Trends in the amplitude of Baltic Sea level annual cycle

Abstract

Baltic Sea tide gauge data and climatic data sets are statistically analysed to investigate the centennial trends in the amplitude of the annual cycle of Baltic sea-level. In almost all gauge stations analysed, an increase of the amplitude (winter-spring sea-level) is detected. These trends are not large compared to the decadal variations of the annual cycle, but they are statistically significant. The magnitude of the trends is almost spatially uniform, with exception of the Skagerrak area. Since inter-annual and decadal variability of sea-level displays a clear spatial pattern, the mechanism responsible for the trends in the annual cycle seem to be not regional, but affect the Baltic Sea basin as a whole. Several hypotheses are proposed to explain these centennial trends on the winter minus spring sea level: the effect of wind (through the SLP field), the barometric effect, temperature and precipitation. Of all hypotheses, the long-term trend in seasonal Baltic precipitation seems to be the most plausible candidate. For the other three, either the sign or the magnitude of the trend makes them problematic to be included as a sole explanation. However, the barometric effect was found to potentially contribute to the trend in the sea-level annual cycle.