Surface melt and ponding on Larsen C Ice Shelf and the impact of föhn winds

Luckman, Adrian; Elvidge, Andrew D.; Jansen, Daniela; Kulessa, Bernd; Munneke, Peter Kuipers; King, John C.; Barrand, Nicholas E.

doi:10.1017/s0954102014000339

Cited by 118 publications

(178 citation statements)

References 60 publications

(94 reference statements)

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“…The threshold is close to the value of 3 dB, which has been successfully used in Radarsat and ERS [32,61]. Horizontally polarized σ 0 increases and decreases with snow depth in coarse-grained and fine-grained snowpacks, indicating a clear boundary between frozen percolation and dry snow radar zones.…”

Section: Discussionsupporting

confidence: 67%

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Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images

Zhou

Zheng

2017

Remote Sensing

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Surface snowmelt causes changes in mass and energy balance, and endangers the stabilities of the ice shelves in the Antarctic Peninsula (AP). The dynamic changes of the snow and ice conditions in the AP were observed by Sentinel-1 images with a spatial resolution of 40 m in this study. Snowmelt detected by the special sensor microwave/imager (SSM/I) is used to study the relationship between summer snowmelt and winter synthetic aperture radar (SAR) backscatter. Radar glacier zones (RGZs) classifications were conducted based on their differences in liquid snow content, snow grain size, and the relative elevations. We developed a practical method based on the simulations of a microwave scattering model to classify RGZs by using Sentinel-1 images in the AP. The summer snowmelt detected by SSM/I and Sentinel-1 data are compared between 2014 and 2015. The SSM/I-derived melting days is used to validate the winter dry snow line (DSL). RGZs derived from Sentinel-1 images suggest that snowmelt expanded from inland of the Larsen C Ice Shelf to the coastal area, whereas an opposite direction was found in the George VI Ice Shelf. The long melting season in the grounding zone of the Larsen C Ice Shelf may result from the adiabatically-dried föhn winds on the east side of the AP. As the uppermost limit of summer snowmelt, DSL was mapped based on the winter Sentinel-1 mosaic of the AP. Compared with the SSM/I-derived melting days, the winter DSL mainly distributed in the areas melted for one to three days in summer. DSL elevations on the Palmer Land increased from south to north.

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Section: Discussionsupporting

confidence: 67%

“…Föhn winds may explain the relatively long melting seasons in the western Larsen C Ice Shelf (Figures 6b and 8). Low relative humidity of the air mass makes snowmelt or sublimation easier due to the adiabatically-dried föhn winds on the east side of the AP, leading to its ponding and thinning [32,64].…”

Section: Discussionmentioning

confidence: 99%

Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images

Zhou

Zheng

2017

Remote Sensing

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“…A spatial correspondence between ice-shelf collapses and mean atmospheric temperature suggests that atmospheric warming may have pushed some ice shelves beyond a thermal limit of viability (Morris and Vaughan, 2003); the northern edge of LCIS is at this limit. Observations of LCIS firn-air thickness confirm that there is sufficient firn air available for compaction, that lower firn air spatially corresponds with higher melting, and that the northward-intensified surface lowering spatially corresponds to areas of high melting and firn compaction (Holland et al, 2011;Trusel et al, 2013;Luckman et al, 2014). Modelled firn compaction entirely offset the lowering in one study of -2008, albeit with a high uncertainty.…”

Section: Introductionmentioning

confidence: 86%

“…In particular, our surveys do not capture the rapid lowering in northern LCIS. Ice divergence may play a part in this, since the known acceleration of LCIS is northward-intensified (Haug et al, 2010;Khazendar et al, 2011), but there are also good reasons to expect changes in surface melting to be largest in the north (Holland et al, 2011;Trusel et al, 2013;Luckman et al, 2014). The pattern of changes in basal melting is unknown.…”

Section: Sources Of Changementioning

confidence: 99%

“…There are significant crevasse fields on LCIS, so we hypothesise that future increases in meltwater ponding could contribute to ice-shelf collapse. Currently, meltwater ponds form in limited areas near the LCIS grounding line (Holland et al, 2011;Luckman et al, 2014), but these do not pose an imminent risk of collapse. Before more extensive ponding can occur it is necessary for the firn to be depleted of its air content, since otherwise meltwater will simply percolate and refreeze.…”

Section: Meltwater-driven Crevassingmentioning

confidence: 99%

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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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Foehn winds link climate‐driven warming to ice shelf evolution in Antarctica

Cape

Vernet

Skvarca³

et al. 2015

JGR Atmospheres

143

172

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Rapid warming of the Antarctic Peninsula over the past several decades has led to extensive surface melting on its eastern side, and the disintegration of the Prince Gustav, Larsen A, and Larsen B ice shelves. The warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the Southern Annular Mode (SAM), which is thought to promote more frequent warm, dry, downsloping foehn winds along the lee, or eastern side, of the peninsula. We examined variability in foehn frequency and its relationship to temperature and patterns of synoptic-scale circulation using a multidecadal meteorological record from the Argentine station Matienzo, located between the Larsen A and B embayments. This record was further augmented with a network of six weather stations installed under the U.S. NSF LARsen Ice Shelf System, Antarctica, project. Significant warming was observed in all seasons at Matienzo, with the largest seasonal increase occurring in austral winter (+3.71 ∘ C between 1962-1972 and 1999-2010). Frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales. Surface temperature and foehn winds were also sensitive to climate variability, with both variables exhibiting strong, positive correlations with the SAM index. Concomitant positive trends in foehn frequency, temperature, and SAM are present during austral summer, with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves. These observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the Larsen B ice shelf.

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Surface melt and ponding on Larsen C Ice Shelf and the impact of föhn winds

Cited by 118 publications

References 60 publications

Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images

Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

Foehn winds link climate‐driven warming to ice shelf evolution in Antarctica

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