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AN ABSTRACT of the THESIS of Nicholas C. Mehmel for the Degree AN ABSTRACT OF THE THESIS OF Nicholas C. Mehmel for the degree of Master of Science in Geology presented on September 15, 2020 Title: Assessment of Extraterrestrial Tracers Ir, Pt and 3He in Polar Ice Cores Abstract Approved: ____________________________________________ Edward J. Brook This thesis focuses on the investigation of extraterrestrial tracers Ir, Pt and 3He in polar ice cores. These tracers may Be used to identify characteristics of interplanetary dust particles, and to quantify the flux of extraterrestrial material during impact events, certain volcanic eruptions, and staBle Background periods. In the first chapter I present novel Ir and Pt concentration records in ice cores from Summit Greenland, spanning the Tambora eruption of 1815 and the Tunguska impact event of 1908. A significant Pt signal is observed within a year of the TamBora eruption, But no oBserved signal is associated with the Tunguska event. Also presented here is a direct comparison between two estaBlished chemical digestion procedures, to assess what portions of the Ir and Pt signal are captured By each. An average Ir concentration of ~0.4 fg/g and average Pt concentration of ~15.7 fg/g are recorded, suggesting a total flux of interplanetary dust particles Between 43.5 – 217 metric tons/day on Earth. In the second chapter, I present 3He concentrations in very large ice samples (3+ kg) from Taylor Glacier, Antarctica, and report an average concentration among 7 samples of 5.32 x 10-17 ccSTP/g, with 3 4 3 4 an average He/ He ratio of 98.77 RA (SD: 34.4 RA), where RA is the atmospheric He/ He ratio comparaBle to stratospheric IDPs. Size fraction experiments and magnetic separation experiments were also performed on 3He- bearing particles in ice samples, and several bulk ice 3 4 samples recorded He/ He ratios over 200 RA. © Copywrite by Nicholas C. Mehmel September 15, 2020 All Rights Reserved Assessment of Extraterrestrial Tracers Ir, Pt and 3He in Polar Ice Cores by Nicholas C. Mehmel A THESIS submitted to Oregon State University in partial fulfilment of the requirements for the degree of Master of Science Presented September 15, 2020 Commencement June 2021 Master of Science thesis of Nicholas C. Mehmel presented on September 15, 2020 APPROVED: _________________________________________________ Major Professor, representing Geology _________________________________________________ Dean of the College of Earth, Ocean, and Atmospheric Sciences _________________________________________________ Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. ______________________________________________________________________________ Nicholas C. Mehmel, Author ACKNOWLEDGEMENTS I would like to thank my advisor, Ed Brook, for his continued support and encouragement throughout the pursuit of this thesis. His expertise and previous experience working with interplanetary dust particles in ice have helped guide me through this difficult exploratory work. He has served as an excellent mentor and role model, reaching above and beyond my expectations, and teaching me what science research is really about. I also greatly appreciate the help provided by the members of my thesis committee. Dave Graham expertly guided me through the laboratory work on 3He presented here, and treated me like a member of his own lab. We faced many challenges and setbacks while performing our measurements, but his complete mechanical mastery of the furnace, vacuum line and mass spec overcame each one. Brian Haley welcomed me to the Keck Lab with great enthusiasm, and his expert background in wet chemistry and trace metal analyses made PGE measurements possible. Maybe one day we will figure out how to get those Hf columns to work. I owe a huge debt to Chris Russo, whose analytical expertise and countless hours helping me perform ICP-MS measurements taught me more than I could imagine about trace metal analyses. Chris performed all PGE measurements during the COVID-19 pandemic, which I can never fully repay him for. I want to thank Ed, Dave, Brian, and Chris, as well as Jesse Muratli, specifically for their logistical and emotional support following the Burt Hall fire of November, 2018. My proximity to the event, and the extreme setbacks it presented, left a heavy mental toll on me. Their timely support and encouragement kept me on track. I must thank Philip Place from Rochester, as well as Geoff Hargreaves from the NSF Ice Core Facility, for retrieving and sending me the relevant ice samples. A great thanks to Monica Arianza and Joe McConnell at DRI for their excellent work dating and providing chemistry on Summit ice. Thank you to Andy Menking and Mike Kalk, for providing me with unique ice samples, and helping me with various tasks in the freezer. And a great thanks to all my friends in the CEOAS community, who helped make this project a success. A resounding thank you must be paid to the Comer Family Foundation, for their generous financial support dedicated to the PGE portion of this research. CONTRIBUTION OF AUTHORS Three co-authors are specified in Chapter 1 of this thesis. Ed Brook provided the impetus for this PGE project by expanding on his previous pilot studies. He provided significant guidance with chapter organization and completed a large portion of chapter editing. Brian Haley helped conceptualize and implement laboratory methods for the project in the OSU Keck Lab, and collaborated on experimental design. Joe McConnell from DRI provided the continuous flow chemistry data presented and is responsible for the age model we used for ice samples. Two co-authors are specified in Chapter 2 of this thesis. Ed Brook provided the impetus for this 3He project as well, building on two previous published works investigating He isotopes in ice cores. He provided the bulk of editing for this chapter. Dave Graham, who runs the noble gas geochemistry lab at OSU, helped design the project and individual experiments from the start. We collaborated closely to perform all 3He measurements presented here. 1 TABLE OF CONTENTS CHAPTER 1: IRIDIUM AND PLATINUM ACCRETION IN POLAR ICE: RECORDS FROM SUMMIT, GREENLAND SPANNING THE TAMBORA ERUPTION OF 1815 AND TUNGUSKA IMPACT OF 1908 Page 1.1 ABSTRACT ........................................................................................................................................................ 2 1.2 INTRODUCTION ................................................................................................................................................ 2 1.2.1 Background: IDP Flux and Entry Heating Process ....................................................................................... 3 1.2.2 Terrestrial Archives, IDP Composition, and Previous Work Towards ET Tracers .......................................... 5 1.2.3 Strong HF Acid Digestion vs. Weak HNO3 Suspension Methods ................................................................. 8 1.2.4 Younger Dryas Boundary Impact Hypothesis ............................................................................................. 9 1.2.5 Volcanic PGE Input ...................................................................................................................................10 1.2.6 Tambora & Tunguska Events ....................................................................................................................13 1.2.7 Research Significance and Primary Research Goals ...................................................................................14 1.3 METHODS .......................................................................................................................................................16 1.3.1 Sample Collection and Dating ...................................................................................................................16 1.3.2 Cutting Procedure ....................................................................................................................................17 1.3.3 Sample Cleaning and Pre-Concentration Procedure ..................................................................................17 1.3.4 Digestion Procedures- Strong HF Digestion ...............................................................................................18 1.3.5 Digestion Procedure- Weak HNO3 Digestion .............................................................................................19 1.3.6 Procedural Blanks ....................................................................................................................................20 1.3.7 PGE and REE Measurement Methods .......................................................................................................20 1.3.8 Method Modification Due to Laboratory Fire ...........................................................................................21 1.3.9 Test of Separating REEs from PGEs Using Column Chemistry ....................................................................22 1.3.10 Oxide Interferences ...............................................................................................................................23 1.3.11 Reducing Blanks & Teflon Digestion Vessel Cleaning Procedures.............................................................25 1.3.12 Data Reduction: Corrections and Uncertainty .........................................................................................26
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