This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Adloff, Markus Title: Quantitative constraints on carbon fluxes and volcanic activity during Oceanic Anoxic Event 1a 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. Quantitative constraints on carbon fluxes and volcanic activity during Oceanic Anoxic Event 1a By Markus Adloff School of Geographical Sciences University of Bristol A dissertation submitted to the University of Bristol in accordance with the requirements of the degree of Doctor of Philosophy in the Faculty of Science. September 2020 Word count: sixty three thousand Abstract The geologic record provides opportunities to study the long-term Earth-System response to exogenic Carbon (C) emissions. In this thesis, I extend and apply the Earth-System model cGENIE to reconstruct and evaluate the uncertainty of C emissions and volcanism during the Oceanic Anoxic Event 1a (OAE 1a) based on sedimentary records of C, Os, Sr, Li and Ca isotopes. OAE 1a (120 Ma) was a major C cycle perturbation featuring the formation of a transient marine organic C sink. Combining C isotope records with reconstructed CO2 concentration changes, I determine the size and isotopic composition of net C fluxes at the event onset. This inverse C flux reconstruction indicates that 4,300 - 29,200 Pg C were emitted, predominantly from volcanism. Radiogenic Os and Sr isotopes have previously been used to reconstruct volcanic activity during the main event, when the effect of enhanced organic C burial prevents C flux reconstructions from the C isotope record. The weathering response has been quantified using Li and Ca isotopes. However, interactions between the C and these metal cycles during C injections are poorly understood. After implementing Os cycling into cGENIE and validating existing parameterisations of Sr, Li and Ca cycling, I show that concurrent changes in volcanism and weathering noticeably affect Os, Sr, Li and Ca isotope excursions in cGENIE simulations, and that further constraints on the isotopic effect of weathering flux changes are required to use trace metals as C flux proxies during long-lasting volcanic episodes. Further analysis of metal cycling prior to OAE 1a reveals that substantial amounts of volcanic C must have been emitted throughout the event to cause the observed isotope excursions and support organic C burial and enhanced weathering for millions of years. C flux reconstructions remain too uncertain to determine the relative importance of these negative C cycle feedbacks. i Dedication and acknowledgements At the beginning of this thesis, I would like to acknowledge and thank the many people who supported me over the last four years. First, I would like to thank my supervisors Sarah E. Greene, Fanny M. Monteiro, Dan Lunt and B. David A. Naafs without whom I could not have written this thesis. I am very grateful that they gave me the opportunity to work with them on this project, and for their extensive support. Their guidance, patience, trust, dedication and encouragement helped me to grow so much over the last four years, academically and personally. I could not have wished for better mentors and collaborators! Secondly, I want to thank all collaborators and project partners for their continued support and valuable inputs to this project. Namely, I would like to thank Steve Hesselbo for inviting me to an unforgettable field trip to the Jurassic Coast and seminars at Exeter University, Ian J. Parkison and Alex Dickson, who helped me understand Os and Sr cycling, and, of course, Andy Ridgwell, who invited me to a research stay in Riverside and whose ideas and support were indispensable for the outcome of this thesis. I am particularly grateful for the social and moral support I received from friends and family. I would like to thank the wonderful new friends I made during my PhD time, who made my life in Bristol such a joyful experience, and my good old friends and family everywhere for being close whatever the distance between us. Thank you to Dominik for his friendship and for making me feel at home in Bristol and Riverside. Thank you to Hazel, Alex, Cara, Olly, Steph and Philip for their friendships and four incredible years of shared meals, houses and invaluable experiences. Finally, I would like to thank NERC and the GW4+ DTP for their financial and administrative support throughout my project. iii 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: .................................. v Table of Contents Page List of Tables xiii List of Figures xvii 1 Introduction 1 1.1 Identifying and quantifying past C emissions......................... 5 1.1.1 Indirect reconstruction of C emissions based on C isotopes ............ 6 1.1.2 Direct reconstruction of C fluxes based on metal isotopes............. 7 1.2 Carbon and metal fluxes during the emplacement of Large Igneous Provinces...... 8 1.2.1 Emission of mantle-derived substances via volcanic eruptions, hydrothermal venting and alteration of fresh basalt ......................... 9 1.2.2 Emissions of surface-derived substances via sediment intrusions, contact meta- morphism and Earth system feedbacks........................ 10 1.3 Oceanic Anoxic Event 1a: window into OAE formation and metal cycle perturbation during LIP emplacements.................................... 10 1.3.1 The Early Aptian, the paleogeographic and -climatological context of OAE 1a . 12 1.3.2 Lithological expression................................. 13 1.3.3 Temperature....................................... 13 1.3.4 CO2 concentrations................................... 14 1.3.5 Biological impact.................................... 14 1.3.6 Marine oxygenation................................... 15 1.3.7 Euxinia.......................................... 15 1.3.8 Weathering........................................ 15 1.3.9 Duration ......................................... 16 1.3.10 The role of volcanism in the formation of OAE 1a ................. 16 1.3.11 Published C flux reconstructions for OAE 1a .................... 17 1.4 Scope and structure of this thesis................................ 17 2 Methods 19 2.1 The cGENIE model ....................................... 19 vii TABLE OF CONTENTS 2.2 cGENIE set-ups.......................................... 22 2.2.1 Pre-Industrial ...................................... 22 2.2.2 Aptian .......................................... 23 2.3 C flux inversions in cGENIE .................................. 27 2.4 Interpreting Sr, Os, Li and Ca isotope excursions as indicators of C cycle perturbations . 27 3 Unravelling the sources of carbon emissions at the onset of Oceanic Anoxic Event (OAE) 1a 29 3.1 Introduction............................................ 30 3.2 Methods.............................................. 32 3.2.1 The Cau section..................................... 32 3.2.2 Model setup and experiment design.......................... 32 3.2.3 Osmium isotope analysis................................ 35 3.3 Results............................................... 36 3.4 Discussion............................................. 38 3.5 Conclusion ............................................ 41 4 Inclusion of a suite of weathering tracers in the cGENIE Earth System Model - muffin release v.0.9.10 43 4.1 Introduction............................................ 44 4.2 Observational constraints .................................... 45 4.2.1 Strontium......................................... 45 4.2.2 Osmium ......................................... 47 4.2.3 Lithium.......................................... 48 4.2.4 Calcium ......................................... 49 4.2.5 Metal distributions in seawater............................. 51 4.2.6 Application of Sr, Os, Li and Ca isotopes as proxies of weathering and mantle emissions........................................