and postseason cruises the observations extended to a depth of about 

 1,500 meters where the depth of water permitted and the dynamic 

 topography was referred to the 1,000-decibar surface. An exception 

 to the foregoing is that the 10 stations occupied in the southward 

 extension of section W during the third survey extended to depths of 

 about 2,500 meters to permit a better examination of the circulation 

 past tliis section w^here the depth of the motionless surface is in the 

 neighborhood of 2,000 meters. In general the intended depths of 

 observation, in meters, were 0, 25, 50, 75, 100, 150, 200, 300, 400, 600, 

 800, 1,000 and thence by 500-meter intervals. Again the 10 stations 

 in the southward extension of section W are an exception. At those 

 stations the intended depths of observation were the same as given 

 above from the surface to 1,000 meters, then 1,200, 1,600, 2,000, and 

 2,500 meters. Temperatures were measured with protected deep-sea 

 reversing thermometers, most of them of Riehter and Wiese manufac- 

 ture but some of them by Negretti and Zambra and some by the GM 

 Manufacturing Co. Depths of observation were based on Riehter 

 and Wiese unprotected thermometers. A program of intercomparison 

 of thermometers was maintained by shifting the thermometers used 

 in pairs. In all, 1,918 comparisons were considered. These gave a 

 probable difference between the corrected readings of a pair of ther- 

 mometers of 0.014° C. As most of the observed temperatures are 

 the means of the corrected readings of such pairs, the probable error 

 is of the order of ±0.01° C. 



The collection, handling and salinity determination of water sam- 

 ples was the same as in previous years, with the accuracy of the 

 salinities only that of the silver nitrate titration method used in 

 calibration of the salinity bridge and the precision about ± 0.005 '^/oo- 

 The salinities have been tabulated to the nearest 0.01 7oo- No minor 

 corrections to the salinities were required and except as noted in the 

 discussion the dynamic topography shown in the figures is in accord- 

 ance with the tabulated temperature and salinity data. 



The oceanographic work was under the supervision of Oceanog- 

 rapher Floyd M. Soule who was assisted by Lt. Leroy A. Cheney. 

 Other assistants in the observational work were Raymond W. Wood, 

 boatswain's mate second class, Francis N. Brown, yeoman second 

 class, Anthony J. Lamb, Jr., aerographer's mate third-class, Donald 

 M. McGill, aerographer's mate third-class, and Hugh R. McCartney, 

 Jr., aerographer's mate third-class. 



Figure 16 shows the dynamic topographic chart of the sea surface 

 resulting from the first survey. The Labrador Current is to be seen 

 flowing southward along the eastern edge of the Grand Banks as 

 far south as about latitude 44° 15' N., where it swings seaward to 

 the 1,000-fathom curve before continuing along the contours of the 

 banks as a slower but broader stream. The distribution of ice from 

 sightings and reports during the period of this survey confirmed the 



65 



