Chemical composition of ocean Fe-Mn ores

The monograph includes the study of chemical and mineral compositions of terrestrial and marine manganese ores, methods of their analysis, dependence of manganese crust geochemistry on tectonic position of their formation, problems of manganese genesis and sources of manganese in ocean ores in connection with geohistorical aspects of ocean formation and development. A hypothesis is offered that formation of giant manganese mineral basins on continental margins resulted from a large asteroid fall to the ocean.

Rare earth elements in standard samples of ocean Fe-Mn nodules and crusts

Contents of rare earth elements (REE) in standard samples of Fe-Mn nodules (SDO-5, 6), Fe-Mn crust (SDO-7), and red clay (SDO-9) have been determined by ICP-MS and instrumental neutron activation analysis. Reproducibility of ICP-MS was 5-6%. These results are discussed and compared with other data. It has been found that distribution of REE in the standard samples of ocean Fe-Mn ores and red clay is highly homogenous.

Average fluorescence and dissolved iron and Fe-binding ligand characteristics during POLARSTERN expedition ANT-XXIV/3 in 2008

Organic complexation of dissolved iron (dFe) was investigated in the Atlantic sector of the Southern Ocean in order to understand the distribution of Fe over the whole water column. The total concentration of dissolved organic ligands ([Lt]) measured by voltammetry ranged between 0.54 and 1.84 nEq of M Fe whereas the conditional binding strength (K') ranged between 10**21.4 and 10**22.8. For the first time, trends in Fe-organic complexation were observed in an ocean basin by examining the ratio ([Lt]/[dFe]), defined as the organic ligand concentration divided by the dissolved Fe concentration. The [Lt]/[dFe] ratio indicates the saturation state of the natural ligands with Fe; a ratio near 1 means saturation of the ligands leading to precipitation of Fe. Reversely, high ratios mean Fe depletion and show a high potential for Fe solubilisation. In surface waters where phytoplankton is present low dissolved Fe and high variable ligand concentrations were found. Here the [Lt]/[dFe] ratio was on average 4.4. It was especially high (5.6-26.7) in the HNLC (High Nutrient, Low Chlorophyll) regions, where Fe was depleted. The [Lt]/[dFe] ratio decreased with depth due to increasing dissolved Fe concentrations and became constant below 450 m, indicating a steady state between ligand and Fe. Relatively low [Lt]/[dFe] ratios (between 1.1 and 2.7) existed in deep water north of the Southern Boundary, facilitating Fe precipitation. The [Lt]/[dFe] ratio increased southwards from the Southern Boundary on the Zero Meridian and from east to west in the Weddell Gyre due to changes both in ligand characteristics and in dissolved iron concentration. High [Lt]/[dFe] ratio expresses Fe depletion versus ligand production in the surface. The decrease with depth reflects the increase of [dFe] which favours scavenging and (co-) precipitation, whereas a horizontal increase in the deep waters results from an increasing distance from Fe sources. This increase in the [Lt]/[dFe] ratio at depth shows the very resistant nature of the dissolved organic ligands.

Speciations of Mn and Fe in Fe-Mn nodules from the western part of the Clarion-Clipperton ore province

Hydrogenic forms of iron and manganese occurrence were studied in samples of ferromanganese nodules sampled within two polygons during Cruise 28 of R/V Dmitry Mendeleeev (1982) in the western part of the Clarion-Clipperton ore province. Contents of labile exchangeable Fe and Mn, amorphous hydroxides and poorly soluble compounds of Fe and Mn were analyzed. In nodules from DM28-2474 Polygon labile exchangeable Fe and Mn and amorphous hydroxides dominated; in nodules from DM28-2483 Polygon poorly soluble compounds dominated. Analysis of contents of labile forms of Fe and Mn occurrence in different morphological types of nodules distinguished predominantly hydrogenous botryoidal nodules, spheroidal and ellipsoidal intergrowth nodules, and hydrogenic-diagenetic discoid nodules.