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Oxygen and Carbon Isotopes and Coral Growth in the Gulf Of View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Texas A&M University OXYGEN AND CARBON ISOTOPES AND CORAL GROWTH IN THE GULF OF MEXICO AND CARIBBEAN SEA AS ENVIRONMENTAL AND CLIMATE INDICATORS A Dissertation by AMY JO WAGNER Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2009 Major Subject: Oceanography OXYGEN AND CARBON ISOTOPES AND CORAL GROWTH IN THE GULF OF MEXICO AND CARIBBEAN SEA AS ENVIRONMENTAL AND CLIMATE INDICATORS A Dissertation by AMY JO WAGNER Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Niall C. Slowey Committee Members, Benjamin Giese Ethan Grossman Thomas P. Guilderson Deborah J. Thomas Head of Department, Piers Chapman December 2009 Major Subject: Oceanography iii ABSTRACT Oxygen and Carbon Isotopes and Coral Growth in the Gulf of Mexico and Caribbean Sea as Environmental and Climate Indicators. (December 2009) Amy Jo Wagner, B.S., Texas A&M University at Galveston; M.S., Texas A&M University Chair of Advisory Committee: Dr. Niall C. Slowey The Gulf of Mexico and Caribbean Sea comprise a sensitive and important region, both oceanographically and climatically. A better understanding of the history of climate and marine environmental conditions in this region provides valuable insight into the processes that affect climate globally. This dissertation furthers our understanding of these factors via investigations of the isotopes of corals and seawater, as well as coral growth. Results improve our understanding of how the isotope and coral growth records from the Gulf of Mexico and Caribbean Sea reflect recent environmental conditions, enhancing our ability to reconstruct the history of climate in this important region. Analysis of the relationship between salinity and oxygen isotopic composition of seawater from the Texas/Louisiana continental shelf and Flower Garden Banks yield improved understanding of the relative contribution of the fresh water sources into the northern Gulf of Mexico, and also the oxygen isotopic composition of open-ocean seawater in this region. Variations in the growth of long-lived coral cores from the Flower Garden Banks are compared to local and regional climate conditions, particularly winter air temperatures. During the latter half of the twentieth century, a close correlation has existed between slow coral growth and cold wintertime air temperatures along the Gulf Coast, which are due to a meridional orientation of the North American jet stream iv (associated with the Pacific/North American climate pattern). Existing long coral growth records are too limited to assess this relationship during earlier years. Knowledge of the marine radiocarbon (14C) reservoir age is important for understanding carbon cycling and calibrating the radiocarbon ages of marine samples. Radiocarbon concentrations in corals from the Flower Garden Banks, Veracruz, and the Cariaco Basin are measured and used to determine the surface ocean 14C reservoir ages for the Gulf of Mexico and Caribbean Sea. Results also indicate that the post-nuclear weapons testing Δ14C values of the Gulf of Mexico and Caribbean Sea differ. This difference is attributed to the advection of 14C-depleted surface water from the Southern Hemisphere into the Caribbean Sea. The results reported in this dissertation provide valuable information for understanding the marine environment when using carbonate proxies to study and reconstruct past climate and marine conditions in the Gulf of Mexico and Caribbean. v DEDICATION To my parents, Bob and Ruth Ann Wagner vi ACKNOWLEDGEMENTS I thank my committee chair, Dr. Slowey, and my committee members, Dr. Giese, Dr. Thomas, Dr. Grossman, and Dr. Guilderson for their patience, guidance and support throughout the course of this research. I would like to extend my gratitude to the Department of Energy Global Change Education Program (GCEP) Graduate Research Environmental Fellowship (GREF) for funding my graduate work and the Texas Sea Grant for providing the funding for this research. Much thanks goes to the crew of the M/V Fling; the Flower Garden Banks National Marine Sanctuary (FGBNMS) staff, E. Hickerson, G.P. Schmal, L. Kurjelja; the Florida Keys National Marine Sanctuary staff, J. Halas, B. Causey, A. Massey; U.S. Geological Survey staff, D. Hichey, C. Reicht; and S. Gittings, and S. Francis for all their help in making a successful coral drilling cruise. I would also like to extend thanks to those who collected water samples for me, E. Hickerson, D. Weaver, K. Deslarzes, S. Meyer-Franco, R. Long, and S. DiMarco. I would also like to thank C. Schmit and R. Mortlock for performing salinity and oxygen isotope analyses. Thanks goes out to my friends and colleagues from the Oceanography Department for making my time at Texas A&M University a great experience. Finally, thanks to my family for their encouragement and never ending support. And thank you to Michael for being so patient and understanding. You have been my rock and I couldn’t have done this without you. vii TABLE OF CONTENTS Page ABSTRACT.............................................................................................................. iii DEDICATION .......................................................................................................... v ACKNOWLEDGEMENTS ...................................................................................... vi TABLE OF CONTENTS.......................................................................................... vii LIST OF FIGURES................................................................................................... ix LIST OF TABLES .................................................................................................... xi CHAPTER I INTRODUCTION................................................................................ 1 II BACKGROUND AND SETTING ...................................................... 4 Gulf of Mexico and Caribbean Sea ................................................ 4 Surface Currents............................................................................. 6 Atmospheric Circulation Patterns .................................................. 8 Sample Sites................................................................................... 10 III OXYGEN ISOTOPES IN SEAWATER ............................................. 17 Introduction .................................................................................... 17 Study Area...................................................................................... 18 Sample Collection and Analytical Methods................................... 23 Results and Discussion................................................................... 24 Summary and Implications............................................................. 29 IV CORAL GROWTH AND CLIMATE VARIABILITY....................... 32 Introduction .................................................................................... 32 Methods.......................................................................................... 33 Results and Discussion................................................................... 39 Conclusions and Implications ........................................................ 54 viii CHAPTER Page V RADIOCARBON................................................................................. 56 Introduction .................................................................................... 56 Background .................................................................................... 60 Methods.......................................................................................... 63 Pre-bomb Results and Discussion.................................................. 65 Post-bomb Results and Discussion ................................................ 70 Summary and Conclusions............................................................. 73 VI CONCLUSIONS.................................................................................. 76 Summary ........................................................................................ 76 Implications.................................................................................... 78 REFERENCES.......................................................................................................... 79 APPENDIX A ........................................................................................................... 91 APPENDIX B ........................................................................................................... 96 APPENDIX C ........................................................................................................... 102 VITA ......................................................................................................................... 106 ix LIST OF FIGURES FIGURE Page 2-1. Map of the Caribbean Sea and Gulf of Mexico ......................................... 5 2-2. PNA Schematic .......................................................................................... 9 2-3. Map of the north-central Gulf of Mexico showing the location of the Flower Garden Banks................................................................................. 11 2-4. Map of the Veracruz Reef System (VRS) off
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