iz8 DISCOVERY REPORTS 



The abundant marine life of the region contains much which is of value to mankind. Whales, 

 fur-seals, guano islands and potentially rich fisheries are all to be found there. Linked up with these 

 features are areas in the open sea along the coast, with extraordinarily low concentrations of oxygen 

 in the subsurface layers ; the bottom deposit of diatomaceous mud is devoid of all but a few highly 

 specialized forms of life capable of existing under almost anaerobic conditions, for sulphuretted 

 hydrogen is evolved through the action of sulphate-reducing bacteria, and locally, under conditions 

 not yet fully understood, this process sometimes increases to such an extent that even the surface 

 waters are affected (Copenhagen, 1934, 1953). This may prove to be one of the factors leading to the 

 recurrent mass mortalities of fish, another peculiar feature usually encountered near the northern 

 limits of the region. Later we shall refer to the lethal effect of oxygen deficiency but it can also 

 reasonably be argued that these mortalities are due more directly to the action of noxious water-bloom, 

 probably of dinoflagellates, since visible discolorations of the sea by super-abundance of living 

 organisms are yet another phenomenon frequently met with, often coincidentally with the mortalities 

 (Brongersma-Sanders, 1948). These mass mortalities and water-bloom formations, which usually 

 take place between midsummer and autumn, seem to link up with seasonal fluctuations in the physical 

 conditions; but the mortalities only assume catastrophic proportions at long intervals, and these show 

 no regular periodicity. Possibly they may follow accentuated deviations from the normal variations 

 in physical factors of the environment, for it will be realized that here again there is close analogy 

 with conditions sometimes encountered off Northern Chile and Peru: the aguaje phenomena, the 

 ' Callao painter ' or ' el Pintor ', and the dreaded ' el Nino ' current. 1 Further data bearing on these 

 problems were among our secondary objectives; primarily the surveys were planned to improve our 

 knowledge of the current system as a whole — the norm against which more pronounced local and 

 temporary deviations can be assessed. 



Most of the earlier observations from the Benguela current formed but a small part of more extensive 

 programmes as the ships concerned passed down the coast on their way to the Indian Ocean; and 

 more recently, although four of the 'Meteor's' transatlantic profiles traversed the area, they were 

 necessarily carried out at widely separated intervals of time, so that the extent to which they are 

 comparable is limited. Dr Brongersma-Sanders, whose recent work provides an invaluable guide to 

 the literature, has also emphasized the need for more data (1947), and pioneer South African workers 

 in several different fields of research have done the same. 



We endeavour to do full justice to previous workers in the next section of this report, but the point 

 has been raised here to show that even such limited observations as could be carried out on a small 

 ship over short periods could still be expected to further the knowledge of the region considerably. 



The plan of the surveys consisted of three main lines of full ' stations ' (off 'Walvis Bay, Sylvia Hill, 

 and the Orange river) worked east and west, that is, nearly normal to the coast and to the main trend 

 of the isotherms ; and four lines of intermediate or subsidiary stations, the first in the northern part 

 of the area east and west, the second south-westward out to the offshore end of the first line of full 

 stations, and from the inshore end of each line of full stations to the offshore end of the next. The 

 east and west lines were disposed almost on the same latitudes as the eastern portions of previous 

 ' Meteor ' profiles, and thus afforded some direct comparison with previous work. Positions of all the 

 stations and the 200 m. depth contour are shown in Figs. 1, 2 and 4 (pp. 143 and 146). 



During the first survey (Fig. 1), we endeavoured to work the outermost station on each east- west 

 line in oceanic depths beyond the continental slope, and the spacing of subsequent stations was 

 therefore determined partly by the width of the shelf in the longitudes chosen and partly by practical 



1 Hitherto known by this name in oceanographical literature, Schweigger (1949) has recently challenged the correctness 

 of this usage. 



