Photo credit: www.sciencenews.org
Beneath the vast, icy expanse of the Antarctic Ice Sheet lies a hidden world of water, comprising numerous streams and lakes that have been largely unexplored. Recent research suggests that failing to account for this subglacial water could lead to significant underestimations of global sea level rise.
A study published on April 7 in Nature Communications proposes that including this subglacial water in computer models could result in sea level rise projections increasing by approximately two meters over the next two centuries. To put this into perspective, scientists estimate that climate change has contributed to a sea level increase of around 0.2 meters during the past century.
“This hidden water beneath Antarctica plays a much more significant role than we thought,” states Chen Zhao, a glaciologist at the University of Tasmania in Hobart. She emphasizes the importance of accurate sea level rise projections for policymakers, as the potential for underestimating the severity of climate impacts could lead to misguided decisions.
Although the Antarctic Ice Sheet is ostensibly frozen, it is a dynamic system. The ice itself deforms due to its immense weight, and components of the ice sheet can slide over the ground, an effect known as basal sliding. This phenomenon is pivotal in the movement of the fastest glaciers pouring into the ocean. Therefore, understanding how basal sliding influences ice flow and rapid sea level rise is essential.
Researchers have long recognized that subglacial water can increase a glacier’s basal sliding velocity. Much like how air allows a puck to glide more freely on an air hockey table, the pressure from subglacial water reduces some of the ice’s weight, facilitating its movement towards the ocean. “It’s sort of lubricating the ground for the ice,” explains glaciologist Mathieu Morlighem from Dartmouth College, who did not participate in the new study.
However, the extent to which this subglacial water enhances glacier flow and contributes to sea level rise is still not well understood. Many computer models that project changes in the Antarctic Ice Sheet tend to overlook subglacial water effects, which may lead to optimistic predictions regarding future sea level rise, Zhao notes.
The research team conducted simulations of the Antarctic Ice Sheet’s behavior as it traversed various channels and lakes beneath the ice. Due to the limited knowledge of how water is distributed under the ice, they tested multiple scenarios regarding the pressure and flow of this water.
For example, one simulation presumed that water beneath the ice could flow relatively freely into the ocean, while others incorporated topographical features to create a more nuanced view of pressure distributions. Some simulations even increased water pressure near the grounding line—where the ice sheet meets the ocean— to gauge its effect on ice movement.
“It makes physical sense,” Morlighem remarked. “They’re making the bed more slippery … as the ice starts to float.” In particular, the simulation characterized by a slippery grounding line proved to be the most extreme, predicting an additional 2.2 meters of sea level rise by the year 2300, compared to the traditional model approaches.
Morlighem asserts that this increase is not unrealistic, considering that two meters accounts for only about 4 percent of the potential sea level rise if the entire Antarctic Ice Sheet—housing roughly 90 percent of the world’s ice—were to melt entirely. The different simulations yielded various estimates concerning their contributions to future sea level rise.
Accurate predictions of how subglacial water will intervene in sea level rise will necessitate further investigation into this largely obscured environment beneath the Antarctic Ice Sheet. “Without knowing what’s under the ice, we have to make assumptions in our simulations that can have big impacts on the predictions,” Zhao emphasizes, underlining the complexities of forecasting future scenarios in a changing climate.
Source
www.sciencenews.org