Evaluating Lake Response to Environmental and Climatic Change Using Lake Core Records and Modeling

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Dissertations & Theses in Earth and Earth and Atmospheric Sciences, Department Atmospheric Sciences of 2009 Evaluating Lake Response to Environmental and Climatic Change using Lake Core Records and Modeling Brandi Bracht-Flyr University of Nebraska at Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/geoscidiss Part of the Geology Commons Bracht-Flyr, Brandi, "Evaluating Lake Response to Environmental and Climatic Change using Lake Core Records and Modeling" (2009). Dissertations & Theses in Earth and Atmospheric Sciences. 4. https://digitalcommons.unl.edu/geoscidiss/4 This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Dissertations & Theses in Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. EVALUATING LAKE RESPONSE TO ENVIRONMENTAL AND CLIMATIC CHANGE USING LAKE CORE RECORDS AND MODELING by Brandi B. Bracht-Flyr A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfilment of Requirements For the Degree of Doctor of Philosophy Major: Geosciences (Geology) Under the Supervision of Professor Sherilyn C. Fritz Lincoln, Nebraska November, 2009 EVALUATING LAKE RESPONSE TO ENVIRONMENTAL AND CLIMATIC CHANGE USING LAKE CORE RECORDS AND MODELING Brandi B. Bracht-Flyr, Ph.D University of Nebraska, 2009 Adviser: Sherilyn C. Frtiz This dissertation evaluates how lakes respond to changes in their environmental and climatic settings. This dissertation consists of two lake modeling projects and the environmental and paleoclimatic reconstructions of four lakes in southwestern Montana. Lakes and their associated biological communities respond to environmental and climatic change on rapid timescales. Lake modeling and lake core stratigraphies are complementary tools for exploration of how lakes and their biota respond to environmental or climatic perturbations. In one modeling approach for exploring these issues, a simple hydro-climatological lake model was developed that classifies lake sensitivity to climatic perturbations based upon lake area, catchment area, precipitation, and evapotranspiration. Using simple ratios of these commonly measured parameters the model classifies lakes into three domains: ephemeral, sensitive to vegetation change, and permanent. The lakes that plot within the sensitive to vegetation change domain should show water balance fluctuations in response to environmental change, and these lakes would make good targets for paleoclimatic stud- ies. Diatom records from four lakes, Crevice Lake, Foy Lake, Morrison Lake, and Reser- voir Lake, in southwestern Montana provide late-Holocene (past 3000 years) records of environmental and climatic variability. The lakes show similarities in the timing of major changes in the fossil diatom assemblages, suggesting regional climate forcings. Spectral analysis of the lake-core records suggest periodic fluctuations at spectral frequencies that are characteristic of oceanic influence on climate, such as the Atlantic Multi-decadal Os- cillation and Pacific Decadal Oscillation. The Crevice Lake core diatom record shows three distinctive diatom communities during the approximately the last 1000 years. The model DYRESM-CAEDYM was used in an inverse modeling approach to provide a means to estimate climate variables during these three stages. The model estimates of climate variables during the Medieval Period, the Little Ice Age, and the 20th century, include incoming shortwave radiation, cloud cover, vapor pressure, and wind speed. The model results suggests that changes in spring seasonality, when the climate variables differ the most, is more important in affecting diatom community composition than total deviations from modern averages. iv DEDICATION I would like to dedicate this dissertation to my wonderful husband, Mike, whose support and laughter kept me sane throughout this entire process. Also, to my parents, Gary and Vicki Bracht, who have never questioned my dreams, or career choice. v ACKNOWLEDGMENTS First and foremost, I would like to acknowledge and thank my advisor, Dr. Sherilyn Fritz for her all her assistance, and for putting up with my writing. I would like to thank the University of Nebraska-Lincoln Department of Geosciences and the Geological Society of America for providing funding and grant assistance. I would like to thank my committee, Dr. Kyle Hoagland, Dr. Robert Oglesby, Dr. John Lenters, and Dr. John Gates for their support and critique of my research efforts. Jeffery Stone and Karlyn Westover sparked my interest in the lake and paleoclimate realm. Without their willingness to teach and friendship, I am not sure I would be at the point I am now. Dr. Eric Grimm and Pietra Mueller cored both Reservoir and Morrison Lakes and provided assistance sampling the cores. The Yellowstone National Park Research Office, particularly Christie Hendrix and Stacey Gunther, provided assistance with field work and research permitting. Gary, Vicki, and Blake Bracht were always willing to assist in field work, regardless of how far I made them hike. I am extremely grateful to all those who helped, in a myriad of ways, to make this dream possible. vi Contents Contents vi List of Figuresx List of Tables xii 1 Introduction1 1.1 Background & Scope............................. 2 1.2 Preface To Chapters.............................. 4 1.2.1 Chapter 2............................... 4 1.2.2 Chapter 3............................... 5 1.2.3 Chapter 4............................... 6 1.2.4 Chapter 5............................... 6 References7 2 A hydro-climatological lake classification model and its evaluation using data9 2.1 Introduction.................................. 11 2.2 Methods.................................... 13 2.2.1 Analytical Model........................... 13 2.2.2 Data.................................. 19 vii 2.3 Results..................................... 21 2.4 Discussion................................... 23 2.5 Conclusion .................................. 28 References 35 3 Synchronous late-Holocene climatic change inferred from four western Mon- tana lakes 43 3.1 Introduction.................................. 44 3.1.1 Environmental Setting ........................ 45 3.1.2 Climatic Setting............................ 47 3.2 Methods.................................... 49 3.2.1 Coring................................. 49 3.2.2 Diatoms & Geochemistry....................... 50 3.2.3 Age Models.............................. 50 3.2.4 Statistical Techniques......................... 51 3.3 Results..................................... 53 3.3.1 Lithology & Geochemistry...................... 53 3.3.2 DCA Results ............................. 53 3.3.3 Spectral Analysis Results....................... 54 3.4 Discussion................................... 55 3.4.1 Limnological History......................... 55 3.4.2 Regional Patterns........................... 62 3.4.3 Forcing of Regional Climate Change................. 65 3.5 Conclusion .................................. 67 References 69 viii 4 Combining lake core records with the limnologic model DYRESM-CAEDYM to estimate climatic parameters during the Little Ice Age and Medieval Warm Period 76 4.1 Introduction.................................. 77 4.1.1 Study Area .............................. 79 4.1.2 Crevice Lake History & Ecology................... 80 4.1.3 DYRESM-CAEDYM......................... 82 4.2 Methods.................................... 83 4.2.1 Weather Data & Lake Temperature.................. 83 4.2.2 Model Setup.............................. 84 4.2.3 Development of LIA and MWP Weather Data............ 85 4.3 Results..................................... 87 4.3.1 Field Data............................... 87 4.3.2 Model Simulations .......................... 87 4.4 Discussion................................... 98 4.4.1 Contemporary Scenario........................ 99 4.4.2 LIA ..................................100 4.4.3 MWP .................................101 4.4.4 Seasonality Effects ..........................101 4.4.5 Model Limitations ..........................102 4.5 Conclusions..................................103 References 105 5 Summary 110 5.1 Conclusions..................................111 5.1.1 Major Findings............................111 ix 5.1.2 Suggestions for Further Research...................112 x List of Figures 2.1 Lake-climate conceptual model.......................... 17 2.2 Locality map ................................... 19 2.3 Lake model .................................... 22 3.1 Map of study area................................. 46 3.2 Lake bathymetric maps.............................. 48 3.3 Lake age models ................................. 51 3.4 Lake DCA results................................. 54 3.5 Lake spectral analysis results........................... 55 3.6 Crevice Lake diatom stratigraphy......................... 57 3.7 Foy Lake diatom stratigraphy........................... 59 3.8 Morrison Lake diatom stratigraphy........................ 60 3.9 Reservoir Lake diatom stratigraphy........................ 61 3.10 Schematic diagram ................................ 64 4.1 Crevice Lake locality map ............................ 79 4.2 Crevice Lake diatom stratigraphy........................

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