The average sea level fluctuations are connected with the occurrence of physical phenomena, such as changes in temperature and salinity, which influence the changes in water density. The sea level change modelling is used widely to evaluate and study shoreline and climate changes. An increase or decrease in water temperature and salinity may have a very important effect on the ecosystem of the Baltic Sea. The aim of the paper is to use the seasonal indicators to estimate the dynamics of changes of sea level and the physical phenomena that have a substantial influence on this changes. Data from satellite altimetry and GRACE (Gravity Recovery and Climate Experiment) satellite mission were used in the research. The analyses of seasonal fluctuations were made for time series for every month in the period between January 2010 and December 2014 in five stations of the Baltic Sea. The absolute and relative indicators showed that, as a consequence of the influence of seasonal factors, the values of the given phenomenon are lower or higher than those estimated with the linear trend function. The results are useful to identify the changes of sea level, water temperature and salinity and can serve as a basis for further improvement and development of tools and methodologies for monitoring these factors.

Key words: GRACE, sea level, salinity, satellite altimetry, water temperature, Baltic Sea