Grease ice is a very thin, soupy layer of frazil crystals clumped together, and only formed in large, open bodies of water most notably the

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

. Grease ice makes the water resemble an

oil slick An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...

, the small crystals of ice held closely together reflect and

refract In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...

light similarly to how oil will on water. Grease ice is the second stage in the formation of ice floes being the stage immediately following the frazil ice stage. Outside the ocean and seas, the Laurentian Great Lakes and

Lake Baikal Lake Baikal is a rift lake and the deepest lake in the world. It is situated in southern Siberia, Russia between the Federal subjects of Russia, federal subjects of Irkutsk Oblast, Irkutsk Oblasts of Russia, Oblast to the northwest and the Repu ...

also form grease ice. New sea ice formation takes place throughout the winter in the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

, and

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

where frazil forms and coalesces in

polynyas A polynya () is an area of open water surrounded by sea ice. It is now used as a geographical term for an area of unfrozen seawater within otherwise contiguous pack ice or fast ice. It is a loanword from the Russian (), which refers to a n ...

or in cold-exposed regions of the open-ocean. Similarly, in seas and lakes, where latent energy is sufficient (

waves United States Naval Reserve (Women's Reserve), better known as the WAVES (for Women Accepted for Volunteer Emergency Service), was the women's branch of the United States Naval Reserve during World War II. It was established on July 21, 1942, ...

, swells, fetch,

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

seiche A seiche ( ) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors, caves, and seas. The key requirement for formatio ...

, etc),

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

mixes the frazil ice down into the upper layer and forms a surface layer of grease ice. The term ‘grease ice’ follows

World Meteorological Organization The World Meteorological Organization (WMO) is a List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology an ...

nomenclature. Grease ice differs from ‘slush’, where slush is similarly created by snow falling into the top layer of an ocean basin, river, or lake. The two terms are related due to the process of ice crystals being blown into a polynya, lake, ocean, or sea which can be the initiation of the grease ice layer, given a minimum level of mixing and cooling on the ocean surface.

Formation

When the water surface begins to lose heat rapidly, the water becomes supercooled. Turbulence, caused by strong winds or flow from a river, will mix the supercooled water throughout its entire depth. The supercooled water will already be encouraging the formation of small ice crystals (frazil ice) and the crystals will be mixed into the upper layer and form a surface layer. Sea ice growth in turbulent water differs from sea ice growth in calm water. In turbulent water, the ice crystals accumulate at the surface, forming a grease-ice layer composed of individual ice crystals and small irregular clumps of ice crystals. In calm water conditions,

nilas Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ic ...

, a thin, almost invisible elastic crust, forms at the surface as water molecules freeze to the ice-water interface.

References

{{Citation , last1 = Smedsrud, first1 = Lars H. , last2 = Skogseth , first2 = Ragnheid , title = Field Measurements of Arctic Grease Ice Properties and Processes , journal = Cold Regions Science and Technology , publisher = Cold Regions Science and Technology 44 , year = 2006 , volume = 44 , issue = 3 , pages = 171–183 , doi = 10.1016/j.coldregions.2005.11.002 , bibcode = 2006CRST...44..171S Sea ice Snow or ice weather phenomena