96 



Even when the case is narrowed down from full seasons and cruise 

 periods to that of individual drifts it is still found that a good agree- 

 ment is actually observable between many berg, wreckage, and ship 

 drifts, on the one hand, and the particular distribution of current 

 that the surface isotherms at the time suggest, on the other. This 

 raises grounds for hope that an intelligent interpretation of the 

 isotherm curves alone can be used to forecast future berg drifts, at 

 least in some regions and cases. 



Let us examine the isotherm and ice charts of the 1928 and 1929 

 ice-patrol seasons and see how much the isotherm charts in their 

 present state of development can be depended upon to indicate berg 

 drifts. The charts should be considered with the usual drifts of 

 bergs about the Grand Banks in mind and with a knowledge of the 

 general subsurface conditions of the region that the oceanographic 

 station work to date has furnished. To depend upon the different 

 isotherm charts alone would be to invite confusion and misinter- 

 pretation. 



Some of the rapid berg drifts indicated by dotted lines south of the 

 forty-third parallel on the ice charts for the months of May and June, 

 1928, show a general agreement with the isotherm chart for the 

 period during which they occurred, May 21 to June 5, 1928. Com- 

 parison of three drifts shown on Figures 9 and 10 with the isotherms 

 on Figure 28 in Coast Guard Bulletin No. 17 suffices to show this. 

 The berg drifts during the period of the seventh and eighth patrol 

 cruises of 1929, from July 3 to August 2, again illustrate the good 

 correlation between the surface isotherms and the regional oceanic 

 circulation in the area of special danger to shipping south and south- 

 east of the Tail. To facilitiate comparison the drift tracks of all of the 

 1929 bergs whose drifts the patrol was able to determine have been 

 placed on the respective isotherm charts appearing in this Coast 

 Guard Bulletin. 



From the comparatively pure Gulf Stream waters just to the south 

 of the limits of bergs many temperature reports are received by the 

 patrol. These waters are found to be often characterized by deep 

 embayment of the isotherms, similar to those that occur in the 

 colder mixed waters just offshore of the Tail. Coming in with the 

 temperature reports from the waters of tropical character there are 

 frequent reports of spars, buoys, and other floating objects. Atten- 

 tion is called to the particular drift of a buoy shown on the isotherm 

 chart for the period June 18-July 2, 1929. This buoy's drift was 

 plotted from a series of reports each so complete and specific as to 

 positively identify it. There were no strong breezes or gales to 

 interfere with the local currents. It can be seen that its successive 

 positions indicate that the local drift among the isotherm cmbay- 

 ments in the warm water was at the time to the northwestward, 



