Anthropogenic chlorofluorocarbons in the Black Sea and the Sea of Marmara

Measurements of the distributions of two chlorofluorocarbons, CCl3F (CFC-11) and CCl2F2 (CFC-12), made during the June/July 1988 R. V. Knorr cruise in the Black Sea indicate that CFC-11 is non-conservative relative to CFC-12 in the strongly reducing anoxic waters. A multi-layer model combining horizontal/vertical renewal and vertical diffusion processes was tuned to the distributions of CFC-12 and salinity in suboxic and anoxic waters and used to estimate the residence times of subsurface waters and first-order in situ removal rate constants for CFC-11. The model-calculated residence times were ∼5 yr in the suboxic zone (80–120 m) and increased to ∼625 yr at 500 m. The first-order CFC-11 in situ removal coefficients were 0.52±0.19 yr−1 for the depth range 160–480 m. Based on the observed CFC-12 concentrations, the residence time of cold intermediate layer water (∼50–100 m) was estimated to be <5 yr. The residence time of the deep water (100–450 m) in the Sea of Marmara was estimated to be 12–19 yr using a box model tuned to CFC-12, implying an in situ oxygen utilization rate of 10–18 μmol kg−1 yr−1.