Complex network of channels beneath an Antarctic ice shelf

Langley, Kirsty; Deschwanden, Angela von; Kohler, Jack; Sinisalo, Anna; Matsuoka, Kenichi; Hattermann, Tore; Humbert, Angelika; Nøst, Ole Anders; Isaksson, Elisabeth

doi:10.1002/2013gl058947

Cited by 44 publications

(45 citation statements)

References 41 publications

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“…In both cases, current understand-R. Drews: Evolution of ice-shelf channels ing suggests that the initial thickness perturbations near the grounding line are amplified farther downstream through a buoyancy-driven plume with enhanced basal melting within the channels. Channelized melting, with significantly higher melt rates inside than outside the channels, has been reported for Petermann Glacier Ice Shelf in Greenland (Rignot and Steffen, 2008;Dutrieux et al, 2014), and for Pine Island Ice Shelf (Vaughan et al, 2012;Mankoff et al, 2012;Stanton et al, 2013;Dutrieux et al, 2013Dutrieux et al, , 2014 and for Fimbul Ice Shelf (Langley et al, 2014) in Antarctica. Channels may weaken ice shelves structurally through crevasse formation (Vaughan et al, 2012), or by breaking up entirely (Rignot and Steffen, 2008).…”

Section: Introductionmentioning

confidence: 83%

Evolution of ice-shelf channels in Antarctic ice shelves

Drews

2015

The Cryosphere

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Abstract. Ice shelves buttress the continental ice flux and mediate ice-ocean interactions. They are often traversed by channels in which basal melting is enhanced, impacting iceshelf stability. Here, channel evolution is investigated using a transient, three-dimensional full Stokes model and geophysical data collected on the Roi Baudouin Ice Shelf (RBIS), Antarctica. The modeling confirms basal melting as a feasible mechanism for channel creation, although channels may also advect without melting for many tens of kilometers. Channels can be out of hydrostatic equilibrium depending on their width and the upstream melt history. Inverting surface elevation for ice thickness using hydrostatic equilibrium in those areas is erroneous, and corresponding observational evidence is presented at RBIS by comparing the hydrostatically inverted ice thickness with radar measurements. The model shows that channelized melting imprints the flow field characteristically, which can result in enhanced horizontal shearing across channels. This is exemplified for a channel at RBIS using observed surface velocities and opens up the possibility to classify channelized melting from space, an important step towards incorporating these effects in ice-ocean models.

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Section: Introductionmentioning

confidence: 83%

Evolution of ice-shelf channels in Antarctic ice shelves

Drews

2015

The Cryosphere

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“…Consequently, we do not capture their spatial (and temporal) variations on the length scales associated with ice shelf channels. Both Drews et al (2016) and Langley et al (2014) found evidence in the shallow radar stratigraphy that the SMB may be locally elevated in those areas, potentially reflecting the deposition of drifting snow at the bottom of surface slopes (Frezzotti et al, 2007). If this holds true, then the systematic underestimation of the SMB would result in a positive bias of the LBMB in those areas.…”

Section: Surface Mass Balancementioning

confidence: 95%

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

et al. 2017

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Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique -based on satellite observations -to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmosphericmodel surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from −14.7 to 8.6 m a −1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a −1 , which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

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“…(i) Bridging stresses can prevent full relaxation to hydrostatic equilibrium (Drews, 2015), and (ii) it may not account for small-scale variations in material density. Evidence for small-scale changes in density was suggested by Langley et al (2014) and Drews (2015), who found that the surface mass balance can be elevated locally within the concave surface associated with ice-shelf channels, which in turn may impact the local densification processes. Atmospheric models typically operate with a horizontal gridding coarser than 5 km (Lenaerts et al, 2014) and cannot resolve such small-scale variations in surface mass balance and density.…”

Section: R Drews Et Al: Density From Wide-angle Radarmentioning

confidence: 98%

“…If this holds true, the increased density observed in the WARR data close to the ice-shelf front is an inherited feature from farther upstream. The channel's surface depressions likely also cause a locally increased surface mass balance (Langley et al, 2014), and in general ice-shelf channels can have a particular strain regime . Both of these factors may also influence the firn densification rate, but given our limited data coverage we refrain from an in-depth analysis here.…”

Section: Radar-and Optv-inferred Densitiesmentioning

confidence: 99%

Constraining variable density of ice shelves using wide-angle radar measurements

Drews

Brown²,

Matsuoka

et al. 2016

The Cryosphere

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Abstract. The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium, for which knowledge of the depthaveraged density is essential. The densification from snow to ice depends on a number of local factors (e.g., temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar data sets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. We reconstruct depth to internal reflectors, local ice thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depthdensity relationship. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggest that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic ice thickness calculations used for determining basal melt rates should account for the denser firn in ice-shelf channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

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Complex network of channels beneath an Antarctic ice shelf

Cited by 44 publications

References 41 publications

Evolution of ice-shelf channels in Antarctic ice shelves

Evolution of ice-shelf channels in Antarctic ice shelves

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

Constraining variable density of ice shelves using wide-angle radar measurements

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