PHYSICAL OCEANOGRAPHY OF THE GULF OF MAliSTE 819 



No bottom samples have been collected on the shoal parts of Nantucket Shoals, 

 but neighboring stations suggest 32 to 32.5 per mills as the probable values there at 

 20 to 40 meters for the summer, autumn, and winter — perhaps slightly lower in 

 spring. 



ALKALINITY 



It has long been known that under normal circumstances sea water is invari- 

 ably a very slightly alkaline solution. Within the last few years attention has been 

 attracted to the seasonal and regional variations in the precise degree of alkalinity 

 in the sea by the probability that this feature of the aquatic environment may be 

 one of the controlling factors in the biology of marine organisms, especially of the 

 unicellular planktonic forms. Seasonal changes in this respect also afford a possible 

 measure of the activity of diatom and other plant flowerings, and thus of the inten- 

 sity of life processes in general in the sea, because marine plants increase the alka- 

 linity of the sea water as they draw carbon from the bicarbonates in solution. 



This whole question is exceedingly technical; so much so that no convenient 

 measure for alkalinity has yet been devised, the meaning of which would be obvious 

 to any one who had not devoted some attention to the subject. Salinity, for exam- 

 ple, is expressed in percentage or per thousand (the more usual terminology), tem- 

 perature in degrees — expressions sufficiently familiar to be readily understood. The 

 degree of alkalinity, however, usually is stated in terms of the concentration of the 

 hydrogen-ion, which can hardly be expected to bring a concrete image to the mind 

 of anyone not a trained chemist. Perhaps to the marine biologist or to the ocean- 

 ographer who is not a trained chemist the following quotation in non-technical lan- 

 guage may help to clarify the matter: 



The unit of hydrogen-ion concentration is 1 normal hydrogen-ion per liter of water, or about 

 1 gram of hydrogen-ion per liter. The finest distilled water contains only about 1 gram of hydro- 

 gen-ion in 10,000,000 liters of water at about 22° C, and thus its hydrogen-ion concentration is 

 about 10~'. Sea water, however, is alkaline and contains only about a tenth this concentration of 

 hydrogenions. (Mayor, 1919, p. 157.) 



The symbol "pH" was invented by Sorensen (1909) and has since been widely 

 adopted to avoid the necessity of writing negative exponents, the notations added 

 thereto being — stated in the baldest possible terms — the logarithm of the reciprocal 

 of the true hydrogen-ion concentration.^" Therefore, the larger the number of pH 

 the less acid or more alkaline is the water, pH 7 being about neutrality, anything 

 below that acid, and anything above that alkaline. 



Determinations of the alkalinity of the sea water can be carried out with little 

 dilBculty at sea by the colorimetric method.^' 



The colorimetric tubes used on the Albatross in 1920 and on the Halcyon were 

 prepared especially for us by Dr. A. G. Mayor and used as prescribed by him 

 (Mayor, 1922, p. 63). These give correct readings for pH if the salinity be 32 to 33 

 per mille, but for higher salinities every additional 1 per mille of salinity requires a 



"> For a fuller explanation of tbe reason for espressing the hydrogen-ion concentration by the term pH, rather than directly, 

 see Mayor (1919 and 1922), Clark (1920), and Atkins (1922). 



!' McClendon, Gault, and Mulholland (1917) and Mayor (1919) give details as to the preparation and use of the comparator 

 tubes for rough and ready use at sea. 



