On the link between surface and basal structures of the Jelbart Ice Shelf, Antarctica

Humbert, Angelika; Steinhage, Daniel; Helm, Veit; Hoerz, Sebastian; Berendt, Jacqueline; Leipprand, Elke; Christmann, Julia; Plate, Carolin; Müller, Ralf

doi:10.3189/2015jog15j023

Cited by 18 publications

(20 citation statements)

References 19 publications

(20 reference statements)

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“…4). Almost all ice shelf channels at RBIS are connected to the grounding line and may arise from water-filled subglacial conduits injecting subglacial melt water into the ice shelf cavity, driving a spatially localized buoyant melt water plume (Jenkins, 2011;Le Brocq et al, 2013;Drews et al, 2017;Sergienko, 2013). Such localized melting near the grounding zone has been previously observed on Pine Island Ice Shelf using similar methods as done here (Dutrieux et al, 2013).…”

Section: Discussionsupporting

confidence: 60%

Detailed response to the reviewes, modifications made on manuscript tc-2017-41 and new supplementary

Berger¹

2017

Preprint

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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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Section: Discussionsupporting

confidence: 60%

Detailed response to the reviewes, modifications made on manuscript tc-2017-41 and new supplementary

Berger¹

2017

Preprint

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“…The surface lowering of the elliptical surface depression is consistently observed over a 3-year time period marking this zone as dynamically active. Two other options are (i) a transient adjustment of the surface towards hydrostatic equilibrium (Humbert et al, 2015) as a response to some unknown event in the past which locally reduced the ice thickness, and (ii) the surface lowering may reflect vertical creeping of a liquid water body through the ice column. In any case, the surface lowering is restricted to a small area and the ice shelf channel farther downstream appears passive (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Although this is not a direct validation, as the field data cover a different period, the comparison is insightful to understand the spatial variability in our LBMB field. The derived LBMB is only valid in freely floating areas, which excludes not only the grounding zone but also other small-scale features such as ice shelf channels where viscous inflow can occur (Humbert et al, 2015;Drews, 2015). (Examples where this may be the case are discussed in Sect.…”

Section: Basal Mass Balance From Mass Conservationmentioning

confidence: 99%

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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“…The presence of basal channels beneath ice shelves and floating glacier tongues can be inferred from the presence of surface depressions seen in satellite imagery (Humbert et al, 2015;Alley et al, 2016). In some cases, surface topography can yield information about channel cross-sectional and plan morphology (Alley et al, 2016).…”

Section: Detection and Characterization Of Ice Shelf Basal Channels 2mentioning

confidence: 99%

“…In some cases, surface topography can yield information about channel cross-sectional and plan morphology (Alley et al, 2016). However, the degree to which surface topography echoes basal topography depends on many factors, including the time ice has had to adjust to the removal of mass from the base, bridging stresses in the ice and the pattern of surface accumulation of mass since the formation of the depression (Luckman et al, 2012;Humbert et al, 2015). Therefore, to obtain detailed and accurate information about the morphology and extent of basal channels beneath ice shelves, it is necessary to image the ice shelf base.…”

Section: Detection and Characterization Of Ice Shelf Basal Channels 2mentioning

confidence: 99%

Channelized Epishelf Lake Drainage Beneath the Milne Ice Shelf, Ellesmere Island, Nunavut

Rajewicz¹

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A depression running across the outer Milne Ice Shelf was hypothesized to overlie a basal channel incised by outflow from the Milne Fiord epishelf lake, a thick layer of freshwater impounded in the fiord by the ice shelf. Ice thickness mapping using ice-penetrating radar revealed the presence of a channel with incision heights of 39 to 45 m (70-80% of mean ice shelf thickness), basal widths of 57-86 m, and mean sidewall slopes of ~40° upward from horizontal. Profiles of salinity, temperature and current speed with depth showed there was a fast flowing jet of epishelf lake water in the channel, with velocities up to 60 cm s -1 , confirming the channel is a drainage outlet for the epishelf lake. The presence of the channel represents a significant structural weakness along which future breakup of the ice shelf is likely to occur.iii AcknowledgementsThis thesis has benefitted from many kinds and sources of support, for which I am extremely grateful.

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On the link between surface and basal structures of the Jelbart Ice Shelf, Antarctica

Cited by 18 publications

References 19 publications

Detailed response to the reviewes, modifications made on manuscript tc-2017-41 and new supplementary

Detailed response to the reviewes, modifications made on manuscript tc-2017-41 and new supplementary

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

Channelized Epishelf Lake Drainage Beneath the Milne Ice Shelf, Ellesmere Island, Nunavut

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