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GDGT distribution in a stratified lake and implications for the application of TEX86 in paleoenvironmental reconstructions
Stockholm University, Faculty of Science, Department of Geological Sciences.
Number of Authors: 3
2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, 34465Article in journal (Refereed) Published
Abstract [en]

We investigated the relationship between distributions of GDGTs, GDGT-based proxies and environmental factors in a stratified lake in northwestern Norway. More than 90% of isoGDGTs were produced at the bottom of the oxycline, indicating a predominance of ammonia-oxidizing Group I.1a of Thaumarchaeota, supported by high crenarchaeol/caldarchaeol ratios. Dissolved oxygen content, rather than temperature, exercised a primary control on TEX86 values. In spite of low BIT value in surface sediment, the reconstructed lake surface temperature was cold biased. MBT values in streams and lake surface water were significantly smaller than those in the catchment soil, suggesting in situ production of brGDGTs in streams. A rapid transition of MBT vs. temperature/pH relationships occurring at the bottom of oxycline indicated the differential production of various brGDGTs with D.O. and depths. Only within the oxycline were CBT-based pH values close to in situ pH. Our results confirm earlier studies calling for caution in applying TEX86 as a surface temperature proxy, or MBT and/or CBT for reconstructing pH, in anoxic or euxinic lakes, estuaries and ocean basins. We propose that caldarchaeol/crenarchaeol ratio, an indicator of contributions from methanogenic archaea, together with the BIT and TEX86 proxies, can help reconstruct past levels of stratification.

Place, publisher, year, edition, pages
2016. Vol. 6, 34465
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-135224DOI: 10.1038/srep34465ISI: 000384428300001OAI: diva2:1046007
Available from: 2016-11-11 Created: 2016-11-01 Last updated: 2016-11-11Bibliographically approved

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Smittenberg, Rienk H.
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