THE OXYGEN AND HYDROGEN ISOTOPIC COMPOSITION OF THE BLACK-SEA

The oxygen (O-18/O-16) and hydrogen (D/H) isotopic ratios have been measured at eight stations in the Black Sea and the Sea of Marmara. Analyses revealed that the O and H isotopic characteristics of the deep water were similar [delta-O-18 = -1.65 parts per thousand (sigma = 0.27), delta-D = -14.29 parts per thousand (sigma = 2.19)] across the entire width. The upper oxic layer however exhibited a high degree of variability related to high rates of evaporation during the summer and probable mixing during the winter. Using an evaporation model it can be calculated that the stable O and H isotopic composition of the Black Sea are relatively insensitive to large variations in the fluxes and isotopic compositions of the inputs. Based on this model it is estimated the delta-O-18 of the Black Sea prior to Mediterranean influence was approximately -3.3 parts per thousand (SMOW -standard mean ocean water). The upper oxic layer could have reached an O and H isotopic composition close to the present day approximately 10 years after the initiation of Mediterranean flow into the Black Sea. Continued changes in the O and H isotopic composition of the upper layer occurred until the lower anoxic portion of the Black Sea reached a steady-state composition, approximately 1000 years after initiation of Mediterranean flow.