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May 6, 2022 03:30 am

Scientists Discover Giant Groundwater System Below Antarctic Ice

An anonymous reader quotes a report from Phys.Org: Now, a team has for the first time mapped a huge, actively circulating groundwater system in deep sediments in West Antarctica. They say such systems, probably common in Antarctica, may have as-yet unknown implications for how the frozen continent reacts to, or possibly even contributes to, climate change. The research appears today in the journal Science. [...] The researchers in the new study concentrated on the 60-mile-wide Whillans Ice Stream, one of a half-dozen fast-moving streams feeding the Ross Ice Shelf, the world's largest, at about the size of Canada's Yukon Territory. Prior research has revealed a subglacial lake within the ice, and a sedimentary basin stretching beneath it. Shallow drilling into the first foot or so of sediments has brought up liquid water and a thriving community of microbes. But what lies further down has been a mystery. The team used a technique called magnetotelluric imaging, which measures the penetration into the earth of natural electromagnetic energy generated high in the planet's atmosphere. Ice, sediments, fresh water, salty water and bedrock all conduct electromagnetic energy to different degrees; by measuring the differences, researchers can create MRI-like maps of the different elements. The team planted their instruments in snow pits for a day or so at a time, then dug them out and relocated them, eventually taking readings at some four dozen locations. They also reanalyzed natural seismic waves emanating from the earth that had been collected by another team, to help distinguish bedrock, sediment and ice. Their analysis showed that, depending on location, the sediments extend below the base of the ice from a half kilometer to nearly two kilometers before hitting bedrock. And they confirmed that the sediments are loaded with liquid water all the way down. The researchers estimate that if all of it were extracted, it would form a water column from 220 to 820 meters high -- at least 10 times more than in the shallow hydrologic systems within and at the base of the ice -- maybe much more even than that. Salty water conducts energy better than fresh water, so they were also able to show that the groundwater becomes more saline with depth. Key said this makes sense, because the sediments are believed to have been formed in a marine environment long ago. Ocean waters probably last reached what is now the area covered by the Whillans during a warm period some 5,000 to 7,000 years ago, saturating the sediments with salt water. When the ice readvanced, fresh melt water produced by pressure from above and friction at the ice base was evidently forced into the upper sediments. It probably continues to filter down and mix in today. The researchers say this slow draining of fresh water into the sediments could prevent water from building up at the base of the ice. This could act as a brake on the ice's forward motion. Measurements by other scientists at the ice stream's grounding line -- the point where the landbound ice stream meets the floating ice shelf -- show that the water there is somewhat less salty than normal seawater. This suggests that fresh water is flowing through the sediments to the ocean, making room for more melt water to enter, and keeping the system stable. The direction of water flow could be reversed if the ice surface were to thin, warn the researchers. "Overlying pressures would decrease, and deeper groundwater could begin welling up toward the ice base," reports Phys.Org. "This could further lubricate the base of the ice and increase its forward motion. Furthermore, if deep groundwater flows upward, it could carry up geothermal heat naturally generated in the bedrock; this could further thaw the base of the ice and propel it forward." If the groundwater begins moving upward, it would bring up the dissolved carbon used by the microbes living in the shallow sediments. "Lateral groundwater flow would then send some of this carbon to the ocean," reports Phys.Org. "This would possibly turn Antarctica into a so-far unconsidered source of carbon in a world already swimming in it."

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