Some Ideas on Sea Ice Climate and Navigation in the Baltic Sea 
77 
and 1993/94 it has to be recognized that in the first season with much less than 50 % of the ice 
extents, the mentioned restrict-ions were valid even some days longer (154:150 days). This 
may indicate that e. g. the severity of the ice cover in a given region is not that much related to 
the ice extent but more to the local ice conditions - perhaps as result of the influence of 
navigation on the ice cover (see Table 2). 
Results and Conclusions 
After a sketch of the development of the winter navigation in the (northern) Baltic Sea, the 
possible influence of the ship traffic on the character and dynamics of the ice cover in highly 
cruised sea areas has been discussed. It is not only the opinion of the author that there is an 
essential influence, which should be somehow considered in models and in the evaluation of 
long-term time series on the different aspects of the ice climate of the Baltic Sea. 
The so far published period for Ice Phase data (1963/64 to 1979/80) has been extended 
backwards to the ice winter 1960/61 and forwards to 1999/2000 from 17 to 40 years. The data 
have been used to characterize the ice winters in a more integrated manner by defining a mean 
ice extent, which takes into account both, the length and the ice covered area of the different 
ice phases reached in an ice season, compared to the single value of its maximum ice extent. 
The respective ranking of the ice winters shows differences that must be discussed considering 
the different ‘weight’ of the used parameters. In addition, some discrepancies e.g. in comparing 
the published data for the maximum ice extent and the occurrence of ice phases became 
obvious. Therefore, the presented data have to be considered to be provisionally, and they 
must be subject to further negotiations and joint ‘tuning’. 
As ‘final idea’ the use of the restrictions to navigation is discussed as possible additional 
parameter to characterize the severity of an ice season, as they integrate aspects of the given 
ice conditions and the ice navigation. An example was calculated for the five seasons 1991 to 
1995. The preliminary result shows that there can be distinct differences between the duration 
of special restrictions and the maximum and mean ice extent, which require further detailed 
cause study and basic discussion. 
Acknowledgement 
The author is particularly grateful Dr. N. Schmelzer, German Ice Service, for computing of 
some of the new ice phase data. 
References 
Berglund, R., Kylanpaa, M., 2003. ICEMAP - An Interactive Ice Charting Application for Ice 
Services. Paper presented at the 4 th Meeting of the International Ice Charting 
Working Group, 3.4.2003, St. Petersburg 
HELCOM Recommendation 25/7, 2004. Safety of Winter Navigation in the Baltic Sea Area. 
http://www.helcom.fi/Recommendations/en_GB/rec25_7/