The ice shelves surrounding Antarctica may feel as remote and alien as any place on Earth, but understanding their behavior is crucial for predicting future sea level rise. That’s why scientists are drilling boreholes into the deepest sections of this ice to get a peek at what’s happening below.
Now, a 2,477-foot-deep borehole drilled on Antarctica’s Ross Ice Shelf—a Spain-sized slab of ice that drains glaciers from both East and West Antarctica—has yielded an important observation. The water directly beneath the ice is extremely cold and fresh, creating a layer of insulation that appears to protect the overlying ice from melting.
“One of the reasons we’re interested in studying the Ross Ice Shelf [is] if we can figure out what makes it so stable, that gives us insight into other ice shelves,” Carolyn Begeman, a glaciologist at the University of California, Santa Cruz who presented the finding Thursday at the 2018 Ocean Sciences Conference in Portland, Oregon, told Earther.
Understanding ice shelf stability is especially important in the so-called grounding zone, where floating ice shelves give way to ice tethered to bedrock. When warm water melts ice in the region, it can destabilize inland glaciers, causing them to flow out to sea faster.
Glaciers in West Antarctica’s Amundsen sea sector are seeing huge levels of submarine ice melt in their grounding zones, raising concerns of widespread ice shelf collapse that could add many feet to global sea levels.
But ice in the grounding zone is often incredibly deep, and because it’s so far away from the edges of the shelf, it’s hard to send ROVs to explore it.
Begeman and her colleagues were able to drill a hole in this difficult-to-access part of the ice in 2015, as part of Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project, which was studying a nearby subglacial lake. After melting their way through nearly half a mile of ice, the team dropped instruments into the shallow ocean cavity below.
When they did, they observed a meter-thick layer of freshwater near the base of the ice. This freshwater layer reduces the amount of heat hitting the underside of the ice from deeper, saltier, warmer water, the result being that ice loss levels in this region are very low, less than 10 centimeters a year.
The finding was a surprise, according to Begeman, because models project that in coastal regions like this, everything would get sloshed around and mixed by the tides.
An important question is whether this freshwater insulation is widespread across the Ross Ice Shelf, and if so, could that help explain why this ice appears relatively stable compared with other coastal regions of Antarctica?
To find answers, scientists are going to need to drill more holes.
Craig Stevens, an oceanographer at the University of Auckland who recently completed a drilling expedition in a different part of the Ross Ice Shelf, told Earther the WISSARD experiment was “amazing work.” He thought the insulation concept was “interesting,” but noted that because a freshwater layer at depth in an ocean will eventually drain upwards and out, it could actually aid in circulation and potentially increase overall melting.
“These are the sorts of questions we’re all seeking to answer,” he said.
Begeman is hoping to go back to Antarctica next summer, along with Stevens and others who plan to drill another grounding-zone hole in a different part of the Ross Ice Shelf. Seeing as humans have only drilled three boreholes all the way through the vast shelf, every new plug in the ice offers a wealth of additional insight.
“It’s really rare to get observations of the ocean cavity in the deep interior of ice shelves,” Begeman said.