Table 1. — Percentage saturation of nitrogen and concentrations of oxygen in excess of saturation according to source, calculated 

 from observed nitrogen and oxygen concentrations. P: photos ynlhelic oxygen, A: atmospheric oxygen. Entries for each 

 month are given chronologically but the dates for each entry do not correspond exactly from year to year; approximate time 

 of month is indicated by the position of each entry in a column. 



Year_. 

 Month 



1966 



saturation 



Excess Oi 



1967 



saturation 



Excess O2 



March. 

 April. . 



June. 



July- 



August - 



September. 



Percent 



Ml./l. 



109 .60 .60 



98 .66 None 



1.25 



.30 



Percent 



' iw' 



117 



'Hi' 

 'm 



107 

 106 



106 

 108 



HI 

 111 

 107 

 111 

 106 



Ml. II. 



"o.'io 



104 None 

 113 None 

 110 . 65 



1.06 



None 



""'1.05' 



None 

 .25 



None 

 None 



.27 

 .70 

 .80 



1.26 

 1.45 



.60 



.55 

 .50 



None 

 .26 



None None 



None . 30 



None None 



None None 



None . 30 



Supersaturation arising from these two processes 

 can be distinguished if the concentration of nitro- 

 gen is known. Nitrogen and oxygen which enter 

 solution from the atmosphere bear a nearly con- 

 stant ratio to one another, expressed by the equa- 

 tion 02 = . 577 N2 — .22 (Rakestraw and Emmel, 

 1938). This equation indicates the amount of oxy- 

 gen which ought to be in solution for any given 

 concentration of nitrogen. Oxygen in excess of this 

 amount represents that added by photosynthesis; 

 the difference between the calculated oxygen con- 

 centration and the oxygen concentration at satura- 

 tion represents the excess or deficit of atmospheric 

 oxygen. 



Nitrogen observations were made only intermit- 

 tently in the present study ; the observations, how- 

 ever, together with source composition of excess 

 oxygen are given in table 1. As can be seen, the 

 greatest nonphotosynthetic oxygen supersatura- 

 tion and supersaturation of nitrogen occurred usu- 

 ally in April or May or occasionally in mid- 

 summer. 



The physical causes of supersaturation could be 

 intensified by the coastal topography. Numerous 

 protected and shallow embayments permit rapid 

 warming of the water; tidal movement is strong 

 and conducive to the mixing of warm and cold 

 saturated water, producing supersaturation of the 

 mixture; warming of subsurface waters is a ix)s- 

 sible result of the flooding of sunheated tidal flats. 

 I have no evidence that these particular processes 

 are, in fact, the cause of nonphotosynthetic oxygen 

 supersaturation, but they are theoretically possible. 



ECOLOGICAL SIGNIFICANCE 



Tiie immediate question posed when the first in- 

 dications of supersaturation were noticed was 

 whether this situation was unusual or a regular 

 annual occurrence. On the basis of 4 years of ob- 

 servations, the answer seems to be that it is a regu- 

 lar occurrence, although annual variations in the 

 seasonal cycle are marked. Longer term trends 

 may also be indicated in the basic annual cycles. 



SUPERSATURATION OF ATMOSPHERIC CASES IN GULF OF MAINE COASTAL WATERS 



121 



