Characteristics and Chronology of Baltic Inflows in October and December 2023 According to NEMO Reanalysis — Virtual Cruise

Barotropic saline Baltic inflows (SBIs) occurred in the period of 01.09.2023–20.02.2024 are analyzed using the NEMO reanalysis data. To test the model product, it is shown that it adequately reproduces the observed time series of salinity and temperature on depth and time of 32 yr long (1993–2024) at a monitoring station BY15 located in the Gotland Deep. The water volume imported to the Baltic Sea with the SBIs being estimated from the in situ observations of the sea level and salinity is found to be highly correlated with the direct estimates based on the NEMO reanalysis data. Comparison of the October and December 2023 SBIs reveals that quantitative characteristics of an SBI, such as the imported water volume and salt mass, being important nevertheless do not fully determine the subsequent evolution of the salinity field in the remote basins of the Baltic Sea. Apart from the imported water volume and salt mass the synoptic variability of the wind field is of paramount importance. Keeping in mind that the salt water transport in the bottom layer of the Bornholm Channel, Słupsk Furrow, and Hoburg Channel towards the deepest Baltic basins is most intense at northwesterly, northerly, and northwesterly winds, respectively, one may expect that a long-lasting northwesterly wind period immediately following the inflow event is the most favorable for ventilation of the Baltic Sea deep layer.

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