AS OBSERVED IN' THE WEDDELL SEA. 
819 
Diatoms. — In the summer countless diatoms made their appearance on the 
surface of the water, on the edges of the ice, and along its under surface ; they 
inserted themselves between the plates and lived actually in the body of the ice 
itself. This may have been simply an effort to get to the light. At the end of 
summer, accordingly, a good number were entangled and became frozen into the ice, 
and so gave it a yellow colour. This discoloured band, therefore, marked the 
interval between two winter periods of freezing, and could be used as an index to the 
age of the floe. The piece of ice, for instance, noted on March 19 had two diatom 
layers ; the second and lower was formed in summer 1915-16 ; the upper presumably 
in 1914-15 ; accordingly the uppermost ( i.e . oldest) portion of the ice must have 
commenced freezing in winter 1914 at latest. 
Change in Structure. — It had been well known to whalers for a long period that 
old hummocked ice could be used for drinking purposes ; but this was knowledge 
which had apparently been lost, for the Discovery in 1901 melted snow for this 
purpose. It is an important point, however, in a ship’s economy to realise the 
freshness of hummocked ice, as snow requires nearly double the amount of heat that 
ice does to produce a given quantity of water. The ice which was suitable for this 
purpose was very different in appearance from freshly formed young-ice with fibrous 
structure.* It had become clear, almost transparent, had a conchoidal fracture, 
might almost be called blue in colour, and had a slightly spotted look. Though 
quite suitable for drinking, it was not entirely fresh ; tested with silver nitrate, the 
solution always became cloudy, showing that some chlorine at least was still present. 
All the water used for chemical experiments on board the Endurance had to be 
distilled on this account. 
This type of ice was apparently that examined by Drygalski near the 'Gauss 
winter quarters in 1903, and by him called “ Blaueis.” He attributes the changes to 
the influence of wind and evaporation (i.e. ablation), basing his contention on the 
smoothed and rounded nature of the ice. That the latter appearance is due to 
ablation is certainly true, but that the change in structure is due to the same cause 
is unproved. The long imprisonment of the Endurance gave the opportunity for 
showing that the structural change was due to the high summer temperatures ; it 
might partly take place in ice still afloat (i.e. not hummocked), but it reached its 
fullest development when the ice had been subjected to a summer’s temperatures as 
a hummock above the water level. 
About half the ice in the Weddell Sea was of this “ spotted” nature (Drygalski’s 
“ Blaueis ”). That the change was not due to wind follows from the fact that ablation, 
however important it may have been round the Gauss winter quarters, is nowhere 
known to be at all effective in the Weddell Sea. That it may play a part nearer 
the coast than the position of the Endurance is quite possible, but, so far as the 
* Called “ fibrous ” for convenience ; young-ice is not really fibrous but platy in structure ; the edges of tbe plates, 
however, give it a fibrous appearance. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART IV (NO. 31). 
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