728 DEPTHS OF THE OCEAN 



we know nothing whatever about the "daily increment" in the 

 producing organisms of the open ocean, and therefore the 

 futility of every attempt at comparison is evident. The small 

 volume of plants and animals peculiar to the upper strata of the 

 warm regions of the ocean cannot, in consequence, justify the 

 conclusion that the production is small. The abundance of 

 animals found in the deeper layers of the open ocean seems to 

 indicate rapid production associated with rapid consumption in 

 the upper plant region of the sea. 



Although it is as yet quite impossible to form an opinion on 

 the absolute magnitude of the production in certain regions, it 

 has been supposed that the relative amount of nutriment 

 contained in various waters might be compared. As mentioned 

 by Gran on pp. 367-381, botanists are of opinion that in the open 

 ocean, far from land, certain of the nutritive substances essential to 

 plant life, especially nitrogen, are present in very small quantities 

 (the minimum of Liebig), and consequently the plants cannot 

 develop as profusely as they otherwise would do. Pelagic 

 plant life draws its principal supply of dissolved or undissolved 

 nitrogen either from the coasts (see remarks on detritus), or 

 from localities where cold and warm currents meet. In these 

 latter localities the conditions may suddenly become favourable 

 for the development of life, just as development in boreal 

 waters begins in spring, when the rays of the sun raise the 

 temperature of the surface water. The organic substances 

 contained in the cold waters become transformed into inorganic 

 salts through the action of bacteria, and these salts are used by 

 the microscopic plants to build up new protoplasm. Murray 

 and Irvine^ first drew attention to the importance of this 

 process in the ocean, which plays a great part wherever large 

 sheets of cold and warm water are mixed,- 



The boreal waters should, accordingly, present favourable 

 conditions for developing an abundant animal life during the 

 warm season, the coast waters carrying detritus spread out 

 over the whole oceanic area, while arctic currents mix with 

 the warm Atlantic Gulf Stream, for instance in the Barentz 

 Sea, north and east of Iceland, and off the coast banks of 

 Labrador and Newfoundland. 



^ " On Coral Reefs and other Carbonate of Lime Formations in Modern Seas," Proc. Roy. Soc. 

 Edin., vol. xvii., 1890. 



2 Similar ideas have been expressed by Nansen, "The Oceanography of the North Polar 

 Basin," N'orwegian North Polar Expedition, Christiania, 1902. 



