Narwhals Mapped Warm Water Invading Greenland’s Most Remote Glacier Inlets

Narwhals Are Performing Ocean Research Ships Couldn’t Accomplish for 200 Years

Six narwhals just did something ships have struggled with for two centuries: they mapped the warm water creeping into Greenland’s most remote coastal inlets, feeding directly into the deep basins that sit in front of glaciers far inland, water that can melt those glaciers from below.

Often nicknamed the unicorns of the sea, these tusked whales spend much of their lives diving deep into the icy waters off East Greenland’s coast, a habit that made them accidental oceanographers. Researchers fitted six narwhals with recording tags that tracked temperature and salinity as the animals dove more than 1,500 meters, into narrow, glacier-carved inlets called fjords that stay choked with pack ice year-round, places research vessels almost never go. The findings, published in Science Advances, combine that narwhal data with historical ocean records dating to 1891 to show that warm, salty water of Atlantic origin has been spreading through East Greenland’s coastal system for decades. The narwhals’ own dives, the only direct measurements ever taken in front of many of these glaciers, reveal that water now reaches some glacier fronts up to 300 kilometers inland.

Scientists have long tracked rising ocean temperatures across the wider Greenland Sea, but almost no one had measured what was happening in the narrow inlets where glaciers actually meet the ocean, because the coastline is nearly impossible to reach by boat. Narwhals filled that gap. Between August 2017 and July 2020, the six tagged whales logged more than 2,000 temperature and salinity profiles, a haul no single ship expedition could match in that window, giving scientists a way to better estimate how ocean warming could affect glacier retreat and ice loss in East Greenland. Other studies have already flagged similar warming and melting at marine-terminating glaciers elsewhere in Greenland, in the northeast and southeast, so what’s happening along this stretch of coast fits a wider pattern rather than standing alone.

Atlantic Water Is Overtaking East Greenland’s Coast

Researchers have a name for what’s happening here: atlantification, the process by which warm, salty Atlantic-origin water gradually takes over Arctic seas, reshaping temperature, salinity, circulation and even sea ice cover along the way. Atlantic water has always flowed near East Greenland’s coast. What’s changed is how far it now pushes, how warm it has gotten and how much it has displaced the cold, fresher Polar Water that once dominated these waters.

Narwhal data show that shift happening in real time. Near the surface, cold Polar Water still rules. But descend past roughly 150 meters and Atlantic-derived water starts muscling in, and below 250 meters in the Blosseville Basin, one of the study’s key regions, it takes over almost entirely, leaving little Polar Water behind to cool things down.

Deep Inlets Put Some Glaciers in Warmer, Saltier Water

Not every glacier faces the same exposure. Glaciers sitting in deep inlets, including those in the Scoresby Sound complex and at Kangerlussuaq, sit in front of significantly warmer, saltier water than glaciers along the shallower Blosseville Coast, where the shape of the seafloor blocks the warm Atlantic layer from ever reaching the ice. Depth turns out to be the deciding factor: glacier fronts in Scoresby Sound sit roughly 800 meters down, and Kangerlussuaq’s sit around 900 meters, deep enough for warm Atlantic water to pool right against the ice. Glaciers along the shallower Blosseville Coast and in Nansen Fjord sit closer to 450 meters, shallow enough that the warmest water often passes overhead instead. Since 1970, that Atlantic-derived layer has warmed by roughly 0.09 to 0.15 degrees Celsius per decade across the areas studied, and near-surface waters in the Blosseville Basin warmed even faster, by close to half a degree per decade between 1960 and 2021.

Deeper glaciers exposed to that warmer water also lost a larger share of their ice through iceberg discharge, a pattern the researchers say is consistent with stronger ocean influence on those glacier fronts. Iceberg calving barely changed month to month, which the study’s authors say suggests Atlantic water may be shaping glacier behavior year-round, not just during the height of summer melt.

Decades of Glacier-Front Data Are Still Missing

Real limits remain in the narwhal record. Only measurements collected from 2017 to 2020 exist for the water directly in front of most glaciers, and historical observations inside Scoresby Sound, the world’s largest fjord system, remain sparse and, in some older cases, of questionable quality. That gap means scientists can describe current conditions with confidence but can’t yet say exactly how long warm water has been reaching specific glacier fronts, or how much of each glacier’s retreat traces back to the ocean rather than surface melt.

None of that undercuts the larger finding. Six whales, doing what they do every day anyway, showed that Atlantic water has already arrived at the doorstep of glaciers once thought too remote to reach. What was once buffered by distance and geography is buffered no longer, and the animals best equipped to notice were the ones already living there.

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