Preprints
https://doi.org/10.5194/tc-2020-303
https://doi.org/10.5194/tc-2020-303

  19 Oct 2020

19 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal TC.

Linking sea ice deformation to ice thickness redistribution using high-resolution satellite and airborne observations

Luisa von Albedyll1, Christian Haas1,2, and Wolfgang Dierking1,3 Luisa von Albedyll et al.
  • 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27570 Bremerhaven, Germany
  • 2University of Bremen, 28359 Bremen, Germany
  • 3Arctic University of Norway, 9019 Tromsø, Norway

Abstract. An unusual, large polynya opened and then closed by freezing and convergence north of the coast of Greenland in late winter 2018. The closing corresponded to a natural, but well-constrained, full-scale ice deformation experiment. We have observed the closing of and deformation within the polynya with satellite synthetic-aperture radar (SAR) imagery, and measured the accumulated effects of dynamic and thermodynamic ice growth 5 with an airborne electromagnetic (AEM) ice thickness survey one month after the closing began. During that time strong ice convergence decreased the area of the former polynya by a factor of 2.5. The AEM survey showed mean and modal thicknesses of the one-month old ice of 1.96 ± 1.5 m and 0.95 m, respectively.We show that this is in close agreement with the modeled thermodynamic growth and with the dynamic thickening expected from the polynya area decrease during that time. In addition,we found characteristic differences in the shapes of ice thickness distributions in different regions of the closing polynya. These closely corresponded to different deformation histories of the surveyed ice that were derived from the high-resolution SAR imagery by drift tracking along Lagrangian backward trajectories. Results show a linear proportionality between convergence and thickness change that agrees well with ice thickness redistribution theory. In addition, the e-folding of the tails of the different ice thickness distributions is proportional to the magnitude of the total deformation experienced by the ice. Lastly, we developed a simple volume-conserving model to derive dynamic ice thickness change from high-resolution SAR deformation tracking. The model has a spatial resolution of 1.4 km and reconstructs thickness profiles in reasonable agreement with the AEM observations. The computed ice thickness distribution resembles main characteristics like mode, e-folding, and width of the observed distribution. This demonstrates that high-resolution SAR deformation observations are capable of producing realistic ice thickness distributions. The MYI surrounding the polynya had a mean and modal total thickness (snow + ice) of 2.1 ± 1.4 m and 2.0 m, respectively. The similar first- and multi-year ice mean thicknesses elude to the large amount of deformation experienced by the closing polynya.

Luisa von Albedyll et al.

 
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Luisa von Albedyll et al.

Luisa von Albedyll et al.

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Short summary
Convergent sea ice motion is important in producing a thick ice cover through ridging. The existing redistribution theory linking sea ice deformation and thickness change is not well constrained by observations. We studied sea ice deformation derived from high-resolution satellite imagery and related it to thickness change. We found that deformation is capable of explaining the observed dynamic thickness change and to produce realistic ice thickness distributions under some general assumptions.