Manganese nodules are generally considered to have accumulated very slowly. Radiometric studies by 230Th, 231Pa, and 234U/238U suggest their growth rates to be a few mm per 10 million yr. This leads to an enigma: how do they escape from burial by associated marine sediments which are accumulating three orders of magnitude faster than the nodules? Though this problem remains open, the postulated slow growth rates might permit manganese nodules to accumulate in a small volume high concentrations of long lived cosmogenic radionuclides 10Be (half tau = 1.5 Myr) and 26Al (half tau = 0.715 Myr) which were formed through the bombardment of atmospheric constituents by galactic cosmic rays. Indeed, Somayajulu4 and Krishnaswami et al.5 have found that three manganese nodules from the Pacific basin concentrate considerable activities of 10Be at their surface (9-68 d.p.m. kg?1). These concentrations are several times higher than those found in pelagic sediments. We report here on a search for 26Al in manganese nodules.
Before analysis the samples were sliced out from the Mn crust and leached in 6NHCl and the part analysed was further separated by dissolution in HF for one part and HCl for another part. Aluminium was then precipitated with ammonium hydroxide and Fe, Mn and Th were removed by further dissolution in NaOH.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1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions.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: Reyss, Jean-Louis; Yokoyama, Y (1976): Aluminium-26 in a manganese nodule. Nature, 262(5565), 203-204
