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The Hydrologic Evolution of Glacial Meltwater: Insights and Implications from Alpine and Arctic Glaciers

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The Hydrologic Evolution of Glacial Meltwater: Insights and Implications from Alpine and Arctic Glaciers The Hydrologic Evolution of Glacial Meltwater: Insights and Implications from Alpine and Arctic Glaciers by Carli Anne Arendt A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Earth and Environmental Sciences) in the University of Michigan 2015 Doctoral Committee: Assistant Professor Sarah M. Aciego, Chair Assistant Professor Jeremy N. Bassis Professor M. Clara Castro Associate Professor Eric A. Hetland Professor Kyger C. Lohmann ACKNOWLEDGMENTS I would like to thank the University of Michigan and the Department of Earth and Environmental Sciences (Geology) for assisting me in my journey to obtain the skills necessary to build my career as a scientist. The majority of my graduate school accomplishments have stemmed from my acquaintance with and mentorship from my thesis adviser, Dr. Sarah Aciego who graciously welcomed me into her lab, convinced me to invest in obtaining a doctorate, and provided me with an abundance of opportunities for which I am incredibly grateful. More importantly, Sarah has been an exemplary role model of what it means to be a successful, young, strong female scientist and has shown me how to gracefully approach countless scenarios that beginning female scientists typically encounter. I would also like to thank the other members of my dissertation committee: Dr. Jeremy Bassis, Dr. Clara Castro, Dr. Eric Hetland, and Dr. Kacey Lohmann for helping me become a better scientist through their continued support and advice, for challenging me to look at my own research critically. I would also like to thank the numerous others who supported me on this academic journey and encouraged me when I encountered challenges along the way. It would be impossible to name everyone who has helped contribute to my success but I would like to recognize: my fiancée and primary support system Ethan Hyland, my GIGL lab members and field companions Emily Stevenson, Yi-Wei Lui, Molly Blakowski and my roommate Sarah Aarons for being supportive of me for my entire journey here at the University of Michigan, the official and unofficial ii members of GEOFRAT who helped me grow along the way Rohit Warrier, Jen Cotton, Rich Fiorella, Tara Smiley, Petr Yakolvev, Clay Tabor, Say Yun Kwon, Katie Loughney, Lydia Staish, Laura Waters and many more, the UMich EARTH office staff especially Anne Hudon for all of their guidance and assistance over the years, my completely loving and supporting parental unit and sister, my undergraduate advisers Dr. Tim Flood and Dr. Nelson Ham for encouraging me to pursue higher education and believe in myself, Dr. Henry Pollack for being a continued inspiration and role model, and the faculty, researchers, postdocs, and students in this department who have helped make the University of Michigan feel like home. SPECIFIC CHAPTERS Chapter 2 This research was funded by the University of Michigan Rackham Graduate School and the Turner Award from the Department of Earth and Environmental Sciences to CAA. I would like to thank Sarah Aarons for her assistance in the collection of samples used for the Athabasca Glacier case study. Datasets supporting this manuscript are available in Supporting Online Material Table S1 and Table S2. I would also like to thank Dr. Sarah Das, Dr. Maya Bhatia, and Dr. Oliver Chadwick for their cooperation and assistance in obtaining the isotopic values and fractional contribution estimations from the original studies of the data used in case studies two and three. Chapter 3 The University of Michigan’s Rackham Graduate School and Department of Earth and Environmental Science provided funding for this project through grants to C.A.A. I thank Parks iii Canada for assistance in permitting and field logistics. The University of Wyoming High Precision Isotope Laboratory personnel are acknowledged for providing support. I would like to wholeheartedly thank Dr. Don Porcelli for his insightful and extremely helpful insights regarding the derivation of the age-relationship equation used in this chapter. Chapter 4 Funding for this project was provided by the University of Michigan’s Rackham Graduate School and Department of Earth and Environmental Science through research grants awarded to C.A.A. and through Packard funding awarded to S.M.A.; and by the Woods Hole Oceanographic Institution’s Ocean and Climate Change Institute Arctic Research Initiative research grant to S.B.D. I thank Air Greenland for assistance with field logistics and the WHOI field team for aiding in sample collection in Ilulissat. I thank Dr. Gideon Henderson for his generosity in allowing us access to the original box-model used in Henderson, 2002. Many thanks to all those who contributed to my success in this thesis! iv TABLE OF CONTENTS ACKNOWLEDGEMENTS…………………………………………………………… ii LIST OF FIGURES…………………………………………………………………… ix LIST OF TABLES……………………………………………………………………. xi LIST OF APPENDICES……………………………………………………………… xii ABSTRACT…………………………………………………………………………… xiii CHAPTER I. Introduction: Glacial Hydrology 1.1 Glaciers and Icesheets……………………………………………… 1 1.1.1 The Subglacial System 1.2 Approach …………………………………………………………… 5 1.2.1 Fraction Contributions to Meltwater 1.2.2 Subglacial Meltwater Residence Time 1.2.3 Impact of Glacial Meltwater U Chemistry on Seawater U Chemistry 1.3 Summary …………………………………………………………… 11 1.4 Publications Resulting From This Dissertation …………………… 12 1.5 References ………………………………………………………… 13 II. An open source Bayesian Monte Carlo isotope mixing model with applications in Earth surface processes Abstract………………………………………………………………… 16 2.1 Introduction………………………………………………………... 17 2.1.1 Bayesian Mixing Model 2.2 Case Studies…………………………………………………….….. 24 2.2.1 Case Study One: Glacial meltwater fractions based on δ18O and δD from the Athabasca Glacier 2.2.1.1 Sample collection and in situ measurements 2.2.1.2 Mass spectrometry 2.2.1.3 Oxygen and hydrogen isotopic composition of glacial meltwater v 2.2.1.4 Fractional contributions to meltwater discharge 2.2.1.5 Snowmelt versus ice melt discharge 2.2.1.6 Potential caveats 2.2.2 Case Study Two: Quantifying surface versus basal glacial melt using δ18O and 222Rn from the Greenland Ice Sheet 2.2.2.1 Fractional contribution to Greenland Ice Sheet bulk meltwater 2.2.3 Case Study Three: Nutrient sources to Hawaiian soils using εNd and 87Sr/86Sr 2.2.3.1 Fractional contribution to Hawaiian soils 2.2.4 Model Limitations 2.2.5 Broader Implications 2.3 Conclusions……………………………………………………….. 54 2.4 References…………………………………………………………. 56 III. Uranium-series isotopes confirm prolonged residence time of subglacial water Abstract………………………………………………………………... 60 3.1 Introduction……………………………………………………..…. 61 3.2 Background……………………………………………………..…. 63 3.2.1 Importance of Subglacial Meltwater Residence Time 3.2.2 U-series, Mixing, and Residence Time 3.2.3 Seasonal Evolution of Subglacial Drainage Network 3.3 U-series Residence Time Equation.……….…………………….…. 70 3.3.1 Derivation of Residence Time Equation 3.3.2 Comparison of Bulk or Average Residence Time with True Residence Time of Water 3.3.3 General U-series Behavior Based on Modeling 3.3.4 Caveats of Residence Time Calculations 3.4 Field Location, Sampling and Chemical Methods………………… 81 3.4.1 The Athabasca Glacier 3.4.2 Sampling 3.4.2.1 Pre-cleaning 3.4.2.2 Collection of filtered subglacial water 3.4.2.3 In-field chemical measurements 3.4.2.4 Channel discharge 3.4.2.5 In-field radon measurements 3.4.2.6 Iron co-precipitation 3.4.3 Column Chemistry 3.4.4 Mass Spectrometry vi 3.4.4.1 Uranium isotope ratios 3.4.4.2 Elemental concentrations 3.4.5 Residence Time Calculations 3.4.6 Positive Degree Days 3.5 Results……………………………………………………..….…… 89 3.5.1 In-Field Measurements 3.5.2 Chemical Measurements 3.5.2.1 Radioactive and radiogenic isotopes 3.5.3 Quantitative Residence Time 3.6 Discussion………………………………………………………… 94 3.6.1 Synthesis of the U-series Residence Time with Traditional Models 3.6.1.1 Traditional analysis and dilution effects 3.6.1.2 Positive degree days and residence times 3.6.1.3 Channel switching, residence times, and transit times 3.6.1.3.1 Reservoir volume 3.6.1.4 Transit time versus residence time 3.6.1.4.1 Comparison with dye-trace studies 3.7 Conclusions………………………………………………………. 103 3.8 References………………………………………………………… 105 IV. Greenland subglacial water residence times and proximal seawater U chemistry: Implications for seawater δ234U on glacial-interglacial timescales Abstract……………………………………………………………… 111 4.1 Introduction……………………………………………………… 112 4.2 Background……………………………………………………… 113 4.2.1 Seawater U Chemistry 4.2.2 Subglacial U Chemistry 4.2.3 Impact of Deglaciation on Seawater Chemistry 4.3 Field Locations………………………………………………… 116 4.3.1 Site Locations and Lithology 4.4 Methods…………………………………………………………… 119 4.4.1 Pre-Cleaning 4.4.2 Sample Collection 4.4.3 Sample Analysis 4.2.3.1 Sample preparation 4.4.3.2 Mass spectrometry 4.4.4 Residence Time Calculations 4.5 Results……………………………………………………………. 122 4.5.1 U-series Subglacial Water Measurements and Residence Times 4.5.2 δ234U Seawater Measurements vii 4.6 Discussion………………………………………………………… 124 4.6.1 Spatial Subglacial Residence Time Comparisons 4.6.2 Subglacial Residence Time and Seawater Chemistry 4.6.2.1 Seawater U chemistry and salinity 4.6.3 Seawater Box Model 4.6.4 Box Model Scenarios 4.6.4.1 Likelihood of box model scenarios 4.6.5 Box Model Caveats and Assumptions 4.6.6 Significance 4.7 Conclusions………………………………………………………… 144 4.8 References………………………………………………………….. 146 V. Conclusion: Geochemical Constraints on Glacial Hydrology 5.1 Summary of Conclusions…………………………………………… 150 5.1.1 Chapter 2: Fraction Contributions to Meltwater 5.1.2 Chapter 3: Subglacial Meltwater Residence Time 5.1.3 Impact of Glacial Meltwater on Seawater U Chemistry 5.2 Future Work………………………………………………………… 154 5.3 References ………………………………………………………….. 158 APPENDICES………………………………………………………………………… 160 viii LIST OF FIGURES Figure 1.1 Transport pathways of glacial hydrology..................................................................... 3 1.2 Generalized map of sample locations........................................................................... 6 2.1 Detailed location map of the Athabasca Glacier .........................................................
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