Elmer/Ice News

Relationship between age and depth at ice divides

isochronesIn Martìn and Gudmundsson (2012), effects of nonlinear rheology, temperature and anisotropy on the relationship between age and depth at ice divides is investigated using Elmer/Ice. 

Abstract: Ice flow in divide areas is strongly anisotropic. The evolution of ice fabric, from the onset of divide flow towards steady state with a fully developed fabric, has been shown to profoundly affect both the stratigraphy and surface topography of ice divides. Here, we investigate the effects of ice flow on the age-versus-depth relationship at ice divides by using a full Stokes thermomechanical model with a non-linear anisotropic constitutive relation between stress and strain rates. We compare our results with analytical approximations commonly employed in age–depth predictions, such as the Dansgaard and Lliboutry approximations. We show that these approximations systematically underestimate the age of ice at fully developed divides by as much as one order of magnitude. We also show that divides with fully developed fabric are ideal locations for ice-core extraction because ice under them can be up to one order of magnitude older than ice at the same depth at the flanks. In addition, these divides have a distinctive morphological structure that allows them to be clearly identified from satellite imagery or ground-penetrating radar data.

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Inverse method for sliding coefficients at Vestfonna ice cap

Comparison between modelled (left) and observed (right) surface velocities

In a recent publication in The Cryosphere Schäfer et al. use a Robin inverse method  to infer the basal  friction from the surface velocities observed in 1995 for the Vestfonna  ice cap on Svalbard. The results demonstrate that especially the ice caps on Nordaustlandet,  with their mixture of static central parts and fast moving outlet glaciers, demand the correct spatial distribution of sliding coefficients and that  - in lack of  a complete understanding of the physics taking place at the bedrock - inverse models for the time being are the only means to deliver that spatial distribution. Further investigations of  comparison of sliding  coefficients  obtained  for datasets taken at different times shall shed further light on the nature of the sliding underneath Vestfonna ice cap.

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