sea temperatures from the Florida Keys to 

 Cape Cod (Walford and Wickland, 1968). 



Low Temperature Core 



Vernal warming forms a layer of warm wa- 

 ter overlying a pool of relatively cool water 

 lying over the shelf. This pool gradually di- 

 minishes as vernal warming progresses. The re- 

 mains of this cool water pool were found in 

 September 1967 (fig. 87). It appears as a core 

 of cool water (less than 8°C) form Cape Cod 

 to the ofl^ng of Chesapeake Bay. Ketchum and 

 Corwin (1969) studied the persistence of 

 "winter" water on the continental shelf for a 

 period of 3 years. They concluded that the pool 

 of cool water is warmed by both vertical mixing 

 with less saline surface water and horizontal 

 mixing with more saline slope water. The type 

 of mixing was related to the heat budget along 

 the shelf. 



One of the processes by which the pool of 

 cool water is dissipated was described as 

 "calving" (Cresswell 1967). In this process, 

 large bubbles of cold water break off and move 

 seaward as they mix with the slope water. The 

 primary cause of calving was ascribed to the 

 shoaling of internal waves. Tidal agitations 

 were described as a secondary cause. The den- 

 sity structure of the water over the shelf edge 

 in September 1967 (figs. 41-50) included a 

 sharp vertical gradient 20 to 30 meters below 

 the surface and either riding over or impinging 

 upon the shelf edge. Thus, conditions for the 

 propagation of internal waves existed in Sep- 

 tember 1967. They did not, however, exist dur- 

 ing December 1967 (figs. 51-56). 



Evidence of the calving process was found in 

 September 1967 (fig. 10) . A relatively small 

 cold bubble (11°C) was found 30 miles sea- 

 ward of the cold water on the shelf edge in 

 section 2. This bubble appeared to be in the 

 final stages of separation from the parent wa- 

 ter mass. It is interesting to note that in this 

 instance and in the examples presented by 

 Cresswell, the bubbles are closer to the surface 

 than their parent water masses. 



The dissolved oxygen content of the cold 

 water bubble (fig. 58) discussed above was 

 higher than that of the surrounding warmer, 

 water, as expected, but it was also higher than 

 that of the parent water mass. This high 

 oxygen content may have been the result of 



photosynthetic activity in the bubble after its 

 detachment and rise into the photic zone. The 

 relatively higher chlorophyll content of the 

 bubble (fig. 73) supports this contention. 



Salinity Distribution 



In September and December, the water over 

 the shelf generally showed weak vertical sal- 

 inity gradients approaching isohaline condi- 

 tions on some .stations (figs. 25-40). The 

 horizontal gradients were relatively strong, 

 however, and reached a maximum near the 

 .shelf edge. In September surface salinity in- 

 creased gradually from less than 31%o near the 

 coastline to greater than 35%o beyond the con- 

 tinental shelf (fig. 5). The same general 

 gradient of surface salinity occurred in Decem- 

 ber with an inshore salinity of less than 32%o 

 (fig. 6) . The increase in salinity during Decem- 

 ber reflects high evaporation rates and low 

 river discharges during winter months. The 

 river discharges of the northern half of the 

 Mid-Atlantic Bight are highest in March, 

 April, and May. Inshore salinity reaches a 

 minimum during this period (Ketchum and 

 Keen, 1955). Bumpus (1969) has associated 

 low river runoffs along the Mid-Atlantic Bight 

 with reversals in the surface drift over the 

 continental shelf. 



A layer of high salinity was found during 

 both crui.ses (figs. 89 and 90) in the same gen- 

 eral location. The salinity values of the layer 

 decreased slightly from September (35.75%o) 

 to December (35.50%o). There was a surfacing 

 of the high salinity layer along section 4 in 

 September (fig. 28). It appears that this was 

 the result of current induced upwelling associ- 

 ated with cyclonic water motion. Assuming 

 geostrophic conditions, the density structure of 

 the water along section 4 (fig. 44) depicts a 

 local cyclonic eddy limited to the upper 50 

 meters. 



Crulf Stream Counlerflow 



Stommel (1957) proposed that a baratropic 

 flow opposite to the Gulf Stream could be main- 

 tained by the sinking of polar water. Swallow 

 and Worthington (1957) observed a deep 

 western boundary current opposite to the Gulf 

 Stream off the Blake Plateau, south of Cape 

 Hatteras. This current was below 2,000 meters 

 and ranged from 9 to 18 cm/sec. Volkmann 



