scholarly journals Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

2017 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite ◽  
Edward C. King
Keyword(s):  
Natural Experiment ◽  
Flow Model ◽  
Structural Integrity ◽  
East Antarctica ◽  
Heterogeneous Structure ◽  
Ice Shelf ◽  
Ice Flow ◽  
Iceberg Calving ◽  
Simple Fracture ◽  
Slow Propagation

Abstract. We report on the recent reactivation of a large chasm in the Brunt Ice Shelf, East Antarctica, in December 2012, and the formation of a 50-km long new rift in October 2016. Observations from a suite of ground based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both cracks in unprecedented detail. Results reveal a steady accelerating trend in the widening of the rifts, in combination with alternating episodes of fast (> 600 m/day) and slow propagation of the crack tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice-flow model and a simple fracture propagation criterion were successfully used to hindcast the observed trajectories, and to simulate future rift progression under different assumptions, showing a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability, and provoke a deeper understanding of similar processes elsewhere in Antarctica.

scholarly journals Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

2018 ◽  
Vol 12 (2) ◽  
pp. 505-520 ◽  
Author(s):  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite ◽  
Edward C. King
Keyword(s):  
Natural Experiment ◽  
Flow Model ◽  
Structural Integrity ◽  
East Antarctica ◽  
Heterogeneous Structure ◽  
High Likelihood ◽  
Ice Shelf ◽  
Ice Flow ◽  
Iceberg Calving ◽  
Slow Propagation

Abstract. We report on the recent reactivation of a large rift in the Brunt Ice Shelf, East Antarctica, in December 2012 and the formation of a 50 km long new rift in October 2016. Observations from a suite of ground-based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast ( > 600 m day−1) and slow propagation of the rift tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice flow model and a simple propagation algorithm based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability and provoke a deeper understanding of similar processes elsewhere in Antarctica.

scholarly journals The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

2021 ◽  
pp. 1-13
Author(s):  
James R. Jordan ◽  
G. Hilmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris R. Stokes ◽  
Bertie W. J. Miles ◽  
...  
Keyword(s):  
Flow Model ◽  
East Antarctica ◽  
Line Position ◽  
Ice Shelf ◽  
Ice Flow ◽  
Mean Sea Level ◽  
Front Position ◽  
Grounding Line ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract The Wilkes Subglacial Basin in East Antarctica contains ice equivalent to 3–4 m of global mean sea level rise and is primarily drained by Cook Glacier. Of concern is that recent observations (since the 1970s) show an acceleration in ice speed over the grounding line of both the Eastern and Western portions of Cook Glacier. Here, we use a numerical ice-flow model (Úa) to simulate the instantaneous effects of observed changes at the terminus of Cook Glacier in order to understand the link between these changes and recently observed ice acceleration. Simulations suggest that the acceleration of Cook West was caused by a retreat in calving-front position in the 1970s, potentially enhanced by grounding-line retreat, while acceleration of Cook East was likely caused by ice-shelf thinning and grounding-line retreat in the mid-1990s. Moreover, we show that the instantaneous ice discharge at Cook East would increase by up to 85% if the whole ice shelf is removed and it ungrounds from a pinning point; and that the discharge at Cook West could increase by ~300% if its grounding line retreated by 10 km.

The effect of Antarctic ice-shelf extent on ice discharge

2021 ◽  
Author(s):  
Jim Jordan ◽  
HIlmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris Stokes ◽  
Stewart Jamiesson ◽  
...  
Keyword(s):  
Mass Loss ◽  
Recent Work ◽  
Flow Model ◽  
Ice Shelf ◽  
Geophysical Research ◽  
Ice Flow ◽  
Ice Shelves ◽  
Grounding Line ◽  
Natural Variance ◽  
Observational Record

<div>The buttressing strength of Antarctic ice shelves directly effects the amount of ice discharge across the grounding line, with buttressing strength affected by both the thickness and extent of an ice shelf. Recent work has shown that a reduction in ice-shelf buttressing due to ocean induced ice-shelf thinning is responsible for a significant portion of increased Antarctic ice discharge (Gudmundsson et al., 2019, but few studies have attempted to show the effect of variability in ice-shelf extent on ice discharge. This variability arises due to ice-shelf calving following a cycle of long periods of slow, continuous calving interposed with calving of large, discrete sections.  These discrete calving events tend to occur on a comparative timeframe to that of the observational record. As such, when determining observed changes in ice discharge it is crucial that this natural variability is separated from any observed trends.  </div><div> </div><div>In this work we use the numerical ice-flow model Úa in combination with observations of ice shelf extent to diagnostically calculate Antarctic ice discharge. These observations primarily date back to the 1970s, though for some ice shelves records exist back to the 1940s. We assemble an Antarctic wide model for two scenarios: 1) with ice shelves at their maximum observed extent and 2) with ice shelves at their minimum observed extent. We then compare these two scenarios to differences in the observed changes in Antarctic ice-discharge to determine how much can be attributed to natural variance .</div><p> </p><p><span>Gudmundsson, G. H.</span><span>, Paolo, F. S., Adusumilli, S., & Fricker, H. A. (2019). </span>Instantaneous Antarctic ice‐ sheet mass loss driven by thinning ice shelves. <em>Geophysical Research Letters</em>, 46, 13903– 13909. </p>

scholarly journals Accumulation patterns around Dome C, East Antarctica, in the last 73 kyr

2018 ◽  
Vol 12 (4) ◽  
pp. 1401-1414 ◽  
Author(s):  
Marie G. P. Cavitte ◽  
Frédéric Parrenin ◽  
Catherine Ritz ◽  
Duncan A. Young ◽  
Brice Van Liefferinge ◽  
...  
Keyword(s):  
Large Scale ◽  
Flow Model ◽  
East Antarctica ◽  
Small Scale ◽  
Time Interval ◽  
Accumulation Rates ◽  
Ice Flow ◽  
Last Glacial ◽  
Prevailing Wind Direction ◽  
The Last Glacial

Abstract. We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, since the last glacial. We use a set of 18 isochrones spanning all observable depths of the ice column, interpreted from various ice-penetrating radar surveys and a 1-D ice flow model to invert for accumulation rates in the region. The shallowest four isochrones are then used to calculate paleoaccumulation rates between isochrone pairs using a 1-D assumption where horizontal advection is negligible in the time interval of each layer. We observe that the large-scale (100s km) surface accumulation gradient is spatially stable through the last 73 kyr, which reflects current modeled and observed precipitation gradients in the region. We also observe small-scale (10 s km) accumulation variations linked to snow redistribution at the surface, due to changes in its slope and curvature in the prevailing wind direction that remain spatially stationary since the last glacial.

Simulation of Aurora basin, East Antarctic

2020 ◽  
Author(s):  
Liyun Zhao ◽  
Yan Zhen ◽  
Rupert Gladstone ◽  
Thomas Zwinger ◽  
John Moore
Keyword(s):  
High Resolution ◽  
Thermal Condition ◽  
Inverse Method ◽  
Flow Model ◽  
Surface Velocity ◽  
Dynamic Processes ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ocean Models ◽  
The Stability

<p>The Aurora basin includes several fast-flowing glaciers (e.g. Totten and Dalton) and has large subglacial areas below sea level, which makes its study an essential part of evaluating the stability of East Antarctic against ocean warming. We use the 3D full-Stokes ice flow model Elmer/Ice to investigate the dynamic processes taking place in this basin. The spatial pattern of basal friction is deduced by inverse method from observed surface velocity. Particular focus is in the thermal condition at the bedrock. We further project the evolution of this basin during the 21st century with parameterized sub-ice shelf melting based provided by high resolution ocean models.</p>

scholarly journals Two decades of dynamic change and progressive destabilization on the Thwaites Eastern Ice Shelf

2021 ◽  
Vol 15 (11) ◽  
pp. 5187-5203
Author(s):  
Karen E. Alley ◽  
Christian T. Wild ◽  
Adrian Luckman ◽  
Ted A. Scambos ◽  
Martin Truffer ◽  
...  
Keyword(s):  
Shear Zone ◽  
Structural Integrity ◽  
Dynamic Change ◽  
Image Data ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Flow ◽  
Landsat 7 ◽  
Rapid Pace ◽  
Elevation Model

Abstract. The Thwaites Eastern Ice Shelf (TEIS) buttresses the eastern grounded portion of Thwaites Glacier through contact with a pinning point at its seaward limit. Loss of this ice shelf will promote further acceleration of Thwaites Glacier. Understanding the dynamic controls and structural integrity of the TEIS is therefore important to estimating Thwaites' future sea-level contribution. We present a ∼ 20-year record of change on the TEIS that reveals the dynamic controls governing the ice shelf's past behaviour and ongoing evolution. We derived ice velocities from MODIS and Sentinel-1 image data using feature tracking and speckle tracking, respectively, and we combined these records with ITS_LIVE and GOLIVE velocity products from Landsat-7 and Landsat-8. In addition, we estimated surface lowering and basal melt rates using the Reference Elevation Model of Antarctica (REMA) DEM in comparison to ICESat and ICESat-2 altimetry. Early in the record, TEIS flow dynamics were strongly controlled by the neighbouring Thwaites Western Ice Tongue (TWIT). Flow patterns on the TEIS changed following the disintegration of the TWIT around 2008, with a new divergence in ice flow developing around the pinning point at its seaward limit. Simultaneously, the TEIS developed new rifting that extends from the shear zone upstream of the ice rise and increased strain concentration within this shear zone. As these horizontal changes occurred, sustained thinning driven by basal melt reduced ice thickness, particularly near the grounding line and in the shear zone area upstream of the pinning point. This evidence of weakening at a rapid pace suggests that the TEIS is likely to fully destabilize in the next few decades, leading to further acceleration of Thwaites Glacier.

scholarly journals Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica

2016 ◽  
Author(s):  
Hongju Yu ◽  
Eric Rignot ◽  
Mathieu Morlighem ◽  
Helene Seroussi
Keyword(s):  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Melt ◽  
Linear Elastic ◽  
Grounding Line ◽  
Iceberg Calving ◽  
Elastic Fracture ◽  
The Difference ◽  
The Impact

Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom crevasses that match radar sounding observations of crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining crevasse formation and iceberg calving.

scholarly journals Assessing Controls on Ice Dynamics at Crane Glacier, Antarctic Peninsula Using a Numerical Ice Flow Model

2021 ◽  
Author(s):  
Rainey Aberle
Keyword(s):  
Antarctic Peninsula ◽  
Flow Model ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Surface Mass ◽  
Climate Conditions ◽  
Ice Shelves ◽  
Tidewater Glacier ◽  
Mass Discharge

The widespread retreat of glaciers and the collapse of ice shelves along the Antarctic Peninsula has been attributed to atmospheric and oceanic warming, which promotes mass loss. However, several glaciers on the eastern peninsula that were buttressed by the Larsen A and B ice shelves prior to collapse in 1995 and 2002, respectively, have been advancing in recent years. This asymmetric pattern of rapid retreat and long-term re-advance is similar to the tidewater glacier cycle, which can occur largely independent of climate forcing. Here, I use a width- and depth-integrated numerical ice flow model to investigate glacier response to ice shelf collapse and the influence of changing climate conditions at Crane Glacier, formerly a tributary of the Larsen B ice shelf, over the last ~10 years. Sensitivity tests to explore the influence of perturbations in surface mass balance and submarine melt (up to 10 m a-1) and fresh water impounded in crevasses (up to 10 m) on glacier dynamics reveal that by 2100, the modeled mass discharge ranges from 0.53-98 Gt a-1, with the most substantial changes due to surface melt-induced thinning. My findings suggest that the growth of a floating ice tongue can hinder enhanced flow, allowing the grounding zone to remain steady for many decades, analogous to the advancing stage of the tidewater glacier cycle. Additionally, former tributary glaciers can take several decades to geometrically adjust to ice shelf collapse at their terminal boundary while elevated glacier discharge persists.

scholarly journals On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

2012 ◽  
Vol 8 (4) ◽  
pp. 1239-1255 ◽  
Author(s):  
F. Parrenin ◽  
S. Barker ◽  
T. Blunier ◽  
J. Chappellaz ◽  
J. Jouzel ◽  
...  
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Convective Zone ◽  
East Antarctica ◽  
Column Height ◽  
Ice Flow ◽  
Depth Difference ◽  
Lock In ◽  
Last Deglacial

Abstract. We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The general agreement of method 4 with methods 2 and 3 confirms that the bipolar seesaw antiphase happened during the last 140 kyr. Applying method 4 to the deeper section of the EDC core confirms that the ice flow is complex and can help to improve our reconstruction of the thinning function and thus, of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggest that it is due to an overestimation of the glacial lock-in depth (LID) by the firn densification model. In contrast, we find that method 1 very likely underestimates Δdepth during Termination II, due either to an underestimated thinning function or to an underestimated LID. Finally, method 2 gives estimates within a few metres of methods 3 and 4 during the last deglacial warming, suggesting that the convective zone at Dome C cannot have been very large at this time, if it existed at all.

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