine and is part of the Climate desk cooperation.
In the Strait of Fram off the west coast of Greenland, Véronique Merten met the foot soldiers of an invasion.
Merten studied the region’s biodiversity using environmental DNA, a method that allows scientists to figure out what species live nearby by sampling the tiny bits of genetic material they shed, such as scales, skin and poop. And here, in a stretch of the Arctic Ocean, 250 miles north of where they had once been seen before: capelin.
And they were everywhere.
The small baitfish found in the northern Atlantic and Pacific Oceans is an avid colonizer. When ocean conditions change, it’s very easy for capelin to expand their range, says Merten, a marine ecologist at the GEOMAR Helmholtz Center for Ocean Research Kiel in Germany.
It is difficult to estimate an animal’s abundance based solely on the amount of DNA in the water. Yet in Merten’s samples, capelin was the most common species – much more than typical Arctic fish such as Greenland halibut and Arctic skate. For Merten, the evidence of so much capelin so far north is a bold sign of a worrying Arctic phenomenon: atlantification.
The Arctic Ocean is warming rapidly – the Fram Strait is almost 2 °C warmer than in 1900. But Atlantification is about more than rising temperatures: it is a process that is changing the physical and chemical conditions of the Arctic Ocean.
Due to the global circulation patterns of the oceans, water routinely flows from the Atlantic Ocean to the North Pole. This exchange usually takes place in deeper water, with currents carrying warm and relatively salty Atlantic water to the north. However, this warm Atlantic water does not mix well with the surface water of the North Pole, which is relatively cool and fresh. Fresher water is less dense than saltier water, so the Arctic water tends to float on it and trap the saltier Atlantic water deep below the ocean’s surface.
However, as the sea ice disappears, the surface of the Arctic Ocean warms. The barrier between the layers is deteriorating and Atlantic water mixes more easily in the top layer. This is the beginning of a feedback loop, where warmer surface water melts more sea ice, further exposing the ocean surface to sunlight, which warms the water, melts the ice and further mixes the Atlantic and Arctic waters. That is Atlantification: the transformation of the Arctic Ocean from colder, fresher and ice-covered to warmer, saltier and increasingly ice-free.
Merten’s discovery of abundant capelin in the Fram Strait — as well as the DNA she found from other Atlantic species, such as tuna and crooked squid, well outside their typical range — is further evidence of how fast Atlantification is happening. And the consequences can be enormous.
In the Barents Sea off the coast of Russia, for example long-term study paints a grim picture of how Atlantification can disrupt Arctic ecosystems. As the Barents Sea has become warmer and saltier, Atlantic species have “moved in and taken over,” said Maria Fossheim, a fisheries ecologist at the Institute of Marine Research in Norway who led the study.
Fish communities in the Barents Sea, says Fossheim, have moved 100 miles north in just nine years – “three or four times faster than [previous studies] had foreseen.” Towards the end of her study, in 2012, Fossheim found that Atlantic species had expanded in the Barents Sea, while Arctic species had largely been driven out.
Merten’s findings suggest that the Fram Strait may be moving in a similar direction. However, because this study is the first to examine the diversity of fish in the Fram Strait, it is unclear how recent these changes really are. “We need these baselines,” says Merten. “That could be it [capelin] happened there years ago, but no one ever checked.”
Anyway, they’re here now. The question is, what will appear next?