Trends in sea level variability in the Baltic Sea

This study aims to investigate sea level variability on the coasts of Finland and its changes over the past 100 years. The sea level probability distributions have apparently changed in shape. The annual maximum sea levels show a significant increasing trend, the increase being concentrated in the latter half of the 20th century. Annual variability shows an apparent increasing trend with the most pronounced increase occurring in the 1960s and 1970s. This was confirmed by examining the standard deviations as well as the spectra of the sea level. Short-period variability of the order of only a few days shows long-term changes that well exceed random variations, and it is therefore permissible to interpret these variations as reflecting the variations of short-term meteorological phenomena. The variations are not the same in different basins, but a minimum in the 1960s and a subsequent increase in the wintertime variability up to the 1980s can be seen in all of them. In the Gulf of Finland a 30 year cycle was found in the short term variability. On the other hand, the overall trend during the 20th century shows only a marginal increase that is not statistically significant. For all Finnish tide gauges, the annual mean sea level was found to be linked significantly with the NAO (North Atlantic Oscillation) air pressure index. The annual standard deviation of the sea level also correlates with the NAO, but the correlation is not statistically significant in every basin.