SOME FEATURES OF THE GULF STREAM OFF CHESAPEAKE BAY 



IN THE SPRING OF 1963i 



By p. a. Mazeika -, Bureau of Commercial Fisheries, Biological Laboratory, Washington, D.C. 20242 



ABSTRACT 



Oceanographic measurements in May and June 1963, 

 showed that water mixing was intense though intermit- 

 tent at the western boundary of the Gulf Stream. 

 Warm, saline water became separated from the Stream 

 and mixed with the slope water as a result of divergence 

 near the surface and upwelling. Data from repeated 

 sections along three transects of the Gulf Stream are 

 analyzed and presented in 22 cross-sectional plots. 

 These plots show that a zone of intense mixing appeared 



intermittently at the western side of the Gulf Stream 

 in an apparently fluctuating manner. Separation of 

 this mixing zone from the Gulf Stream resulted from 

 local ascent of cool water from the subsurface levels 

 where there was a zone of steeply sloping isotherms. 

 The results suggest that part of the mixed, dense water 

 sank to about 200 m. below the depth at which it was 

 produced and returned to the Gulf Stream. 



Data for this report were obtained during 

 Cruise 1 of the Bureau of Commercial Fish- 

 eries research ship Geronimo (May 8 to June 

 7, 1963). Although the primary purpose of the 

 cruise was to test the ship and its gear, exten- 

 sive physical and biological oceanographic 

 observations were also made. The principal 

 physical investigation was a study of the prop- 

 erties of the Gulf Stream along three transects 

 described as follows (fig. 1) : 



Transect 1—16 sections across the left 

 (inshore or western) boundary of the Gulf 

 Stream— 12 with bathythermograph obser- 

 vations only, and 4 with oceanographic 

 stations (Nansen bottle casts) and BT"s. 



Transect II— four sections across the left 

 boundary (all with oceanographic stations 

 and BT's). 



Transect III— three sections across the 

 left boundary (all with oceanographic sta- 

 tions and BT's). 

 Most of the data used in this report were 

 gathered by repeated occupation of these tran- 

 sects. For each transect, one section was ex- 



^ Contribution No. 53. Bureau of Commercial Fisheries Tropical 

 Atlantic Biological Laboratory. Miami. Fla. 33149, 



^ Now at U.S. Naval Oceanographic Office. Code 7240, Naval 

 Research Laboratory, Washington. D.C. 203<i0. 



Published February 1968. 



FISHERY BULLETIN: VOLUME 66, NO. 2 



tended southeastward into the Sargasso Sea. 

 The I'ight (offshore or eastern) boundary of 

 the Gulf Stream was crossed six times. 



Bathythermograph observations were taken 

 every 5 nautical miles (9.3 km.), except that 

 on a supplementary run from transect II to 

 transect I along the left boundary, BT's were 

 taken every 10 miles (18.5 km.). Observations 

 at the oceanographic stations were limited to 

 the upper 600 m. The last one or two digits in 

 the numbers of the hydrographic station loca- 

 tions used in this report (fig. 1) indicate their 

 chronology. 



Continuous records of surface temperature 

 were made with a Foxboro ' thermograph and 

 were checked by measurements with two 

 thermistors and one bucket thermometer at the 

 location of each BT observation. Portions of 

 the Foxboro temperature records are repro- 

 duced (figs. 2 and 3 to 25). The lower trace on 

 the temperature record is used when the upper 

 trace exceeds the scale and is usually set IC^ 

 C. below the upper. The lower trace was not 

 well controlled during this study, and the dif- 

 ference at times exceeds 10*^ C. 



' Trade names referred to here do not imply endorsement of 

 commercial products. 



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