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

Abstract

Abstract. The discovery of Antarctica's deepest subglacial trough beneath the Denman Glacier, combined with high rates of basal melt at the grounding line, has caused significant concern over its vulnerability to retreat. Recent attention has therefore been focusing on understanding the controls driving Denman Glacier's dynamic evolution. Here we consider the Shackleton system, comprised of the Shackleton Ice Shelf, Denman Glacier, and the adjacent Scott, Northcliff, Roscoe and Apfel glaciers, about which almost nothing is known. We widen the context of previously observed dynamic changes in the Denman Glacier to the wider region of the Shackleton system, with a multi-decadal time frame and an improved biannual temporal frequency of observations in the last 7 years (2015–2022). We integrate new satellite observations of ice structure and airborne radar data with changes in ice front position and ice flow velocities to investigate changes in the system. Over the 60-year period of observation we find significant rift propagation on the Shackleton Ice Shelf and Scott Glacier and notable structural changes in the floating shear margins between the ice shelf and the outlet glaciers, as well as features indicative of ice with elevated salt concentration and brine infiltration in regions of the system. Over the period 2017–2022 we observe a significant increase in ice flow speed (up to 50 %) on the floating part of Scott Glacier, coincident with small-scale calving and rift propagation close to the ice front. We do not observe any seasonal variation or significant change in ice flow speed across the rest of the Shackleton system. Given the potential vulnerability of the system to accelerating retreat into the overdeepened, potentially sediment-filled bedrock trough, an improved understanding of the glaciological, oceanographic and geological conditions in the Shackleton system are required to improve the certainty of numerical model predictions, and we identify a number of priorities for future research. With access to these remote coastal regions a major challenge, coordinated internationally collaborative efforts are required to quantify how much the Shackleton region is likely to contribute to sea level rise in the coming centuries.

The Multi-decadal Collapse of East Antarctica’s Conger-Glenzer Ice Shelf

“…This more than 50 m of thinning over 15 years is consistent with estimated basal melt rates 41 (Extended Data Figure 6) which were variable but averaged positive (melting) between 1992-2002, negative 2003-2013, and positive 2013-2018, suggesting less thinning during the middle period. Overall however, since ~2011, melt rates have increased, implying an increase in ocean temperature 42 , consistent with observations at neighboring SIS 43,44 . Between 2019-2021, ICESat-2 provided high-resolution along-track sampling, illuminating feature-level details of ice shelf topography 45,46 (Extended Data Fig.…”

Oceanic Regime Shift to a Warmer Continental Shelf Adjacent to the Shackleton Ice Shelf, East Antarctica

“…Modeling work along the Totten Glacier showed that freshwater input from ice shelf melting was enough to offset the salt flux from sea ice production, preventing top‐to‐bottom convection (Silvano et al., 2018). Given there were no significant changes in the icescape of the Shackleton‐Denman System in the last 60 years (S. S. Thompson et al., 2023) or in the activity of the Shackleton Polynya (sea ice production increases 0.09% per year from 1992 to 2013; Tamura et al., 2016), it seems the freshening of DSW is more likely the result of melting (and thinning; Paolo et al., 2015) of the SIS.…”

“…East of the SIS (97-102°E), mCDW is not present near the ice front, with the exception of one profile that shows cold mCDW at the edge of the Scott Glacier. Given the calving front of the Scott Glacier advanced about 10 km from 1962 to 1991 before retreating back to the same position it was in 1962 in recent years (S. S. Thompson et al, 2023), this profile was likely to be near the ice front rather than underneath it, as Figures 2 and 3 might suggest. Data from the east of the SIS are limited though, and mostly sampled in shallower areas, meaning the possibility of a wider presence of mCDW, especially at depth, should not be discarded.…”

“…The thinning of the SIS (Paolo et al., 2015) and retreat of the grounding line of the Denman Glacier (Brancato et al., 2020) may indicate an increase in ocean heat transport to the Shackleton‐Denman System. The Shackleton‐Denman System is located at the boundary of the Knox and Queen Mary Coasts of Wilkes Land, comprising three major outlet glaciers (Denman, Scott and Roscoe) and their distinctive tongues, the SIS, and an area of fast ice to the northwest of the Denman tongue (Figure 1a; Fraser et al., 2021; S. S. Thompson et al., 2023). The Shackleton polynya west of the SIS (colored contours of Figure 1b) produces 123 ± 12 Gt yr −1 of sea ice (Tamura et al., 2016).…”

Brief Communication: Rapid acceleration of the Brunt Ice Shelf after calving of iceberg A-81

“…The rapid acceleration of the Brunt Ice Shelf following calving represents a departure from the typical behaviour observed for this ice shelf over the last sixty years. Velocities of this magnitude are usually only measured on the ice shelves fed by exceptionally fast flowing outlet glaciers such as Thwaites, Pine Island and Denman Glaciers (Miles et al, 2020;Thompson et al, 2023). The Brunt Ice Shelf does not have a fast-flowing outlet glacier feeding it and under high velocities it is not fully replenished by ice from the continental interior.…”