Ice conditions in coastal lakes of the southern Baltic Sea

Abstract

This paper describes spatio-temporal variability of the basic ice condition parameters, relationships between selected lakes in terms of those parameters, and frequency of fast (ice cover) and floating ice. Attention is also paid to morphology and topography of ice cover in lakes Jamno, Bukowo, Gardno, and Łebsko during 1960/61-1999/2000. Based on data archived at the Institute of Meteorology and Water Management, the following ice parameters were analysed: date of the first ice appearance; date of the first ice cover formation, date of disintegration of the last ice cover, date of disappearance of the last ice, ice season duration, number of days with ice, number of days with ice cover, ice conditions continuity, and maximum ice thickness in winter. Lakes Jamno and Bukowo, located in the western part of the Polish coast, are characterised by milder ice conditions, compared to the more eastward lakes (the Gardno and the Łebsko). Ice parameters were found to correlate closely, with statistical significance exceeding α = 0.01 and correlation coefficients usually higher than 0.90, between individual lakes, particularly the neighbouring ones. The highest frequencies of fast and floating ice, 70-75 % and about 10 %, respectively (altogether more than 80 %), were recorded in the last pentade of January. Fast ice (ice cover), accounting for 80 % of all the ice types, was found to dominate in the lakes studied; fast ice domination is typical of small and shallow water bodies. Ice cover is formed as a result of uniform increase in ice rind thickness. After the fast ice has decayed, an ice field pushed by the wind may form ice piles rising to a few metres above the water surface. At the beginning of the ice season, the piled ice appears most often on the western and northern shores, while at the end of the season it tends to stay on the eastern shores. The processes, associated with the presence of piled ice on the shore, are destructive not only for the shore, but also for constructions deployed within the ice range. The ice piles also affect transport and accumulation of sediment, mainly in the shore zone.