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Biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux

Biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux
Biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux
The TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a proxy for sea surface temperature (SST) based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether (GDGT) membrane lipids synthesized by marine pelagic Thaumarchaeota. One of the caveats of this proxy is the production of additional GDGTs by sedimentary Euryarchaeota involved in anaerobic oxidation of methane (AOM) that occurs at deep-sea methane seeps but is also widespread in many continental shelf settings. Here, GDGT distributions are investigated through the sulfate-methane transition zone (SMTZ) in Aarhus Bay, Denmark, to examine the extent the TEX86 proxy is compromised in such a continental shelf setting where AOM is characterized by a diffusive rather than rapid advective methane flux. Both free extractable and non-extractable lipid fractions were analyzed as it was expected that pelagic-derived and sediment-derived GDGTs could become incorporated into the molecular and sedimentary matrix to a different extent. The results show a large change of TEX86 values mainly due to the relative high amounts of GDGT-2 produced by AOM-related Archaea, both in the free and non-extractable lipid fractions. This additional GDGT input renders calculation of SSTs based on TEX86 inappropriate at the SMTZ. The AOM-related GDGT signature, however, did not persist into deeper sediments, perhaps reflecting rapid remineralization of the GDGTs at the SMTZ. Although the process of AOM at Aarhus Bay might not be representative for all continental margin settings, it illustrates that AOM in a variety of settings, not just cold seeps, can influence sedimentary GDGT distributions.
1525-2027
Q10010
Weijers, Johan W.H.
a4382583-2c58-420d-867d-537c5a3f5a23
Lim, Katie L.H.
70e2cd3f-635b-403d-bd60-ef309ffa8a61
Aquilina, Alfred
a5ce0174-e2d4-40ee-baa5-86ba2f24058c
Sinninghe Damsté, Jaap S.
fd4f1f34-17ad-4615-b723-906beeafe701
Pancost, Richard D.
5914e19e-7777-4304-9fd8-86e2e9cfe8a1
Weijers, Johan W.H.
a4382583-2c58-420d-867d-537c5a3f5a23
Lim, Katie L.H.
70e2cd3f-635b-403d-bd60-ef309ffa8a61
Aquilina, Alfred
a5ce0174-e2d4-40ee-baa5-86ba2f24058c
Sinninghe Damsté, Jaap S.
fd4f1f34-17ad-4615-b723-906beeafe701
Pancost, Richard D.
5914e19e-7777-4304-9fd8-86e2e9cfe8a1

Weijers, Johan W.H., Lim, Katie L.H., Aquilina, Alfred, Sinninghe Damsté, Jaap S. and Pancost, Richard D. (2011) Biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux. Geochemistry, Geophysics, Geosystems, 12 (10), Q10010. (doi:10.1029/2011GC003724).

Record type: Article

Abstract

The TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a proxy for sea surface temperature (SST) based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether (GDGT) membrane lipids synthesized by marine pelagic Thaumarchaeota. One of the caveats of this proxy is the production of additional GDGTs by sedimentary Euryarchaeota involved in anaerobic oxidation of methane (AOM) that occurs at deep-sea methane seeps but is also widespread in many continental shelf settings. Here, GDGT distributions are investigated through the sulfate-methane transition zone (SMTZ) in Aarhus Bay, Denmark, to examine the extent the TEX86 proxy is compromised in such a continental shelf setting where AOM is characterized by a diffusive rather than rapid advective methane flux. Both free extractable and non-extractable lipid fractions were analyzed as it was expected that pelagic-derived and sediment-derived GDGTs could become incorporated into the molecular and sedimentary matrix to a different extent. The results show a large change of TEX86 values mainly due to the relative high amounts of GDGT-2 produced by AOM-related Archaea, both in the free and non-extractable lipid fractions. This additional GDGT input renders calculation of SSTs based on TEX86 inappropriate at the SMTZ. The AOM-related GDGT signature, however, did not persist into deeper sediments, perhaps reflecting rapid remineralization of the GDGTs at the SMTZ. Although the process of AOM at Aarhus Bay might not be representative for all continental margin settings, it illustrates that AOM in a variety of settings, not just cold seeps, can influence sedimentary GDGT distributions.

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Published date: 2011
Organisations: Geochemistry

Identifiers

Local EPrints ID: 341051
URI: http://eprints.soton.ac.uk/id/eprint/341051
ISSN: 1525-2027
PURE UUID: 98677398-7ca8-4859-ac0b-8a8cc4788387

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Date deposited: 16 Jul 2012 13:37
Last modified: 14 Mar 2024 11:34

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Contributors

Author: Johan W.H. Weijers
Author: Katie L.H. Lim
Author: Alfred Aquilina
Author: Jaap S. Sinninghe Damsté
Author: Richard D. Pancost

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