Oxygen Fluxes, Redox Processes and the Suboxic Zone in the Black Sea

We use the results of numerical modeling, calibrated and verified againsthistorical data from 1960 to 1995 and the most recent data from the 2001 Knorr cruise,to investigate the redox budget of the Black Sea water column and the main processesgoverning this budget. The results can be summarized as follows: (1) Injection of Mediterranean water, through the Bosporus, into the Black Sea results in intrusions of oxygen in the suboxic and anoxic layers; (2) The intensity of ventilation of the CIL andthe export production of organic matter are the primary control on interannualvariations in the thickness of the suboxic zone; (3) The lateral influx of oxygen resultsin oxidation of sulfide inside the anoxic zone. Almost 70% of the total vertical flux of sulfide is oxidized by this oxygen, mainly through redox Mn(II) – Mn(III,IV) cycling;(4) Nitrate seams to be responsible for oxidation of dissolved Mn(II) in the suboxiczone and Mn(III,IV) hydroxides, the end-products of this oxidation, sink and oxidizeabout 25% of the total flux of sulfide; (5) The vertical flux of oxygen at the onset of sulfide may account for consumption of a small fraction (less than 1%) of the total fluxof sulfide; (6) The lateral flux of oxygen also appears to be the main reason for the presence of the suboxic layer.