Spatial variability of diploptene δ<sup>13</sup>C values in thermokarst lakes: the potential to analyse the complexity of lacustrine methane cycling release_ff52emsu7zdd3gcl33wmctzpqy

by K. L. Davies, R. D. Pancost, M. E. Edwards, K. M. Walter Anthony, P. G. Langdon, L. Chaves Torres

Published in Biogeosciences Discussions by Copernicus GmbH.

2015   Volume 12, Issue 15, p12157-12189

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 δ&lt;sup&gt;13&lt;/sup&gt;C values (lower than −38 &amp;permil;) in all sediments analysed, suggesting methane oxidation was widespread. The most δ&lt;sup&gt;13&lt;/sup&gt;C-depleted diploptene was found in the area of highest methane ebullition emissions in Ace Lake (δ&lt;sup&gt;13&lt;/sup&gt;C diplotene values between −68.2 and −50.1 &amp;permil;), suggesting a positive link between methane production, oxidation, and emission in this area. In contrast, significantly less depleted diploptene δ&lt;sup&gt;13&lt;/sup&gt;C values (between −42.9 and −38.8 &amp;permil;) were found in the area of highest methane ebullition emissions in Smith Lake. Lower δ&lt;sup&gt;13&lt;/sup&gt;C values of diploptene were found in the central area of Smith Lake (between −56.8 and −46.9 &amp;permil;), where methane ebullition rates are low but methane diffusion appears high. Using δ&lt;sup&gt;13&lt;/sup&gt;C-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 δ&lt;sup&gt;13&lt;/sup&gt;C 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.
In application/xml+jats format

Archived Files and Locations

application/pdf  840.3 kB
file_vbuc7sd43ncexcjz3q5pbqcyse
web.archive.org (webarchive)
eprints.soton.ac.uk (web)
Read Archived PDF
Preserved and Accessible
Type  article-journal
Stage   published
Date   2015-08-04
Language   en ?
Container Metadata
Open Access Publication
Not in DOAJ
In ISSN ROAD
In Keepers Registry
ISSN-L:  1810-6285
Work Entity
access all versions, variants, and formats of this works (eg, pre-prints)
Catalog Record
Revision: 51a5af29-9ca7-4102-80fd-6594058d2753
API URL: JSON