Regime shift in sea-ice characteristics and impact on the spring bloom in the Baltic Sea

Abstract

We evaluated the temporal and spatial trends of the hydrological (temperature and sea ice) and biochemical (chlorophyll-a concentration) characteristics in springtime in the Baltic Sea. Both are strongly affected by climate change, resulting in a decrease in the duration of sea-ice melting in the previous decade. A new regime of sea ice began in 2008 and in all basins of the Baltic Sea, a rapid warming during spring could be detected. Using satellite data, the temporal and spatial variations in spring bloom were analysed during severe and warmer winters. Using a coupled hydrodynamic-biogeochemical model, we tested the response of spring bloom to the changing ice conditions. The results of the modelling indicated that the presence of ice significantly influences the predicted chlorophyll-a concentration values in the Baltic Sea. Therefore, it is necessary that any coupled model system has a realistic ice model to ensure the best simulation results for the lower trophic food web as well.