826 
MR J. M. WORDIE ON THE NATURAL HISTORY OF PACK-ICE 
Arctic Archipelago. Nansen and Weyprecht both mention them as occurring 
in the neighbourhood of Franz Josef Land ; the latter cites melting of the ice on 
the upper surface as the rule, and even maintains that this process may go on 
while the ice is still increasing by freezing on the lower surface. The evidence 
for this, however, was based on observations of the ice at the ship’s stern, in the 
very place where abnormal conditions would be expected ; practically no weight, 
therefore, can be given to Weyprecht’s statement that ice in northern latitudes 
melts about 1 metre on the surface each year. 
Experience in the Weddell Sea makes it certain that there, at any rate, surface 
melting as a factor did not count. It must be regarded as abnormal. Except in 
summer there was no ablation, and even then it only affected the snow covering 
and not the ice beneath. The snow became granular and almost moist. 
Other processes must be invoked to explain the decay, namely melting on the 
under surface and mechanical attrition. Probably there is little or no ice melted 
from below till the whole thickness reaches the melting-point. By all accounts, 
however, this is what happens in the Arctic ; the diagrams obtained by 
plotting time against ice -thickness, based on the figures of the different expedi- 
tions, show at first a steep gradient until the thickness is about 8 inches ; then 
a steady falling off in steepness, down to what appears to be the local average 
thickness ; and then a line almost horizontal, until it suddenly steepens at the 
melting period. The steepness of the diagram at the melting period is ever so 
much greater than that at the initial freezing, indicating that the ice as a 
whole first reaches the melting-point and then melts practically all at once. On 
one occasion there was proof that this might happen in the. Weddell Sea — on 
December 30, 1915, when it was possible to drive an ice-axe up to its head into the 
soft ice; but no large floe was ever actually seen to melt. Melting of this nature 
may be looked for, however, in sheltered bays, and is known to occur in the 
Ross Sea; but in the Antarctic ice-fringe as a whole the pack seems hardly 
ever to reach the melting stage until it has come under the influence of swells 
from the open sea. 
In distinguishing drift-ice from pack-ice, it was pointed out that the former is 
opener and looser and moves faster accordingly ; it lacks the inertia belonging to 
close-ice. This has a very important consequence, for it means that the outer edge 
is continually scaling off, so to speak, and the swell getting access to more extensive 
areas of ice than it would otherwise have operated on. The swell soon reduces the 
size of the floes, and this in turn helps on the formation of more drift-ice ; and so 
on. Meantime, the movement of the floe up and down in the water is mechanically 
eroding the ice, apart from actual melting ; melting alone would produce honey- 
combing, but this was a rare feature in the drift-ice fringing the pack ; it looked, 
therefore, as if mechanical wear and tear was the most successful factor in producing 
decay. 
