McGovern, Andrew Dominic;
(2000)
Geochemical investigations of sedimented organic matter in a Scottish mountain lake with respect to late holocene climate change.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Recent research has shown that many mountain lakes are particularly sensitive to environmental change, including climate change. Lochan Uaine, at an elevation of 910 m in the Cairngorms of Scotland, is thought to be one such lake. Previous high resolution analyses undertaken at the lake reveal quasi-cyclic variations in the loss-on- ignition profiles of two cores. It is hypothesised that these cycles are driven by fluctuations in lake primary productivity. In turn, this productivity is thought to be driven by climatic variability, possibly through the influence of winter ice cover duration on growing season. Fluctuations in LOI comparable to those seen previously are evident in a more recent core from Lochan Uaine (core UACT6) representing the last c. 2000 yr of sediment accumulation. This core is dated by correlation of the LOI profile with that of a radiometrically-dated core, although attempts to validate the chronology by identifying microtephra layers were unsuccessful. Analysis of the sediment organic fraction reveals concurrent fluctuations in total organic carbon content, chlorin content, and bulk organic δ13C with LOI. Although few studies have been undertaken in lake sediments, the chlorin profile is thought to represent variations in lake primary productivity. Similarly, bulk organic δ13C may reflect variations in the relative inputs of autochthonous and allochthonous material to the sediment. To further investigate these hypotheses, organic geochemical analysis of the unbound lipid fraction is described. Certain lipids identified in the sediment record are assigned to particular organic sources through comparison with published data, analysis of vegetation collected from the lake catchment, and compound-specific δ13C analysis. Lipid biomarkers attributed to higher plant sources show little downcore variation in concentration, whereas those attributed to algal and bacterial sources show variations similar to the LOI profile. These results support the hypothesis that LOI fluctuations are driven by changes in lake productivity. The productivity changes are discussed in relation to late Holocene climate variability, although an unambiguous correlation between productivity and climate is prevented by the uncertain chronology of UACT6, and our current inadequate understanding of Holocene climate variability in temperate latitudes.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Geochemical investigations of sedimented organic matter in a Scottish mountain lake with respect to late holocene climate change |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Thesis digitised by ProQuest. |
| Keywords: | Earth sciences; Holocene climate change |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10100546 |
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