IV. BIOLOGICAL OCEANOGRAPHY 



17 GEOGRAPHIC VARIATIONS IN PRODUCTIVITY 



J. H. Ryther 



1. Introduction 



The production of organic matter on land is determined by numerous 

 environmental factors which limit photosynthesis or plant growth. The more 

 important of these include the nature of the physical substratum, temperature, 

 moisture, carbon dioxide, chemical nutrients and illumination. Several of these 

 factors may also limit the growth of marine plants in restricted coastal and 

 estuarine situations, but in the open sea it is only the latter two, nutrients and 

 light, which are significant. It is the variability of these factors and of the 

 hydrographic features which control their availability that are responsible for 

 the geographic variations in marine productivity. It is, therefore, pertinent to 

 discuss in some detail and without reference to specific locations, the manner 

 in which and the degree to which light and nutrients control and limit the rate 

 of primary production in the sea. With that information as a background, the 

 range and magnitude of the process in representative parts of the ocean will 

 be considered. While these regions will be selected to illustrate the various 

 controlling mechanisms which will be discussed, the selection is limited by 

 the availability of data. This chapter, then, will consist primarily of a discussion 

 of illustrated principles. No attempt will be made to describe the productivity 

 of the oceans as a whole or even to summarize all of the existing data on the 

 subject. 



2. Incident Radiation 



One of the most obvious variable factors influencing plant production is the 

 amount of solar energy reaching the ocean's surface. Changing weather patterns 

 may cause extreme short-term variations in incident radiation of an order of 

 magnitude or more which may appreciably influence day-to-day rates of 

 primary production (e.g. Sorokin and Koblentz-Mishke, 1958; Currie, 1958; 

 McAllister et ah, 1959). However, these effects would presumably average out 

 over longer periods of time to values relating to the mean radiation for the 

 period. Radiation data, averaged over periods of a month or longer, are more 

 or less constant and predictable for a given season and latitude, and such data 

 have been compiled by Kimball (1928), Kennedy (1949), Budyko (1955) and 

 others. 



On the basis of an empirically derived relationship between light intensity 

 and the photosynthesis of some marine planktonic algae, the relative 



[MS received June, I960] 347 



