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Abstract. 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.
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Glacier geometry and flow speed determine how Arctic marine-terminating glaciers respond to lubricated beds
Abstract. Basal conditions directly control the glacier sliding rate and the dynamic discharge of ice. Recent glacier destabilization events indicate that some marine-terminating glaciers quickly respond to lubricated beds with increased flow speed, but the underlying physics, especially how this vulnerability relates to glacier geometry and flow characteristics, remains unclear. This paper presents a 1D physical framework for glacier dynamic vulnerability assuming sudden basal lubrication as an initial perturbation. In this new model, two quantities determine the scale and the areal extent of the subsequent thinning and acceleration after the bed is lubricated: Péclet number (Pe) and the product of glacier speed and thickness gradient (dubbed J0 in this study). To validate the model, this paper calculates Pe and J0 using multi-sourced data from 1996 to 1998 for outlet glaciers in the Greenland ice sheet and Austfonna ice cap, Svalbard, and compares the results with the glacier speed change during 1996/1998–2018. Glaciers with lower Pe and J0 are more likely to accelerate during this 20-year span than those with higher Pe and J0, which matches the model prediction. A combined factor of ice thickness, surface slope, and initial flow speed physically determines how much and how fast glaciers respond to lubricated beds in terms of speed, elevation, and terminus change.
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- Award ID(s):
- 1928406
- PAR ID:
- 10352853
- Date Published:
- Journal Name:
- The Cryosphere
- Volume:
- 16
- Issue:
- 4
- ISSN:
- 1994-0424
- Page Range / eLocation ID:
- 1431 to 1445
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Bering‐Bagley Glacier System (BBGS), Alaska, Earth's largest temperate surging glacier, surged in 2008–2013. We use numerical modeling and satellite observations to investigate how surging in a large and complex glacier system differs from surging in smaller glaciers for which our current understanding of the surge phenomenon is based. With numerical simulations of a long quiescent phase and a short surge phase in the BBGS, we show that surging is more spatiotemporally complex in larger glaciers with multiple reservoir areas forming during quiescence which interact in a cascading manner when ice accelerates during the surge phase. For each phase, we analyze the simulated elevation‐change and ice‐velocity pattern, infer information on the evolving basal drainage system through hydropotential analysis, and supplement these findings with observational data such as CryoSat‐2 digital elevation maps. During the quiescent simulation, water drainage paths become increasingly lateral and hydropotential wells form indicating an expanding storage capacity of subglacial water. These results are attributed to local bedrock topography characterized by large subglacial ridges that dam the down‐glacier flow of ice and water. In the surge simulation, we model surge evolution through Bering Glacier's trunk by imposing a basal friction representation that mimics a propagating surge wave. As the surge progresses, drainage efficiency further degrades in the active surging‐zone from its already inefficient, end‐of‐quiescence state. Results from this study improve our knowledge of surging in large and complex systems which generalizes to glacial accelerations observed in outlet glaciers of Greenland, thus reducing uncertainty in modeling sea‐level rise.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/tc-16-1431-2022
