Sulfur and Iodine Speciation in the Water Column of the Black Sea

Abstract

Voltammetric methods have been applied to determine sulfur and iodine speciation and to understand the chemistry and cycling of sulfur and iodine in Black Sea waters. The only reduced dissolved inorganic sulfur species detected in the water column was hydrogen sulfide. The minimum detectable limit for sulfide analysis is 0.1 nM using a cathodic stripping square wave voltammetry (CSSWV) method. Thus, the precise boundary between the “free” hydrogen sulfide (sulfidic) zone and the upper (oxic / suboxic) water column was determined at the three stations studied. It is apparent that this boundary has moved up by about 50 m in the past 20 years. Although there has been a change in this boundary, the sulfide gradient (near 52 mmole m−4) is similar to that reported by Brewer and Spencer (1974). The sulfide results reported here helped to demonstrate that there are three chemically distinct zones of water in the Black Sea. These zones in the western and central basins are (1) the oxic [0 – 65 m], (2) the anoxic and non-sulfidic [65 – 100 m] and (3) the sulfidic [> 100 m].