While the surface looks almost motionless, British scientists say unseen underwater “tsunamis” triggered by collapsing glaciers may be churning the Southern Ocean, stirring up heat and nutrients and quietly feeding back into the global climate system.
When glaciers trigger invisible tsunamis
Most people think of an iceberg calving event as a brief bit of polar theatre. A wall of ice cracks, tumbles into the sea, a splash rises, cameras click, and then the bay seems calm again. That calm is misleading.
Researchers working in West Antarctica have found that the real drama plays out below the surface. As huge blocks of ice hit the water, they generate powerful internal waves that roll through the water column for kilometres.
These underwater waves can rise several metres high inside the ocean, mixing cold and warm layers like a giant invisible blender.
Unlike classic tsunamis that race across the surface and hit coastlines, these waves stay trapped in the interior. They move through layers of different temperature and salinity, shaking them up and redistributing heat, oxygen and nutrients.
Oceanographers had long known that some mixing happens near icy fronts. What they had not fully grasped was how much energy each collapse of ice can inject into the sea, and how frequently this happens around Antarctica’s vast, crumbling edges.
An Antarctic surprise born from chance measurements
A British ship happens to be in the right place
The story began almost by accident. The British research vessel RRS James Clark Ross, then operated by the British Antarctic Survey, was monitoring ocean conditions close to a glacier front when a calving event occurred nearby.
Instruments on moorings and on the ship captured data just before, during and after the collapse. Temperature and current profiles suddenly shifted. The signals were too strong and too deep to be explained by wind, tides or surface cooling alone.
Scientists realised they were watching something different: energetic waves radiating away from the impact point, ricocheting through the fjord and out into the open ocean.
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Those measurements hinted at a previously overlooked engine of mixing, driven not by storms or tides but by the glaciers themselves.
The RRS James Clark Ross has since been sold to Ukraine’s National Antarctic Scientific Center and renamed Noosfera. Yet the data gathered during that mission still fuels a growing line of research into how ice and ocean interact.
A mixing engine rivaling the wind
Until recently, most climate and ocean models assumed that three main processes stirred the waters around Antarctica: strong westerly winds, rising and falling tides, and heat loss from the surface in winter.
The new work suggests calving-induced internal tsunamis could rival the mixing effect of the wind and, in some regions, exceed the role of tides.
- Wind: drives surface waves and large-scale currents.
- Tides: push water against seafloor slopes, generating internal tides.
- Surface cooling: creates dense water that sinks and stirs layers.
- Glacier calving: injects energy at the ice front through massive impacts.
This extra mixing sounds beneficial at first. More nutrients near the surface can feed phytoplankton, the microscopic algae that underpin Antarctic food webs. Better oxygenation helps marine life as well.
But there is a catch. Deep waters in the Southern Ocean store a lot of heat. When internal waves shake those layers, some of that warmth rises and reaches the base of the ice shelves and glacier fronts.
By dragging warmer water upward, these waves can nibble away at the ice from below and speed up Antarctic melt.
That sets up a troubling loop: a glacier collapses, strong internal waves form, mixing brings in more warm water, the glacier base weakens, and more ice breaks off. The process does not act alone, but it can amplify other drivers of ice loss already in play as the climate warms.
Rothera and the hunt for hidden waves
A frontline research station
To get a clearer view of this process, teams have based themselves at Rothera Research Station on the Antarctic Peninsula. From there, scientists head out by boat or on the new polar ship RRS Sir David Attenborough to active glacier fronts where ice breaks away frequently.
Each calving event becomes an unrepeatable natural experiment. No laboratory can easily simulate the scale of a falling iceberg the size of a city block. The only option is to measure the ocean’s response during real events, in real time.
High-tech tools for a fleeting phenomenon
Capturing short-lived underwater tsunamis demands a mix of tools scattered across ice, sea surface and seafloor.
- Satellites and shore-based cameras watch glacier faces and flag cracks and collapses.
- Drones fly close to towering ice cliffs that would be dangerous for crewed helicopters.
- Autonomous underwater vehicles slip beneath the ice where humans cannot safely go.
- Moorings and seafloor instruments log pressure, currents and turbulence as waves pass.
- Machine-learning algorithms scan satellite images to identify calving episodes.
- Computer models simulate how each iceberg splash sends waves through the fjord and beyond.
Professor Michael Meredith, an oceanographer at the British Antarctic Survey, has stressed that the aim is not just to describe a curious phenomenon. The real goal is to feed these processes into global climate simulations so that projections of future sea-level rise and ocean circulation become more realistic.
Without including this hidden form of mixing, models might underestimate how quickly Antarctic ice can respond to a warming ocean.
Sheldon Glacier as a natural laboratory
One of the focal points of this research is Sheldon Glacier, a relatively accessible but highly active ice front. Here, underwater robots map the water column metre by metre while the glacier periodically sheds ice blocks into the bay.
These vehicles measure temperature, salinity, currents and tiny changes in water density. They also track nutrient levels and plankton abundance before and after major calving events.
The data show how strong mixing can temporarily fertilise surface waters. Nutrient-rich deep water reaches the light-filled upper layers, fuelling phytoplankton blooms that in turn support krill, fish, seals and whales.
| Process | Short-term effect | Long-term risk |
|---|---|---|
| Underwater tsunamis | Strong mixing and nutrient uplift | More warm water onto glacier bases |
| Phytoplankton response | Local boosts in productivity | Possible shifts in species composition |
| Ice shelf melt | Weakened ice near calving fronts | Faster flow of inland ice to the ocean |
So the same waves that help feed Antarctic marine life may also undermine the ice platform that many species depend on for habitat and stable conditions.
A global project for a shared climate risk
The research around these internal tsunamis forms part of a wider effort called POLOMINTS, led by the British Antarctic Survey. Teams from the UK, the United States and Poland contribute, alongside institutions such as the Scripps Institution of Oceanography and the University of Southampton.
Funding from the UK Natural Environment Research Council highlights how these under-ice processes matter far beyond scientific curiosity. Antarctic mixing helps shape how heat and carbon move through the global ocean, which in turn influences climate patterns from Europe to the tropics.
Changes in the Southern Ocean do not stay in the Southern Ocean; they ripple through weather, sea level and marine ecosystems worldwide.
By better representing under-ice mixing, researchers hope to narrow the wide range of future sea-level projections, giving coastal planners clearer information on risks faced over the coming decades.
Key concepts behind underwater Antarctic tsunamis
What scientists mean by “internal waves”
These Antarctic tsunamis are technically internal waves. Instead of running along the sea surface, they travel along boundaries between lighter water above and heavier water below.
Think of the ocean as a layered cake. A shove at one point – such as a massive iceberg plunging in – sends a ripple along those internal layers. In strongly stratified polar waters, these waves can grow quite large and travel long distances while remaining almost invisible from above.
Where the seafloor rises or the coastline narrows, internal waves can break and produce turbulence, much like a normal wave crashing on a beach, except the action happens dozens or hundreds of metres down.
Why this matters for everyday life
For people living far from Antarctica, this may sound abstract. Yet the Southern Ocean works as a climate regulator. It absorbs a large share of the excess heat and carbon dioxide that humans add to the atmosphere.
If internal tsunamis change how that ocean ventilates and how much warm water reaches ice shelves, they can influence:
- the speed at which global sea level rises,
- the strength and position of major ocean currents,
- storm tracks and rainfall patterns in the Southern Hemisphere,
- habitats for commercially valuable species such as krill and certain fish.
Some climate models are now running scenario tests. In one set of simulations, calving-induced mixing remains weak, and Antarctic ice loss tracks the lower range of current estimates. In another, these underwater waves grow more intense as glaciers destabilise, and sea level climbs faster, particularly after mid-century.
The reality probably sits between these extremes, but without solid measurements the uncertainty stays wide. That is why scientists keep returning to isolated places like Sheldon Glacier and Rothera Station, chasing fleeting signals from waves that most of us will never see – yet may still feel, one day, at our own shorelines.
