SECT. 4] GEOGRAPHIC VARIATIONS IN PRODUCTIVITY 357 



not appreciably mixed. These conditions are eminently favorable for phyto- 

 plankton growth and may result in brief intermittent bursts of plant growth 

 throughout the winter in temperate seas. Riley (1957) discusses such occurrences 

 in the North Atlantic and one particular example has been described by Ryther 

 and Hulbert (1960). Conversely, violent storms may temporarily destroy 

 the thermocline in tropical and temperate summer seas, enriching the surface 

 layers sufficiently to stimulate production briefly. The importance of this 

 factor is perhaps questionable in tropical regions where the waters are highly 

 stratified. Francis and Stommel (1953) noted that gale force winds were capable 

 of deepening the mixed layer by no more than 20-30 ft in the Gulf of Mexico. 

 However, Steele (1956) considers wind action an important stimulus to summer 

 production in the less stable waters of the North Sea. 



6. Productivity of the Major Oceanic Regions 



The following section will consist of a brief resume of selected studies of 

 primary production in the principal oceanic regions of the world, i.e. in tropical, 

 semi-tropical, temperate and sub-polar, arctic and antarctic. Excluded from 

 this discussion will be areas of special interest, such as upwelling, convergences 

 and divergences, which will be treated separately in the following section. It 

 will be the purpose of this review to illustrate the principles and substantiate 

 the hypotheses presented in the preceding discussions. The realization of the 

 objectives is made difficult by the fact that data are widely scattered geo- 

 graphically, usually limited to single observations for a given location, and 

 often may not be comparable because of the use of different methods. Although 

 no attempt will be made to include all of the pertinent literature on the subject, 

 some of the major oceanic regions are not represented by any productivity 

 studies as such and must be evaluated by indirect evidence seasoned with 

 speculation. Productivity data reported here will be limited to those expressed 

 on an areal basis as grams of carbon fixed beneath a square meter of sea surface 

 per day and, for comparative purposes, will be largely restricted to those 

 obtained by the 14 C technique or to methods which are believed to give 

 comparable results. 



A . Tropical Seas 



During the Galathea expedition, Steemann Nielsen and Jensen (1957) 

 measured productivity in the tropical Atlantic, Pacific and Indian Oceans. 

 Jitts and Rotschi (1958), on expedition "Equipac", made measurements in 

 the Coral Sea and between the New Hebrides and Gilbert Islands. Holmes 

 et al. (1957) conducted studies in the tropical Eastern Pacific (expedition 

 "Eastropic"). Ryther and Menzel (1960) have measured production between 

 Bermuda and the West Indies on two oceanographic cruises in March, 1959, 

 and January-February, 1960. In all of these studies variations of the 14 C 

 method of Steemann Nielsen (1952) were employed. 



