Salt fingering
Encyclopedia
Salt fingering is a mixing process that occurs when relatively warm, salty water overlies relatively colder, fresher water. It is driven by the fact that heated water diffuses more readily than salty water. A small parcel of warm, salty water will sink downwards into a colder, fresher region will lose its heat before losing its salt, making the parcel of water increasingly denser than the water around it and sinking further. Likewise, a small parcel of colder, fresher water will be displaced upwards and gain heat by diffusion from surrounding water, which will then make it lighter than the surrounding waters, and cause it to rise further. Paradoxically, the fact that salinity diffuses less readily than temperature means that salinity mixes more efficiently than temperature due to the turbulence caused by salt fingers.
Salt fingering was first described mathematically by Professor Melvin Stern
of Florida State University
in 1960 and important field measurements of the process have been made by Raymond Schmitt of the Woods Hole Oceanographic Institution
and Mike Gregg and Eric Kunze of the University of Washington, Seattle. A particularly interesting area for salt fingering is found in the Caribbean Sea, where it is responsible for producing a "staircase" of well-mixed layers a few metres in thickness that extend for hundreds of kilometres.
A classic paper by the American oceanographer Henry Stommel
(pre-dating the work of Stern) discussed the creation of a large-scale salt finger in which a column of water would be surrounded by a membrane that would allow diffusion of temperature but not salinity. Once primed by the movement of colder, fresher intermediate water upwards, the resultant "perpetual salt fountain" would be able to draw energy (heat) from the local ocean water stratification.
Salt fingering was first described mathematically by Professor Melvin Stern
Melvin Stern
Melvin Stern is a U.S. academic oceanographer who focuses on fluid dynamics. He serves as the Ekman Professor of Oceanography at Florida State University and is an elected member of both the National Academy of Sciences and the American Academy of Arts & Sciences. Dr...
of Florida State University
Florida State University
The Florida State University is a space-grant and sea-grant public university located in Tallahassee, Florida, United States. It is a comprehensive doctoral research university with medical programs and significant research activity as determined by the Carnegie Foundation...
in 1960 and important field measurements of the process have been made by Raymond Schmitt of the Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...
and Mike Gregg and Eric Kunze of the University of Washington, Seattle. A particularly interesting area for salt fingering is found in the Caribbean Sea, where it is responsible for producing a "staircase" of well-mixed layers a few metres in thickness that extend for hundreds of kilometres.
A classic paper by the American oceanographer Henry Stommel
Henry Stommel
Henry Melson Stommel was a major contributor to the field of physical oceanography. Beginning in the 1940s, he advanced theories about global ocean circulation patterns and the behavior of the Gulf Stream that form the basis of physical oceanography today...
(pre-dating the work of Stern) discussed the creation of a large-scale salt finger in which a column of water would be surrounded by a membrane that would allow diffusion of temperature but not salinity. Once primed by the movement of colder, fresher intermediate water upwards, the resultant "perpetual salt fountain" would be able to draw energy (heat) from the local ocean water stratification.