On horizontal and vertical transport of Ford water

Abstract

Abstract Three transects of shelf-origin water (Ford water) at the slope water — Gulf Stream boundary between 69 °30′W and 72 °10′W (August 1–5, 1992) were run with a towed scanning profiler equipped with conductivity-temperature-depth probe. The sections from the surface to 200 m depth with horizontal resolution of about 1 km demonstrate simultaneous propagation of the surface and subsurface Ford water connected by a thin and narrow (several km wide) transition area. The thermohaline structure and sharp density fronts at the former water boundaries are maintained downstream. Transport is estimated at 460 ∗ 10 3 m 3 / s (with 33% of shelf water, whose salinity is taken to be 32%.) that is 4.6 times greater than a previous estimate. It is suggested that evidence is found of intermittent vertical transport of freshened water from the surface band to the subsurface one. The subsurface band separates in two features in the transition area from predominent thermoclinicity of the Gulf Stream front to its noticeable baroclinicity owing to the increasing slope of the isopycnal ≅ 26σ t , the lower feature being subducted along the property front to a local depth of the isopycnal bounding the feature from below. Thermohaline intrusion of the freshened water in the Gulf Stream thermocline in the same transition area provides cross-frontal transport of the water, a trace of which is found in the Gulf Stream water at a depth of ≅ 190 m. The association of formation of the intrusion, whose axis is inclined to isopycnal surfaces, with thermohaline parameters of the front and ageostrophic circulation at the site of its cyclonic curvature due to a spin-off eddy is discussed.