Frost flower (sea ice)
Encyclopedia
Frost flowers are ice crystals
commonly found growing on young sea ice
and thin lake ice
in cold, calm conditions. The ice crystals are similar to hoar frost, and are commonly seen to grow in patches around 3–4 cm in diameter. Frost flowers growing on sea ice have extremely high salinities
and concentrations of other sea water chemicals and, because of their high surface area
, are efficient releasers of these chemicals into the atmosphere.
A different phenomenon, in which ice is extruded from freezing plants, is also referred to as frost flowers.
is found directly above the sea ice, caused by the sublimation of ice into the dry, cold air. As the warmer, wet air meets the overlying cold air it becomes supersaturated and can condense as hoar-frost like crystals on the sea ice surface. In general, frost flowers only form in relatively windless conditions; in high winds the supersaturated layer is scrubbed from the surface and blowing snow obscures the ice surface.
On lake ice, frost flowers are effectively identical to hoar frost crystals. On sea ice, brine
is wicked up onto the hoar frost crystals, which leads to high salinities of up to 100psu (ppt) (approximately three times more salty than sea water).
Frost flowers are most commonly found on young sea ice in polar region
s as the large temperature differences between the ice and air are suitable for growth. When the ice grows too thick, the upper surface of the ice cools down and frost flowers no longer grow. This means that frost flowers typically only grow in the first few days of ice coverage.
but similarly to hoar frost can grow in rod-like morphologies. When warm brine is wicked up onto the ice crystals, it can also give the frost flower a 'clumped' appearance as the facet
s of the ice crystals are partly melted.
. High chemical concentrations and high surface area means that chemicals can be released efficiently in the atmosphere. In particular studies have shown that high concentrations of frost flowers can be linked to high concentrations of tropospheric
bromine monoxide (an ozone depleting chemical), and higher quantities of sea-salt aerosol (airborne salt particles).
Ice crystals
Ice crystals are a small crystalline form of ice including hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. The highly symmetric shapes are due to depositional growth, namely, direct deposition of water vapour onto the ice crystal...
commonly found growing on young sea ice
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 ....
and thin lake ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
in cold, calm conditions. The ice crystals are similar to hoar frost, and are commonly seen to grow in patches around 3–4 cm in diameter. Frost flowers growing on sea ice have extremely high salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
and concentrations of other sea water chemicals and, because of their high surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
, are efficient releasers of these chemicals into the atmosphere.
A different phenomenon, in which ice is extruded from freezing plants, is also referred to as frost flowers.
Formation
Frost flowers are formed on thin sea ice when the atmosphere is much colder than the underlying ice. Typically a temperature difference between the ice surface and the air of at least 15°C is required, though this can be reduced if the air is very humid. In these conditions a layer of supersaturated vapourSupersaturation
The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances...
is found directly above the sea ice, caused by the sublimation of ice into the dry, cold air. As the warmer, wet air meets the overlying cold air it becomes supersaturated and can condense as hoar-frost like crystals on the sea ice surface. In general, frost flowers only form in relatively windless conditions; in high winds the supersaturated layer is scrubbed from the surface and blowing snow obscures the ice surface.
On lake ice, frost flowers are effectively identical to hoar frost crystals. On sea ice, brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...
is wicked up onto the hoar frost crystals, which leads to high salinities of up to 100psu (ppt) (approximately three times more salty than sea water).
Frost flowers are most commonly found on young sea ice in polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. 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 as the large temperature differences between the ice and air are suitable for growth. When the ice grows too thick, the upper surface of the ice cools down and frost flowers no longer grow. This means that frost flowers typically only grow in the first few days of ice coverage.
Morphology
The ice crystals in frost flowers are usually dendriticDendrite (crystal)
A crystal dendrite is a crystal that develops with a typical multi-branching tree-like form. Dendritic crystal growth is very common and illustrated by snowflake formation and frost patterns on a window. Dendritic crystallization forms a natural fractal pattern...
but similarly to hoar frost can grow in rod-like morphologies. When warm brine is wicked up onto the ice crystals, it can also give the frost flower a 'clumped' appearance as the facet
Facet
Facets are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure...
s of the ice crystals are partly melted.
Aerosol release
Frost flowers have attracted interest as a possible source of polar atmospheric aerosolAerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
. High chemical concentrations and high surface area means that chemicals can be released efficiently in the atmosphere. In particular studies have shown that high concentrations of frost flowers can be linked to high concentrations of tropospheric
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
bromine monoxide (an ozone depleting chemical), and higher quantities of sea-salt aerosol (airborne salt particles).