SCIENTIFIC EESLTLTS H 



11) found ill the Arctic Ocean was 14.59 U/UO, tliis beinj;- a sample 

 cut from a sheet of thin ice that had been exposed to the very low 

 temperature of al)Out -40° C. (-40° F.). It is ti-ue that the ice 

 cover is continually 1 icings rended apart exposing the water to ex- 

 tremely fri<rid temperatures. But the total amount of the salty ice 

 thus produced is comi)aratively small, because in relatively few in- 

 stances tloes ice form under supercooled conditions. 



The two principal rejiions of ice formation in the Arctic Ocean 

 are: 



(a) The shallow waters of the Eurasian shelf and in the north- 

 ern North American country. 



(b) The underside of the ])ermanent polar ice cap. 



In the case of {<() the sea surface normally becomes covered early 

 in the autumn before the atmosphere has ^reatly cooled, and tends 

 to remain more or less screened duriii<r the winter. Cases (a) and 

 (b) are now similar and new ice is added throu<rhout the colder 

 months of the year, on the underside of the cover, where tiie water 

 is beyond the reach of severe atmospheric chillin<jf. 



The fact that the amount of salt in sea ice varies directly witii the 

 rate of freezing (inversely as the temperature), causes the toj) of a 

 •rlacon or floe, the part exposed to the coldest temperature, to be 

 • composed of the saltiest ice." Several writers on polar phenomena 

 I have reported the presence of solid salt on the surface of ice sheets, 

 i which sometimes coats them so heavily that it has l)een likened to 

 j the early morning collection of hoar frost." The growth in thickness 

 I of yoimg sea ice from the top surface downward proceeds at a 

 I slower and slower rate the further the underside retreats from the 

 source of freezing. Similarly the insulating etfect of a snow cover 

 in retarding the freezing processes is proved by the formation of 

 I fresher ice on the underneath sides of those floes that are heavily 

 jsnow decked. The heat conductivity of ice is very poor, about one- 

 hundredth part that of iron. The upper surface of old ice l)eing com- 

 iparatively fresh is a much jioorer heat conductor than is young, salty 

 I ice, and similarly, retards freezing. A set of salinity observations by 

 jMalmgren (1928, p. G) through the vertical cross section of a young 

 sheet, gives the following distribution of salt with depth: 



Depth of ice from surface (cm.) (► 6 i;3 25 45 82 95 



Salinity of the ice (0/00) (i. 74 5.28 5. :31 3.84 4.37 3.48 3.17 



{ The fact that the surface layers of the sea are normally fresher 

 than those deeper down appears to have no appreciable efl'ect in 



I varying the salinity of the ice, top to bottom, because its thickness 

 includes only a very small part of the range of salinity with depth 

 of water. 



Since the underside of the cover is not only the freezing surface 

 hut the plane of contact between the ice and the concentrated brine, 

 one might naturally reason that the thicker the ice became, the 

 richer it would gi-ow in salts. The fact that the salinity of ice 

 decreases with the depth, hoAvever, indicates (a) that the processes 

 of precipitation are more than sufficient to counterbalance the increase 

 in salt concentration of the mother liquid: (h) that the mother 



'A thin veneer of new ice may often overlay young ice formed early in autumn from 

 tne thaw water of the Arctic pack. 



"^Weyprecht (1879, p. 58) states that the salt is not pure, but consists of fine needles 

 or ice tipped with small salt crystals. 



