Ko. Buesseler et al., STABILITY OF THE OXIC ANOXIC INTERFACE IN THE BLACK-SEA, Deep-sea research. Part 1. Oceanographic research papers, 41(2), 1994, pp. 283-296
We have examined the position of the oxic, suboxic and anoxic interfac
es in the Black Sea between 1965-1992. It appears as if the suboxic zo
ne (i.e. depths where DO and H2S <5 muM) has been a common feature thr
oughout the Black Sea, and only recently been observed due to advances
in sampling and analytical procedures. The upper boundary of the subo
xic zone is identified based upon a minimum in the PO4 profile at a de
nsity of 15.95 sigma(t). The lower boundary at 16.20 sigma(t) is ident
ified by the onset of H2S. These densities show seasonal and interannu
al variations of the order of 0.05-0. 10 sigma(t), but no directional
trend over the past 2-3 decades. The position of the suboxic zone is c
onsistent with T-S data. Large variations in T-S characteristics are s
een between years and seasons above the suboxic layer, as ventilation
is quite rapid. Below the DO <5 muM horizon, entrainment processes bri
ng surface water to depth, thus forming a suboxic layer as DO and H2S
are consumed. T-S characteristics vary slightly below 16.2 sigma(t), a
nd are constant below 17.0 sigma(t), indicating that these waters are
ventilated less frequently.