364 



DEPTHS OF THE OCEAN 



below 100 metres was extremely scanty. The maximum in 

 the ocean nearly always lay at about 50 metres, which is 

 what Lohmann also found in the case of the Mediterranean 

 coccolithophoridse. At the surface there was less than down 

 in the 20 to 50 metres zone, though the plankton nearly always 

 approached its maximum value as soon as we reached a depth 

 of 10 to 20 metres. At 75 metres the quantity diminished 

 to about half of that found at 50 metres, and at 100 metres it 

 had dwindled to at most a fifth. These were the values on our 

 southern section. On the northern crossing the quantity of 

 plankton fell away even more rapidly as we went deeper down ; 

 at Station 92, where there was a slight admixture of coast- 

 water near the surface, and the lighter surface layer was 

 separated from the pure Atlantic water somewhere between 25 

 and 40 metres, there were upwards of 250,000 plant cells per 

 litre in the surface layer ; whereas at 50 metres the plankton 

 was less abundant than at any of our previous stations, and only 

 amounted to 2213 cells per litre. 



These results quite bear out the most valuable investigations 

 so far made regarding the vertical distribution of algse in the 

 ocean, namely Schimper's observations in the Antarctic during 

 the " Valdivia" Expedition. He found that the entire produc- 

 tion was practically limited to the uppermost 200 metres, that 

 the bulk was to be found above 100 metres, and that the 

 maximum lay between 20 and 80 metres, or to be more precise, 

 between 40 and 60 metres. We were able to confirm this, after 

 comparing the volume of the samples taken with nets on those 

 few occasions when there was a sufficiently large quantity of 

 plankton at our stations to make such volume-measurements of 

 any real value. There was, however, a different vertical dis- 

 tribution everywhere along the coasts where diatoms abounded, 

 for then the exuberant plant production was limited to the 

 surface layer, which was mixed with fresh water from the 

 land. 



As illustrating our investigations at a station in the warmest 

 part of the Atlantic, I give particulars of what I found at 

 Station 64 (lat. 34° 44' N., long. 47" 52' W.) in water-samples 

 from 50 metres (150 cc.) and 75 metres (300 c.c). The figures 

 denote the number of individuals per litre. 



