They were tracking a routine chunk of ice breaking from a glacier when their instruments lit up. What looked like a simple collapse at the surface unleashed something far more dramatic below: powerful underwater waves surging through the Southern Ocean, with consequences that may reach well beyond the polar circle.
Glacier collapse that triggers invisible tsunamis
When a glacier sheds an iceberg, the show above water looks brief and almost theatrical. Towering walls of ice crack, plunge, and send spray skyward. Minutes later, the surface often calms. For decades, researchers largely treated these events as local episodes, impressive but short‑lived.
New observations now tell a different story. Each major calving event, when pieces of glacier break off into the sea, can unleash a burst of energy that drives what scientists call “internal tsunamis” beneath the waves.
Ces hidden waves travel within the ocean, not on its surface, reaching heights of several metres and running for kilometres.
Rather than racing toward coastlines, these waves roll through the water column. They mix layers of cold and warm water, shuffle oxygen and nutrients, and stir up sediments. That mixing matters: the Southern Ocean plays a huge role in regulating Earth’s climate by storing heat and absorbing carbon dioxide. Disturb its balance, and the effects can propagate worldwide.
A chance find aboard a British research ship
The first clear evidence did not come from satellites or fancy new observatories. It started, almost by accident, aboard the British ice‑capable research vessel RRS James Clark Ross, operated at the time by the British Antarctic Survey.
During a routine campaign near a calving glacier front, the team had a rare stroke of luck. Their instruments were already in place, measuring the ocean just before, during and after a major break‑up of ice. As the glacier fractured and icebergs crashed into the sea, the data went wild.
Temperature, currents and pressure shifted sharply over a short period. The patterns did not match tides, winds, or typical surface cooling. They pointed to something more energetic: waves generated by the impact of falling ice, ripping through the depths and triggering intense turbulence.
That initial dataset pushed the team to look again at how Antarctic glaciers might be shaking the ocean far beneath the surface.
As strong as the wind: a new engine of ocean mixing
Climate models usually treat Antarctic mixing as a three‑part story: winds stir the surface, tides tug at the water, and heat loss cools and sinks surface waters. Glaciers were seen mostly as passive victims, not active players.
The new measurements suggest that these internal tsunamis belong on that shortlist of drivers.
Early estimates indicate that waves from calving glaciers can rival the mixing power of strong winds, and at times exceed the influence of tides.
Each time a large section of ice hits the ocean, it displaces a massive volume of water. That sudden push sets off internal waves that bounce off the seabed and the underside of sea ice, creating swirling, chaotic flows.
This mixing pulls relatively warm water up from deeper layers. Near glacier fronts, that warmth can reach the ice base, melting it from below. Scientists worry this forms a feedback loop:
- Calving sends ice into the ocean.
- The impact triggers underwater waves and strong mixing.
- Warmer deep water rises and undercuts the glacier.
- The glacier weakens and sheds yet more ice.
In a region that already holds enough frozen water to raise global sea levels by many metres, any extra push toward faster melt matters for coastal societies worldwide.
Rothera station: a front‑row seat to hidden waves
To track these underwater tsunamis more systematically, scientists set up at Rothera Research Station, on the Antarctic Peninsula, and aboard the new British polar ship RRS Sir David Attenborough. Their target: active glacier fronts where ice fractures and topples into the sea.
The teams watch for the tell‑tale signs of calving events and coordinate deployments of instruments in the hours before and after. Each collapse becomes a natural experiment that no laboratory can reproduce.
They want to know what controls the strength of the waves. Does the shape of the glacier front matter? Does the depth of the fjord amplify the signal? How do sea‑ice cover and seasonal changes in temperature alter the outcome?
High‑tech tools for a fleeting phenomenon
These internal tsunamis leave almost no trace at the surface. A casual observer might see a splash and a few ripples, then nothing. Catching the real action demands a suite of tools spread from space to the seafloor.
From satellites to seafloor sensors
Researchers now combine several technologies to piece together each event:
- Satellites and remote cameras track cracks and collapses along glacier fronts in near real time.
- Drones provide close‑up footage of ice walls and falling blocks from above the waterline.
- Autonomous underwater vehicles (AUVs) swim beneath the surface, measuring currents, turbulence and temperature where humans cannot go safely.
- Instruments anchored to the seabed record pressure changes and passing waves over months at a time.
- Machine‑learning algorithms scan huge archives of satellite images to flag calving events that might have produced strong internal waves.
- Numerical models simulate the waves’ birth and journey through complex under‑ice topography.
The aim is not just to describe the waves, but to plug them into climate and sea‑level models so their long‑term impact can be assessed.
That requires translating bursts of data from a single Antarctic fjord into formulas that can represent similar processes all around the frozen continent.
Sheldon glacier: a natural laboratory under the ice
One of the main test sites lies at Sheldon Glacier, a relatively accessible glacier front that still calves frequently. For scientists, it acts as a controlled setting where instruments can stay in place long enough to catch multiple events.
Autonomous vehicles there patrol back and forth across the front, mapping the water column metre by metre. They log tiny shifts in temperature, salinity and dissolved oxygen before and after ice breaks away.
The team also tracks biological signals. Intense mixing can lift nutrients from depth into sunlit waters, where microscopic algae thrive.
| Parameter | Before calving | After calving |
|---|---|---|
| Temperature near glacier base | Colder, more stratified | More variable, with warm pulses |
| Nutrient levels in upper waters | Relatively low | Often boosted by mixing |
| Plankton activity | Steady background | Short‑term spikes possible |
The “underwater tsunamis” therefore affect more than ice and physics. They can jolt entire food webs, from microscopic plankton to fish, seabirds and whales that rely on predictable feeding grounds.
An international effort with global stakes
The project, known as POLOMINTS, brings together scientists from the UK, the United States and Poland, along with institutions such as the Scripps Institution of Oceanography and the University of Southampton. Funding from the UK’s Natural Environment Research Council highlights the scale of the stakes.
By combining fieldwork, remote sensing and modelling, the consortium aims to reduce one of the big blind spots in climate projections: how exactly the Southern Ocean will respond as Antarctic ice loss accelerates.
Internal tsunamis turn calving glaciers from passive symbols of warming into active engines that can reshape circulation far beyond the polar seas.
Better knowledge of this link will feed into assessments of future sea‑level rise, shifts in storm tracks, and changes in how much heat the oceans continue to absorb from the atmosphere.
Why hidden waves matter for everyday life
For most people, an underwater wave in a remote Antarctic fjord seems abstract. Yet the processes uncovered there tie directly to issues that affect daily life far from the ice: coastal flooding risk, fisheries, and even the strength of weather extremes.
When Antarctic mixing patterns change, the oceans can store heat differently. That may alter how quickly surface temperatures rise, or where marine heatwaves appear. Fisheries can also feel the impact as nutrient pathways shift and plankton blooms move or weaken.
Key terms worth unpacking
Two scientific concepts sit at the heart of this research:
- Internal waves: waves that travel within the ocean, along boundaries between layers of different density. They can be large and energetic while leaving the sea surface almost flat.
- Calving: the process by which chunks of a glacier or ice shelf break off into the ocean, forming icebergs. The size of these chunks, and the depth of water they fall into, helps set the strength of internal tsunamis.
As models improve, researchers are already testing scenarios where calving‑driven mixing intensifies around parts of Antarctica. Some simulations suggest it could speed up the thinning of ice shelves that currently buttress the vast ice sheet, loosening the brake on inland ice and raising long‑term sea‑level projections.
Other outcomes are more nuanced. In certain regions, extra mixing might enhance nutrient supply, boosting local marine productivity in the short term. Yet any such gains would sit beside the broader risks of faster ice loss and rearranged ocean circulation. The new waves under the ice add another moving piece to a climate system that is already changing quickly—and they are only just beginning to be measured.
