The long-term climate variability

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Table of contents

1 Past and present Antarctic Climate, a search for temperature changes
1.1 Importance of Antarctic temperature in the global climate
1.2 Use of paleoclimate records to understand the natural variability
1.3 Regional differences in Antarctic temperature records
1.4 Sensitivity of Antarctic climate to atmospheric modes of variability
1.5 Diversity of temperature proxies
1.6 Organization of the manuscript
2 Tools for understanding temperature and climate from ice core records
2.1 Characteristics of ice sheets allowing for ice coring
2.2 General information on stable isotopes
2.2.1 Definition of stable isotopes
2.2.2 Partitioning of stable isotopes during fractionating processes
2.2.2.1 Equilibrium fractionation
2.2.2.2 Kinetic fractionation
2.3 Water stable isotopes
2.3.1 Isotopes in polar precipitation
2.3.1.1 Evaporation at moisture source
2.3.1.2 Transport and condensation of precipitation
2.3.2 Mitigation of the climate signal related to snow deposition
2.3.2.1 Deposition
2.3.2.2 Snow-vapor exchanges
2.3.2.3 Diffusion
2.3.3 Calibration of isotope – temperature slope
2.3.4 Analytical methods
2.3.4.1 Cavity Ring-Down Spectroscopy
2.3.4.2 Fluorination and mass spectrometry
2.3.4.3 Working standards
2.3.5 Summary of water isotope signal in ice cores
2.4 Gases Stable isotopes
2.4.1 Structure of the firn
2.4.2 Firn fractionation processes
2.4.2.1 Gravitational fractionation
2.4.2.2 Thermal Fractionation
2.4.2.3 Convective disequilibrium
2.4.3 Fractionation during close-off
2.4.4 Analytical methods
2.5 Firn model and temperature reconstructions
2.5.1 Forward diffusion-advection model
2.5.2 Inversion of the model for temperature reconstruction
2.6 Borehole temperature
2.7 Atmospheric models and reanalysis
2.8 Conclusion
3 Evaluation of the climate variability at Aurora Basin North, using atmospheric climate models
3.1 Introduction
3.2 Methods
3.2.1 Site description
3.2.2 The regional climate model MAR
3.3 ABN as a tracer of East Antarctic Climate
3.4 Climatology of the precipitation in the MAR model
3.4.1 Distribution of precipitation events
3.4.2 Seasonality and variability of precipitation
3.4.3 Synoptic conditions driving snowfall
3.4.4 Temperature anomaly associated with precipitation events.
3.5 Conclusions
4 Warm synoptic event control of the snow isotope variability in East Antarctic Plateau evidenced from snow record and isotope-enabled atmospheric circulation model
4.1 Introduction
4.2 Material and methods
4.2.1 The isotope-enabled general circulation model ECHAM5-wiso
4.2.2 Snow isotope records
4.3 Annual dating of snow
4.3.1 Snow record age models
4.3.2 Comparison of accumulation records
4.4 Water stable isotopes in ECHAM5-wiso
4.4.1 Sensitivity to temperature and precipitation
4.4.2 Spatial correlation of isotope signal
4.5 Comparison of isotope records and climate from 2005 to 2014
4.5.1 Effect of post-deposition processes
4.5.2 Isotopic signature of the winters with warm events
4.5.3 Influence of the Southern Annular Mode
4.5 Calibration of the isotope – temperature slope
4.6 Conclusions
Appendix 4.A – Computation of weighted statistics
5 The Aurora Basin North main core
5.1 Motivation for ice coring in Aurora Basin North
5.2 Dating the ice
5.3 Accumulation history
5.4 Borehole temperature
5.5 Ice rheology
5.5.1 Ground penetrating radar
5.5.2 Elevation changes
5.5.3 Temperature changes
5.6 Water stable isotopes
5.6.1 Measurements of δ18O and δD
5.6.2 Flow-correction with spatial δ18O calibration
5.6.3 Conversion to temperature
5.6.4 Deuterium excess
5.6.5 17O-excess
5.7 Gas concentrations
5.8 Conclusion
6 Reconstruction of temperature from δ40Ar, δ15N, and borehole temperature 
6.1 Measurement of δ15N and δ40Ar from air trapped in ice
6.1.1 Wet extraction of Nitrogen and Argon gases
6.1.1.1 Ice preparation
6.1.1.2 Line preparation
6.1.1.3 Ice melt, oxygen removal, and transfer
6.1.2 Preparation of Air samples from free Atmosphere and firn
6.1.2.1 Air standards
6.1.2.2 Firn air samples
6.1.3 Mass Spectrometry
6.1.3.1 Description of the mass spectrometer
6.1.3.2 Introduction of gases
6.1.3.3 Measurement
6.1.4 Data calibration and correction
6.1.4.1 Pressure imbalance correction
6.1.4.2 Chemical Slope correction
6.1.4.3 Drift correction
6.1.4.4 Normalization to atmosphere
6.1.4.5 Argon gas loss
6.1.4.6 Detection of Outliers
6.1.4.7 Multiple-sample-based smoothing
6.2 Reconstruction of the temperature history
6.2.1 Quantification of gravitational and thermal fractionation of gases
6.2.2 Convection in the shallow firn and evolution of the lock-in depth
6.2.3 Gas Age model
6.2.3.1 Firn compaction
6.2.3.2 Adjustments with methane
6.2.3.3 Implications for the Lock-in Depth
6.2.4 Modeling of temperature diffusion in the firn and ice
6.2.5 Linearization and inversion of temperature history
6.2.5.1 Simulation of multiple scenarios bi of temperature history: forward model
6.2.5.2 Recombination of temperature history scenarios to match the temperature gradients estimated from gases
6.2.6 Sensitivity of temperature inversion
6.2.6.1 Influence of Borehole Temperature in the temperature inversion
6.2.6.2 Initial temperature hypothesis
6.2.6.3 Constant delta-temperature shift to firn-ice δ40Ar correction
6.2.6.4 Seasonal temperature cycle amplitude
6.2.6.5 Accumulation
6.2.6.6 Lock in depth
6.2.6.7 Summary
6.2.7 Glaciological correction
6.3 Conclusions on the temperature reconstruction
7 Climate interpretations of the Aurora Basin North data
7.1 Climate at ABN
7.1.1 Summary of the temperature records
7.1.2 Possible causes for the divergence of temperature reconstructions
7.1.2.1 Moisture source effect on the δ18O
7.1.2.2 Boundary layer changes
7.1.2.3 Change in seasonality of the precipitation events
7.1.2.4 Post deposition effects on water stable isotopes
7.2 Teleconnections and climate variability in the southern hemisphere during the last 2000 years
7.2.1 Comparison with other ice cores in the region
7.2.2 Influence of the Southern Annular Mode
7.2.3 Relationship with sea ice records
7.2.4 Relationship with Pacific South America patterns
7.2.5. Inter-hemispheric coupling
7.3 Conclusions
8 Conclusion and perspectives
8.1 The Aurora Basin North temperature record
8.2 Perspectives
8.2.1 Explore the influence of other climate modes on ABN temperature
8.2.2 Confirm our interpretations with further analyses
8.2.3 Further explore moisture source variability
8.2.4 Reproduce the 15Nexcess and borehole temperature inversion at other ice core locations