Sea ice

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Sea ice

Sea ice is formed from ocean water that freezes. Because the ocean

Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
s consist of saltwater, this occurs at about -1.8 °C

Celsius

Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death....
(28.8 °F

Fahrenheit

Fahrenheit is a temperature scale named after the physicist Daniel Gabriel Fahrenheit , who proposed it in 1724. Today, the scale has largely been replaced by the Celsius scale; it is still in use for non-scientific purposes in the United States and a few other countries such as Belize....
).

Sea ice may be contrasted with iceberg

Iceberg

An iceberg is a large piece of freshwater ice that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice or come to rest on the seabed in shallower water, causing ice scour....
s, which are chunks of ice shelves

Ice shelf

An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface....
or glacier

Glacier

A glacier is a large, slow-moving mass of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity and high pressure....
s that calve into the ocean. Icebergs are compacted snow and hence fresh water

Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve....
.

Sea ice may be deliberately created or manipulated, see Arctic geoengineering

Arctic geoengineering

Temperatures in the Arctic region have tended to increase more rapidly than the global average, and the effects of global warming on the region have been generally well represented in climate models....
for details.
-fast ice, or simply fast ice

Fast ice

Fast ice is sea ice that has frozen along coasts along the shoals, or to the sea floor over shallow parts of the continental shelf, and extends out from land into sea....
, is sea ice that has frozen along coasts ("fastened" to them) or to the sea floor over shallow parts of the continental shelf

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during Ice age such as the current epoch by relatively shallow seas and Bay....
, and extends out from land into sea.

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Encyclopedia

Sea ice is formed from ocean water that freezes. Because the ocean

Ocean

Celsius

Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death....
(28.8 °F

Fahrenheit

Iceberg

Ice shelf

An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface....
or glacier

Glacier

Fresh Water

Arctic geoengineering

Types of sea ice

Land-fast ice, or simply fast ice

Fast ice

Continental shelf

Drift ice

Drift ice is ice that floats on the surface of the water in cold regions, as opposed to fast ice, which is attached to a shore. Usually drift ice is carried along by winds and sea currents, hence its name, "drift ice"....
consists of ice that floats on the surface of the water, as distinguished from the fast ice, attached to coasts. When packed together in large masses, drift ice is called pack ice. Pack ice may be either freely floating or blocked by fast ice while drifting past.

The most important areas of pack ice are the polar ice packs

Polar ice packs

Seawater

Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%, or 35 parts per thousand . This means that every 1 kg of seawater has approximately 35 grams of sea salt ....
in the Earth's polar region

Polar region

Earth polar regions are the areas of the globe surrounding the geographical pole also known as Geographical zone. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica....
s: the Arctic ice pack of the Arctic Ocean

Arctic Ocean

The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic North Pole region, is the smallest and shallowest of the world's five major oceanic divisions....
and the Antarctic ice pack of the Southern Ocean

Southern Ocean

The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean south of 60th parallel south latitude....
. Polar packs significantly change their size during seasonal changes of the year. Because of vast amounts of water added to or removed from the oceans and atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
, the behavior of polar ice packs have a significant impact of the global changes in climate

Climate

Climate encompasses the temperatures, humidity, atmospheric pressure, winds, rainfall, atmospheric particle count and numerous other Meteorology elements in a given region over long periods of time, as opposed to the term weather, which refers to current activity of these same elements....
, see "Polar ice packs

Polar ice packs

Polar ice packs are large areas of pack ice formed from seawater in the Earth's polar regions, known as polar ice caps: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean, fringing the Antarctic ice sheet....
" for details.

An ice floe is a floating chunk of ice that is less than 10 kilometers (six miles) in its greatest dimension. Wider chunks of ice are called ice fields.

Formation of sea ice

Only the top layer of water needs to cool to the freezing point. Convection of the surface layer involves the top 100–150 m, down to the pycnocline

Pycnocline

A pycnocline is a rapid change in water density with water column. In freshwater environments such as lakes this density change is primarily caused by water temperature, while in seawater environments such as oceans the density change may be caused by changes in water temperature and/or salinity....
of increased density.

In calm water, the first sea ice to form on the surface is a skim of separate crystals which initially are in the form of tiny discs, floating flat on the surface and of diameter less than 2-3 mm. Each disc has its c-axis vertical and grows outwards laterally. At a certain point such a disc shape becomes unstable, and the growing isolated crystals take on a hexagonal, stellar form, with long fragile arms stretching out over the surface. These crystals also have their c-axis vertical. The dendritic arms are very fragile, and soon break off, leaving a mixture of discs and arm fragments. With any kind of turbulence in the water, these fragments break up further into random-shaped small crystals which form a suspension of increasing density in the surface water, an ice type called frazil or grease ice
Frazil ice

Frazil ice is a collection of loose, randomly oriented needle-shaped ice crystals in water. It resembles slush and has the appearance of being slightly oily when seen on the surface of water....
. In quiet conditions the frazil crystals soon freeze together to form a continuous thin sheet of young ice; in its early stages, when it is still transparent, it is called nilas. When only a few centimetres thick this is transparent (dark nilas) but as the ice grows thicker the nilas takes on a grey and finally a white appearance. Once nilas has formed, a quite different growth process occurs, in which water molecules freeze on to the bottom of the existing ice sheet, a process called congelation growth. This growth process yields first-year ice, which in a single season may reach a thickness of 1.5–2 m.

In rough water, fresh sea ice is formed by the cooling of the ocean as heat is lost into the atmosphere. The uppermost layer of the ocean is supercooled
Supercooling

Supercooling is the process of lowering the temperature of a liquid or a gas below its melting point, without it becoming a solid.A liquid below its standard freezing point will crystallization process in the presence of a nucleation around which a crystal structure can form....
to slightly below the freezing point, at which time tiny ice platelets, known as frazil ice, form. As more frazil ice forms, the ice forms a mushy surface layer, known as grease ice
Grease ice

Grease ice is a very thin, soupy layer of frazil ice crystals clumped together, which makes the ocean surface resemble an oil slick. This ice is the second stage in the formation of solid sea ice after ice floes and then frazil ice....
. Frazil ice formation may also be started by snow
Snow

Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of this precipitation is called snowfall....
fall, rather than supercooling.

Slush

Slush can mean any of the following:* Slush — a slurry mixture of liquid and solid forms of water.* Slush — a pejorative and slang combination of the likewise derogatory terms slut and lush....
is a floating mass formed initially from snow

Snow

Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of this precipitation is called snowfall....
and water. Shuga is formed in agitated conditions by accumulation of slush or grease ice into spongy pieces several inches in size.

Waves and wind then act to compress these ice particles into larger plates, of several metres in diameter, called pancake ice
Pancake ice

Pancake ice is a form of ice that consists of round pieces of ice with diameters ranging from a few inches to many feet in diameter, depending on the local conditions that affect ice formation....
. These float on the ocean surface, and collide with one another, forming upturned edges. In time, the pancake ice plates may themselves be rafted over one another or frozen together into a more solid ice cover, known as consolidated ice pancake ice. Such ice has a very rough appearance on top and bottom.

The sea ice is largely fresh, since the ocean salt is expelled from the forming and consolidating ice by a process called brine rejection. The resulting highly saline (and hence dense) water is an important influence on the ocean overturning circulation.

Russian scientist Vladimir Yulyevitch Vize

Vladimir Wiese

Professor Vladimir Yulyevitch Vize , was a Russian scientist History of Germans in Russia and the Soviet Union who devoted his life to the study of the Arctic Sea ice....
(1886 - 1954) devoted his life to study the Arctic ice pack and developed the Scientific Prediction of Ice Conditions Theory, for which he was widely acclaimed in academic circles. He applied this theory in the field in the Kara Sea

Kara Sea

The Kara Sea is part of the Arctic Ocean north of Siberia. It is separated from the Barents Sea to the west by the Kara Strait and Novaya Zemlya, and the Laptev Sea to the east by the Severnaya Zemlya....
, which led to the discovery of Vize Island

Vize Island

Vize Island or Wiese Island is an isolated island located in the Arctic Ocean at the northern end of the Kara Sea, roughly midway between Franz Josef Land and Severnaya Zemlya, its latitude is 79? 30' N and its longitude 76? 54' E....
.

Ecology

Sea ice is part of the Earth's biosphere

Biosphere

The biosphere is the global sum of all ecosystems. From the broadest Geophysiology point of view, the biosphere is the global ecology system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and Earth's atmosphere....
. Solid sea ice is permeated with channels filled with salty brine. These briny channels and the sea ice itself have its ecology, referred to as "sympagic ecology".

The decline of seasonal sea ice is putting the survival of Arctic species such as ringed seal

Ringed Seal

The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the northern coasts....
s and polar bear

Polar Bear

The polar bear is a bear native to the Arctic Ocean and its surrounding seas. The world's largest carnivore found on land, and shares the title of largest land predator with the Kodiak Bear, an adult male weighs around , while an adult female is about half that size....
s at risk.

External links

Chapter from Nathaniel Bowditch
Nathaniel Bowditch

Nathaniel Bowditch was an early American mathematician remembered for his work on ocean navigation. He is often credited as the founder of modern maritime navigation; his book American Practical Navigator, first published in 1802, is still carried onboard every commissioned U.S....
's American Practical Navigator
.
(North Pole webcam view)

Sea ice

Types of sea ice

Formation of sea ice

Ecology

See also

External links