EFFECTS OF CLIMATE CHANGE AND PERTURBATION IN BIOGEOCHEMICAL CYCLES ON OXYGEN DISTRIBUTION AND OCEAN ACIDIFICATION by TERESA MARIE BEATY-SYKES Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON DECEMBER 2014 Copyright © by Teresa Marie Beaty-Sykes 2014 All Rights Reserved ii Dedication I dedicate my dissertation work to the memory of my father, Gerald W Beaty, for all the guidance and support throughout my life. It was his unconditional love, support, and encouragement that empowered me to pursue my love of science. I grew up watching him work miracles in the back yard using science and engineering. He built planes, model aircraft, and cars; sometimes building the needed parts from scratch. He had many talents and many hobbies. One of my fondest childhood memories was building the 16-inch telescope, which I still have to this day. He was my real-life MacGyver and an inspiration. My father was an amazing man who could fix anything, build anything, and fly anything. I only hope that I can become half the person he was and everything he hoped I could be. iii Acknowledgements I would like to acknowledge all those who have worked on and with the HAMOCC model; the late Dr. Ernst Maier-Reimer, Dr. Christoph Heinze, and Dr. Virginia Palastanga. I would also like to thank Dr. Heinze for the use of his plotting program. This dissertation would not have been possible without the guidance and patience of my Ph.D advisor Dr. Arne Winguth who introduced me to high-performance computing and set me on my way in a world that was totally alien to me at the beginning of this adventure. I would also like to thank all of my committee members Dr. Hu, Dr. Sattler, Dr. Griffith, and Dr. Mydlarz for their time and guidance on this project. Finally, I would like to thank my family, my daughter Genesis, and everyone who stood beside me, pushed me, and put up with me while I worked toward this degree. Plotting was accomplished on NCAR computers, which are supported by the National Science Foundation. This research is supported by NSF grants EAR-0628336 and EAR 0745817 as well as NSF STEM support and UTA graduate dissertation fellowship. November 21, 2014 iv Abstract EFFECTS OF CLIMATE CHANGE AND PERTUBATION IN BIOGEOCHEMICAL CYCLES ON OXYGEN DISTRIBUTION AND OCEAN ACIDIFICATION Teresa Marie Beaty-Sykes, PhD The University of Texas at Arlington, 2014 Supervising Professor: Arne Winguth Dissolved oxygen (DO) concentration in the ocean is an important component of the marine biogeochemical cycles. In this study a global oceanic carbon cycle model (HAMOCC 2.0) was used to address how oxygen minimum zones (OMZ) respond to changes due to CO2 radiative forcing. Atmospheric pCO2 was increased at a rate of 1% annually and the model is stabilized at 2 X, 4 X, 6 X, and 8 X preindustrial pCO2 levels. With an increase in CO2 radiative forcing, the OMZ in the Pacific Ocean was controlled largely by changes in particulate organic carbon (POC) export. In contrast, the vertical expansion of the OMZs within the Atlantic and Indian Oceans were the result of changes to oxygen solubility. Changes in oxygen solubility also lead to the formation of a new OMZ in the western sub-tropical Pacific Ocean. The response of the pH value to a total carbon emission of 4480 PgC or 8 times preindustrial pCO2 was found to be comparable to the ocean acidification at the PETM (56 Ma). The HAMOCC 2.0 simulations indicate a significant relationship between the pH value and the DO concentration at intermediate depth. This can lead to stress for the marine ecosystem by further decreasing pH due to respiratory processes. Improved parameterization may enhance the predictability of regions with low DO concentrations and pH value. A 50% increase in atmospheric dust deposition did not significantly alter the regions of Fe limitation of export production and v hence did not resulted in significant changes in DO in the twilight zone and at intermediate depth. However, a 50% reduction in dust deposition significantly expanded the regions of Fe-limited export production thereby reducing the vertical particle flux of POC and the extent of the OMZs. This counteracted the OMZ expansion due to the increased CO2 radiative forcing. vi Table of Contents Acknowledgements ............................................................................................................ iv Abstract .............................................................................................................................. v List of Illistrations………………………………………………………………………………….x List of Tables ................................................................................................................... xvii Chapter 1 Introduction ....................................................................................................... 1 1.1 Climate change ........................................................................................................ 1 1.2 Biogeochemical cycles and dissolved oxygen distribution in the ocean .................. 5 1.2.1 Marine carbon cycle ......................................................................................... 5 1.2.2 Marine phosphorus cycle ................................................................................. 9 1.2.3 Dissolved ocean oxygen distribution .............................................................. 11 Chapter 2 Objectives ....................................................................................................... 13 2.1 Introduction ............................................................................................................ 13 2.2 Response of the oxygen minimum zone and pH value to CO2 radiative forcing ... 13 2.3 Reduced biology and atmospheric oxygen concentration experiments ................. 16 2.4 Fe fertilization experiments .................................................................................... 17 Chapter 3 HAMOCC 2.0 Model Description and Reference Simulation .......................... 21 3.1 Model description ................................................................................................... 21 3.2 The reference experiment ...................................................................................... 30 3.2.1 Initial and boundary conditions used .............................................................. 30 3.2.2 Reference run results and discussion ............................................................ 32 Chapter 4 Response of Export Production and Dissolved Oxygen Concentrations to pCO2 and Temperature Stabilization Scenarios .............................................................. 42 4.1 Introduction ............................................................................................................ 42 4.2 Experimental design .............................................................................................. 43 vii 4.3 Results ................................................................................................................... 45 4.3.1 Sensitivity of the dissolved oxygen distribution to reduced biological pump and atmospheric pO2 ...................................................................................................... 45 4.3.1.2 Sensitivity of dissolved oxygen to reduced atmospheric pO2 ...................... 46 4.3.2 Sensitivity of the oxygen minimum zone to CO2 radiative forcing .................. 47 4.3.2.4 Simulated OMZ formation in the western tropical Pacific Ocean in response to CO2 radiative forcing. .......................................................................................... 54 4.4 Discussion ............................................................................................................. 59 4.5 Conclusion and future research ............................................................................. 64 Chapter 5 Response of Ocean Acidification to Anthropogenic-Induced Carbon Emission ........................................................................................................................... 69 5.1 Introduction ............................................................................................................ 69 5.2 Experimental design .............................................................................................. 71 5.3 Results ................................................................................................................... 71 5.3.1 Sensitivity of ocean acidification to atmospheric carbon input. ...................... 71 5.3.2 Regression analyses of O2, total DIC, and pH. .............................................. 75 5.4 Discussion ............................................................................................................. 79 5.5 Conclusion and future research ............................................................................. 83 Chapter 6 Affects of Changes in Atmospheric Dust Deposition on Iron Fertilization and Dissolved Oxygen Concentration in the Ocean ............................................................... 86 6.1 Introduction ............................................................................................................ 86 6.2 Experimental design .............................................................................................. 87 6.3 Results ..................................................................................................................