A group of narwhals has helped scientists fill major gaps in observations of East Greenland’s coastal waters, providing measurements from places that research vessels rarely reach.
Measurements collected by sensors attached to narwhals have revealed how warm Atlantic water penetrates deep into remote fjords in East Greenland, providing new insights into conditions near some of the region’s glaciers.
The study, published in Science Advances, used data collected by instruments attached to six narwhals between 2017 and 2020. The sensors collected a total of 2,060 oceanographic profiles of temperature, salinity and depth.
Where research ships cannot go
East Greenland’s deep fjords remain poorly observed. Sea ice, icebergs and difficult access limit measurements from research vessels, particularly farther inside the fjord system.
Tagging narwhals made it possible to collect measurements from some of these difficult-to-access waters. The animals naturally travel through the ice-covered fjords and repeatedly dive through the water column, sometimes to depths beyond 1,500 metres. Sensors attached to the animals recorded conditions during their dives, with the collected data transmitted by satellite when the narwhals surfaced.
The six animals were captured near Scoresby Sound with the help of local hunters and fitted with CTD sensors. CTD stands for conductivity (from which salinity can be calculated), temperature and depth, allowing measurements recorded during a dive to provide a vertical profile of some of the ocean’s fundamental properties.
The tags were deployed for between 85 and 332 days. Researchers combined the resulting measurements with historical and current oceanographic profiles sourced from the World Ocean Database to examine spatial and long-term changes in ocean conditions across the region.
Atlantification of East Greenland
Waters in East Greenland’s fjords contain relatively cold and fresh Polar Water originating in the Arctic, generally overlying warmer, saltier and therefore denser Atlantic Intermediate Water.
According to the study, analysis of the observations points to a long-term warming trend and an increasing influence of Atlantic water. The researchers report a thickening of the Atlantic water layer and a thinning of the overlying Polar Water layer. They estimate that temperatures in the upper 500 metres of the Blosseville Basin increased by about 0.047°C per year between 1960 and 2021.
The study also documents Atlantic Intermediate Water penetrating farther into East Greenland’s fjords than previously documented, reaching deep basins in front of marine-terminating glaciers as far as 300 kilometres inland. The authors argue that this warmer water can deliver heat directly to submerged glacier fronts, promoting submarine melting and contributing to glacier mass loss. They suggest that better observations of these waters could therefore help improve estimates of future Greenland ice loss.
Marine mammals in oceanography
Using instrumented narwhals to collect oceanographic measurements is unusual, but not unprecedented. More broadly, marine mammals have been used for ocean observation for decades, and today the practice operates on a remarkable scale.
Animal tagging is commonly associated with learning about the animals themselves, such as where they travel and how they behave. In this type of research, however, the instruments they carry also turn the animals into platforms for observing the ocean itself, collecting measurements from places where conventional observations can be extremely difficult.
The international Marine Mammals Exploring the Oceans Pole to Pole (MEOP) programme provides a striking example. It brings together oceanographic measurements collected by instrumented marine mammals around the world. More than 800,000 profiles of ocean temperature and salinity have been collected since 2004, with seals accounting for most of the instrumented animals.
Measurements collected in this way have helped fill substantial gaps in observations of the world’s oceans. The potential some researchers see in this practice is perhaps best illustrated by the authors of the East Greenland study themselves, who argue that approaches involving “unconventional collaborators” can “revolutionize oceanographic research.”
Dr. Yana Kirichenko, PolarJournal