226 DISCOVERY REPORTS 



The results for the National or Plankton expedition are based on the settlement volumes of quanti- 

 tative fine-net hauls mostly from c. 200 m. to the surface (Hensen, 1895, table 2, p. 8). 



The Dana results are compiled from Jespersen (1923, fig. 1 ; 1935, table 36) and are the volumes 

 (measured by drainage in a graduated sieve) of macroplankton, caught per 1 hr. tow (with c. 50 m. 

 wire out) using a 1 \ or 2 m. stramin net. 



The Carnegie results are those from Wilson (1942, pp. 15-168), and they represent the combined 

 settlement volume in cc. of Pacific Ocean samples at o and 50 m. with \ and 1 m. nets. 



The B.A.N.Z.A.R.E. results are the displacement volumes of vertical hauls with a 70 cm. Dis- 

 covery net and are given in Sheard (1947, table 8, p. 11). As there are so few of them only the mean 

 1 00-0 m. volumes for latitudes 30-40 S, 40-50 S and 60-70 S are shown in Fig. 19; they are 

 indicated by a cross. 



The results of all the expeditions (Fig. 19) show a marked similarity of gradation, from the maximal 

 quantities of plankton in high latitudes to the minimal values in low latitudes. There is, however, 

 great variation in the ratio, which ranges from 14 : i(' Meteor ') to 4-5 : 1 (' Discovery '). This is probably 

 due both to the varying degrees of sampling in different latitudes and times of year, and to the differences 

 in the sorts of organism caught. On the whole the greatest ratios are from nannoplankton and macro- 

 plankton catches, and were the Discovery data for these particular groups of organisms available they 

 would probably show a comparable — if not greater — difference. Dr T. J. Hart believes that centri- 

 fuging would yield at least a 10:1 ratio for Antarctic microplankton as against that of warm seas. 

 (This is merely a personal opinion based on unpublished results of some 120 Antarctic stations and a 

 few sub-Antarctic and sub-tropic stations during 1933-35.) The Antarctic macroplankton would 

 include ' krill ', and again the ratio would be considerably increased, since there is no comparable form 

 in warmer seas (see p. 218). 



The smallest catches are not necessarily those nearest the equator and the Atlantic results of the 

 ' National ', ' Meteor ', and ' Dana ' expeditions show a marked rise in the quantity of plankton in this 

 region. This is due largely to local areas of fertility near the Ascension and Cape Verde Islands (the 

 Kongo-Zunge and Kapeverden-Zunge of Hentschel, 1936, fig. 2. p. 10; see also Jespersen, 1935, p. 30). 

 The Deutschland results, in similar latitudes but in the Central Atlantic area, show a smaller increase 

 (Lohmann, 1919, fig. 2). 



In the Pacific also there is an increase in the abundance of plankton near the equator, as is shown 

 by the Carnegie results. Graham (1941), using plankton dry weight as a measure of productivity, has 

 confirmed this, while King & Demond (1953) have shown that the area of greatest abundance is north 

 of the equator when related to a convergence and to the south when there is no marked convergence. 

 In spite, however, of local areas of increase in the tropics the overall picture from Fig. 19 is one of 

 greatest standing crop of plankton in the cold waters of high latitudes. 



Of the many expeditions that have penetrated the Southern Ocean as far as the pack-ice only the 

 B.A.N.Z.A.R.E. results have been analysed in relation to the standing crop of plankton (Sheard, 

 1947). The samples, which were collected during the 1930-31 summer season (November-April) 

 from sub-Antarctic and Antarctic waters are on the whole greater in volume than those described for 

 similar months and depths in this paper. This may, however, be due to the inclusion of gelatinous 

 organisms or phytoplankton in the measurements given by Sheard. From his results (Sheard, 1947, 

 table 8) it is apparent that the vertical distribution of the plankton is typical of summer months with 

 most of the plankton concentrated in the upper 100 m. of water. There are too few observations for 

 a close comparison to be made with the variations in a north-south direction shown from the results 

 of other expeditions in Fig. 19. The three mean values for latitudes 30°-40° S, 4o°-5o° S, and 6o°-70° S 

 which are indicated by a ' x ' show, however, that the B.A.N.Z.A.R.E. results are not at variance with 



