PLANKTON 277 



dance. To take an example from our own seas/ Professor 

 Benjamin Moore and his assistants, in their work at the Port 

 Erin Biological Station in successive years from 1912 onwards, 

 have shown that the sea around the Isle of Man is a good deal 

 more alkaUne in spring (say April) than it is in summer (say 

 July). The alkalinity, which gets low in summer, increases 

 somewhat in autumn, and then decreases rapidly, to disappear 

 during the winter ; and then once more, after several months 

 of a minimum, begins to come into evidence again in March, 

 and rapidly rises to its maximum in April or May. This 

 periodic change in alkalinity will be seen to correspond 

 roughly with the changes in the living microscopic contents 

 of the sea represented by the phyto-plankton annual curve, 

 and the connection between the two will be seen when we 

 realize that the alkahnity of the sea is due to the relative 

 absence of carbon dioxide. In early spring, then, the 

 developing myriads of Diatoms in their metabolic processes 

 gradually use up the store of carbon dioxide accumulated 

 din-ing the winter, or derived from the bi-carbonates of 

 calcium and magnesium, and so increase the alkalinity of the 

 water, till the maximum of alkahnity, due to the fixation of 

 the carbon and the reduction in amount of carbon dioxide, 

 corresponds with the crest of the phyto-plankton curve in, 

 say, April. 



Prof. B. Moore has calculated that the annual turnover 

 in the form of carbon which is used up or converted from the 

 inorganic into an organic form probably amounts to some- 

 thing of the order of 20,000 or 30,000 tons of carbon per 

 cubic mile of sea-water, or, say, over an area of the Irish 

 Sea measuring 16 square miles and a depth of 50 fathoms ; 

 and this probably means a production each season of about 

 two tons of dry organic matter, corresponding to at least 

 ten tons of moist vegetation, per acre — which suggests at 



^ I have already referred to these variations in alkalinity in the 

 chapter on Hydrography, but they require to be noticed here in 

 their relation to plankton production. 



