RHINCALANUS GIGAS 



291 



indicated as a dotted line in Figs. 3 and 1 1 and is a region of very marked upwelling of 

 warm deep water towards the surface. These regions of upwelhng deep water are of im- 

 portance, since they have pronounced effects upon the plankton. 



In the surface water of each of the two main water masses in the Falkland Sector — 

 the Weddell Sea current and the Bellingshausen Sea current — it has been found possible 

 to distinguish four main types of water each having fairly distinctive characters. Figs. 5, 

 6 and 7 show the isotherms in the Falkland Sector during the seasons 193 1-2 and 



Fig. 7. Isotherms (°C.), calculated from the average temperature of the surface 100 m., in the Falkland 

 Sector of the Antarctic, February, March 1933. (Dotted lines represent the conjectural position of the 

 isotherms.) 



1932-3, based upon the average temperature of the surface hundred metres at each 

 station. The following four types of water are distinguishable: 



(a) Very cold water with a temperature less than — 1-5° C, carrying pack-ice which 

 is not melting. 



(b) Warmer water with a temperature between — 1-5 and — i-o° C, carrying melting 

 pack-ice. 



{c) Water with a temperature between — i-o and o-o° C, in which pack-ice has 

 recently melted. 



(d) Water with a temperature between o-o and i-o° C. in the Weddell Sea current and 

 between o-o and 2-0° C. in the Bellingshausen Sea current. 



Thus there is established a conception of the "age" of water of various types, since 



