Tesis doctoral de Marina Escala Pascual
Since 2002, several climate proxies based on biomarkers of archaea and bacteria have been developed and applied in sedimentary archives worldwide. These biomarkers are the glycerol dialkyl glycerol tetraethers or gdgts. Among the proposed proxies, the tex86 index is applied in sediments to reconstruct sea surface temperatures (sst) and lake surface temperatures (lst); the mbt and cbt indices are together applied as a proxy for past surface air temperature and the bit index is measured in sediments to assess qualitatively relative inputs of pelagic-originated material versus soil material. Given the novelty of these proxies, there is plenty of scope to improve upon a range of issues regarding their measurement and application. Consequently, the aim of this thesis has been to tackle analytical methodological issues to gain in analytical reliability and sample throughput, and expand the range of environments where gdgt proxies have been appraised, particularly in lake environments. in the analytical section of the thesis, two sample clean-up methods, i.E. Alumina fractionation and alkaline hydrolysis are compared. Additional tests compare alumina and silica in their activated and deactivated states as adsorbents onto which gdgts are fractionated. Results show that tex86 values are robust using these methodologies, while bit values are dependant on adsorbent activation state. Regarding the chromatographic analysis, an increase in the analysis velocity and a reduction of flow are effectively implemented without loss of chromatographic peak resolution. Additionally, two mass spectrometer designs, i.E. An ion-trap system and a quadrupole system, are used for the measurement of a wide range of values of tex86 and bit indices, and results confirm the comparability of both systems. However, bit values are found to be extremely sensitive to the ms tuning conditions. in order to find out the main factors influencing the gdgts distribution in lacustrine environments, a suite of surface sediments from 38 iberian lakes are surveyed. Principal component analysis of the relative concentrations of gdgts indicates that terrestrial versus lacustrine origin, combined with degree of cyclization and degree of methylation of the lipids are the principal factors accounting for the gdgt distribution in the sediments. The measurement of the mbt/cbt proxy represents a pioneer application of these indices in lake sediments. Tex86 and mbt/cbt are shown to have a limited applicability in predicting the lake temperature, likely due to a complex combination of factors influencing the gdgt abundances. Using cluster analysis a subset of lakes is selected with a rather linear relationship of tex86 and cbt/mbt with instrumental air temperatures. in the study conducted in lake baikal in siberia, sediment traps, surface sediments and two cores spanning the last glacial-interglacial cycle are analysed in the north and south basins of the lake. Bit values both for the particulate material collected and the surface sediments suggest low influence of soil-derived material. Tex86 derived lst from the water column particulate material and sediments are in the range of measured annual lst. The down-core variations of the tex86 and mbt/cbt proxies reveal a climatic signal, inferred both from the reconstructed transition from glacial to interglacial conditions and the partial agreement with reconstructed changes in lake baikal region derived from other proxies applied in the sediments. finally, an exploratory study in the bosumtwi impact structure in africa reveals the presence of gdgts in the deeply buried impacted rocks and three hypotheses are discussed for their origin and relative age. the work presented extends the range of analytical techniques that can be reliably used for the measurement of the gdgt indices and provides deeper knowledge on the application and validation of gdgts as climate proxies in lacustrine sediments, in particular from the iberian and siberian regions.
Datos académicos de la tesis doctoral «Application of tetraether membrane lipids as proxies for continental climate reconstruction in iberian and siberian lakes«
- Título de la tesis: Application of tetraether membrane lipids as proxies for continental climate reconstruction in iberian and siberian lakes
- Autor: Marina Escala Pascual
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 04/06/2009
Dirección y tribunal
- Director de la tesis
- Antoni Rosell Melé
- Tribunal
- Presidente del tribunal: rainer Zahn
- erin Mcclymont (vocal)
- (vocal)
- (vocal)