286 DISCOVERY REPORTS 



of the South-west African region there is evidence that sinking and death of the phytoplankton occurs 

 on a large scale. This, together with the ephemeral nature of the upwelling, leads one to question the 

 efficiency of the grazing and to suppose that it may not reach its potential level, and that much 

 organic matter may be lost at this early stage in the organic cycle. 



It is tempting to speculate on the possible interactions of primary production, sinking and grazing 

 in a region such as this, but our data do not permit us to put any time-scale on the processes involved 

 and so at best such a discussion would be truly speculative. Clearly this would be one of the prime 

 considerations in any more extensive a study which might be contemplated in the future. It is quite 

 outside the scope of an exploratory survey such as was made by the 'William Scoresby'. 



SUMMARY 



The R.R.S. 'William Scoresby' made two surveys of the waters off the South-west African coast as 

 part of a more extensive programme of oceanography and whale-marking in the Atlantic and Indian 

 Oceans. 



These surveys, the first in autumn (March) and the second in spring (September-October) 1950, 

 were planned to obtain a more detailed picture of the water movements and biological features of this 

 region than had hitherto been attempted. Furthermore, the comparison of this region with the Peru 

 coastal current which had at an earlier date been surveyed by the same ship and with other upwelling 

 regions was one integral part of the wider field of work, the study of organic production in the oceans. 



The report commences with a brief account of the early voyages and previous scientific work in this 

 region, notably referring to the work of the 'Meteor' expedition, 1925-7, some of whose observations 

 were made in South-west African waters. 



The oceanographical methods used on these surveys are described together with the various 

 laboratory techniques and methods of analysis which were later used in interpreting the observations. 

 This section on the work of the R.R.S. ' William Scoresby ' is concluded with a detailed account of the 

 itinerary of each survey. 



A description of the topography of the coastal region of South-west Africa and the adjacent sea-floor 

 follows. An outstanding feature of the coast is an extensive arid desert, the Namib desert, whose 

 existence is intimately connected with the presence of cool surface-waters along the coast. On the 

 sea-floor, the continental shelf has a width of some 40-80 miles and from the edge the bottom slopes 

 away steeply into the abyssal depths of the Cape and Angola basins. These basins are separated by 

 the Walvis Ridge, a prominent feature which connects the continent of Africa to the Central Atlantic 

 ridge. 



The wind system over the south-west African region is shown to be divided into two well-defined 

 components, the south-east trade wind which predominates over the oceanic waters and the diurnally 

 variable coastal winds which prevail in a belt extending seawards some 80 miles from the coast. The 

 trade wind can be considered as the eastern limb of the anti-cyclonic circulation of air over the South 

 Atlantic and the coastal winds as a divergence of the coastal boundary of the trade winds, resulting 

 from the extensive diurnal pressure changes over the continent. The coastal wind of importance is 

 S.S.W., which brings warm, moist air from the ocean over the cool coastal waters, and leads to the 

 formation of fogs and the aridity of the land to leeward. 



During the surveys, the trade wind was weaker in March (survey I) and better developed in 

 September-October (survey II). The coastal winds were on the whole weak in March and stronger in 

 September-October. 



The sea-surface currents are, like the winds, divisible into two clearly defined circulations. In the 



