Impact of Winter Cooling on the Interannual Variability in the Vertical Oxygen Distribution in the Black Sea: Evidence from Bio-Argo Floats

— An effect of winter cooling on the interannual variability in the vertical oxygen distribution depending on temperature was studied and qualitative and quantitative estimate of mutual relationships between winter convection and variations in the oxygen concentration in various isopycnic layers of the deep-water part of the Black Sea was carried out using the data of high-frequency measurements of Bio-Argo floats during 2011–2020. The concentration of oxygen in the layer with a relative density (σ θ ) of 14.25–15.4 kg/m 3 increased by 20–100 μM after the most severe winters of the studied period (in 2012 and 2017) compared to the warm years. The high values of the oxygen concentration are registered throughout the next year and penetrate into much deeper isopycnic layers. The highest values of the inverse correlation coefficients between the oxygen concentration in the warm period and winter temperature fall on isopycnic layers of 14.4–15.4 kg/m 3 . The effect of temperature can be traced up to an isopycnic layer of 15.4 kg/m 3 , where a sharp decrease in temperature causes an increase in the oxygen concentration by 20 μM. Thus, the intensity of winter convection has a significant effect on the oxygen concentration in the CIL layer as well as in the layers below the main pycnocline.