Underwater tsunamis created by calving glaciers cause a vigorous stirring of the oceans

Science Advances (2022). DOI: 10.1126/sciadv.add0720″ width=”800″ height=”530″/>

Field area and glacier retreat due to calving. (A) Location of Börgen Bay on the West Antarctic Peninsula. Bathymetry from ETOPO 1 global relief model (74). (B) Bathymetry of Börgen Bay from multibeam echosounder data and coastline/topography from Landsat images (see Materials and Methods). The dots mark the locations of the conductivity-temperature-depth (CTD) profiles used here, with the profiles taken before (red) and after (blue) the calving event. (C) Landsat images of the William Glacier front from (top) January 17, 2020 and (bottom) January 24, 2020. In both panels, the orange line marks the glacier front on January 17, 2020 to highlight glacier retreat between those dates. Credit: The progress of science (2022). DOI: 10.1126/sciadv.add0720

Scientists on a research vessel in Antarctica watched the front of a glacier disintegrate and their measurements ‘went off the scale’. In addition to witnessing disruptions on the ocean’s surface, they recorded house-high “inland” underwater tsunamis, a phenomenon that had previously eluded understanding of ocean mixing and in computer models.

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

Internal tsunamis are a major factor in ocean mixing, affecting life in the ocean, temperatures at different depths, and how much ice the ocean can melt. Ice in Antarctica flows towards the coast along valleys filled with glaciers. While some of the ice melts into the ocean, much breaks up into icebergs, ranging in size from tiny chunks up to the size of a country.

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

William Glacier typically has one or two major calving events a year, and the team estimated that this calved approximately 78,000 square feet of ice, around the area of ​​10 football fields, with the front of the glacier that rises 40 meters above sea level.

Before it broke off, the water temperature was cooler at about 50-100 meters down, and warmer below. After calving, this changed dramatically, with much more uniform temperatures at different depths.

Lead author of the study, Professor Michael Meredith, Polar Oceans team lead at BAS, said: ‘It was extraordinary to see and we were lucky to be in the right place at the right time. Their ends regularly split 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 life in the sea, such as hot is it at different depths and how much ice can it melt This is important for us to understand better.

‘The mixing of the oceans affects where nutrients are found in the water and this is important for ecosystems and biodiversity. We thought we knew what caused this mixing. In the summer, we thought it was mainly wind and tides, but it never occurred to us that the calving of the iceberg 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 Chief Science Officer on the RRS James Clark Ross at the time of the calving event, which was captured by a team from Sky News on board at the time .

Two other Exeter scientists were instrumental in interpreting the captured data, Dr Katy Sheen and the PhD. student Tobias Ehmen of the Penryn Campus Center for Geography and Environmental Science.

“Often the most important and exciting scientific discoveries are serendipitous—you happen to be in the right place at the right time with the right tools and the right people—and since you know it’s important, just be sure to adjust your 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 quickly 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.

Inland tsunamis, caused by landslides, have been noted in a handful of places. Until now, no one had noticed it happening around Antarctica, probably all the time due to the thousands of glaciers calving there. Other places with glaciers are also likely to be affected, including Greenland and other parts of the Arctic.

This casual observation and understanding is important, as glaciers are set to retreat and calve more as global warming continues. This could likely increase the number of inland 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 our understanding of what it means for climate, ecosystems and sea level rise.

Professor Meredith noted: ‘Our serendipitous timing shows how much more we need to learn about these remote environments and how much they matter to our planet.’

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

Provided by the University of Exeter

Citation: Underwater tsunamis created by calving glaciers cause vigorous mixing of oceans (2022, Nov. 24) Retrieved Nov. 24, 2022 from https://phys.org/news/2022-11-underwater-tsunamis-glacier-calving-vigorous .html

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