UTILIZATION OF SOLAR ENERGY BY AQUATIC ORGANISMS 



31 



001 



PERCENTAGE OF SURFACE LIGHT 



0.05 01 05 I 5 10 



100% 



200 



Fig. 4. Comiiarison of rates of ])ciictration of four regions of the spectrum into tlie water of the 

 Gulf Stream and Sargasso Sea. The curves represent the average values of the extinction coeftieient 

 as measured bv Oster and Clarke (1935) and by Clarke (1933). The rate of penetration into dis- 

 tilled water for light at the wave length where absorption is least (4730a, k = 0.005) and for light 

 extending 500A each side of this (av. k = 0.010) (from tlie data of James and Birge 1938). 



assumed that tlie transparency of the water 

 is uniform at all depths. This has often 

 been found to be true especially where the 

 water has been rendered quite homogeneous 

 through effective mixing. In certain fjords 

 and lakes, however, abrupt changes in 

 transparency with depth have been re- 

 ported (Pettersson 1934, AVhitney 1938a). 

 These indicate discrete layers of suspended 

 material which mav be of either f)rganic or 



inorganic origin, and which ma}' have an 

 important function as a "false bottom." 

 The exact identification of the material con- 

 stitnting such strata presents an inviting 

 l)roblem. 



The angular distribution of the light be- 

 comes altered after it enters the water not 

 only because of refraction at the surface 

 but also because of scattering witliin the 

 water mass. The upward comi)onent was 



