This image produced by Tom Agnew from the Canadian Meteorological Service uses the Advanced Microwave Scanning Radiometer (AMSR_E) data obtained from the National Snow and Ice Data Center (NSIDC). The images are in the standard sea ice polar stereographic 6.25 km grid and are colorized using both H and V polarization 89 Ghz channels. Sea ice shows up as various shades of grey and open ocean as blue. Each image is a snapshot of sea ice cover each day with the date shown in the lower part of each image.

What controls the evolution of the sea ice cover ?

The physics involved in the evolution of the sea ice cover is often schematically divided into thermodynamic processes and dynamic processes. The thermodynamic processes control melting, freezing and dissolving. Example of such processes are thermal conduction, brine convection and solar radiation absorption. Dynamic processes on the other hand control the motion and deformation of the ice cover and the redistribution of its thickness. Examples processes are air and ocean drag and ice rheology. In reality thermodynamics and dynamics are often intertwined and the distinction is often blurred. For example, regions of ice that are heavily ridged would have different freezing and melting rates than young thin ice (see for example [Tsamados2013] and ). A rheological formulation that results in more leads opening up could result in an increased formation of ice [Girard2011]. Of course sea ice is not decoupled from its environment and both dynamic and thermodynamic processes involve coupled interactions with the atmosphere and the ocean.

Can sea ice get stuck in narrow passages ? Can we model that ?

Hibler et al [Hibler2006] compared the aptitude of different rheologies (with cavitating fluid, sine wave, Mohr-Coulomb, sine-lens, square and elliptical yield curves) to reproduce the seasonal stoppage or reduction of ice flow through narrow passages (such as the ones in the figure above) which collectively constrain the Arctic sea-ice cover to an enclosed basin. The authors showed that the volume of ice exported through these "gates" is strongly rheology dependent. More precisely, rheologies that account for large cohesive strengths (the ability to sustain uniaxial stress) are also able to produce static arches that obstruct the ice flow. (Note that the question is still open whether the current visco-plastic sea ice model are able to reproduce realistically the arching phenomenon [Dumont2009, Losch2012]). In addition, Hibler showed that "even without cohesive strength, a large shear strength can reduce outflow through passages. If the ice pack has substantial shear strength that approaches cohesive strength, the mass flow through a passage displays a highly peaked character, with the flow peaking at some mean ice thickness and then decreasing as the thickness increases further. With a model that has true cohesive strength, as ice thickness increases the flow eventually totally stops".

A simple mass balance argument that illustrates the importance of the sea ice rheology

Hibler generalised this ideal analysis of one passage to combine it with thermodynamic effects and fluctuating wind fields in an Arctic basin dynamic–thermodynamic sea-ice model with multiple outlet passages. The results demonstrate that the capability for multiple flow states existing through passages depends on the initial conditions and general ‘climate’ state, and yield insight into the general parameter range over which the seasonal stoppage might irreversibly shift to an unconstrained outflow regime. The figure on the right shows that for the highly idealized case of a fixed spatially homogeneous ice thickness over the Arctic basin three equilibrium point emerge by equating the amount of ice that is formed due to ice growth and the amount of ice that is exported out of the Arctic basin. Point (1) and (3) are stable equilibrium points while point (2) is unstable. As the bell-shaped curve corresponding to the ice outflow is rheology dependent this simple argument illustrates that in order to predict the Arctic sea ice future equilibrium state its mechanical properties must be well understood.

Total outflow and basin-averaged growth rates for fixed spatially constant ice thicknesses and fixed wind forcing. The units of outflow are m2 s–1, and can be converted to m3 s–1 with a conversion factor of 42 000 m. The units of growth rate are m2 s–1 and have been normalized by 42 000 m.


[Tsamados2013] M. Tsamados, D. L. Feltham, and A. V. Wilchinsky, "Impact of a new anisotropic rheology on simulations of arctic sea ice," J. geophys. res. oceans, p. n/a--n/a, 2013.
author = {Tsamados, M. and Feltham, D. L. and Wilchinsky, A. V.},
title = {Impact of a new anisotropic rheology on simulations of Arctic sea
journal = {J. Geophys. Res. Oceans},
year = {2013},
pages = {n/a--n/a},
month = jan,
abstract = {A new rheology that explicitly accounts for the subcontinuum anisotropy
of the sea ice cover is implemented into the Los Alamos sea ice model.
This is in contrast to all models of sea ice included in global circulation
models that use an isotropic rheology. The model contains one new
prognostic variable, the local structure tensor, which quantifies
the degree of anisotropy of the sea ice, and two parameters that
set the time scale of the evolution of this tensor. The anisotropic
rheology provides a subcontinuum description of the mechanical behavior
of sea ice and accounts for a continuum scale stress with large shear
to compression ratio and tensile stress component. Results over the
Arctic of a stand-alone version of the model are presented and anisotropic
model sensitivity runs are compared with a reference elasto-visco-plastic
simulation. Under realistic forcing sea ice quickly becomes highly
anisotropic over large length scales, as is observed from satellite
imagery. The influence of the new rheology on the state and dynamics
of the sea ice cover is discussed. Our reference anisotropic run
reveals that the new rheology leads to a substantial change of the
spatial distribution of ice thickness and ice drift relative to the
reference standard visco-plastic isotropic run, with ice thickness
regionally increased by more than 1 m, and ice speed reduced by
up to 50%.},
file = {Tsamados2013.pdf:Tsamados2013.pdf:PDF},
issn = {2169-9291},
keywords = {sea ice, stress, anisotropy, arctic, model, rheology, 0750 Sea ice,
0798 Modeling, 0774 Dynamics, 8032 Rheology: general},
owner = {mct},
timestamp = {2013.01.30},
url = {}
[Girard2011] L. Girard, S. Bouillon, J. Weiss, D. Amitrano, T. Fichefet, and V. Legat, "A new modeling framework for sea-ice mechanics based on elasto-brittle rheology," Annals of glaciology, vol. 52, iss. 57, p. 123, 2011.
author = {Girard, L. and Bouillon, S. and Weiss, J. and Amitrano, D. and Fichefet,
T. and Legat, V.},
title = {A new modeling framework for sea-ice mechanics based on elasto-brittle
journal = {Annals of Glaciology},
year = {2011},
volume = {52},
pages = {123},
number = {57},
file = {Girard2011.pdf:Girard2011.pdf:PDF}
[Hibler2006] W. Hibler, J. Hutchings, and C. Ip, "Sea-ice arching and multiple flow states of arctic pack ice," Annals of glaciology, vol. 44, iss. 1, pp. 339-344, 2006.
author = {Hibler, WD and Hutchings, JK and Ip, CF},
title = {Sea-ice arching and multiple flow states of Arctic pack ice},
journal = {Annals of Glaciology},
year = {2006},
volume = {44},
pages = {339--344},
number = {1},
file = {Hibler2006.pdf:Hibler2006.pdf:PDF},
issn = {0260-3055},
publisher = {International Glaciological Society}
[Dumont2009] D. Dumont, Y. Gratton, and T. E. Arbetter, "Modeling the dynamics of the north water polynya ice bridge," Journal of physical oceanography, vol. 39, p. 1448, 2009.
author = {Dumont, D. and Gratton, Y. and Arbetter, T.E.},
title = {Modeling the Dynamics of the North Water Polynya Ice Bridge},
journal = {Journal of Physical Oceanography},
year = {2009},
volume = {39},
pages = {1448},
file = {Dumont2009.pdf:Dumont2009.pdf:PDF}
[Losch2012] M. Losch and S. Danilov, "On solving the momentum equations of dynamic sea ice models with implicit solvers and the elastic–viscous–plastic technique," Ocean modelling, vol. 41, pp. 42-52, 2012.
author = {Losch, Martin and Danilov, Sergey},
title = {On solving the momentum equations of dynamic sea ice models with
implicit solvers and the elastic–viscous–plastic technique},
journal = {Ocean Modelling},
year = {2012},
volume = {41},
pages = {42--52},
number = {0},
abstract = {Experiments with idealized geometry are used to compare model solutions
of implicit VP- and explicit EVP-solvers in two very different ice-ocean
codes: the regular-grid, finite-volume Massachusetts Institute of
Technology general circulation model (MITgcm) and the Alfred Wegener
Institute Finite Element Ocean Model (FEOM). It is demonstrated that
for both codes the obtained solutions of implicit VP-and EVP-solvers
can differ significantly, because the EVP solutions tend to have
smaller ice viscosities (“weaker” ice). EVP solutions tend to
converge only slowly to implicit VP solutions for very small sub-cycling
time steps. Variable resolution in the unstructured-grid model FEOM
also affects the solution as smaller grid cell size leads to smaller
viscosity in EVP solutions. Models with implicit VP-solvers can block
narrow straits under certain conditions, while EVP-models are found
to always allow flow as a consequence of lower viscosities.},
file = {Losch2012.pdf:Losch2012.pdf:PDF},
issn = {1463-5003},
keywords = {Numerical sea ice modeling, Viscous–plastic rheology, EVP, ICE stress},
owner = {mct},
timestamp = {2012.01.03},
url = {}