6o 



MEASURING THE PRODUCTIVITY OF THE SEA 



Now there are also ocean regions where the water slowly sinks, a typi- 

 cal example being the Sargasso Sea, in the south-western area of the 

 North Atlantic. The only way by which nutrient salts can reach the sur- 

 face of this area is with the surface currents from adjacent regions. As 

 a result, the production of the Sargasso Sea is small (see map below). 



A measurement of the production of the Sargasso Sea will prove to 

 be fairly typical of production throughout the year, as the conditions 

 governing it — light, supply of nutrient salts, and temperature — ■ are 

 practically uniform all the year round. 



In the North Sea, however, there is a considerable seasonal variation, 

 and to obtain the annual production we must take samples at least a 

 few times a month. Our studies on the Galathea, being mostly in the 

 Tropics, give a much better picture than we should have got by adopting 

 the same procedure in temperate or cold regions. 



The map on p. 6i, giving measurements of production in the section 

 extending from New Zealand to California, shows astonishing uniformity. 

 Only the coastal regions of New Zealand and California, and the above- 

 mentioned area of eddies just north of the Equator, show appreciably 

 different values. The variations between the remaining stations range from 



0,11* 



20° 



The explored section between Panama and Europe passed through the Sargosso Sea, where pro- 

 duction was very small. Grams of carbon per square metre of surface per day. 



