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Taraxerol abundance as a proxy for in situ Mangrove sediment

Sefton, Juliet P.; Kemp, Andrew C.; Vane, Christopher H.; Kim, Alexander W.; Bernhardt, Christopher E.; Johnson, Jonathan; Engelhart, Simon E.

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Authors

Juliet P. Sefton

Andrew C. Kemp

Christopher H. Vane

Alexander W. Kim

Christopher E. Bernhardt

Jonathan Johnson



Abstract

Mangrove sediments are valuable archives of relative sea-level change if they can be distinguished in the stratigraphic record from other organic-rich depositional environments (e.g., freshwater swamps). Proxies for establishing environment of deposition can be poorly preserved (e.g., foraminifera) in mangrove sediment. Consequently, differentiating mangrove and freshwater sediment in the stratigraphic record is often subjective. We explore if biomarkers can objectively identify mangrove sediment with emphasis on their utility for reconstructing relative sea level. Our approach is specific to identifying in situ sediment, which has received less attention than identifying allochthonous mangrove organic matter. To characterize mangrove and non-mangrove (freshwater) environments, we measured n-alkane, sterol, and triterpenoid abundances in surface sediments at three sites in the Federated States of Micronesia. Elevated taraxerol abundance is diagnostic of sediment accumulating in mangroves and taraxerol is particularly abundant beneath monospecific stands of Rhizophora spp. Taraxerol was undetectable in freshwater sediment. Other triterpenoids are more abundant in mangrove sediment than in freshwater sediment. Using cores from Micronesian mangroves, we examine if biomarkers in sediments are indicative of in situ deposition in a mangrove, and have utility as a relative sea-level proxy. Taraxerol concentrations in cores are comparable to surface mangrove sediments, which indicates deposition in a mangrove. This interpretation is supported by pollen assemblages. Downcore taraxerol variability may reflect changing inputs from Rhizophora spp. rather than diagenesis. We propose that taraxerol is a proxy that differentiates between organic sediment that accumulated in mangrove vs. freshwater environments, lending it utility for reconstructing relative sea level.

Citation

Sefton, J. P., Kemp, A. C., Vane, C. H., Kim, A. W., Bernhardt, C. E., Johnson, J., & Engelhart, S. E. (2024). Taraxerol abundance as a proxy for in situ Mangrove sediment. Organic Geochemistry, 191, Article 104767. https://doi.org/10.1016/j.orggeochem.2024.104767

Journal Article Type Article
Acceptance Date Mar 9, 2024
Online Publication Date Mar 26, 2024
Publication Date May 1, 2024
Deposit Date Mar 15, 2024
Publicly Available Date Mar 18, 2024
Journal Organic Geochemistry
Print ISSN 0146-6380
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 191
Article Number 104767
DOI https://doi.org/10.1016/j.orggeochem.2024.104767
Public URL https://durham-repository.worktribe.com/output/2330027

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