It must be remembered that the currents on the two sides of the ocean flow in opposite directions.  Along the coast of Africa, we have the Benguela Current, flowing from south to north; on the American side the Brazil Current flows from the tropics southward.  The former current is therefore comparatively cold and the latter comparatively warm.  This is clearly seen on the chart, which shows the distribution of temperatures and salinities on the surface.  In lat. 20deg.  S. it was only about 17deg.  C. off the African coast, while it was about 23deg.  C. off the coast of Brazil.

The salinity depends on the relation between evaporation and the addition of fresh water.  The Benguela Current comes from

[Fig. 7]

Fig. 7. —­ Salinities and Temperatures at the Surface in the South Atlantic (June —­ August, 1911) regions where the salinity is comparatively low; this is due to the acquisition of fresh water in the Antarctic Ocean, where the evaporation from the surface is small and the precipitation comparatively large.  A part of this fresh water is also acquired by the sea in the form of icebergs from the Antarctic Continent.  These icebergs melt as they drift about the sea.

Immediately off the African coast there is a belt where the salinity is under 35 per mille on the surface; farther out in the Benguela Current the salinity is for the most part between 35 and 36 per mille.  As the water is carried northward by the current, evaporation becomes greater and greater; the air becomes comparatively warm and dry.  Thereby the salinity is raised.  The Benguela Current is then continued westward in the South Equatorial Current; a part of this afterwards turns to the north-west, and crosses the Equator into the North Atlantic, where it joins the North Equatorial Current.  This part must thus pass through the belt of calms in the tropics.  In this region falls of rain occur, heavy enough to decrease the surface salinity again.  But the other part of the South Equatorial Current turns southward along the coast of Brazil, and is then given the name of the Brazil Current.  The volume of water that passes this way receives at first only small additions of precipitation; the air is so dry and warm in this region that the salinity on the surface rises to over 37 per mille.  This will be clearly seen on the chart; the saltest water in the whole South Atlantic is found in the northern part of the Brazil Current.  Farther to the south in this current the salinity decreases again, as the water is there mixed with fresher water from the South.  The River La Plata sends out enormous quantities of fresh water into the ocean.  Most of this goes northward, on account of the earth’s rotation; the effect of this is, of course, to deflect the currents of the southern hemisphere to the left, and those of the northern hemisphere to the right.  Besides the water from the River La Plata, there is a current flowing northward along the coast of Patagonia —­ namely, the Falkland Current.  Like the Benguela Current, it brings water with lower salinities than those of the waters farther north; therefore, in proportion as the salt water of the Brazil Current is mixed with the water from the River La Plata and the Falkland Current, its salinity decreases.  These various conditions give the explanation of the distribution of salinity and temperature that is seen in the chart.