The low-temperature geochemical cycle of iron: From continental fluxes to marine sediment deposition

• DOI: 10.2475/ajs.302.9.774
• Publication Date: 2006-06-28T21:37:46Z
• Authors: S. W. Poulton
• Keywords: Authigenic; Meltwater; Terrigenous sediment

Suspended sediments from 34 major rivers (geographically widespread) and 36 glacial meltwater streams have been examined for their variations in different operationally-defined iron fractions; Fe~HR~ (iron oxides soluble dithionite), Fe~PR~ boiling HCl but not dithionite) Fe~U~ (total less that HCl). River particulates show a close association between total (FeT), reflecting the effects of chemical weathering which derive oxide from, retain it with, iron. Consistent with this, continental-scale average Fe~HR~/FeT ratios vary runoff (average river per unit area/average precipitation area). By contrast, diminished produce no recognizable FeT particulates, instead both are closely correlated FeT, essentially pristine mineralogy. A comparison globally-averaged compositions riverine marine reveals latter depleted Fe~HR~, enriched Fe~U~. The particulate data combined estimates authigenic, hydrothermal, atmospheric coastal erosive fluxes literature to global budget Fe~PR~, FeT. This suggests differences can be explained by; (i) preferentially removing flux by deposition into inner shore reservoirs such as floodplains, salt marshes estuaries; (ii) mixing resulting Fe~HR~-depleted particulates. Preliminary measurements consistent above. Phanerozoic modern normal similar speciation characteristics, implies existence long-term steady state cycle. could maintained glacioeustatic feedback, where Fe~HR~-enriched *either* more effectively trapped when sealevel is high (small ice masses, erosion), *or* mixed greater masses low (large enhanced erosion). Further important controls on operate through formation euxinic ironstones, also provide sealevel-dependent sinks sediment.