Narwhals Help Scientists Track Warm Atlantic Water Near Greenland

If you find yourself in an unfamiliar environment, a local guide can sometimes be the best person to lead the way.

Narwhals – hard-to-find toothed whales renowned for their extraordinary, unicorn-like tusks – spend much of their time swimming through and beneath some of the Arctic's “most remote and inaccessible” ice formations. These include Scoresby Sound, the world's biggest fjord system.

Researchers were keen to learn more about the ways the water in this area is shifting. Yet people are hardly equipped to investigate such icy seas.

Even from vessels, crews find it difficult to make their way through the dense sea ice and unstable icebergs lining East Greenland's coast.

Narwhals reveal Atlantic water in Scoresby Sound

This is also precisely the area where an Atlantic ocean current, heated by the build-up of warmth caused by fossil-fuel emissions, is pushing towards the Greenland ice sheet – the world's second-largest expanse of ice.

To gain a clearer picture of these changing waters, scientists from the Greenland Institute of Natural Resources, the University of Copenhagen and other organisations enlisted narwhals as inadvertent research assistants.

Their results have now appeared in Science Advances.

This marks only the third successful use of this method to study ocean warming. Earlier research using the approach examined Baffin Bay and Melville Bay, which are likewise in Greenland.

“The narwhals have been in parts of the fjords where very few measurements have been taken before. And there, 300 kilometers [186 miles] from the coast, we find traces of Atlantic water,” marine biologist Mads Peter Heide-Jørgensen, of the Greenland Institute of Natural Resources, explains.

“It is completely new that we can show this.”

Finding narwhals is not straightforward, although local hunters from Ittoqqortoormiit, Greenland, are particularly skilled at it.

With the hunters' assistance, the team attached satellite-transmitting sensors to six narwhals between August 2017 and July 2020. The devices gathered information on diving depth, water temperature and electrical conductivity, the latter serving as an indicator of salinity.

Programmed to take readings during each narwhal's two deepest daily dives, the sensors returned between 85 and 332 days of data for every animal participant.

How warm Atlantic water reaches Greenland's glaciers

Cold polar water released by melting sea ice and the Greenland ice sheet remains above 150 metres because of its low salt content.

Far below that layer, however, lies an influx of considerably warmer and saltier water originating in the North Atlantic.

“Often, this water is prevented from entering fjords by a 'sill' – an underwater ridge at the mouth of the fjord,” glaciologist Tom Chudley, who did not take part in the study, explained in an article for The Conversation.

“However, when sills are deep and Atlantic water is abundant, warm water can spill over the sill and approach the front of glaciers.”

Warm water hastens the retreat of glaciers, but the difficulty of accessing this intricate system – one so closely linked to the planet's future – has limited climate modelling.

“In the large climate models used to predict future climate change, glacier melt plays a major role,” mathematical biologist Susanne Ditlevsen of the University of Copenhagen explains.

“That is why it is crucial that we improve our understanding of it, particularly because Greenland contains so much ice.”

Narwhal data maps changing fjord layers

By combining the narwhal readings with historical records from the Scoresby Sound area, the researchers confirmed that the delicate balance between cold Arctic polar water and warm, saline Atlantic Ocean water is changing.

The resulting view offers a level of detail that measurements collected from boats could not have achieved.

“We used the two large datasets to build a robust model showing how temperature, salinity, and depth are related,” says Ditlevsen.

“The models show that the layer consisting of Atlantic water has become thicker, while the upper layer of polar water has become thinner.”

Warm Atlantic water is moving far into the fjord systems and reaching glacier fronts in ways that would have remained unseen without the narwhals.

“Now we suddenly have measurements from places we can use in our models, giving us a much more complete picture of the ocean. It is absolutely fantastic to use the animals in this way,” says Ditlevsen.

The study was published in Science Advances.

This article was fact-checked and edited by Clare Watson. Although we take pride in our process, we are only human. If you notice an error, please tell us.