scholarly journals Glaciological setting of the Queen Mary and Knox coasts, East Antarctica, over the past 60 years, and implied dynamic stability of the Shackleton system

2021 ◽  
Author(s):  
Sarah Susan Thompson ◽  
Bernd Kulessa ◽  
Stephen Cornford ◽  
Adrian Luckman ◽  
Jacqueline Halpin
Keyword(s):  
Sea Level Rise ◽  
Surface Structure ◽  
Sea Level ◽  
Temporal Frequency ◽  
Flow Speed ◽  
East Antarctica ◽  
Small Contribution ◽  
Ice Flow ◽  
Geological Conditions ◽  
Grounding Line

Abstract. The discovery of the deepest subglacial trough beneath the Denman Glacier, combined with high rates of basal melt at the grounding line, have caused significant concern over its vulnerability to retreat. Recent attention has therefore been focusing on understanding the governing dynamic controls, although knowledge of the wider regional context and timescales over which the future responses may occur remains poor. Here we consider the whole Shackleton system, comprising of the Shackleton ice shelf, Denman Glacier and adjacent Scott, Northcliffe, Roscoe and Apfel glaciers, about which almost nothing is known. We widen the context of previously observed dynamic changes in the Denman Glacier into the wider region of the Queen Mary and Knox coasts; with a multi-decadal timeframe and an improved biannual temporal frequency of observations in the last seven years (2014–21). We integrate new satellite observations of ice structure, changes in ice front position and ice-flow velocities to investigate changes in the system. We furthermore use the BISICLES ice sheet model to assess the sensitivity and simulate the response times of the Queen Mary and Knox coasts to hypothetical disintegration of its floating ice areas, in response to coupled ocean and atmospheric forcing. Over the 60-year period of observation, the Queen Mary and Knox coasts do not appear to have changed significantly and higher frequency observations have not revealed any significant annual or sub-annual variations in ice flow. A previously observed increase in the ice flow speed of the Denman Glacier has not continued beyond 2008, and we cannot identify any related change in the surface structure of the system since then. We do, however, observe more significant change in the Scott Glacier, with an acceleration in ice flow associated with calving and progressing from the ice front along the floating tongue since early 2020. No changes in surface structure or ice flow speed are observed closer to the grounded ice. Our upper limit numerical simulations for a 400-year period are consistent with noticeable grounding line retreat in the Denman Glacier in the next two centuries if all floating ice were lost, before stabilising again in the third century from now. This equates to around 6 cm of sea level rise, a small contribution when compared to other areas of East Antarctica expected to change over the same time frame. It is clear that current knowledge is insufficient to explain the observed spatial and temporal changes in the dynamic behaviour of the grounded and floating sections in the Shackleton system. Given the potential vulnerability of the system to accelerating retreat better data recording the glaciological, oceanographic, and geological conditions in the Queen Mary and Knox coasts are required to improve the certainty of numerical model predictions. With access to these remote coastal regions a major challenge, coordinated internationally collaborative efforts are required to quantify how much the Queen Mary and Knox coastal region is likely contribute to sea level rise in the coming centuries.

scholarly journals Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven by grounding line retreat and changes in ice tongue configuration

2021 ◽  
Vol 15 (2) ◽  
pp. 663-676
Author(s):  
Bertie W. J. Miles ◽  
Jim R. Jordan ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson ◽  
G. Hilmar Gudmundsson ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Sea Level Rise ◽  
Sea Level ◽  
Flow Speed ◽  
Recent Change ◽  
East Antarctica ◽  
Ice Flow ◽  
Geological Evidence ◽  
Flow Acceleration ◽  
Grounding Line

Abstract. After Totten, Denman Glacier is the largest contributor to sea level rise in East Antarctica. Denman's catchment contains an ice volume equivalent to 1.5 m of global sea level and sits in the Aurora Subglacial Basin (ASB). Geological evidence of this basin's sensitivity to past warm periods, combined with recent observations showing that Denman's ice speed is accelerating and its grounding line is retreating along a retrograde slope, has raised the prospect that its contributions to sea level rise could accelerate. In this study, we produce the first long-term (∼50 years) record of past glacier behaviour (ice flow speed, ice tongue structure and calving) and combine these observations with numerical modelling to explore the likely drivers of its recent change. We find a spatially widespread acceleration of the Denman system since the 1970s across both its grounded (17±4 % acceleration; 1972–2017) and floating portions (36±5 % acceleration; 1972–2017). Our numerical modelling experiments show that a combination of grounding line retreat, ice tongue thinning and the unpinning of Denman's ice tongue from a pinning point following its last major calving event are required to simulate an acceleration comparable with observations. Given its bed topography and the geological evidence that Denman Glacier has retreated substantially in the past, its recent grounding line retreat and ice flow acceleration suggest that it could be poised to make a significant contribution to sea level in the near future.

scholarly journals Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven by grounding line retreat and changes in ice tongue configuration

2020 ◽  
Author(s):  
Bertie W. J. Miles ◽  
Jim R. Jordan ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson ◽  
G. Hilmar Gudmundsson ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Sea Level ◽  
Flow Speed ◽  
Recent Change ◽  
East Antarctica ◽  
Ice Flow ◽  
Geological Evidence ◽  
Flow Acceleration ◽  
Grounding Line ◽  
Global Sea Level

Abstract. Denman Glacier is one of the largest in East Antarctica, with a catchment that contains an ice volume equivalent to 1.5 m of global sea-level and which sits in the Aurora Subglacial Basin (ASB). Geological evidence of this basin’s sensitivity to past warm periods, combined with recent observations showing that Denman’s ice speed is accelerating, and its grounding line is retreating along a retrograde slope, have raised the prospect that it could contribute to near-future sea-level rise. In this study, we produce the first long-term (~ 50 years) record of past glacier behaviour (ice flow speed, ice tongue structure, and calving) and combine these observations with numerical modelling to explore the likely drivers of its recent change. We find a spatially widespread acceleration of the Denman system since the 1970s across both its grounded (17 ± 4 % acceleration; 1972–2017) and floating portions (36 ± 5 % acceleration; 1972–2017). Our numerical modelling experiments show that a combination of grounding line retreat, ice tongue thinning and the unpinning of Denman’s ice tongue from a pinning point following its last major calving event are required to simulate an acceleration comparable with observations. Given its bed topography and the geological evidence that Denman Glacier has retreated substantially in the past, its recent grounding line retreat and ice flow acceleration suggest that it could be poised to make a significant contribution to sea level over the coming century.

scholarly journals Sensitivity of grounding line dynamics to the choice of the friction law

2017 ◽  
Vol 63 (241) ◽  
pp. 854-866 ◽  
Author(s):  
JULIEN BRONDEX ◽  
OLIVIER GAGLIARDINI ◽  
FABIEN GILLET-CHAULET ◽  
GAËL DURAND
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Basal Slip ◽  
Ice Streams ◽  
Ice Flow ◽  
Friction Law ◽  
Flow Models ◽  
Friction Laws ◽  
Grounding Line ◽  
Physically Based

ABSTRACTBasal slip accounts for a large part of the flow of ice streams draining ice from Antarctica and Greenland into the ocean. Therefore, an appropriate representation of basal slip in ice flow models is a prerequisite for accurate sea level rise projections. Various friction laws have been proposed to describe basal slip in models. Here, we compare the influence on grounding line (GL) dynamics of four friction laws: the traditional Weertman law and three effective pressure-dependent laws, namely the Schoof, Tsai and Budd laws. It turns out that, even when they are tuned to a common initial reference state, the Weertman, Budd and Schoof laws lead to thoroughly different steady-state positions, although the Schoof and Tsai laws lead to much the same result. In particular, under certain circumstances, it is possible to obtain a steady GL located on a reverse slope area using the Weertman law. Furthermore, the predicted transient evolution of the GL as well as the projected contributions to sea level rise over a 100-year time horizon vary significantly depending on the friction law. We conclude on the importance of choosing an appropriate law for reliable sea level rise projections and emphasise the need for a coupling between ice flow models and physically based subglacial hydrological models.

scholarly journals Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

2017 ◽  
Vol 11 (4) ◽  
pp. 1851-1878 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Power Law ◽  
Coulomb Friction ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Grounding Line ◽  
Basal Sliding

Abstract. The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet–ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a−1 under freely floating ice shelves, up to 6 m for a 50 m a−1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be integrated in large-scale Earth system models.

scholarly journals Ice-shelf retreat drives recent Pine Island Glacier speedup

2021 ◽  
Vol 7 (24) ◽  
pp. eabg3080
Author(s):  
Ian Joughin ◽  
Daniel Shapero ◽  
Ben Smith ◽  
Pierre Dutrieux ◽  
Mark Barham
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Flow Model ◽  
Velocity Data ◽  
Ice Shelf ◽  
Ice Flow ◽  
The Past ◽  
Grounding Line

Speedup of Pine Island Glacier over the past several decades has made it Antarctica’s largest contributor to sea-level rise. The past speedup is largely due to grounding-line retreat in response to ocean-induced thinning that reduced ice-shelf buttressing. While speeds remained fairly steady from 2009 to late 2017, our Copernicus Sentinel 1A/B–derived velocity data show a >12% speedup over the past 3 years, coincident with a 19-km retreat of the ice shelf. We use an ice-flow model to simulate this loss, finding that accelerated calving can explain the recent speedup, independent of the grounding-line, melt-driven processes responsible for past speedups. If the ice shelf’s rapid retreat continues, it could further destabilize the glacier far sooner than would be expected due to surface- or ocean-melting processes.

scholarly journals Sensitivity of the dynamics of Pine Island Glacier, West Antarctica, to climate forcing for the next 50 years

2014 ◽  
Vol 8 (5) ◽  
pp. 1699-1710 ◽  
Author(s):  
H. Seroussi ◽  
M. Morlighem ◽  
E. Rignot ◽  
J. Mouginot ◽  
E. Larour ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Three Dimensional ◽  
Major Contributor ◽  
West Antarctica ◽  
Climatic Impact ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Grounding Line

Abstract. Pine Island Glacier, a major contributor to sea level rise in West Antarctica, has been undergoing significant changes over the last few decades. Here, we employ a three-dimensional, higher-order model to simulate its evolution over the next 50 yr in response to changes in its surface mass balance, the position of its calving front and ocean-induced ice shelf melting. Simulations show that the largest climatic impact on ice dynamics is the rate of ice shelf melting, which rapidly affects the glacier speed over several hundreds of kilometers upstream of the grounding line. Our simulations show that the speedup observed in the 1990s and 2000s is consistent with an increase in sub-ice-shelf melting. According to our modeling results, even if the grounding line stabilizes for a few decades, we find that the glacier reaction can continue for several decades longer. Furthermore, Pine Island Glacier will continue to change rapidly over the coming decades and remain a major contributor to sea level rise, even if ocean-induced melting is reduced.

scholarly journals Contrasting the modelled sensitivity of the Amundsen Sea Embayment ice streams

2016 ◽  
Vol 62 (233) ◽  
pp. 552-562 ◽  
Author(s):  
ISABEL J. NIAS ◽  
STEPHEN L. CORNFORD ◽  
ANTONY J. PAYNE
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Mass Conservation ◽  
Physical Parameters ◽  
Ice Streams ◽  
Amundsen Sea ◽  
West Antarctic ◽  
Grounding Line

AbstractPresent-day mass loss from the West Antarctic ice sheet is centred on the Amundsen Sea Embayment (ASE), primarily through ice streams, including Pine Island, Thwaites and Smith glaciers. To understand the differences in response of these ice streams, we ran a perturbed parameter ensemble, using a vertically-integrated ice flow model with adaptive mesh refinement. We generated 71 sets of three physical parameters (basal traction coefficient, ice viscosity stiffening factor and sub-shelf melt rate), which we used to simulate the ASE for 50 years. We also explored the effects of different bed geometries and basal sliding laws. The mean rate of sea-level rise across the ensemble of simulations is comparable with current observed rates for the ASE. We found evidence that grounding line dynamics are sensitive to features in the bed geometry: simulations using BedMap2 geometry resulted in a higher rate of sea-level rise than simulations using a rougher geometry, created using mass conservation. Modelled grounding-line retreat of all the three ice streams was sensitive to viscosity and basal traction, while the melt rate was more important in Pine Island and Smith glaciers, which flow through more confined ice shelves than Thwaites, which has a relatively unconfined shelf.

Viscoelastic modeling results of the 79°N Glacier, Greenland

2020 ◽  
Author(s):  
Julia Christmann ◽  
Martin Rückamp ◽  
Ole Zeising ◽  
Daniel Steinhage ◽  
Niklas Neckel ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Greenland Ice Sheet ◽  
Material Model ◽  
Outlet Glacier ◽  
Tidal Forcing ◽  
North East ◽  
Periodic Movement ◽  
Grounding Line ◽  
Horizontal Displacements

<p>Grounding line/zone dynamics of floating-tongue glaciers is of major importance for changes in their contribution to sea-level rise. For floating-tongue glaciers, thermal forcing of oceanic heat and tidal forcing are the major processes acting in that zone. Here we deal with the response to tidal forcing. The 79°N Glacier, an outlet glacier of the North East Greenland Ice Stream, is the focus of the Greenland Ice Sheet Ocean Interaction project (GROCE) funded by the German Ministry of Education and Research. We present a study of this region considering the deformation of the glacier in response to ocean tidal forcing by means of observations and modeling. GPS measurements realized in 2017-2018 are analyzed for vertical and horizontal displacements of the glacier and its floating tongue. Observations on fully-grounded ice reveal a periodic horizontal displacement in response to ocean tidal forcing in a distance of more than 35 km upstream from the grounding line. In the hinge zone, i.e. the transition between grounded and floating ice, the tidal forcing leads to a measurable vertical bending of the ice and a periodic movement of the grounding line. Understanding the mechanisms of grounding line migration is important to better evaluate the contribution of grounded ice discharge to sea-level rise.</p><p>In order to model the measured displacements, a viscoelastic material model is required using the observed vertical displacements at the floating ice tongue as external forcing. Geometries obtained from AWI’s new ultrawideband radar form the basis for finite-element simulations in COMSOL. With the viscoelastic Maxwell material model, the response of the ice to ocean tidal forcing can successfully be modeled. Results obtained with a nonlinear Glen-type viscosity agree very well with the observed bending near the grounding line. The expected phase shift of the horizontal displacements upstream from the grounding line is well reproduced in the model.</p>

Response of the East Antarctica ice sheet to sea-level rise

1984 ◽  
Vol 89 (C4) ◽  
pp. 6487 ◽  
Author(s):  
Richard B. Alley ◽  
Ian M. Whillans
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
East Antarctica

scholarly journals Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?

2018 ◽  
Author(s):  
Michael J. Wolovick ◽  
John C. Moore
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Dynamic Feedback ◽  
West Antarctica ◽  
Ice Shelf ◽  
Long Run ◽  
Grounding Line ◽  
Individual Source ◽  
Engineering Projects

Abstract. The Marine Ice Sheet Instability (MISI) is a dynamic feedback that can cause an ice sheet to enter a runaway collapse. Thwaites Glacier, West Antarctica, is the largest individual source of future sea level rise and may have already entered the MISI. Here, we use a suite of coupled ice–ocean flowband simulations to explore whether targeted geoengineering using an artificial sill or artificial ice rises could counter a collapse. Successful interventions occur when the floating ice shelf regrounds on the pinning points, increasing buttressing and reducing ice flux across the grounding line. Regrounding is more likely with a continuous sill that is able to block warm water transport to the grounding line. The smallest design we consider is comparable in scale to existing civil engineering projects but has only a 30 % success rate, while larger designs are more effective. There are multiple possible routes forward to improve upon the designs that we considered, and with decades or more to research designs it is plausible that the scientific community could come up with a plan that was both effective and achievable. While reducing emissions remains the short-term priority for minimizing the effects of climate change, in the long run humanity may need to develop contingency plans to deal with an ice sheet collapse.

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