Physical Studies on the Turbidity in the Sea Water, with Special Reference to the Relation of the Radiant Energy

Abstract

Turbidity in the sea was discussed from the physical point of view, especially with its relation to radiation energy. This study was advanced along the following course.
(1) Absorption of solar heat radiation in the sea, and its relation to the turbidity of the sea water.
By using a thermopile, radiation energies which reach different depths in the sea were directly measured in Maizuru Bay and Turuga Bay. An equation was derived which relates these energies to the wave-length of light and the turbidity of the sea water. Computed values of the energies from this equation were compared with observational data. For facility in use, the amounts of total energies as different depths and for different extinction coefficients were represented in a graph and a table.
(2) Distribution of extinction coefficients of light in the sea.
Among data on underwater illumination, which have been obtained by many investigators, there are only few which have illustrated together with the state of sea concerned. The present author have attempted to obtain the reduction of intensity of light on a vertical distance using a simple submarine photometer, together with the water temperature, the chlorinity, etc. Various types of the distribution of extinction coefficients were found in different areas and in vertically stratified layers, and the change with time of extinc tion was also shown.
(3) Measurement of turbidity of sea water, and the character of turbidity.
Measurements of underwater illumination are restricted by natural conditions, so that a series of laboratory experiments was made of turbidity of sea water samples by measuring photoelectric current of transmitted ray of light through the samples. The method of measurement was explained in detail. The influence of plankton and of salinity upon turbidity Was discussed. experimentally for the former, and theoretically for the latter. Physical character of seston, which may play an important role in the turbidity of seawater, was examined, with regard to factors such as the size distribution of seston, and the time-change of seston itself.
(4) Distribution of turbidity in the sea.
The above laboratory method was applied to actual cases in the sea. Various types of distribution of turbidity were found to exist, which have not been detectable by means of a transparency disc. A close correlation was noted between the distribution of turbidity, so found and the sea conditions, which are estimated by such quantities as temperature, salinity, etc. This indicates that turbidity may become one of the elements characterizing the sea conditions.