Evolution of anthropogenic Pb and Pb isotopes in the deep North Atlantic Ocean and the Indian Ocean

Abstract

, in partial fulfillment of the Requirement for the degree of Doctor of PhilosophyPb and Pb isotopes in the ocean have varied on decadal to centennial time scales due to anthropogenic Pb inputs. Thus, tracing the temporal variation of Pb and Pb isotopes in the ocean provides information on the major sources of Pb and the transport of Pb from sources to the ocean surface and into the ocean interior. In this thesis study, first, a method was developed for the analysis of dissolved Pb and other trace elements in seawater using single batch nitrilotriacetate resin extraction and isotope dilution ICP-MS, which was applied in analyzing seawater Pb concentrations in the rest of the study. A -550 year history of the Pb and Pb isotopes in the deep North Atlantic Ocean is reconstructed using a deep-sea coral, showing the infiltration of anthropogenic Pb to deep sea. Comparing the results to the surface North Atlantic Ocean Pb record using a Transit Time Distribution model, the mean transit time of Pb is estimated to be -64 years. This is longer than the transit time estimate assuming simple advection from a source, showing the importance of advective-diffusive mixing in the transport of Pb to the ocean interior. The later part of the thesis investigates Pb in the Indian Ocean, where no useful Pb data have been previously reported. First, using annually-banded surface growing corals, I reconstruct variations of Pb and isotopes in the surface waters of the central and eastern Indian Oceans during the past half-century. Results of the study show the increase of Pb concentrations from the mid-1970s, and major sources of the Pb are discussed, including leaded gasoline and coal burning, based on their emission histories and Pb isotope signatures. Second, Pb concentration and isotope profiles are presented from the northern and western Indian Oceans. AcknowledgementI would like to thank all the people who made this work possible. First, I owe a big thank to my advisor Ed Boyle. He taught me a lot about trace metal techniques, guided me to find right and important scientific questions whenever I was lost, and supported all my work. Not only that, he was also supportive of me having a family, very understanding and patient, which I cannot be grateful enough.I'd like to thank my committee: Bill Jenkins, Carl Lamborg, Phoebe Lam, and Konrad Hughen. Interests they showed during committee meetings were so inspiring and encouraging. I usually had this magical experience that my work, which looked so boring beforehand, turns into the most interesting one in the world after the committee meeting.I also would like to thank Jess Adkins and Selene Eltgroth, who provided the deep-sea coral and the radiocarbon data used in Chapter 3, and shared their expertise in deep-sea coral analysis with me. My work in Chapter 4 and 5 could not be completed without these people who helped me to collect corals and seawater samples from the Indian Ocean: Miriam Pfeiffer, Aron Meltzner, Kerry Sieh, Bambang Suwargadi, Danny Natawidjaja, Toshitaka Gamo, Hajim...