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Reconstructing Past Sea Surface Temperatures Near the Iceland-Faroe K’ Ridge Using Alkenone Paleothermometry (U 37 )

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Reconstructing Past Sea Surface Temperatures Near the Iceland-Faroe K’ Ridge Using Alkenone Paleothermometry (U 37 ) ENVS 4902 Stefanie Mellon Reconstructing past sea surface temperatures near the Iceland-Faroe k’ Ridge using alkenone paleothermometry (U 37 ) By: Stefanie Mellon in B.Sc. Honours Co-op Environmental Science, Dalhousie University Supervisor: Dr. Markus Kienast, Professor of Oceanography, Dalhousie University [email protected] April 3, 2015 1 ENVS 4902 Stefanie Mellon Table of Contents 1.0 ACKNOWLEDGEMENTS ................................................................................................................. 3 2.0 LIST OF ABBREVIATIONS ............................................................................................................. 3 3.0 ABSTRACT ......................................................................................................................................... 3 4.0 INTRODUCTION ............................................................................................................................... 4 4.1 BACKGROUND INFORMATION .......................................................................................................................... 5 4.2 SUMMARY OF LITERATURE REVIEW AND KNOWLEDGE GAPS ................................................................... 7 4.3 OBJECTIVES OF STUDY ...................................................................................................................................... 7 5.0 LITERATURE REVIEW ................................................................................................................... 9 5.1 INTRODUCTION ................................................................................................................................................... 9 5.2 CIRCULATION IN THE NORTHERN NORTH ATLANTIC OCEAN ................................................................. 10 5.3 OCEANOGRAPHY OF THE ICELAND BASIN AND ICELAND-FAROE RIDGE .............................................. 11 5.3.1 Bathymetry ................................................................................................................................................ 11 5.3.2 Circulation and Water Masses .......................................................................................................... 12 5.3.3 Environmental Characteristics ......................................................................................................... 14 5.4 ICELANDIC VOLCANISM .................................................................................................................................. 14 5.5 PALEORECONSTRUCTIONS IN THE NORTHERN NORTH ATLANTIC OCEAN ........................................... 16 5.5.1 Holocene SST reconstructions in the northern North Atlantic and Nordic Seas ........ 16 5.5.2 SST Reconstruction in the Last Glacial Maximum .................................................................... 17 5.6 KNOWLEDGE GAPS AND CONCLUSIONS ...................................................................................................... 19 6.0 METHODS ........................................................................................................................................ 20 6.1 OVERVIEW ........................................................................................................................................................ 20 6.2 CORE SAMPLING .............................................................................................................................................. 20 6.3 ALKENONE EXTRACTION ............................................................................................................................... 21 6.4 DATA ANALYSIS ............................................................................................................................................... 22 6.5 DELIMITATIONS AND LIMITATIONS ............................................................................................................. 25 6.6 REVIEW OF ALKENONE RELIABILITY AND UNCERTAINTIES ................................................................... 25 7.0 RESULTS .......................................................................................................................................... 27 7.1 GLOBAL CALIBRATION DATA ........................................................................................................................ 27 7.2 DOWNCORE RECORD OF UK’37 AND SST .................................................................................................. 28 8.0 DISCUSSION .................................................................................................................................... 30 8.1 APPLYING THE PRELIMINARY AGE MODEL TO CORE 909-2 GC ........................................................... 30 8.2 APPLYING AGE MODELS BY ALIGNING TRENDS IN UK’37 RESULTS WITH TRENDS IN THE NGRIP ICE CORE ......................................................................................................................................................................... 33 8.2.1 Assuming Core 909-2 GC dates back to the Eemian interglacial period ........................ 33 8.2.2 Assuming Core 909-2 GC dates back to Marine Isotope Stage 3 ........................................ 36 8.3 INTERPRETING THE MAJOR TRENDS IN CORE POS457-909 ................................................................ 38 8.3.1 Holocene Cooling .................................................................................................................................... 38 8.3.2 Last Glacial Maximum .......................................................................................................................... 40 9.0 CONCLUSIONS ................................................................................................................................ 42 10.0 BIBLIOGRAPHY ........................................................................................................................... 44 11.0 APPENDIX: LAB PROCEDURE ................................................................................................. 53 12.0 APPENDIX: GANTT CHART ...................................................................................................... 54 2 ENVS 4902 Stefanie Mellon 1.0 Acknowledgements I would like to thank my supervisor, Dr. Markus Kienast, for his continuous support throughout the entire process of writing this honours thesis. I greatly appreciate the guidance provided by our Honours class instructor, Dr. Tarah Wright. I would like to thank Dr. Dirk Nürnberg and Maryam Mirzaloo for hosting me at GEOMAR Helmholtz Centre for Ocean Research Kiel, and for providing sample material and ancilliary data. I also thank Claire Normandeau for her help with laboratory work. And lastly, I would like to acknowledge TOSST Transatlantic Research School and NSERC for funding my summer research, in both Halifax, Canada and Kiel, Germany. 2.0 List of Abbreviations LGM- Last Glacial Maximum LSW- Labrador Slope Water MOC- Meridional Overturning Circulation NAC- North Atlantic Current NAO- North Atlantic Oscillation SST- Sea Surface Temperature 3.0 Abstract Understanding the ocean and its past behaviour is important because it gives insight into rates and amplitudes of global change. This thesis uses a paleoceanographic k’ technique (Simplified Ketone Unsaturation Index (U 37)) that reconstructs sea surface temperatures (SST) of the past ocean in deep-sea sediment cores. SST is an important parameter because it is the temperature of the interface between oceanic and atmospheric heat reservoirs. The study site is located southeast of Iceland, which is of particular interest to oceanographers because it is a key region of deep-water formation. These data can be used to test the reliability of general circulation models (GCM). If GCMs can accurately simulate conditions of the past, then we can have more confidence in the models’ predictions of future climate change. Results of the study show two warm periods in the past that were both warmer than present day SSTs, and that the amplitude between warm and cold periods was 9 ±1.5°C. The exact age of the observed trends cannot be determined due to a lack of radiocarbon dating, therefore three potential age models are discussed in this thesis, based on lightness data of the core and the Northern Greenland Ice Core Project δ18O record. Assuming that these age models are correct, we can conclude that the late Holocene (present day) was cooler than the early Holocene (11,700 years BP), and that the Last k’ Glacial Maximum was warmer than present day SST values, based on U 37 paleothermometry. The causes and implications of these findings will be discussed in the context of the literature. It is suggested that further research take place using another proxy measure and more sediment cores in order to better illustrate the past climate of this region. 3 ENVS 4902 Stefanie Mellon 4.0 Introduction Paleoceanography is the study of the geologic history of the ocean in terms of its chemistry, biology, climate, and circulation patterns. Scientists use chemical indicators deposited in deep-sea sediments, called proxies, to reconstruct these ocean characteristics through time, often going back hundreds of thousands of years. We want to be able to use these proxy measures to reconstruct past climates so that we can have a better understanding of major climate events. These data can also be used to test the reliability of general circulation models (GCM). If GCMs can accurately simulate
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