822 



BULLETIN OF THE BUREAU OF FISHERIES 



alkaline seas, as might have been expected from its comparatively low salinity and 

 temperature. Within the gulf, however, the pH from station to station does not 

 correspond to the differences in salinity or in temperature; neither have I been able 

 find any definite parallelism between the pH and the abundance of diatoms — cer- 

 tainly no decided rise even at the times and stations when these pelagic plants are 

 flowering most freely. In short, the volume of water is too large and its circulation 

 too free for any given flowering to reflect its active photosynthesis by an appreciable 

 local rise in pH. 



The fact that in March the deeper of two samples vi^as in several cases the 

 more alkaline, but that in May the reverse was true, may be significant, the phyto- 

 plankton being most abundant in the well-illuminated strata near the surface. It is 

 not improbable, also, that a larger number of observations carried out through the 

 the year would reveal a seasonal fluctuation of pH, with the maximum in early 

 spring and summer following the vernal flowerings of diatoms and the summer mul- 

 tiplication of peridinians, such as occurs in the Irish Sea^^ (Moore, Prideaux, and 

 Herdman, 1915; Bruce, 1924). 



VISUAL TRANSPARENCY 



Measurements of the transparency of the water were taken at 18 stations dur- 

 the summer of 1912 with the ordinary "Secchi" disk — a metal plate 14 inches in 

 diameter, painted white, and rigged with a bridle, so that it hangs horizontal. This 

 is viewed through a water glass ^^ while being lowered, and the depth at which it 

 disappears from view is recorded. 



In the clearest water the disk was visible to 8.2 fathoms, but at most of the 

 stations it disappeared at 4 to 5 fathoms. Local variations in transparency did not 

 paraflel the variations in color (p. 823), for while the water was most transparent 

 when bluest, it was not least so where greenest, but where the percentage of yellow 

 was only 20 (station 10038). 



The transparency does not measure the penetration of sunlight, for water 

 cloudy with silt or with diatoms may still be translucent, like ground or opal glass, 

 though transparent to only a small degree. 



Transparency, in meters 



July n.. 



July 17.. 

 July 23. 

 July 24. 

 July 25. 

 July 26. 

 Aug. 7 . 

 Do. 

 Aug. 8 . 



Date, 1912 



Station 



Transpar- 

 ency 



10004 



10011 



10012b; 



10014 



10016 



10016 



10022 



10023 



10025 



6.4 



11 



11 



11 

 8.2 

 6.4 



13 



15 



12 



Aug. 15. 

 Aug. 20. 

 Aug. 21.. 

 Aug. 22.. 

 Do... 

 Aug. 24.. 

 Aug. 29.. 

 Aug. 31. 



Date, 1912 



Station 



Transpar- 

 ency 



10031 

 10036 

 10037 

 1003S 

 10039 

 10040 

 10043 

 10044 



7.3 

 7.3 

 7.3 

 5.5 

 11 

 9.1 

 9.1 

 9.1 



"See Nelson (1924) for an account o( rapid diurnal variations of pH in the estuarine waters of New Jersey. 

 « Tiie use of the water glass is necessary to escape the effect of reflections from the surface. 



