Reading temperatures with lens
The open spaces, the lanes, and the rifts in the ice are, of course, produced, like the pressure and packing, by the shifting winds and the tidal currents that set the ice drifting first in one direction, then in another. And they best prove, perhaps, how the surface of the Polar Sea must be considered as one continuous mass of ice-floes in constant motion, now frozen together, now torn apart, or crushed against each other.
During the whole of our drift I paid great attention to this ice, not only with respect to its motion, but to its formation and growth as well. In the Introduction of this book I have pointed out that, even should the ice pass year after year in the cold Polar Sea, it could not by mere freezing attain more than a certain thickness. From measurements that were constantly being made, it appeared that the ice which was formed during the autumn in October or November continued to increase in size during the whole of the winter and out into the spring, but more slowly the thicker it became. On April 10th it was about 2.31 metres; April 21st, 2.41 metres; May 5th, 2.45 metres; May 31st, 2.52 metres; June 9th, 2.58 metres. It was thus continually increasing in bulk, notwithstanding that the snow now melted quickly on the surface, and large pools of fresh water were formed on the floes. On June 20th the thickness was the same, although the melting on the surface had now increased considerably. On July 4th the thickness was 2.57 metres. On July 10th I was amazed to find that the ice had increased to 2.76 metres, notwithstanding that it would now diminish several centimetres daily from surface melting. I bored in many places, but found it everywhere the same—a thin, somewhat loose ice mass lay under the old floe. I first thought it was a thin ice-floe that had got pushed under, but subsequently discovered that it was actually a new formation of fresh-water ice on the lower side of the old ice, due to the layer of fresh water of about 9 feet 9 inches (3 metres) in depth, formed by the melting of the snow on the ice. Owing to its lightness this warm fresh water floated on the salt sea-water, which was at a temperature of about -1.5° C. on its surface. Thus by contact with the colder sea-water the fresh water became cooler, and so a thick crust of ice was formed on the fresh water, where it came in contact with the salt water lying underneath it. It was this ice crust, then, that augmented the thickness of the ice on its under side. Later on in the summer, however, the ice diminished somewhat, owing to melting on the surface. On July 23d the old ice was only 2.33 metres, and with the newly formed layer 2.49 metres. On August 10th the thickness of the old ice had decreased to 1.94 metres, and together the aggregate thickness to 3.17 metres. On August 22d the old ice was 1.86 metres, and the aggregate thickness 3.06 metres. On September 3d the aggregate thickness was 2.02 metres, and on September 30th 1.98 metres. On October 3d it was the same; the thickness of the old ice was then 1.75 metres. On October 12th the aggregate thickness was 2.08 metres, while the old ice was 1.8 metres. On November 10th it was still about the same, with only a slight tendency to increase. Further on, in November and in December, it increased quite slowly. On December 11th the aggregate thickness reached 2.11 metres. On January 3d, 1895, 2.32 metres; January 10th, 2.48 metres; February 6th, 2.59 metres. Hence it will be seen that the ice does not attain any enormous thickness by direct freezing. The packing caused by pressure can, however, produce blocks and floes of a very different size. It often happens that the floes get shoved in under each other in several layers, and are frozen together so as to appear like one originally continuous mass of ice. Thus the Fram had got a good bed under her.
Juell and Peter had often disputed together during the winter as to the thickness of ice the Fram had under her. Peter, who had seen a good deal of the ice before, maintained that it must at least be 20 feet thick, while Juell would not believe it, and betted 20 kroner that it was not as thick as that. On April 19th this dispute again broke out, and I say of it in my diary: “Juell has undertaken to make a bore, but unfortunately our borer reaches no farther than 16 feet down. Peter, however, has undertaken to cut away the 4 feet that are lacking. There has been a lot of talk about this wager during the whole winter, but they could never agree about it. Peter says that Juell should begin to bore, while Juell maintains that Peter ought to cut the 4 feet first. This evening it ended in Juell incautiously offering 10 kroner to any one who would bore. Bentzen took him at his word, and immediately set to work at it with Amundsen; he thought one did not always have the chance of earning 10 kroner so easily. Amundsen offered him a kroner an hour, or else payment per foot; and time payment was finally agreed to. They worked till late on into the night, and when they had got down 12 feet the borer slipped a little way, and water rose in the hole, but this did not come to much, and presently the borer struck on ice again. They went on for some time, but now the borer would reach no farther, and Peter had to be called up to cut his four feet. He and Amundsen worked away at cutting till they were dripping with perspiration. Amundsen, as usual, was very eager, and vowed he would not give in till he had got through it, even if it were 30 feet thick. Meanwhile Bentzen had turned in, but a message was sent to him to say that the hole was cut, and that boring could now begin again. When it was only an inch or an inch and a half short of 20 feet the borer slipped through, and the water spurted up and filled the hole. They now sank a lead-line down it, and at 30 feet it again brought up against ice. Now they were obliged to give it up. A fine lump of ice we are lying on! Not taking into account a large, loose ice-floe that is lying packed up on the ice, it is 16 inches above the water; and adding to this the 2 feet which the Fram is raised up above the ice, there is no small distance between her and the water.”
Peter Henriksen in a brown study. July 6, 1894
(From a photograph)
The temperature on the ice in summer is about thawing-point, but gradually as the winter cold comes on, it, of course, falls rapidly on the surface, whence the cold slowly penetrates deeper and deeper down towards the lower surface, where it naturally keeps at an even temperature with the underlying water. Observations of the temperature of the ice in its different layers were constantly taken in order to ascertain how quickly this cooling-down process of the ice took place during the winter, and also how the temperature rose again towards spring. The lowest temperature of the ice occurred in March and the beginning of April, when at 1.2 metres it was about 3.2° Fahr. (-16° C), and at 0.8 metre about 22° Fahr. below zero (-30° C). After the beginning of April it began to rise slowly.