Glaciological history and structural evolution of the Shackleton Ice Shelf system, East Antarctica, over the past 60 years

The discovery of Antarctica's deepest subglacial troughbeneath the Denman Glacier, combined with high rates of basal melt at thegrounding line, has caused significant concern over its vulnerability toretreat. Recent attention has therefore been focusing on understanding thecontrols driving Denman Glacier's dynamic evolution. Here we consider theShackleton system, comprised of the Shackleton Ice Shelf, Denman Glacier,and the adjacent Scott, Northcliff, Roscoe and Apfel glaciers, about whichalmost nothing is known. We widen the context of previously observed dynamicchanges in the Denman Glacier to the wider region of the Shackleton system,with a multi-decadal time frame and an improved biannual temporal frequencyof observations in the last 7 years (2015-2022). We integrate newsatellite observations of ice structure and airborne radar data with changesin ice front position and ice flow velocities to investigate changes in thesystem. Over the 60-year period of observation we find significant riftpropagation on the Shackleton Ice Shelf and Scott Glacier and notablestructural changes in the floating shear margins between the ice shelf andthe outlet glaciers, as well as features indicative of ice with elevatedsalt concentration and brine infiltration in regions of the system. Over theperiod 2017-2022 we observe a significant increase in ice flow speed (up to50 %) on the floating part of Scott Glacier, coincident with small-scalecalving and rift propagation close to the ice front. We do not observe anyseasonal variation or significant change in ice flow speed across the restof the Shackleton system. Given the potential vulnerability of the system toaccelerating retreat into the overdeepened, potentially sediment-filledbedrock trough, an improved understanding of the glaciological,oceanographic and geological conditions in the Shackleton system arerequired to improve the certainty of numerical model predictions, and weidentify a number of priorities for future research. With access to theseremote coastal regions a major challenge, coordinated internationallycollaborative efforts are required to quantify how much the Shackletonregion is likely to contribute to sea level rise in the coming centuries.

Automated summary

The recent discovery of Antarctica's deepest subglacial trough beneath the Denman Glacier and the high rates of basal melt at the grounding line have raised concerns about the glacier's vulnerability to retreat. This study expands previous observations of the Denman Glacier's dynamic changes to the wider Shackleton system, revealing significant rift propagation and structural changes in the floating margins between the ice shelf and outlet glaciers. Moreover, an increase in ice flow speed on the floating part of the Scott Glacier, along with small-scale calving and rift propagation, has been observed. However, no seasonal variation or significant change in ice flow speed has been observed in the rest of the Shackleton system. The research highlights the need for a better understanding of the glaciological, oceanographic, and geological conditions in the Shackleton system to improve predictions and identifies priorities for future research in these remote coastal regions.