Basal crevasses and associated surface crevassing on the Larsen C ice shelf, Antarctica, and their role in ice-shelf instability

McGrath, Daniel; Steffen, Konrad; Scambos, Ted; Rajaram, Harihar; Casassa, Gino; Lagos, Jose Luis Rodriguez

doi:10.3189/2012aog60a005

Cited by 60 publications

(96 citation statements)

References 49 publications

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“…LAIS and LBIS both accelerated before collapsing (Bindschadler et al, 1994;Rignot et al, 2004), and LBIS apparently collapsed after weakening of the shear zones between ice flow units (Khazendar et al, 2007;Vieli et al, 2007;Glasser and Scambos, 2008). The shear zones in LCIS are less strongly sheared (Khazendar et al, 2011) and hence more stable, but the ice is already quite damaged (Jansen et al, 2010;McGrath et al, 2012;Borstad et al, 2013). The uncertainties in this interaction are large and we are unable to assess a timescale for this risk.…”

Section: Crevassing Weakens Shear Zonesmentioning

confidence: 86%

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

et al. 2015

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Abstract. The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr −1 ) is caused by both ice loss (0.28 ± 0.18 m yr −1 ) and firn-air loss (0.037 ± 0.026 m yr −1 ). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.

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Section: Crevassing Weakens Shear Zonesmentioning

confidence: 86%

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

et al. 2015

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“…Khazendar et al (2011) noted that rifts and other fractures were linked to large spatial variations in the inferred rheology of the shelf. Several recent studies of the ice shelf have observed basal crevasses along longitudinal transects of the shelf using ground-penetrating radar (McGrath et al, 2012;Luckman et al, 2012), indicating that basal crevasses are likely widespread on the ice shelf.…”

Section: Application To Larsen C Ice Shelfmentioning

confidence: 99%

“…Schoof, 2007), which has motivated a number of recent numerical studies of the relationship between ice shelf buttressing and grounding line stability for a marine ice sheet (Goldberg et al, 2009;Gagliardini et al, 2010;Favier et al, 2012;Gudmundsson, 2013). However, in spite of the widespread recognition of the importance of fractures for the flow and stability of ice shelves (e.g Jezek et al, 1985;Doake and Vaughan, 1991;Vaughan, 1993;van Der Veen, 1998a;Scambos et al, 2000;Kenneally and Hughes, 2004;Larour et al, 2004a;Glasser et al, 2009;Khazendar et al, 2009;Jansen et al, 2010;Albrecht and Levermann, 2012;Luckman et al, 2012;McGrath et al, 2012), little attention has been given to the impact of fractureinduced weakening on ice shelf buttressing.…”

Section: Introductionmentioning

confidence: 99%

Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

et al. 2013

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Abstract. Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds would increase by 25 % or more over an area the size of the former Larsen B ice shelf. Such a perturbation could potentially destabilize the northern part of Larsen C along pre-existing lines of weakness, highlighting the importance of the feedback between buttressing and fracturing in an ice shelf.

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“…1) (Luckman et al, 2012;McGrath et al, 2012;Jansen et al, 2013;Kulessa et al, 2014;McGrath et al, 2014). Surveys were carried out using antennas of different frequencies (25, 100, or 200 MHz) depending on the field campaign.…”

Section: Ground-penetrating Radarmentioning

confidence: 99%

Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica

et al. 2017

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Abstract. The surface mass balance (SMB) of the Larsen C ice shelf (LCIS), Antarctica, is poorly constrained due to a dearth of in situ observations. Combining several geophysical techniques, we reconstruct spatial and temporal patterns of SMB over the LCIS. Continuous time series of snow height (2.5-6 years) at five locations allow for multi-year estimates of seasonal and annual SMB over the LCIS. There is high interannual variability in SMB as well as spatial variability: in the north, SMB is 0.40 ± 0.06 to 0.41 ± 0.04 m w.e. year −1 , while farther south, SMB is up to 0.50 ± 0.05 m w.e. year −1 . This difference between north and south is corroborated by winter snow accumulation derived from an airborne radar survey from 2009, which showed an average snow thickness of 0.34 m w.e. north of 66 • S, and 0.40 m w.e. south of 68 • S. Analysis of ground-penetrating radar from several field campaigns allows for a longer-term perspective of spatial variations in SMB: a particularly strong and coherent reflection horizon below 25-44 m of waterequivalent ice and firn is observed in radargrams collected across the shelf. We propose that this horizon was formed synchronously across the ice shelf. Combining snow height observations, ground and airborne radar, and SMB output from a regional climate model yields a gridded estimate of SMB over the LCIS. It confirms that SMB increases from north to south, overprinted by a gradient of increasing SMB to the west, modulated in the west by föhn-induced sublimation. Previous observations show a strong decrease in firn air content toward the west, which we attribute to spatial patterns of melt, refreezing, and densification rather than SMB.

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Basal crevasses and associated surface crevassing on the Larsen C ice shelf, Antarctica, and their role in ice-shelf instability

Cited by 60 publications

References 49 publications

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica

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