Major Baltic Inflows do not have long-lasting consequences for 20th-century hypoxia in the central Baltic Sea

Abstract Marginal seas with pronounced stratification are susceptible to low dissolved oxygen concentrations, which can lead to hypoxia or anoxia below the pycnocline. In the Baltic Sea, the Major Baltic Inflows ventilate the deep basins while further strengthening stratification. It was suggested that the largest-ever measured Major Baltic Inflow, which occurred in 1951, triggered the deoxygenation of the central Baltic Sea because it significantly strengthened stratification. With the help of a coupled hydrodynamical-ecosystem numerical model, we conducted a couple of numerical experiments and statistically analyzed the hypoxic volume and stratification strength variability on multidecadal timescales. We demonstrate that, although it had some short-term influence, the Major Baltic Inflow in 1951 did not significantly impact the stratification or hypoxia in the Baltic Sea on longer timescales. We provide quantitative estimates of the Major Baltic Inflows’ influence on multidecadal variability of stratification and hypoxia in the central Baltic Sea basins.