Evolution of Derwael Ice Rise in Dronning Maud Land, Antarctica, over the last millennia

Drews, Reinhard; Matsuoka, Kenichi; Martín, Carlos; Callens, Denis; Bergeot, Nicolas; Pattyn, Frank

doi:10.1002/2014jf003246

Cited by 37 publications

(87 citation statements)

References 64 publications

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“…The data are geolocated with kinematic GNSS and migrated using Kirchoff depth migra- tion with a velocity-depth function that accounts for the low firn air content in this area. More details about acquisition and processing of the radar data are given in Drews et al (2015). We use the radar ice thickness to validate the hydrostatic ice thickness (Sect.…”

Section: On-site Geophysical Measurementsmentioning

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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Section: On-site Geophysical Measurementsmentioning

confidence: 99%

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

et al. 2017

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“…Such arches are clearly visible in the LF data between −2 and +3 km (Fig. 2a) and have been investigated by Drews and others (2015) to infer ice-rise evolution using a full Stokes model.…”

Section: The Forward Modelmentioning

confidence: 99%

Temporally stable surface mass balance asymmetry across an ice rise derived from radar internal reflection horizons through inverse modeling

et al. 2016

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ABSTRACT. Ice rises are locally grounded parts of Antarctic ice shelves that play an important role in regulating ice flow from the continent towards the ocean. Because they protrude out of the otherwise horizontal ice shelves, ice rises induce an orographic uplift of the atmospheric flow, resulting in an asymmetric distribution of the surface mass balance (SMB). Here, we combine younger and older internal reflection horizons (IRHs) from radar to quantify this distribution in time and space across Derwael Ice Rise (DIR), Dronning Maud Land, Antarctica. We employ two methods depending on the age of the IRHs, i.e. the shallow layer approximation for the younger IRHs near the surface and an optimization technique based on an ice flow model for the older IRHs. We identify an SMB ratio of 2.5 between the flanks and the ice divide with the SMB ranging between 300 and 750 kg m −2 a −1. The SMB maximum is located on the upwind side, ∼4 km offset to today's topographic divide. The large-scale asymmetry is consistently observed in time until 1966. The SMB from older IRHs is less-well constrained, but the asymmetry has likely persisted for >ka, indicating that DIR has been a stable features over long time spans.

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“…Errors in the firn-air content propagate approximately with a factor of 10 into the hydrostatic ice thickness, which then substantially alters the magnitude of derived basal melt rates. Using the same parameters as Drews et al (2015), we compare the WARR-derived ice thickness with the hydrostatic ice thickness for each site. We find a maximum deviation of 19 m for Site 2, and a minimum deviation of 4 m for Site 3 (Table 1).…”

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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Evolution of Derwael Ice Rise in Dronning Maud Land, Antarctica, over the last millennia

Cited by 37 publications

References 64 publications

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

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

Temporally stable surface mass balance asymmetry across an ice rise derived from radar internal reflection horizons through inverse modeling

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

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