Hydrographical Observations from the Danmark Expedition. 401 



-\- 7°) which blew on those days. On June 23rd there were channels 

 about Yo m. deep in the ice round the ship, which were formed by the 

 outflowing, warm river-water. The temperature of the melting snow 

 and ice water in the channels varied between 0.0 and + 3.0° C. In 

 a few deeper holes — 0.3° C. was measured at the bottom. In other 

 holes in the ice, containing dark excrement of dogs, the temperature 

 Avas + 2° С decreasing upwards to + 0.3° С at the surface. 



On June 26th the thickness of the ice had decreased somewhat 

 and on July 8th already the ice was breaking up. Below the winter 

 ice there were at that time several layers of newly frozen freshwater 

 ice, which indicated the various lower boundaries for the freshwater 

 layers when they froze to ice on coming into contact with the ice- 

 cold sea-water. The lowermost of these layers was at a depth of 

 ca. 165 cm. 



In the uppermost layers the ice was almost rotten, so that a 

 single blow of an iron lever broke through it; the lower layers were 

 somewhat tougher. 



Whilst the ice in the harbour was decreasing so greatly in thick- 

 ness, chiefly owing to the warm river-water, it only decreased ca. 

 5 cm. out in the mouth of Øresund at Maroussia. It was not until 

 the following days, 28th June — 7th July, that the warmer melting 

 water reached out there and the ice was then attacked from above 

 by the atmosphere (after the snow and snow-layer had melted), from 

 below by the heated melting water and in a vertical direction by the 

 particles of air set free, which forced their way up through the por- 

 ous ice. On July 18th the ice was breaking up. 



There was a great contrast between the rapid thawing of the ice 

 in July 1908 and the quite unchanged thickness of the ice in July 

 1907; as the air and surface-water temperatures were nearly the same 

 in the two years, the cause of this great difference must be sought 

 for essentially in the different structure of the ice, due to the special 

 conditions of precipitation when the ice was being formed. 



In both summers openings in the ice appeared in Øresund at the 

 same places, namely: 



(1) off the large rivers, 



(2) along the east side of Koldewey Island, 



(3) from Cape Bornholm towards Baadskær, 



(4) in the sounds between Cape Bismarck and Renskær (see 

 PI. XIV). 



At these places (\vith exception of 1) the tidal current was run- 

 ning strongest and, owing to mixing processes, heat was here carried 

 up from deeper layers in the sea. 



Openings appeared finally round about grounded icebergs, where 

 the fjord-ice was broken up owing to its rise and fall with the tides. 

 XLI. 2(5 



