The kinetics of calcium carbonate, nucleation and growth María del Pilar Ramírez-García Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment October 2018 3 Declaration The candidate confirms that the work submitted is her own, except where work which has formed part of jointly-authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. The work in Chapter 4 of the thesis reproduces a manuscript in preparation for submission to Geology. Ramírez-García, M.P., Newton, R.J. and Benning, L.G., in prep. Temperature does not affect CaCO3 polymorph distribution in the Phanerozoic “aragonite” and “calcite” seas. MPRG performed all the experimental work, data collection and analyses, and concept development. ICP-MS analyses were carried out by S. Reid at the University of Leeds. EPMA analyses were carried out with the support of technical staff at the GeoForschungsZentrum Postdam. Data interpretation, writing and production of figures was done by MPRG with contributions from all co-authors. The work in Chapter 5 of the thesis reproduces a manuscript in preparation for submission to Geology. Ramírez-García, M.P., Newton, R.J. and Benning, L.G., in prep. The role of pCO2 on switching between calcite and aragonite seas. MPRG performed all the experimental work, data collection and analyses, and concept development. ICP-MS analyses were carried out by S. Reid at the University of Leeds. EPMA analyses were carried out with the support of technical staff at the GeoForschungsZentrum Postdam. Data interpretation, writing and production of figures was done by MPRG with contributions from all co-authors. The work in Chapter 6 of the thesis reproduces a manuscript in preparation for submission to Geochimica Cosmochimica Acta. 4 Ramírez-García, M.P., Newton, R.J. and Benning, L.G., in prep. Influence of magnesium, sulfate and temperature on calcium carbonate morphogenesis. MPRG performed all the experimental work, data collection and analyses, and concept development. ICP-MS analyses were carried out by S. Reid at the University of Leeds. The analyses of the precipitates were done by MPRG with support of technical staff at the University of Leeds. EPMA analyses were carried out with the support of technical staff at the GeoForschungsZentrum Postdam. Data interpretation, writing and production of figures was done by MPRG with contributions from all co-authors. For the work presented in Chapter 7 “The incorporation of Mg and SO4 into calcium carbonate and their possible role in regulating past ocean composition”: MPRG performed all the laboratory synthesis of precipitates. ICP-MS analyses were carried out by S. Reid at the University of Leeds. The analyses of the precipitates were done by MPRG with support of technical staff at the University of Leeds. EPMA analyses were carried out with the support of technical staff at the GeoForschungsZentrum Postdam. STXM experiments were completed by MPRG, LGB, RJN and McCutcheon, Jenine and technical staff at Canadian Light Source (CLS) and Diamond Light Source. Data processing was done by MPRG and technical staff at Diamond Light Source. The right of María del Pilar Ramírez-García to be identified as Author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988. © 2018 The University of Leeds and María del Pilar Ramírez-García 5 Acknowledgements I would like to thank Liane G. Benning and Robert J. Newton for always being immensely supportive and encouraging, for giving me endless opportunities to gain new experiences and enlarge my knowledge. They complement each other and form a balanced and easy-going team to work with. I would like to thank the whole Cohen geochemistry group, especially to Andrea, Adriana, Daniela and Taher for keeping me smiling. Special thanks to all the technicians (including those from GeoForschungsZentrum Postdam) for their help and awesome work in the labs. I am sincerely grateful to the Marie Skłodowska-Curie actions for sponsoring my PhD as part of the CO2-REACT Initial Training Research network and all the fancy network meetings I was allowed to go to. And finally, I must express my very profound gratitude to my family, who has always supported me, no matter what I decided to do, and special thanks to my husband Marce, without your unfailing support throughout these years, this thesis would simply not exist. 6 7 Abstract During the Phanerozoic, ocean chemistry has oscillated to favour the dominant non- biogenic polymorph of calcium carbonate (CaCO3) to be either calcite or aragonite. The main driving force controlling these aragonite-calcite seas conditions is the Mg:Ca ratio of seawater. However, other parameters such us SO4, temperature and partial pressure of carbon dioxide (pCO2) are also known to influence CaCO3 polymorph formation but are often overlooked in the context of aragonite-calcite seas. The main aim of this research project was to evaluate and quantify the key effects as well as the relative effects of changes in Mg:Ca ratio, SO4 concentration, temperature and pCO2 have on the formation, transformation and structure of CaCO3 phases, in order to provide a better synergistic approach than those taken by previous studies. We confirm seawater Mg:Ca ratio and SO4 concentration as dominant drivers since small differences in their values can be invoked as controlling the variation in abiotic CaCO3 polymorphs. We propose lower Mg:Ca and SO4 thresholds on seawater chemistry for calcite predominance seas (Mg:Ca≤ 0.65, SO4≤ 10 mM) than those suggested by the geological records (Mg:Ca≈ 2). Our work demonstrates that there is not a significant response of abiotic marine CaCO3 mineralogy to changing temperature. Our experimental data also reveal that neither changes in pCO2 in the range 400 to 3000 ppm, or their respective changes in seawater pH (8.2, to 7.6) lead to major variations in the stability fields for aragonite and calcite precipitation. Hence, the view of Phanerozoic aragonite-calcite seas should not be temperature and atmospheric pCO2 or seawater pH corrected. We validate abiogenic calcite Mg:Ca as a reliable and quantitative proxy for past global seawater temperature change if its dependence on both the temperature and the Mg:Ca ratio of the seawater is considered. We propose SO4 content in abiogenic calcite as a reliable and quantitative proxy for past seawater pH and atmospheric pCO2, but our results indicated that it is not possible to provide a single SO4–pH calibration and the use of seawater SO4-specific equations is needed. It can also be concluded that switches between aragonite and calcite seas calculated from the stability fields from our experimental results would only match the proxy 8 data for seawater chemistry in the geological record if the lowest suggested seawater SO4 concentrations are considered ([SO4] ≤ 10 mM). Furthermore, this study shows that Mg, SO4 and temperature significantly influence calcium carbonate morphology and addresses temperature turning out to be an important parameter for the control of particle size. 9 Table of Contents Acknowledgements .................................................................................................... 5 Abstract ...................................................................................................................... 7 Table of Contents ...................................................................................................... 9 List of Tables ........................................................................................................... 12 List of Figures .......................................................................................................... 13 List of Acronyms and Abbreviations..................................................................... 18 Chapter 1 Introduction ....................................................................................... 19 1.1. Background ............................................................................................... 19 1.2. Aims and objectives .................................................................................. 23 1.3. Thesis outline ............................................................................................ 25 References ........................................................................................................ 26 Chapter 2 Literature Review ............................................................................. 29 2.1. Chemical evolution of seawater during the Phanerozoic .......................... 29 2.1.1. Calcite - Aragonite seas ................................................................ 32 2.2. Carbonate mineralogy ............................................................................... 35 2.3. Influence of solution chemistry and physical factors on the formation and stability of CaCO3 ............................................................ 37 2.3.1. Magnesium .................................................................................... 38 2.3.2. Sulphate ......................................................................................... 40 2.3.3. Temperature .................................................................................