REACTION IN WATER 101 



acteristic of salt water. The results of the presence of quantities of 

 this substance are several. Colloidal sulphur, which is the most toxic 

 form, often occurs under certain hydroclimatic conditions and kills 

 many of the existing aerobic bottom organisms. Hydrogen sulphide 

 is also acted upon by a remarkable group of sulphur bacteria (John- 

 stone, 1928:147), and a portion of it, after reaching water containing 

 dissolved oxygen, is transformed into sulphur dioxide. This finally 

 becomes sulphurous acid, which often occurs in minute quantities be- 

 low depths of about 50 meters. 



Reaction also operates necessarily upon the mineral solutes, reduc- 

 ing them as a consec}uence of food making by chlorophyll-bearing 

 organisms, and restoring them through the oxidation exercised by bac- 

 teria, especially the nitrifying ones. Calcium is utilized in large 

 amounts by shelled animals, but the quantity present is constantly 

 renewed by inflow from the land, so that its use is chiefly significant 

 in connection with the reaction of deposit. The situation is quite dif- 

 ferent with respect to nitrates, phosphates, and silica, owing to the 

 relatively small amounts present, and the reduction due to utilization 

 is frequently the limiting factor, both as to species and abundance. 

 Finally, the organic matter in solution in sea water is an outcome of 

 the presence of living organisms, and a somewhat similar reaction may 

 be the basis for the appearance of growth-stimulating substances in 

 the sea (Johnstone, 1928:165). 



Reaction on the Bottom in Deep Water. The most characteristic 

 reaction upon the bottom of oceans is that of deposit, dead material 

 being contributed by all the pelagic communities above and accumu- 

 lating wherever currents are slight or lacking. Such deposits consist 

 of organic detritus derived from most of the organisms of the sea and 

 their excreta, with which may be mingled more or less terrigenous 

 material, especially in the vicinity of coasts. The continental shelf 

 and adjacent shallower waters are covered with terrigenous deposits of 

 gravel, sand, and mud, but the greater part of the ocean floor is 

 characterized by deposits chiefly of animal origin. From 2,000 to 

 5,000 meters, approximately, globigerina ooze is the most widely dis- 

 tributed; it consists of the calcareous shells of Foraminifera living in 

 the pelagic climax, and accumulates at the rate of about 2 milli- 

 meters per year. Coral mud and sand occur in the neighborhood of 

 coral reefs and islands, and pteropod ooze is often associated with 

 them, though it develops also on oceanic ridges in warm seas. Radio- 

 larian ooze is restricted to certain tropical waters; diatom ooze is con- 

 fined to colder seas, both in the southern and northern hemisphere. 

 The last two types, by contrast with the others, consist of siliceous 



