AREAL VARIATION IN ICE COVER THICKNESS ON LAKE MORSKIE OKO (TATRA MOUNTAINS)

This study presents the changes in ice cover thickness on the surface of a mountain lake Morskie Oko (33.5 ha, 1392.8 m a.s.l.) located in the Tatra National Park in the Tatra Mountains (the highest mountain range of the Carpathians). The course of ice phenomena is similar to those observed on lakes in other parts of the world: over the last forty years the duration of ice phenomena decreased (by 9 days.decade(-1)), similarly to the duration of compact ice cover (9.5 days.decade(-1)) and the maximum ice cover thickness (2.2 cm.decade(-1)). Another issue is the variation in the areal ice cover thickness - still little discussed comparing to long-term studies of ice phenomena. The thickness of ice on Morskie Oko was measured during eight field investigations carried out over years 2006-2012 and jointly 160 boreholes were made in different part of that water body. Results obtained from those field works showed a great areal variation in a given year as well as between consecutive years. Differences in ice cover thickness sometimes were slight and amounted to 3cm (24.03.2010) while in other cases turned out to be considerable (31 cm on 9.05.2006). The local conditions, for example topography (which influenced the shadowing of part of the lake, i.e. resulted in the isolation from sunlight) were the main factors that differentiated the aerial distribution of ice cover. The unshaded areas are subjected to faster ice melting which strongly influences the thickness of ice cover. Another phenomenon observed on 20.02.2012 was strictly connected with the under-ice circulation of water which washed away the ice.