Underwater tsunamis created by calving glaciers cause vigorous ocean mixing



Scientists from a research vessel in Antarctica observed the disintegration of a glacier’s front and their measurements “exceeded the scale”.

In addition to witnessing disturbances on the surface of the ocean, they recorded “internal” underwater tsunamis as high as a house, a phenomenon hitherto ignored in understanding ocean mixing and in computer models.

The team, led by researchers from the British Antarctic Survey (BAS), report their findings today in the journal Science Advances.

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

Ice in Antarctica flows towards the coast along glacier-filled valleys.

While some of the ice melts into the ocean, much breaks up into icebergs, which range in size from small chunks to the size of a country.

A team aboard the BAS RRS research vessel James Clark Ross was taking ocean measurements near William Glacier on the Antarctic Peninsula as the front of it disintegrated dramatically into thousands of small pieces.

William Glacier typically has one or two major calving events a year, and the team estimated that this broke off around 78,000 square meters of ice – around the area of ​​10 football pitches – with the front of the glacier rising 40 m above sea level.

Before it broke away, the water temperature was cooler at around 50-100m depth and warmer below.

After calving this changed drastically, with a much more even temperature at different depths.

The study’s lead author, Professor Michael Meredith, Polar Oceans Team Leader at BAS, said: “It was remarkable to see, and we were lucky to be in the right place in the right place. moment.

“Many glaciers end in the sea and their ends regularly split into icebergs.

“It can cause big waves on the surface, but now we know it also creates waves inside the ocean.

“When they break, these internal waves cause the sea to mix, which affects the life in the sea, its heat at different depths, and the amount of ice it can melt.

“It is important for us to better understand.

“The mixing of the oceans influences the location of nutrients in the water and this matters for ecosystems and biodiversity.

“We thought we knew what was causing this mixing – in the summer we thought it was mainly wind and tides, but it never occurred to us that iceberg calving could cause internal tsunamis that would mix things up so substantially.”

Professor James Scourse, head of the Department of Earth and Environmental Sciences at the University of Exeter, was the lead science officer for RRS James Clark Ross at the time of the calving event, which was captured by a Sky News crew on board at the time. .

Two other Exeter scientists played central roles in interpreting the data captured, Dr Katy Sheen and PhD student Tobias Ehmen from the Center for Geography and Environmental Science on the Penryn Campus.

“Often the most important and exciting discoveries in science happen by chance – you’re in the right place at the right time with the right instruments and the right people – and because you know it’s important, you just make sure you’re there. ‘adjust the work plan to make the most of what nature has given you,’ said Professor Scourse.

“We did this in Börgen Bay in January 2020 and as a result produced the first data on a process that has implications for how fast the ocean is able to melt ice sheets. This has implications for all of us.

Unlike waves caused by wind and tides, tsunamis are caused by geophysical events where water is suddenly displaced, such as by an earthquake or landslide.

Internal tsunamis have been noticed in a handful of locations, caused by landslides.

Until now, no one had noticed that they were happening around Antarctica, probably all the time because of the thousands of glaciers calving there.

Other places with glaciers are likely also affected, including Greenland and elsewhere in the Arctic.

This serendipitous observation and understanding is important because glaciers are set to retreat and calve more as global warming continues.

This could likely increase the number of internal tsunamis created and the mixing they cause.

This process is not accounted for in current computer models that allow us to predict what might happen around Antarctica.

This discovery changes our understanding of how the ocean around Antarctica is mixed and will improve knowledge of what this means for climate, ecosystem and sea level rise.

Prof Meredith said: “Our fortuitous timing shows how much more we need to know about these remote environments and their importance to our planet.”

The James Clark Ross RRS research cruise was part of the ICEBERGS project and was funded by the Natural Environment Research Council.

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