21 
comparison between long and short sections, 
Moreover, the effect of upwelling occurring mainly in 
a narrow coastal zone at a depth of less than 300 m 
becomes more evident, 
During METEOR's work off the Mauretanian coast, norther- 
ly winds with a mean force of 5 Bft. were prevailing, 
On several days the mean wind velocity was 7-8 Bft, 
(cf, DOD lists, p. 25). 
From the horizontal charts and vertical sections the 
effect of upwelling south of Gibraltar is clearly re- 
cognisable. The mean trade winds blowing from the North 
caused upwelling phenomena by which water masses near 
the coast were brought up into the surface layer. 
The sections reveal that upwelling is limited to the 
upper 150 to 200 m, The width of the upwelling area is 
between 20 and 50 km. 
The structures in the distribution of temperature and 
salinity in the upwelling area suggest, however, that 
the upwelling phenomena are not uniform due to the 
changing force of the wind and its offshore component, 
Furthermore, the horizontal advection of different water 
mnasses plays an important role and complicates the 
simple phenomenon of upwelling,. 
The horizontal near-surface gradients caused by vertical 
movements are relatively weak, compared with the condi- 
tions farther south along the coast of Mauretania, 
0n the basis of the general hydrographic situation this 
may be explained as follows; 
1, The oceanic surface water which is not influenced by 
upwelling is cooler (and more saline) in higher la- 
titudes, 
„IM 
Appreciable vertical gradients only occur beneath the 
upper layer of 100 to 150 m thickness in higher lati-