94 



of water samples are to be handled. The comparative cheapness, 

 light weight, and availability of the titrating outfits, however, make 

 them preferable to the electric-salinity cabinets, unless over 1,000 

 samples of water are to be analyzed per ship per season. The former 

 are from twenty-five to fifty times cheaper and lighter than the 

 electrical outfits. For worth-while residts both methods require 

 well-trained and conscientious operators. Under comparable condi- 

 tions the accuracies obtainable by the two methods are probably 

 about equal. 



The large number of bergs south of the forty-eighth parallel during 

 the 1929 ice season claimed the patrol's almost undivided attention. 

 If the ice had been less, either in extent or amount, more oceano- 

 graphic work woidd have been done. In a general way, and as in 

 previous years, the currents that the dynamic oceanographic compu- 

 tations showed theoretically should exist, actually did exist in fact, 

 as shown hj occasional iceberg and patrol-ship drifts. 



2. POSSIBILITY OF PREDICTING ICEBERG DRIFTS 



A. SURFACE ISOTHERMS AS BASIS FOR PREDICTION 



Berg-drift predictions are highly necessary for the information 

 and guidance of the patrol itself, even though the conclusions should 

 not be accurate enough to send out in the broadcasts. Therefore, 

 any method simpler than the dynamic one that the patrol ships 

 could employ without interfering too much with their primary scout- 

 ing and trailing duties is much to be desired. Having explained at 

 some length in the preceding chapter the features of some of the 

 problems confronting the ice patrol, the matter of predicting berg 

 drifts can now be taken up with clearer understanding. 



The only other method besides dynamic mapping that has been 

 suggested for picturing the varying circulation in the ice-patrol 

 area has been that based on a study of surface isotherm charts. 

 The surface isotherms have always been assinned to give a broad 

 general idea of the prevailing water and ice movements m and about 

 the Labrador Current throughout the season. The main reason 

 why the patrol vessel carefully plots both her own surface-temperature 

 observations and those coming in from other ships is because the ice 

 in general is expected to be found and to remain where the water is 

 coldest. 



The cruise isotherm charts have been considered valuable enough 

 to reproduce each year in the ice patrol's bulletins, but they have 

 not been given important consideration when attempting to fore- 

 cast movements of bergs that have not been sighted or reported 

 for some time. The reason for this lack of confidence lies in the 

 numerous discrepancies that have been noted when bergs did not 

 move parallel to the isotherms or even close to the dii-ection which 

 the surface isotherms seemed to indicate thev should take. 



