mechanism of mixing during some phase of an 

 interaction cycle, the cross-current component 

 would be produced as a chain effect, and the 

 tendency toward divergence might conse- 

 quently result in an effective upwelling. 



ORIGIN OF THE COLD STRIPES 



The cold stripes at the left side of the Gulf 

 Stream are of Shelf water origin, as shown by 

 Ford, Longard. and Banks (1952). Their con- 

 clusions were based mainly on two sections (at 

 about long. 55° and 57°) of "Operation Cabot" 

 (1950), which extended over strongly mean- 

 dering parts of the Gulf Stream. Stommel 

 (1958) , generalizing on their results, concluded 

 that the influx of Shelf water must occur some- 

 where near Cape Hatteras, that the integrity of 

 the cold stripe is maintained for 1,600 miles 

 (2,963 km.), and that water exchange across 

 the boundary is, therefore, negligible. 



No such integrity of the cold stripe could be 

 observed during the Geronimo cruise. Clear 

 indications that local generation of cold stripes 

 was caused by ascent of cool water may be seen 

 in sections 4 to 7 (figs. 6 to 9) . A rather simple 

 boundary structure and no significant cold 

 stripe appear in section 4 (fig. 6). About 12 

 hours later, when section 6 (fig. 8) was made, 

 the boundaiy seen in figure 6 was at the same 

 location, but a new boundary and cold stripe 

 were developing strongly 25 miles to the right, 

 far into the Gulf Stream. 



The outcropping of cool water seems to have 

 reached a maximum in section 7 (fig. 9). The 

 old boundary is disintegrating below the sur- 

 face, and the major zone of steeply sloping 

 isotherms is located at the new boundary. 



When interaction systems were ,f ully devel- 

 oped and separated from the Gulf Stream by a 

 cold stripe (figs. 10, 14, 16, 17, and 22), the 

 presence of a well-developed mixed layer on 

 both sides of (but not in) the stripe, indicated 

 a strong ascending process. Furthermore, the 

 temperatures and salinities of the cold stripes 

 were similar to those in deeper water. For 

 example, the surface temperature m the cold 

 stripe in figure 9 (section 7) is 18- C. No sur- 

 face salinity values are available for this part 

 of the section, but the previous section (fig. 8) 

 shows a surface salinity of 36.04 "/im in the 

 newly forming cold stripe (BT 65), while con- 



siderably higher surface salinities occur on 

 either side. Salinities and temperatures similar 

 to those found at the surface in the cold stripe 

 in sections 6 and 7 (figs. 8 and 9) were found 

 at a depth of about 160 m. in section 10 at 

 oceanographic station 032-IIO02 (fig. 13) — 

 about 20 miles right of the boundary where the 

 isotherms slope steeply. A similar example is 

 provided by the surface conditions at the BT 

 number 269 in figure 17. In figure 22, the sur- 

 face salinity near the cold stripe (BT 375) is 

 similar to the salinity of the Gulf Stream at 

 210 m. (station 076-HO40). The hypothesis 

 that the cold stripes were caused by upwelling 

 of water from the area of steeply sloping iso- 

 therms seems to be in agreement with the posi- 

 tions of the frontal outcrop as observed from 

 an airplane (Von Arx, Bumpus, and Richardson, 

 1955). As previously pointed out, a supply of 

 cold, low-salinity water by injection (cold 

 tongues) was also observed during the Geron- 

 imo cruise. In some portions of the Gulf Stream, 

 this source of cold water to the left of the Gulf 

 Stream may be predominant. 



PHOSPHATE DISTRIBUTION 



In general, phosphate values were consid- 

 erably higher in the surface waters of the inter- 

 action systems than in the Gulf Stream. Also, 

 phosphate values fluctuated in the interaction 

 systems, associated with interchanging tongues 

 of cold and warm water, and the observed 

 cold-water masses usually showed higher phos- 

 phate values. The higher phosphate content of 

 interaction systems could come from various 

 sources, including— although the evidence is 

 sparse— the ascending water. To illustrate this 

 assumption, the only oceanographic station 

 close enough to the cold stripe to be indicative 

 (station 055-HO23 in fig. 17) shows high phos- 

 phate values from the surface to about 130 m., 

 low values from about 130 to 300 m.. and high 

 values again below 300 m. It seems that at this 

 particular station, ascending water was present 

 above 130 m., and descending mixed water (ex- 

 hausted of phosphate) between 130 and 300 m. 

 At station 056-HO24 (fig. 17) the phosphate 

 content of the 15^^ C. water along the steeply 

 sloping isotherms at about 220 m. was about 

 the same. Water in the cold stripe was evi- 

 dently ascending obliquely at this station, fol- 



GULF STREAM OFF CHESAPEAKE BAY 



421 



