Records of All Stations and of a Tank of Sea-Water

Blackman and Smith, working on fresh-water plants, showed that photosynthesis is about doubled by a rise of 10° in temperature and varies directly with tension in the water and illumination. Their maximal values, reduced to 30°, were about as follows, in cubic centi meters per square centimeter per hour: Fontinalis 0.149, Elodea 0.093, Ceratophyllum 0.245.

Most of the determinations were made with

Elodea and some leaves overlapped, so that the average thickness was a little more than that of one leaf. If we assume a thickness of 0.1 mm. and a specific gravity of unity, 9,300 c.c. of per kilogram per hour were consumed in photosynthesis (about 10 per cent of this was re-formed by respiration of the plant during the day and the same amount during the night, so that perhaps 9,000 c.c. was converted into oxygen for the use of animals). This is a maximum value and would be reduced in case of marine plants by decrease in light due to clouds, inclination of the sun, and absorption by the water. A very rapid use of by seaweed causes a crust of to form on the surface, thus keeping out light and CO2.

The number of cubic centimeters of 02 used per hour per kilogram by various groups of animals is shown in table 10 (Krogh's average of various species at 20°, and Montuori's at 25° as compared with my determinations and calculations at 30°).

The discrepancies are due to differences in size, activity, and species. The calculations (in parentheses) were made on the assumption that the respiration at 30° is double that at 20° and 1.414 times that at 25°. A kilogram of the small fish I studied would use up all of the 02 in 3,600 liters of the sea-water of the Gulf Stream in 24 hours. The respiration of the very active animals studied by others is about half as rapid and there is great variation with the species in sluggish animals.

With 1 kg. of fish in 300,000 liters of warm sea-water we should be able to detect a distinct fall in 02 concentration during the night. In order to attain this effect there need be organisms, the equivalent of 1 kg. of fish, to 10 square meters of bottom in water 30 meters deep.

It will be seen from the foregoing sections that the changes in the sea that were considered are very complicated. If the dirunal curves are plotted they show secondary notches. It was thought probable that the secondary notches in the diurnal curves of the sea-water at station A might be due to horizontal and vertical currents and eddies. In order

to exclude some of these currents the diurnal variation of a model lagoon was studied. A glass tank about 4 by 6 by 4 feet was placed in the open air and filled with sea-water and a few cassiopeas placed on the bottom. Convection currents stirred up the water in the tank, but there were necessarily no extensive horizontal currents over bottoms of different character and depth. The curves of the diurnal variations were smooth—that is, without secondary notches. The extremes (maxima and minima) of the curves were at about 5h40°' a. m. and 4 p. m. The morning extreme was a little delayed, owing to partial shading of the tank for a short time, before and after sunrise, but there was a corresponding shading before sunset and therefore the curves were not skewed. The smooth curves obtained with the tank indicate that the notches in the diurnal curves at station A are due to currents in the water and not to technical errors. On partially cloudy days it seems possible for clouds to make notches in the diurnal curves, and sudden squalls have a similar effect.

On July 10, 19, 20, 21, 22, 23, 24, and 25 very frequent determina tions were made, so that the notches in the curves could be studied. With the omission of these small notches, the diurnal curves are plotted in figure 6. It may be observed that there was a general upward drift in temperature during July of about 2°. As a consequence of rise in temperature and increased cloudiness, there was a fall in the oxygen concentration in the sea-water during July. July 10 was an unusually calm day (up to 9 p. m., when a brief squall appeared) and shows great extremes in all determinations. Contrasted with this are the windy days, July 13, 14, 15, and 16, during which the oxygen curves were very much flattened out. This shows that the oxygen content of the sea water is somewhat influenced by the atmosphere. In figure 3 it may be observed that the oxygen content of the water north of Hatteras is increased with decreasing temperature and increasing absorption coefficient, which is another demonstration that the oxygen content of the water is influenced by the air. On the other hand, shallow water is not nearly in equilibrium with the air in regard to oxygen. At stations B and H samples of water were obtained which were 20 per cent undersaturated and 69 per cent oversaturated respectively.