Characteristics of thermohaline steps off the northeast coast of South America, July 1983

Abstract

XBT and CTD measurements made in the Atlantic Ocean southeast of Barbados reveal a series of large thermohaline steps lying between the salinity maximum of the Subtropical Underwater at about 100 m and the salinity minimum of the Antarctic Intermediate Water at about 800 m. Historical data indicate that the steps are a permanent feature of the area extending over some 10 6 km 2. At two multicast stations in July 1983 the average step was 19.0 dbar in thickness, and the average interface between steps was 2.1 dbar thick. Mean potential temperature, salinity and potential density changes across the interfaces were, respectively, 0.526°C, 0.084 psu, and 0.030. Internal structure was noted in some of the steps, as well as features resembling intrusions. The low value of the density ratio, approximately 1.5, supports the hypothesis that the steps are caused by intense salt finger activity. Estimates of vertical fluxes of heat and salt through the staircases are large enough to suggest that the process plays a major role in vertical exchange across the thermocline in this region and, consequently, a major role in determining the T-S properties of the equatorial thermocline and of the Caribbean Current-Gulf Stream system.