Saturday, May 5, 2012

A term in oceanography: brinicle for a salty ice stalactite

The term brinicle immediately raises associations with the words brine and icicle: a brinicle looks like an icicle and forms in cold or icy solutions of salt in water. Due to the fluid mechanics of cold, freezing seawater the overall form of a brinicle resembles more the shape of a tornado funnel than that of a straight, downward-pointing icicle.

Jeremy Berlin describes a brinicle descending about seven feet from the surface ice in antarctic waters, which was filmed by two British cameramen as it formed [1].  Ice stalactites look like they are out of a science fiction novel or computer animation, but they occur for real. American oceanographers Paul Dayton and Seelye Martin described them in 1971. Brinicles were successfully generated in a laboratory study by injecting cold, dense brine into an insulated tank of sea water held at its freezing point [2]. 

Sea water in polar regions, freezing at the ocean surface, can concentrate brine entrapments to very high salinities. Such brine pockets, which can have complex geometries, result into drainage tubes. When conditions are right, high-salinity drainage may descend as brine plume, “forming long, delicate, thin-walled hollow ice stalactites that on occasion can extend up to 6 m below the bottom of the sea ice ...” [3]

Brinicles are too slow forming to freeze anything in. There is no danger to submarines [1]. Brinicles are fragile and can be broken apart by currents as well as seals and divers. 

Keywords: fluid dynamics, frigid waters, seawater, dense brine.

References and more to explore
[1] Jeremy Berlin: In the frigid waters of Antarctica, briny tubes of ice can stretch down to the seafloor. National Geographic May 2012, 221 (5), pp. 30-31.
[2] Martin Seelye: Ice stalactites: comparison of a laminar flow theory with experiment. Journal of Fluid Mechanics 1974, 63, pp. 51-79. DOI: 10.1017/S0022112074001017.
[3] Austin Kovacs: Sea Ice. Part I. Bulk Salinity Versus Ice Floe Thickness. US Army Corps of Engineers - Cold Regions Research & Engineering Laboratory, CRREL Report 96-7, June 1996; Figure 3 [].

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