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From Greenhouse to Icehouse: Understanding Earth's Climate Extremes Through Models and Proxies

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From Greenhouse to Icehouse: Understanding Earth's Climate Extremes Through Models and Proxies From Greenhouse to Icehouse: Understanding Earth’s Climate Extremes Through Models and Proxies Clay Richard Tabor A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology) in the University of Michigan 2016 Doctoral Committee: Professor Chris J. Poulsen, Chair Associate Professor Jeremy N. Bassis Associate Professor Brian K. Arbic Senior Scientist David Pollard Acknowledgements Foremost, I would like to thank my advisor Chris Poulsen for his exceptional mentoring throughout my time as a graduate student. My accomplishments over the past five and a half years were the result of his continual assistance, understanding, and friendship. I look forward to our continuing and future collaborations. I would also like to thank my collaborator and committee member Dave Pollard. His impressive body of work and guidance were the foundation for my research; my dissertation would not have been possible without his help. To my other committee members, Brian Arbic and Jeremy Bassis, who graciously gave their time to many fruitful conversations, I would like to thank you for your help improving this dissertation. Thanks to my other collaborators, Bette Otto-Bleisner, Nan Rosenbloom, and Dan Lunt, for sharing your experience and research with me; I am excited about our ongoing collaboration. I would like to thank the past and current members of the Climate Change Research Lab for their numerous discussions and friendship over the years. Ran Feng, Rich Fiorella, Louise Jeffery, Dan Horton, Jing Zhou, Adam Herrington, Nadja Insel, Sierra Petersen, Chris Skinner, Chana Tilevitz, Phoebe Aron, Alex Thompson, Hong Shen, and Dan Lowry, you all have kept the lab both entertaining and productive. Further I would like to thank Mike Messina for tolerating my Unix ignorance time and time again. Beyond research, I am grateful to my friends. They have been a constant source of relaxation, entertainment, and support throughout my graduate career. I would not have made it this far without them. Finally, I would like to thank my family, especially my parents, who have always supported and believed in me, even when I clearly have no idea what I am doing. Thank you for reading! ii Table of contents Acknowledgements ....................................................................................................................... ii List of figures .............................................................................................................................. vii List of tables ............................................................................................................................... viii Chapter 1 Introduction ................................................................................................................................... 1 1.1 Motivation ............................................................................................................................ 1 1.2 Methods ................................................................................................................................ 2 1.3 Background .......................................................................................................................... 2 1.3.1 Quaternary ice ages ........................................................................................................ 2 1.3.2 Cretaceous Greenhouse .................................................................................................. 4 1.4 Outline .................................................................................................................................. 5 1.5 Publications and abstracts resulting from this dissertation ............................................ 6 Chapter 2 Mending Milankovitch Theory: Obliquity Amplification by Surface Feedbacks ................. 11 2.1 Abstract .............................................................................................................................. 11 2.2 Introduction ....................................................................................................................... 11 2.3 Methods .............................................................................................................................. 13 2.4 Results ................................................................................................................................. 15 2.4.1 Climate-only experiments ............................................................................................ 15 2.4.2 Climate-ice sheet experiments ...................................................................................... 20 2.5 Discussion and conclusion ................................................................................................. 22 2.6 Caveats ................................................................................................................................ 24 2.7 Acknowledgements ............................................................................................................ 26 2.8 Appendix A ......................................................................................................................... 26 iii Chapter 3 How Obliquity Cycles Powered Early Pleistocene Global Ice-Volume Variability .............. 34 3.1 Abstract .............................................................................................................................. 34 3.2 Introduction ....................................................................................................................... 34 3.3 Methods .............................................................................................................................. 36 3.3.1 Earth system model ...................................................................................................... 36 3.3.2 Experiment design ........................................................................................................ 37 3.4 Results ................................................................................................................................. 37 3.4.1 Ice-volume spectral power ........................................................................................... 37 3.4.2 Climate signal decomposition ...................................................................................... 38 3.4.3 Summer season feedbacks ............................................................................................ 39 3.4.4 Precession seasonal insolation offset ............................................................................ 41 3.4.5 Cycle frequencies and nonequilibrium ......................................................................... 42 3.5 Discussion ........................................................................................................................... 43 3.5.1 Orbital bias ................................................................................................................... 43 3.5.2 Ice-volume hemispheric offset ..................................................................................... 44 3.5.3 GHG fluctuations .......................................................................................................... 45 3.5.4 Response changes after the mid-Pleistocene transition ................................................ 45 3.6 Conclusion .......................................................................................................................... 46 3.7 Acknowledgements ............................................................................................................ 46 3.8 Appendix B ......................................................................................................................... 46 Chapter 4 Simulating the Mid-Pleistocene Transition Through Regolith Removal ............................... 56 4.1 Abstract .............................................................................................................................. 56 4.2 Introduction ....................................................................................................................... 56 4.3 Methods .............................................................................................................................. 58 4.3.1 Model and Coupling ..................................................................................................... 58 4.3.2 Experiment Design ....................................................................................................... 59 4.4 Results ................................................................................................................................. 61 4.4.1 Ice-Volume and Area ................................................................................................... 61 iv 4.4.2 Spectral Power .............................................................................................................. 64 4.4.3 Ice Dynamics ................................................................................................................ 64 4.4.4 Climate feedbacks ........................................................................................................ 66 4.5 Discussion ........................................................................................................................... 69 4.5.1 Role of CO2 .................................................................................................................
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