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Manganese accumulation and solid-phase speciation in a 3.5 m thick mud sequence from the estuary of an acidic and Mn-rich creek, northern Baltic Sea

Författare och institution:
C. X. Yu (-); J. J. Virtasalo (-); P. Osterholm (-); E. D. Burton (-); P. Peltola (-); A. E. K. Ojala (-); Johan Hogmalm (Institutionen för geovetenskaper); M. E. Astrom (-)
Publicerad i:
Chemical Geology, 437 s. 56-66
Artikel, refereegranskad vetenskaplig
Sammanfattning (abstract):
In sediments, manganese (Mn) is typically enriched in the form of authigenic Mn hydroxides at the water-sediment interface where intensive redox cycling of Mn occurs. Here we show, based on existing hydrochemical and geochemical (sediment core) data and new detailed chemical and mineralogical characterization of a 3.5 m long sediment core from a Boreal estuary, that the behavior of Mn can be profoundly different and more complex in estuarine settings receiving an abundance of terrestrial Mn. The most notable feature in the 3.5 m long sediment core is two depth intervals (60-155 cm and 181-230 cm) where there are strong fine-scale variations in Mn concentrations with peaks episodically reaching up to 10-25 g kg(-1) and 6.7-12 g kg(-1), respectively. X-ray absorption spectroscopy and sequential chemical extraction show that Mn occurs mainly as authigenic rhodochrosite at these two depth intervals and is mainly surface-sorbed in other sections with relatively low and stable Mn concentrations. The data suggests that the strong fine-scale variations in Mn concentrations are a reflection of the extent of formation and settling of Mn hydroxides, the precursors of the authigenic rhodochrosite (and also of the surface-sorbed Mn), rather than Mn input to the estuary or redox-related Mn translocation within the sediment. There was agreement between the results of linear combination fitting of extended X-ray absorption fine structure data and a 7-step sequential chemical extraction (SCE) in terms of quantification of surface-sorbed Mn species, whereas the SCE experiment failed to fractionate a majority of rhodochrosite into SCE step-2 (1M NH4-acetate at pH 6), which is frequently employed to dissolve carbonate. We ascribe this discrepancy to only partial dissolution of rhodochrosite in the weakly acidic (pH = 6) NH4-acetate leach.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Geovetenskap och miljövetenskap
Estuarine sediments, Mn speciation, X-ray absorption spectroscopy, Rhodochrosite, Acid sulfate soil, ray-absorption spectroscopy, ferruginous lake matano, anoxic, marine-sediments, sulfate soil runoff, black-shale basins, organic-matter, western finland, iron reduction, icp-ms, sulfide, Geochemistry & Geophysics
Postens nummer:
Posten skapad:
2016-07-25 11:51

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