Distribution of dissolved and particulate forms of iron and manganese in the Black Sea

Erdoğan, Selahattin
The principal aim of this study is to examine the behavior of dissolved inorganic and particulate forms of manganese and iron compounds in the oxic/anoxic transition (suboxic) zone of the western cyclone and coastal margin of the Black Sea. The samples were collected from the stations visited during three cruises of RV/Bilim at July 2000, September 2000, July 2001 and RV/Knorr at July 2001 in the Black Sea. In addition, real time profiles of dissolved Mn and Fe(ll) were obtained using a continuous profiling system attached to a multi-channel auto-analyzer during the Knorr-2001 cruise. The present results and other related parameters have also been compared with the Knorr-88 data published previously (Murray, 1991, Murray and Izdar, 1989) in order to understand long-term stability of the vertical structures of these metals that are very sensitive to redox potential changes in the suboxic/anoxic interface zone of the Black Sea. In the western cyclone of the Black Sea, the onset of dissolved Mn (>0. 1 uM) profiles has been located at about (crp15.85 surface depth, very consistent with the Knorr-88 findings (Murray et al. 1995). At this boundary, the concentration of dissolved ox ygen (DO) drops below 5 uM but the nitrate ions (NO3") still exist at 1.5 - 2.0 pM levels whilst the dissolved reactive phosphate profile displays acoherent minimum (as low as 0.05 - 0.1 uM). Not unexpectedly, the onset of dissolved Fe(ll) (> 0.025 uM) profile commences at greater density surfaces, at = 15.90 depths, where the hydrogen sulphide still does not appear and the phosphate profile displays a coherent maximum. Thus, there exists a consistent shift between the onsets of dissolved Mn and Fe profiles for the open sea. These characteristic features are modified in the southern coastal waters by such physical processes as Rim current, the formation of anticyclonic eddies and the intrusion of oxygenated Bosphorus inflow. For example, the dissolved Mn appears at greater density surfaces and show variable (increasing/decreasing) gradients in the anoxic interface due to dilution by the Bosphorus inflow. Similar variations appear in the dissolved ammonia profiles. Moreover, the DO, nitrate (NO3), ammonia (NH3) and dissolved Mn ions co-exist in this interface at a few micro molar levels, indicating slower oxidation rates of dissolved Mn (II) and ammonia (Nhfe) as compared to that of hydrogen sulphide by dissolved oxygen.


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Citation Formats
S. Erdoğan, “Distribution of dissolved and particulate forms of iron and manganese in the Black Sea,” Middle East Technical University, 2002.