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Postglacial Evolution of Biogenic Silica Productivity in Lago Castor, Northern Chilean Patagonia

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Postglacial Evolution of Biogenic Silica Productivity in Lago Castor, Northern Chilean Patagonia FACULTY OF SCIENCES Master of Science in geology Postglacial evolution of biogenic silica productivity in Lago Castor, northern Chilean Patagonia Géraldine Fiers Academic year 2015–2016 Master’s dissertation submitted in partial fulfillment of the requirements for the degree of Master in Science in Geology Promotor: Prof. Dr. S. Bertrand Co-promotor: Dr. M. Van Daele Jury: Prof. Dr. M. De Batist, Prof. Dr. E. Verleyen Cover image. View on Lago Castor (picture taken by Maarten Van Daele during the field expedition to Chile in 2011) Acknowledgements Before reading this thesis, I would like to seize the opportunity to thank some people who supported me during this master thesis. First of all, I would like to thank my promotor, Sébastien Bertrand, who gave me the opportunity to work on the Lago Castor project. Your door was always open for any kind of advice and I really appreciate all your help, the many suggestions you made and the constructive discussions we had. I learned a lot from your scientific expertise and especially in the way of thinking like a real geologist. For that, I’m very grateful having you as promotor. The people who participated to the expedition to Chile and collected the composite core and additional samples are thanked because without them this study would not have been possible. I want to thank Maarten Van Daele for giving me all the information and data I needed of Lago Castor, for helping me working with global mapper and for revising my thesis. I would also like to thank the people working at the Renard Centre of Marine Geology for helping me in the laboratory and the guidance with several software programs. I am especially grateful to Veerle Vandenhende from the laboratory staff of the Department of Geology for helping me in the laboratory and for performing the ICP analysis on my samples. I would like to thank my fellow students who became real friends during our studentship. The great times we had during class, on field trips and other non-geological related activities are unforgettable and made the past five years a very pleasant studentship. Finally, I would like to thank my family and my boyfriend for their great support and encouragement during my student years. Thank you and enjoy reading! Géraldine Table of contents List of figures List of tables 1. Introduction.......................................................................................................................... 1 1.1 State-of-the-art ....................................................................................................................... 1 1.2 Research objectives ................................................................................................................. 2 2. Regional setting .................................................................................................................... 5 2.1 Location and site description .................................................................................................. 5 2.2 Geological setting .................................................................................................................... 6 2.3 Late Quaternary evolution ...................................................................................................... 6 2.4 Present-day climate and vegetation ....................................................................................... 7 3. Material and methods ........................................................................................................... 9 3.1 Previous research .................................................................................................................... 9 3.1.1 Core acquisition, logging and XRF scanning .................................................................... 9 3.1.2 Chronology..................................................................................................................... 10 3.1.3 Sedimentology ............................................................................................................... 11 3.1.4 Bulk organic geochemistry ............................................................................................ 11 3.1.5 Pigment analysis ............................................................................................................ 12 3.1.6 Diatom quantification and paleoecology ...................................................................... 12 3.2 Biogenic silica analysis ........................................................................................................... 13 3.2.1 Introduction ................................................................................................................... 13 3.2.2 Alkaline extraction technique ........................................................................................ 13 3.2.3 Scanning XRF ................................................................................................................. 15 4. Results ................................................................................................................................ 17 4.1 Biogenic silica analysis: alkaline extraction technique .......................................................... 17 4.1.1 Lithogenic correction factor ........................................................................................... 17 4.1.2 Downcore results ........................................................................................................... 17 4.2 Scanning XRF ......................................................................................................................... 17 4.3 Sediment composition........................................................................................................... 19 4.3.1 Components ................................................................................................................... 19 4.3.2 Smear slides ................................................................................................................... 20 5. Discussion ........................................................................................................................... 23 5.1 Biogenic silica ........................................................................................................................ 23 5.1.1 Comparison of the different biogenic silica proxies ....................................................... 23 5.1.2 Comments on the calculation of the lithogenic correction factor ................................. 24 5.1.3 Absolute diatom abundance versus diatom biovolume ................................................ 26 5.2 Variations in sediment composition ...................................................................................... 27 5.3 Postglacial wind and precipitation variability ....................................................................... 30 5.3.1 Deglaciation ................................................................................................................... 32 5.3.2 Postglacial evolution of precipitation and westerly wind strength ............................... 32 5.4 Postglacial changes in lake productivity ................................................................................ 34 5.4.1 Relations between opal and aquatic organic carbon .................................................... 34 5.4.2 Postglacial evolution of lake productivity ...................................................................... 34 5.4.3 Relations between climate change and lake productivity during the deglaciation ...... 36 5.4.4 Relations between climate change and lake productivity during the Holocene ........... 37 6. Conclusion .......................................................................................................................... 39 References ................................................................................................................................. 41 Appendix ................................................................................................................................... 47 List of figures Figure 1 Simplified vegetation map of northern Chilean Patagonia ....................................................5 Figure 2 (a) Annual mean precipitation in Patagonia. (b) Correlation between monthly precipitation at Coyhaique Alto and zonal wind speed ...............................................................................8 Figure 3 Present-day climatology of Coyhaique alto: monthly precipitation (1985-2010) and monthly temperature (1994-2010) ......................................................................................................8 Figure 4 Bathymetry map of Lago Castor with locations of composite core (CAST01), short core (CAS- 09; Elbert et al., 2013) and soil samples (SS) ..........................................................................9 Figure 5 The age-depth model of the Lago Castor sedimentary record ........................................... 10 Figure 6 Bulk organic geochemical results of Granon (2015): C/N versus δ13C biplots of the core samples, river sediment samples and suspended particulate matter (SPM) of river and lake samples ................................................................................................................................ 11 Figure 7 Schematic illustration of silica released from minerals and diatoms during the alkaline extraction process ..............................................................................................................
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