Six narwhals living near Scoresby Sound, on Greenland’s east coast, were equipped with small sensors. These measured temperature, salinity and depth during the animals’ natural movements. Between 2017 and 2020, they provided 2,060 ocean profiles, some descending to more than 1,500 m.
This method addresses a very practical problem. Sea ice and isolation make some fjords difficult to explore by ship. Narwhals, by contrast, can travel through these waters for long periods. Their movements therefore provided measurements in areas where direct observations were scarce.
A group of narwhals swims at the surface of the Arctic Ocean.
Credit: Kristin Laidre / NOAA, public domain.
Image Wikimedia
The researchers found traces of Atlantic water as far as about 300 km from the coast. This water is warmer and saltier than the polar water above it. It can reach deep basins near glaciers that end directly in the sea.
To understand changes over several decades, the team added more than 2,200 historical profiles from a global database of ocean measurements. In the study region, the temperature of waters less than 500 m deep increased by about 0.047 °C per year between 1960 and 2021. The Atlantic water layer also thickened, while the polar layer became thinner.
This influx of heat matters for glaciers. When relatively warm water reaches their submerged portions, it promotes melting below the surface. The glaciers of Scoresby Sound and Kangerlussuaq are exposed to warmer and saltier waters than those along the shallower Blosseville Coast.
Satellite view of Scoresby Sound, a vast fjord system on Greenland’s east coast.
Credit: NASA, public domain.
Image Wikimedia
Animal measurements do not, however, replace all conventional observations. Narwhals choose their own routes and mainly frequent cold waters. Some areas or seasons therefore remain less well covered. The value lies in combining their dives with historical measurements collected from ships and the models used by researchers.
These new data can now improve estimates of glacier melt in climate models. They also pave the way for more measurements in difficult-to-access fjords. Other marine animals equipped with sensors could complement ships and fixed instruments wherever the ocean remains poorly observed.