Wittkop, C, Swanner, ED, Grengs, A et al. (6 more authors) (2020) Evaluating a primary carbonate pathway for manganese enrichments in reducing environments. Earth and Planetary Science Letters, 538. 116201. ISSN 0012-821X
Abstract
Most manganese (Mn) enrichments in the sedimentary rock record are hosted in carbonate minerals, which are assumed to have formed by diagenetic reduction of precursor Mn-oxides, and are considered diagnostic of strongly oxidizing conditions. Here we explore an alternative model where Mn-carbonates form in redox-stratified water columns linked to calcium carbonate dissolution. In ferruginous Brownie Lake in Minnesota, USA, we document Mn-carbonates as an HCl-extractable phase present in sediment traps and in reducing portions of the water column. Mn-carbonate becomes supersaturated in the Brownie Lake chemocline where dissolved oxygen concentrations fall below 5 μM, and Mn-oxide reduction increases the dissolved Mn concentration. Supersaturation is enhanced when calcite originating from surface waters dissolves in more acidic waters at the chemocline. In the same zone, sulfate reduction and microaerobic methane oxidation add dissolved inorganic carbon (DIC) with negative . These observations demonstrate that sedimentary Mn enrichments may 1) develop from primary carbonate phases, and 2) can occur in environments with dissolved oxygen concentrations <5 μM. Primary Mn-carbonates are likely to originate in environments with high concentrations of dissolved Mn (>200 μM), and where Mn and Fe are partitioned by S cycling, photoferrotrophy, or microaerophilic Fe-oxidation. A shallow lysocline enhances Mn-carbonate production by providing additional DIC and nucleation sites for crystal growth. This carbonate model for Mn-enrichments is expected to be viable in both euxinic and ferruginous environments, and provides a more nuanced view of the relationships between Mn and carbon cycling, with applications throughout the rock record.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | Crown Copyright © 2020 Published by Elsevier B.V. All rights reserved. This is an author produced version of an article published in Earth and Planetary Science Letters. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | manganese; carbonates; carbon isotopes; ferruginous lake; redox-stratified |
Dates: |
|
Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 02 Mar 2020 11:43 |
Last Modified: | 13 Mar 2021 01:38 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.epsl.2020.116201 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:157891 |
Downloads
Filename: wittkop_etal_2020_EPSL_preprint.pdf
Licence: CC-BY-NC-ND 4.0
Filename: Wittkop_etal_2020_EPSL_Supplement.pdf
Licence: CC-BY-NC-ND 4.0