海水中の懸濁質に関する研究-I

Abstract

Previously, HANAOKA and MURAKAMI reported a relation expressed by the equation IT=I0exp(-aTb) where T is the visible transparency depth of Secchi disc, I0 and IT the underwater daylight illumination in the sea at the surface and the depth T respectively, and “a” “b” are constants. The present authors confirmed experimentally that the relation can exist in such various suspensions, in which the particles have comparabfe sizes to the wave-length of incident light (Table 2) and not the RAYLEIGH-scattering but probably the MIE-scattering may take place. The experiments showed that the extinction coefficient (μ) in these suspensions was related to the visible transparency T by the equation μ=aT-b' (Fig. 1) Applying this relation to the LAMBERT's equation Id=I0exp(-μd). we obtain IT=I0exp(-aT1-b')=I0exp(-aTb) which snows a good fit with the observations (Table 1, Fig. 2) At the same time there was another observed relation expresed by the equation T=αC-β where C is the concentration of suspended material (Fig. 3). Therefore, from these relations we obtain μ=KCB (Fig. 4) In the case of the RAYLEIGH-scattering, there applies a relation μ=KC, called BEER's Law, but in our case B is not equal to unity. In natural sea water, the value of “b” can be estimated to be a constant, 0.7, in neritic as well as inshore sea waters, while “a”, in general, varies depending on water measles, higher in the more neritic waters and lower in the more oceanic waters. In the sea was also found a relation μ=KS0.2 where S is dried weight in mg of the residue per 1 liter of the sea weter filtered by molecular filter (APD 250 mμ), when the filtrate shows almost the same absorption coefficient as that of distilated water, and k is represented by the equation k=0.86a-0.154 (Fig. 5) It is shown here that when “b” is constant, the higher the value of “a”, the smaller the size of suspended particles. On the other hand, we obtain S=γτ (Fig. 6) where τ is the absorbtion coefficient to the light. So “a” is expressed in terms of μ and τ as follows a=0.92μτ-0.2+0.179 (Fig. 7) Thus we can compute the value of “a” by knowing μ and S or τ, instead of T, even in the case where T cannot be observed or the value “a” is required, by layer. Both “a” and “b” do not depend on the concentration of suspended matter, but “a” depends only on the particle size when “b” stays constant. So we would like to call “a” “suspensionfactor”. It can show not only the micro-construction of water masses in the sea, but also seems to correlate with the distribution and growth of various filter-feeding organisms. For instance, oyster, Ostrea gigas appears to show its optimal growth in such regions where “a” is between 0.4-0.5 (Fig. 8), while in its seed-bed, it has some higher value. We obtain also the value of 0.4 in the pearl oyster bed, and 0.8-0.9 on Mogai Anadara suberenata bed.