Satellite image of Fennoscandia in winter. The Gulf of Bothnia and White Sea are covered with sea ice.

Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C (28.8 °F).

Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Icebergs are compacted snow and hence are fresh water from the beginning; sea ice loses its salt during its process of formation from sea water and thus eventually is fresh as well.

Types of sea ice[link]

Pancake ice is sea ice that has been compressed by the action of waves on frazil ice. Plates are typically 1 - 3 meters across.

Land-fast ice, or simply fast ice, is sea ice that has frozen along coasts ("fastened" to them) or to the sea floor over shallow parts of the continental shelf, and extends out from land into sea. Unlike drift ice, it does not move with currents and wind.

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.

Pancake ice is sea ice broken into small round chunks looking like pancakes.

The most important areas of pack ice are the polar ice packs formed from seawater in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. 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, the polar ice packs experience a significant impact from global changes in climate; see "Polar ice packs" 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[link]

Satellite image of sea ice forming near St. Matthew Island in the Bering Sea.

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 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. 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 centimeters 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 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. Frazil ice formation may also be started by snowfall, rather than supercooling.

Slush is a floating mass formed initially from snow 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 meters in diameter, called pancake ice. 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.

Sea ice is largely fresh, since a lot of the ocean salt is expelled during ice formation. The resulting ice is riddled with minute brine-filled channels and consequently is still salty (about 1% salt, compared with about 3.5% salt in the ocean).^[1] The expelled brine has an important bearing on the ocean circulation.

If sufficient snow falls on sea ice to depress the freeboard below sea level, sea water will flow in and a layer of ice will form of mixed snow/sea water. This is particularly common around Antarctica.

Russian scientist Vladimir Vize (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, which led to the discovery of Vize Island.

Yearly freeze and melt cycle[link]

Seasonal variation and annual decrease of Arctic sea ice volume as estimated by measurement backed numerical modelling.^[2]

Sea ice freezes and melts due to a combination of factors, including the age of the ice, air temperatures, and solar insolation. During the winter the area of the Arctic Ocean covered by sea ice increases, usually reaching a maximum extent during the month of March. The area covered in sea ice then decreases, reaching its minimum extent in September most years. First-year ice melts more easily than older ice for two reasons: 1) First-year ice is thinner than older ice, since the process of congelation growth has had less time to operate; and 2) first-year ice is less permeable than older ice, so summer meltwater tends to form deeper ponds on the first-year ice surface than on older ice, and deeper ponds mean lower albedo and thus greater solar energy capture.

Monitoring and observations[link]

Satellite data has allowed the tracking of sea ice extents since 1978. During the warmest years, like the winter of 2005-2006, sea ice is observed to reach a winter maximum extent that is smaller than in the years before or after. The summer minimum Arctic ice extent for 2010 was the third lowest over the period of satellite observations of the polar ice. The minimum record summer Arctic sea ice extent was in 2007.^[3]

Ecology[link]

Sea ice is part of the Earth's biosphere. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the Bald notothen, fed upon in turn by larger animals such as Emperor penguins and Minke whales.^[4]

The decline of seasonal sea ice is putting the survival of Arctic species such as ringed seals and polar bears at risk.^[5][6][7]

• 

  Change in extent of the Arctic Sea ice between March and September.

• 

  Sea ice off Baffin Island.

• 

  Sea ice imitates the shoreline along the Kamchatka Peninsula.

• 

  Clear view of the Antarctic Peninsula, the Larsen Ice Shelf, and the sea ice covered waters around the region.

See also[link]

Wikimedia Commons has media related to: Sea ice

• Arctic sea ice ecology and history
• Arctic shrinkage
• Drift ice station
• Drift station
• Ice class
• Ice pier
• Ice shelf
• Measurement of sea ice
• Polynya
• Sea ice concentration
• Sea ice growth processes
• Vladimir Wiese
• Zhubov scale

References[link]

• Rothrock, D.A. and J. Zhang (2005). "Arctic Ocean Sea Ice Volume: What Explains Its Recent Depletion?". J. Geophys. Res. 110 (C1): C01002. Bibcode 2005JGRC..11001002R. DOI:10.1029/2004JC002282. 
• "How Does Arctic Sea Ice Form and Decay?". NOAA Arctic theme page. http://www.arctic.noaa.gov/essay_wadhams.html. Retrieved April 25, 2005. 
• "NSIDC Sea ice". All About Sea Ice. http://nsidc.org/seaice/. Retrieved October 6, 2005. 
• Konstantin Y. Vinnikov, Donald J. Cavalieri, and Claire L. Parkinson, V33, L05704, A model assessment of satellite observed trends in polar sea ice extents.

External links[link]

• NOAA Arctic theme page
• Ice in the Sea Chapter from Nathaniel Bowditch's American Practical Navigator
• Cryosphere Today: Current Arctic sea ice conditions
• Data source for sea ice picture
• Marine Modeling and Analysis Branch
• Everything you ever wanted to know about sea ice but were afraid to ask
• NSIDC Sea Ice Index
• Global Sea Ice Extent and Concentration: What sensors on satellites are telling us about sea ice
• BBC News, 28 September 2005, "Arctic ice 'disappearing quickly'"
• German remote-sensing sea ice group including high-resolution ice maps.
• Video that depicts the formation of sea ice in the Baltic sea
• The Arctic ice sheet True color satellite map with daily updates.

The sea at La Jolla, California in the Gulf of Catalina

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean.^[1] It is also used sometimes to describe a large saline lake that lacks a natural outlet, such as the Caspian Sea.

Arctic (belonging to the Arctic Ocean) and Antarctic (Southern Ocean) seas, as well as some other seas freeze in winter. This occurs below the freezing point of pure water, at about -1.8 °C (28.8 °F). Frozen salt water becomes sea ice.^[2]

History[link]

Phoenician (yellow) and Greek (red) colonies in the Mediterranean in the 1st millennium BC

Humans navigated seas from antiquity. Ancient Egyptians and Phoenicians navigated the Mediterranean Sea and the Red Sea. Hannu was the first see explorer of whom there is any information. He sailed along the Red Sea and further to the Arabian Peninsula and the African Coast around 2750 BC.^[3] In the 1st millennium BC, Phoenicians and Greeks established colonies all over the Mediterranean, including its outlets like the Black Sea. The seas along the eastern and the southern Asian coast were used by Arabs and Chinese for navigation, and the North Sea and the Baltic Sea were known to Europeans in Roman times. Other seas were not used for navigation in the antiquity and were actually discovered.

The White Sea was known to Novgorodians and used for navigation since not later that the 13th century.^[4] Pomors, living at the White Sea coast, also sailed to Svalbard, but the Barents Sea got its name later, due to the 16th century Dutch expedition headed by Willem Barentsz. Other seas in Arctic Russia were explored in connection with the search of the Northern Sea Route. In the first half of the 17th century the Kara Sea was already used on a regular basis for navigation between the city of Arkhangelsk and the mouth of the Ob River and upstream to the city of Mangazeya (Mangazeya Trade Route) and to the mouth of the Yenisei River (Yenisey Trade Route).^[5] In 1648, Semyon Dezhnev led an expedition down the Kolyma River, around the cape now known as Cape Dezhnev, and to the mouth of the Anadyr River.^[6] By the end of the 17th century, the seas along what is now Arctic and Pacific coasts of Russia were already discovered, although the systematic description and reliable mapping of the coast line only started in the 18th century, and the geographical locations of all islands were only established in the first half of the 20th century, when aviation was employed.

List of seas[link]

[edit] Atlantic Ocean

[edit] Mediterranean Sea

Aegean Sea Mirtoon Sea Sea of Crete Thracian Sea Adriatic Sea

Alboran Sea Balearic Sea Catalan Sea Cilician Sea

Gulf of Sidra Ionian Sea Levantine Sea Libyan Sea

Ligurian Sea Sea of Sardinia Sea of Sicily Tyrrhenian Sea

[edit] Baltic Sea

Archipelago Sea Bay of Bothnia Bothnian Sea

Central Baltic Sea Gulf of Bothnia Gulf of Finland

Gulf of Riga Oresund Strait Sea of Åland

Archipelago Sea

Others[link]

Argentine Sea Bay of Biscay Bay of Campeche Bay of Fundy Black Sea[7] Caribbean Sea Celtic Sea

Chesapeake Bay Davis Strait Denmark Strait English Channel Gulf of Guinea Gulf of Maine

Gulf of Mexico Gulf of St. Lawrence Gulf of Venezuela Irish Sea Labrador Sea Marmara Sea[7]

North Sea Norwegian Sea Sargasso Sea Sea of Azov[7] Sea of the Hebrides Wadden Sea

[edit] Arctic Ocean

Amundsen Gulf Baffin Bay Barents Sea Beaufort Sea Chukchi Sea

East Siberian Sea Greenland Sea Hudson Bay James Bay Kara Sea Kara Strait

Laptev Sea Lincoln Sea Prince Gustav Adolf Sea Pechora Sea White Sea

Beaufort Sea

[edit] Southern Ocean

Amundsen Sea Bass Strait Bellingshausen Sea Cooperation Sea Cosmonauts Sea

Davis Sea D'Urville Sea Drake Passage Great Australian Bight Gulf St Vincent

King Haakon VII Sea Lazarev Sea Mawson Sea Riiser-Larsen Sea Ross Sea

Scotia Sea Somov Sea Spencer Gulf Weddell Sea

[edit] Indian Ocean

Andaman Sea Arabian Sea Bay of Bengal

Gulf of Aden Gulf of Oman

Laccadive Sea Mozambique Channel Persian Gulf

Red Sea Timor Sea

[edit] Pacific Ocean

Arafura Sea Banda Sea Bering Sea Bismarck Sea Bohai Sea Bohol Sea (also known as the Mindanao Sea) Camotes Sea Celebes Sea Ceram Sea

Chilean Sea Sea of Chiloé Coral Sea East China Sea Flores Sea Gulf of Alaska Gulf of California (also known as the Sea of Cortéz) Gulf of Carpentaria Gulf of Thailand

Halmahera Sea Java Sea Koro Sea Molucca Sea Philippine Sea Salish Sea Savu Sea Sea of Japan Sea of Okhotsk

Seto Inland Sea Sibuyan Sea Solomon Sea South China Sea Sulu Sea Tasman Sea Visayan Sea Yellow Sea

[edit] Landlocked seas

Some large inland lakes, usually brackish, are called "seas".

Aral Sea Caspian Sea

Dead Sea Sea of Galilee

Great Salt Lake Salton Sea

List of seas by surface area[link]

No.	Name of the Water Body	Surface area (sq.mi)	Surface area (sq.km)
1	Philippine Sea	2,000,000	5,177,762
2	Coral Sea	1,850,000	4,791,000
3	Arabian Sea	1,491,130	3,862,000
4	South China Sea	1,351,936	3,500,000
5	Weddell Sea	1,081,548	2,800,000
6	Caribbean Sea	1,063,000	2,754,000
7	Mediterranean Sea	965,000	2,500,000
8	Tasman Sea	900,000	2,330,000
9	Bering Sea	873,000	2,260,100
10	Bay of Bengal	838,970	2,172,000

Rank	Body of water	Square miles (square kilometres)
1	Pacific Ocean	64,196,000 sq mi (166,270,000 km2)
2	Atlantic Ocean	33,400,000 sq mi (87,000,000 km2)
3	Indian Ocean	28,400,000 sq mi (74,000,000 km2)
4	Southern Ocean	20,327,000 sq mi (52,650,000 km2)
5	Arctic Ocean	5,100,000 sq mi (13,000,000 km2)
6	Arabian Sea	1,491,000 sq mi (3,860,000 km2)
7	South China Sea	1,148,000 sq mi (2,970,000 km2)
8	Caribbean Sea	971,000 sq mi (2,510,000 km2)
9	Mediterranean Sea	969,000 sq mi (2,510,000 km2)
10	Bering Sea	873,000 sq mi (2,260,000 km2)
11	Bay of Bengal	838,612 sq mi (2,172,000 km2)
12	Gulf of Mexico	582,000 sq mi (1,510,000 km2)
13	Sea of Okhotsk	537,000 sq mi (1,390,000 km2)
14	Sea of Japan	391,000 sq mi (1,010,000 km2)
15	Hudson Bay	282,000 sq mi (730,000 km2)
16	East China Sea	257,000 sq mi (670,000 km2)
17	Andaman Sea	218,100 sq mi (565,000 km2)
18	Red Sea	175,000 sq mi (450,000 km2)
19	Black Sea	168,500 sq mi (436,000 km2)
20	North Sea	165,000 sq mi (430,000 km2)
21	Baltic Sea	147,000 sq mi (380,000 km2)
22	Yellow Sea	113,500 sq mi (294,000 km2)
23	Persian Gulf	88,800 sq mi (230,000 km2)
24	Adriatic Sea	60,000 sq mi (160,000 km2)
25	Gulf of California	59,000 sq mi (150,000 km2)

Bodies of water which are missing from this table, and their approximate areas, include:

• Philippine Sea (2,000,000 sq mi)
• Coral Sea (1,849,800 sq mi)
• Sargasso Sea (roughly 1,400,000 sq mi)
• Weddell Sea (1,080,000 sq mi)
• Tasman Sea (900,000 sq mi)
• Gulf of Alaska (592,000 sq mi)
• Barents Sea (542,000 sq mi)
• Greenland Sea (465,000 sq mi)
• Mozambique Channel (roughly 425,000 sq mi)
• Argentine Sea (386,000 sq mi)
• Ross Sea (370,000 sq mi)
• East Siberian Sea (361,000 sq mi)
• Scotia Sea (350,000 sq mi)
• Kara Sea (340,000 sq mi)
• Solomon Sea (280,000 sq mi)
• Laptev Sea (276,000 sq mi)
• Baffin Bay (266,000 sq mi)
• Arafura Sea (250,000 sq mi)
• Timor Sea (235,000 sq mi)
• Chukchi Sea (225,000 sq mi)
• Norwegian Sea (222,000 sq mi)
• Gulf of Aden (205,000 sq mi)
• Beaufort Sea (184,000 sq mi)
• Banda Sea (180,000 sq mi)
• Gulf of Thailand (roughly 146,000 sq mi)
• Caspian Sea (142,800 sq mi)
• Java Sea (124,000 sq mi)
• Gulf of Carpentaria (120,000 sq mi)
• Celebes Sea (110,000 sq mi)
• Sulu Sea (100,000 sq mi)
• Flores Sea (93,000 sq mi)
• Bay of Biscay (86,000 sq mi)
• Aegean Sea (83,000 sq mi)
• Molucca Sea (77,000 sq mi)
• Gulf of Saint Lawrence (60,000 sq mi)
• This list is incomplete.

Nomenclature[link]

• The Sea of Galilee is a small freshwater lake with a natural outlet, which is called Lake Tiberias or Lake Kinneret on modern Israeli maps, but its original name remains in use.
• The Sea of Cortés is more commonly known as the Gulf of California.
• The Dead Sea is actually a lake, as is the Caspian Sea and the mainly dried up Aral Sea.

See also[link]

• Oceanography
• European Atlas of the Seas
• Inlet
• International Maritime Organization
• List of places on land with elevations below sea level
• Pole of inaccessibility: the locations farthest from any coastline
• Marine debris
• Sea level
• Sea level rise
• Sea salt
• Seven Seas
• Borders of the oceans

References[link]

1. ^ "Sea - Definition and More from the Free Merriam-Webster Dictionary". Merriam-webster.com. http://www.merriam-webster.com/dictionary/sea. Retrieved 2012-03-13. 
2. ^ "Sea ice (ice formation)". Britannica Online Encyclopedia. 2012 [last update]. http://www.britannica.com/EBchecked/topic/939404/sea-ice. Retrieved 5 March 2012. 
3. ^ "The Ancient World - Egypt". marinersmuseum.org. Mariners' Museum. 2012 [last update]. http://www.marinersmuseum.org/education/ancient-world-egypt. Retrieved 5 March 2012. 
4. ^ "Зацепились за Моржовец" (in Russian). Русское географическое общество. 2012 [last update]. http://www.rgo.ru/2010/08/zacepilis-za-morzhovec/. Retrieved 5 March 2012. 
5. ^ Урванцев, Н. Н. (1969). "История открытия и освоения медно-никелевых руд Сибирского Севера" (in Russian). Moscow: Недра. http://library.ikz.ru/hronologiya-osvoeniya-sibiri/Mangazeya. Retrieved 7 March 2012. 
6. ^ Howgego, Ray (2001 [last update]). "Discoverers Web: Dezhnev". win.tue.nl. http://www.win.tue.nl/~engels/discovery/dezhnev.html. Retrieved 7 March 2012. 
7. ^ ^{a b c} often treated as part of Mediterranean Sea

External links[link]

Look up sea in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Seas

• Oceans at the Open Directory Project
• National Oceanic and Atmospheric Administration

v t e Earth's oceans and seas Arctic Ocean Amundsen Gulf Barents Sea Beaufort Sea Bering Strait Chukchi Sea East Siberian Sea Fram Strait Greenland Sea Gulf of Boothia Kara Sea Kara Strait Laptev Sea Lincoln Sea Prince Gustav Adolf Sea Pechora Sea Wandel Sea White Sea Atlantic Ocean Adriatic Sea Aegean Sea Alboran Sea Archipelago Sea Argentine Sea Baffin Bay Balearic Sea Baltic Sea Bay of Biscay Bay of Bothnia Bay of Campeche Bay of Fundy Black Sea Bothnian Sea Caribbean Sea Celtic Sea Davis Strait Denmark Strait English Channel Foxe Basin Greenland Sea Gulf of Bothnia Gulf of Finland Gulf of Lion Gulf of Guinea Gulf of Maine Gulf of Mexico Gulf of St. Lawrence Gulf of Venezuela Hudson Bay James Bay Ionian Sea Irish Sea Irminger Sea Labrador Sea Levantine Sea Libyan Sea Ligurian Sea Marmara Sea Mediterranean Sea Myrtoan Sea North Sea Norwegian Sea Saint Lawrence Seaway Sargasso Sea Sea of Åland Sea of Azov Sea of Crete Sea of the Hebrides Thracian Sea Tyrrhenian Sea Indian Ocean Andaman Sea Arabian Sea Bay of Bengal Gulf of Aden Gulf of Aqaba Gulf of Khambhat Gulf of Kutch Gulf of Oman Gulf of Suez Laccadive Sea Mozambique Channel Persian Gulf Red Sea Strait of Malacca Timor Sea Pacific Ocean Arafura Sea Bali Sea Banda Sea Bering Sea Bismarck Sea Bohai Sea Bohol Sea Camotes Sea Celebes Sea Ceram Sea Chilean Sea Coral Sea East China Sea Flores Sea Gulf of Alaska Gulf of California Gulf of Carpentaria Gulf of Fonseca Gulf of Thailand Gulf of Tonkin Halmahera Sea Java Sea Koro Sea Makassar Strait Molucca Sea Moro Gulf Philippine Sea Salish Sea Savu Sea Sea of Japan Sea of Okhotsk Seto Inland Sea Sibuyan Sea Solomon Sea South China Sea Sulu Sea Tasman Sea Visayan Sea Yellow Sea Southern Ocean Amundsen Sea Bellingshausen Sea Cooperation Sea Cosmonauts Sea Davis Sea D'Urville Sea King Haakon VII Sea Lazarev Sea Riiser-Larsen Sea Mawson Sea Ross Sea Scotia Sea Somov Sea Weddell Sea Landlocked seas Aral Sea Caspian Sea Dead Sea Salton Sea

lez:Гьуьл

A natural block of (water) ice

Snowflakes (ice crystals) by Wilson Bentley, 1902

Ice is water frozen into the solid state. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions. The addition of other materials such as soil may further alter the appearance.

Ice appears in nature in forms of snowflakes, hail, icicles, glaciers, pack ice, and entire polar ice caps. It is an important component of the global climate, and plays an important role in the water cycle. Furthermore, ice has numerous cultural applications, from ice cooling of drinks to winter sports and the art of ice sculpting.

The molecules in solid ice may be arranged in different ways, called phases, depending on the temperature and pressure. Usually ice is the phase known as ice I_h, which is the most abundant of the varying solid phases on the Earth's surface. The most common phase transition to ice I_h occurs when liquid water is cooled below 0°C (273.15K, 32°F) at standard atmospheric pressure. It can also deposit from vapour with no intervening liquid phase, such as in the formation of frost.

The word is derived from Old English īs, which in turn stems from Proto-Germanic isaz.

Characteristics[link]

Crystal structure of hexagonal ice. Grey dashed lines indicate hydrogen bonds.

As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral.^[1] It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H-O-H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. It is a weak bond, but is critical in controlling the structure of both water and ice.

An unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8.3% less dense than liquid water. The density of ice is 0.9167 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is densest, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals^[2] of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).^[3]

The effect of expansion during freezing can be dramatic, and is a basic cause of freeze-thaw weathering of rock in nature. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes, then leak water after thawing.

The result of this process is that ice (in its most common form) floats on liquid water, which is an important feature in Earth's biosphere. It has been argued that without this property natural bodies of water would freeze, in some cases permanently, from the bottom up,^[4] resulting in a loss of bottom-dependent animal and plant life in fresh and sea water. Sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates a sheltered environment for bacterial and algal colonies. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the Bald notothen, fed upon in turn by larger animals such as Emperor penguins and Minke whales.^[5]

When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. During the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase the thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.

As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen-hydrogen (O-H) bond stretch. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than for liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice.^[6]

Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green.^[6]

Slipperiness[link]

Frozen waterfall in southeast New York

It has long been believed that ice is slippery because the pressure of an object in contact with it causes a thin layer to melt. For example, the blade of an ice skate, exerting pressure on the ice, melts a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in 19th century. This however did not account for skating on ice temperatures lower than -3.5 °C, whereas skaters often skate on lower temperature ice. In 20th century an alternative explanation, called "friction heating" was proposed, whereby friction of the material was causing the ice layer melting. However, this theory also failed to explain skating at low temperature. In fact, neither explanation explained why ice is slippery when standing still even at below-zero temperatures.^[7]

This explanation has come into doubt with the proposal that ice molecules in contact with air cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semiliquid state, providing lubrication regardless of pressure against the ice exerted by any object.^[8]

Formation[link]

Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (i.e. −22 °F).

Ice that is found at sea may be in the form of sea ice, pack ice, or icebergs. The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is often an important source of seasonal fresh water.

Rime is a type of ice formed on cold objects when drops of water crystallize on them. This can be observed in foggy weather, when the temperature drops during the night. Soft rime contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Hard rime is comparatively denser.

Aufeis is layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.

Ice can also form icicles, similar to stalactites in appearance, or stalagmite-like forms as water drips and re-freezes.

Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice.

Pancake ice is a formation of ice generally created in areas with less calm conditions.

Candle Ice is a form of Rotten Ice that develops in columns perpendicular to the surface of a lake.

Ice discs are circular formations of ice surrounded by water in a river.

The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on.^[9]

Ice pellets[link]

An accumulation of ice pellets

Ice pellets are a form of precipitation consisting of small, translucent balls of ice. This form of precipitation is also known as sleet.^[10] Ice pellets are usually (but not always) smaller than hailstones.^[11] They often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL.^[12]

Ice pellets form when a layer of above-freezing air is located between 1,500 metres (4,900 ft) and 3,000 metres (9,800 ft) above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of any snowflakes falling through the warm layer. As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. A temperature profile showing a warm layer above the ground is most likely to be found in advance of a warm front during the cold season,^[13] but can occasionally be found behind a passing cold front.

Hail[link]

A large hailstone, about 6 cm (2.36 in) in diameter

Like other precipitation, hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm's updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.^[14] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in). GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, use the coding of GS, which is short for the French word grésil.^[12] Stones just larger than golf ball-sized are one of the most frequently reported hail sizes.^[15] Hailstones can grow to 15 centimetres (6 in) and weigh more than .5 kilograms (1.1 lb).^[16] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.^[17] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.^[18]

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).^[14] Hail-producing clouds are often identifiable by their green coloration.^[19][20] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).^[21] Entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.^[22]

Snowflakes[link]

Snowflake viewed in an optical microscope

Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; −0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus." Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F).^[23] In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor — what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,^[24] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.^[25]

Once a droplet has frozen, it grows in the water-supersaturated air, when the temperature remains below the freezing point. The droplet then grows by condensation of water vapor onto the ice surfaces. Air saturation with water is maintained by continuous simultaneous evaporation of water droplets. Thus ice crystals grow at the expense of water droplets in a process called the Wegner-Bergeron-Findeison process. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their weight, and may collide and aggregate in clusters. These aggregates are snowflakes, and are usually the type of ice particle that falls to the ground.^[26] Guinness World Records list the world’s largest snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 38 cm (15 inches) wide.^[27]

The exact details of the sticking mechanism remain controversial. Possibilities include mechanical interlocking, sintering, electrostatic attraction as well as the existence of a "sticky" liquid-like layer on the crystal surface. The individual ice crystals often have hexagonal symmetry. Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean that the crystals often appear white in color due to diffuse reflection of the whole spectrum of light by the small ice particles.^[28] The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.^[26] Rarely, at a temperature of around −2 °C (28 °F), snowflakes can form in threefold symmetry — triangular snowflakes.^[29] The most common snow particles are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing. It is unlikely that any two snowflakes are alike due to the estimated 10¹⁹ (10 quintillion) water molecules which make up a typical snowflake,^[30] which grow at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.^[31] The METAR code for snow is SN, while snow showers are coded SHSN.^[12]

Diamond dust[link]

Diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40 °F (−40 °C) due to air with slightly higher moisture from aloft mixing with colder, surface based air.^[32] The METAR identifier for diamond dust within international hourly weather reports is IC.^[12]

Production[link]

Harvesting ice on Lake Saint Clair in Michigan, c. 1905

B&W film of 1919 ice harvest at Pocono Manor in the Poconos

An ice manufacturing plant in East Midnapore, India

Ice is now mechanically produced on a large scale, but before refrigeration was developed ice was harvested from natural sources for human use.

Ice harvesting[link]

Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). This was a large underground space (up to 5000 m³) that had thick walls (at least two meters at the base) made out of a special mortar called sārooj, composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was known to be resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a Qanat, and often contained a system of windcatchers which could easily bring temperatures inside the space down to frigid levels on summer days. The ice was used to chill treats for royalty.

There were thriving industries in the 16/17th century in UK whereby low lying areas along the River Thames estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was copied from the Chinese who had been doing it for thousands of years. This was reportedly copied by an Englishman who had seen the same activity in China.^[33] Ice was imported into England from Norway on a considerable scale as early as 1823.^[34]

In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina in 1799,^[34] and by the first half of the 19th century, ice harvesting had become big business. Frederic Tudor, who became known as the “Ice King,” worked on developing better insulation products for the long distance shipment of ice, especially to the tropics; this became known as the ice trade.

Triest sent ice to Egypt, Corfu, and Zante; Switzerland sent it to France; and Germany sometimes was supplied from Bavarian lakes.^[34]

Until recently,^[when?] the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning. Icehouses were used to store ice formed in the winter, to make ice available all year long, and early refrigerators were known as iceboxes, because they had a block of ice in them. In many cities, it was not unusual to have a regular ice delivery service during the summer. The advent of artificial refrigeration technology has since made delivery of ice obsolete.

Ice harvesting is still done for ice and snow sculpture events. A swing saw is used to get ice out of the river for the Harbin International Ice and Snow Sculpture Festival each year. A swing saws is used to cut ice out from the frozen surface of the Songhua River.^[35] Many ice sculptures are made from the ice.

Commercial production[link]

Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.^[36] Most commercial ice makers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.^[36] Large batch ice makers can produce up to 75 tons of ice per day.^[37]

Ice production is a large business; in 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.^[38]

For small-scale ice production, many modern home refrigerators can also make ice with a built in icemaker, which will typically make ice cubes or crushed ice. Stand-alone icemaker units that make ice cubes are often called ice machines.

Uses[link]

Sports[link]

Ice sailing on the Żnin Small Lake

Ice also plays a central role in winter recreation and in many sports such as ice skating, tour skating, ice hockey, ice fishing, ice climbing, curling, broomball and sled racing on bobsled, luge and skeleton. Many of the different sports played on ice get international attention every four years during the Winter Olympic Games.

A sort of sailboat on blades gives rise to ice yachting. The human quest for excitement has even led to ice racing, where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to dirt track racing). The sport has even been modified for ice rinks.

Other uses[link]

• Ice cubes or crushed ice can be used to cool drinks. As the ice melts, it absorbs heat and keeps the drink near 0 °C (32 °F).
• Ice can be used to reduce swelling (by decreasing blood flow) and pain by pressing it against an area of the body.^[39]

Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

• Engineers used formidable strength of pack ice when they constructed Antarctica's first floating ice pier in 1973.^[40] Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally-occurring frozen seawater in McMurdo Sound until the dock reaches a depth of about 22 feet (6.7 m). Ice piers have a lifespan of three to five years.
• Structures and ice sculptures are built out of large chunks of ice. The structures are mostly ornamental (as in the case with ice castles), and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas. Igloos are another example of a temporary structure, made primarily from snow.
• During World War II, Project Habbakuk was a British programme which investigated the use of pykrete (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a large deck could be constructed, but the idea was given up when there were not enough funds for construction of a prototype.
• Ice can be used to start a fire by carving it into a lens which will focus sunlight onto kindling. A fire will eventually start.^[41]
• Ice has even been used as the material for a variety of musical instruments, for example by percussionist Terje Isungset.^[42]
• Ice was once used to cool refrigerators in the 19th century, which is reflected in the name "iceboxes."
• Ice can be used to store cooling, which has the same effect as storing electricity Thermal energy storageAir conditioning

Ice and transportation[link]

U.S. Coast Guard icebreakers near McMurdo Station, February 2002

Ice can also be an obstacle; for harbors near the poles, being ice-free is an important advantage; ideally, all year long. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø (Norway). Harbors which are not ice-free are opened up using icebreakers.

Ice forming on roads is a dangerous winter hazard. Black ice is very difficult to see, because it lacks the expected frosty surface. Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Driving safely requires the removal of the ice build-up. Ice scrapers are tools designed to break the ice free and clear the windows, though removing the ice can be a long and laborious process.

Far enough below the freezing point, a thin layer of ice crystals can form on the inside surface of windows. This usually happens when a vehicle has been left alone after being driven for a while, but can happen while driving, if the outside temperature is low enough. Moisture from the driver's breath is the source of water for the crystals. It is troublesome to remove this form of ice, so people often open their windows slightly when the vehicle is parked in order to let the moisture dissipate, and it is now common for cars to have rear-window defrosters to solve the problem. A similar problem can happen in homes, which is one reason why many colder regions require double-pane windows for insulation.

When the outdoor temperature stays below freezing for extended periods, very thick layers of ice can form on lakes and other bodies of water, although places with flowing water require much colder temperatures. The ice can become thick enough to drive onto with automobiles and trucks. Doing this safely requires a thickness of at least 30 cm (one foot).

For ships, ice presents two distinct hazards. Spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, and to require it to be hacked off or melted with steam hoses. And icebergs — large masses of ice floating in water (typically created when glaciers reach the sea) — can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous probably being the Titanic.

Ice formation on window glass of high altitude flying airplane

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. During the first non-stop flight of the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions – Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.

A particular icing vulnerability associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes adiabatic cooling. So, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. For this reason, aircraft reciprocating engines with carburetors are provided with carburetor air intake heaters. The increasing use of fuel injection—which does not require carburetors—has made "carb icing" less of an issue for reciprocating engines.

Jet engines do not experience carb icing, but recent evidence indicates that they can be slowed, stopped, or damaged by internal icing in certain types of atmospheric conditions much more easily than previously believed. In most cases, the engines can be quickly restarted and flights are not endangered, but research continues to determine the exact conditions which produce this type of icing, and find the best methods to prevent, or reverse it, in flight.

Phases[link]

Ice may be any one of the 15 known solid phases of water.

Most liquids freeze at a higher temperature under pressure, because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: water freezes at a temperature below 0 °C under a pressure higher than 1 atm (0.10 MPa). Consequently, water also remains frozen at a temperature above 0 °C under a pressure lower than 1 atm. The melting of ice under high pressures is thought to contribute to the movement of glaciers.

Ice, water, and water vapour can coexist at the triple point, which is exactly 0.01 °C or 273.16 K (by definition) at a pressure of 611.73 Pa. Unlike most other solids, ice is difficult to superheat. In an experiment ice at −3 °C was superheated to about 17 °C for about 250 picoseconds.^[43]

Subjected to higher pressures and varying temperatures, ice can form in fifteen separate known phases. With care all these phases except ice X can be recovered at ambient pressure and low temperature. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are IV and XII. Ice XII was discovered in 1996. In 2006, XIII and XIV were discovered.^[44] Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I_h, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143 °C.^[45] At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa^[46] or 5.62 TPa.^[47]

As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW), low-density amorphous ice (LDA), high-density amorphous ice (HDA), very high-density amorphous ice (VHDA) and hyperquenched glassy water (HGW).

In outer space, hexagonal crystalline ice (the predominant form found on Earth) is extremely rare. Amorphous ice is more common; however, hexagonal crystalline ice can be formed via volcanic action.^[48]

Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.

Other ices[link]

Detail of an ice cube

The solid phases of several other volatile substances are also referred to as ices; generally a volatile is classed as an ice if its melting point lies above ~100 K. The best known example is dry ice, the solid form of carbon dioxide.

A "magnetic analogue" of ice is also realized in some insulating magnetic materials in which the magnetic moments mimic the position of protons in water ice and obey energetic constraints similar to the Bernal-Fowler ice rules arising from the geometrical frustration of the proton configuration in water ice. These materials are called spin ice.

See also[link]

• Density of ice versus water
• Ice famine
• Pumpable ice technology

References[link]

External links[link]

Look up ice in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Ice

• The National Snow and Ice Data Center, based in the United States
• The phase diagram of water, including the ice variants
• Webmineral listing for Ice
• MinDat.org listing and location data for Ice
• The physics of ice
• The phase diagrams of water with some high pressure diagrams
• 'Unfreezable' water, 'bound water' and water of hydration
• Electromechanical properties of ice
• Estimating the maximum thickness of an ice layer
• Sandia's Z machine creates ice in nanoseconds
• Amazing ice at Lac Leman
• The Surprisingly Cool History of Ice