Permeability, Growth and Morphology of Coastal Ice - Site Study in Van Mijenfjorden, Svalbard
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- Institutt for fysikk 
Coastal ice includes the parts of the sea ice that are stressed and deformed by tidal motion; the ice foot (the inner part that is frozen to the ground) and the hinge zone (the zone where cracking occurs due to tidal elevation of the floating ice). This thesis presents in situ measurements of first-year coastal ice conducted in a sound close to the head of the fjord Van Mijenfjorden, Sval- bard, in the period between January and May 2014. During in total 6 field trips measurements of temperature, salinity, density, thickness and freeboard were done both on the coastal ice and on the free-floating ice. The latter was done at a point 200 m offshore. Temperature oscillations with periods similar to the tides and amplitudes up to 0.5◦C were found inside the ice in the hinge zone during a 10-days period, indicating a high permeability of the ice. Since the ice there was grounded at low tide and floating at high tide, the water level was constantly varying relative to the ice and could thereby drive a column of brine/seawater up and down through the ice cover. This observation corresponded well with the calculated average permeabilities, which were much higher before the temperature oscillations occurred (2.3·10−11 m2) than after they had disappeared (1.1·10−11 m2).Freeboard and surface water measurements discovered buckling of the ice in the lower parts of the hinge zone, which varied with the tide. In May, the ice was clearly buckled at high tide and stretched out at low tide. Creation of new ice inside the tidal cracks, caused by inflow of water during the tidal cycle, and thermal expansion are factors suggested to cause elongation of the ice sheet. Since the shortest distance between two points is a straight line, the ice is more likely to be buckled at high tide than at low tide when it is lowered in the middle of the sound. Maximum recorded amount of surface water was 18 cm, and through the season at least 20 cm of superimposed ice had been accumulating on the ice in the lower parts of the hinge zone. During cold periods, growth rates in the different parts of the ice varied; the ice foot was hardly growing at all, the free-floating ice was growing in moderate rates, whereas in the hinge zone the maximum growth was very high. The largest recorded ice thicknesses were 84 cm in the free-floating ice and 171 cm in the hinge zone. In the lower parts of the hinge zone the average ice temperatures were warmer than in the free-floating ice. Both the rapid growth and the temperature differences are expected to be caused by frequent flooding of the ice in the lower parts of the hinge zone, which often resulted in creation of a new layer of ice on top of the original layer. The release of latent heat connected to this process, in addition to direct heating by the warmer surface water, is believed to be the main reason for the warmer ice. Also along the shore, large spatial variations in ice thickness were observed; two shore- perpendicular sections going across the hinge zone, 11 m from each other, showed that the maximum ice thickness differed with 70 cm. Mean salinities in the ice foot were relatively low, varying from 0.6 to 1.2 ppm, whereas in the hinge zone they varied between 4.9 and 7.2 ppm. In the free-floating ice, average salinities between 4.7 and 6.6 ppm were recorded.