no changes were observed in the SST of the surrounding cold water. Dif- 

 ferential heating across the air-sea interface, as discussed previously, 

 and mixing between the two water masses could simultaneously maintain SST 

 in the cold water while causing a decrease of SST in the warm water. 

 Complete dissipation or movement out of the survey area of one system and 

 replacement by a second may also have occurred during the interval between 

 phases . 



Origin of the warm water in the Gulf Stream is likely. An orderly 

 progression which might be associated with a warm-water gyre would include 

 (1) formation of a meander in the northern edge of the Gulf Stream upstream 

 from Cape Hatteras by processes as yet unknown, (2) intrusion of the meander 

 as a tongue into coastal water north of Cape Hatteras, (3) deformation of the 

 tongue from shear between the coastal current and the Gulf Stream, (4) 

 severance of the tongue from the Gulf Stream by excessive shear and formation 

 of an eddy as described by Ichiye, and (5) eventual dissipation through 

 mixing and heat loss to the atmosphere unless replenished by a later intru- 

 sion. Energy supplied by the Gulf Stream would probably impart northerly 

 movement to the gyre. Data are presently insufficient to support the above 

 supposition. 



Temperature inversions observed at the base of the seasonal thermocline 

 are probably a cold wedge and offshore bubble described by Cresswell (1967). 

 According to Cresswell, the steps in the formation of the wedge and the off- 

 shore bubble are (1) formation of cold bottom shelf water over the shelf 

 during winter months; (2) projection over the slope with size of the result- 

 ing wedge determined by the amount of shelf water formed; (3) elimination 

 of the excess water through mixing processes (calving), probably by tidal 

 agitation and shoaling of internal waves; and (4) introduction of parcels 

 of the eliminated water into the intermediate water, thus forming the off- 

 shore bubble. Absence of the wedge at two of the three sections repeated 

 during Phase II and reduction in wedge size in the third section suggest 

 that the wedge is in the final stages of its annual cycle. The wedge at 

 37°N is probably more representative of wedge structure along most of the 

 shelf than the wedge farther to the south. The latter wedge appears to 

 have been deformed by currents associated with the warm gyre. The three 

 deepest Hansen bottles at Station C (35, 40, and 45 meters) and a single 

 bottle at Station M (48 meters) appear to be in the wedge and are shown in 

 the composite T-S envelope (figure 11) as points with temperature less than 

 13.5°C and a salinity range between 32.4 and 33.4°/oo. This water, having 

 formed during the previous winter, should be called old shelf water to dif- 

 ferentiate it from water modified during summer. Temperatures in the off- 

 shore bubble are generally greater than those in the wedge and cannot be 

 distinguished from shelf water on the T-S envelope. 



Formation of an isothermal surface layer with corresponding deepening 

 in layer depth as observed during the interval between phases is in 

 agreement with Bigelow's (1933) description of autumnal processes over 

 the shelf. No evidence of bottom warming caused by intrusion of oceanic 



