potential impact from radiation heating not described by the model, as well as by
natural irregularities in the thickness of the ice cover.
One of the important features of ice formation in shallow waters is the stabilization of ice thickness caused by a substantial water salinity increase [3, 4]. The
calculations performed suggested that strong winter cooling maintains a very thin
under-ice brine layer (a few mm thick), in which water salinity reaches 800 psu
(Fig. 5b), corresponding to water freezing temperatures below −40 °C (Fig. 5c).
This makes the liquid in the under-ice layer similar to unfrozen water in the soil.
The presence of the thin brine layer theoretically prevents the consolidation of fast
ice with the bottom sediment layer, even at very low Arctic temperatures. This
finding does not contradict the results of laboratory experiments on ice adhesion in
salt water (see [7] for details). As follows from the simulations, the restraining effect
of the salinity increase reduces as bottom depths exceed 3 m; at depths greater than
3 m, this effect becomes insignificant.
Simulated heat fluxes through the ice (EH) demonstrate a clear tendency to
decrease from autumn through spring, resulting in the corresponding reduction in
ice growth rate for thick fast ice (Fig. 5d). In the second half of winter, temperature
at the lower ice interface becomes higher than at the upper one, due to an increase
of the air temperature (Fig. 3a). This temperature distribution suggests a change in
the direction of heat fluxes through the ice cover. Following Stefan’s condition (6b),
these heat fluxes result in ice melting despite continued negative air temperatures.
This effect is especially strong in the shallow water, where cooling of the brine layer
is more intense. In these zones, the fast ice will melt, while in the deeper parts of the
Gulf it will continue to grow at the same air temperatures.
The features of fast ice growth and salinization of the under-ice brine layer
determine the evolution of the mushy zone in the bottom sediment layer (Fig. 6).
The consequent decrease in water temperatures in winter leads to deeper freezing of
the soil, accompanied by a decrease in its moisture content. Simulations performed
with the model demonstrate the partial freezing of the upper layers of the soil
(Fig. 6). As expected, the layer of bottom sediments is frozen most rapidly and
deeply at the minimum depth (i.e., in the model experiment with 1-m bottom
depth). The contents of unfrozen liquid in the two-phase zone is strongly affected
by the depth of the basin (Fig. 6d). For instance, when bottom depth decreases from
3 to 1 m, the simulated water content equivalent of the two-phase zone decreases by
almost an order of magnitude (from ∼0.07 to ∼0.007). This decrease is explained
by a faster transition of liquid pore moisture into the solid state in the upper soil
layer at shallow depths.
According to the conditions of thermodynamic equilibrium, ice formation in the
layers of sea water and the bottom sediments begins simultaneously at all depths.
The rates of ice formation in these two layers vary considerably over time. For
example, if the highest growth rates of fast ice occur during the initial period of ice
formation, the fastest consolidation of the bottom sediment layer coincides with the
maximal development of unfrozen sub-ice brine layer (Fig. 6c).
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P. V. Bogorodskii et al.
natural irregularities in the thickness of the ice cover.
One of the important features of ice formation in shallow waters is the stabilization of ice thickness caused by a substantial water salinity increase [3, 4]. The
calculations performed suggested that strong winter cooling maintains a very thin
under-ice brine layer (a few mm thick), in which water salinity reaches 800 psu
(Fig. 5b), corresponding to water freezing temperatures below −40 °C (Fig. 5c).
This makes the liquid in the under-ice layer similar to unfrozen water in the soil.
The presence of the thin brine layer theoretically prevents the consolidation of fast
ice with the bottom sediment layer, even at very low Arctic temperatures. This
finding does not contradict the results of laboratory experiments on ice adhesion in
salt water (see [7] for details). As follows from the simulations, the restraining effect
of the salinity increase reduces as bottom depths exceed 3 m; at depths greater than
3 m, this effect becomes insignificant.
Simulated heat fluxes through the ice (EH) demonstrate a clear tendency to
decrease from autumn through spring, resulting in the corresponding reduction in
ice growth rate for thick fast ice (Fig. 5d). In the second half of winter, temperature
at the lower ice interface becomes higher than at the upper one, due to an increase
of the air temperature (Fig. 3a). This temperature distribution suggests a change in
the direction of heat fluxes through the ice cover. Following Stefan’s condition (6b),
these heat fluxes result in ice melting despite continued negative air temperatures.
This effect is especially strong in the shallow water, where cooling of the brine layer
is more intense. In these zones, the fast ice will melt, while in the deeper parts of the
Gulf it will continue to grow at the same air temperatures.
The features of fast ice growth and salinization of the under-ice brine layer
determine the evolution of the mushy zone in the bottom sediment layer (Fig. 6).
The consequent decrease in water temperatures in winter leads to deeper freezing of
the soil, accompanied by a decrease in its moisture content. Simulations performed
with the model demonstrate the partial freezing of the upper layers of the soil
(Fig. 6). As expected, the layer of bottom sediments is frozen most rapidly and
deeply at the minimum depth (i.e., in the model experiment with 1-m bottom
depth). The contents of unfrozen liquid in the two-phase zone is strongly affected
by the depth of the basin (Fig. 6d). For instance, when bottom depth decreases from
3 to 1 m, the simulated water content equivalent of the two-phase zone decreases by
almost an order of magnitude (from ∼0.07 to ∼0.007). This decrease is explained
by a faster transition of liquid pore moisture into the solid state in the upper soil
layer at shallow depths.
According to the conditions of thermodynamic equilibrium, ice formation in the
layers of sea water and the bottom sediments begins simultaneously at all depths.
The rates of ice formation in these two layers vary considerably over time. For
example, if the highest growth rates of fast ice occur during the initial period of ice
formation, the fastest consolidation of the bottom sediment layer coincides with the
maximal development of unfrozen sub-ice brine layer (Fig. 6c).
620
P. V. Bogorodskii et al.