HYDROLOGY u 



mixture in the path of the two currents. This mixing of waters may have a profound 

 influence upon the plankton production, and so upon the distribution of the whales in 

 the area; a discussion of this will be reserved for a later section. 



Figs. 7 and 8 show the vertical distribution of the temperature, salinity and oxygen 

 content of the upper 500 m. of water round South Georgia during the December- 

 January survey, 1926-7. The cold, poorly saline, Antarctic surface layer is clearly shown, 

 and below it the warmer, more saline, intermediate layer. The difference in character 

 between the Bellingshausen Sea water and the Weddell Sea water we have said is very 

 slight; how slight it is will be seen by comparing the "A" line and outside end station of 

 the " G " line, which are Bellingshausen water, with the outside station of the " C ", " D " 

 and "E" lines, which are Weddell Sea water. The Bellingshausen Sea water is slightly 

 warmer at the immediate surface than the Weddell Sea water. The warm area of mixture 

 of the two currents to the west of the island on the " G " line and round the south of the 

 island is clearly seen and is shown again in the temperature map in Fig. 41 on p. 82. 

 Figs. 9 and 10 show the vertical distribution of the temperature and salinity (and oxygen 

 content at one station only) at the deep-water stations on the oceanic lines between 

 South Georgia and the Falkland Islands in February 1927, and between South Georgia 

 and Tristan da Cunha in February 1926. For the positions of these stations see the 

 maps in Figs. 14 and 11. They each show clearly the differences in hydrological con- 

 ditions in the Antarctic and the sub-Antarctic Zones on each side of the line of Antarctic 

 Convergence. 



Further reference will be made to this information put at our disposal when we are 

 discussing the relation of the plankton to these hydrological conditions in the later 

 sections of the paper. The details of temperature, salinity, oxygen and phosphate dis- 

 tribution and water movements will then be considered. In the present section we are 

 giving a brief outline of the geography of the region under consideration. We are 

 dealing with the plankton from three distinct surface masses of water. There is the 

 sub-Antarctic water to the north which we sampled at a few stations between Tristan 

 da Cunha and South Georgia, and between South Georgia and the Falkland Islands, 

 and there are the two water masses lying within the Antarctic Zone, one on each side 

 of South Georgia. We have also sampled the plankton from the warmer intermediate 

 layer, and occasionally at very deep stations penetrated into the cold bottom layer. 



Lastly, in this brief sketch of the geography of the area we must not omit reference 

 to the strong and frequent gales. Whilst over the whole area under consideration the 

 prevailing winds are from the south-west, it appeared to us that South Georgia itself, 

 with its high range of snow-covered mountains, was the centre of many local disturb- 

 ances of great violence. These frequent storms might be thought to churn up the 

 water to such an extent that the vertical distribution of the plankton in the shallow 

 regions over the continental shelf would be seriously affected ; evidence is presented 

 on p. 268 to show that this is not so. 



