Atlantic manganese nodules and encrustations are most abundant in areas of slow sedimentation beneath the carbonate compensation depth or where currents inhibit sediment accumulation. They principally contain the minerals todorokite and ?MnO2, which are selectively concentrated into nodules and encrustations, respectively, and which show an environmental differentiation thought to be related to redox potentials. Excluding the continental margins, todorokite is most abundant in deepwater deposits. Mineralogical differences between nodules influence their chemical compositions, Ni and Cu being most abundant in samples rich in todorokite and Co in those rich in ?MnO2. Chemically, the deposits differ from those in other major oceans principally in their higher Fe and lower Ni and Cu contents, which may be due to higher rates of supply of Fe to the deposits than those in the other oceans. Regional variations occur in the concentrations of several elements, Mn, Ni, and Cu being enriched in deepwater deposits from areas of slow sedimentation between the Mid-Atlantic Ridge and the continental margins and Co being enriched in some deposits from elevated localities. These variations are thought to be due to variation in the sources of the elements concerned and in the depositional environment.
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1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions.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: Cronan, David S (1975): Manganese nodules and other ferromanganese oxide deposits from the Atlantic Ocean. Journal of Geophysical Research, 80(27), 3831-3837
