Baltic sea deep salinity: an initial and boundary value problem

The Baltic Sea salinity is modelled using a two-box model. The simplistic approach allows for very long integrations where a large part of the phase space of the model can be probed. Particular emphasis is put on the salinity dynamics in the deeper parts of the sea and how they are affected by boundary and initial conditions. Multiple statistically steady states, corresponding to forcing from different years, are examined and the route to them through the model’s phase space is traced out. The model is forced with freshwater fluxes and sea level variations at its boundary. The respective roles of these two forcing terms is investigated using a factorization technique, and it is found the sea level variability is the dominant one for the deep salinity dynamics. The role of natural variability is also examined, and the probability for deep salinity changes for different forcing years is computed.