Changes in the hydrochemistry of the Black Sea inferred from water density profiles

Decline of the Black Sea oxygen inventory

“…In the early 1990s, the transient recovery of the three oxygenation diagnostics (Figs. 6a, b, c, 7a) provided arguments supporting the stability of the oxic interface (Tugrul et al, 1992;Buesseler et al, 1994). This stabilization matched the convenient perception of a general recovery of the Black Sea ecosystem after the reduction of nutrient load around 1990 (Kroiss et al, 2006).…”

“…In the stratified Black Sea, properties expressed in terms of depth coordinates (m) present a high spatial variability due to mesoscale features (Kempe et al, 1990) and to the general curvature of Black Sea isopycnals (Öszoy and Ünlüata, 1997;Stanev et al, 2014). As an alternative, using density (isopycnal levels, σ θ ) as vertical coordinate is generally considered a stable solution to assess the vertical migration of the chemocline on a decadal scale (Tugrul et al, 1992;Saydam et al, 1993;Murray et al, 1995). However, the spatial confinement of the lateral oxygen injections associated with the Bosporus plume, as well as the spatial variability of diapycnal ventilating processes (Zatsepin et al, 2007), imposes a horizontal structure to the oxygen penetration depth when expressed in terms of density (Stanev et al, 2004;Glazer et al, 2006).…”

“…In the lower part of the halocline, a permanent suboxic layer separates the Black Sea surface oxygenated waters ([O 2 ] > 20 µM) from the deep sulfidic waters ([H 2 S] > 20 µM) (Murray et al, 1989(Murray et al, , 1995Tugrul et al, 1992). More precisely, Murray et al (1989) considered a threshold of 10 µM of oxygen because they analyzed highquality oxygen data.…”

Documenting the suboxic zone of the Black Sea via high-resolution real-time redox profiling

“…More recent studies have confirmed vertical separation between oxygen and sulfide in the Black Sea water column (Tugrul et al, 1992). Natural barriers inhibiting vertical fluxes are established through density stratification of the water column (Sorokin, 1983;Anderson et al, 1988;Murray et al, 1995;Pers and Rahm, 2000;Scranton et al, 2001), caused by sharp increases in salinity (Anderson et al, 1988) and/or decreases in temperature (Scranton et al, 2001).…”

Modern views about contour structure of aquatic environment and new approaches for the Black Sea and Azov Sea monitoring

“…Below CIL the sharp halocline causes the permanent anoxia. The depth of the oxic/anoxic boundary coincides with a density σ-theta=16.2 (Vinogradov and Nalbandov, 1990;Tugrul et al, 1992). Both the depth of the boundaries and extension of the layers vary at temporal and spatial scales, depending on the water dynamics.…”