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



more abundant in regions that are vigorously stirred, so that the C(>2 

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

 that of the sea-water bathing the respiratory surfaces. The C0 2 

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

 determine accurately. 



It has been supposed that the amount of C0 2 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 CO 2 of the sea, since there is about 

 30 tunes as much C0 2 in the sea as in the air. There is always a 

 superabundance of C0 2 in sea-water to supply the needs of green, red, 

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

 water. It seems probable that the plants grow rapidly until the P H 

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

 the fact that the P H of the great oceans to the depth penetrated by light 

 is more constant than the CO-.* tension, the P H varying from about 8.0 

 to 8.25 and the C0 2 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 P H of the blood through the action of the 

 respiratory center. The sea regulates the P H 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 C0 2 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 C0 2 

 from an atmosphere of the pure gas by C0 2 -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 C0 2 

 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 hi 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 C0 2 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 CO 2 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 C0 2 of the air seems to be deter- 

 mined by an equilibrium between gain in CO 2 over some regions of the 

 sea surface and loss over others. The partial pressure of C0 2 in the 



