Physical oceanography sets the scene for the Marine Strategy Framework Directive implementation in the Baltic Sea

A challenge of the EU's Marine Strategy Framework Directive (MSFD) is to ensure comparable status assessments for good environmental status (GES) in the European seas. To this end, the role of dynamic oceanographic features affecting GES must be understood. Natural variability is recognized in the MSFD, but only vague advice is available for scientists and managers about how to apply this in the marine strategies. In this paper it is illustrated how physical factors, and their pronounced natural variability, e.g., irregularity of Major Baltic Inflows (MBI), strong and persistent upwelling, and varying ice conditions, affect status indicators and possibly several of the 11 descriptors of GES in the Baltic Sea. It is recommended that these effects are better understood in all regional seas. They may lead to insights that promote adaption of environmental monitoring programmes, as well as re-definitions of GES and other elements of the marine strategy.