Dataset for Response of a semi-enclosed sea to perturbed freshwater and open ocean salinity forcing

This dataset contains relevant data supporting the paper entitled "Response of a semi-enclosed sea to perturbed freshwater and open ocean salinity forcing", EGUsphere, https://doi.org/10.5194/egusphere-2025-4735, 2025. Abstract. The sensitivity of Baltic Sea salinities to changed fresh water forcing and other forcing factors have been debated during the last decades, since changed salinities would have large impacts on the marine ecosystems, and since this parameter still shows a high degree of uncertainty in regional climate projections. In this study we performed a sensitivity study where fresh water forcing and salinities at the outer boundaries of the North Sea were perturbed in a systematic way in order to obtain a second-order Taylor polynomial of the statistical steady state mean salinity. The polynomial was constructed based on perturbations of a 57-year long hindcast run for the period 1961–2017 with a regional ocean model covering the North Sea and the Baltic Sea. The results show that the Baltic sea is highly sensitive to fresh water forcing and that only about one third of the boundary salinity change propagates into the Baltic Sea. The results are also analysed in terms of a total exchange flow analysis in the entrance region, and it is found that the Baltic Sea salinity sensitivity to a large degree can be explained by increased freshwater input causing (1) dilution inside the Baltic Sea, (2) decreased inflows caused by changes to the mean sea level gradient in the entrance region, and (3) reduced inflow salinities due to recirculation of outflowing Baltic water in the entrance region where the inflow water consists of about two parts outflowing Baltic water and one part North Sea water. The dataset contains five files: meansalinity.zip is a zip file containing 11 netcdf4 files with annual means of volume averaged salinities for the Baltic Sea for the years 1961 to 2017, for each of the runs specified in Table 1 of the paper. The data were used to produce Figs. 4 and 6. depthmeansalinity.zip contains 11 11 netcdf4 files with depth averaged salinities for the whole model grid, averaged over the years 1990 to 2017, for each of the runs specified in Table 1 of the paper. The data were used to produce Figs. 5. inflows.zip contains one netcdf4 file for each year 1961-2017, each of the 11 runs in Table 1, and each of the three transects shown in Fig. 1: The northern Kattegat transect (inflows_kat*), the Drogden sill transect to the south-east (inflows_drog*), and the Darss sill transect furthest to the south (inflows_darss*). Each file contains daily averages of inflows of volume and salt in salinity intervals S - dS/2 to S + dS/2 where S is a salinity vector and dS is the salinity intervals in the vector (1 psu): q: volume flux (m3/s) qS: salinity flux (psu m3/s) qin: sum of all volume fluxes in grid cells with positive inflows (m3/s) qout: sum of all volume fluxes in grid cells with negative inflows (m3/s) qSin: sum of all salinity fluxes in grid cells with positive inflows (psu m3/s) qout: sum of all salinity fluxes in grid cells with negative inflows (psu m3/s). q and qS are used to produce Figs. 8 - 12. data_fig2_fig3.tar.gz contains netcdf4 files with the observational and model data in Figs. 2 and 3. meanSSH.zip contains two netcdf4 files with mean sea levels for the period 1990-2017 for the runs CTL and RP+.