071 Changes in the Sea and Their Relation to Organisms. 



253 



intense in places where calcium salts, nitrates, and nitrites are carried 

 from the land into the sea. 



That calcium carbonate is withdrawn from surface waters of the sea 

 is shown by chemical analyses. Dittmar found an average of 0.44 

 per cent less calcium in surface waters than in deeper waters. This is 

 true, notwithstanding the fact that calcium carbonate is constantly 

 being added to the surface waters. The drainage of the land contains 

 an excess of calcium carbonate and flows out on the surface of the sea, 

 where the water evaporates, leaving the excess of CaCOs in the sea- 

 water. The action of organisms in building calcareous structures may 

 account for a large part of the depletion of surface waters, but the pre- 

 cipitation of calcareous mud at Tortugas has been observed by Vaughan. 



The analj^sis of the calcium content of sea-water requires double 

 precipitation and filtration for separation from magnesium, and hence 

 large samples and great care are required for accuracy. Theoretically, 

 however, we may detect differences in calcium content by titration. 

 Dittmar showed that sea-water is remarkably constant in composition, 

 except for H2O, calcium, and gases. The water content is inversely 

 proportional to CI and the gases may be eliminated by boiling after 

 the addition of enough acid to decompose the carbonates. If we dis- 

 regard carbonic acid, there is an excess of bases in sea- water — i. e., 

 the sum of the base equivalents is greater than the sum of acid equiva- 

 lents. Since calcium is added to or taken from sea-water in the form 

 of CaCOs, any change in the calcium content causes an equivalent 

 change in the excess base or alkaline reserve, as it is called by chemists. 

 The alkaline reserve may be titrated while boiling the sea-water to 

 eUminate CO2. The exact value of the titration depends on the indi- 

 cator used and the exact color of the indicator that is taken as the end- 

 point; hence only those titrations done in the same manner can be 

 strictly compared (see method described in first part of this paper). 

 The alkaline reserve per liter was recorded and some titrations were 

 made at 20° and others at 30°, but the errors due to change in volume 

 of the sea-water is within the limits of accuracy of the method. If the 

 sea-water is diluted with rain-water, the alkaUne reserve will be low- 

 ered, but this error may be compensated by dividing by CI. In other 

 words, a change in the quotient of the alkaline reserve by CI indicates 

 a gain or loss of CaCOs. 



Table 24. 



Sea-water from- 



San Diego 



Wood's Hole 



Gulf Stream, off Miami 



Giilf Stream, off Tortugas 



Average, Tortugas, June and July . . 

 Average, Kej' West, June and July . 



Alk. res. 

 CI 



X 10,000 



1.257 

 1.356 

 1.257 

 1.257 

 1.235 

 1.185 



