The isopycnal swallow float-A simple device for tracking water parcels in the ocean

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A standard Swallow float can be converted into a passive, isopycnal follower by the addition of a 'compressee', a spring-backed piston in a cylinder designed to give the float the compressibility of seawater. Thus, no Archimedian buoyancy is created due to changes in depth. In addition, the float must have a coefficient of thermal expansion significantly smaller than that of seawater. An instrument meeting these requirements, ballasted to a chosen isopycnal, will approximately follow that isopycnal, on time scales longer than the local buoyancy period. Two preliminary field experiments were conducted in the upper main thermocline near the North Wall of the Gulf Stream. During August 1981, a spherical glass float was deployed 200 km downstream from Cape Hatteras, and was tracked for approximately 100 km. Neutrally buoyant in the oxygen minimum near 380 m, the float tracked the δT = 27.12 ± 0.01 as determined from CTD data during its passage through a mini-meander. During September 1982, a cylindrical float was tracked for approximately 100 km east of Cape Hatteras. Deployed in the Gulf Stream near the 250 m level, the float tracked the δT = 26.74 ± 0.01 isopyncal surface during a gradual descent and cross-stream motion over the 24 hr sampling period. Thus, the floats tracked nearly isopycnally in both field tests. Clusters of these instruments used in concert with hydrographic surveys have the potential for unique studies of mixing, entrainment and topographic effects. © 1985.

Publication Title, e.g., Journal

Progress in Oceanography