Chapter II — 19 — The Marine Environment 



of phosphate-P (AxKms, 1923). Surface water at high latitudes usually 

 contains more phosphate than surface water in tropical seas. The cycle 

 of phosphorus in the sea has been reviewed by Seiwell (1935) and Renn 

 (1937a), the latter emphasizing the role of bacteria. 



Organic matter is quite evenly distributed throughout the sea, the 

 content being uniformly small except in the vicinity of land or in bottom 

 deposits. Krogh (193 i), found an average of only 2.36 gm. of organic 

 carbon per cubic meter of sea water or 2.36 parts per million. 



One might expect to find appreciably more organic matter in the eu- 

 photic zone than at greater depths in the sea due to the preponderance of 

 plant and animal life in this zone, but actually only a small proportion of 

 the organic content occurs as organized protoplasm. Gran and Ruud 

 (1926) estimated that the ratio of particulate to dissolved organic matter 

 in the sea is 1:7. Krogh (1934) placed the ratio at 1 1300. Bigelow and 

 Sears (1939) report i :ioo to i :4ooo. The demarcation between dissolved 

 and particulate organic matter is poorly defined, the separation usually 

 being made upon a basis of the ability of the organic fraction to pass 

 through filters of various dimensions or to be removed by centrifuging. 

 In spite of the experimental difficulties in obtaining quantitative results, 

 however, there is unquestionably considerably more unorganized organic 

 matter (dissolved, colloidal, or minute particles) than that which occurs 

 in organized protoplasm. 



An average of 56 per cent of the organic matter in sea water consists of 

 carbon and about a tenth as much is nitrogen. The ratio of carbon to 

 nitrogen in marine organic matter ranges from about 8:1 to 12:1. Much 

 of the organic matter is fairly refractory to decomposition by biological 

 agencies (Waksman and Carey, 19350). 



Bottom deposits and the juxtaposed water contain much more organic 

 matter than the overlying water. According to Trask (1939), oceanic 

 deposits contain an average of i.o per cent organic matter while near shore 

 deposits contain an average of 2.5 per cent organic matter. 



Dissolved gases and the pH of sea water : — The pH encountered in 

 the sea ranges from 7.5 to 8.5. When in equilibrium with the CO2 of the 

 atmosphere, the pH. of sea water ranges from 8.1 to 8.3. In the euphotic 

 zone photosynthetic plants may reduce the CO2 content of the water until 

 the pH. reaches 8.3 to 8.5 during the hours of intense sunlight. Below the 

 euphotic zone the pK decreases with depth to a minimum of 7.5 at depths 

 exceeding 1000 meters. 



In marine bottom deposits, tide pools, bays, and estuaries, the pH. may 

 exceed 8.5 or fall below />H 7.0. There are several ways in which the 

 activities of microorganisms influence the />H of sea water by producing 

 or destroying organic acids, nitrates, nitrites, ammonium, sulfates, hydro- 

 gen sulfide, etc. Some of the biological effects of the pH of sea water are 

 discussed by Harvey (1928). 



Bicarbonates constitute the principal buffer system of sea water. 

 Borates play a minor role. Phosphates and proteinaceous materials are 

 far too dilute to exert a detectable influence on the ^H of sea water. 



The CO2 content of sea water decreases as the pH increases. In sea 

 water more alkaline than pH 7.5, there is virtually no free CO2 in solution, 

 most of it occurring in combination as bicarbonates or carbonates. The 

 effect of pYL on the relative concentrations of free CO2, bicarbonate, and 

 carbonate in sea water is shown by Figure i which is prepared from data 

 given by Moberg et al. (1934). 



