transects I and II. None of these five stations 

 was entirely out of Gulf Stream influence; 

 therefore, the values are not entirely repre- 

 sentative of typical slope water. 



Table 1. — Mean mines of surface properties in the Gulf Stream 

 and adjacent tcater masses (Geronimo Cruise 1) 



slope water - . 



(iulf Stream (all 



atationa) 



Gulf Stream (warm core 



stations only) 



Sargasso Sea . 



Temper- 

 ature 



"C. 

 12.88 



25.01 



25.61 

 21.64 



Salinity 



/oo 

 33.59 



36.42 



36.36 

 36.57 



25.34 

 24.41 



24.20 

 25.49 



Oxygen 



ml. /I. 

 6.31 



4.76 



4.66 

 5.08 



PO.-P 



(Iff. a'-/'- 

 0.35 



The water masses of the slope water, Gulf 

 Stream, and Sargasso Sea were distinctly dif- 

 ferent in all properties, both at the surface and 

 in the subsurface layers. The subsurface prop- 

 erties left of the Gulf Stream were character- 

 istically erratic; in the Gulf Stream and Sar- 

 gasso Sea the properties tended to be regular, 

 except for phosphate, which varied greatly to 

 about 300 m. 



INTERACTION OF THE SLOPE WATER 

 AND THE GULF STREAM 



The present data draw special attention to 

 the transient nature of the intermediate zone 

 at the left side of the Gulf Stream. In the first 

 section with oceanographic stations (transect 

 I, fig. 13), one sharp boundary appears where 

 the surface temperature increased from 13- to 

 22° C. in about 2.5 miles (4.6 km.) ; the inter- 

 mediate zone was almost nonexistent at the 

 surface. In the transect of 24 hours later (fig. 

 14), the situation has changed drastically: the 

 intermediate zone extends over 15 miles (27.8 

 km.), and two surface temperature boundaries 

 are distinct. The variability of the width of the 

 intermediate zone and its intermittent disap- 

 pearance tend to demonstrate that its existence 

 was the result of interaction between two water 

 masses. 



INTER.\CTION SYSTEMS 



The intermediate zone has, of course, a verti- 

 cal dimension. In the following interpretation, 

 therefore, it is convenient to use the term ' ' in- 

 teraction system" for the entire volume of 

 intermediate water. 



The dimensions, shape, and internal struc- 

 ture of the interaction system shown in figures 



3 and 4 change and transform rapidly, but the 

 formation of the system seems to have a certain 

 repetitive pattern. In figure 3 the intermediate 

 zone is well developed. The two boundaries, en- 

 closing the intermediate zone, are clearly 

 marked on the surface temperature record. 

 Temperature increases sharply by 7° C. at the 

 slope water boundary, between the BT numbers 



4 and 5. The intermediate zone is composed of 

 two cold-water belts and two shallow warm- 

 water cores. At the boundary between the in- 

 termediate zone and the Gulf Stream the tem- 

 perature rises in two steps from about 15° in 

 the cold belt to 24^^ in the Gulf Stream. A 

 complicated pattern of the interaction extends 

 in this section to about 230 m. 



When the next section (fig. 4) was taken 2 

 days later, the boundary structure had changed. 

 The intermediate zone with shallow currents 

 and cold-water bands disappeared. Only one 

 boundary was at the surface between the slope 

 water (temperature 11.6° C. and salinity 

 33.75%n) and the Gulf Stream (temperature 

 23.2° C. and salinity 36.29"/oo); within the 

 warm core the temperature was 24.2° C. and 

 salinity 36.41''/oo. Some traces in the interac- 

 tion system can be observed in the subsurface. 

 The surface temperature trace is relatively 

 smooth along the steep temperature gradient in 

 the boundary zone. 



In the following section (fig. 5) the boundary 

 was crossed about 6 hours later. The boundary 

 zone is narrower than in the previous section. 

 The temperature changes from 11.8° C. to 23° 

 C. in about 4 miles (7.4 km.), and the surface 

 temperature trace rises almost vertically, but, 

 in general, the boundary structure does not 

 change between the two sections. A large mass 

 of 12° C. water is enclosed by cooler water in 

 the subsurface. 



The section in figure 6 shows the boundary 

 about 5 hours later. The surface temperature 

 trace shows a small disturbance within the 

 boundary. The disturbance was not present in 

 the previous section. In the subsurface the 12° 

 C. water has been reduced in volume and has 

 separated. A bubble of 13° C. water is at 45 m., 

 but it is not certain whether it has been ad- 



406 



U.S. FISH AND WILDLIFE SERVICE 



