Isotope composition of oxygen and hydrogen in the black sea waters as a result of the dynamics of water masses

Abstract

The isotope composition of hydrogen and oxygen in the water of the central part of the Black Sea and at the continental slope was studied in detail. The vertical distribution of the δD and δ18O values allows one to distinguish four water masses: from the surface of the sea to the core of the Cold Intermediate Layer (CIL), from the CIL core to 500 m within the pycnocline, the deep water mass at 500–1750 m, and the Bottom Convective Layer (BCL) deeper than 1750 m. The surface layer is homogenous in the center of the sea despite the formation of cyclonic and anticyclonic eddies. The main variations in the δD and δ18O values take place within the pycnocline beneath the CIL core to the depth of 500 m. The salinity increases by 3‰ with the growth of the delta values by 0.8 and 5‰ for the δ18O and δD, respectively. Deeper than the layer of 500 m down to the bottom, including the BCL, the δD and δ18O values practically do not vary. The isotope composition of the oxygen and hydrogen in water is linearly dependent on the variations in salinity. This fact allows one to describe the formation of the Black Sea waters using a simple model of mixing of the waters of the lower Bosporus current and a hypothetical freshwater component of isotope composition formed by the riverine runoff, atmospheric precipitation, and evaporation.