Abstract
Abstract. The recent rapid growth of rifts in the Brunt Ice Shelf appears to signal the onset of its largest calving event since records began in 1915. The aim of this study is to determine whether this calving event will lead to a new steady state in which the Brunt Ice Shelf remains in contact with the bed, or an unpinning from the bed, which could predispose it to accelerated flow or possible break-up. We use a range of geophysical data to reconstruct the sea-floor bathymetry and ice shelf geometry, to examine past ice sheet configurations in the Brunt Basin, and to define the present-day geometry of the contact between the Brunt Ice Shelf and the bed. Results show that during past ice advances grounded ice streams likely converged in the Brunt Basin from the south and east. As the ice retreated, it was likely pinned on at least three former grounding lines marked by topographic highs, and transverse ridges on the flanks of the basin. These may have subsequently formed pinning points for developing ice shelves. The ice shelf geometry and bathymetry measurements show that the base of the Brunt Ice Shelf now only makes contact with one of these topographic highs. This contact is limited to an area of less than 1.3 to 3 km2 and results in a compressive regime that helps to maintain the ice shelf's integrity. The maximum overlap between ice shelf draft and the bathymetric high is 2–25 m and is contingent on the presence of incorporated iceberg keels, which protrude beneath the base of the ice shelf. The future of the ice shelf depends on whether the expected calving event causes full or partial loss of contact with the bed and whether the subsequent response causes re-grounding within a predictable period or a loss of structural integrity resulting from properties inherited at the grounding line.
Highlights
Compilations of marine geophysical data have shown that the Coats Land ice shelves bordering the Weddell Sea in East Antarctica have historically retreated towards the grounding line once detached from pinning points on the seabed (Hodgson et al, 2018).The Brunt Ice Shelf (BIS) is the only large ice shelf that remains intact in Coats Land south of 74◦ S (Fig. 1)
The subglacial topography and bathymetry show that the grounded ice occupies a complex bedrock terrain (Fig. 4c)
A steep coastal slope marks the transition between grounded and floating ice masses. Downstream of this grounding line, the trough originating under the BIS is oriented south to north, whilst the trough originating beneath the SWGT is oriented east to west
Summary
The Brunt Ice Shelf (BIS) is the only large ice shelf that remains intact in Coats Land south of 74◦ S (Fig. 1). It is formed by a series of unnamed glaciers that cross a steep grounding line at a feature known as the Brunt Icefalls (75◦55 S, 25◦0 W; Fig. 2a). This zone extends for about 80 km and marks the transition between the grounded and floating ice masses. The glaciers and the surrounding ice sheet calve into a 10–20 km wide zone of icebergs (sometimes referred to as the ice mélange, Fig. 2a), which are eventually fused together by sea ice and falling and drifting snow layers to form a structurally heterogeneous ice shelf (King et al, 2018).
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