intermediate water mass to 4°C ± 0.3 C°. A 

 seasonal isothermal layer was present from late 

 October through early May (figs. 28-33), with 

 a maximum depth of 300 m observed in early 

 March. This isothermal feature was caused by 

 the erosion and deepening of the seasonal ther- 

 mocline which was influenced by increased con- 

 vection due to cooling temperatures and wind 

 mixing. A time-series plot is presented in figure 

 24 in support of the discussions of temporal 

 variations in temperature. 



The upper seasonal layer displayed maximum 

 surface temperatures and stratification during 

 the autumnal equinox; the minimum tempera- 

 tures and the deepest thermocline erosion (iso- 

 thermal layer) coincided with the vernal equinox. 



The salinity structure (fig. 25) of the upper 

 seasonal zone followed a trend similar to that 

 of the temperature. An isohaline layer developed 

 in December, with a maximum depth of 300 m 

 occurring in early March, and was followed by 

 the establishment of a halocline in May. This 

 seasonal halocline blended into the permanent 

 halocline which extended down to about 700 m. 

 The intermediate water (600-1,750 m) main- 

 tained a nearly constant salinity range of 34.92%o 

 -35.00%o. 



The vertical distribution of salinity for each 

 cruise is shown in figures 39-51. The salinity 

 maximum located at 100 m from August to De- 

 cember (figs. 39-42, 51 and Table 3) may have 

 been an intrusion of the North Atlantic Current. 

 The greater mixing forces that occurred during 

 the months from January to May eroded this 

 prominent feature into an isohaline layer (to 



approximately 300m) with only an occasional 

 maximum at greater depths. This seems to indi- 

 cate that the mixing processes were of sufficient 

 magnitude to destroy any changes that could be 

 brought about by intrusions from the North At- 

 lantic Current. 



Table 3 summarizes the variations of the predo- 

 minant characteristics of salinity in the upper 

 800 m at OS DELTA. 



Description of Observed Processes 



Observations made in a limited geographical 

 area over a relatively short period (one year) do 

 not lend themselves to a comprehensive analysis 

 of physical processes. However, it was possible 

 to observe changes in physical properties at OS 

 DELTA due to the variation in position and 

 intensity of the North Atlantic Current. 



Comparison of the physical properties of OS 

 DELTA was made with those observed for Stan- 

 dard Section A-3 (SSA3) (Robe, 1971) in an 

 attempt to determine the geographic relation 

 between OS DELTA and the Polar Front. Only 

 three dates were comparable (due to limited ob- 

 servations on the eastern end of SSA3): 4 No- 

 vember 1967, 3 February 1968, and 5 August 

 1968. During those times the Front was located 

 255, 285, and 200 nautical miles, respectively, 

 west of OS DELTA. 



It would be difficult to make an estimate of 

 the Front's distance to the north of OS DELTA, 

 due to a lack of data in that direction. However, 

 at no time did the observed water characteristics 

 indicate that the Front had traveled southward 

 through OS DELTA. Passage of the Front or 



Table 3. — Summary of the variations of the predominant characteristics of salinity in the upper 800 meters at Ocean Station 



DELTA, 27 August 1967 to 25 August 1968. 



*Casts during this period were taken for the first time at OSD with an STD. 



