Stagnant oceanic bottom water

The concentration and behaviour of iron in ocean waters have been briefly outlined in Section 12.1.1 and Table 12-1. (For overviews see also Marine Chemistry , Vol.50 (1995 Nos. 1-4) and Vol. 57 (1997 p. 137-186)). For the determination of open-ocean Fe concentrations (i.e., in the sub-nanomol range) sufficient care must be taken not to contaminate the samples. The methods, specialized procedures and equipment necessary to cope with these extremely low concentrations are described in detail in Section 12.1. and 12.2.1. Here, we outline a spectrophotometric procedure for dissolved Fe concentrations in the pmol/L range. Such amounts occur in the marine environment under anoxic conditions and pH values of around 7 (e.g., in the Baltic or Black Sea). It can be explained by a steady diffusion of Fe(/7) species from organic-rich sediments into stagnant bottom water resulting in the enrichment of rather soluble iron(/l)sulphide. 

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