A comparative study of iron and manganese diagenesis in continental slope and deep sea basin sediments off Uruguay (SW Atlantic) Abstract Pore water and solid phase from surface sediments of the continental slope off Uruguay and from the Argentine Basin (southwestern Atlantic) were investigated geochemically to ascribe characteristic early diagenetic reactions of iron and manganese. Solid-phase iron speciation was determined by extractions as well as by Mössbauer spectroscopy. Both methods showed good agreement ( < 6% deviation) for total-Fe speciation. The proportion of easy reducible iron oxyhydroxide relative to total-Fe oxides decreased from the continental slope to the deep sea which is attributed to an increase in crystallinity during transport as well as to a general decrease of iron mobilization. The product of iron reoxidation is Fe oxyhydroxide which made up less than 5% of total Fe. In addition to this fraction, a proportion of smectite bound iron was found to be redox reactive. This fraction made up to 10% of total Fe in sediments of the Argentine Basin and was quantitatively extracted by 1 N HCl. The redox reactive Fe(+II) fraction of smectite was almost completely reoxidized within 24 h under air atmosphere and may therefore considerably contribute to iron redox cycling if bioturbation occurs. In the case of the slope sediments we found concurrent iron and manganese release to pore water. It is not clear whether this is caused by dissimilatory iron and manganese reduction at the same depth or dissimilatory iron reduction alone inducing Mn(+IV) reduction by (abiotic) reaction with released Fe 2+ . The Argentine Basin sediment showed a significant manganese solid-phase enrichment above the denitrification depth despite the absence of a distinct pore-water gradient of Mn. This implies a recent termination of manganese mobilization and thus a non-steady-state situation with respect to sedimentation or to organic carbon burial rate.

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To determine the role of the histamine H3-receptor on basophils, different specific H3-antagonists were investigated. Incubation of washed leukocytes with N alpha-acylated histamine-derivatives (N alpha-ahd) induced elevated histamine levels. This process turned out to be dependent on dose, time and temperature, but independent of Ca2+ and Mg2+ ions. IgE-mediated histamine release was not modulated. [3H]-L-histidine was not decarboxylated into [3H]-histamine in spite of the observed histamine increase. Highly purified basophils did not show any histamine elevation but purified neutrophils and eosinophils were found to have increased histamine levels even after disintegration and subsequent incubation with N alpha-ahd. It seems that the increased histamine levels result from the cleavage of the applied histamine amides. Other potent H3-antagonists (e.g. thioperamide) neither produced increased histamine levels nor influenced IgE-mediated release from basophil leukocytes. The existence of H3-receptors on human basophils therefore seems unlikely.

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