Physics of Sea Ice

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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. Motion * 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.

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