Glaciers that plunge into the Southern Ocean not only fracture into icebergs but also generate powerful underwater waves that ripple below the surface. These internal waves behave like tsunamis, a phenomenon recently documented by researchers, and their frequency appears to be rising with global warming.
In February 2020, researchers from the British Antarctic Survey aboard a research vessel observed, almost by chance, the calving of William Glacier in Börgen Bay, mid Antarctica. The glacier spans about 4.5 kilometers in width and sits roughly 42 meters above sea level. The calving detached more than a kilometer in front of the ice front, a movement described as frequent and widespread between 2015 and 2021, with some years showing as many as six notable breaks according to satellite data.
effects on the ocean
At the moment of separation, measurements exceeded normal ranges, signaling dramatic oceanic responses. Before the front fractured, surface water was cooler at depths around 50 to 100 meters and warmer deeper down. After calving, temperature profiles became markedly more uniform across depths, indicating a rapid reorganization of heat within the water column.
This is why researchers highlight ongoing submarine waves, sometimes recorded with amplitudes comparable to a small house, alongside the visible surface waves documented by traditional ocean observations, as reported in Science Advances.
“It was amazing to witness and to be in the right place at the right time,” said the study’s lead author, Professor Michael Meredith, head of the polar oceans team at BAS. “Many glaciers terminate in the sea and their termini often shed icebergs. This can trigger large surface waves, but we now know it also excites waves beneath the surface.” He noted that inland waves influence sea mixing and heat distribution, which in turn can affect how much ice melts and how warm the water is at various depths.
As ice from these glaciers melts, it tends to break into pieces ranging from small flakes to chunks the size of a country. Previously, researchers blamed summer winds and tides for ocean mixing, not realizing that iceberg calving can drive substantial internal wave activity, according to Meredith.
a rising phenomenon
Tsunamis are typically caused by geophysical events like earthquakes or landslides that jolt the water. The idea that glacier breakup could generate such internal waves had not been considered until now.
Researchers therefore propose that underwater tsunamis are a recurring phenomenon in Antarctica, given the sheer number of glaciers calving there. The same process is expected to occur in Greenland and other Arctic regions as warming accelerates ice loss.
The phenomenon is likely to intensify as global temperatures rise, accelerating glacier collapse. For William Glacier alone, retreat has averaged about 55 meters per year since the mid-20th century due to destabilizing landslides.
Existing computer models do not yet account for this mechanism, limiting predictions about Antarctic ocean dynamics. The discovery reshapes our understanding of how the Southern Ocean mixes, with implications for climate, marine ecosystems, and sea level rise. Ongoing work aims to translate these findings into improved climate models and better assessments of regional ocean heat budgets.
Key reference: Science Advances, doi: 10.1126/sciadv.add0720. Additional observations and analyses from the BAS team support these conclusions and encourage further study of internal wave dynamics linked to ice shelf calving (Science Advances, 2020).
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