606 



The Tropospheric Circulation 



3. Other Currents of the Oceanic Troposhere 



(a) The Guiana Current and the Current Conditions of the American Mediterranean 



The stream lines of the tropospheric undercurrents of the Southern Hemisphere 

 converge from the whole of the South Atlantic towards the area off Cape San Roque 

 on the east coast of South America and the water of the South Equatorial Current 

 flows into the Northern Hemisphere at this point. The subtropical salinity maximum 

 of 36-7%o at about 120 m depth can be followed far to the north (as far as the West 

 Antilles and beyond) in a salinity section following the course of the Guiana Current 

 north-westwards along the South American coast. The character of this water remains 

 almost unchanged from the area of South Equatorial Current in the Southern Hemis- 

 phere to the Antilles. For the most part the current axis remains over the broad shelf 

 off the mouths of the Amazon and the Orinoco. The corresponding pressure gradient 

 could be determined so far only from very few stations. The direction of the pressure 

 gradient in a gradient current must be reversed on passing from the Southern to the 

 Northern Hemisphere. This can be seen in the sea level topography given in Fig. 271. 

 South of the equator the higher pressure occurs at the coast with the lower pressure 

 farther out; north of the equator this is reversed and here the Guiana Current is accom- 

 panied along its right-hand edge by a narrow ridge of high water level with a down slope 

 towards the coast which in accord with the great strength of the current is quite 

 considerable. The Guiana Current, together with the southern part of the North 

 Equatorial Current, flows into the Caribbean through the passages between the Lesser 

 Antilles (sill depth less than 1000 m). The observational data for this sea has been 

 evaluated principally by Parr (1935, 1937«, 1938a); see also Seiwell (1938) and 

 Rakestraw and Smith (1937) on chemical aspects and a review of these conditions 

 by Dietrich (1939). The tropospheric currents between 100 and 200 m are very 

 clearly shown by the salinity maxima of the undercurrents which are a continuation of 

 those of the North and South Equatorial Currents. Figure 280 shows a chart of surface 



Fig. 280. Distribution of salinity in the core of the subtropical salinity maximum in the 

 American Mediterranean (according to Dietrich). 



