Collecting ocean measurements in East Greenland often depends on whether a ship can get through the ice. Many fjords extend far inland, leaving research crews with little information about the water surrounding their glaciers.
Near Scoresby Sound, local hunters helped a research team briefly capture six narwhals and fit them with ocean sensors. Once released, the whales carried the devices on their regular dives through the fjord system.
When researchers examined the readings, they found that warmer, saltier water from the Atlantic had traveled as far as 186 miles (300 kilometers) inland. The findings, published in Science Advances, could help climate models better account for the ocean heat reaching Greenland’s glaciers.
“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,” said co-author Susanne Ditlevsen in a press release.
How Narwhals Became Ocean Data Collectors
The narwhals carried conductivity, temperature, and depth sensors, commonly called CTD sensors. The devices recorded water temperature and salinity at different depths while tracking the animals’ locations.
A field team attaches an ocean sensor to a narwhal.
(Image Credit: Carsten Egevang)
Each whale was held for less than 30 minutes while its sensor was attached. The tags stayed in place for 85 to 332 days. Altogether, the narwhals collected 2,060 sets of ocean measurements between 2017 and 2020, with some readings extending beyond 4,900 feet (1,500 meters).
Explore All OptionsRather than recording every dive, the tags saved measurements from the deepest qualifying dive during each 12-hour period, producing up to two sets of readings per day.
Read More: A Narwhal's Mysterious Tusk Is Actually Made Up of Two Opposing Spirals
Warm Atlantic Water Reaches Remote Glacier Fronts
One of the sensors attached to a narwhal
(Image Credit: Mads Peter Heide-Jørgensen)
East Greenland’s fjords are layered, as colder, relatively fresh Polar Water tends to sit near the surface, while warmer and saltier water of Atlantic origin moves beneath it.
The researchers combined the narwhal records with more than 2,200 earlier sets of temperature and salinity measurements and modeled how conditions changed with depth, location, and season.
Their models pointed to a growing Atlantic presence below the surface and a shrinking cap of cold Polar Water. Between 1960 and 2021, ocean temperatures in the region increased by about 0.047 degrees Celsius per year.
Researchers call this growing Atlantic influence on Arctic environments “atlantification.” The Atlantic water had traveled through channels into basins hundreds of miles from the open coast. Deeper fjords allowed more of it to reach glaciers, with Scoresby Sound and Kangerlussuaq showing higher temperatures and salinity than the shallower Blosseville Coast.
“This is the water that helps melt the glaciers. We show how the warm water can contribute to accelerating the rate at which glaciers lose ice,” said lead author Mads Peter Heide-Jørgensen in the press release.
The study also linked greater summer iceberg discharge with higher temperatures and salinity below about 660 feet (200 meters). That relationship does not show exactly how much ice the Atlantic water melted, but it shows that some remote glaciers are exposed to more ocean heat.
Why Narwhal Data Could Improve Climate Models
When Greenland’s glaciers lose ice, freshwater enters currents flowing toward the North Atlantic, where it can affect ocean circulation. More accurate readings near glacier fronts could help climate models estimate future ice loss.
Narwhals favor cold water, so they may have sampled the warmer Atlantic layer less often than the Polar Water above it. Because they followed their own routes rather than survey lines, the readings did not cover every fjord or water layer evenly.
To the narwhals, these were ordinary dives through familiar fjords. To researchers, those same dives traced warm Atlantic water toward Greenland’s ice.
Article Sources
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- This article references information from a study published in Science Advances: Narwhals document atlantification of East Greenland
