Boron proxies (δ11B and B/Ca) were introduced nearly three decades ago, with subsequent strides being made in understanding their mechanistic functioning. This text reviews current knowledge about the aqueous systematics, the inorganic and biological controls on boron isotope fractionation and incorporation into marine carbonates, as well as the analytical techniques for measurement of boron proxies. Laboratory and field calibrations of the boron proxies are summarized, and similarities between modern calibrations are explored to suggest estimates for proxy sensitivities in marine calcifiers that are now extinct. Example applications illustrate the potential for reconstructing paleo-atmospheric pCO2 from boron isotopes. Also explored are the sensitivity of paleo-ocean acidity and pCO2 reconstructions to boron isotope proxy systematics that are currently less well understood, including the elemental and boron isotopic composition of seawater through time, seawater alkalinity, temperature and salinity, and their collective impact on the uncertainty of paleo-reconstructions.
The B/Ca proxy is based on the same mechanistic principles as the boron isotope proxy, but empirical calibrations suggest seawater pH is not the only controlling factor. B/Ca therefore has the potential to provide a second carbonate parameter that could be paired with δ11B to fully constrain the ocean carbonate system, but the associated uncertainties are large. This text reviews and examines what is currently known about the B/Ca proxy systematics. As more scientists embark on characterizing past ocean acidity and atmospheric pCO2, Boron in Paleoceanography and Paleoclimatology provides a resource to introduce geoscientists to the opportunities and complications of boron proxies, including potential avenues to further refine them.
Table of Contents
Preface vii
Acknowledgments viii
About the Companion Website ix
1 Introduction and Concepts 1
1.1 Why Are we Interested in Reconstructing Marine Carbonate Chemistry? 1
Acknowledgments 8
References 8
Further Reading/Resources 12
2 Boron Systematics 13
2.1 Introduction 14
2.2 What Determines the Sensitivity of δ11B and B/Ca to Marine Carbonate Chemistry? 15
2.3 Boron Proxy Systematics in Synthetic Carbonates 21
2.4 Boron Isotopes in Biogenic Marine Carbonates 42
2.5 Secular Evolution of [BT] and δ11B in Seawater 81
2.6 The B/Ca Proxy in Foraminifera 88
References 105
3 Reconstructing Paleo‐Acidity, pCO2 and Deep‐Ocean [CO32-] 120
3.1 Introduction 120
3.2 Estimating Paleoseawater pH from Boron Isotopes 122
3.3 Estimating Marine Carbonate Chemistry from B/Ca Ratios 150
3.4 Guidelines for Selecting Sediment Core Sites and Sample Sizes 155
References 156
4 Boron Concentration and Isotope Ratio Analysis 165
4.1 Introduction 165
4.2 Inter‐Laboratory Comparison Studies 170
4.3 Standard Reference Materials and Data Quality Assurance 172
4.4 Boron Concentration and Isotope Ratio Analysis 175
4.5 Sample Preparation and Cleaning 179
4.6 Boron Separation and Purification 183
4.7 Instrumental Techniques 188
4.8 Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) 201
4.9 Secondary Ion Mass Spectrometry (SIMS) 204
4.10 Other Techniques 206
4.11 Outlook and Future Directions 210
References 211
Index 224
