THE HEAT BUDGET OF THE OCEANS 



55 



the curves showing the energy spectrum. In the inserted diagram the 

 total energy, expressed as percentage of the energy penetrating the sur- 

 face, as well as the corresponding percentages of the energy in the visible 

 part of the spectrum, are plotted against depth. The figure shows that 

 pure water is transparent for visible radiation only. 



For sea water the percentage of the total energy reaching various 

 depths has been computed for the clearest oceanic water, for average 

 oceanic water, for average coastal water, and for turbid coastal water, 

 using the extinction coefficients shown in table 4. The results are 

 presented in table 8. In even the clearest offshore water 62.3 per cent 

 of the incoming energy is absorbed in the first meter. The absorption is 

 often increased in the upper one meter because of the presence of foam 



•^VIOLET ^^ BLUE 



^ YELLOW ^° ORANGE ^^ y- RED 



Fig. 9. Energy spectra at a depth of 10 m in different types of water. Curves 

 marked 0, 1,2, 3, and 4 represent energy spectra in pure water, clear oceanic, average 

 oceanic, average coastal, and turbid coastal sea water, respectively. Inset: Energy 

 spectra at a depth of 100 m in clear oceanic water and at 10 m in turbid coastal water. 



and air bubbles. This increased absorption, when dealing with the 

 penetration of light, is referred to as ''surface loss." If this process is 

 disregarded, the values clearly demonstrate that the greater amount of 

 energy is absorbed very near the sea surface and that the amount which 

 penetrates to any appreciable depth is considerable only when the water is 

 exceptionally clear. At 10 m, 83.9 per cent has been absorbed in the 

 clearest water and 99.55 per cent in the turbid coastal water. 



The absorption of energy is illustrated in fig. 9, which shows the 

 energy spectra in different types of water at a depth of 10 m. At this 

 depth the maximum energy in the clearest water is found in the blue-green 

 portion of the spectrum, whereas in the turbid coastal water the maximum 

 has been displaced toward the greenish-yellow part. This displacement 

 is further illustrated by the inserted curve in the upper right-hand corner 

 of the figure, which shows the energy spectra at 100 m in the clearest water 

 and at 10 m in the most turbid water. 



