Environmental Engineering Reference
In-Depth Information
are probably overestimated. Rate measurements and modeling data give the
median sulfide oxidation rates in the range from 20 to 50 Tg yr
−
1
[64].
The role of dissolved oxygen intrusions in sulphide removal is a subject
of intensive scientific debate. The annual Bosporus flux into the Black Sea
is estimated to be 120-312 km
3
[90]. In regard of the significant variability
in the magnitude and direction of water exchange through the Bosporus, and
the absence of quantitative information on the volumes of entrained waters
during the cascade-like intrusions to the anoxic zone, satisfactory estimates
of the sulphide removal rates by the Lower Bosporus Current are impossible
at the moment. Qualitatively, the significant role of the modified Bosporus
waters in the entrainment of the Black Sea interior was confirmed by direct in
situ measurements of physiochemical parameters in the areas adjacent to the
Bosporus (reviewed by Murray and Yakushev, this volume).
Sulphide oxidation in the anoxic interior was estimated using reported in
the literature entrainment ratios and simple chemistry of the sulphide oxidation
by Neretin et al. [64]. The authors have found that sulphide consumption with
Bosporus intrusions may vary in the range 4.4-9.2 Tg yr
−
1
, which roughly
represents 10-20% of the sulphide oxidation at the oxic/anoxic interface. The
modeling approach has shown that the oxygen flux below the anoxic interface
may be responsible for as much as 50-70% of the total sulphide consumption
in the Black Sea water column [42].
Apart from oxygen intrusions with the entrained modified Bosporus waters,
other lateral sources of oxygen were discussed in the literature. Mesoscale
dynamics characterized by the existence of anticyclonic gyres described in the
Sections 4 and 5 may provide an efficient mechanism for the ventilation of the
anoxic zone. In addition, in some years intensified density convention in winter
superimposed by internal wave forcing may cause the erosion of the upper
pycnocline and ventilate the upper anoxic layers [44, 89]. Lateral intrusions of
oxygen are not specific for the Black Sea only and have been reported in other
anoxic marine basins such as the Cariaco Basin (Scranton et al., this volume),
Framvaren Fjord [109], and the Mariager Fjord [112]. At the moment, without
extensive temporal and special studies, the contribution of these processes
in sulphide removal below the oxic/anoxic interface for the whole basin is
difficult to estimate. The cumulative effect of the modified Bosporus waters
together with mesoscale eddies providing dissolved oxygen laterally may have
significant impact on the total sulphide oxidation in the basin and need to be
addressed by future studies.
9.4 Fe Sulphide Formation in the Black Sea Water
Column
Pyrite formation in the water column of the Black Sea is the subject of several
studies [14, 58, 88, 98]. Some authors suggested that that most syngenetic
