Scientists Put Sensors on Narwhals. They Revealed Something Troubling Beneath Greenland’s Glaciers

If you’re out of your element, sometimes it’s best to get a local to show you around.

Narwhals – elusive, toothed whales famous for their bizarre unicorn-like tusks – spend much of their lives swimming around and beneath some of the “most remote and inaccessible” ice formations in the Arctic, including the Scoresby Sound, the world’s largest fjord system.

Scientists wanted to find out more about how the waters in this region are changing, but humans are not exactly cut out to explore these frigid waters.

Even on boats, crews struggle to navigate the thick sea ice and precarious icebergs that encrust East Greenland’s coast.

But that is exactly where an ocean current from the Atlantic, warmed by the accumulating heat we have trapped with our fossil fuel emissions, is encroaching on the Greenland ice sheet – the second largest body of ice in the world.

So, to better understand these changing seas, scientists from the Greenland Institute of Natural Resources, the University of Copenhagen, and other institutions have recruited narwhals as unwitting research assistants.

Their findings have just been published in Science Advances.

It’s only the third time scientists have successfully taken this approach to investigate ocean warming, with previous efforts focused on Baffin Bay and Melville Bay, also 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.”

It’s not easy to track down a narwhal, but local hunters from Ittoqqortoormiit in Greenland have a knack.

With their help, the researchers fitted six narwhals with satellite-transmitting sensors between August 2017 and July 2020 to collect data about dive depth, water temperature, and how well the water conducted electricity (as a proxy for salinity).

The sensors, which were programmed to record during the narwhal’s two deepest dives each day, collected between 85 and 332 days’ worth of data for each animal assistant.

Cold polar water, shed from the melting sea ice and the Greenland ice sheet, floats above 150 meters (492 feet) due to its low salt content.

But deep below is an injection of warmer, much saltier water, which originates 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 was not involved in the research, 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.”

This warm water accelerates glacier retreat, but the inaccessibility of this complex system, so closely tied to our planet’s future, has been a barrier to climate modeling.

“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.”

Pairing the narwhal data with historic records for the Scoresby Sound region, the researchers have confirmed that the careful balance of cold, polar water from the Arctic and warm, salty water from the Atlantic Ocean is tipping.

The picture is emerging in clearer detail than boat-based measurements could have ever captured.

“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.”

Related: Sea Levels Are Rising Globally. Around Greenland, They’re Projected to Fall.

The warm Atlantic water is penetrating deep into the fjord systems, reaching the glacier fronts in ways we could not have seen without the help of 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 research was published in Science Advances.