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Abstract
High-resolution velocity shear, CTD, and microstructure measurements were made simultaneously from the research submarine Dolphin in Monterey Bay in October 1984. During three consecutive dives, the Dolphin cycled between the surface and 110 m along predetermined tracks 10 miles northwest of Monterey. Inside the seasonal thermocline, the vertical velocity shear appeared to be concentrated in layers 10 m thick extending several kilometers horizontally. The thickness of the shear layers is consistent with the typical size of turbulent patches encountered in the seasonal thermocline. In contrast, no large shear layers were observed below a 50 m depth. The depth levels at which the shear layers were observed were nearly constant throughout each dive, suggesting that the shear layers, with some unknown degree of intermittency, might extend horizontally over several square kilometers. The shear vector inside the seasonal themocline (at σt = 25.5) rotated 360° over an inertial period, but did appear to propagate vertically over the 30-hour observation period. These observations suggest that the passage of a storm caused the upper thermocline to ring, creating a local jetlike flow below the mixed layer.
Abstract
High-resolution velocity shear, CTD, and microstructure measurements were made simultaneously from the research submarine Dolphin in Monterey Bay in October 1984. During three consecutive dives, the Dolphin cycled between the surface and 110 m along predetermined tracks 10 miles northwest of Monterey. Inside the seasonal thermocline, the vertical velocity shear appeared to be concentrated in layers 10 m thick extending several kilometers horizontally. The thickness of the shear layers is consistent with the typical size of turbulent patches encountered in the seasonal thermocline. In contrast, no large shear layers were observed below a 50 m depth. The depth levels at which the shear layers were observed were nearly constant throughout each dive, suggesting that the shear layers, with some unknown degree of intermittency, might extend horizontally over several square kilometers. The shear vector inside the seasonal themocline (at σt = 25.5) rotated 360° over an inertial period, but did appear to propagate vertically over the 30-hour observation period. These observations suggest that the passage of a storm caused the upper thermocline to ring, creating a local jetlike flow below the mixed layer.
In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations supported by the National Science Foundation research icebreaker Nathaniel B. Palmer. This article describes the experiment, in which fluxes of heat, mass, and momentum were measured in the upper ocean, sea ice, and lower-atmospheric boundary layer. Initial results illustrate the importance of oceanic heat flux at the ice undersurface for determining the character of the sea ice cover. They also show how the heat flux depends both on high levels of turbulent mixing during intermittent storm events and on large variability in the stratified upper ocean below the mixed layer.
In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations supported by the National Science Foundation research icebreaker Nathaniel B. Palmer. This article describes the experiment, in which fluxes of heat, mass, and momentum were measured in the upper ocean, sea ice, and lower-atmospheric boundary layer. Initial results illustrate the importance of oceanic heat flux at the ice undersurface for determining the character of the sea ice cover. They also show how the heat flux depends both on high levels of turbulent mixing during intermittent storm events and on large variability in the stratified upper ocean below the mixed layer.
