ANTARCTIC SURFACE WATER , 7 



All the above stations were made south of 6o° S except St. 15 10, and several were at 

 the edge of the pack-ice north of the continent. The phytoplankton catches during this 

 cruise showed that production had begun earlier in the east than in the west, even 

 allowing for the time interval involved in a west to east cruise lasting 20 days. In general 

 terms it may be stated that in the west (Sts. 1510 to 1523) the phytoplankton was 

 evidently not yet at its maximum, in the centre (Sts. 1525 to 1533) the phytoplankton 

 was in much greater quantity and was probably at its maximum, while from St. 1535 

 eastwards we entered a "grazed down" area. This area was one in which the diatom 

 nets contained large numbers of euphausian faecal pellets, while the actual catch of 

 undamaged phytoplankton organisms was small. The faeces contained numerous diatom 

 fragments, indicating a previous heavy production of phytoplankton which had been 

 consumed by zooplankton. A striking result of an inspection of the surface values is 

 the general lowness of the phosphate having regard to the average high latitude of 

 the stations. Although production of phytoplankton in the southern region does 

 not come to a maximum until the third week in February ( + 2 weeks) there must 

 have been a steady drain on the available phosphate from November onwards. It must 

 be remembered that in the southern region of the Antarctic zone the phytoplankton 

 production is a long steady process of small concentration, as opposed to the rapid rise 

 and fall of the huge concentration in the northern region. 



From these same stations in Table I some idea can be gained of the amount of phos- 

 phate that is withdrawn from the surface layer by the phytoplankton. Thus at St. 1543, 

 an ice-edge station in 42I E, the phosphate content between 40 and 400 m. is uniformly 

 128 mg., which figure may be taken as a typical pre-production value for the surface 

 layer at the ice-edge. On an average this value is reduced to about 87 mg. at the sur- 

 face in February, i.e. a consumption of 41 mg. out of 128 mg. or about 32 per cent at 

 the surface at the ice-edge. Exceptionally the consumption at the ice-edge may be 

 greater, at the above station (1543), for example, a consumption of 56 mg. has taken 

 place or a withdrawal of the order of 44 per cent of available phosphate. North of the 

 ice-edge in 20 E the phosphate was even more reduced as the following figures from 

 St. 1529 in 64 547' S, 20 oo-6' E show: 



Depth m. o 10 20 30 40 50 60 80 100 



P 2 5 mg./m. 3 68 64 64 65 112 120 124 124 124 



Thus out of an available 124 mg. throughout the surface layer, as much as 60 mg. or 

 over 48 per cent of available phosphate has been withdrawn at 10 m. through the agency 

 of phytoplankton. This reduction in phosphate content was accompanied by a very 

 large concentration of phytoplankton, and it is of great importance to note that the 

 reduction was confined to a shallow layer from the surface to a depth of 30 m., below 

 which a considerable discontinuity existed. At this station the 0-30 m. layer was un- 

 doubtedly the extent of the photosynthetic layer in this high latitude, and it is interesting 

 to note that the value at 10 m. was lower than the surface value. Had a sample been 

 taken at 5 m. it might have shown the seat of maximum utilization of the phosphate. 



