añado algo de información relacionada (en inglés y castellano),
El hielo marino aumenta en densidad según la temperatura mengua hasta alcanzar el punto de congelación. La forma que adopta el hielo marino depende de varias condiciones, y particularmente del grado de turbulencia en las capas superiores del océano.
Los primeros cristales que se forman son diminutas esferas de hielo puro; éstas crecen rápidamente en discos delgados, y entonces, en condiciones de calma, a estrellas hexagonales que van apilándose en forma de largas agujas.
Las turbulencias marinas rompen este proceso y convierten las formaciones en una especie de hielo granizado llamado "Frazil", que alcanza varios metros de profundidad, dándole al mar una apariencia de sopa espesa o balsa de aceite, que por efecto del viento y oleaje generan unas suaves y llamativas ondulaciones, muy diferentes de las clásicas marejadillas. Si las turbulencias persisten, los cristales se funden en sus bordes y toman apariencia redondeada, creando lo que se llama "Pancake ice"; Bajo estos campos de hielo donde las condiciones están más en calma, los "Pancake" toman formas mayores. Más al fondo, el "Frazil" se consolida creando unas delgadas hojas de hielo de unos 10 cm. llamadas "Nilas".
Las nuevas formas de hielo, tienen no obstante sus mejores condiciones en el mar de aguas abiertas, donde las temperaturas del océano y atmósfera tienen mayores diferencias.
En el verano antártico, el hielo marino cubre una superficie aproximada de 3 millones de km2, pero durante el otoño e invierno, las reducidas temperaturas comienzan a helar las aguas marinas más próximas al continente. La formación de hielo marino durante este proceso se estima en la increíble media de 57 km/2 por minuto.
Para finales del invierno, en septiembre, el hielo ha logrado una cobertura máxima de aproximadamente 20 millones de km/2, lo que supone una extensión tres veces más grande que Australia, y se extiende tan lejos como a 2.200 km. de la costa.
El espesor del hielo suele ser de 1 m., pero en ciertas condiciones puede llegar a 10 m. El espesor del hielo es importante para que los científicos puedan determinar los efectos en la iteración Océano-atmósfera. Es también un indicador de como puede afectar al Cambio Climático, por ello, es importante entender el crecimiento y decaimiento del hielo marino y la forma en que actúan recíprocamente las aguas antárticas y el hielo que albergan, con la atmósfera global.
Parte de esta interrogante y elemento común al clima global son también los factores de temperatura, corrientes oceánicas, mareas y vientos que influencian el crecimiento y distribución del hielo del mar
Formación y distribución del hielo marino (http://www.natureduca.com/ant_cienc_glac_hielo.php)
Ice Formation
The first stage in sea ice development is the formation of individual ice crystals in the surface layer of the ocean. These crystals, known as frazil, form in open water areas when the temperature of the water is below -1.8°C. Frazil ice gives the water an oily appearance and with further freezing the crystals coagulate together to form a soupy layer at the surface known as grease ice.
How the sea ice proceeds to develop depends on whether the surface is calm or disturbed. With calm conditions the frazil and grease ice may consolidate into continuous flexible sheets called nilas. Nilas may be up to 10 cm thick, but is easily rafted under pressure, which can rapidly increase its thickness. Ice 10-30 cm thick is termed young ice, and with further rafting and ridging it develops into first-year ice (>30 cm). Finger rafting is a common process observed with nilas, where interlocking fingers of ice are thrust alternately over and under each other where two nilas sheets converge.
A common process of sea ice development in the Antarctic, which occurs under rougher conditions, is the "pancake cycle". With the influence of wind and wave action the frazil crystals coagulate, eventually consolidating into small circular discs of ice called pancakes. The pancakes have raised rims due to collisions with other pancakes, and grow by accumulating ice crystals from the surrounding water. By rafting and bonding together the pancakes may rapidly increase to a few metres in diameter and up to 40 cm thick, and eventually freeze together to form larger floes or a consolidated ice cover.
Although new ice forms most rapidly in open water areas with the development of frazil crystals, ice also grows on the underside of existing floes as heat is conducted from the ice-water interface through the floe. This ice is called congelation ice and consists of characteristic long columnar crystals, distinct from the small randomly oriented crystals of frazil ice.
New ice may also be formed from the freezing of flooded snow overlaying the sea ice. When the weight of the snow is sufficient, the ice surface may be depressed below sea level. The influx of sea water through the permeable snow saturates the lower layers of snow which may subsequently refreeze to form "snow-ice". Snow ice has a similar texture to ice formed from coarse grained frazil but may be discriminated from frazil by stable isotope analysis. Compared with sea water, Antarctic snow is relatively depleted in the heavy stable isotope, 18O, and therefore has a highly negative del18O value.
Analysis of 173 cores taken on six voyages into the East Antarctic pack between 1991 and 1995 revealed that on average the pack was comprised of 39% columnar ice, 47% frazil ice and 13% snow ice, with other ice types making up the remaining 1%. These figures indicate the importance of the dynamic processes within the pack, which favour the growth of frazil ice. Snow ice is also seen to make a significant contribution to the total ice mass of the region.
About Sea Ice (http://www.aspect.aq/formation.html)
(https://foro.tiempo.com/imagenes/imagen-no-existe.png)
Characteristics: Ice Formation (http://nsidc.org/seaice/characteristics/formation.html)
Cooling the water down
Consider a fresh water body being cooled from above, for instance a lake at the end of summer experiencing subzero air temperatures. As the water cools the density increases so the surface water sinks, to be replaced by warmer water from below, which is in its turn cooled. This creates a pattern of convection through which the whole water body gradually cools. When the temperature reaches 4°C, the lake reaches its maximum density. Further cooling results in the colder water becoming less dense and staying at the surface. This thin cold layer can then be rapidly cooled down to the freezing point, and ice can form on the surface even though the temperature of the underlying water may still be close to 4°C. Thus a lake can experience ice formation while considerable heat still remains in the deeper parts.
This does not apply to sea water. The addition of salt to the water lowers the temperature of maximum density, and once the salinity exceeds 24.7 parts per thousand (most Arctic surface water is 30-35), the temperature of maximum density disappears. Cooling of the ocean surface by a cold atmosphere will therefore always make the surface water more dense and will continue to cause convection right down to the freezing point - which itself is depressed by the addition of salt to about -1.8°C for typical sea water. It may seem, then, that the whole water column in an ocean has to be cooled to the freezing point before freezing can begin at the surface, but in fact the Arctic Ocean is composed of layers of water with different properties, and at the base of the surface layer there is a big jump in density (known as a pycnocline), so convection only involves the surface layer down to that level (about 100-150 metres). Even so, it takes some time to cool a heated summer water mass down to the freezing point, and so new sea ice forms on a sea surface later in the autumn than does lake ice in similar climatic conditions.
How ice forms in calm water
In quiet conditions 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 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 in the Arctic reaches a thickness of 1.5-2 m.
How ice forms in rough water
If the initial ice formation occurs in rough water, for instance at the extreme ice edge in rough seas such as the Greenland or Bering Seas, then the high energy and turbulence in the wave field maintains the new ice as a dense suspension of frazil, rather than forming nilas. This suspension undergoes cyclic compression because of the particle orbits in the wave field, and during the compression phase the crystals can freeze together to form small coherent cakes of slush which grow larger by accretion from the frazil ice and more solid through continued freezing between the crystals. This becomes known as pancake ice because collisions between the cakes pump frazil ice suspension onto the edges of the cakes, then the water drains away to leave a raised rim of ice which gives each cake the appearance of a pancake. At the ice edge the pancakes are only a few cm in diameter, but they gradually grow in diameter and thickness with increasing distance from the ice edge, until they may reach 3-5 m diameter and 50-70 cm thickness. The surrounding frazil continues to grow and supply material to the growing pancakes.
At greater distances inside the ice edge, where the wave field is calmed, the pancakes may begin to freeze together in groups and eventually coalesce to form first large floes, then finally a continuous sheet of first-year ice known as consolidated pancake ice. Such ice has a different bottom morphology from normal sea ice. The pancakes at the time of consolidation are jumbled together and rafted over one another, and freeze together in this way with the frazil acting as "glue". The result is a very rough, jagged bottom, with rafted cakes doubling or tripling the normal ice thickness, and with the edges of pancakes protruding upwards to give a surface topography resembling a "stony field".The rough bottom is an excellent substrate for algal growth and a refuge for krill. The thin ice permits much light to penetrate, and the result is a fertile winter ice ecosystem.
In the Arctic, a key area where pancake ice forms the dominant ice type over an entire region is the so-called Odden ice tongue in the Greenland Sea. The Odden (the word is Norwegian for headland) grows eastward from the main East Greenland ice edge in the vicinity of 72-74°N during the winter because of the presence of very cold polar surface water in the Jan Mayen Current, which diverts some water eastward from the East Greenland Current at that latitude. Most of the old ice continues south, driven by the wind, so a cold open water surface is exposed on which new ice forms as frazil and pancake in the rough seas. The salt rejected back into the ocean from this ice formation causes the surface water to become more dense and sink, sometimes to great depths (2500 m or more), making this one of the few regions of the ocean where winter convection occurs, which helps drive the entire worldwide system of surface and deep currents known as the thermohaline circulation (or "Great Ocean Conveyor Belt").
How Does Arctic Sea Ice Form and Decay? (http://www.arctic.noaa.gov/essay_wadhams.html)