BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 



■Si 



mouth of Vineyard Sound, on the same day, the surface temperature was 67 F. Tem- 

 peratures were likewise taken west of No Mans Land and south of Narragansett Bay 

 in 29 fathoms. These agree in being considerably lower than the temperatures known 

 to occur at the same time in the more inclosed waters of the neighborhood. The pres- 

 ent writers have found still more extreme conditions to prevail at certain points imme- 

 diately to the east of Cape Cod. At Crab Ledge, a few miles to the east of Chatham 

 (chart 223), at a mean depth of \y}4 fathoms, two observations on August 12, 1909, 

 gave a mean surface temperature of 65 F. and a mean bottom temperature of 47. 2 F. 

 These figures accord pretty well with some obtained at nearly the same point by Robert 

 Piatt, United States Navy, on September 14 and 15, 1877.° The latter found a mean 

 surface temperature of 60.3 F. and a mean bottom temperature (28 fathoms) of 48. 2° F. 

 It is interesting to compare the figures obtained by us on August 10 and 12, 1909, for 

 a series of points between Woods Hole and Crab Ledge. These are presented in the 

 following table : 





Depth. 



Surface 

 temper- 

 ature. 



Bottom 

 temper- 

 ature. 





SK 



63-0 



62.5 



"70.5 











070.2 

 69-5 







a The mean of two determinations on different days. 



Verrill explained the low temperatures of the outer waters by invoking the aid 

 of "an offshoot of the arctic current," which he believed to pass westward into Long 

 Island Sound. The question whether or not there is a definite southward (and west- 

 ward) flowing current which affects this part of the coast has already been discussed 

 briefly on another page. No conclusive answer to this question appears to be forth- 

 coming at present. Undoubted, however, is the fact that during the summer months 

 there lies a comparatively cold zone between the warm coastal water and the yet warmer 

 Gulf Stream. This may, as has been suggested, merely represent the normal ocean 

 water which would be proper to this latitude in the absence of the Gulf Stream. If this 

 view be accepted, the higher temperature attained during the summer months by the 

 waters of Buzzards Bay and of Nantucket and Vineyard Sounds is simply the result 

 of their shallowness and comparative detachment from the great reservoir of ocean 

 water outside, just as we know that salt marshes or shallow lagoons become even 

 warmer than this during the summer months. 



The question here suggests itself why the coastal waters north of Cape Cod, e. g., 

 at Gloucester and at Boothbay, do not likewise become much warmer than they do 

 during the summer months. We have seen (p. 49) that the relations between the 

 temperatures at these points and those at Woods Hole are not such as are wholly 

 explained by differences in latitude. It is highly probable that one factor in the case is 

 the far greater depth of the waters north of Cape Cod, at slight distances from shore. 

 For example, the 50-fathom line passes within from 5 to 10 (nautical) miles of Cape 

 Ann and of many parts of the Maine coast ; while at the nearest point it lies over 50 



" These data were furnished us by the Superintendent of the Coast and Geodetic Survey. 



