Simulating Transient Climate Evolution of the Last deglaciation with CCSM3 by Feng He A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF SCIENCES (Atmospheric and Oceanic Sciences) Supported by the Center for Climatic Research Gaylord Nelson Institute for Environmental Studies at the University of Wisconsin-Madison 2010 - 2 - Simulating Transient Climate Evolution of the Last deglaciation with CCSM3 by Feng He Under the supervision of Professor Zhengyu Liu ABSTRACT The transient climate evolution of last deglaciation (22,000 to 7,000 years ago) provides key observations for constraining climate sensitivity and understanding global carbon cycle. Here we present the first complete synchronously coupled atmosphere-ocean general circulation model simulation of the last deglaciation. Our model reproduces many major features of the deglacial climate evolution in Greenland, Antarctic, tropical Pacific, Southern and Deep Ocean, suggesting our model exhibits reasonable climate sensitivity in those regions and is capable of simulating abrupt climate change events. - 3 - In particular, our simulation supports the view that the last deglaciation is triggered by the enhanced spring-summer insolation locally in the Northern Hemisphere. Northern Hemisphere glacial meltwater is able to induce the early deglacial warming of the Southern and Deep Ocean, and accounts for the lead-lag relationship among the Southern Ocean, tropical Pacific and Northern Hemisphere observed during the last deglaciation. Furthermore, by inducing deep ocean warming and Southern Ocean sea ice retreat, Northern Hemisphere glacial meltwater likely plays an active role in deglacial CO2 rise and gives an explanation for the associations between Heinrich events and atmospheric CO2 rise. - 4 - ACKNOWLEDGEMENTS The completion of this thesis would have not been possible without the help from many people. I am deeply indebted to my adviser, Professor Zhengyu Liu, who brought me into the fascinating field of the paleoclimatology and provided me his full trust that I am capable of doing one of the most epic numerical modeling in the climate community to date. I am always encouraged by his passion on science and appreciate his special insights during our discussions. It is my great pleasure to have this opportunity to work under Professor Liu's guidance. I am also grateful to the other TraCE-21000 project members: Esther Brady, Anders Carlson, Peter Clark, Eric Davidson, Robert Jacob, Bette Otto-Bliesner, Nan Rosenbloom and Robert Tomas. With their encouragement, I had a smooth and quick start on my journey of the paleoclimate modeling. Their continuous scientific insights and technique supports guided me to eventually complete transient simulation of the last 21,000 years in CCSM3 within three years. I am also grateful to my PhD committee members: Anders Carlson, Matt Hitchman, Zhengyu Liu, Galen McKinley and Jack Williams. Without their encouragement and scientific comments, I cannot complete my PhD thesis. I would also like to thank Pat Behling and Kevin Braun for computer assistant and advice on this study. I also want to express my gratitude to Julie Nielson for her excellent administrative work that provided the most comfortable research environment I ever had. I would also want to thank all the faculties and researchers in CCR, especially the students in our research group: Jun Cheng, Yafang Zhong, Yun Liu, Guangshan Chen, Wei Liu, - 5 - Shu Wu, John-Paul Argenti. The weekly student meeting has always broadened my horizon on climate research. A special thanks goes to my bachelor thesis adviser, Dr. Jiwei Tian, who introduced me into global climate research and provided me with the framework of my knowledge on climate dynamics. I am also grateful for the support from my parents and parent-in-laws. It is their prayers that helped me to overcome the difficulties. As always, my wife, Xiaoyi Sun and my son, Zijun He (Le Le), deserve the most gratitude from me. We enjoy every minute of our life and share with each other the happiness as well as the sadness. It is their love that gives me the strength to move forward and enjoy my work as a climate researcher. I would like to thank Michael Notaro, Steve Vavrus, John Kutzbach, Kenji Kawamura, and Jinming Yu for very useful comments at various stages of this study. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. The simulation was conducted on supercomputers Phoenix and Jaguar and the results were analyzed on the analysis server lens. - 6 - Contents Abbreviations: ............................................................................................................................. - 9 - Chapter 1 Transient climate evolution of the last deglaciation ........................................... - 10 - 1.1 Greenland and Antarctic temperature ........................................................................ - 10 - 1.2 Northern hemisphere ice sheet ................................................................................... - 12 - 1.3 Northern hemisphere insolation ................................................................................. - 12 - 1.4 Atmosphere CO2 concentration .................................................................................. - 13 - 1.5 Atlantic meridional overturning circulation (AMOC) ............................................... - 14 - 1.6 Challenges of transient simulation of the last deglaciation ........................................ - 15 - References ............................................................................................................................. - 17 - Figure Captions: .................................................................................................................... - 22 - Figures: ................................................................................................................................. - 23 - Chapter 2 TraCE-21000 simulation ..................................................................................... - 25 - 2.1 Introduction ................................................................................................................ - 25 - 2.2 Model setup: ............................................................................................................... - 25 - 2.3 Meltwater forcing: ...................................................................................................... - 27 - 2.4 TraCE-21000 scheme: ................................................................................................ - 28 - 2.4.1 Spin-up: the LGM simulation with DGVM ........................................................ - 28 - 2.4.2 22~19ka: the role of transient orbital forcing ..................................................... - 28 - 2.4.3 The sensitivity of AMOC and Greenland temperature to the location of meltwater forcing at the LGM ........................................................................................................... - 31 - 2.4.4 The sensitivity of AMOC and Greenland temperature to the magnitude of meltwater forcing at the LGM .......................................................................................... - 34 - 2.4.5 TraCE-21000 simulation of H1 .......................................................................... - 35 - 2.4.6 AMOC hysteresis ................................................................................................ - 36 - 2.4.7 TraCE-21000 simulation between H1 and BA ................................................... - 39 - 2.4.8 TraCE-21000 simulation of MWP-1A................................................................ - 47 - 2.4.9 TraCE-21000 simulation between MWP-1A and YD ........................................ - 51 - 2.4.10 TraCE-21000 simulation of YD.......................................................................... - 52 - 2.4.11 TraCE-21000 simulation of Holocene ................................................................ - 58 - 2.5 Summary .................................................................................................................... - 62 - References ............................................................................................................................. - 65 - Figure captions: ..................................................................................................................... - 74 - Tables: ................................................................................................................................... - 83 - - 7 - Figures: ................................................................................................................................. - 95 - Chapter 3 North hemisphere meltwater and the last deglaciation ..................................... - 121 - 3.1 Introductions............................................................................................................. - 121 - 3.2 The simulation of deglacial climate evolution ......................................................... - 122 - 3.3 The deglacial phasing between NH, SH and Tropics............................................... - 124 - 3.4 The trigger for the initial NHMW ............................................................................ - 126 - 3.5 Deep ocean warming and atmospheric CO2