Antarctic ice shelf potentially stabilized by export of meltwater in surface river

Abstract

Meltwater stored in ponds and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers and ice streams, thereby raising sea level globally. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks-interconnected streams, ponds and rivers-on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf's meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica-contrary to present Antarctic ice-sheet models, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

Widespread movement of meltwater onto and across Antarctic ice shelves

“…We also identified evidence for surface drainage on the Larsen, Nansen, Nivlisen, Roi Baudouin, George VI and Amery ( Fig. 1) ice shelves, where surface streams have been observed 13,14,15,18,19,20,21 . Surface streams exist at latitudes from 64.0° S on the Antarctic Peninsula to 85.2° S on Shackleton Glacier (Figs 1 and 2) and elevations from near sea level to more than 1,300 m above sea level (Figs 2, 3 and 4a).…”

“…Rock-melt-thinning feedbacks may be most effective where nunataks exist upstream of ice shelves that, owing to their stress state, are vulnerable to collapse. Elsewhere, such as on Nansen Ice Shelf 20 , surface drainage systems deliver meltwater directly into the ocean. How efficiently water is transported depends on changing snow properties and ice-shelf mass balance.…”

Intense Winter Surface Melt on an Antarctic Ice Shelf

“…Current mass loss of the Antarctic Ice Sheet is made up almost entirely of ice shelf basal melting and iceberg calving (Depoorter et al, ). Although supraglacial and englacial runoff has been widely observed, especially in regions of low albedo such as blue ice and bare rock (Bell et al, ; Kingslake et al, ; Lenaerts et al, ), models suggest that only a small fraction (<%) of the ∼115 Gt (1 Gt = 10 12 kg) of surface meltwater produced annually (Trusel et al, ; Van Wessem et al, ) runs off directly into the ocean. Instead, it is refrozen within underlying snow and firn layers (Kuipers Munneke, Picard, et al, ).…”

“…As a consequence, winter melt warms the snowpack, allowing for an earlier start of the main melt season in spring and summer and heating of the deeper ice layers. Also, it forms relatively impermeable infiltration ice (Hubbard et al, ) that can act as a runoff surface for meltwater (Bell et al, ).…”

Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?

“…The intervention we proposed relies on the buttressing force provided by the floating ice shelf in order to work, but surface meltwater damages the structural integrity of ice shelves and can cause them to disintegrate catastrophically, as Larsen B did in 2002 (Scambos et al, 2003). However, some ice shelves are protected by surface rivers that efficiently export 10 meltwater off the shelf (Bell et al, 2017). Future research is required to determine the extent to which surface meltwater reduces the probability of success for glacial geoengineering, to quantify how that probability reduction depends on atmospheric warming and hence on carbon emissions, and to determine whether it would be possible to deliberately modify supraglacial hydrology so as to encourage meltwater export.…”