Vulnerability of Antarctica’s ice shelves to meltwater-driven fracture

Abstract

Atmospheric warming threatens to accelerate the retreat of the Antarctic Ice Sheet by increasing surface melting and facilitating 'hydrofracturing' [1][2][3][4][5][6][7] , where meltwater flows into and enlarges fractures, potentially triggering ice-shelf collapse [3][4][5][8][9][10] . The collapse of ice shelves that 'buttress' [11][12][13] the ice sheet accelerates ice flow and sea-level rise [14][15][16] . However, we do not currently know if and how much of the buttressing regions of Antarctica's ice shelves are vulnerable to hydrofracture if inundated with water. Here we provide two lines of evidence suggesting that many buttressing regions are vulnerable. First, we train a deep convolutional neural network (DCNN) to map the surface expressions of fractures in satellite imagery across all Antarctic ice shelves. Second, we develop a fracture stability diagram based on linear elastic fracture mechanics (LEFM) to predict where basal and dry surface fractures form under today's stress condition. We find close agreement between the theoretical prediction and the DCNN-mapped fractures, despite limitations associated with detecting fractures in satellite imagery. Finally, we use the LEFM theory to predict where surface fracture would become unstable if filled with water. Many regions regularly inundated with meltwater today are resilient to hydrofracturing -stresses are low enough that all water-filled fractures are stable. Conversely, 60% ±10% of ice shelves (by area) both buttress upstream ice and are vulnerable to hydrofracture if inundated with water. The DCNN-map confirms the presence of fractures in these buttressing regions. Increased surface melting 17 could trigger hydrofracturing if it leads to water inundating the widespread vulnerable regions we identify. These are regions where atmospheric warming may have the largest impact on ice-sheet mass balance.

Surface Melt and Runoff on Antarctic Ice Shelves at 1.5°C, 2°C, and 4°C of Future Warming

“…However, because this study does not consider ice and ocean dynamical drivers of ice shelf destabilization, this precludes a definitive prediction of which ice shelves are most likely to collapse. Of those ice shelves where considerable runoff is simulated (Figure 4), the dynamical stress regime on the Amery, King Baudoin, and George VI shelves suggest they are resilient to hydrofracture (Lai et al., 2020). However, the Larsen C, Wilkins, Pine Island, and Shackleton ice shelves are identified as vulnerable by both Lai et al.…”

The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula

“…5.2 Near-surface and surface melting over the northern GVIIS, 1979to 2020From 1979/1980/2020(excluding the 1987/1988, the microwave radiometer data show that 2019/2020 was the largest melt season over the northern GVIIS in terms of the most spatially extensive melt (i.e. 100 % of the AOI) for the greatest number days (Fig.…”

“…These first two sets of lakes appear to remain in similar locations each year due to the ice shelf's overall compressive flow; i.e. unlike the situation on most ice shelves where lakes move with ice flow towards the shelf front (Banwell et al, 2014;Langley et al, 2016;Arthur et al, 2020b). The third set of lakes are the deepest and exist within pressure ridge complexes along the western margin of the ice shelf, onto which ice shelf flow is directed (Reynolds, 1981).…”

“…The near-complete collapse of the Larsen B Ice Shelf in 2002 is arguably the most famous break-up event due to its rapidity and extent (e.g. Scambos et al, 2003) and may have been driven by the drainage of ∼ 3000 lakes (Banwell et al, 2013;Robel and Banwell, 2019;Leeson et al, 2020). However, surface melting has also been implicated in the large-scale collapse events of the Prince Gustav and Larsen A ice shelves over just a few days in late January 1995 (Rott et al, 1996;Doake et al, 1998;Scambos et al, 2003;Glasser et al, 2011) and in other, smaller-scale collapses of the Wilkins, Larsen B, George VI, and Larsen A ice shelves (Scambos et al, 2003(Scambos et al, , 2009Cook and Vaughan, 2010).…”

Breaking the Ice: Identifying Hydraulically Forced Crevassing

“…Hydraulically forced surface crevassing, also referred to as hydrofracture, has the potential to significantly influence the stability of glaciers, ice sheets, and ice shelves (Lai et al, 2020). On glaciers and ice sheets, hydraulically forced crevassing provides a potential pathway for surface meltwater to reach and lubricate the bed (Das et al, 2008;Van Der Veen, 1998;Weertman, 1973), enhancing basal sliding of ice into the ocean (Rignot & Kanagaratnam, 2006), accelerating sea level rise.…”