94 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



on its underneath layers. But in spite of this it is probable that 

 by the process of mixing the higher layers are in a certain degree 

 cooled also. One must, however, keep in mind that the Labrador 

 current is a surface stream, whose depth is not great, and the volume 

 of the water-mass which it transports is relatively small. Care must 

 therefore be taken not to overload this relatively small current with 

 the work of cooling the whole Atlantic Ocean, as is so often done. 

 It is something quite different, however, to consider that the water 

 of the whole Atlantic Ocean in the north is cooler than it is farther 

 south and that a depression of the temperature within a region must 

 occur when this colder northern water-mass is brought down by one 

 or another cause toward the south. 



It is clear that the masses of ice carried along by the Labrador 

 current such as drift ice and icebergs which are driven far toward 

 the south, must particularly by their melting tend to cool the sur- 

 face layers of the ocean. But meanwhile it must not be forgotten 

 that the quantities of heat required to melt these ice-masses are 

 vanishingly small compared with the quantities of heat which are 

 transported by the water-masses of the Atlantic Ocean currents. 



If we examine our material closely in order to see what light it 

 throws upon such a water transportation of heat as we have been 

 speaking of, we may draw the conclusion from the curves of our 

 io° fields given in figure 20 that the w^ater in February between 50° 

 and 60° west longitude was uncommonly cold and also in the more 

 eastern fields between 50° and 30° west longitude. So far to the 

 east as between 20° and 30° west longitude the surface tempera- 

 ture was in February below the normal (see pi. 26). On the other 

 hand in the most easterly region, between 10° and 20° west longi- 

 tude, the cooling did not appear to be noticeable. In our last decade 

 group, March-April, in 1903, the surface temperature was further 

 cooled in the fields between 50° and 60° west longitude and this 

 gradual cooling from February to March- April made itself felt in 

 all the fields eastward as shown in figure 20 and plate 27. If we 

 may judge by our curves it continued through the whole year, so 

 that the surface temperatures in February, 1904, were considerably 

 cooler than in March-April, 1903, in all of our 10° longitude fields 

 between 50° and 10° west longitude, but not in the field between 50° 

 and 60° west longitude, as shown in figure 20. In March-April, 

 1904, the surface temperature began to rise, but particularly in the 

 field between 40° and 50° west longitude, and this rise made itself 

 felt in all the fields eastward thereof. Hence we may assume that 

 at this time the coldest part of the minimum had been passed. 



