Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

• Published in: Journal of Glaciology
• Main Authors: CHRISTIAN T. WILD, OLIVER J. MARSH, WOLFGANG RACK
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2017
• Subjects: glaciological model experiments; ice shelves; ice/ocean interactions; ice rheology; remote sensing; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Antarctic; McMurdo Ice Shelf; Antarc*; Ice Sheet; Ice Shelf; Ice Shelves; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2017.15; https://doaj.org/article/474d913df7674a67a1d3cdd65ce07cd9

Grounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements >35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.