The accumulation of river water b;twc;n Cape Cod and Chesapeake Bay 349 



the water supplied by river drainage. The remaining 80% must be transported 

 through the region by advection and eddy diffusion, and mixed away in ihe more 

 sahne water offshore. 



The Gulf Stream flows offshore, separated from the waters of the continental 

 shelf by the slope water of intermediate characteristics (Lsixin, 1936, 1940). The 

 upper 200 metres or so of the slope water is generally less saline than corresponding 

 waters of the Gulf Stream, reflecting the effects of varying amounts of coastal water 

 at different times of the year. Ultimately the river water which is not evaporated 

 locally must be entrained, via the slope water, in the Gulf Stream system. The volume 

 transport of the Gulf Stream varies between 76 and 93 milhon cubic metres per second 

 (ISELIN, 1940). This flow is twenty thousand times greater than the rate of addition 

 of river water to this part of the continental shelf, so that direct assimilation of all 

 of this river water in the Gulf Stream would not make a measurable change in its 

 salinity. 



The general westerly and southerly drift of the inshore water is well known, and is 

 indicated by the temperature and salinity sections given by Bighlow (1933) and 

 BiGELOW and Sears (1935). Extensive current measurements from lightships through- 

 out the area south of New York show non-tidal drifts largely paralleling the coast 

 of from 1-8 to 2-8 nautical miles per day (Zeskind and LeLacheur, 1926; Hak.ht. 

 1938; Marmer, 1935). The non-tidal current observed at Ambrose Lightship flows 

 nearly east, and Uttle or no residual drift was observed at Nantucket Shoals Lightship 

 except for transitory effects of the winds. The Current Atlas of the North Atlantic 

 Ocean (Hydrographic Office, 1946) gives consistent westerly and southerly drifts, 

 paralleling the coast for the inshore areas south of New York, with frequent easterly 

 components over the mid shelf area south of Martha's Vineyard and east of both 

 the Delaware and Chesapeake Bays. 



The general character of these coastal drifts has been recently confirmed by drift 

 bottle studies (Redfield and Walford, 1951; Miller, 1952). Practically all of the 

 bottles released close to shore south of New York drifted southward. Only two 

 bottles, of several thousand released north of Cape Hatteras, were recovered south o{ 

 that point, indicating an abrupt reversal of the current. Many of the bottles released 

 to the east of New York were recovered north of the point of release, along the Long 

 Island shore. The percentage returns of bottles released close to the coast was high, 

 but decreased rapidly with increasing distance from the coast. Few bottles released 

 more than 20 miles offshore were recovered on the beach, though several of these 

 have crossed the Atlantic and have been recovered on European shores. 



The question arises whether these drifts can be expected to add substantial amounts 

 of fresh water to this area of the continental shelf. To the south, the Gulf Stream is 

 very close inshore and the shelf is only 30 miles wide at Cape Hatteras. Bigelc.w and 

 Sears (1935 p 87) state: "Just south of Cape Hatteras a wedge of pure oceanic 

 water presses in across the shelf entirely separating the shelf and slope water bands 

 to the north from the low coastal salinities farther south ". All of the ev.dencc thus 

 indicates that no significant increment of fresh water may be expected to enter the 



area from the south. , 



The possibility that freshened Gulf of Maine water may enter the area through 

 the Martha's Vineyard section cannot be categorically excluded. B.gelow (1915) 

 concluded that northern water in this area was hardly appreciable, except perhaps m 



