38 



more closely with those observed. Figures 28 and 29 demonstrate 

 very clearly that current surveys based on too few stations, or simply 

 on a line of stations, are apt to be misleading. A well-planned station 

 network is fcbe only means whereby it can be hoped to construct a 

 really useful dynamic current map. Indeed, simple observation of 

 the slant from the vertical of the sounding wire at an oceanographic 

 station is often a better guide to the direction of current than insuffi- 

 cient, fragmentary, maps based on dynamic calculations. 



3. ISOTHERMS AS CURRENT INDICATORS 



Examination of a number of 1930 berg and patrol ship drifts 

 strongly confirms the opinion expressed in last year's ice-patrol bulle- 

 tin (pp. 94-100, U. S. Coast Guard Bulletin No. 18) to the effect that 

 the surface isotherms can at times be taken as a reliable guide concern- 

 ing the probable future drift of bergs. The 1930 dynamic calculations 

 also confirm this opinion. The isotherm charts. Figures 2-10, and the 

 ice charts, Figures 16-24, furnish several remarkable instances of 

 long berg drifts along the cold walls. The currents observed in the 

 case of strongly developed cold walls were always such that the warm 

 water was on the right and the cold water on the left of the line of 

 drift. 



In the future, as was done in 1930, at least two good isotherm charts 

 should be constructed during each patrol cruise for experimental pur- 

 poses and frequently consulted. Such charts based on the observa- 

 tions of the patrol ship, as supplemented by those from about 100 

 cooperating vessels, are better and far more practicable to construct 

 without prejudicing the primary ice scouting duties than any dynamic 

 current maps which it has been possible to make since 1927. 



Of course it is not possible to make absolutely accurate deductions 

 regarding berg drifts from inspection of isotherm maps, but a good 

 idea can usually be obtained regarding the particular area which 

 should be searched for a certain berg upon the clearing up of a pro- 

 longed period of fog, or when for any other reason, it has not been 

 sighted or reported for one or more days. Should isothermic indica- 

 tions pointing to the probable drifting of a berg across the ''A" or 

 "B" traffic lanes exist during the continuance of a period of low visi- 

 bility, there should be no hesitancy about placing definite cautionary 

 warnings in the patrol's broadcasts. 



4. MISCELLANEOUS 



Figure 30, shows the detailed distribution of surface temperature 

 and the approximate distribution of surface salinity and density in 

 the immediate vicinity of a large berg that was on the temperature 

 wall. This berg had been moving rapidly along the wall for several 



