Some Ideas on Sea Ice Climate and Navigation in the Baltic Sea 
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Table 2. Results of ice navigation 
• In former days the ice cover developed under natural conditions only. It staid ‘virgin’ 
and changed only due to the hydro-meteorological conditions or to stress factors like 
wind, current and waves. 
• Nowadays powerful icebreakers and vessels navigate under nearly all ice 
conditions. 
- They cut navigation channels through the coastal fast ice up to the maximum 
possible thickness of about 120 cm. 
Even heavy ridges are forced with the help of new propulsion systems like 
nozzles and azipodes. 
• The ice is broken parallel and normal to the coast. 
• The level ice cover is permanently broken, floes are transferred into ice cakes, ice 
cakes into brash ice. 
• The ice at sea is crossed by a steadily increasing number of leads parallel to the 
main shipping lanes. Where today is a lead, there can be tomorrow an open fracture 
or a new ridge 
• The approaches to the harbours or to the fast ice inlets (channels) develop to 
funnel-shaped brash ice fields with difficult navigation under converging (e. g. on- 
land wind) conditions. 
• The traffic parallel to the coasts favours the development of open coastal leads or 
ridges, respectively, according to the prevailing wind conditions. 
• Altogether winter navigation destroys the natural ice cover, decreases the floe size, 
favours the development of leads and ridges, and consequently makes the ice cover 
more dynamic - facts that have to be considered not only for the navigation 
conditions but for ice or climate models, too. 
Ice Phases and other Natural Characteristics 
Ice formation and development (increase and decay) of the ice cover in the different sea areas 
are mostly depending on the meteorological conditions (as temperature regime, prevailing wind 
directions and strength) during a given season. However, superimposed on this development 
are natural factors of the region as coastal morphology (type) and seabed configuration, water 
depth, heat content and salinity, currents and tides etc. For example, in German waters the ice 
winter type is defined by the length of the ice occurrence in the sections inner coastal water (a), 
outer coast (b) and open sea (c). These stages of ice development are normally correlated with 
special categories of ice thickness and ice concentration as shown in Table 3.