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Spatial variability of diploptene δ13C values in thermokarst lakes: the potential to analyse the complexity of lacustrine methane cycling

Spatial variability of diploptene δ13C values in thermokarst lakes: the potential to analyse the complexity of lacustrine methane cycling
Spatial variability of diploptene δ13C values in thermokarst lakes: the potential to analyse the complexity of lacustrine methane cycling
Cryospheric changes in northern high latitudes are linked to significant greenhouse gas flux to the atmosphere, including methane release that originates from organic matter decomposition in thermokarst lakes. The connections between methane production in sediments, transport pathways and oxidation are not well understood and this has implications for any attempts to reconstruct methane production from sedimentary archives. We assessed methane oxidation as represented by methane oxidising bacteria across the surface sediments of two interior Alaska thermokarst lakes in relation to methane emissions via ebullition (bubbling). The bacterial biomarker diploptene was present and had low ?13C values (lower than ?38 ‰) in all sediments analysed, suggesting methane oxidation was widespread. The most ?13C-depleted diploptene was found in the area of highest methane ebullition emissions in Ace Lake (?13C diplotene values between ?68.2 and ?50.1 ‰), suggesting a positive link between methane production, oxidation, and emission in this area. In contrast, significantly less depleted diploptene ?13C values (between ?42.9 and ?38.8 ‰) were found in the area of highest methane ebullition emissions in Smith Lake. Lower ?13C values of diploptene were found in the central area of Smith Lake (between ?56.8 and ?46.9 ‰), where methane ebullition rates are low but methane diffusion appears high. Using ?13C-diplotene as a proxy for methane oxidation activity, we suggest the observed differences in methane oxidation levels among sites within the two lakes could be linked to differences in source area of methane production (e.g. age and type of organic carbon) and bathymetry as it relates to varying oxycline depths and changing pressure gradients. As a result, methane oxidation is highly lake-dependent. The diploptene ?13C values also highlight strong within-lake variability, implying that single-value, down-core records of hopanoid isotopic signatures are not secure indicators of changing methane flux at the whole-lake scale.
12157-12189
Davies, K.L.
16988cb4-fb89-4ccf-a43f-662ebce1c3e0
Pancost, R.D.
893ebd86-164b-437e-8d26-cfe0d5ed6b14
Edwards, M.E.
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Walter Anthony, K.M.
c18714f2-e563-429d-9986-a506cfa7ebe0
Langdon, P.G.
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Chaves Torres, L.
a3db0cdb-b54b-4884-82a1-1954b09ae383
Davies, K.L.
16988cb4-fb89-4ccf-a43f-662ebce1c3e0
Pancost, R.D.
893ebd86-164b-437e-8d26-cfe0d5ed6b14
Edwards, M.E.
4b6a3389-f3a4-4933-b8fd-acdfef72200e
Walter Anthony, K.M.
c18714f2-e563-429d-9986-a506cfa7ebe0
Langdon, P.G.
95b97671-f9fe-4884-aca6-9aa3cd1a6d7f
Chaves Torres, L.
a3db0cdb-b54b-4884-82a1-1954b09ae383

Davies, K.L., Pancost, R.D., Edwards, M.E., Walter Anthony, K.M., Langdon, P.G. and Chaves Torres, L. (2015) Spatial variability of diploptene δ13C values in thermokarst lakes: the potential to analyse the complexity of lacustrine methane cycling. Biogeosciences, 12 (15), 12157-12189. (doi:10.5194/bgd-12-12157-2015).

Record type: Article

Abstract

Cryospheric changes in northern high latitudes are linked to significant greenhouse gas flux to the atmosphere, including methane release that originates from organic matter decomposition in thermokarst lakes. The connections between methane production in sediments, transport pathways and oxidation are not well understood and this has implications for any attempts to reconstruct methane production from sedimentary archives. We assessed methane oxidation as represented by methane oxidising bacteria across the surface sediments of two interior Alaska thermokarst lakes in relation to methane emissions via ebullition (bubbling). The bacterial biomarker diploptene was present and had low ?13C values (lower than ?38 ‰) in all sediments analysed, suggesting methane oxidation was widespread. The most ?13C-depleted diploptene was found in the area of highest methane ebullition emissions in Ace Lake (?13C diplotene values between ?68.2 and ?50.1 ‰), suggesting a positive link between methane production, oxidation, and emission in this area. In contrast, significantly less depleted diploptene ?13C values (between ?42.9 and ?38.8 ‰) were found in the area of highest methane ebullition emissions in Smith Lake. Lower ?13C values of diploptene were found in the central area of Smith Lake (between ?56.8 and ?46.9 ‰), where methane ebullition rates are low but methane diffusion appears high. Using ?13C-diplotene as a proxy for methane oxidation activity, we suggest the observed differences in methane oxidation levels among sites within the two lakes could be linked to differences in source area of methane production (e.g. age and type of organic carbon) and bathymetry as it relates to varying oxycline depths and changing pressure gradients. As a result, methane oxidation is highly lake-dependent. The diploptene ?13C values also highlight strong within-lake variability, implying that single-value, down-core records of hopanoid isotopic signatures are not secure indicators of changing methane flux at the whole-lake scale.

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Accepted/In Press date: 8 July 2015
Published date: 4 August 2015
Organisations: Geography & Environment

Identifiers

Local EPrints ID: 384376
URI: https://eprints.soton.ac.uk/id/eprint/384376
PURE UUID: f56c7be6-3641-43d4-b822-c59cd79671ec
ORCID for M.E. Edwards: ORCID iD orcid.org/0000-0002-3490-6682
ORCID for P.G. Langdon: ORCID iD orcid.org/0000-0003-2724-2643

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Date deposited: 25 Nov 2015 10:27
Last modified: 24 Oct 2018 00:35

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