The Hydrogen-ion Concentration, etc., of Sea-Water. 37 



more abundant in regions that are vigorously stirred, so that the CO2 

 tension of a sample of the sea-water may be considered almost equal to 

 that of the sea-water bathing the respiratory surfaces. The CO2 

 tension has been one of the most difficult characteristics of sea-water to 

 determine accurately. 



It has been supposed that the amount of CO2 in sea-water regulates 

 the growth of seaweed, but the reverse is probably more nearly 

 correct. The respiratory quotient of marine organisms seems to be 

 about 0.7 to 1.0 and the respiration of animals and plants reciprocal. 

 Some marine bacteria take their oxygen from nitrates, but this effect 

 must be minute, since the supply of nitrates is small. The atmosphere 

 can not be the chief regulator of the CO2 of the sea, since there is about 

 30 times as much CO2 in the sea as in the air. There is always a 

 superabundance of CO2 in sea- water to supply the needs of green, red, 

 or brown seaweed, but by using it the plants increase the Ph of the 

 water. It seems probable that the plants grow rapidly until the Pg 

 that is most favorable to them is exceeded. This is in harmony with 

 the fact that the Ph of the great oceans to the depth penetrated by hght 

 is more constant than the CO2 tension, the Ph varying from about 8.0 

 to 8.25 and the CO2 tension from about 0.00015 to 0.0005 atmosphere. 

 The sea may be compared to the body of one of the higher vertebrates. 

 The mammal regulates the Ph of the blood through the action of the 

 respiratory center. The sea regulates the Ph of its surface-water most 

 probably through the action of seaweed. The limit in the supply of 

 oxygen probably prevents animal life from getting the upper hand 

 temporarily and thus endangering the communal life in the sea. 



It seems probable that seaweeds regulate the CO2 of the atmosphere. 

 The gaseous exchange between sea and air is necessarily at the surface 

 and is comparatively slow. Bohr observed that the absorption of CO2 

 from an atmosphere of the pure gas by C02-free water that is stirred 

 (probably more vigorously than the sea ever is) is about 0.1 c.c. per 

 square centimeter of surface per minute. Since the difference in CO2 

 tension between air and sea seems never to exceed 0,02 per cent of that 

 in Bohr's experiment, except in the polar regions, the rate of diffusion 

 would not exceed 0.00001 c.c. per square centimeter per minute or 

 0.1 c.c. per square meter per minute in a storm, and necessarily much 

 less in calm weather on account of the lessened rate of stirring at the 

 surface. When we consider the volume of the sea and air compared 

 to the sea-air surface, the fact becomes intelligible that the CO2 in the 

 air is relatively constant (3 per 10,000) in the different regions of the 

 world where it has been accurately measured, whereas the CO2 tension 

 of the sea-surface varies from 1.5 to 5 per 10,000. The air is stirred 

 more rapidly than the sea, and the CO2 of the air seems to be deter- 

 mined by an equilibrium between gain in CO2 over some regions of the 

 sea surface and loss over others. The partial pressure of CO2 in the 



