Some Ideas on Sea Ice Climate and Navigation in the Baltic Sea 
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Some Ideas on Sea Ice Climate and Navigation in the Baltic Sea 
Klaus Striibing 
Retired from Federal Martime and Hydrographic Agency of Germany (BSH) 
Email ksa1939@aol.com 
Abstract 
Sea ice has a great influence on navigation acting as an obstacle for the vessels in winter 
navigation or even preventing not suitable vessels from entering ice covered sea areas. 
Otherwise, mainly in the Baltic Sea with the over the last decades ever increasing sea traffic, 
there is also an essential influence of the icebreakers and assisted vessels on the character of 
the ice cover. Both aspects, the development of winter navigation in the Baltic Sea and the 
influence of navigation on the ice cover, are highlighted in this paper. 
One of the major objectives of the Baltic Sea Ice Climate Workshops is the discussion of the 
different methods and parameters to be used for the classification of the ice winters in the Baltic 
Sea - either for the whole region, for sub-regions or single coastal and sea areas. In this paper 
the idea is discussed, to blend the parameter Maximum Ice Extent, presented since many 
years by the Finnish colleagues, with the length and the ice extent of the Ice Phases, also 
originating from Finland. The ice phases, characterising special stages of ice development 
mainly in the northern region of the Baltic Sea, depend mostly on natural conditions of the 
coastal and sea areas, and may describe the character of an ice winter in a better way than just 
the sometimes rather short maximum phase of the ice extent. In addition, also the possibility of 
making use of the restrictions to navigation to classify the severity of an ice winter is discussed. 
As some of the data still are under negotiation, this paper has to be considered as a working 
paper, see note on page 73. 
Introduction 
Most typical for the seasonal sea ice conditions in the Baltic Sea is the great variability in ice 
extent, thickness and concentration. Each ice season is different from the other, which is 
stressed e. g. by the wide range of maximum ice extent, which varies between about 51,000 
km 2 (=12 % of the total area) and a total ice cover of the whole area of 420,000 km 2 . And also 
the length of the ice winter varies considerably. It can start in late October and end in early 
June, but can last only from mid-December to the first decade of May. This was found in former 
times as well as in recent days, and it is documented e. g. by the relevant time series provided 
by the Finnish Institute of Marine Research - FIMR (Seina and Palosuo, 1993).