If the ice is thick enough, ridging occurs, where the sea ice bends or fractures and piles on top of itself, forming ridges on the surface. If the motion is strong enough, rafting occurs, where thin sheets of ice slide over one another. A signature feature of pancake ice is raised edges or ridges on the perimeter, caused by ocean waves bumping the pancakes into each other. In rough ocean waters, the frazil crystals accumulate into slushy circular disks, called pancakes or pancake ice, because of their shape. Congelation ice crystals are long and vertical because they grow much slower than frazil ice. This bottom ice growth is called congelation ice. Ice continues growing when crystals grow directly on the bottom of the ice surface. As the ice thickens into a more stable sheet with a smooth bottom surface, frazil ice production ceases in the relatively still waters under the ice. Currents or light winds often push the nilas around so that they slide over each other, a process known as rafting. Initially, the sheet is very thin and dark (called dark nilas), becoming lighter as it thickens. Grease ice develops into a continuous, thin sheet of ice called nilas. In calm waters, frazil crystals form smooth, thin ice, called grease ice for its resemblance to an oil slick. Depending upon the climatic conditions, the ice formation process follows one of two paths. Sheets of sea ice form when frazil crystals float to the surface, accumulate and bond together. Because salt doesn't freeze, the crystals expel salt into the water, and frazil crystals consist of nearly pure fresh water. These crystals are typically 3 to 4 millimeters (0.12 to 0.16 inches) in diameter. Stages of ice formationĪs the ocean water begins to freeze, small needle-like ice crystals called frazil form. Furthermore, other factors cause sea ice formation to be a slow process. Generally, the top 100 to 150 meters (300 to 450 feet) of water must cool to the freezing point for sea ice to form. As a result, salt water sinks away from the surface before it cools enough to freeze. Secondly, in contrast to fresh water, the salt in ocean water causes the density of the water to increase as it nears the freezing point. First, the freezing temperature of salt water is lower than freshwater ocean temperatures must reach -1.8☌ (28.8☏) to freeze. Sea ice forms more slowly than freshwater for two main reasons. Lake ice tends to freeze as a smooth layer, while sea ice develops into various shapes because of the constant turbulence of ocean water. This sets it apart from other forms of ice like icebergs, glaciers, and lake ice, which form from fresh water or snow. Sea ice grows, forms, and melts strictly in salty ocean water. 13, 2012, in the Bellingshausen Sea with the Digital Mapping System (DMS) on board the NASA DC-8 flying laboratory. This complex mixture of different types of Antarctic sea ice was photographed on Oct. Multiyear ice is ice that has survived a summer melt season and is much thicker than younger ice, typically ranging from 2 to 4 meters (78.7 to 157.5 inches) thick.First-year ice is thicker than 30 centimeters (11.8 inches), but has not survived a summer melt season.gray-white ice (15 to 30 centimeters, or 5.9 to 11.8 inches thick).gray ice (10 to 15 centimeters, or 3.9 to 5.9 inches thick).Young ice is sometimes split into two subcategories, based on color: As the ice thickens, it enters the young ice stage, defined as ice that is 10 to 30 centimeters (3.9 to 11.8 inches) thick.New ice is a technical term that refers to ice less than 10 centimeters (3.9 inches) thick.The World Meteorological Organization (WMO) has defined the following categories: However, for some applications more detailed classification is used, such as for navigational purposes, where finer detail on the age and thickness of the sea ice is needed. A simple classification categorizes sea ice into two primary age groups: first-year or multiyear. Sea ice is classified by stages of development that relate to thickness and age. Exchange for Observations and Local Knowledge of the Arctic (ELOKA).
#Blue planet deep sea brine sea archive#
NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC).Greenland Today & Antarctic Ice Sheet Today.
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