580 BULLETIN OF THE BUREAU OF FISHERIES 



may be expected to prevail there earlier in the season. The profile run across the 

 shelf abreast of Shelburne, Nova Scotia, the day before (stations 10291 to 10295, 

 June 23 and 24, 1915) corroborates this apparent tendency for the cold Nova Scotian 

 current to swing offshore abreast Cape Sable at the time, instead of flowing past the 

 cape into the eastern side of the Gulf of Maine, as it does earlier in the season. This 

 profile (fig. 41) lies outside the geographic limits of the present discussion; it will be 

 enough, then, to point out that it cuts across a lenticular mass of water colder than 

 2°, occupying the whole breadth of the continental shelf at the 40 to 100 meter level, 

 with a minimum reading of only 0.7° (station 10292, 50 and 75 meters) in the trough 

 between the land and La Have Bank. 



The high temperatures recorded for the Eastern Channel in June, 1915, prove 

 Browns Bank the westerly boundary for the icy water at the time; but it may 

 extend across the Eastern Channel to Georges Bank earher in the month in some 

 years, a question discussed below in connection with the July temperatures of the 

 bank (p. 919). 



Unfortunately, no temperatures have been taken below the surface on any part 

 of Georges Bank in June. It is probable that the vernal expansion of the cold Nova 

 Scotian current maintains temperatures lower than 10° on the eastern part of the 

 bank untU the first of the month, and Dickson (1901) so represents it on his chart 

 of surface temperatures for June, 1897, contrasting with temperatures higher than 

 12° in the western side of the gulf, on the one hand, and outside the continental 

 edge, on the other. July temperatures (p. 594), however, suggest that the surface on 

 the western end of the bank may be expected to warm to 10° to 11° by mid June, 

 except locally, where strong tidal currents and rips sweep around its shoaiest portions. 

 Considerable variations develop in the temperature gradient on Nantucket Shoals 

 by that month, however, according to the local activity of the tidal stirring, for the 

 Halcyon found the temperatures almost exactly the same on bottom in about 30 

 meters depth (8.3°) as at the surface near Round Shoal on June 7, 1925, but the 

 bottom more than 5° colder than the surface '^ in water of about 40 meters depth 

 only 6 miles to the eastward. 



Judging from daily readings made at Nantucket lightship in the years 1881 to 

 1885 (Rathbun, 1887), and from the Halcyon temperatures just cited, surface tem- 

 peratures of 10° to 12° (varying somewhat from year to year) are to be expected in 

 the Nantucket Shoals region generally by the middle of June. 



GENERAL DISTRIBUTION OF TEMPERATURE 



A graphic picture of the June state for the gulf as a whole results from combin- 

 ing the June stations for the various years (fig. 39). Unfortunately, the obser- 

 vations not only include possible annual differences, but cover too long a space in 

 time for this surface chart to be as satisfactory as might be wished at a season when 

 the water is absorbing heat from the sun as rapidly as happens through June. It will 

 serve, however, as an indication of the regional distribution and approximate values 

 that may be expected in various parts of the gulf at the middle of the month. Its 

 feature of chief interest is that the temperature is higher in the western side than 



"Surface 11.7°; bottom 6.4°. 



