Climate Variability in Southwest France During the Last 2000 Years
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UNIVERSITÉ PARIS-SUD ÉCOLE DOCTORALE 534 Modélisation et Instrumentation en Physique, Energies, Géosciences et Environnement Laboratoire des Sciences du Climat et de l’Environnement (LSCE) DISCIPLINE Sciences de la Terre THÈSE DE DOCTORAT soutenue le 14/05/2014 par Inga LABUHN Climate Variability in Southwest France During the Last 2000 Years Proxy Calibration and Reconstruction of Drought Periods Based on Stable Isotope Records from Speleothems and Tree Rings Directeurs de thèse : Valérie DAUX Maître de conférences, HDR (LSCE) Dominique GENTY Directeur de recherche (LSCE) Composition du jury : Président du jury : Christelle MARLIN Professeur (Université Paris-Sud) Rapporteurs : Gerhard HELLE Senior Scientist (German Research Centre for GeoSciences) Christoph SPÖTL Professeur (University of Innsbruck) Examinateurs : Valérie MASSON-DELMOTTE Directeur de recherche (LSCE) Hubert VONHOF Associate professor (VU University Amsterdam) Contents 1 Introduction 1 1.1 Climate Variability and Climate Reconstruction..................2 1.2 Motivation and Objectives..............................4 1.3 Structure of this Thesis...............................6 I BACKGROUND7 2 Stable Isotope Theory and Notation9 2.1 Mass Spectrometry.................................. 11 3 Stable Isotopes in the Hydrological Cycle 13 3.1 Precipitation..................................... 13 3.1.1 Spatial Variability of Isotopes in Precipitation............... 15 3.1.2 Temporal Variability of Isotopes in Precipitation............. 15 3.2 Soil Water....................................... 16 3.3 Applications to Palaeoclimatology......................... 18 4 Speleothems as Palaeoclimate Archives 21 4.1 The Cave Environment................................ 21 4.2 The Formation of Speleothems........................... 22 4.3 Dating of Speleothems................................ 25 4.4 Fluid Inclusions.................................... 27 4.5 Stable Isotopes in Calcite.............................. 29 4.5.1 Oxygen.................................... 29 4.5.2 Carbon.................................... 30 4.5.3 Isotopic Equilibrium and “Hendy Test”................... 33 4.6 Other Proxies from Speleothems.......................... 34 4.6.1 Morphology and Growth Rate........................ 34 4.6.2 Trace Elements................................ 35 4.6.3 Clumped Isotopes.............................. 35 5 Tree Rings as Palaeoclimate Archives 37 5.1 Tree Growth and Ring Formation.......................... 37 5.2 Crossdating and Standardization.......................... 39 5.3 Tree Ring Proxies and their Links with Climate.................. 40 5.3.1 Tree Ring Width and Density........................ 41 5.3.2 Oxygen Isotopes in Cellulose........................ 41 5.3.3 Carbon Isotopes in Cellulose........................ 45 II STUDY AREA AND METHODS 49 6 Sites and Samples 51 6.1 The Climate of Southwest France.......................... 51 6.1.1 Present-Day Climate............................. 51 6.1.2 Climate Trends in the Twentieth Century................. 52 6.1.3 The Isotopic Composition of Precipitation................. 53 6.2 Villars Cave...................................... 55 6.2.1 Speleothem Samples from Villars Cave................... 56 6.3 Braconne Forest and Le Mas............................ 57 6.3.1 Living Tree and Timber Samples...................... 57 7 Speleothem Data and Methods 61 7.1 Dating and Age Models............................... 61 7.2 Fluid Inclusion Measurements............................ 62 7.3 Other Proxies from Speleothems.......................... 62 8 Tree Ring Data and Methods 65 8.1 Ring Width Measurement, Crossdating, and Standardization.......... 65 8.2 Oxygen Isotope Ratios in Cellulose......................... 65 8.2.1 Selection of Samples for Stable Isotope Analysis.............. 65 8.2.2 Pooling of Trees............................... 67 8.2.3 Sample Preparation............................. 67 8.2.4 Mass Spectrometric Analysis of Cellulose................. 68 8.3 Results with Implications for Further Analysis Strategy............. 69 8.3.1 Replicate Measurements........................... 69 8.3.2 The Effect of Tree Age on Cellulose δ18O................. 69 8.3.3 Inter-Tree and Inter-Site Variability: Implications for Pooling...... 70 8.3.4 Should Samples Be Weighed Before Pooling?............... 70 III RECORDS OF CLIMATE VARIABILITY IN SOUTHWEST FRANCE 73 9 The Relationship Between Precipitation and Cave Drip Water 77 10 Fossil Water in Stalagmites as a Record of Past Drip Water δ18O 103 11 Climatic and Non-Climatic Influences on the δ18O of Cellulose 125 12 Reconstruction of Summer Droughts Based on Tree Rings 145 13 A Multi-Proxy Approach to Drought Reconstruction 165 IV CONCLUSIONS 173 References 177 List of Symbols and Abbreviations 211 Appendix 213 Acknowledgements 221 List of Figures 1.1 Reconstructed Northern Hemisphere temperature during the last 2000 years..2 1.2 Components of the climate system and associated processes...........3 1.3 Climate archives and proxies used in this thesis..................5 2.1 Schematic representation of an isotope ratio mass spectrometer......... 11 3.1 The global hydrological cycle............................ 14 3.2 Fractionation of oxygen isotopes in atmospheric water.............. 15 3.3 Global pattern of isotopes in precipitation..................... 16 3.4 Soil water profiles................................... 18 3.5 The isotopic composition of water in palaeoclimate archives........... 19 4.1 Stalactites....................................... 22 4.2 Photograph of Cussac cave, France......................... 23 4.3 Dissolution and precipitation of calcium carbonate in the karst system..... 24 4.4 Reaction pathways from dripwater to the precipitation of calcite......... 25 4.5 Chemical evolution of a typical dripwater..................... 26 4.6 Annually laminated stalagmite........................... 27 4.7 Photographs of thin sections from three stalagmites with fluid inclusions.... 28 4.8 Processes in the ocean, atmosphere, soil, epikarst, and the cave which influence the δ18O of speleothem calcite............................ 30 4.9 Fractionation of oxygen isotopes during calcite precipitation........... 31 4.10 Speleothem carbon sources and transfer processes................. 32 4.11 Fractionantion of carbon isotopes during calcite precipitation.......... 33 5.1 Cross-section of a tree stem............................. 38 5.2 Annual rings of an oak tree............................. 39 5.3 Molecular structure of cellulose........................... 39 5.4 Schematic illustration of crossdating........................ 40 5.5 Controls on the fractionation of oxygen isotopes in cellulose........... 42 5.6 Controls on the fractionation of carbon isotopes in cellulose........... 46 6.1 Location of the study sites.............................. 51 6.2 Annual cycle of temperature and precipitation in the study area......... 52 6.3 Temperature and precipitation trends in the study area............. 53 6.4 Annual cycle of isotopes in precipitation and LMWL for Villars and Le Mas.. 54 6.5 Photograph and cross-section of Villars cave.................... 55 6.6 Map of Villars cave and speleothem samples.................... 56 6.7 Historic buildings near Angoulême and roof beams................ 58 7.1 The Amsterdam Device for fluid inclusion measurement............. 63 8.1 Overview of the tree samples............................ 66 8.2 Standardization of tree ring width series...................... 67 8.3 Tree cores selected for stable isotope analysis................... 68 9.1 Locations of the precipitation sampling stations and the corresponding cave sites 80 9.2 Variability of mean monthly temperature, monthly precipitation sums and monthly precipitation δ18O at the studied sites.................. 81 9.3 Comparison between calculated monthly δ18O values and the original measured values......................................... 84 9.4 Monthly precipitation δ18O time series for all French GNIP stations...... 86 9.5 Scatter plot of δD vs. δ18O in cave drip water and precipitation......... 87 9.6 Scatter plots between mean monthly temperature and monthly precipitation δ18O 89 9.7 Scatter plots between mean annual temperature and annual precipitation δ18O 89 9.8 Comparison between measured precipitation δ18O and REMOiso simulations.. 91 9.9 Precipitation and drip water δ18O time series at Villars cave........... 94 9.10 Precipitation and drip water δ18O time series at Chauvet cave.......... 95 9.11 Drip water δ18O and flow rates at four monitoring stations in Villars cave... 97 9.12 Conceptual model of the infiltration in Villars cave................ 99 10.1 Fluid inclusion samples................................ 108 10.2 Meteoric water line graph for fluid inclusions in modern calcite samples..... 110 10.3 Age model for stalagmite vil-stm1.......................... 112 10.4 Meteoric water line graph for fluid inclusions in stalagmite vil-stm1 and stand- ard water....................................... 114 10.5 Stalagmite vil-stm1 proxy records.......................... 115 10.6 Stalagmite vil-stm1 trace element concentrations................. 117 10.7 Stalagmite vil-stm1 fluid inclusions vs. trace elements............... 118 10.8 Fluid inclusions vs. temperature and NAO reconstructions............ 121 11.1 Location of the study area.............................. 128 11.2 Mean monthly temperature and precipitation for Angoulême........... 128 11.3 Sample time spans.................................. 130