Back to Search
Start Over
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.
- Source :
-
Chemical Geology . Oct2016, Vol. 437, p56-66. 11p. - Publication Year :
- 2016
-
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 (1 M NH 4 -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) NH 4 -acetate leach. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00092541
- Volume :
- 437
- Database :
- Academic Search Index
- Journal :
- Chemical Geology
- Publication Type :
- Academic Journal
- Accession number :
- 116487305
- Full Text :
- https://doi.org/10.1016/j.chemgeo.2016.05.016