Physics of Sea Ice

Physics of Sea Ice
Sea ice is frozen sea water. Salt ions in the water complicate the growth of ice crystals, and makes sea ice much more dynamic than freshwater ice. Sea ice covers nearly 7% of the Earth?s surface, has a huge effect on global climate, and is one of the largest, single biomes on Earth.

Ice is the solid, crystalline form of water, which solidifies at 0ºC. Roughly 9 polymorphs of ice are defined, only one, however, occurs naturally on Earth. This common form of ice is known as ice 1h, and its lattice displays six-fold rotational symmetry.The incorporation of sea salt or other ions in the crystal lattice of ice faces both size and charge restrictions, thus the salt and water do not form solid solution. This means that as the ice grows, the ions are rejected and most of them are returned to the water. Some, however, are retained within the ice matrix as liquid inclusions; creating a network of channels through with this brine travels.

The network of channels and associated brine inclusions greatly contribute to what makes sea ice different from freshwater ice. These inclusions change the deformational, thermal, and optical properties of ice; making sea ice unique in several different ways.

Growth of Sea Ice

The latent heat of freezing, or the enthalpy of freezing, for the phase transition from water to ice is 334J/g for pure water and just slightly lower for sea water.
The energy (heat) released from the freezing layer of water is conducted through the ice and released into the atmosphere.
The thermal properties of the ice and snow cover, as well as the energy balance at the top and bottom of the growing ice sheet determine the rate at which heat can be pushed out.
For an ice surface that is in thermal equilibrium with the atmosphere, conservation of energy mandates that the heat must flux in and out of the ice .
This can be expressed mathematically, and using calculus techniques the thickness to which an ice sheet can grow can be predicted for given surface temperature conditions.

Sea ice does not float freely on the polar oceans , but rather is moved around, tossed about, and deformed as a result of several forces which act on the ice pack.
As with many physical systems, the forces which act on sea ice can be easily defined, and expressed mathematically.
The sum of these forces result in motion of sea ice floes, and eventually collisions with other floes, producing deformation of the ice on the micro- and macro- levels.
The motion of sea ice causes floes to move around and collide with one another, but these ice floes can also be ripped apart, as seen in this photograph. Those are my bunny boot imprints there, and I assure you that crack was not there when I made those prints.
Another effect of collisions is the oh-so-hard to walk on rubble fields, the result of strong collisions that break up the ice and jumble the blocks up into fields before they freeze together.
Motion of sea ice has been observed to cause both collisions and rifting. These convergent and divergent regimes break and deform the ice on both the macro and micro scales. One of the major effects of these regimes is on ice thickness: thinning the ice at divergent zones and thickening it at the convergent zones. Ice thickness in turn as a great effect on heat flux in and out of the ice, as well as how long in the season a given area may or may not be ice free, and can thus have an effect on weather patterns.

In for a viscoelastic material such as ice, the stress σ can be related to the product of the strain ε and the Young?s modulus Y. Given by the equation σ= Yε
Sea ice, and natural ice in general, acts like a giant mirror on the surface of the Earth. The ice reflects a fraction of light back into space, a property known as the albedo of the ice. Not all of the light, however, is reflected. Some penetrates the surface, and is refracted within the crystal structure, and some makes it all the way through to the water column (a property of many minerals, known as birefringence). The high concentration of brine inclusions (and some sediment, too) in sea ice give its an opaque, vitreous appearance, giving sea ice a much higher albedo than freshwater ice.The high albedo of sea ice has a huge effect on the global climate, reflecting much of the solar radiation that bombards the Earth back into space.

Physics of Sea Ice 8.3 of 10 on the basis of 1287 Review.