Grease ice is a very thin, soupy layer of

frazil Frazil ice is a collection of loose, randomly oriented ice crystals millimeter and sub-millimeter in size, with various shapes, e.g. elliptical disks, dendrites, needles and of an irregular nature. Frazil ice forms during the winter in open-wat ...

crystals clumped together, which makes the ocean surface 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 ...

. Grease ice is the second stage in the formation of solid sea ice after ice floes and then

frazil ice Frazil ice is a collection of loose, randomly oriented ice crystals millimeter and sub-millimeter in size, with various shapes, e.g. elliptical disks, dendrites, needles and of an irregular nature. Frazil ice forms during the winter in open-wate ...

. New sea ice formation takes place throughout the winter in the

Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

. The first ice that forms in a

polynya 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 полынья (), which r ...

are loose ice crystals called frazil ice. If the level of turbulence is sufficient, the frazil ice will be mixed down into the upper layer and form a surface layer of grease ice. The term ‘grease ice’ follows

World Meteorological Organization The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO originated from the Inter ...

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 which can be the initiation of the grease ice layer, given a minimum level of mixing and cooling of 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 Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...

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, a thick elastic crust, forms at the surface, which thickens 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 , publisher = Cold Regions Science and Technology 44 , year = 2006 , pages = 171–183 Sea ice Snow or ice weather phenomena