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As well as witnessing disruptions on the ocean surface, they recorded ‘internal’ underwater tsunamis as tall as a house, a phenomenon previously missed in the understanding of ocean mixing. The team which included �鶹��ý����� researchers, and led by the British Antarctic Survey, report their in the journal .

Internal tsunamis are an important factor in ocean mixing, which affects life in the ocean, temperatures at different depths, and how much ice the ocean can melt. 

Ice in Antarctica flows to the coast along glacier-filled valleys. While some ice melts into the ocean, a lot breaks off into icebergs, which range in size from small chunks up to the size of a country. A team on board the British Antarctic Survey (BAS) research ship RRS James Clark Ross were taking ocean measurements close to the William Glacier, situated on the Antarctic Peninsula, as the front of it dramatically disintegrated into thousands of small pieces. 

The William Glacier typically has one or two large calving events per year, and the team estimated this one broke off around 78,000 square metres of ice – around the area of 10 football pitches – with the front of the glacier towering 40m above sea level. Before it broke away, the water temperature was cooler at around 50-100m in depth and warmer below this. After the calving, this changed dramatically, with the temperature becoming more even across different depths. 

Katrien Van Landeghem and postgraduate student, Kate Retallick from �鶹��ý�����’s School of Ocean Sciences joined the surveys in the West Antarctic Peninsula to map the seafloor of the fjords directly in front of the retreating glaciers. 

The vessel was often so close to the glaciers, that they could also map the shape of the ice front where it sits on the bed. This unique data reveals the role of geological processes in glacier retreat, and helps uncover the effects a disintegrating ice front has on the entire body of water and the ecosystems that thrive there.

Katrien said: 
“After witnessing the sudden calving event up close, the team spotted that the large icebergs breaking off the glaciers caused an “internal” underwater tsunami and mixed the water column. With glaciers predicted to disintegrate even more dramatically in our warming oceans, the importance of understanding the impact such calving events has on the rest of the polar ecosystems should be considered on a larger scale.”