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Variations of sedimentary Fe and Mn fractions under changing lake mixing regimes, oxygenation and land surface processes during Late-glacial and Holocene times

Makri, Stamatina ; Wienhues, Giulia ; Bigalke, Moritz ; Gilli, Adrian ; Rey, Fabian ; Tinner, Willy ; Vogel, Hendrik ; Grosjean, Martin (2022)
Variations of sedimentary Fe and Mn fractions under changing lake mixing regimes, oxygenation and land surface processes during Late-glacial and Holocene times.
In: Science of The Total Environment, 2021, 755
doi: 10.26083/tuprints-00022542
Article, Secondary publication, Publisher's Version

Abstract

Global spread of anoxia in aquatic ecosystems has become a major issue that may potentially worsen due to global warming. The reconstruction of long-term hypolimnetic anoxia records can be challenging due to lack of valid and easily measurable proxies. The sedimentary Mn/Fe ratio measured by X-ray fluorescence (XRF) is often used as a proxy for past lake redox conditions. Yet the interpretation of this ratio can be problematic when Fe and Mn accumulation is not solely redox driven. We used the varved sediments of Lake Moossee (Switzerland) to examine the partitioning of Fe and Mn in seven fractions by sequential extraction under various oxygen conditions over the last 15,000 years. We combined this data with XRF scans and an independent diagnostic proxy for anoxia given by a hyperspectral imaging (HSI)-inferred record of bacteriopheophytin, to validate the use of the XRF-Mn/Fe ratio as redox proxy. In the 15,000-year long record, Fe was bound to humins and amorphous, crystalline, sulfide and residual forms. Mn was mainly present in carbonate and amorphous forms. Higher erosion, prolonged anoxia, diagenesis and humic matter input affected Fe and Mn accumulation. Under holomixis the XRF-Mn/Fe ratio successfully reflected lake redox conditions. Periods with higher detrital Fe input obscured the applicability of the ratio. During phases of permanent anoxia, intensified early diagenetic processes trapped Mn in the sediments in carbonate, crystalline oxide and humic forms. Our study shows that the single use of the XRF-Mn/Fe ratio is often not conclusive for inferring past lake redox conditions. The application of the XRF-Mn/Fe as a proxy for anoxia requires taking into account the individual lake characteristics and changes in lake environmental conditions, which affect the accumulation of Fe and Mn in the sediments.

Item Type: Article
Erschienen: 2022
Creators: Makri, Stamatina ; Wienhues, Giulia ; Bigalke, Moritz ; Gilli, Adrian ; Rey, Fabian ; Tinner, Willy ; Vogel, Hendrik ; Grosjean, Martin
Type of entry: Secondary publication
Title: Variations of sedimentary Fe and Mn fractions under changing lake mixing regimes, oxygenation and land surface processes during Late-glacial and Holocene times
Language: English
Date: 2022
Place of Publication: Darmstadt
Year of primary publication: 2021
Publisher: Elsevier
Journal or Publication Title: Science of The Total Environment
Volume of the journal: 755
Collation: 12 Seiten
DOI: 10.26083/tuprints-00022542
URL / URN: https://tuprints.ulb.tu-darmstadt.de/22542
Corresponding Links:
Origin: Secondary publication service
Abstract:

Global spread of anoxia in aquatic ecosystems has become a major issue that may potentially worsen due to global warming. The reconstruction of long-term hypolimnetic anoxia records can be challenging due to lack of valid and easily measurable proxies. The sedimentary Mn/Fe ratio measured by X-ray fluorescence (XRF) is often used as a proxy for past lake redox conditions. Yet the interpretation of this ratio can be problematic when Fe and Mn accumulation is not solely redox driven. We used the varved sediments of Lake Moossee (Switzerland) to examine the partitioning of Fe and Mn in seven fractions by sequential extraction under various oxygen conditions over the last 15,000 years. We combined this data with XRF scans and an independent diagnostic proxy for anoxia given by a hyperspectral imaging (HSI)-inferred record of bacteriopheophytin, to validate the use of the XRF-Mn/Fe ratio as redox proxy. In the 15,000-year long record, Fe was bound to humins and amorphous, crystalline, sulfide and residual forms. Mn was mainly present in carbonate and amorphous forms. Higher erosion, prolonged anoxia, diagenesis and humic matter input affected Fe and Mn accumulation. Under holomixis the XRF-Mn/Fe ratio successfully reflected lake redox conditions. Periods with higher detrital Fe input obscured the applicability of the ratio. During phases of permanent anoxia, intensified early diagenetic processes trapped Mn in the sediments in carbonate, crystalline oxide and humic forms. Our study shows that the single use of the XRF-Mn/Fe ratio is often not conclusive for inferring past lake redox conditions. The application of the XRF-Mn/Fe as a proxy for anoxia requires taking into account the individual lake characteristics and changes in lake environmental conditions, which affect the accumulation of Fe and Mn in the sediments.

Uncontrolled Keywords: Sequential extraction, Paleolimnology, Late-Glacial/Holocene, Mn/Fe ratio, Seasonal anoxia, Meromixis
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-225427
Additional Information:

The data are available in BORIS at https://boris.unibe.ch/id/eprint/148053

Classification DDC: 500 Science and mathematics > 550 Earth sciences and geology
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Earth Science > Department of Soil Mineralogy and Soil Chemistry
Date Deposited: 07 Nov 2022 14:34
Last Modified: 08 Nov 2022 06:15
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