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Reconstruction of Paleo-Circulation in the Western Reconstruction of Quaternary Paleo-circulation in the Western Arctic Ocean Based on a Neodymium Isotope Record from the Northwind Ridge Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Rachael Elizabeth Gray, B.S. Graduate Program in Geological Sciences The Ohio State University 2012 Thesis Committee: Lawrence Krissek, Advisor Leonid Polyak W. Berry Lyons Copyright by Rachael Elizabeth Gray 2012 Abstract An understanding of past ocean circulation in the Arctic is critical for interpretations of past global ocean and atmospheric circulation, as well as predictions of future conditions. The Arctic Ocean plays a major role in global climate, due to its contributions to both the North Atlantic Deep Water (and subsequently the Atlantic Meridional Overturning Circulation) and the planet's albedo (due to sea ice cover). A sediment core from the Northwind Ridge in the western Arctic Ocean, ~800 km north of Alaska, has been sampled for measurement of radiogenic isotope ratios of neodymium and strontium. Sediment grain coatings were leached from the bulk sediment and measured for 87/86Sr and εNd, a proxy for seawater source. Two leaching solutions, one using buffered acetic acid and the second using hydroxylamine hydrochloride, were applied to sediments. Strontium data suggests that acetic acid best captures the seawater signal, while hydroxylamine hydrochloride leaching likely caused clay contamination of the hydrogenous data. εNd ratios were compared with independent lithologic proxies measured on the core and with results of earlier radiogenic-isotope studies in the Arctic Ocean. Data obtained suggest that radiogenic waters dominated the western Arctic Ocean during the estimated Early Pleistocene, probably due to increased Pacific water inputs and/or enhanced brine exclusion from sea ice formation on the Siberian shelves. These conditions likely indicate relatively warm climatic environments with predominantly seasonal sea ice, and thus can be potentially used as a paleo-analog for the ii projected near-future state of the Arctic. Further upcore, in the estimated Middle to Late Pleistocene, εNd values decrease overall, with high-amplitude fluctuations corresponding to glacial-interglacial cyclicity. Strongly non-radiogenic values in glacial intervals suggest the predominance of inputs from the Canadian Shield eroded by the Laurentide ice sheet. More radiogenic but gradually decreasing interglacial values indicate a change from Pacific to Atlantic water influence during the Middle to Late Pleistocene. Further isotope work on other cores may clarify the mechanisms and extent of this shift in circulation patterns. iii Acknowledgments I would like to thank, first and foremost, my advisor, Dr. Leonid Polyak, without whom this thesis simply would not have been possible. I also owe my thanks to Dr. Brian Haley for his scientific and technical contributions to this project, as well as his patience and sense of humor. Thanks also to my committee members, Dr. Larry Krissek and Dr. W. Berry Lyons for valuable feedback. I would also like to acknowledge my fellow students at Ohio State, particularly the past and present members of the paleoceanography group at Byrd Polar Research Center. A special thank-you goes to Dr. Harunur Rashid for his advice and encouragement. Thanks to the faculty, staff and students of Oregon State’s College of Ocean and Atmospheric Sciences, who helped make my trips to Corvallis much more productive and enjoyable. Tracie Fisher-Kline performed initial sediment sampling for this research. Allison Kreinberg and Maya Wei-Haas generously assisted with laboratory equipment and space. Edward Council and Chuang Xuan provided unpublished data cited in this thesis. Finally, I would like to thank my friends, who have made the past few years some of the best of my life, and to my family, who have always believed in me. This research was supported by NSF-OPP award ARC-1003777 to L. Polyak. iv Vita 2009................................................................B.S. Geology, The Ohio State University 2009................................................................B.A. English, The Ohio State University 2009 to present ..............................................Graduate Research Associate, Byrd Polar Research Center, The Ohio State University Fields of Study Major Field: Geological Sciences v Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iv Vita ...................................................................................................................................... v List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii Chapter 1: Introduction ...................................................................................................... 1 Chapter 2: Arctic Ocean Physiography and Water Masses ................................................ 4 Chapter 3:Radiogenic Isotopes in the Arctic Ocean ........................................................... 8 Chapter 4: Material ........................................................................................................... 14 Chapter 5: Methods ........................................................................................................... 21 Chapter 6: Results ............................................................................................................. 24 Chapter 7: Discussion ....................................................................................................... 28 Chapter 8: Summary ......................................................................................................... 36 References ......................................................................................................................... 38 Appendix: Additional Data Tables ................................................................................... 46 vi List of Tables Table 1. Major sources of Nd isotopes in the Arctic Ocean waters .................................. 11 Table 2. Acetic acid leach data for P23 ........................................................................... 47 Table 1. Hydroxylamine hydrochloride leach data for P23 ............................................. 48 Table 1. Leach data from Winter et al. (1997) ................................................................. 49 vii List of Figures Figure 1. Index map of the Arctic Ocean ............................................................................ 3 Figure 2. Downcore variability in sedimentary proxies in P23 ....................................... 16 Figure 3. Correlation of P23 with CESAR cores ............................................................. 20 Figure 4. Flowchart of sample processing procedure ....................................................... 22 Figure 5. P23 downcore distribution of εNd and 86/87Sr .................................................. 25 Figure 6. Comparison of acetic acid and hydroxylamine hydrochloride leaching results for core P23 ....................................................................................................................... 27 Figure 7. Comparison of P23 acetic acid leaching data with oxalic acid leaching data from Winter et al. (1997) .................................................................................................. 30 Figure 8. Acetic acid εNd results of P23 plotted with Mn and Ca contents ..................... 32 Figure 9. Comparison of P23 acetic acid εNd values with results from ACEX ............... 35 viii Chapter 1: Introduction The Arctic Ocean is an important region for study of paleoclimate and paleoceanography due to its role in global oceanic and atmospheric circulation patterns combined with its sensitivity to climate change (e.g., Aagaard et al., 1985; Holland and Bitz, 2003). The Arctic discharge affects the formation of the North Atlantic Deep Water and thus of the Atlantic Meridional Overturning Circulation (Peterson et al., 2006), one of the major modulators of the Earth’s climate. The sea ice coverage of the Arctic also plays an important role in global climate due to its impact on the planet's albedo (Serreze et al., 2007). Current dramatic reduction in Arctic sea ice cover (Fig. 1) (Stroeve et al., 2012, and references therein) and related changes in oceanic and atmospheric circulation as well as biological and societal impacts (e.g., Wassmann, 2011; Allison et al., 2009) underline the urgency of comprehending this region and its behavior during past major shifts in climate. Accurate records of climate and ocean conditions from the past are essential for understanding the region now and predicting future conditions. Due to logistical constraints, detailed high-quality sediment core records for the Arctic Ocean have been difficult to obtain until recent years, when icebreaker research expeditions have allowed the gathering of sediment cores across the Arctic Ocean including previously inaccessible regions (e.g., Darby et al., 2005; Polyak and Jakobsson, 2011). Measurements
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