at the initial moment and is inversely proportional to the speed of ice formation. In fresh ice 

 formed under calm conditions these bubbles in most cases are very elongated and thread-like, with 

 a certain thickening in the upper part. The diameter of such thread-like bubbles equals several 

 tenths of a mm and the length 1 to 2 cm. More rarely, such bubbles have a round or pear-like 

 form. 



Another group of bubbles forms as a result of gases that have separated from the water and 

 bottom sedimentation and have floated up to the underside of the ice. Primarily, these are flat- 

 tened convex bubbles 10 cm and more in diameter. Particularly, great accumulations of such 

 bubbles are found in the ice that had formed over areas where an intensive decomposition of organic 

 matter occurs on the bottom with a consequent separation of gases. In shallows, the amount of 

 these gases is sometimes so great that they form hollows the size of a fist and make the lower 

 surface of the ice uneven. * 



Still another group of bubbles in sea ice results when algae frozen into the ice continue to 

 produce gases in the form of tiny bubbles. 



Finally, air bubbles form due to the replacement of brine with air which had seeped out of 

 the sea ice in the course of time. These bubbles ordinarily form chains stretched out in a vertical 

 direction. The last group of air bubbles has the greatest significance for sea ice in open seas. 



Let us assume that the brine had completely seeped out of the salt cells and had been re- 

 placed with air. Such an assumption is completely possible for the above-water parts of ice, es- 

 pecially for the upper parts of hummocks. In Section 65 we have seen that the volume of 1 g of sea 

 ice is 



St 5s^ \ St I S 



where the first member on the right side represents the volume occupied by the brine and the sec- 

 ond represents the volume occupied by pure ice. 



On the assumptions made, and with the porosity of ice defined as the ratio of the volume oc- 

 cupied by the bubbles of air to the datal volume of ice, expressed in percentage, we obtain 



Si 100 

 n = -F- "s T- • (2) 



Table 48 is computed according to formula (2). 



This table makes clear the importance of a rise in air temperature and the corresponding 

 warming of the above water parts of ice. The brine cells in this case increase their volume con- 

 siderably, the brine is able to drain down, and as a result, porosity increases greatly. 



According to Bruns' measurements in September 1934, the sea ice of the Barents Sea some- 

 times contained 12 to 13 per cent gas by volume. The results of an analysis of the composition of 

 the gases in the bubbles are shown in table 49. 



*In the Laptev strait, Ermolaev has observed a vigorous separation of methane rising from the 

 bottom of the ice and burning above the surface of the frozen sea with a bluish flame. 



166 



