Preliminary data products generated onboard the SEWARD JOHNSON are presented. Velocity vectors from the LADCP observations are superimposed on property fields to illustrate the distributions of temperature and salinity at the sea surface; salinity and temperature of the salinity maximum representative of Subtropical Underwater; salinity of the salinity minimum respresentative of Antarctic Intermediate Water, and salinity at the level of PALACE float drift, 1000m.
At the sea surface (Fig. 13), the dominant currents are the coastally trapped and narrow North Brazil Current (NBC) crossed at 6oS and 6oN; at 6oN, the retroflection of the NBC is characterized by southeastward flow; and the North Equatorial Countercurrent (NECC) that extends across the entire basin at 6oN. At 6oS, the offshore currents typically include a southward component, most likely indicative of Ekman transport, the latter probably masked by the intense NECC at 6oN.
The sea surface temperature field (Fig. 13) includes the summer cold water tongue of the tropical Atlantic Ocean with minimum temperatures less than 22oC on the equator centered at about 13oW. There is some additional structure in the XBT representation of SST (Fig. 1) but not significantly more. The surface salinity field has few regions of intense gradients except for some low salinity lenses in the extreme west at 6oN and low salinity on the eastern extremes of the 6oS and 6oN transects (Fig. 14).
Currents and salinity field at the depth of the shallow salinity maximum characteristic of SUW are shown in Figure 15. SUW depths are typically about 100m in the western tropical Atlantic. The input of high salinity SUW formed in the southern hemisphere by the NBC is apparent along the western end of the 6oS section. The Equatorial Undercurrent is also apparent along the equator transporting this higher salinity water eastward after a portion of the NBC retroflects at the boundary. High salinity from the SUW if present would only be found along the western edge of the 6oN section.
The cold water tongue is still apparent at the depths of maximum salinity in the eastern Atlantic (Fig. 16). Warmer waters are advected north by the NBC along the Brazilian coast. The closed contours just north of the equator on the western boundary are compatable with the Amazon Eddy reported on by earlier investigators.
The salinity and velocities at the depth of the minimum salinity characteristic of Antarctic Intermediate Water (AAIW) are given in Figure 17. AAIW is typically found at about 600 m in this region. Gradients are primarily zonal with only the slighest suggestion of throughflow of low salinity water on the western boundary. Currents at this depth along the equator are generally to the west.
The current vectors and salinity field at 1005m, the approximate depth of PALACE float drift, are shown in Figure 18. At 6oN, flow in the west is predominantely to the north and/or east and to the north and west along the eastern portion of the section. Equatorial flows are primarily zonal and the the west. Flow at 6oS is generally to the east along the section with no predominant meridional direction obvious.