Application of SMOS SSS L4 data to improve the understanding of the salinity dynamics and circulation of the Baltic Sea

The Baltic Sea is a semi-enclosed shelf sea and characterized by its distinct geographical and oceanographic features. One of the Baltic’s most remarkable features is its surface salinity gradient that is horizontally decreasing from the saline North Sea to the near fresh Bothnian Sea in the north, and Gulf of Finland in the east. Additionally, a vertical gradient and strong stratification separate between less saline surface water and deep saline water. These salinity features are mainly driven by a combination of river runoff, net precipitation, wind conditions, and geographic features that lead to restricted and irregular inflow of saltwater into the Baltic and limited mixing. The overall positive freshwater balance causes the Baltic to be much fresher compared to fully marine ocean waters with a mean salinity of only about 7 g/kg. The Baltic Sea is particularly sensitive to climate change and global warming due to its shallowness,  small volume and limited exchange with the world oceans. Consequently, it is changing more rapidly than other regions. Recent changes in salinity are less clear due to a high variability but overall surface salinity seems to decrease with a simultaneous increase in the deeper water layers. Furthermore. the overall salinity distribution is indirectly linked to the general circulation of the Baltic Sea which consists mainly of cyclonic circulation cells comprising the main sub-basins of the Baltic Sea. Thus, improving the understanding of the salinity dynamics ultimately leads to a better understanding of the circulation in the Baltic Sea. 

Within the project 4DBALTDYN highly spatially resolved SMOS SSS (Sea Surface Salinity) satellite data will be combined with in situ observational data and numerical modeling to improve our understanding of the salinity dynamics of the Baltic Sea. SMOS SSS data (2011-2019) provide a continuous monitoring of the evolution of the surface salinity of the entire area of the Baltic Sea.