Relationship Between Attenuation Index of Directed 

 Radiation and Chlorophyll Content 



One of the goals of ocean monitoring is the rapid 

 measurements of parameters such as chlorophyll content. As 

 applied to hydrooptics. the simplest way to attain this objective 

 is to establish statistical relationships between chlorophyll 

 concentration and optical parameters of water. Consider now 

 the attenuation index at wavelength >.=530 nm. The attenuation 

 index was layer-averaged, beginning with surface, and down to 

 the maximum possible depth of probing; chlorophyll content 

 from the surface to the lowest depths sampled. In shallow parts 

 of the sea these depths coincided. 



(e) and (Chi a) . The average attenuation index (i.e., the 

 average content of particulates) was proportional to the average 

 content of chlorophyll (Figs. 1,16). The northern part of the 

 Bering Sea manifested less pigment content in cloudier water. 

 These facts can be easily explained when considering the 

 angular and integral characteristics of light scattering in the 

 areas mentioned. In the Gulf of Anadyr, in the western half of 

 the Bering Strait, and in the Chukchi Sea. the subsurface and 

 middle horizon waters contained diatoms. The eastern part of 

 the Bering Strait has a different particulates composition as 

 judged by integral characteristics of light scattering. Apparently ' 

 the particulates here had lower specific content of pigments; 

 even though the concentration of particles was higher here, the 

 average content of chlorophyll was lower. 



Now we consider how some quantitative assessments can 

 be derived. Figure 17 shows how (Chi a) relation depends on 

 (e). One can see that relationship between these characteristics 

 bears a dual nature. In productive waters of the Chukchi and 

 Bering Seas, the relationship will be other than that in clear and 

 potentially bioactive waters of the Gulf of Anadyrand in waters 

 with low productivity, such as in the eastern part of the Bering 

 Strait. 



A useful criterion may be correlation between optical 

 properties of these waters and angular and integral characteristics 

 of light scattering by "developed" diatom particulates. The 

 latter is distinguished by lowest values of P (83-84%). 



Unfortunately, it is problematic to establish reliable 

 statistics. Because of the lack of experimental points ( we have 

 data on chlorophyll content only for some, not all, stations) and 

 their great dispersion. The latter is partially due to the fact that, 

 for technical reasons, the probing procedure was undertaken 

 10-20 min after assaying, thus rendering measurements 

 asynchronous. Besides, chlorophyll average content was 

 calculated only on the basis of 5-8 assays. Nevertheless, for a 

 rough estimate, we shall consider that interrelationship between 

 (Chi a) and (e) in productive waters will look as follows: 

 (Chi a) = 12.5(e>-5, in other -(Chi a) = 1.5(e>. 



In view of higher diatom particulates content in the Chukchi 

 Sea, an attempt was made to calculate a linear regression 

 equation for the current values of e and Chi a. On the whole. 



Station No. 



Fig. 15. Section 1 1. (Stations 76-81) Vertical structure ot transmittance. (See Figure 5 legend). 



149 



