The Black Sea biogeochemistry: focus on temporal and spatial variability of oxygen

Abstract

Abstract. The temporal and spatial variability of the upper ocean hydrochemistry in the Black Sea down to its suboxic zone was analyzed using data originating from historical observations, profiling floats with oxygen sensors and numerical simulations carried out with a coupled three-dimensional circulation-biogeochemical model including 24 biochemical state variables. The validation of the numerical model against observations demonstrated that it replicated in a realistic way the statistics seen in the observations. The suboxic zone shoaled in the central area and deepened in the coastal area, which was very well pronounced in winter. Its depth varied with time in concert with the variability of the physical system. Two different regimes of ventilation of the pycnocline were clearly identified: gyre-dominated regime in winter and eddy dominated regime in summer. These contrasting regimes were characterized by very different pathways of oxygen intrusions along the isopycnals. The contribution of the three-dimensional modeling to the understanding of the Black Sea hydro-chemistry, and in particular the coast-to-open-sea diapycnal mixing was also demonstrated.