724 



DEPTHS OF THE OCEAN 



The abundant plankton peculiar to boreal waters in summer 

 (August) apparently accumulates in those layers where the 

 highest specific gravity occurs, the volume thence decreasing in 

 the deep uniform layers below 500 metres. A series of hauls 

 taken close to the Wy ville Thomson Ridge in the southern part 

 of the Norwegian Sea at Station 113 gave the following 

 results : — 



100 to o metres gave 10 c.c. containing 

 300 to 100 ,, 5 „ 



500 to 300 „ 12 ,, 



1000 to 500 „ 140 



species of Crustaceans. 



5Ldo 



.5 6 r £ 



90 a- yo 60 5» 



9 n.o .1 J. Ji 

 2° /» 



^ .5 ^ .7 .G. 



'N. 



\ 



Fig. 518. — Curves of Temperature (t°) and 



Specific Gravity (cr,), Station 8o. 



(Off Newfoundland Bank.) 



The curve for specific gravity shows here (see Fig, 519) a 

 rapid rise down to 100 metres, then a slow rise down to 

 about 300 metres, and finally a rapid rise down to about 600 or 

 700 metres. A pronounced minimum in the volume of Crustacea 

 occurs between 300 and 100 metres, and an enormous increase 

 is found between 1000 and 500 metres, where the volume is 

 fifty times larger than the volume in the surface layers of the 

 Sargasso Sea. 



In my opinion these facts prove the correctness of the 

 hypothesis that minute pelagic Crustacea (and consequently 

 nourishment suitable for larger organisms) tend to accumulate 

 at those depths where a pronounced rise in the specific gravity 



