Radium isotopes as tracers of boundary inputs of nutrients and trace elements to the coastal and open ocean by Lauren Elizabeth Kipp B.S. Chemistry, University of North Carolina Wilmington, 2013 Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY and the WOODS HOLE OCEANOGRAPHIC INSTITUTION September 2018 © 2018 Lauren Elizabeth Kipp. All rights reserved. The author hereby grants to MIT and WHOI permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature of Author ___________________________________________________________________________________________ Joint Program in Oceanography/Applied Ocean Science and Engineering Massachusetts Institute of Technology and Woods Hole Oceanographic Institution August 3, 2018 Certified by ___________________________________________________________________________________________ Dr. Matthew A. Charette Thesis supervisor Woods Hole Oceanographic Institution Accepted by ___________________________________________________________________________________________ Dr. Shuhei Ono Chair, Joint Committee for Chemical Oceanography Massachusetts Institute of Technology 2 Radium isotopes as tracers of boundary inputs of nutrients and trace elements to the coastal and open ocean by Lauren Elizabeth Kipp Submitted to the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution on August 3, 2018, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography. Abstract Nutrients and trace metals are vital for supporting life in the ocean, but the boundary processes that control the distributions of these elements are poorly constrained. Radium isotopes are well suited to studying inputs of elements from ocean margins because they are produced in sediments and soluble in seawater. The half-lives of the four isotopes (223Ra, 224Ra, 228Ra, 226Ra) range from days to thousands of years, thus these isotopes can be used to study oceanographic processes occurring over a range of time scales. In this thesis I have applied the quartet of radium isotopes to investigate boundary inputs, including seafloor hydrothermal vents, continental shelves, and rivers. First, radium isotope ratios were used to constrain the age of hydrothermal plumes emanating from vents along the Mid-Atlantic Ridge and East Pacific Rise. These radium-derived ages were applied to determine the iron residence time in the Pacific plume that emanates from near 15°S, providing an important constraint on the hydrothermal delivery of iron to the deep ocean. Next, 228Ra was used to show that shelf inputs to the Arctic Ocean have increased over the last decade, implying that the fluxes of other shelf-derived materials are also increasing and could impact primary production in this basin. The ratio of 228Ra and 226Ra was also applied to determine the ventilation time of Arctic intermediate waters with respect to shelf inputs, and the first measurements of 226Ra in the deep Canada Basin were used to estimate the residence time of deep waters with respect to benthic sediment inputs. Finally, a study of the Mackenzie River Estuary illustrated the importance of deltaic and estuarine processing on the ultimate delivery of nutrients, trace metals, dissolved organic matter, and radium to the Arctic Ocean. By applying radium isotopes as tracers of boundary inputs in these diverse environments, the work presented in this thesis improves our understanding of nutrient and trace metal inputs to the coastal and open ocean. Thesis supervisor: Dr. Matthew A. Charette Title: Senior Scientist, Woods Hole Oceanographic Institution 3 4 ACKNOWLEDGEMENTS No one achieves anything alone, and this thesis represents the culmination of five years of support and encouragement from the people mentioned below and many others. My advisor, Matthew Charette, has been an excellent teacher, role model, editor, and mentor, and has helped me grow into an independent and confident scientist. I am very grateful for all of the opportunities Matt has given me to conduct interesting research, travel all over the world, and become part of the GEOTRACES community. I have learned so much from Matt during my time here, and I will continue to learn from his example as I work to become a successful scientist and advisor myself. Paul Henderson provided essential logistical and technical assistance for all of the research presented in this thesis, but more importantly he has been a great friend and lab mate over the last five years. No matter how busy he was Paul always made time to answer my questions and help me with whatever I needed, whether it was preparing for a cruise, chipping away at permafrost, or putting up Christmas decorations. Steven Pike was also a huge help during my time at WHOI, particularly during the Arctic GEOTRACES cruise, and taught me a lot about working at sea. I am very thankful for the support of my committee, Billy Moore, Meg Tivey, Bob Pickart, and David McGee, who always made time to discuss my work and provide thoughtful feedback. In addition to offering insights that improved my thesis, Billy, Meg, Bob, and David have all been great mentors and helped me navigate important career decisions. I am also grateful for the mentorship of multiple senior scientists at WHOI and in the GEOTRACES community; in particular, the support and encouragement of Scott Doney, Bob Anderson, Phoebe Lam, and Michiel Rutgers van der Loeff have helped me build my confidence as a scientist and made me feel welcome in the oceanographic community. I owe many thanks to the members of the Academic Programs Office (Jim Yoder, Meg Tivey, Delia Oppo, Julia Westwater, Christine Charette, Lea Fraser, and Valerie Caron) for keeping this program running smoothly and having an open door policy that made me feel welcome to seek advice on anything from travel reimbursements to postdoc decisions. The Marine Chemistry & Geochemistry administrative staff (Sheila Clifford, Donna Mortimer, Mary Murphy, and Mary Zawoysky) were similarly willing to answer any and all of my questions, and brightened my days on the fourth floor of Clark. I have also appreciated the support of the MC&G department chairs and education coordinators during my time here: Jeff Seewald, Bernhard Peucker- Ehrenbrink, and Scott Doney. These have been the best five years of my life, thanks in large part to the people I have been able to spend them with. To my friends, Gabriela Farfan, Danielle Gruen, Tyler Rohr, Gualtiero Spiro Jaeger, Virginie Sanial, Megan May, Net Charoenpong, Cristina Schultz, Paul Lerner, Alison Agather, and Jessica Dabrowski: thank you for keeping me sane, making me laugh, and being the best cheerleaders when I was having a rough day. To Erin Black: put simply, I don’t know what I would have done without you. Thank for you teaching me so much about life in the Joint 5 Program, chemical oceanography, and life at sea. You continue to be a fantastic role model and mentor, and you inspire me to be a better scientist and person. My love for the ocean is thanks to my parents, who brought my brother Jonathan and I on family vacations to Sea World and Cape Cod when we were kids, and who brought me to visit WHOI when I told them I wanted to be an oceanographer. Thank you Mom and Dad for teaching me that I could do whatever I set my mind to, and giving me the confidence to pursue my dreams. Jonathan, you have kept me inspired and motivated to achieve this goal through the bravery and dedication with which you have pursued your own ambitions. My husband, Ryan Murphy, has been an essential source of love and laughter in my life long before I decided to pursue this PhD. Despite the fact that the last few years have included work- filled weekends, long periods of time when I was away at sea, and lots of parties where the main topic of conversation was some aspect of oceanography, his support and encouragement has never wavered. Ryan, I cannot express how thankful I am that you have always supported my career goals, no matter where in the world they take me. Being able to come home and share my day with you has gotten me through the rough parts of this program and made the good parts even better. Thank you for being there through all of it. Financial support Funding for the GEOTRACES work was provided by the U.S. National Science Foundation (awards OCE-1232669, OCE-0925158, and OCE-148305 to Matthew Charette; and OCE- 1231221, OCE-0926559, and OCE-1458424 to Willard Moore). The Mackenzie River study was funded by a Graduate Student Research Award from the North Pacific Research Board, and awards from the Woods Hole Oceanographic Institution Ocean Ventures Fund. I completed most of the work presented in this thesis while being supported by a DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. 6 TABLE OF CONTENTS Abstract 3 Acknowledgements 5 List of Figures 10 List of Tables 14 Ch 1: Introduction 15 1.1 Radioactive isotopes as oceanographic tracers 16 1.2 Radium isotopes as tracers of boundary inputs 17 1.3 Introduction to this thesis 18 References 19 Ch 2: Radium isotopes as tracers of hydrothermal inputs and neutrally buoyant plume dynamics in the deep ocean 27 Abstract 27 2.1 Introduction 28 2.2 Methods 29 2.2.1 Sample Collection 29 2.2.2 Sample Analysis 30 2.3 Results and discussion