The rate of elimination of by animals and its absorption by plants in the sunlight is directly proportional to the difference in tension just outside and inside of the respiratory surfaces. Life in the sea is more abundant in regions that are vigorously stirred, so that the tension of a sample of the sea-water may be considered almost equal to that of the sea-water bathing the respiratory surfaces. The tension has been one of the most difficult characteristics of sea-water to determine accurately.
It has been supposed that the amount of 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 of the sea, since there is about 30 times as much in the sea as in the air. There is always a superabundance of in sea-water to supply the needs of green, red, or brown seaweed, but by using it the plants increase the P. of the water. It seems probable that the plants grow rapidly until the P. that is most favorable to them is exceeded. This is in harmony with the fact that the P. of the great oceans to the depth penetrated by light is more constant than the tension, the P. varying from about 8.0 to 8.25 and the 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. of the blood through the action of the respiratory center. The sea regulates the P. 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 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 from an atmosphere of the pure gas by 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 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 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 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 of the air seems to be deter mined by an equilibrium between gain in over some regions of the sea surface and loss over others. The partial pressure of in the air is therefore the average tension of the sea-surface. The burn ing of a billion tons of coal per year is probably changing the content of the sea and of rocks and not of the atmosphere.
Regnard kept a tall open tube filled with a solution that became colored in the presence of oxygen at constant temperature to prevent convection currents. At the end of one year oxygen had diffused 4 meters deep into the solution. Although some oxygen was used in coloring the indicator, the experiment illustrates the slowness of diffu sion in liquids.
Since both the conversion table for content and the one for tension are based on the assumption that the non-volatile buffer and the excess base in sea-water are constant, further work is being done on this subject. It seems probable that the weak bases in sea water may assist the buffer action. The concentration of is small, but is added to the total buffer value; it is non-volatile under the conditions present at the surface of the sea and is constantly being replenished by rain as it is used by organisms. Aluminium can act both as weak base and weak acid, but probably acts as a weak base in the sea. Organic acids besides may be classed as non-volatile buffers. Their destruction in warm seas is probably due to the action of denitrifying bacteria, which catalyze the oxidation of organic matter with nitric and nitrous acids, as shown by Drew. The concentration of organic acids is probably maintained just below that which can be appreciably utilized by these bacteria.