'Like a boiling pot' - How the maelstrom under Greenland's glaciers may help slow sea level rise

There are stadium-sized blocks of ice crashing from the soaring face of the Kangerlussuup glacier in western Greenland, fierce underwater currents of meltwater shooting out from its base and visibility below the surface is virtually zero owing to a torrent of suspended mud and sand. It's little wonder scientists have never explored this maelstrom.

- Damian Carrington

Yet today, they are sending in a multimillion-dollar remotely operated submarine, potentially to its death. As the scientists onboard the Celtic Explorer research ship repeatedly say: "It's a high-risk, high-reward mission."

The reward is solving a mystery that could transform the understanding of the most profound long-term impact of the climate crisis: surging sea levels. Glaciers fed by ice caps are increasingly disintegrating, and how fast this will accelerate directly affects a billion people in the world's great coastal cities.

However, current models do not take into account a key possible factor: the huge mounds of ground rock that some glaciers pile up in front of them, blocking their paths and insulating them from ever-hotter oceans. These could be "speed bumps" slowing the impact of global heating. But the role this plays is unknown because researchers have never been able to scrutinise the zone where glaciers, rock and ocean meet.

Now, they are. "Oh my God, what is that?" says Prof Ginny Catania, the expedition's chief scientist, from the University of Texas (UT). She is looking at the screens in the ship's tense control room. The live sonar feed from the submersible has revealed a vast underwater cavern in the glacier's face.

The engineer Victor Naklicki is piloting the sub, a feat of fierce concentration over the 10-hour dive. Afterwards, he says: "It was pretty crazy down there - we saw the big cave and you could feel the thrusters working very hard to not get sucked right in. We made it 50 metres into it, but it went even deeper - it was an abyss."

The move inside went against all conventional piloting wisdom, he says, as putting a remotely operated sub under anything means it cannot float back to the surface if something goes wrong. "But the prize is collecting data that has never been collected before."