Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica
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...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-11-01
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| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/11/2675/2017/tc-11-2675-2017.pdf |
| Summary: | 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, atmospheric-model 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<sup>−1</sup> 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<sup>−1</sup>, 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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| ISSN: | 1994-0416 1994-0424 |