CIRCULATION OF THE MACROPLANKTON 373 



Table II shows that in 8o° W, as in other parts of the Antarctic, a large part of the 

 plankton is made up of the Copepods Rhincalanus gigas and Calanns acatus, and the 

 Chaetognath Eukrohnia hatnata ; but the adult Calanus propinquus which is very abund- 

 ant in some parts of the Atlantic sector was here comparatively scarce. Certain small 

 Calanoids were sometimes taken in large numbers. C. simillimus made up a certain 

 proportion of these but the majority were difficult to identify, and there was usually 

 some doubt as to whether they should be picked out or disregarded as being too small. 

 Some species such as Parathemisto gaudichaudi and Primno macropa were usually clearly 

 adult or definitely smaller and clearly immature. In such cases the large and small 

 examples have been listed separately. The sizes of others, such as Rhincalanus and 

 Eukrohnia were too evenly graded for such a distinction to be made. 



THE DRIFT OF THE PLANKTON 



The distribution and movements of the various water masses of the Southern Ocean 

 have been described in a number of recent publications. The movements of certain of 

 these layers however are intimately concerned with the subject of this paper, and a brief 

 account of them must therefore be repeated here. For fuller information reference 

 should be made to Wiist (1928 and 1933), Clowes (1933), Deacon (1933 and 1937) and 

 Sverdrup (1933). 



"In the Antarctic Zone the surface layer is composed of cold poorly saline water, 

 which lies in a shallow well-defined layer above warmer deep water. It has a depth of 

 100-250 m., and is separated from the warm water below it by a discontinuity layer, 

 within which the temperature and salinity increase rapidly with depth." (Deacon, 1933, 

 p. 173). This layer of Antarctic surface water is bounded in the south by the Antarctic 

 continent and in the north by the Antarctic convergence where it meets the warmer sub- 

 Antarctic water. Below it is the much thicker layer of the warm deep water, and below 

 that again is the Antarctic bottom water. Except in the highest latitudes the movement 

 of all these layers in the Southern Ocean is in general from west to east, but there is a 

 northerly component in the movement of the surface and bottom layers and a compen- 

 sating southerly component in the movement of the warm deep water. In the Antarctic 

 surface layer there is thus a continuous transport of water to the north, and when this 

 water reaches the Antarctic convergence it sinks abruptly below the sub-Antarctic 

 water, and there is a sharp rise of temperature at the surface. 



Fig. 2 is a vertical section of the first 1000 m. of water in the meridian of 8o° W and 

 shows diagrammatically the disposition of the surface and warm deep waters and the 

 north and south components in the movement of the water. The principal flow of the 

 water may be imagined as taking place at right angles to the plane of the page and to- 

 wards the observer, and the arrows represent the tendency for the water to work gradu- 

 ally northwards at the surface and southwards deeper down. It will be noticed that the 

 warm deep water tends to rise towards the surface as it moves south, but it must be 

 remembered that the vertical scale of the section is greatly exaggerated. The relative 

 strength of the easterly and northerly components of the drift of the Antarctic surface 



