3. The number of icebergs that drift south 

 of 43° North latitude and become an active 

 threat to transatlantic shipping. 



Lenczyk (1965) stated that the average num- 

 ber of icebergs that have drifted south of 

 latitude 48° North latitude each year since 

 1900 was 377. In 1964, an estimated 369 ice- 

 bergs drifted south of 48° North latitude, so 

 it w^as chosen as a normal year using criterion 

 2. Using criterion 3, 1954 was adjudged to be 

 a "normal" year. Data taken during April of 

 these years at stations corresponding to the 

 present stations of Standard Section 3 were 

 used to construct the vertical temperature and 

 salinity sections shown in Figures 26 through 

 29. The surface dynamic topography along 

 these sections is shown in Figures 30 and 31. 

 Because of the variation in the bottom topog- 

 raphy, it is believed that the 1954 section 

 was occupied slightly to the south of the 1964 

 section. Considering the vertical sections of 

 surface dynamic topography first, the most 

 apparent feature is the sharp slope indicating 

 the southward flowing Labrador Current. 

 There is also a varying in strength compensa- 

 tory northward flow on both sections. 



In 1954 and 1964, there was a second south- 

 west flow in the eastern portion of the section. 

 This contrasted with the gentle northward 

 flow indicated to the east by the surface dy- 

 namic topography of the April normal chart. 

 However, the eastern pai't of Standard Section 

 3 extended into a region of high standard 

 deviations of surface dynamic height which 

 might account for the differences. 



Figures 26 and 27 show the 1954 vertical 

 temperature and salinity distribution. They 

 show southward flowing cold ( — 1.0° C), rel- 

 atively fresh (33.0%o) water. Approximately 

 centered around station 5326 there was a 

 northward flow of this same cold relatively 

 fresh water. This cold water to the west was 

 obviously the Labrador Current. Note particu- 

 larly from Figure 28 that this cold fresh water 

 was directly under the portion of the surface 

 dynamic heights indicating the swiftest sur- 

 face current. The cold fresh water sampled at 

 station 5326 indicated either a local eddy or 

 that a portion of Labrador Current water was 

 moving along the eastward side of the trough 

 region and had not mixed sufficiently to lose 

 its identity. 



The 1.0° C isotherm indicates that the Lab- 

 rador Current can be considered as a thin 

 ribbon of rapidly moving water acting as a 

 boundary that prevents the cold, fresh water 

 overlaying the continental shelf from overflow- 

 ing the warmer, more dense water of the 

 Labrador Sea and trough region. 



Figures 28 and 29 show the 1964 vertical 

 temperature and salinity structure. They show 

 a large amount of cold relatively fresh water 

 moving southward. This time there is not the 

 compensatory northward flow of similar cold, 

 fresh water to the east. Figure 31 shows the 

 highest surface velocity between stations 8837 

 and 8838. Notice that this high velocity flow 

 was located east of the majority of the cold 

 water. 



The volume of southerly flowing water of 

 less than 4.0° C had in both cases displaced 

 the 4.0° C isotherm to the east. Several closed 

 cores, as indicated by isotherms and isohalines, 

 were observed to the east. If the copious 

 amount of southerly flowing cold, low saline 

 water shown in these cross sections was indic- 

 ative of the normal condition of the Labrador 

 Current in early April, then comparison with 

 the property cross sections observed this year 

 illustrate the extremely anomalous conditions. 

 It will be shown in the discussion of volume 

 transports that the anomalous condition was 

 not a small transport value for the Labrador 

 Current but rather a normal volume transport 

 with temperature salinity characteristics dif- 

 fering significantly from the normal. This 

 water was more dense level for level in the top 

 200 meters and warmer level for level at all 

 depths. 



THREE SERIAL CGC EVERGREEN 



OCCUPATIONS OF STANDARD SECTION 3, 



16-21 April 1966 



Three partial occupations of Section 3 were 

 conducted in April 1966. A reference buoy like 

 that described in the instrument section was 

 moored at 44°37'N and 49°12.5'W to provide 

 a fixed starting point. 



Occupations were conducted from west to 

 east as rapidly as weather conditions per- 

 mitted. Two occupations consisting of 6 sta- 

 tions were made on 16-17 April and 18-19 

 April, and one of 5 stations on 21 April 1966. 



10 



