Ferromanganese concretions cover large areas of the Gulf of Bothnia. They are flat to well-rounded, the rounded ones being richer in oxyhydroxides of iron and manganese. Rounded and ellipsoidal nodules, particularly those in the northern Gulf of Bothnia, are richest in Mn, Ni, Ba and Cu, which probably coexist in a Mn oxyhydroxide phase. Flat nodules are enriched in Fe, P, rare earths and As, probably associated with an Fe oxy-hydroxide component. Aluminum, V, Cr and Ti occur in still another phase. The sediments of the gulf generally consist of a 10-50 mm-thick layer of oxidized surface sediment, enriched in Mn, Ba, P and Ni lying on top of reduced sediments which are diagenetically depleted in these elements. The remobilized elements have redeposited in the nodules, but this process cannot explain the origin of all the nodular material. Some released Mn, Ba and Ni furthermore enter into suspended phases, which eventually leave the Baltic Sea. The economic value of the nodules in the Gulf of Bothnia is probably limited at present.

From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis...) not present in the NOAA-MMS database.

Supplement to: Boström, Kurt; Wiborg, L; Ingri, J (1982): Geochemistry and origin of ferromanganese concretions in the Gulf of Bothnia. Marine Geology, 50(1-2), 1-24