58 MEASURING THE PRODUCTIVITY OF THE SEA 



bottles to the depths from which the samples were taken, keeping them 

 suspended there for 24 hours. They are then taken up and the algae 

 filtered off. When the radioactivity has been measured, the rest is a 

 matter of straightforward calculation. 



Usually, a costly research ship will be unable to stand by for so long as 

 24 hours. A period of six hours, from sunrise to noon or from noon to 

 sunset, will, however, suffice. There being no production at night, the 

 result will be correct if the amount obtained is multiplied by two. But even 

 six hours is a long time, and on the Galathea would have cost about £50. 



In order to collect a large amount of data in a short space of time we 

 were obhged to make a small alteration in the method. Instead of lowering 

 the samples to their original depth after the addition of C^*, we placed 

 them in a sort of aquarium at the same temperature as in the sea, illu- 

 minating them with artificial light of a known intensity. 



To be able to use this method it is necessary to know how the inten- 

 sity of light diminishes from the surface downwards. The submarine light 

 is therefore measured with a submarine photometer, to which we will 

 return later. Once we know the effect of light intensity on production and 

 the variations in the light intensity at the surface throughout the day, it 

 becomes a matter of calculation to find out the rate of organic produc- 

 tion per unit area. By means of this modification of the C^* method we suc- 

 ceeded in carrying out a large number of measurements. 



Our first scientific study, made on the trial trip, was a measurement 

 of the organic production off the Skaw. The last was a similar measure- 

 ment at the same place on our return. We measured the production of 

 the sea in every area which we visited. While the life nerve of the ship's 

 zoological deep-sea research - — ■ the large winch - — occasionally failed, 

 this never happened to the equipment used for measuring production. 

 The hand-winch employed for bringing up samples of water for these 

 studies is sturdier than the large and complicated winch used for deep- 

 sea trawling. The highly complex equipment used in radioactive work 

 also proved reliable. We had two complete sets, and one at least was always 

 functioning. 



We (had expected to see the rate of production vary from region to 

 region; by how much we could not say as there has been no previous 

 studies of the oceans. Although we found large variations in the rate, 

 they were smaller than we had expected. It is not easy to sit at a desk and 

 work out the behaviour of Nature. 



The principle factor which influences the rate of production is the 

 amount of nutrient salts present in the water, chief among these being 



