Author(s): Matti Lepparanta
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Abstract: In cold regions, lakes are covered by ice. Seasonally freezing lakes cover a large zone from the latitudes 40–45° to high-polar regions, and the ice thickness can reach ½ – 2 m. Perennially icecovered lakes are rare, found mainly in northern Canada and in dry valleys of Antarctica. Lake ice differs from other types of floating ice, river ice and sea ice. Lake ice grows as congelation ice and snow-ice while in rivers frazil ice formation is common, and lake ice, in freshwater lakes, has a very low level of impurities compared with sea ice. Lake ice cover forms a stable lid but in rivers and marine basins the motion of ice has major consequences. At extreme, saline lakes have ice similar to sea ice, and in very large lakes drift of ice is important. Research of lake ice has largely risen from practical needs. Safety questions related to travelling on ice have been the key issue. The bearing capacity depends on the thickness and strength of the ice and ice thickness models have been widely examined. Ice phenology data have been collected due to the general interest in nature phenomena and due to the importance of the ice season to local communities, and the understanding of the variability of freezing and breakup dates is quite good. For lake ecology, solid ice cover cuts off the renewal of oxygen, and when covered by snow, lights will be turned off. Winter fish kills may take place when the ice season is long. The ice cover stabilizes temperature structure of lakes in winter. In spring, solar radiation melts ice across its thickness, and any impurities contained in the ice are released into the water column. In the present world, the influence of climate changes on the lake ice season is of major interest to understand the impact to practical winter conditions and ecology. These questions have been approached by time-series analyses and mathematical models. Climate variations also bring qualitative changes to lake ice seasons by moving boundaries of different ice climate zones. In future research, physics and modelling of ice melting, mechanical breakage of ice, and the full two-dimensional ice–water interaction need much efforts.
Year: 2014