SCIENTIFIC RESULTS 13 



snow freezes upon reaching the frigid sea. But as increased solar 

 warming raises the temperature, s(^ it increases the rate of melting, 

 and the Hoe timdly becomes thinner. 



Tlie loss of salts during the warmer months of tlie year leaves the 

 pohir cap mantled with fresh ice possessing a higher melting point 

 and therefore greater permanence. Old sea ice accordingly survives 

 nuich longer than the young, provided both samples be of the same 

 volume, when exposed to similar melting conditions. Many people 

 have regarded with considerable skepticism the statement that sea 

 ice furnishes a supply of very good drinking water. Experienced ice 

 jiavigators, however, are well aware of the freshening of sea ice with 

 age, since the fresh-water pools on old pans have long been utilized 

 as a never-failing supply. The rule is to moor the ship Avith ice 

 anchors to a well-selected old floe and then run a hose to a near-by 

 pool, where water has collected either from the weathered side of 

 the ice itself or from the preceding winter's snow cover. It is im- 

 portant to pump only from pools located well in from the edge of 

 the floe to avoid the possibility of contamination by salt spray.^ 



The physical behavior of salt water when subjected to freezing 

 temjieratures is different from that of fresh water under similar con- 

 ditions, because the former contracts right to the freezing point," 



The fact that salt-water ice is formed Avhen the freezing mass is 

 at maximum density, causes it, therefore, to be slightly heavier than 

 fresh-water ice. The fact that it does not float lower is due mainly to 

 the considerable quantity of air Avhich is in the water when it freezes. 

 The density of pure, fresh- water ice, according to Barnes (1928, p. 

 25) is O.DIGTG, and that of sea ice formed from the water of the salin- 

 itv that normallv comes under freezing conditions ranges from 0.857 

 to 0.924.11 



The relatively great range in the specific gravity of sea ice is due, 

 according to Malmgren (1928, p. 17), partly to large quantities of 

 air or water Avhich the ice may absorb during the summer directly 

 from the atmosphere. The reason that Avater is not sucked up from 

 below into the spongelike vacuoles (caused by the escape of salts) is 

 liccause nmch of the lower layers of the sea ice in polar regions remain 

 unmelted even in summer and, therefore, Avaterproof. If, however, 

 sea ice drifts out of the Arctic into Avaters Avarmer than 0° C. (32° 

 F.). melting Avill begin beloAv the Avater line, causing ingestion and 

 a' droAvning of the ice. Arctic pack ice, therefore, in the North 

 Atlantic floats loAAer than it did nearer its source. 



As a corollary to the above, if sea ice is exposed to temperatures 

 as low as —20°"^ C. (—40° F.), nearly all the brine globules freeze 

 into salt crystals, causing the ice to SAvell to a maximum volume. 



The i)hysical appearance of sea ice is (juite different from that of 

 fresh-Avater ice; the former exhibiting an opaque slaty Avhiteness. 



" I'lttcissoii ( 18S3, p. 304) collected sea ice floating iu the iwlar drift current northwest 

 of S|iitsl)iTj;en which contained less than one-fourth the amount of chlorides found in the 

 drinking water of Stockholm. 



^" As a matter of fact the saltiest water, i. e.. pure ocean water, seldom reaches a 

 freezing temperature, because it is usually protected by warm couvectional currents. The 

 freezing regions of the hydrosphere are conlined mostly to the shallow waters of conti- 

 nental shelves and to epi-continental seas, where the salinity of the surface layers rarely 

 excpt'ds ;« 00 : so tliat freezing takes pl.Tce at a temperature of —1.8° C. (28.8° F.). 



11 We iierformeil the following experiment : X fpiart of sea water of salinity ?>4.3 0/00 

 was frozen into a cake of solid ice, with no opportunity for any of the salts to escape, 

 .•Hid despite its high specific gravity the block floated in a jar of fresh water. The height 

 of flotation was noticeably lower than in the case of fresh-water ice, but the experiment 

 definiti'ly shows, nevertheless, that ordinary sea ice has reserve buoyancy. It is often 

 observed, for instance, floating off river mouths where the water is comparatively fresh. 



