Abstract Evaluating Holocene Precipitation
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ABSTRACT EVALUATING HOLOCENE PRECIPITATION VARIABILITY IN THE BALTIC REGION USING OXYGEN ISOTOPES OF LACUSTRINE CARBONATE FROM ESTONIA Carolyn Fortney, M.S. Department of Geology and Environmental Geosciences Northern Illinois University, 2016 Nathan D. Stansell, Director Oxygen isotopes derived from authigenic carbonate from open lake systems record variations in seasonal precipitation source. This study focuses on the sediment record from Lake Nuudsaku in southern Estonia to evaluate how winter versus summer precipitation has changed throughout the Holocene as a result of fluctuating North Atlantic Ocean conditions, primarily the North Atlantic Oscillation (NAO). Estonia receives precipitation with a lower δ18O value from the North Atlantic and Baltic Sea during the winter months. In contrast, during the summer months Estonia receives precipitation with greater δ18O values from warmer North Atlantic waters and from the Mediterranean Sea and Black Sea. Therefore, lower δ18O values in the carbonate record were interpreted as periods of time in which there were increases in the amount of winter precipitation. Oxygen isotope data indicate relatively wet winters during the early Holocene (9960 to 8800 cal yr BP) followed by a shift toward drier winters during the middle of the Holocene (8800 to 4200 cal yr BP). The late Holocene (4200 cal yr BP to the present) was characterized by the wettest winters recorded in the oxygen isotope record. The periods of increased winter precipitation in the Baltic region generally coincided with periods of increased NAO index between 5200 cal yr BP and 1000 cal yr BP. There was an inverse relationship between winter precipitation and NAO index during the Medieval Climate Anomaly and the Little Ice Age (900 to 100 cal yr BP). The positive relationship between NAO index and winter precipitation in Northern Europe is present once again in the modern setting and has persisted since at least AD 1950. NORTHERN ILLINOIS UNIVERSITY DEKALB, ILLINOIS AUGUST 2016 EVALUATING HOLOCENE PRECIPITATION VARIABILITY IN THE BALTIC REGION USING OXYGEN ISOTOPES OF LACUSTRINE CARBONATE FROM ESTONIA BY CAROLYN FORTNEY ©2016 Carolyn Fortney A THESIS SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF SCIENCE DEPARTMENT OF GEOLOGY AND ENVIRONMENTAL GEOSCIENCES Thesis Director: Nathan D. Stansell ACKNOWLEDGEMENTS I would like to thank my advisor, Nathan Stansell, for providing me the opportunity, knowledge and material to make this project possible. I also thank my committee members Justin Dodd and Eric Klein for their guidance and support. In addition, I would like to thank Jaanus Terasmaa, Tanel Vainura, Kristyn Hill, Elizabeth Olson, Anna Buczynska, Matthew Finkenbinder, Sten Sarap, Evelin Stansell, Luule Lauk and the Paavel family for additional assistance and Northern Illinois University’s Geology and Environmental Geosciences Department for financial support to complete fieldwork and lab work. TABLE OF CONTENTS Page LIST OF FIGURES ............................................................................................................... vi Chapter 1. INTRODUCTION ................................................................................................. 1 Site Description ............................................................................................. 4 Chemical Environment of Lake Nuudsaku ................................................... 9 2. METHODS ............................................................................................................ 11 Fieldwork ....................................................................................................... 11 Analytical Work ............................................................................................ 12 Age Model ......................................................................................... 12 Physical and Chemical Composition ................................................. 15 Delta Notation ................................................................................... 17 Water Isotopes ................................................................................... 17 Calcite Isotopes ................................................................................. 18 Paleo-Water Isotopes ......................................................................... 19 3. RESULTS .............................................................................................................. 21 Physical Changes in Lake Nuudsaku ............................................................ 21 Age Model ..................................................................................................... 21 X-Ray Diffraction Results ............................................................................. 24 Principal Component Analysis ...................................................................... 24 iv Chapter Page SEM Images .................................................................................................. 24 Biogenic Silica ............................................................................................... 28 Loss on Ignition ............................................................................................. 28 Water Chemistry Data ................................................................................... 28 Bathymetric Profile ....................................................................................... 30 Modern Water Isotopes ................................................................................. 30 Calcite Isotopes ............................................................................................. 31 Calculated Paleo-Water Composition ........................................................... 34 4. DISCUSSION ........................................................................................................ 37 North Atlantic Influence ................................................................................ 37 North Atlantic Oscillation ................................................................. 37 Applications of Paleolimnology .................................................................... 38 Calcite Precipitation ...................................................................................... 39 Sediment Constituents ................................................................................... 41 Lake Hydrology ............................................................................................. 42 Relationship Between δ13C and δ18O ................................................ 42 Global Meteoric Water Line .............................................................. 43 δ18O Drivers in Lake Nuudsaku .................................................................... 44 Temperature ....................................................................................... 44 Seasonal Precipitation Changes ......................................................... 46 Paleo-water Composition .............................................................................. 47 Oxygen Isotope Record ................................................................................. 48 v Chapter Page 9963 to 8800 cal yr BP ...................................................................... 48 8800 to 4200 cal yr BP ...................................................................... 48 4200 to 1200 cal yr BP ...................................................................... 48 1200 cal yr BP to Present .................................................................. 49 Regional Climate Reconstructions ................................................................ 49 NAO Reconstructions .................................................................................... 52 NAO Between 5200 and 300 cal yr BP ............................................. 52 NAO Between 900 and -65 cal yr BP ............................................... 54 Deviations from NAO Index Records ............................................... 55 Other Baltic Region Climate Drivers ............................................................ 57 Societal Importance ....................................................................................... 58 5. CONCLUSIONS ................................................................................................... 59 REFERENCES ...................................................................................................................... 61 APPENDIX ........................................................................................................................... 68 LAKE NUUDSAKU DATA ..................................................................................... 68 LIST OF FIGURES Figure Page 1. Seasonal changes in precipitation source and 18O values in Estonia ......................... 2 2. Location of Estonia in the Baltic Region .................................................................... 5 3. Temperature variations in Tartu and Karksi-Nuia ....................................................... 6 4. Precipitation variations in Tartu and Karksi-Nuia ....................................................... 7 5. Bathymetric profile of Lake Nuudsaku ....................................................................... 8 6. Water chemistry data from August 2014 ..................................................................... 10 7. Water