CHEMISTRY OF THE SEA 171 



water, a compensating current rises from the depths. Such currents 

 stir up the bottom strata rich in nitrogenous compounds and carry 

 them to the surface where they become available as foodstuffs. Their 

 origin is betrayed by the coldness of the water. "No oceanic waters 

 swarm with so much life as the upward streams of deep water in 

 tropical latitudes. Such regions are consequently adapted to extensive 

 sea-fisheries." 12 Such localities are the Algerian coast, with its renowned 

 sardine fisheries, some places on the Portuguese coast, the west coast 

 of Morocco and the African coast opposite the Canary and Cape Verde 

 Islands, and the coast of southwest Africa. The astonishing richness 

 of the fish fauna in the cold-water areas of the Arabian Sea near 

 Oman, and at Cape Hafun on the Somali Coast, is even more striking. 

 The coast of Chile, with its cold upward currents, is especially notable 

 for the wealth of its marine life; 13 the guano deposits of the outlying 

 Peruvian islands are indirectly due to the same cause; and the luxuri- 

 ance of the submarine forests of algae (Macrocystis ■pyrifera) on the 

 coast of Chile, with their rich fauna, is doubtless also due to the 

 fertilization from this source. 14 



The Kiel Fiord exhibits an occasional upward current of cold 

 water. A southwest or west wind drives the surface water out of this 

 bay so that the bottom waters rise; when the westerly wind prevails 

 for a considerable time, as in early spring, the waters of the fiord 

 become grass green from the multitude of diatoms. 15 The development 

 of diatoms is slight with northerly and easterly winds. Deep-sea cur- 

 rents may be diverted into an upward direction by submarine banks 

 and ridges, as by the Wyville-Thomson Ridge, south of the Faeroes, 

 where the surface water is also rich in life. 



Vertical mixing also appears in places where a warm current passes 

 a cold one, in consequence of the differing densities of the adjacent 

 masses of water, and in the polar seas the deepest waters are involved 

 in the movement. Examples are presented by the Newfoundland Banks, 

 where the Labrador current and the Gulf Stream adjoin, and the 

 west coast of Japan where the warm Kuro-shio and the cold Oja-shio 

 pass each other. Both localities are the sites of important fisheries. 

 Deep water is drawn to the surface even when two neighboring cur- 

 rents have a similar temperature if the currents are diverted in oppo- 

 site directions by the rotation of the earth. The existence of the 

 so-called "tongue of cold" of the South Equatorial Current, north of 

 Ascension Island, with its richness in plankton, may be ascribed to 

 this cause. The Straits of Messina also have a rich plankton; the waters 

 are mixed in consequence of the different tidal phases of the Tyrrhenian 



