Abstract
Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use 2 decades of in situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration, are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.
Highlights
Icebergs that calve from the floating margins of the Antarctic Ice Sheet account for up to 50 % of ice discharge into the Southern Ocean (Depoorter et al, 2013)
Because ice shelves act as a barrier around the grounded ice and buttress its seaward flow through lateral drag and local grounding in shallow water (Dupont and Alley, 2005), any loss of buttressing around the periphery of Antarctica as a result of calving-induced changes in ice shelf geometry will adversely affect glacier flow (Scambos et al, 2004; Rignot et al, 2004; Rott et al, 2011) and induce additional ice discharge into the Southern Ocean
The results are divided into three parts: in Sect. 4 we present a timeline of changes in glaciological stress that led to the initiation of the rifts; in Sect. 5 we discuss the drivers of subsequent rift propagation; in Sect. 6 we compare the observed dynamical changes before and after rift formation to model projections, and quantify model errors related to the absence of a suitable calving law
Summary
Icebergs that calve from the floating margins of the Antarctic Ice Sheet account for up to 50 % of ice discharge into the Southern Ocean (Depoorter et al, 2013). The long-term observational record of the BIS provides unprecedented coverage of glaciological changes over a full calving cycle, from the last calving event in the early 1970s to present day Based on this record and earlier observations of the ice front location in 1915, 1958, and 1986 (Anderson et al, 2014) and flow speed measurements since the 1950s (Gudmundsson et al, 2017), a repeating pattern of glaciological changes emerged. We use the BIS as an example to demonstrate the link between naturally evolving glaciological conditions, the initiation of ice shelf rifts, and the mechanical drivers that govern subsequent rift propagation.
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