Big Pic: 820-Foot-High Tunnels Discovered Under Antarctic Ice

This is the camp from which scientists discovered 820-foot-high channels underneath an ice shelf—a piece of ice jutting out into the ocean from land—in Antarctica. The tunnels are nearly as high as the Eiffel tower.

Researchers from several universities in the U.K. and the British Antarctic Survey flew a plane over the Flichner-Ronne Ice Shelf in West Antarctica. (You can see the plane, a Twin Otter, parked at camp above.) Radar from the plane, as well as satellite photos, revealed that surface features on the ice corresponded to tunnels at the bottom of the ice. 

The placement of the channels suggests they were formed from meltwater flowing underneath the ice, over land, and into the ocean. That also suggests water underneath ice sheets pours out into the ocean in focused channels, sort of like under-ice rivers. Scientists previously thought overland meltwater flowed underneath ice sheets in thin, continuous layers.

The British team will now use its newfound knowledge of the under-ice tunnels to predict how exactly that ice shelf will melt in response to climate change. The researchers published a paper about their work in the journal Nature Geoscience.

An Under-Ice Channel This illustration shows the survey plane getting measurements of the height of a channel underneath the Flichner-Ronne Ice Shelf. It also shows the channel's size compared to the Eiffel Tower and to the Tower Bridge in London. Anne Le Brocq
The subglacial meltwater also influences ocean circulation beneath ice shelves, initiating meltwater plumes that entrain warmer ocean water and cause high rates of melting. However, despite its importance, the nature of the hydrological system beneath the grounded ice sheet remains poorly characterized.

Here we present evidence, from satellite and airborne remote sensing, for large channels beneath the floating Filchner–Ronne Ice Shelf in West Antarctica, which we propose provide a means for investigating the hydrological system beneath the grounded ice sheet.

We observe features on the surface of the ice shelf from satellite imagery and, using radar measurements, show that they correspond with channels beneath the ice shelf. We also show that the sub-ice-shelf channels are aligned with locations where the outflow of subglacial meltwater has been predicted. This agreement indicates that the sub-ice-shelf channels are formed by meltwater plumes, initiated by subglacial water exiting the upstream grounded ice sheet in a focused (channelized) manner.

Meltwater generated beneath the Antarctic Ice Sheet exerts a strong influence on the speed of ice flow, in particular for major ice streams.

The existence of a channelized hydrological system has implications for the behaviour and dynamics of ice sheets and ice shelves near the grounding lines of ice streams in Antarctica.