An unmanned submarine mapping West Antarctica’s Dotson Ice Shelf reported strange under-ice structures, then went silent ten miles beneath it.
The vehicle, called Ran, had spent weeks scanning an ice area roughly fifty square miles, revealing patterns that upend simple melt models.
Ran’s mission beneath Dotson ice shelf
The work was led by Anna Wåhlin, a professor of oceanographic physics at University of Gothenburg, coordinating the Ran missions in West Antarctica.
Her research focuses on how ocean currents erode ice shelves from below, changing glacier stability and future sea level.
Ran is an autonomous underwater vehicle, a robot submarine that navigates alone under ice for hours.
During a 2022 campaign, Ran spent 27 days weaving under Dotson’s floating ice, eventually reaching about eleven miles into the hidden cavity.
The mission aimed to explain the sharp contrast between Dotson’s thick, slow-melting eastern side and its thinner, faster-melting western side.
Ran saw strange things then vanished
Using sonar, Ran mapped 54 square miles of ice underside beneath Dotson Ice Shelf. The maps revealed flat plateaus, terraced steps, and teardrop-shaped pits, all carved by basal melt, melting that attacks the ice from below.
In the east and center, Ran saw icy terraces stacked like steps, while the west looked smoother, with channels and scooped depressions.
None of these terraces or teardrop pits show up on satellite images, so they had remained completely hidden until Ran’s mission.
Warm deep water, uneven melting
Around Antarctica, Circumpolar Deep Water, a warm salty current from the Southern Ocean, moves onto the shelf and melts ice shelves from below.
Satellite altimetry over Dotson shows that melt channels lose ice at about 40 feet per year, a thinning pattern linked to warm water.
Analysis of measurements under Dotson indicates that this ice shelf added 0.02 inches to sea level between 1979 and 2017.
The under-ice maps show that this warm inflow focuses erosion on Dotson’s western side, while colder water leaves the eastern flank protected.
Terraces, teardrops, and turbulence
Where currents move slowly, the base of the ice looks like stacked ledges, formed as melting eats away flats and leaves small steps.
In the fast outflow region, currents create smoother surfaces with grooves, where shear-driven turbulence, mixing caused by sliding water layers, drives rapid melting.
Some pits are teardrop shaped, 984 feet long and 164 feet deep, carved by currents near the ice base.
Elsewhere, the terraced plateaus probably record bursts of slightly warmer water entering the cavity, slowly peeling away layers of ice over many years.
Hellbound and Down 