Ekström Ice Shelf, Antarctica

Thyssen, F.; Grosfeld, Klaus

doi:10.1017/s0260305500006510

Cited by 8 publications

(9 citation statements)

References 5 publications

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“…We would expect some kind of penetration, at least for the long-pulse datasets, if marine ice were present. (3) Thyssen and Grosfeld (1988) compared the RES-inferred ice thickness over the Ekström Ice Shelf to those inferred from a hydrostatic equilibrium and found no positive anomalies, therefore concluding that no accreted ice is present. Similarly, in an enhanced dataset of RES lines, Sandhäger and Blindow (2000) interpreted the bottom reflection from the Ekström Ice Shelf as the ice/ocean interface.…”

Section: Methodsmentioning

confidence: 93%

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Basal melting at the Ekström Ice Shelf, Antarctica, estimated from mass flux divergence

Neckel

Drews²,

Rack

et al. 2012

Ann. Glaciol.

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We characterize the basal mass balance of the Ekström Ice Shelf, Dronning Maud Land, Antarctica, using interferometrically derived surface velocities and ice thickness measurements from radio-echo sounding (RES). The surface velocities are based on data from European Remote-sensing Satellites-1 and -2 (ERS-1/2) during 1994–97. The ice thickness grid consists of 136 RES profiles acquired between 1996 and 2006. Mass fluxes are calculated along selected RES profiles where possible, to reduce uncertainties from ice thickness interpolation. Elsewhere large-scale mass fluxes are calculated using interpolated ice thickness data. Themass flux into the Ekström Ice Shelf from the main grounded drainage basins is estimated to be 3.19±0.4Gt a–1. The mass flux near the ice shelf front is 2.67±0.3Gt a–1. Assuming steady state, and based on the equation of continuity, we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting/refreezing. Using net snow accumulation rates from previous studies, we link the mass flux divergence in irregular-shaped polygons to processes beneath the ice shelf. The highest subglacial melt rates of ~1.1ma–1 are found near the grounding zone of two main inflow glaciers, and around the German station Neumayer III. The detection of unlikely refreezing in a small area ~15 km west of Neumayer III is attributed to both dataset inaccuracies and a (possibly past) violation of the steady-state assumption. In general, the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies.

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Section: Methodsmentioning

confidence: 93%

“…Snow accumulation estimates from snow pits and firn and ice-core drillings were interpolated to an accumulation map for western Dronning Maud Land by Rotschky and others (2007). Ice thickness has been measured using RES since the 1980s (Thyssen and Grosfeld, 1988). We used ice thickness measurements from 1996 to 2006 (Fig.…”

Section: Previous Studiesmentioning

confidence: 99%

Basal melting at the Ekström Ice Shelf, Antarctica, estimated from mass flux divergence

Neckel

Drews²,

Rack

et al. 2012

Ann. Glaciol.

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“…1). At the outset of the field program, only one airborne radio-echo profile existed close to the investigated area (Thyssen and Grosfeld, 1988), as well as some accumulation-rate and surface-elevation measurements obtained during several overland crossings in the previous 10years (Fütterer, 1987, 1988; Miller and Oerter, 1990). Together with a visible break of the surface slope at times of low-angle solar illumination, this allowed us to locate the approximate position of the grounding line during a first reconnaissance of the terrain.…”

Section: Field Datamentioning

confidence: 99%

Ice-dynamic conditions across the grounding zone, Ekströmisen, East Antarctica

Mayer

Huybrechts

1999

J. Glaciol.

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A detailed investigation was performed of ice-dynamic conditions across the southern grounding zone of Ekströmisen, at the mouth of a regular East Antarctic outlet glacier not characterized by ice-streaming. Accurate field measurements along a profile 20 km long served as input in a two-dimensional numerical ice-flow model in order to calculate the variation of stress, strain rate and velocity with depth. The model results point to a sharp transition between the mechanics of grounded and floating ice, with a transition zone of only a few km between the two. Vertical shear, most of it near the base, was found to be the dominant flow mechanism in grounded ice. This part is also characterized by a distinct succession of surface undulations which are in turn controlled by variations in resistive stresses at the bottom. The associated phase shift between driving stress and basal drag was found to be accommodated by differential longitudinal pushes and pulls at the base. The flow in the upper half of the profile, on the other hand, is extensive everywhere. The adjacent ice shelf is characterized by small stress and velocity gradients in both the vertical and horizontal directions of the vertical section, and therefore has little deformation. A derived longitudinal deviatoric normal stress of only one-tenth of the value required for freely floating ice shelves reflects a large back-stress originating from friction along the side-walls of the narrow embayment.

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“…Through hydrostatic balance, surface heights were derived from ice thicknesses (Bamber and Bentley, 1994), and ice thicknesses from surface heights (Vaughan and others, 1995), or geopotential models were locally evaluated by the hydrostatic balance requirement (Shabtaie and Bentley, 1987; Jenkins and Doake, 1991). Apparent violations of hydrostatic balance gave indications for grounding (Shabtaie and Bentley, 1987), for varying firn and ice structures (Budd and others, 1982; Bamber and Bentley, 1994), for sediments transported by the ice (Thyssen and Grosfeld, 1988) or for marine ice frozen to the shelf ice bottom (Thyssen, 1988; Jenkins and Doake, 1991).…”

Section: Introductionmentioning

confidence: 99%

Nivlisen, an Antarctic ice shelf in Dronning Maud Land: geodetic–glaciological results from a combined analysis of ice thickness, ice surface height and ice-flow observations

et al. 2006

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Extensive observations on Nivlisen, an ice shelf at Antarctica's Atlantic coast, are analysed and combined to achieve a new-quality description of its complex glaciological regime. We generate models of ice thickness (primarily from ground-penetrating radar), ellipsoidal ice surface height (primarily from ERS-1 satellite altimetry), freeboard height (by utilising precise sea surface information), and ice flow velocity (from ERS-1/2 SAR interferometry and GPS measurements). Accuracy assessments are included. Exploiting the hydrostatic equilibrium relation we infer the 'apparent air layer thickness' as a useful measure for a glacier's density deviation from a pure ice body. This parameter exhibits a distinct spatial variation (ranging from ≈ 2 m to ≈ 16 m) which we attribute to the transition from an ablation area to an accumulation area. We compute mass flux and mass balance parameters on a local and areally integrated scale. The combined effect of bottom mass balance and temporal change averaged over an essential part of Nivlisen is −654±170 kg m −2 a −1 which suggests bottom melting processes to dominate. We discuss our results in view of temporal ice mass changes (including remarks on historical observations), basal processes, near-surface processes, and ice-flow dynamical features. The question for temporal changes remains open from the data at hand, and we recommend further observations and analyses for its solution.

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Ekström Ice Shelf, Antarctica

Cited by 8 publications

References 5 publications

Basal melting at the Ekström Ice Shelf, Antarctica, estimated from mass flux divergence

Basal melting at the Ekström Ice Shelf, Antarctica, estimated from mass flux divergence

Ice-dynamic conditions across the grounding zone, Ekströmisen, East Antarctica

Nivlisen, an Antarctic ice shelf in Dronning Maud Land: geodetic–glaciological results from a combined analysis of ice thickness, ice surface height and ice-flow observations

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