In Greenland, the largest ice reserve in the northern hemisphere, the retreat of glacial fronts has accelerated so rapidly that it can no longer be explained solely by what we see on the surface. The missing piece points to giant, invisible internal waves that reactivate the water beneath the ice. and accelerate their wear and tear. retreat of glacial fronts
An international consortium led by the University of Zurich and the University of Washington has tracked how iceberg calving triggers persistent underwater movement. Data collected in a fjord in southern Greenland paints a picture of a mechanism capable of intensifying melting from below long after the surface regains its calm. intensify the melting from below
The technology that unlocks the hidden engine of the fjord
To “listen” to the seabed, the team laid a fiber optic cable about ten kilometers long in front of the Eqalorutsit Kangilliit Sermiat glacier, one of the most active in the region. Each section of the cable acted as a sensor thanks to the DAS (Distributed Acoustic Sensing) method, recording minute vibrations associated with fractures, waves, and density changes.
The system turned the fjord into a continuous laboratory: after each break and fall of ice, unique acoustic signals were detected that made it possible to distinguish types of waves and their path. The reading revealed not only surface “tsunamis”, but also an internal wave train traveling between layers of water with different densities.
The monitored glacier discharges an annual volume of ice equivalent to almost three times that of the Swiss Rhône, giving a constant pulse to the fjord. That underwater “heartbeat” sustains a mixture of waters that exposes the base of the glacial front to higher temperatures than expected. sea level rise
Internal waves the size of buildings and their domino effect
The detected internal waves reach heights comparable to skyscrapers when measured between ocean layers. Although they are not visible from above, They keep the water column in motion for long periodseven when the surface seems calm. internal waves detected
Their role is critical: They push relatively warmer water towards the base of the glacier, intensifying erosion and creating conditions that favor further icefalls. This is why researchers describe this process as a melt multiplier.
- Forced mixing between waters of different densities.
- Ascent of warmer water towards the base of the ice.
- Increased erosion of the glacial wall and acceleration of calving.
- Propagation of internal waves along kilometers of the fjord.
Until now, the scientific community had mainly observed the visible part: surface waves and vibrations collected on land. Direct measurements from inside the fjord revealed a great void, which this technique covers with unprecedented resolution.
Implications for Europe: from sea level to the Atlantic current
The Greenland ice sheet supports part of the planet's climate balance. If it were to melt completely, the sea level would rise by about seven meters.with catastrophic consequences. Without reaching that extreme, partial accelerations are already putting pressure on European ports, beaches, and coastal aquifers, including Spain. The sea level would rise by about seven meters.
The massive influx of fresh water can alter the circulation of the North Atlantic, which is key to heat distribution. A change in the intensity of the meridional circulation and the Gulf Stream It would have effects on temperatures, storms and precipitation patterns in the Iberian Peninsula and the rest of the continent.
In this context, having real measurements of what is happening under the ice helps to refine regional projections. Improving the models means adjusting coastal adaptation plans for vulnerable cities, infrastructure and ecosystems of the European coast.
A leap forward in polar monitoring: non-invasive fiber optics
The use of DAS avoids drilling and intrusive equipment in high-risk environments due to ice fall and drifting icebergs. A simple cable resting at the bottom turns every meter into a measurement point., capable of capturing everything from microfractures to high-energy internal waves.
The field campaign, integrated into the GreenFjord project and featured in high-impact publications, It allows for the near real-time documentation of glacial retreat., anticipate major events and quantify the strength of these hidden waves. world after the thaw
Fjords in transformation: nutrients, fauna and water chemistry
The vertical mixing forced by internal waves modifies the temperature and salinity profile of the fjords. This "blender" alters the availability of nutrients and the structure of plankton., with cascading effects on fish, birds and marine mammals. chain effects
Experts stress that Large ice sheets only remain stable under very specific climatic conditions.Changing the underwater motor of the system means pushing the balance towards a faster retreat.
What the data says and what remains to be measured
Records show that each calving event leaves its own acoustic signature, with waves that propagate for several kilometers and stir the fjord from withinEven so, work remains to be done to translate that energy into precise melt rates at different glaciers and seasons. accurate melting rates
The next step is to extend this approach to more fronts in Greenland and Antarctica, integrating DAS with satellite observation and classical oceanography to refine estimates of sea level rise and its timing.
The evidence gathered relocates the focus of the melting: It's not just what breaks the glacier on the outside, but what stirs the ocean on the insideWith the internal waves as silent protagonists, measuring the bottom of the fjord is no longer optional to understand the speed of change.
