Abstract
ABSTRACTTidal flexure in ice shelf grounding zones has been used extensively in the past to determine grounding line position and ice properties. Although the rheology of ice is viscoelastic at tidal loading frequencies, most modelling studies have assumed some form of linear elastic beam approximation to match observed flexure profiles. Here we use density, radar and DInSAR measurements in combination with full-Stokes viscoelastic modelling to investigate a range of additional controls on the flexure of the Southern McMurdo Ice Shelf. We find that inclusion of observed basal crevasses and density dependent ice stiffness can greatly alter the flexure profile and yet fitting a simple elastic beam model to that profile will still produce an excellent fit. Estimates of the effective Young's modulus derived by fitting flexure profiles are shown to vary by over 200% depending on whether these factors are included, even when the local thickness is well constrained. Conversely, estimates of the grounding line position are relatively insensitive to these considerations for the case of a steep bed slope in our study region. By fitting tidal amplitudes only, and ignoring phase information, elastic beam theory can provide a good fit to observations in a wide variety of situations. This should, however, not be taken as an indication that the underlying rheological assumptions are correct.
Highlights
The grounding zone, where ice transitions from grounded to freely floating, is a narrow but crucial portion of marine ice sheets
We use a nonlinear regression to fit an analytical elastic beam solution to our modelled flexure profiles in order to evaluate the performance of this technique and discuss what can be gained from such an exercise
The crevassed meshes used in this work are relatively crude they are a first step in assessing the importance of ice damage in this respect and we have the benefit of knowledge about crack spacing and frequency in this domain. It is unclear from the work presented here whether the basal crevasses on the Southern McMurdo Ice Shelf have formed due to the flexure itself, as a result of the shearing flow with the Ross Ice Shelf in this area or a combination of the two, there is no doubt that many other grounding zones will be crevassed and these effects should be considered relevant to most tidal flexure studies
Summary
The grounding zone, where ice transitions from grounded to freely floating, is a narrow but crucial portion of marine ice sheets. Ice in the grounding zone bends to accommodate the vertical motion of the adjoining ice shelf resulting from ocean tides. In the past this has typically been modelled as some form of elastic beam/plate equation (Holdsworth, 1969, 1977; Lingle and others, 1981; Smith, 1991; Vaughan, 1995; Schmeltz and others, 2002; Sykes and others, 2009; Sayag and Worster, 2011, 2013; Walker and others, 2013; Marsh and others, 2014; Hulbe and others, 2016). We question the validity of some of the approaches listed above
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