The Tweeting ice shelf components were installed in December 2014 on the Roi Baudouin ice shelf in East Antarctica (see map). The ice shelf is more or less the size of Belgium and holds back the ice sheet feeding in this area due to the presence of ice rises, such as the Derwael Ice Rise. This is a grounded feature (ice in contact with the underlying bedrock) contrary to the ice shelf that is floating (no friction at the base). The ice rises slow down the flow of ice shelves, so they play a crucial role in the stability of ice sheets. But also the ice shelves are complex, as they are not homogeneous floating plates. As one sees on the satellite image, several lines stretch from the southeast to the northwest along which the ice shelf fractures close to the ocean front. These lines are depressions in the shelf hardly 15m lower than the surrounding surface of the ice shelf. However, since the whole shelf is floating, Archimedes teaches us that the ice thickness in these hollows is significantly lower than elsewhere. Radar measurements have shown that these hollows are 150 deeply incised cavities under the ice shelf. For an ice shelf with a mean thickness of 300 m, the hollows are half as thick, which makes them weak point in the ice shelf. The purpose of the Tweeting Ice Shelf project is to investigate how these cavities behave: how do they move? do they become wider? do they enhance the ice flow? is there active melting under the shelf in these hollows or not?
The Roi Baudouin Ice shelf and the position of the Tweeting Ice Shelf components (arrow)

We therefore installed three GPS systems, one inside the depression and two on the flanks. The ones on the flanks are simple GPS systems that record there position every hour and transmit these data over satellite phone twice a day. They are called GPS CGEO (from Cercle de GĂ©ographie et de GĂ©ologie de l'ULB) and GPS CDS (from Cercle des Sciences). The Cercle des Sciences co-sponsored the project.

GPS CGEO and CDS prior to installment

Besides these GPS we also burried a radar system in the center of the channel, which is as well equipped with a GPS. That system - a phase-sensitive radar acquired on a FNRS project - enables to monitor on a hourly basis the internal structure of the ice shelf. A radar signal is transmitted through the ice and reflects off the contact with the ocean. The second antenna receives the reflected signal that has been attenuated while going through ice impurities and denser layers of ice. The phase sensitive radar (or pRES) is capable of detecting changes in the position of these layers. So, we will be capable of measuring the internal flow of the ice shelf. But we will also be capable detecting changes at the contact with the ice shelf, whether there is melting, how much and when precisely.

Installation of the pRES radar in the snow. The whole system is buried under the snow surface.

Happy that the job is done!

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