770 BULLETIN OF THE BUREAU OF FISHERIES 



In the northwestern part of the gulf variations in the distribution of salinity 

 from summer to summer show that the movements of the surface water are variable 

 in detail. 



Thus, in July and August, 1912, the isohaline for 32.4 per mille (the critical one 

 in this particular summer) marked a definite expansion of coastal water off Penobscot 

 Bay (Bigelow, 1914, pi. 2). In August, 1913 (fig. 135), the undulations of the 

 isohaline for 32.5 per mille again suggested an anticlockwise swirl off the bay, drawing 

 Salter water into its northern and eastern sides, fresher water into its western and 

 southern sides. In August, 1914 (fig. 136), the surface salinity of this part of the 

 gulf was more uniform, with no evidence of any such outflow off the Penobscot; nor 

 is anything of the sort indicated in the surface chart for 1915 (fig. 137). 



In the Massachusetts Bay region, by contrast, the regional distribution of salin- 

 ity at the surface has been more nearly constant from summer to summer. Thus, 

 in August, 1922 (apparently a representative year in this respect), when the surface 

 at 13 stations ranged from 30.96 to 31.29 per naille, the distribution was of the usual 

 coastwise type — i. e., slightly lowest (30.9 to 31 per mille) close to Gloucester (sta- 

 tion 10633), off the mouth of Boston Harbor (station 10638), and close to land in 

 Cape Cod Bay (stations 10643 and 10644) ; uniformly slightly higher across the mouth 

 of the bay (31.2 per mille at stations 10631 and 10632). Three stations on a line 

 crossing the mouth of the bay on August 31, 1912, showed no greater variation than 

 this on the surface, though all of them gave slightly higher readings (31.67 to 32.03 

 per mille). It is probable that the surface of the bay would have been found less 

 saline than this in August, 1916, judging from a surface reading of 31.27 per mille off 

 the tip of Cape Cod on the 29th (station 10398) and from the fact that the mouth 

 of the bay had been only 30.5 to 31.2 per mille a month earlier (stations 10340 to 

 10342). In 1913 the August value was somewhat higher at the mouth of the bay — 

 i. e., about 32.1 per mille. 



Observations taken in the offing of Nantucket and on the northwestern part 

 of Georges Bank in July of 1913, 1914, and 1916 show all this area included within 

 the influence of the low salinity of the coastal belt, with surface values close to 

 32 per mille over Nantucket Shoals, rising to 32.1 to 32.5 per mille over the 

 neighboring parts of Georges Bank (fig. 136; Bigelow, 1922, fig. 36). Surface 

 readings make it probable that in July, 1914 (fig. 136), the band of low temperature 

 described above (p. 608) as crossing the bank from northeast to southwest was 

 reflected in an expansion of low salinity from the southwestern part of the bank 

 out across its seaward slope, as outlined by the isohaline for 33 per mille. 



It is probable that the regions of low surface temperature over the shoaler 

 parts of Georges Bank, where the water is chm'ned by strong tidal currents (p. 594), 

 are equally characterized by a surface salinity higher than that of the general 

 neighborhood. Our visits thither have afforded two instances that may be inter- 

 preted in this way — namely, a slightly higher value at one station on the eastern 

 part (32.59 per mille at station 10223) on July 23, 1914, than at neighboring stations 

 to the north, south, or east of it, and a value equaUy high on the western side on the 

 same date of 1916 (station 10348, 32.54 per mifle), again with slightly less saline 

 surface water to the south, west, and apparently to the north. A similar pool of 



