BIGELOW: COAST WATER EXPLORATION OF 1913. 221 



Density in the Gulf of Maine. 



In the Gulf, in August (Fig. 55) the surface water was lightest close 

 to shore north of Cape Ann (1.0231), off Cape Cod (Station 100S5, 

 1.0231), and, in an isolated region, over the western basin (Station 

 lOOSS, 1.0229) ; the latter was a local phenomenon, due to high surface 

 temperature. Surface density was highest on German Bank (1.0254) 

 and along the northern part of the coast of Maine (1.025), i. e., in 

 those regions where tidal currents cause the most effective vertical 

 mixing of the water. And the surface was only slightly less dense 

 off Lurcher Shoal, owing to its low surface temperature. We likewise 

 encountered surface water of high density off Matinicus (Station 10101, 

 1.0248); And no doubt many other anomalies of this kind might be 

 found in the Gulf, caused by local surface cooling by tide rips and 

 vertical currents. 



The surface density of most of the Gulf was 1.0236-1.0248, increasing 

 from southwest to northeast; i. e., considerably higher than over the 

 continental shelf south of Cape Cod a month earlier; had the observa- 

 tions been taken simultaneously the discrepancy would have no doubt 

 been greater, it being only reasonable to assume that the surface of 

 the Gulf would have been cooler early in July than early in August, 

 but with nearly the same salinity (1914a). 



The table of density (p. 344) shows that the water was lightest at 

 the surface, heaviest on the bottom, /. e., was in stable equilibrium, 

 everywhere in the Gulf. Where vertical and tidal circulation is active, 

 as on German Bank, the stability was so slight as to offer little resist- 

 ance to vertical overturning of the water. But where tides are weak, 

 as for example off Massachusetts Bay, over the western basin, and in 

 the trough west of Jeffrey's Ledge, the difference between surface and 

 bottom density, and hence the vertical stability, is great. In the 

 western parts of the Gulf in general there was a very rapid rise of 

 density from the surface down to about 20-30 fathoms, corresponding 

 to the rapid rise of salinity and fall in temperature in this zone; fol- 

 lowed by a very much slower, though continuous increase, down to the 

 bottom. But the density curves, like those for temperature are pro- 

 gressively straighter and straighter, passing across the Gulf from south- 

 west to northeast. And in the northern end of the eastern basin, as 

 well as on the Nova Scotian and Maine banks, the rise in density, 

 whether great or little, was nearly uniform in rate, from surface to 

 bottom ; most nearly so where the stability of the water was slightest 

 {i. c, German Bank). 



