The Northeast Greenland Ice Stream (NEGIS) is the largest in the country. Its drainage basin covers 15 percent of Greenland’s glacial ice and connects it with the Atlantic Ocean. In some places, the ice that is transported by NEGIS moves at speeds of up to 500 metres per year. However, none of the current ice-sheet models can explain why the ice stream exists in the first place. It can only be simulated using observed surface velocities to adjust the model’s basal boundary conditions. “Radar images suggest that roughly 500 kilometres upstream from the coast, directly below the Greenland ice sheet, the bottommost ice layers are gone and the layers above them are now collapsing downwards. One possible explanation for this is a volcanic hotspot beneath the ice sheet. This would also explain why NEGIS begins in precisely this area, and not elsewhere. Currently, the most popular theory is that the ice is melting from below at this point and starts sliding as a result, forcing the complete ice sheet to flow faster in places. Be we haven’t been able to prove this yet.”
The researchers from Denmark, Germany, the USA and nine other countries selected a level and easily accessible site about 400 kilometres upstream from the coast for the EastGRIP camp. Here the 2500-metre-thick ice sheet moves at a speed of 65 metres per year. “To what extent we’ll notice that movement during drilling is an interesting question, and one that we’ll only be able to answer in the field,” says Weikusat.
To date, researchers have assumed that down to a drilling depth of at least 1000 metres, the flow will extend uniformly over the ice column. If so, the camp and borehole will move with the ice, so that the vertical drilling shaft will hardly bend at all. “In the lower section of the ice column, the distortion will be more apparent. Just how much depends on the extent to which the total shift towards the ocean is due to basal slippage or distortion of the ice sheet. This has been estimated using models, but we simply don’t know for sure, so we’re very excited to see how these experiments turn out,” adds the glaciologist.
The drilling itself will be led by the Danish scientists – supported by four specialists from the AWI Ice Core Drilling Team. In the meantime, Ilka Weikusat and her colleagues will examine the freshly drilled ice cores in a laboratory beneath the snow. “Time is of the essence, since believe it or not: compared to rocks or other materials whose properties our work focuses on, ice really is hot. It’s constantly just below the melting point and so ‘warm’ that it rapidly recrystallises and its crystals change easily. That’s why we have to measure the physical properties right away and can’t leave it lying around for any length of time,” explains Weikusat.
Microscopes from the AWI ice core laboratories have also been set up in the field lab, where Ilka Weikusat and her team will use them to investigate the microstructure of the ice. “When ice flows, it becomes distorted, leaving marks in the microstructure – for example, the grain boundaries shift, the crystal axes rotate, or we find the remains of trace elements that make the ice softer, and therefore flow faster. My Young Researchers Group is evaluating all this information to gain a better understanding of the fundamental flow mechanisms and processes. This drilling mission will enable us to handle fast-moving ice from a great depth for the first time and will hopefully provide us with valuable real-world data that we can compare with the microstructure model we developed in cooperation with the University of Tübingen. We can hardly wait to get started,” enthuses Ilka Weikusat.
If everything goes according to plan, the AWI’s ice-dynamics experts will help to fill an important gap in ice-sheet modeling. To date, the models have been based on a flow behaviour law from the 1960s, the application of which is often very creative and debated. According to Ilka Weikusat: “We want to understand the flow processes right down to the microscopic level so that we can better describe them using physical formulas. Why? Because with more accurate descriptions, we will ultimately be able to better model the ice stream’s flow behaviour and more accurately predict sea-level rises. But that’s a long way down the road.”