Underwater tsunamis created by calving glaciers cause vigorous ocean mixing

Underwater tsunamis created by calving glaciers cause vigorous ocean mixing

Scientists progress (2022). DOI: 10.1126/sciadv.add0720″ width=”800″ height=”530″/>
Field size and retreat of glaciers due to calving. (A) Location of Börgen Bay in the Western Antarctic Peninsula. Bathymetry of the global relief model ETOPO 1 (74). (B) Bathymetry of Börgen Bay from multibeam echosounder data and coastline/topography from Landsat imagery (see Materials and methods). Dots mark the locations of the conductivity-temperature-depth (CTD) profiles used here, with profiles taken before (red) and after (blue) the calving event. (C) Landsat images of the front of William Glacier from (top) January 17, 2020 and (bottom) January 24, 2020. In both panels, the orange line marks the front of the glacier on January 17, 2020 to highlight the retreat of the glacier between these dates. Credit: Scientists progress (2022). DOI: 10.1126/sciadv.add0720

Scientists on 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 ocean surface, they recorded “internal” undersea tsunamis as high as a house, a phenomenon hitherto ignored in understanding ocean mixing and in models. computers.

The team, led by researchers from the British Antarctic Survey (BAS), report their observations today in the journal Scientists progress.

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 of it breaks up into icebergs, which range in size from small chunks all the way up 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 meters above sea level.

Before it broke away, the water temperature was cooler at around 50-100 meters 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, head of the Polar Oceans team at BAS, said: “It was remarkable to see, and we were lucky to be in the right place at the good time. Many glaciers end in the sea, and their ends regularly separate into icebergs. This can cause large waves on the surface, but we now know that it also creates waves inside the ocean. When they break, these internal waves cause the sea to mix and this affects the life in the sea, how warm it is at different depths and how much ice can melt is important for us to better understand.

“Ocean mixing influences where nutrients are located in the water and that 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 much.”

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 captured data, Dr Katy Sheen and Ph.D. 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,” Prof Scourse said. “We did this in Börgen Bay in January 2020 and as a result we produced first data on a process that has implications for the rate at which 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, for example, 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.

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

More information:
Michael P. Meredith et al, Internal tsunamigenesis and ocean mixing driven by glacier calving in Antarctica, Scientists progress (2022). DOI: 10.1126/sciadv.add0720

Provided by the University of Exeter

Quote: Underwater tsunamis created by glacier calving cause vigorous ocean mixing (2022, November 24) Retrieved November 24, 2022 from https://phys.org/news/2022-11-underwater-tsunamis-glacier-calving -vigorous.html

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