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Final Copy 2018 06 19 Rem This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Remmelzwaal, Serginio Title: Assessing past oxygen in the ocean using Cr isotopes as a palaeo-proxy General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Assessing past oxygen in the ocean using Cr isotopes as a palaeo-proxy Serginio R.C. Remmelzwaal MSci Hons (University College London), 2014 Fellow of the Geological Society A dissertation submitted to the University of Bristol in accordance with the requirements for the award of the degree of Doctor of Philosophy in the Faculty of Science. School of Earth Sciences 6th of April 2018 Supervisors: Dr I.J. Parkinson, Professor D.N. Schmidt, Dr F.M. Monteiro Word Count: 49926 ‘Omnium rerum principia parva sunt’ Marcus Tullius Cicero Acknowledgements First and foremost, I would like to thank my supervisors Ian Parkinson, Daniela Schmidt and Fanny Monteiro. Without their expertise, input, and life advice completing my Ph.D. research would not have been possible. I would also like to express my gratefulness to Aleksey Sadekov, for his help and advice have proven invaluable to large parts of my work and he has been like a mentor to me. I would also like to thank all my friends for pulling me through my Ph.D., which was testing at times. Please accept my apologies for complaining so much to you and I promise to make more time for you now! I would like to especially mention my lovely flatmates, Emily, Rose and Gael for providing so much emotional support during my write-up, and all-star Elwyn for providing comic relief (or in his own words: “a funny distraction thanks to his chaotic personality”). Coming back to home-cooked dinner and your loveliness after work has made this process just so much more bearable! A special mention should also go to my lab buddy Lucie. The many hours of column chemistry, vial cleaning and mass spectrometry adventures would not have been fun without you there (although breaking the Neptune was maybe a little too adventurous!). I also thank Taryn and Hojung for being wonderful people I can talk to about all my problems at any point of the day despite the physical distance between us. Lastly, but definitely not least, to Chulinya, mama and oma I would like to say how much I appreciate having you as my family and that without you I would not have been able to have started this Ph.D. in the first place. Thank you for always supporting my choices and being such a steadfast rock to hold onto at all times. Dankwoord Ten eerste wil ik mijn begeleiders Ian Parkinson, Daniela Schmidt en Fanny Monteiro bedanken voor hun hulp. Zonder hun expertise, inbreng en levensadvies zou het voltooien van mijn promotie- onderzoek niet mogelijk zijn geweest. I wil graag ook Aleksey Sadekov bedanken. Zijn hulp en advies waren onmisbaar voor grote gedeeltes van dit werk en hij was als een mentor voor mij. Ik wil ook al mijn vrienden bedanken voor hun steun en begrip tijdens soms lastige tijden. Ik beloof dat ik niet meer zoveel zal klagen over mijn werk! Een speciaal bedankje gaat ook uit naar mijn huisgenoten, Emily, Rose en Gael voor de emotionele steun tijdens het schrijven van mijn promotie-onderzoek en Elwyn voor de vrolijke noot die hij is. Dat ik na een dag hard werken thuis kon komen en een warme maaltijd en jullie stralende gezichten voorgeschoteld kreeg maakte het allemaal draaglijk! Mijn dank gaat ook uit naar mijn labmaatje Lucie. De vele uren in het laboratorium zouden veel minder plezierig zijn geweest zonder jouw aanwezigheid. Ik bedank ook Taryn en Hojung, omdat ze een geweldige steun zijn geweest en ik hen, ondanks de fysieke afstand tussen ons, op elk willekeurig tijdstip heb kunnen bellen om mijn problemen te bespreken. Ik wil graag ook tegen Chulinya, mama en oma zeggen hoeveel ik het waardeer om jullie als mijn familie te hebben en dat ik zonder jullie nooit maar zelfs ervan had kunnen dromen om dit onderzoek te kunnen uitvoeren. Vanuit de grond van mijn hart bedank ik jullie voor jullie onvoorwaardelijke steun en dat ik altijd op jullie kan bouwen. Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University’s Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate’s own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED: …………………………………… DATE: …………………………………… Abstract As greenhouse gas emissions into the atmosphere persist, both oceanic and atmospheric temperatures are projected to continue rising with major consequences for the marine environment. One of the major environmental hazards of this century is the spread of low-oxygen environments or ocean deoxygenation. While modern hypoxic environments are closely monitored, the mechanisms leading to these conditions are not fully understood in the context of an Earth system. Past ocean deoxygenation can be used as an analogue to shed light on oceanic dissolved oxygen responses to global warming. The aim of this study is to ground truth the palaeo-redox proxy of the Cr isotopic composition of foraminifera and bulk carbonates to elucidate the processes that led to and the eventual extent of hypoxic and anoxic environments during past climatic events. The potential of foraminiferal Cr isotopes as a new redox proxy was assessed by determining element partitioning and isotopic fractionation of Cr by foraminifera using a variety of geochemical techniques (LA-MC-ICP-MS, (MC-)ICP-MS, nanoSIMS). To date, Cr isotopes in biogenic carbonates have been interpreted to record the seawater δ53Cr composition at the site of test mineralisation in the surface ocean. While Cr is distributed throughout the foraminiferal test in both fossil and modern samples, sediment (fossil) core-top samples have up to two orders of magnitude more Cr than non-sedimentary and culture samples. Iron and Cr cross-plots suggest that although at least part of the Cr signal in foraminifera is primary, the Cr signal is overprinted by the uptake of Cr in bottom and pore waters. In sediment samples, there is no interspecies isotope fractionation (“vital effect”) and the Cr isotopic composition of tests is related to the size of the test through surface area/volume ratio effects on secondary Cr incorporation. This study concludes that Cr in foraminifera is mostly post-depositional and records bottom/pore water signals. Chromium isotopes in carbonates were applied to study how climate change influenced ocean deoxygenation during the Pleistocene, Palaeocene-Eocene Thermal Maximum, Eocene Thermal Maximum 2, Ocean Anoxic Event 2 and Ocean Anoxic Event 1a. Chromium isotopes in carbonates record local seawater deoxygenation during these events. Open ocean deoxygenation can mainly be pinned to rising temperatures in intermediate ocean waters. Deoxygenation through the direct effects of temperature on the solubility of dissolved oxygen do not account for the inferred expansion of low- oxygen conditions. Indirect effects of elevated temperatures (e.g. enhanced microbial metabolic rates and remineralisation) are needed in addition to fully account for the episodic deoxygenation during the Cenozoic. The Cr isotope excursions during the Cretaceous are not governed by thermal effects in the same manner as during the Cenozoic which may be attributed to fundamental climatic and palaeogeographical differences between the Cretaceous and Cenozoic. Page | i Page | ii Table of contents Abstract ................................................................................................................................................... i List of Figures ....................................................................................................................................... ix List of Tables ......................................................................................................................................... xi List of Acronyms ................................................................................................................................ xiii Chapter 1: Introduction and Methods ................................................................................................
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