1) Calm winds. We can’t have these beauties blown away can we?
2) Cold, cold air. It has to be about 20C less than the water and since seawater freezes around -2C, that means the air must be about -22C or -7.6F. BRRR.
Frost flowers form when newly formed ice sublimates, that is ice changes directly from a solid to a gas totally bypassing the liquid stage. Initially, the water vapor formed by sublimation is the same temperature as the sea ice, but gets quickly cooled by the cold air. The air is then becomes supersaturated with water vapor, which means the air has too water much in it. Air really doesn’t want to hold all that excess water vapor, so when the supersaturated air touches another ice crystal the water vapor quickly turns back into ice. (Click the image to enlarge)
via The icy plumage of the Arctic | Deep Sea News.This process is called nucleation, on little chunks of ice that are sticking up out of the water or even ice crystals floating in air. Over time, more and more crystals form on existing ice. The crystals expand outward in spiky arms, creating the little punks we know as frost flowers. Frost flowers are found in the Arctic, the Antarctic and even grow on freshwater ponds.
But in the ocean, frost flowers have a really unusual characteristic. Unlike normal ice, which is extremely fresh, frost flowers are salty. The porous sea ice on which frost flowers form squeezes out salt water in a process known as brine rejection. Frost flowers wick up the salty brine onto the crystals, causing the salinity of frost flowers to reach 100 psu, nearly three times the salinity of sea water! Perfect for pickling.
I’ve never seen frost flowers in the wild. But you don’t have to go all the way to the poles to see beautiful ice. Just look in your freezer to find a close relative of frost flowers, hoar frost. You just might call it “freezer burn.”