"I"'" I" 



TRANSECT JZ 





TBMSCCT J 



ft: 



,^ 



LEGEND 



s FIRST CROSS SECTION 

 ' SECOND CNOSS SECTION 

 3 TMIflO CROSS SECTION 

 "■■"'■I CROSS SECTION 



i.l I I ...Ill i.illl uilumLLi'a.iiill I n , I, 



Figure 1. -Locations of transects and (oceanographic) 

 stations of R.V. Gcronimo Cruise 1. 



Continuous representation of the Gulf Stream 

 structure along its axis is not possible because 

 the observations were concentrated on transect 

 lines about 140 miles (259.4 km.) apart. The 

 detailed observations along each line do reveal 

 a number of common properties among the 



.# 



Figure 2.— Thermograph record of surface temperature 

 change across the right boundary of the Gulf Stream 

 between transects II and III. Temperatures greater 

 than 25° C. are read from the lower of the two traces 

 by adding 10° C. to the individual values. Bathyther- 

 mogram numbers and locations are indicated along the 

 temperature trace. 



transects. Most sections extend across only the 

 left boundary of the Gulf Stream; therefore, 

 my main intent is to interpret some variable 

 and transient features of that boundary. 



BOUNDARY SYSTEM 



In defining the boundary system, I will de- 

 scribe the temperature structure in the area 

 between the slope water and the Sargasso Sea. 



SLOPE WATER— INTERMKUI.VrE 

 VVWTER BOUND.\RY 



From the slope water to the Gulf Stream, the 

 surface temperature increased in two steps 

 along most of the sections. In a typical case 

 (fig. 10), the first step was a positive gradient 

 of about 8° C. in less than 1 mile (1.9 km.); 

 this temperature increase was the off'shore 

 (eastern) boundary of the slope water. Beyond 

 this first step was a rather wide intermediate 

 area of very irregular surface temjieratures. 

 Another steep, positive surface gradient of 

 about 4° to 6- C. was at the left boundary of 

 the Gulf Stream; in mo.st sections this gradient 

 was above or slightly left of the zone of steeply 

 sloping isotherms in the subsurface layers. 

 Iselin (1936) reported similar observations of 

 the slope water and Gulf Stream boundaries. 



INTERMEDIATE ZONE 



The width of the intermediate zone— between 

 the offshore slope water and the inshore Gulf 

 Stream boundaries— varied greatly. At times 

 it was not observed at all; at other times it was 

 as wide as 60 miles (111.1 km.). For example, 

 the zone is practically nonexistent in figure 5, 

 where surface temjierature increased from 12° 

 to 22° C. in about 3 miles (5.6 km.), followed 

 by an increase of only about 2" more in the 

 next 20 miles (37 km.) (the distance to the 

 warm core). A contrasting situation is illus- 

 trated in figure 18, in which the intermediate 

 zone is about 50 miles (92.6 km.) wide and the 

 warm core of the Gulf Stream is immediately 

 to the i-ight of tlie Gulf Stream boundary. 



LEFT BOUNDARY OF THE GULF STREAM 



The left boundary of the Gulf Stream is de- 

 fined here as the first strong thermal gradient 

 crossing at the surface from the Gulf Stream 

 toward the slope water. The mean location of 



388 



U.S. FISH AND WILDLIFE SERVICE 



