The Antarctic water puzzle – how flooding contributes to ice melt

In the autumn of 2021, an international team of researchers from New Zealand’s Antarctic Science Platform set off towards the South Pole. Their destination was the Ross Ice Shelf in West Antarctica, a floating ice sheet about ten times the size of Switzerland. New Zealand has been operating the Scott research station on the coast since 1957. From there, the expedition team continued south. Two weeks and 1,200 kilometres later, they reached their destination on the Kamb Ice Stream, a glacier, 350 km long, 100 km wide and many hundreds of metres deep that runs from the interior of Antarctica towards the sea, meeting the Ross Ice Shelf on the coast.

Hot water borehole through the Antarctic ice

At this remote location on the permanent ice, the support team built a temporary research station with its own airstrip and tent accommodation for 26 people. The scientists used the favourable conditions of the Antarctic summer for their research work, with temperatures of -10°C, light winds and 24-hour daylight. Drilling 500 metres through the ice sheet to the Antarctic mainland beneath, they encountered water and sedimentary rock. For the hot water drilling, they used a high-pressure nozzle and water at 80°C. With a diameter of 30 cm, the borehole was large enough to lower a camera and various measuring equipment down into the depths to explore the conditions at the base of the ice flow.

“We struck water at the end of the borehole and with the help of our camera, we even discovered a school of lobster-like creatures, 400 kilometres from the open ocean,” reports expedition leader Huw Horgan who has been working as a researcher at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL under Professor Daniel Farinotti for two years. The borehole is a scientific milestone: researchers have long suspected that water flows from under the ice sheet. The water exists due to geothermal heat and other factors, and scientists had already discovered several hundred lakes under the ice caps of West and East Antarctica using satellites. But the watercourses in the depths of the ice caps still hold many secrets. The borehole through the Kamb Ice Stream is the first ever successful attempt to observe such a watercourse meeting the sub-ice-shelf ocean cavity up close.

Veritable floods beneath the ice

The researchers used their measuring equipment to analyse the properties of the watercourse, including the temperature, salinity and sediment content. Using an echo sounder, they were able to estimate the cross-section of the water-carrying ice channel to be around 100 by 200 metres. The subglacial flow should not be thought of as a fast-flowing river. It is actually a reasonably calm body of water, and most of the water comes from the sea. Only a small amount – less than one cubic metre per second – is fresh water, i.e. water that flows towards the sea below the Kamb Ice Stream. “This amount of water is much smaller than what the existing models had predicted,” notes Huw Horgan, summarising a key finding of the study.

No less important for the research team is a second result: the subglacial watercourse does not flow continuously, instead its course fluctuates greatly over time. “We suspect that the water comes from subglacial lakes upstream. These lakes fill and empty in certain cycles. When they empty, a flood of water rushes towards the sea,” says Horgan. The researchers proved that such flood events do in fact occur by analysing sediment samples from the ground beneath the ice stream. According to these findings, large flood events occur approximately every ten years. In addition, there may be smaller flood events that the researchers cannot prove using current methods.

Important foundations for climate research

The study by the international team of researchers is a stepping stone towards better understanding the watercourses beneath the Antarctic ice sheet. At the same time, it will help the consequences of global warming to be assessed more reliably in the coming decades. The melting processes in the Antarctic ice shelf are an important cause of the anticipated rise in sea levels. This is because the Ross Ice Shelf and other ice shelf formations act as a barrier, holding back the ice streams on the Antarctic mainland and preventing them from melting as they flow into the sea.

“The subglacial watercourses play a central role in the melting of the ice shelf,” emphasises Huw Horgan. “Our findings are therefore a prerequisite for developing new models that describe the melting of the ice shelf and predict sea level rise even more accurately.”

Consequences of global warming

The changes in the ice cover at the Earth’s South Pole remain a key issue in global climate research. Polar researcher Horgan will return to the Antarctic in the southern summer of 2025/2026. During that expedition, the research team hope to collect data that documents the long-term behaviour of the West Antarctic ice sheet. In particular, the focus will be on warmer periods, such as those that the Earth will experience in the coming decades and centuries.