Shallow, dynamic subglacial water systems provide lubrication, which facilitates the movement of the upper ice. The fast-flowing ice streams of Antarctica drain the ice sheet, controlling the speed of subglacial water systems. The current understanding of these water systems is limited to the shallow parts around the ice bed interface, although deeper groundwater can also affect ice flow.
A team of six research institutions has for the first time confirmed the presence of large amounts of liquid water in subglacial sediments. They mapped a vast, actively circulating giant system of deep-seated groundwater in West Antarctica.
The amount of groundwater they found was so significant. This probably affects the processes of ice flow, scientists say.
Most of Antarctica’s known sedimentary basins are significantly deeper, and most of its ice is much thicker, beyond the reach of aerial instruments. Scientists had drilled sediments through the ice in several places, but their instruments could only reach the first few meters. Therefore, patterns of ice cover behavior include only hydrological systems in or just below the ice.
In this new study, scientists are concentrating on the 60-mile-wide Whillans ice stream. The Wilans Ice Stream is one of half a dozen fast-moving streams feeding the Ross Ice Shelf, the world’s largest, about the size of the Yukon Canadian Territory. A previous study revealed an subglacial lake in the ice and a sedimentary basin that stretches beneath it.
Ice, sediments, fresh water, salt water and rock base conduct electromagnetic energy to varying degrees. Scientists have used magnetotelluric images and passive seismic data from Whillans Ice Stream to measure the penetration of natural electromagnetic energy into the earth. Seismic data helps them distinguish between rocks, sediments and ice.
According to their findings, the sediments stretch from half a kilometer to almost two kilometers below the ice base before hitting the main rock, depending on the location. They also confirmed that the sediments are saturated with liquid water everywhere. According to scientists, if all this is extracted, it will form a water column with a height of 220 to 820 meters, at least ten times higher than the shallow hydrological systems located in and at the base of the ice, perhaps much higher.
Kerry Key, a geophysicist from Lamont-Doherty, said: “Salt water conducts energy better than fresh water, so they also showed that groundwater becomes saltier with depth. This makes sense because sediments are thought to have formed in the marine environment long ago.
“Ocean waters probably last reached the present-day area covered by Wilens during a warm period about 5,000 to 7,000 years ago, saturating the sediments with salt water. When the ice moved again, fresh molten water produced by top pressure and friction at the base of the ice was apparently pushed into the upper sediments. It’s probably still being filtered and mixed today. “
“This slow flow of fresh water into the sediments can prevent water from accumulating in the ice base. This can act as a brake on the movement of the ice forward. Measurements by other scientists on the ground line of the ice stream – the point where land-related ice flow meets the floating ice shelf – show that the water there is slightly less salty than normal seawater. This suggests that fresh water flows through the sludge to the ocean, making room for more molten water to enter and keeping the system stable.
Scientists note: “However, if the ice surface thins – a different option as the climate warms – the direction of water flow can be reversed. Pressures will decrease and deeper groundwater may begin to rise to the ice base. This can further crush the base of the ice and increase its forward movement. “
“Furthermore, if deep groundwater flows upwards, it could transfer geothermal heat naturally generated in the rock base; this can further thaw the base of the ice and move it forward. But whether and to what extent this will happen is unclear. “
Chloe Gustafson, who studied as a graduate student at Columbia University’s Lamont-Doherty Observatory, said: “Ultimately, we don’t have big limits on the permeability of sludge or how fast water will flow. Would there be a big difference that would provoke a quick reaction? Or is groundwater a minor player in the great flow of ice?
The scientists said: “Confirmation of the existence of deep groundwater dynamics is transforming our understanding of ice flow behavior and will require modification of groundwater patterns.
Journal reference:
- Chloe D. Gustafson et al. Dynamic system for saline groundwater, mapped under the Antarctic ice stream. DOI: 10.1126 / science.abm3301
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