and the station just west of the trough, figure 

 31, shows again that the reason for the large 

 volume flow on 13 May is that the water in 

 the trough becomes denser while the water 

 west of the trough becomes lighter. 



Although the causes of the high-volume flow 

 are dynamically obvious, the reasons for the 

 conditions causing the dynamic stands at sec- 

 tion A3 on 13 May are not clear. Recirculation 

 of the Labrador Current south of section A3 

 and mixing probably formed the cold-salinity 

 water responsible for the low dynamic stand 

 at station 9929. The presence of unusually 

 warm fresh water between 265 and 415 meters 

 at station 9928 is difl^cult to explain. It may 

 be that there was a cyclonic circulation and 

 sinking of normal mixed water type from 

 the 100-meter level. Smith (1937) gives ex- 

 amples in surface dynamic topographies of such 

 recirculation. Even though such a recirculation 

 may be possible, the sigma-t profile at section 

 A3, figure 16, shows that such a recirculation, 

 if it occurred on isentropic surfaces, probably 

 took place well north of section A3. 



The possibility that an error in the depth 

 of no motion caused the large flow at section 

 A3 on 13 May can be examined. Defant (1961), 

 describes a method of determining the depth of 

 no motion between two stations by examining 

 the difi'erence in dynamic height between the 

 stations as a function of depth. The depth at 

 which the diff"erence in dynamic height is con- 

 stant with depth is assumed to be a depth of 

 no motion. Figure 32 shows that, by Defant's 

 criteria, the depth of no motion is at least as 

 deep as 1,500 meters. This would indicate that 

 the flow is even greater than 11 sverdriips. 



Examination of the time-series plot for the 

 east-west leg of section A2 (fig. 26) shows that 

 on 15 May the flow was at a minimum. This 

 hardly agrees with the maximum at section A3 

 only 2 days previous. The net flow, with respect 

 to the 700-decibar surface, between stations 

 9928 in section 3 and 9940 in section A2 was 

 8.1 sverdrups east-southeastward. This repre- 

 sents an average current of 4 cm/sec. The flow 

 at right angles to this was, of course, indeter- 

 minant, but it is most likely that the east- 

 southeastward flow represents the greater por- 

 tion of the flow. It thus appears that most of 

 the flow at the latitude of section A2 in May 



spilled over the northeast corner of the Grand 

 Banks west of the westernmost station in the 

 section. 



Previously unpublished results from a cur- 

 rent meter attached 50 meters below a buoy 

 moored by the Ice Patrol in position 44-53 N., 

 48-54 W., near the western end of section A3, 

 in 1961 give support to the notion of large 

 short-term changes in the Labrador Current 

 in spite of reservations about the adequacy of 

 the record obtained. The instrument failed to 

 give reasonable readings of current direction, 

 but did yield a readable record of current speed 

 for a period of 48 days between 28 May and 

 15 July. Recently the speed record alone was 

 read by eye in an effort to retrieve any usable 

 data. Readings were made every 20 minutes, 

 yielding 3,460 consecutive speed values. The 

 average speed was 29.6 cm/sec, with maximum 

 and minimum speeds of 64.2 and 6.5 cm/sec 

 respectively. 



The data after subjection to spectral analysis 

 showed peaks in kinetic energy density at two 

 points. Evidence of a slow-running clock in 

 the instrument was seen in the fact that these 

 peaks fit the inertial (17.0 hours) and the 

 semidiurnal tidal (12.4 hours) periods when 

 multiplied by a factor of 0.93. Thus it can be 

 inferred that inertial and tidal periodicities 

 can be expected in the flow along the eastern 

 edge of the Grand Banks. 



The time plot of the current record also 

 revealed a marked 14- to 15-day periodicity, 

 but the length of the record is far too short to 

 draw any firm conclusions. 



In summary, analysis of the data for 1967 

 has again shown the possibility of high fre- 

 quency variability in the physical oceanography 

 of this most interesting region where two major 

 currents impinge upon each other. A part of 

 the general problem of iceberg drift and de- 

 terioration must include not only better infor- 

 mation on what periods of variability are 

 significant in various areas of the region, but 

 also understanding of the reasons for such 

 variability. 



REFERENCES 



Defant, Albert (1961). Physical Oceanography, Vol. 

 1, Macmillan Co. p. 494-497. 



