Variations in climatic conditions from the Cayman Islands through stable isotope and element analyses from corals and sediment cores; a 500,000 year record by Simone Booker A thesis submitted in partial fulfi llment of the requirements for the degree of Doctor of Philosophy Department of Earth and Atmospheric Sciences University of Alberta © Simone Booker, 2020 ii ABSTRACT The Caribbean region is particularly important to understanding global climate change and feedback systems because the tropics are the primary source of heat and water vapor for the atmosphere. The Caribbean region, however, is a relatively understudied area in terms of tracking climate change through time. The Cayman Islands, specifi cally, have little documentation of climate change before the 1980’s, apart from anecdotal records of past storms. Climate change has been increasingly studied in recent years due to the current and proposed future impacts of such changes on global environments. Numerous proxies (δ18O, δ13C, Sr/Ca, Mg/Ca, U/Ca, Sr-U, Li/Ca, Li/Mg, Mg/Li, Ba/Ca, B11/Ca, trace and rare earth elements) for past environmental conditions (sea surface temperature (SST), salinity, photosynthetic light activity, water depth, upwelling, riverine run-off , atmospheric moisture variability) have been developed for use with coral skeletons and sediment cores. The application of these proxies, however, is complicated as many factors that may control the incorporation of these proxies into the geologic records (vital eff ects, geographic location, sampling analytics) are still debated. Interpretations based on geochemical proxies (stable isotope, element/Ca ratios, and elemental concentrations) derived from sediment cores and modern and fossil corals (Orbicella annularis and Montastrea cavernosa) from the Cayman Islands over the last 500,000 years record alternating cool (SST < 28.5°C; current average water temperature for Grand Cayman) and warm (SST >28.5°C) periods in the Caribbean Sea. Coral skeletons from Grand Cayman and Cayman Brac are the baseline for the development of an oxygen isotope geothermometer that accurately reconstructs SST within the range of measured Caribbean water temperatures. Using this δ18O- geothermometer, these coral skeletons record two cool periods, one warm period, and one mild period over the last ~540 years around the Cayman Islands. These temperature periods correlate with climate change in the wider Caribbean region. Oxygen isotopes compositions and elemental concentrations from sediment cores in North Sound, iii Grand Cayman’s largest lagoon, record fi ve periods of climate (SST and atmospheric moisture variability) change over the last ~6000 years. These climate periods correlate to phases of climatic variability in the Caribbean and at higher latitudes in the Northern Hemisphere. The global nature of these climate periods can be related to the movements of the Intertropical Convergence Zone and the phase of the North Atlantic Oscillation. Although it has been shown that modern corals can reliably reconstruct SST, application to older corals is more complicated. Determination of SST from older corals is only possible if their aragonitic skeletons have undergone little to no diagenetic alteration. For corals from the Pleistocene Ironshore Formation (Units A-F; 80 to 500 ka), SST calculations are only viable if the coral skeleton has >95wt% aragonite, no 18 cements, Mg/Ca ratios <12.0 mmol/mol, Sr/Ca ratios >8.0 mmol/mol, δ OVSMOW values 13 >25.1‰, and δ CVPDB values >–3.0‰. Based on these criteria the corals from Units A-C (229 to 500 ka) cannot be used, whereas those from Units D-F (125 to 80 ka) produce reliable SST records. The temperature profi les developed from U nits D-F correlate with temperature reconstructions from other localities during the Pleistocene (e.g., the Caribbean, North Atlantic, Coral Sea, South China Sea, and Antarctica). This work is signifi cant as tracking changes in climate from the past may provide indicators for future climate trends. iv PREFACE This thesis is the original work completed by Simone Booker, with the assistance of Dr. Brian Jones. The overall theme of this thesis was initially outlined by Dr. Jones and then developed through discussions between the two of us. Chapters three and fi ve of this thesis were published as the following two papers: Booker, S., Jones, B., Chacko, T., Li, L., 2019. Insights into sea surface temperatures from the Cayman Islands from corals over the last ~540 years. Sedimentary Geology, 389, 218-240. The samples and measured water temperature data for this paper came from the Department of Environment, Cayman Islands. For this paper, I undertook the data analysis and produced the initial drafts of the manuscript, which were extensively edited by Dr. Jones. Co-authors provided valuable feed-back throughout the preparation of this manuscript. Booker, S., Jones, B., Li, L., 2020. Diagenesis in Pleistocene corals (80 to 500 ka) corals from the Ironshore Formation: implications for paleoclimate reconstructions. Sedimentary Geology, 399. This paper was based on samples collected by Dr. Jones over the last 30 years. I performed the data analysis and produced the initial drafts of the manuscript, which were extensively edited by Dr. Jones. The co-author provided valuable feed-back throughout the preparation of this manuscript. Chapter two: Assessing the applicability of nine element/Ca proxies for paleotemperature reconstructions using modern tropical corals: insights into the future of element/Ca geothermometry. The samples and measured water temperature data used in this chapter came from the Department of Environment, Cayman Islands. For this paper, I undertook the data analysis and produced the initial drafts of the manuscript, which were extensively edited by Dr. Jones. v Chapter four: A 6000 year record of chnage from stable isotopes and rare earth elements from sediment cores from North Sound lagoon, Grand Cayman, B.W.I. The samples used in this chapter were collected by Dr. Jones in the 1980’s. I performed the data analysis and produced the initial drafts of the manuscript, which were edited by Dr. Jones. All papers refl ect the fact that all authors were actively involved in their development and writing. vi ACKNOWLEDGEMENTS There are many people I would like to thank for helping and supporting me throughout this thesis research. I am grateful to my supervisor Dr. Brian Jones for his advice, encouragement, constructive criticism, patiences, innumerable hours of editing, allowing me to go on many trips to expand my scientifi c knowledge, and for helping me build up my rhinoceros’ skin. Without his help I would not have been able to complete this thesis! As well as T. Austin and G. Ebanks-Petrie, the Department of Environment, Cayman Islands who collected the corals that were used in this study and imported them to the University of Alberta with a CITES Export Permit; The Water Authority and Department of Environment of the Cayman Islands, who provided and gave permission to use the water temperature data from Grand Cayman. I would also like to thank Dr. Long Li for providing his laboratory for the stable isotope analyses, Dr. Thomas Chacko for his help in developing the oxygen-isotope geothermometer used in this study, Drs. Duane Froese and Dr. Alberto Reyes for help interpreting the carbon-14 dates used in this study, Dr. Murray Gingras for providing his X-Ray machine, Dr. Andy DuFrane and Mr. Guangecheng Chen for providing the laboratory and running the ICP-MS analyses, Dr. Nathan Gerein, who took the SEM photomicrographs, Mrs. Diana Caird, who ran the XRD analyses, Mr. Mark Labbe for cutting the coral specimens, Mr. Mark van Dollen and Mr. Walter Harley for making the thin sections, Ms. Kathrine Snihur who did the element water analyses, and Mrs. Shanna Cameron, Innotech Alberta, who operated the CT scanner used in this study. Thanks must also be given to the Natural Science Sciences and Engineering Research Council of Canada (Grant A635 to Jones) for providing the funding for this research. Lastly, I would like to thank my family for the constant support and encouragement over the course of my project! vii TABLE OF CONTENTS CHAPTER 1: INTRODUCTION 1 1. Introduction 1 2. Study area and methods 6 2.1. Study area 6 2.2. Samples 11 2.3. Methods 11 2.3.1. Coral samples 11 2.3.2. Sediment cores 12 2.3.3. Water samples 13 3. Previous work 14 3.1. Geochemical proxies 14 3.2. Corals 15 3.3. Sediment cores 16 3.4. Ironshore Formation 17 4. Objectives 18 References 20 CHAPTER 2: REVIEW OF ELEMENT/CA PROXIES FOR DERIVING PALEOTEMPERATURES FROM MODERN TROPICAL CORALS: INSIGHTS INTO THE FUTURE OF ELEMENT/CA GEOTHERMOMETRY 30 1. Introduction 30 2. Datasets 32 3. Element/Ca geothermometers 34 viii 3.1. Sr/Ca ratios 35 3.2. Mg/Ca ratios 36 3.3. U/Ca ratios 37 3.4. Sr-U 38 3.5. Li/Ca ratios 39 3.6. Li/Mg and Mg/Li ratios 40 3.7. Ba/Ca ratios 40 3.8. B11/Ca ratios 42 4. Vital eff ects 42 4.1. Interspecies and intraspecies diff erences 43 4.2. Size, age, and growth rate 44 4.3. Corals microstructure 46 4.4. Rayleigh fractionation 47 4.5. Temporal change in vital eff ects 48 5. Geographic variability 49 6. Sampling analytics 50 6.1. Instrument measured water temperatures 50 6.2. Methodology 50 7. Calculated water temperature 55 7.1. Sr/Ca geothermometry 55 7.2. Mg/Ca geothermometry 55 7.3. U/Ca geothermometry 59 7.4. Sr-U geothermometry 59 7.5. Li/Ca geothermometry 61 7.6. Li/Mg and Mg/Li geothermometry 61 7.7. Ba/Ca geothermometry 62 7.8. B11/Ca geothermometry 62 8. Cayman coral temperature reconstruction 62 8.1.