74 The Sea-water and its Physical and Chemical Properties 



reaction and is very largely present in the form of carbonates and bicarbonates. Since 

 Tornoe, it is also known as the "alkalinity", a term which is also used for the hydrogen- 

 ion concentration. To avoid confusion the sum of the carbonate and bicarbonate ions 

 is termed in oceanography (following Buch) the "titration alkalinity". This is ex- 

 pressed in the equation 



A = 2[C02-] + [HCO3], 



and can be found by simple titration with hydrochloric acid (Wattenberg, 1933; see 

 also 1930). 



The alkaline reserve in sea-water is largely combined with carbonic acid, but a 

 smaller part is also combined with other acids the most important of which is boric 

 acid. Sea-water of 35%o S contains 4-7 mg/1. of boric acid (Buch, 1933). The last 

 anomalies in the carbon dioxide system of sea-water have only been eliminated by 

 taking this acid into consideration since it and its ions are definitely concerned in the 

 equilibrium despite their small concentration. 



Since the individual constituents of the salt in sea-water are in almost constant 

 ratio to one another, it would be expected that the amount of base available for the 

 formation of carbonate and bicarbonate, that is the titration alkalinity, would be 

 directly dependent on the salinity. This is the case. The dependence between the two 

 was first shown by Hamberg (1885) and the investigation by Brennecke of the surface 

 samples collected on the "Deutschland" Expedition gave the relationship between 

 them as A = 0-06119S (according to Schulz, 1921). Later investigations have shown 

 that for the open ocean the dependence of alkalinity on the salinity is given with 

 suflftcient accuracy by the relationship 



A = 0-068S%o = 0-123 CI (in milliequivalents). 



This simple proportionality does not apply to the sea-water of the marginal and ad- 

 jacent seas as has been shown by Ruppin and Buch; these variations appear to be due 

 to the inflow of fresh water from the land. The North Sea and the Baltic, especially in 

 coastal areas, show alkalinity values that are higher than would correspond to the 

 salinity (addition of carbonate in river water). Similar conditions are found in the 

 Gulf of Bothnia, the Gulf of Finland and in the Adriatic. 



Carbonate at the sea bottom passing into solution has the same effect as the addi- 

 tion of carbonate from the land. The investigations of the "Challenger" Expedition 

 clearly indicated that the water immediately above the sea bottom was more alkaline 

 than that at the surface or in the middle layers (Dittmar, 1884; Brennecke, 1921). 

 The more accurate alkalinity determinations of the "Meteor" Expedition 1925-7 

 showed definitely that the specific alkalinity (the ratio of alkalinity to chlorinity, 

 A : CI) almost always increased near the sea bottom. This increase can only be ex- 

 plained by calcium carbonate from the bottom sediments going into solution (see 

 p. 85). 



Hydrogen-ion concentration. Pure water dissociates according to the equation 



HoO ^ H+ + OH-. 



