Numerical Modeling of Ocean Circulation and Ice Cover over the Continental Shelf

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  • 1 Department of Fisheries and Oceans, Physical and Chemical Sciences, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada
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Abstract

A six-level ocean model is coupled with Hibler's sea-ice model to examine oceanic roles in seasonal ice advance off the east coasts of continents. The model has the straight coast to the west and the steplike shelf break, along with three open boundaries to north, east and south. With dynamics simplified by a cross-shore geostrophic balance, the model describes processes such as wind-driven and buoyancy-driven flows, convective overturning, planetary Rossby waves and coastal-trapped waves. Nonlinear (advection–diffusion) equations for temperature and salinity are solved for heat and salt balances. The model is driven by idealized forcing: for example, alongshore wind stress, inflow through the northern boundary and parameterized cooling.

Several individual physical mechanisms are examined by the model; when cooling is applied, convective overturning transfers oceanic heat stored in the lower ocean to the surface layer and tends to reduce ice formation. An intense inflow over the shelf break through the northern boundary tends to merge shoreward, constraining the cold and fresh shelf water over the shelf. This shoreward flow has the significant baroclinic component that is supported by interactions between an alongshore density gradient, which is maintained by upwelling due to the shoreward flow, and the shelf break. The shoreward flow brings significant heat to the shelf region, canceling negative heat flux due to a southward flow over the shelf. Ice cover is insensitive to northerly wind stresses, which contribute southward ice advection (and southward ocean currents also) and reduce ice formation by shoreward Ekman flow carrying the warm offshore water.

Abstract

A six-level ocean model is coupled with Hibler's sea-ice model to examine oceanic roles in seasonal ice advance off the east coasts of continents. The model has the straight coast to the west and the steplike shelf break, along with three open boundaries to north, east and south. With dynamics simplified by a cross-shore geostrophic balance, the model describes processes such as wind-driven and buoyancy-driven flows, convective overturning, planetary Rossby waves and coastal-trapped waves. Nonlinear (advection–diffusion) equations for temperature and salinity are solved for heat and salt balances. The model is driven by idealized forcing: for example, alongshore wind stress, inflow through the northern boundary and parameterized cooling.

Several individual physical mechanisms are examined by the model; when cooling is applied, convective overturning transfers oceanic heat stored in the lower ocean to the surface layer and tends to reduce ice formation. An intense inflow over the shelf break through the northern boundary tends to merge shoreward, constraining the cold and fresh shelf water over the shelf. This shoreward flow has the significant baroclinic component that is supported by interactions between an alongshore density gradient, which is maintained by upwelling due to the shoreward flow, and the shelf break. The shoreward flow brings significant heat to the shelf region, canceling negative heat flux due to a southward flow over the shelf. Ice cover is insensitive to northerly wind stresses, which contribute southward ice advection (and southward ocean currents also) and reduce ice formation by shoreward Ekman flow carrying the warm offshore water.

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