scholarly journals Ice-shelf fracture due to viscoelastic flexure stress induced by fill/drain cycles of supraglacial lakes

2015 ◽  
Vol 27 (6) ◽  
pp. 587-597 ◽  
Author(s):  
Alison F. Banwell ◽  
Douglas R. Macayeal
Keyword(s):  
Lake Basin ◽  
Ice Shelf ◽  
Successive Cycle ◽  
Thin Beam ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
Lake Bottom ◽  
Extended Zone ◽  
Plate Analysis ◽  
Power Law Creep

AbstractUsing a previously derived treatment of viscoelastic flexure of floating ice shelves, we simulated multiple years of evolution of a single, axisymmetric supraglacial lake when it is subjected to annual fill/drain cycles. Our viscoelastic treatment follows the assumptions of the well-known thin-beam and thin-plate analysis but, crucially, also covers power-law creep rheology. As the ice-shelf surface does not completely return to its un-flexed position after a 1-year fill/drain cycle, the lake basin deepens with each successive cycle. This deepening process is significantly amplified when lake-bottom ablation is taken into account. We evaluate the timescale over which a typical lake reaches a sufficient depth such that ice-shelf fracture can occur well beyond the lake itself in response to lake filling/drainage. We show that, although this is unlikely during one fill/drain cycle, fracture is possible after multiple years assuming surface meltwater availability is unlimited. This extended zone of potential fracture implies that flexural stresses in response to a single lake filling/drainage event can cause neighbouring lakes to drain, which, in turn, can cause lakes farther afield to drain. Such self-stimulating behaviour may have accounted for the sudden, widespread appearance of a fracture system that drove the Larsen B Ice Shelf to break-up in 2002.

scholarly journals A model of viscoelastic ice-shelf flexure

2015 ◽  
Vol 61 (228) ◽  
pp. 635-645 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Olga V. Sergienko ◽  
Alison F. Banwell
Keyword(s):  
Thin Plate ◽  
Initial Step ◽  
Maxwell Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
In Series ◽  
Iceberg Calving ◽  
Power Law Creep ◽  
Creep Deformations

AbstractWe develop a formal thin-plate treatment of the viscoelastic flexure of floating ice shelves as an initial step in treating various problems relevant to ice-shelf response to sudden changes of surface loads and applied bending moments (e.g. draining supraglacial lakes, iceberg calving, surface and basal crevassing). Our analysis is based on the assumption that total deformation is the sum of elastic and viscous (or power-law creep) deformations (i.e. akin to a Maxwell model of viscoelasticity, having a spring and dashpot in series). The treatment follows the assumptions of well-known thin-plate approximation, but is presented in a manner familiar to glaciologists and with Glen’s flow law. We present an analysis of the viscoelastic evolution of an ice shelf subject to a filling and draining supraglacial lake. This demonstration is motivated by the proposition that flexure in response to the filling/drainage of meltwater features on the Larsen B ice shelf, Antarctica, contributed to the fragmentation process that accompanied its collapse in 2002.

scholarly journals Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Chris R. Stokes ◽  
Jack E. Sanderson ◽  
Bertie W. J. Miles ◽  
Stewart S. R. Jamieson ◽  
Amber A. Leeson
Keyword(s):  
Ice Sheet ◽  
Ice Shelf ◽  
Typically Develop ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
Marginal Areas ◽  
Surface Slopes ◽  
Highly Sensitive ◽  
Ice Sheet Mass Balance ◽  
High Resolution Satellite Imagery

Abstract Supraglacial lakes are important to ice sheet mass balance because their development and drainage has been linked to changes in ice flow velocity and ice shelf disintegration. However, little is known about their distribution on the world’s largest ice sheet in East Antarctica. Here, we use ~5 million km2 of high-resolution satellite imagery to identify >65,000 lakes (>1,300 km2) that formed around the peak of the melt season in January 2017. Lakes occur in most marginal areas where they typically develop at low elevations (<100 m) and on low surface slopes (<1°), but they can exist 500 km inland and at elevations >1500 m. We find that lakes often cluster a few kilometres down-ice from grounding lines and ~60% (>80% by area) develop on ice shelves, including some potentially vulnerable to collapse driven by lake-induced hydro-fracturing. This suggests that parts of the ice sheet may be highly sensitive to climate warming.

scholarly journals Seasonal evolution of Antarctic supraglacial lakes in 2015–2021 and links to environmental controls

2021 ◽  
Author(s):  
Mariel Christina Dirscherl ◽  
Andreas J. Dietz ◽  
Claudia Kuenzer
Keyword(s):  
Antarctic Peninsula ◽  
Time Lags ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Shelf Stability ◽  
Air Content ◽  
Supraglacial Lakes ◽  
Environmental Controls ◽  
Lake Formation ◽  
Increased Risk

Abstract. Supraglacial meltwater accumulation on ice shelves may have important implications for future sea-level-rise. Despite recent progress in the understanding of Antarctic surface hydrology, potential influences on ice shelf stability as well as links to environmental drivers remain poorly constrained. In this study, we employ state-of-the-art machine learning on Sentinel-1 Synthetic Aperture Radar (SAR) and optical Sentinel-2 satellite imagery to provide new insight into the inter-annual and intra-annual evolution of surface hydrological features across six major Antarctic Peninsula and East Antarctic ice shelves. For the first time, we produce a record of supraglacial lake extent dynamics for the period 2015–2021 at unprecedented 10 m spatial resolution and bi-weekly temporal scale. Through synergetic use of optical and SAR data, we obtain a more complete mapping record enabling the delineation of also buried lakes. Our results for Antarctic Peninsula ice shelves reveal below average meltwater ponding during most of melting seasons 2015–2018 and above average meltwater ponding throughout summer 2019–2020 and early 2020–2021. Meltwater ponding on investigated East Antarctic ice shelves was far more variable with above average lake extents during most of melting seasons 2016–2019 and below average lake extents during 2020–2021. This study is the first to investigate relationships with climate drivers both, spatially and temporally including time lag analysis. The results indicate that supraglacial lake formation in 2015–2021 is coupled to the complex interplay of varying air temperature, solar radiation, snowmelt, wind and precipitation, each at different time lags and directions and with strong local to regional discrepancies, as revealed through pixel-based correlation analysis. Southern Hemisphere atmospheric modes as well as the local glaciological setting including melt-albedo feedbacks and the firn air content were revealed to strongly influence the spatio-temporal evolution of supraglacial lakes as well as below or above average meltwater ponding despite variations in the strength of forcing. Recent increases of Antarctic Peninsula surface ponding point towards a further reduction of the firn air content implying an increased risk for ponding and hydrofracture. In addition, lateral meltwater transport was observed over both Antarctic regions with similar implications for future ice shelf stability.

scholarly journals The flexural dynamics of melting ice shelves

2013 ◽  
Vol 54 (63) ◽  
pp. 1-10 ◽  
Author(s):  
Douglas R. MacAyeal ◽  
Olga V. Sergienko
Keyword(s):  
Surface Water ◽  
Antarctic Peninsula ◽  
Numerical Solutions ◽  
Water Mass ◽  
Gradual Increase ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
Mass Loads ◽  
The Antarctic

AbstractA conspicuous precursor of catastrophic ice-shelf break-up along the Antarctic Peninsula, reported widely in the literature, is the gradual increase in surface melting and consequent proliferation of supraglacial lakes and dolines. Here we present analytical and numerical solutions for the flexure stresses within an ice shelf covered by lakes and dolines, both isolated and arrayed. We conclude that surface water promotes ice-shelf instability in two ways: (1) by water-assisted crevasse penetration, as previously noted, and (2) by the inducement of strong tensile flexure stresses (exceeding background spreading stress by 10–100 times) in response to surface water mass loads and ‘hydrostatic rebound’ occurring when meltwater lakes drain.

scholarly journals Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

2020 ◽  
Author(s):  
Jennifer F. Arthur ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson ◽  
J. Rachel Carr ◽  
Amber A. Leeson
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
East Antarctica ◽  
Katabatic Wind ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Shelf Stability ◽  
Seasonal Evolution ◽  
Supraglacial Lakes ◽  
Area And Volume

Abstract. Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica’s northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m, and a mean total meltwater volume of 7.45 x 106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 per km2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below average seasonal (December-January-February, DJF) temperatures are associated with below average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability.

Evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

2020 ◽  
Author(s):  
Jennifer Arthur ◽  
Chris Stokes ◽  
Stewart Jamieson ◽  
Rachel Carr ◽  
Amber Leeson
Keyword(s):  
Climate Model ◽  
High Surface ◽  
Surface Melting ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Shelf Stability ◽  
Supraglacial Lakes ◽  
Surface Melt ◽  
The Impact

&lt;p&gt;Supraglacial lakes (SGLs) enhance surface melting and their development and subsequent drainage can flex and fracture ice shelves, leading to their disintegration. However, the seasonal evolution of SGLs and their potential influence on ice shelf stability in East Antarctica remains poorly understood, despite a number of potentially vulnerable ice shelves. Using optical satellite imagery, climate reanalysis data and surface melt predicted by a regional climate model, we provide the first multi-year analysis (1974-2019) of seasonal SGL evolution on Shackleton Ice Shelf in Queen Mary Land, which is Antarctica&amp;#8217;s northernmost remaining ice shelf. We mapped &gt;43,000 lakes on the ice shelf and &gt;5,000 lakes on grounded ice over the 45-year analysis period, some of which developed up to 12 km inland from the grounding line. Lakes clustered around the ice shelf grounding zone are strongly linked to the presence of blue ice and exposed rock, associated with an albedo-lowering melt-enhancing feedback. Lakes either drain supraglacially, refreeze at the end of the melt season, or shrink in-situ. Furthermore, we observe some relatively rapid (&amp;#8804; 7 days) lake drainage events and infer that some lakes may be draining by hydrofracture. Our observations suggest that enhanced surface meltwater could increase the vulnerability of East Antarctic ice shelves already preconditioned for hydrofracture, namely those experiencing high surface melt rates, firn air depletion, and extensional stress regimes with minimum topographic confinement. Our results could be used to constrain simulations of current melt conditions on the ice shelf and to investigate the impact of increased surface melting on future ice shelf stability.&lt;/p&gt;

Quantification of the Impact of Supraglacial Lakes and Slush on Surface Energy Balance of Ice Shelves

2020 ◽  
Author(s):  
Naomi Lefroy ◽  
Neil Arnold
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Mass Balance ◽  
Surface Energy Balance ◽  
Google Earth ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
Extra Energy ◽  
Energy Exchanges

&lt;p&gt;Despite the well-researched implications of SGL development and drainage for changes in mass balance and dynamics on Greenland, little is known about the role of energy absorption by lakes on Antarctica. Supraglacial lakes (SGLs) are prevalent features of Antarctic surface hydrology forming mainly on ice shelves (&lt;100 m a.s.l) and efficiently conveying atmospheric energy to the ice interior (Lenaerts et al., 2017; Bell et al., 2018). SGLs on Antarctic Ice Shelves are significant for mass balance given lower surface albedo and drainage-induced collapse of fringing ice shelves and consequent increased discharge from tributary outlet glaciers (Stokes et al., 2019).&lt;/p&gt;&lt;p&gt;There have been few efforts to quantify the energy exchanges between SGLs, atmosphere and ice to calculate their effects on glacier ablation (Law et al., 2018), although Miles et al. (2016) find that ponds on a debris-covered mountain glacier input large amounts of energy to underlying ice. Therefore, it is proposed that ice-sheet ponds also act as a significant energy exchange surface inputting large amounts of energy to the ice.&lt;/p&gt;&lt;p&gt;This study aims to code a computationally efficient surface energy balance model (SEB) in Google Earth Engine Editor to quantify how much extra energy is absorbed by SGLs at the during 2019 melt season. The most prolific surface melt is associated with the Antarctic Peninsula, but several East Antarctic ice shelves experience upwards of 60 days/yr of melting (Bell et al., 2018). Near-grounding line negative mass balance of the Nivlisen Ice Shelf (70 &lt;sup&gt;&amp;#8728;&lt;/sup&gt;S, 12 &lt;sup&gt;&amp;#8728;&lt;/sup&gt;E) in central Dronning Maud Land, East Antarctica, is sufficient to form SGLs and will be used to test SEB accuracy.&lt;/p&gt;&lt;p&gt;The one-dimensional numerical energy-balance SGL model GlacierLake, developed by Law et al. (2018), will be implemented in Google Earth Engine to code for surface energy exchanges. GlacierLake is most sensitive to the proportion of shortwave radiation absorbed at the surface which indicates that it is responsive to surface energy fluxes and is useful for the purposes of this study. A variety of methods, including NDWI and Principle Components Analysis, will be evaluated for use to classify lake and slush extents.&lt;/p&gt;&lt;p&gt;Given that it takes 3.4 x 10&lt;sup&gt;5&lt;/sup&gt; J/kg of latent heat to melt ice at 0 &amp;#176;C, the volume of liquid water on the Nivlisen ice shelf implies how much atmospheric energy has been transferred to the ice shelf. The modelled quantification of extra energy absorbed by lakes will be compared to the observed water volume on the Nivlisen Ice Shelf to test model accuracy.&lt;/p&gt;&lt;p&gt;Whilst this study will focus on the Nivlisen Ice Shelf, the SEB model may be applied at pan-Antarctic scales to calculate the ice-sheet wide extra energy absorbed by surface meltwater pooling. A precise quantification of the present impact of energy absorption by lakes on mass balance and dynamics provides a baseline to gauge how meltwater contribution could evolve under atmospheric warming.&lt;/p&gt;

scholarly journals Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

2020 ◽  
Vol 14 (11) ◽  
pp. 4103-4120 ◽  
Author(s):  
Jennifer F. Arthur ◽  
Chris R. Stokes ◽  
Stewart S. R. Jamieson ◽  
J. Rachel Carr ◽  
Amber A. Leeson
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
East Antarctica ◽  
Katabatic Wind ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Shelf Stability ◽  
Seasonal Evolution ◽  
Supraglacial Lakes ◽  
Area And Volume

Abstract. Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica's northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m and a mean total meltwater volume of 7.45×106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 km−2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below-average seasonal (December–January–February, DJF) temperatures are associated with below-average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high-magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic-wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability.

scholarly journals Treatment of ice-shelf evolution combining flow and flexure

2021 ◽  
pp. 1-18
Author(s):  
Douglas R. MacAyeal ◽  
Olga V. Sergienko ◽  
Alison F. Banwell ◽  
Grant J. Macdonald ◽  
Ian C. Willis ◽  
...  
Keyword(s):  
Longitudinal Deformation ◽  
Physical Processes ◽  
Ice Shelf ◽  
Plan View ◽  
Ice Shelves ◽  
Supraglacial Lakes ◽  
Plate Flexure ◽  
Shallow Stream ◽  
First Time ◽  
Shelf Flow

Abstract We develop a two-dimensional, plan-view formulation of ice-shelf flow and viscoelastic ice-shelf flexure. This formulation combines, for the first time, the shallow-shelf approximation for horizontal ice-shelf flow (and shallow-stream approximation for flow on lubricated beds such as where ice rises and rumples form), with the treatment of a thin-plate flexure. We demonstrate the treatment by performing two finite-element simulations: one of the relict pedestalled lake features that exist on some debris-covered ice shelves due to strong heterogeneity in surface ablation, and the other of ice rumpling in the grounding zone of an ice rise. The proposed treatment opens new venues to investigate physical processes that require coupling between the longitudinal deformation and vertical flexure, for instance, the effects of surface melting and supraglacial lakes on ice shelves, interactions with the sea swell, and many others.

Inter-annual variability in supraglacial lakes around East Antarctica

2021 ◽  
Author(s):  
Jennifer Arthur ◽  
Chris Stokes ◽  
Stewart Jamieson ◽  
Rachel Carr ◽  
Amber Leeson
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Flow Acceleration ◽  
Air Content ◽  
Supraglacial Lakes ◽  
Global Sea Level

&lt;p&gt;Surface meltwater ponding can weaken and trigger the rapid disintegration of Antarctic ice shelves which buttress the ice sheet, causing ice flow acceleration and global sea-level rise. While supraglacial lakes (SGLs) are relatively well documented during some years and selected ice shelves in Antarctica, we have little understanding of how Antarctic-wide SGL coverage varies between melt seasons. Here, we present a record of SGL evolution around the peak of the melt season on the East Antarctic Ice Sheet (EAIS) over seven consecutive years. Our findings are based on a threshold-based algorithm applied to 2175 Landsat 8 images during the month of January from 2014 to 2020. We find that EAIS-wide SGL volume fluctuates inter-annually by up to ~80%. Moreover, patterns within regions and on neighbouring ice shelves are not necessarily synchronous. Over the whole EAIS, total SGL volume was greatest in January 2017, dominated by the Amery and Roi Baudouin ice shelves, and lowest in January 2016. Excluding these two ice shelves, SGL volume peaked in January 2020. Preliminary results suggest EAIS-wide total SGL volume and extent are weakly correlated with firn model simulations of firn air content, surface melt and minimum ice lens depth predicted by the regional climate model MAR. On certain ice shelves, years with peak SGL volume correspond with minimum firn air content. This work provides important constraints for numerical ice-shelf and ice-sheet model predictions of future Antarctic surface meltwater distributions and the potential impact on ice-sheet stability and flow. &amp;#160;&lt;/p&gt;

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