Sunday, 23 February 2020

Thwaites Science

Erin dragging the GPR across the ice shelf. 
Having written about my experiences working on Thwaites Glacier in my previous blog post, I thought that it would be insightful to write a bit about the research which was carried out. This, after all, was the reason we were there.
Myself and Christian enjoying a brew at a ApRes site.
Thwaites Glacier is one of the most rapidly changing areas in Antarctica, and these changes have the potential to significantly contribute to sea level rise. The Thwaites Glacier drains a huge area (roughly the size of Britain). The land surface below much of this drainage basin (and West Antarctica in general) is below sea level. If the sea was able to infiltrate under the ice, it could lead to a significant destabilisation of the ice sheet, which would lead to significant sea level rise. For this reason the area has been described as the soft underbelly of West Antarctica.
Digging in Geophones for Atsu's seismic work. He can just be seen at the end of this line of geophones about 400m away. 
The Thwaites project is a multi-year collaborative project which attempts to understand the changes that are occurring in the area, and what the future might hold for it. This season there were a number of science teams working on and around the Thwaites Glacier. I was working with the TARSAN team. The acronym TARSAN stands for Thwaites-Amundsen Regional Survey and Network Integrating Atmosphere-Ice-Ocean Processes. There were two aspect to TARSAN, one being ship based, and one other being ice based. I was to be part of the latter which was based on a small ice shelf around 20km across called the East Thwaites Ice Shelf. It is held in place by being grounded on undersea rise. It is however, starting to show signs of instability.

Another benefit of drilling through the ice sheet,
you can dry your sock on the water heater. 
The project got some attention from the media. There was a team from the BBC at another field camp (MELT) who were based about 30km away from ourselves. Their report does a pretty good job of explaining the purpose of the work  https://www.bbc.co.uk/news/science-environment-51097309.   More information about the project in general and the specific teams can be found at  https://thwaitesglacier.org/.

There were two aspects to the science that TARSAN carried out; geophysics and the  drilling/AMIGO. A variety of geophysical techniques were used to collect data on ice shelf properties over as much of the ice shelf as it was deemed safe to travel.
A 300 metre hole through the ice sheet. 
One method was ApRes. This  uses radar to accurately measure ice thickness at specific locations. This was done for grid of around forty locations. By marking these locations with flags, and then repeating the measurements at least a week later, the ice thinning/melting rates could be calculated. Repeat GPS measurements of these points was also carried out to measure the velocity of the ice shelf. The whole ice shelf was moving at around two meters per day.

Ground Penetrating Radar (GPR) involved dragging a radar device along at a very steady speed to create a profile of ice thickness and properties. A number of different frequencies were used, in general the lower the frequency the deeper into the ice the radar looked.  This was done on foot by one individual who dragged the radar a total of about 270km during the her time out in the field. It was found that the underside of the ice shelf was anything but flat with some interesting steps in ice thickness.
The final geophysics method used was active seismics. This involved digging long lines of geophones into the snow, and then detonating small buried explosive charge at the end of the geophone line. The geophones would record the echo of the explosion as it bounced of the base of the ice and the of the sea floor. From this the thickness of the ice and the depth of the ocean below can be calculated.
Raising the AMIGO tower. Photo Karen Alley.
The other major aspect of the project was the drilling/AMIGO. This involved drilling a couple of holes in the ice shelf. At the location of the first hole the ice was about 300m thick, at the second hole it was around 250 meters. After the holes were drilled instruments were lowered down to measure ocean salinity, temperature and acoustics, and samples of the ocean bed were taken. After this other instruments were installed to monitor temperature throughout the ice and ocean, and to record data about the ocean currents. A tower called an AMIGO was then erected. This would monitor weather conditions at the site, and transmit this and the ocean data back to the science teams over the next few years. The aim is to return in a few years to collect dig out and remove the AMIGOs.

The AMIGO tower with the camp in the background. 






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