By Marge Sidney (BCLSS Director)
They aren’t flowers, of course. They are more like ice sculptures that grow on the border between the water and air. These spiky little bunches of ice belong to a class of vapour-related phenomena that includes freezing fog, hoar frost and dew and form on thin and new ice in the Arctic and Antarctic Oceans (most common) and lakes (rarer). This delightful event occurred at one of our BCLSS lakes, Gun Lake. Gun Lake is a lake and unincorporated community in the Bridge River area of the Coast Mountains located 5 miles northwest of the community of Gold Bridge. The lake is approximately 10 km long and 3 ¾ km wide at the widest point.
So what causes frost flowers to bloom? They only form under special conditions: very calm air, new ice, and a temperature difference of at least 20°C between the water and the air. Frost flowers form when newly formed ice changes (or “sublimates”) directly from a solid to a gas totally bypassing the liquid stage. The large temperature difference is important for this to occur. Initially, the water vapor formed by sublimation is the same temperature as the ice, but is quickly cooled by the cold air and the air becomes supersaturated with water vapor. Air does not have a lot of capacity for excess water vapor, so when the supersaturated air touches another ice crystal the water vapor quickly turns back into ice. This process is called nucleation, and it occurs on little ice crystals 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 frost flowers. When the ice grows too thick, the upper surface of the ice cools down and frost flowers no longer grow. In windy conditions the supersaturated layer is scrubbed from the surface and blowing snow obscures the ice surface so they are not given a chance to form.
How big do the frost flowers get? Researchers have only been studying them in the Arctic for the past few years and have measured frost flowers 3 – 8 cms.
On sea ice, frost flowers have a really unusual characteristic. Unlike lake ice, which is extremely fresh, frost flowers from the ocean 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, (practical salinity units), nearly three times the salinity of sea water. They also have extremely high concentrations of other sea water chemicals and, because of their high surface area, are efficient releasers of these chemicals into the atmosphere. Another fascinating characteristic is that sea frost flowers have been found to house microorganisms. In fact, the bacteria found in the frost flowers is much more dense than in the frozen water below it, meaning each flower is essentially a temporary ecosystem. Scientists found that an frost flower allowed to melt produced a very small (1 – 2 ml), salty puddle containing about a million bacteria! That was very surprising considering these conditions (very salty, extremely cold and intense sunshine) are not what bacteria are used to. One may wonder if the frost flowers at Gun Lake contain such ecosystems. The lake isn’t salty but it is a marl lake, meaning that it is a hard water lake with lots of chemicals. The only other freshwater lake found on the internet with reference to frost flowers was Champlain Lake on the Canadian Shield, another hard water lake. Interesting!
Scientists are predicting that frost flowers will become more common at the Poles with more new ice forming in the early winter. One wonders if they will become rarer on lakes away from the Poles where the temperature gradient between the air and the water will decrease with climate change.
Wikipedia. 2013. Frost Flowers. http://en.wikipedia.org/wiki/Frost_flower Accessed March 20, 2013.
New Scientist. 20 May 2009. http://www.newscientist.com/article/dn17166-mystery-of-frost-flower-growth-explained.html.
thisiscolossal.com. 11 Dec 2012. http://www.thisiscolossal.com/2012/12/frost-flowers-blooming-in-the-arctic-ocean-are-found-to-be-teaming-with-life/ Professor Jody Deming and graduate student Jeff Bowman, University of Washington
Originally published in BCLSS Newsletter Volume 16, Issue 1 (April 2013)
Photo credit: Michelle Nortje