Dynamical modelling of Kara Sea land-fast ice

Abstract

In this thesis land-fast ice is modelled based on the internal dynamics of sea ice. The region of interest is the Kara Sea, which has a well documented semi-permanent fast-ice cover. The Kara Sea fast ice is especially interesting because it forms over relatively deep waters compared to the maximum thickness of pressure ridges. This means that internal ice stresses must play an important role, in addition to the well-known grounding of pressure ridges. The main objective here is therefore to model the internal stresses of the ice well enough to reproduce the observed fast-ice cover. This has not been done successfully before. The model and methods developed here are general and should be applicable to other areas of fast-ice growth. In order to accurately model land-fast ice an improved version of the well-known viscous-plastic model is used. To produce a more physically realistic model material different yield curves are proposed while some numerical properties of the model are improved. The transition from plasticity to viscosity and the role of linear viscosity is also reconsidered. In an idealised stand-alone setup the model is used to investigate some general properties of polynya formation in the model. Coupling the ice model to an ocean model, realistic decadal simulations of the ice and ocean in the Kara Sea are then carried out testing some dynamic and thermodynamic properties of the model. Having thus confirmed that the model produces realistic results attempts are made to model land-fast ice. First the winter of 1997©-98 is considered in which various model parametrisations are tested and evaluated. Utilising the improved model and correct parametrisations the observed fast-ice cover can be reproduced during the height of the fast-ice season. After further tuning the fast-ice cover in 1967©-74 and 1997©-2005 could also be reproduced. The longer runs allow us to give an estimate of the minimum ice thickness required for fast ice to form over the deeper areas of the Kara Sea.