Generation of submesoscale vortices: A new mechanism

Small‐scale, intense vortices composed of water with anomalous values of quasi‐conservative tracers have been observed in many oceans. They are particularly numerous in the Beaufort Gyre of the Arctic Ocean. Possible mechanisms responsible for the generation of these features are examined. Conservation of temperature, salinity, and nutrients requires that Beaufort Sea vortices be created from water that flows into the Arctic Ocean from the Pacific Ocean across the broad, shallow Chukchi Sea. Much of this water passes through Barrow Canyon, near Point Barrow, Alaska. Observations in the canyon show the generation of vortices of approximately the same size as those observed in the Beaufort Sea. Barrow Canyon is therefore a likely site for the generation of Beaufort Sea vortices. Most observed Beaufort Sea vortices have a central potential vorticity near zero because of a relative vorticity close to −ƒ. Their Chukchi Sea source water is typically stratified with little relative vorticity, so that its potential vorticity is nonzero. A key step in the generation of the vortices is therefore the reduction of the potential vorticity of Chukchi Sea water to nearly zero. It is proposed that this occurs through the action of frictional torques occurring as the Chukchi Sea water flows through Barrow Canyon, rather than througji the action of vertical mixing. Because this flow is driven by a downstream pressure gradient, it is concentrated on the right‐hand wall of the canyon by the Coriolis force. The frictional torques thus preferentially reduce the potential vorticity of the fluid. Anticyclonic vortices are therefore preferentially generated. It is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the Mediterranean and Labrador seas.