SECT. 2] PRODUCTIVITY, DEFINITION AND MEASUREMENT 141 



Table III 



O2 Experiments with Surface Water from the Sargasso Sea, 3-6 June, 1952. 

 Triplicates used each titrated twice, mg O2/I. ±0.01. (After Steemann 



Nielsen, 1958.) 



Water Initial bottles Clear bottles Dark bottles 



Non -filtered 6.60 6.57 6.51 



Paper filtered 6.59 6.61 6.37 



In some way or other, light must be able to reduce the bacterial activity in 

 the bottles containing oligotrophic ocean water. The problem seems to be rather 

 complicated. Probably more than one cause may be found. Some species of 

 bacteria ordinarily found together with planktonic algae are definitely in- 

 fluenced by even weak daylight filtered through several layers of glass (see 

 Jorgensen and Steemann Nielsen, 1960). In light and dark bottle experiments 

 with sea-water the results have been conflicting. Doty (1958, table IV) found, 

 for example, that the bacteria developed much faster in the dark bottles 

 whereas Vaccaro and Ryther (1954) did not find any difference between the 

 two kinds of bottles. Possibly the concentration of planktonic algae is of 

 importance, a light-induced decrease being conspicuous only in plankton-poor 

 water. 



E. The Carbon-14 Technique 



Radioactive tracers have given rise to a revolution in methods used in many 

 parts of biology and also in the exploration of oceanic primary production. 

 Whereas ordinary chemical methods can be used if the rates of the processes 

 exceed a certain, often relatively high, minimum value, an isotope technique 

 may be employed even when the rate of a process is extremely low. Carbon-14 

 was used for measuring the rate of primary production in the sea for the first 

 time by the Danish Galathea Expedition round the world, 1950-1952. The 

 technique was described by Steemann Nielsen (1952) and in more detail by 

 Steemann Nielsen and Aabye Jensen (1957). Different details and minor 

 modifications of the method have been presented for example by Doty (1958) 

 and by Sorokin (1958). 



In principle the technique is rather simple. The practical application of the 

 carbon-14 technique in field-work does not require any expert knowledge. On 

 the other hand, both technical skill and familiarity with tracer work is necessary 

 when preparing 14 C ampoules to be used in field-work and when measuring 

 radioactivity both in the ampoules and in the samples collected during the field 

 work. In order to facilitate the work for laboratories without staff members 

 having the necessary expert knowledge, UNESCO has provided funds for an 

 international centre at Charlottenlund Castle. Denmark. This centre distributes 



