7i6 DEPTHS OF THE OCEAN 



Pettersson's observations made by the aid of his ingenious 

 self-registering appHances are of very great interest, but it must 

 be pointed out that the relations between the phases of the 

 moon and the waves are not very well marked. Further, it is 

 well known that similar oscillations in the water-layers of the 

 Scottish lochs are produced by the varying winds that blow 

 over the surface.^ 



Nordgaard has compiled an account recording the 

 months of the year when southern Atlantic fish-species are 

 stranded on the coasts of Norway, and has found that such 

 strandings generally occur from January to May. On this 

 subject he remarks : " It is hardly accidental that so many 

 specimens of these pelagic deep-sea fishes arrive on the coast 

 during the first months of the year, during the time of the cod 

 fisheries (when the shoals of cod appear in order to spawn). 

 It is obvious that during this season especially the deeper 

 layers move towards the land, probably as a compensation 

 current in deep water caused by the off-shore winds forcing 

 the surface layers out to sea." If we look at Fig. 509, show- 

 ing the annual changes of temperature in the sea off western 

 Norway, we shall see that towards the new year and during 

 spring a marked drop in temperature occurs in the surface 

 layers. We must take it for granted that the organisms con- 

 sequently tend to move towards the surface, the specific gravity 

 and viscosity of the water increasing enormously compared 

 with the conditions in warmer seasons. 



These conditions and their influence upon animal life are 

 to a great extent mere guess-work, but they open up a vast 

 field for future oceanic research. 



Nutrition 



Sir John Murray divides marine deposits (see p. 161) into 

 two main groups: (i) Terrigeno2LS deposits formed in deep 

 and shallow water close to the land masses ; and (2) Pelagic 

 deposits formed in deep water remote from land. 



Corresponding to this division we may define the nourish- 

 ment of marine animal life as derived from two main sources : 

 (i) Organic detritus carried into the sea from land or formed by 

 disintegration of the plants of the coast belt and the animals 

 living upon them ; and (2) Pelagic plants. 



As a third source, Putter has suggested the organic com- 



1 See Murray, Scott. Geogr. Mag., vol. iv. p. 345, 1888, and vol. xiii. p. i, 1897. 



