i 34 DISCOVERY REPORTS 



Perhaps the best known of all upwelling regions, owing to its ready accessibility, is the Californian 

 current. Abundant recent researches into its oceanography carried out by various leading workers 

 show essentially similar relationships to those which we have found in the Benguela current. The 

 numerous references in later sections should show how valuable this work has been in interpreting 

 the present data. 



One feature of the Benguela current region which has attracted widespread interest is the occurrence 

 of fish mortalities, particularly in the vicinity of Walvis Bay, and their possible causes, biological or 

 otherwise. The whole subject has been comprehensively discussed by Dr Brongersma-Sanders (1948) 

 who treats all the relevant literature thoroughly. This and further recent work, in particular some of 

 the results of the Danish ' Galathea ' Expedition (1950-2), will be discussed in the appropriate sections. 



The work of the 'Meteor' expedition 

 The extensive data collected by the ' Meteor ' in 1925-7 have revealed the general pattern of the circula- 

 tion in the South Atlantic (Wiist, 1950) and the disposition of the observations was such that some of 

 them fell within the South-west African region. This enabled Defant (1936) to present the most 

 complete account of the region so far. 



The ' Meteor ' observations consisted of several more or less latitudinal lines of stations across the 

 Atlantic Ocean. The eastern ends of five of those great sections fell within the Benguela current, and 

 it is those stations which Defant used. Defant supplemented his study of the ' Meteor ' observations 

 by a new analysis of the Dutch surface current observations. These he meaned in one degree areas 

 (one degree of latitude by one degree of longitude) for each quarter of the year, and his results 

 (Fig. 6) present us with an interesting new interpretation of the surface water-movements. The out- 

 standing feature of these current charts is that they reveal a one-sided line of divergence. It lies- in 

 a N.N.W. direction along the coast, from about 20 to 30 S. In the south it is about 160 sea-miles 

 from the coast, and in the north 300-350 sea-miles. To the west of this line the current sets to the 

 west, but to the east of it the current runs more or less parallel to the divergence but is somewhat 

 irregular on its coastal boundary. 



Comparing this system with the iso-anomaly lines of surface temperature (the lines of equal 

 difference from the latitudinal mean) Defant further finds that the region of strongest negative 

 anomaly, the coldest water, is confined to the coastal current, and is most marked in the region between 

 23 and 31 S. where the divergence is also most pronounced. 



The vertical thermo-haline distribution on the five ' Meteor ' ' Profits ' shows a correspondingly good 

 agreement with the surface picture. 'Profil' IV in 34 S. shows but little evidence of upwelling close 

 against the land, while on 'Profils' II (28A S.) and VII (22 S.) the characteristic uplift of the iso- 

 therms and isohalines against the coast indicates the upwelling of the subsurface-waters from a depth 

 of about 300 m. The more northerly 'profils' suggest a sinking rather than an uplift of water against 

 the coast. In 'Profil' VI (15-16 S.) the isotherms and isohalines, at a depth of 30-40 m., descend 

 toward the coast, and in 'Profil' VIII (9 S.) this is even more pronounced. Thus the region of most 

 intense upwelling, as adduced from the vertical pictures, corresponds with the position of the most 

 marked negative surface temperature anomaly and the most well-defined divergence in the surface 

 currents. 



Defant then considers theoretically the problem of the circulation by examining the effect of winds 

 on two bodies of water of different density lying in a canal. This will be discussed in more detail later, 

 but for the present it will suffice to say that by applying his derived theory to the South-west African 

 waters, he concludes that outside the divergence there must be a vertical eddy in the upper layers. 

 Below the axis of this eddy the water will move towards the east, ascending to the surface inside the 



