that the rapid change of properties occurs 

 above 300 m. (figs. 3, 16, 17, 18, and 22). 



The geostrophic velocity computed with ref- 

 erence to 600 m. between stations 054-1 1022 

 and 055-HO23 (fig. 17) was 23 cm. sec. The 

 velocity must be considerably greater in the 

 warm-water core of the interaction system (be- 

 tween hydrographic station 055-HO23 and the 

 location of BT number 266, for example) . The 

 mean geostrophic velocity, with reference to 

 600 m. between stations 054-HO22 and 056- 

 H024, was 60 cm./sec, and between stations 

 055-HO23 and 056-HO24, it was 128 cm. sec. 

 Because station 056-HO24 was located in the 

 warm core of the Gulf Stream, the data are not 

 applicable to the evaluation of energj' left in 

 the interaction system. The 600-m. reference 

 level may be satisfactory for stations 054- 

 H022 and 055-HO23 but not for station 056- 

 H024. Additionally, this station is on the Gulf 

 Stream side of the cold stripe. The mean geo- 

 strophic velocity computed between stations 

 054-HO22 and 055-HO23 appears realistic. No 

 great velocities within the interaction systems 

 were observed f)-om the Geronimo. 



PROCESS OF INTERACTION 



Apparently Gulf Stream water was supplied 

 to the interaction systems in two principal 

 ways. During the present observations, the 

 dominant supply was furnished by separation. 

 A large volume of water is separated from the 

 left flank of the main body of the Gulf Stream 

 —for example see figure 8. 



A supplementary supply of water was by 

 injection. Tongues of warm and cold water 

 alternating vertically extended over a consider- 

 able horizontal distance (fig. 24). The injec- 

 tions tended to be moderate to weak when the 

 main interaction system was strong (figs. 8 and 

 16) ; conversely, the injection tongues tended 

 to be actively developed when the main inter- 

 action system was nearly dissipated (figs. 10 

 and 11). A general idea of the dimensions of 

 the warm-water tongues can be obtained from 

 a profile based on BT observations along the 

 slope water of the left boundary of the Gulf 

 Stream, between transects I and II (fig. 26). 

 The figure, which covers a distance of 140 miles 

 (259.3 km.), shows one well-developed, warm- 



water tongue and a few cold tongues. The well- 

 developed tongues were about 30 miles (55.6 

 km.) wide (parallel to the Gulf Stream bound- 

 ary) and about 40 m. thick (vertical dimen- 

 sion) near the base. Their average projection 

 was about 8 miles (14.8 km.) in the direction 

 normal to the boundary, as evaluated from 11 

 well-developed examples in various sections. 

 Gulf Stream water was not a contributing fac- 

 tor to numerous other tongues that seemed to 

 have developed within the interaction system 

 after separation (figs. 9 and 10). 



DEVELOPMENT AND DISSIPATION 



Two principal questions may be asked re- 

 garding the interaction systems; How or why 

 do they develop, and what happens to the water 

 mass separated from the Gulf Stream? When 

 an interaction system had dissipated at the 

 surface— whatever its dimensions or character 

 —there remained just one sharp surface bound- 

 ary between the slope water and Gulf Stream 

 (figs. 5 and 13). It seems, however, that in 

 depths from about 40 to 200 m., the interaction 

 systems persisted for longer periods; possibly 

 they never decayed completely. The sequence 

 shown in figures 4 through 8 reveals that the 

 remnants of an old interaction .system appear 

 to be absorbed by a new one. If volumes of 

 water as large as those involved in interaction 

 systems are disposed of by absorption within 

 the neighboring water masses, perceptible 

 changes in the character of these masses could 

 be expected. Yet in our repeated sections along 

 transect I (in a 1-month period), even though 

 several interaction systems developed and dis- 

 sipated, no appreciable change of properties 

 was observed in the adjacent Gulf Stream and 

 slope water. A small rise in temperature in the 

 slope water can be attributed to heating as the 

 warming season progressed. Slope water was 

 less distinctly uniform at transect II than at 

 transect I, but because the observation jieriod 

 was comparatively brief, no definite conclusions 

 can be reached about the persistence of prop- 

 erties. 



The slope water was warmer— by about 2° 

 to 3° C.-at transect III than at transect I. The 

 multistream structure of the Gulf Stream as 

 represented by Fuglister (1951) was probably 

 absent at transect I, but may have been start- 



414 



U.S. FISH AND WILDLIFE SERVICE 



