Reactive iron in Black Sea Sediments: implications for iron cycling

The distribution of reactive iron in sediments of the northwestern shelf, t he shelf edge and the abyssal part of the Black Sea has been studied. In th e euxinic Black Sea, iron sulfides (pyrite and iron monosulfide) are formed in the upper part of the anoxic water column and sink to the deep-sea floo r where they are buried in the sediment. This flux of iron sulfides from th e water column is reflected in enhanced concentrations of highly reactive i ron and a high degree of pyritization (0.57-0.80) for the deep-water sedime nts of the Black Sea. The iron enrichment of deep-water sediments is balanc ed by a loss of highly reactive iron from the oxic continental shelf. Calcu lations: from a numerical diagenetic model and reported in situ flux measur ements indicate that the dissolved iron flux out of the shelf sediments is more than sufficient to balance the enrichment in reactive iron in deep-sea sediments, and that the majority of the dissolved iron efflux is redeposit ed on the continental shelf. This iron mobilization mechanism likely operat es in most shelf areas, but its net effect becomes only apparent when react ive iron is trapped in sulfidic water bodies as iron sulfides or when iron is incompletely oxidized in low oxygen zones of the ocean and transported o ver long distances. (C) 2001 Elsevier Science B.V. All rights reserved.