An unmanned submarine exploring deep beneath West Antarctica’s Dotson Ice Shelf transmitted startling images of unfamiliar under ice formations, then vanished without a trace. The autonomous vehicle, known as Ran, had spent weeks mapping the ice shelf’s hidden underside, uncovering complex melt patterns that challenge simplified views of how Antarctic ice is eroded by the ocean. Its disappearance only heightened the significance of the data it managed to send back. The mission was led by Anna Wåhlin, a professor of oceanographic physics at the University of Gothenburg, whose work focuses on how warm ocean currents destabilise ice shelves from below. These floating ice platforms play a crucial role in slowing the flow of inland glaciers, and their thinning is closely linked to future sea level rise.

Exploring a Hidden World Beneath the Ice

Ran is an autonomous underwater vehicle designed to operate for long periods without human control or real time communication. During a 2022 campaign, the robot submarine spent 27 days navigating beneath the Dotson Ice Shelf, weaving through a dark cavity that stretches miles under the ice. Over the course of the mission, Ran travelled roughly eleven miles into this concealed environment and mapped an area of about 54 square miles. The objective was to understand why Dotson’s eastern side remains relatively thick and stable, while its western side melts faster and appears more fragile. From the surface, satellite data suggested uneven thinning, but the processes driving this imbalance were poorly understood.

Unexpected Shapes Carved From Below

Using sonar, Ran revealed a surprisingly complex ice underside. Instead of a smooth surface, the maps showed flat plateaus, stepped terraces, deep channels, and teardrop shaped pits carved into the ice by basal melting. In the eastern and central regions, the ice base appeared layered, resembling a staircase formed by slow, persistent melt over long periods. In contrast, the western side looked smoother and more eroded, marked by channels and scooped depressions where melting was more aggressive. None of these features are visible from satellite imagery, meaning they had remained completely hidden until the submarine’s survey. Their discovery suggests that melt processes beneath ice shelves are far more structured and localised than previously assumed.

Warm Currents and Uneven Erosion

The contrasting patterns beneath Dotson are closely linked to how ocean water circulates under the ice. Around Antarctica, a warm and salty current known as Circumpolar Deep Water flows from the Southern Ocean onto the continental shelf. When this water intrudes beneath ice shelves, it accelerates melting from below. Data collected by Ran indicate that this warm inflow concentrates erosion on Dotson’s western flank, while colder, slower moving water helps shield the eastern side. Satellite measurements show that melt channels in the region thin by roughly 40 feet per year, and overall melting beneath Dotson contributed about 0.02 inches to global sea level rise between 1979 and 2017.

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Turbulence, Terraces, and Teardrops

The shapes observed beneath the ice offer clues about how water moves through the cavity. Where currents flow slowly, melting tends to form terraces, flat ledges separated by small steps that record gradual ice loss over many years. In faster flowing zones, shear driven turbulence smooths the ice and carves grooves and channels. Some of the most striking features are teardrop shaped pits, nearly 1,000 feet long and more than 160 feet deep. These forms appear to have been sculpted by focused currents swirling close to the ice base. Elsewhere, the terraced plateaus may preserve a record of episodic pulses of warmer water entering the cavity and peeling away layers of ice over time.

Fractures That Accelerate Ice Loss

Ran also imaged fractures slicing through the full thickness of the ice shelf. Many of these cracks are widened and smoothed at their bases by melting, effectively turning them into conduits that funnel warm water deeper into the ice. Satellite records show that some of these fractures have existed since the 1990s, and the oldest ones show the deepest melt scars. These narrow passages act as hidden highways for heat, concentrating damage in ways that large scale ice models often fail to capture. Most current simulations treat melting in broad averages, overlooking how fractures and channels can steer warm water and amplify local ice loss.

Why These Findings Matter for Sea Levels?

Since 1979, Antarctic ice loss has raised global sea levels by about 0.55 inches, with West Antarctica accounting for a large share. Ice shelves like Dotson float over deep basins that allow warm ocean water to reach their undersides. When these shelves thin or break apart, they lose their ability to buttress the glaciers behind them, allowing land based ice to flow more rapidly into the ocean. By revealing how melt is shaped by terraces, channels, and fractures, the Dotson observations help scientists refine estimates of how quickly inland glaciers might respond as the climate warms. Better representation of these processes could narrow the uncertainty around future sea level projections.

Operating Without a Lifeline Under the Ice

Ran operated without real time contact, as radio waves and GPS signals cannot penetrate hundreds of feet of solid ice. Instead, it relied on onboard navigation systems and acoustic instruments to track its position relative to the seafloor and ice ceiling. Missions could last from several hours to more than a full day, meaning any problem deep under the ice would only become apparent if the vehicle failed to surface. Despite these risks, the team completed 14 successful missions in 2022, assembling a dataset that is already reshaping scientific understanding of ice ocean interactions.

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When the Signal Went Silent

During a later return to Dotson, Ran was deployed again to extend the survey. This time, it did not reappear at the recovery point. Attempts to re establish contact failed, and searches found no signal or debris. With no live feed, the cause remains unknown, ranging from mechanical failure to a collision with ice ridges. Although the loss of the vehicle was a setback, researchers emphasise that its earlier missions fundamentally changed how they view the underside of ice shelves.

A Rare Window Into Antarctica’s Hidden Machinery

The maps Ran transmitted show that the base of an ice shelf is not a uniform surface but a dynamic landscape shaped by currents, fractures, and turbulence. Each feature responds differently to ocean heat, and together they control how quickly ice is lost from below. Incorporating these details into climate and ice models could improve predictions of West Antarctica’s future and its contribution to sea level rise. For now, Ran’s data remain a rare glimpse into one of Earth’s least explored environments, a reminder of how much of the planet’s climate system still lies hidden beneath the ice.

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