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Implications for Continental Methane Cycling

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Implications for Continental Methane Cycling Novel Concepts Derived From Microbial Biomarkers In The Congo System: Implications For Continental Methane Cycling Charlotte Louise Spencer-Jones Supervised by Dr. Helen M. Talbot and Prof. Thomas Wagner A thesis submitted to Newcastle University in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of Science, Agriculture and Engineering School of Civil Engineering and Geoscience Drummond Building Newcastle University United Kingdom October 2015 Declaration I hereby certify that the work presented in this thesis is my original research work, with the exception of a subset of 120 ODP 1075 samples included in Chapters 4, 5, and 7 and 22 ODP 1075 samples in Chapter 6, however, the subsequent interpretation of the results are my own. Total organic carbon measurements (TOC) for 210 ODP 1075 samples were carried out by Holtvoeth et al. (2005) and are cited as such in Chapter 4. Wherever contributions of others are involved, every effort is made to indicate this clearly, with due reference to the literature and acknowledgement of collaborative research and discussions. No part of this work has been submitted previously for a degree at this or any other university. Charlotte Louise Spencer-Jones i Abstract Methane is a climatically active gas and is a potential source of rapid global warming. Future climate change scenarios predict increased global temperatures, which, could destabilise large reservoirs of organic carbon currently locked in sediments and soils and further accelerate global warming. Comparable to the Arctic, the tropics store a large proportion of sedimentary carbon that is potentially highly vulnerable to climate change. However, the significance of tropical methane sinks in modifying methane emissions during past climate warm periods remains unresolved. This study focussed on determining the importance of aerobic methane oxidation (AMO) within the Congo during modern conditions and the Pleistocene. Bacteriohopanepolyols (BHPs), specifically aminobacteriohopane-31,32,33,34-tetrol (aminotetrol) and 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol) are diagnostic molecular markers preserved in soils and sediments that can be used to trace AMO and, therefore, CH4 cycling within both modern and ancient systems (hereafter termed CH4 oxidation markers). In this project, BHP distributions were determined within modern samples from the Congo catchment, including; 22 soils, 6 Malebo pool wetlands and an estuarine sediment. To complement this work on modern systems, BHPs were also analysed within ancient sediments from the Congo fan (ODP 1075) dated to 2.5 Ma, including high resolution studies of marine isotope stages (MIS) 5, 11 and 13. Within ODP 1075, high concentrations of CH4 oxidation markers are observed with no strong down core degradation signature. The study presents the oldest reported occurrence of CH4 oxidation markers, to date, with these biomarkers detected in sediments dated to 2.5 Ma (226 meters composite depth). Similarly, high concentrations of aminotetrol and aminopentol are also observed within the modern Malebo pool wetland and estuarine sediment, suggesting these sites as likely sources of CH4 oxidation markers to the Congo Fan. High concentrations of CH4 oxidation markers were found during MIS 5, 11 and 13 within ODP 1075 sediments. The CH4 oxidation marker signature during MIS 5 and MIS 11 coincides with high global CH4 concentrations (EPICA Dome C), whereas MIS 13 was characterised by low atmospheric CH4 concentrations. The strong similarities in CH4 oxidation marker concentrations during all three interglacial suggests a non-linear response in BHP production/burial and global CH4. This ii disparity could be due to the displacement of main sediment supply to the Congo fan and/or the relative similarity of CH4 sources during these time intervals. Alternatively, these differences could also be due to a threshold behaviour between methanogenesis – methanotrophy and the synthesis of diagnostic BHPs. A long term reduction in the mean concentration of CH4 oxidation markers is observed between 1.7 Ma and 0.3 Ma, suggesting a long term trend towards greater continental aridity within the Congo, consistent with changes in vegetation zones. Significant uncertainty still remain about the response of tropical CH4 sources and sinks during global climate perturbations, however, this study emphasises the large potential of BHPs as powerful novel tracers for methane cycling, both on land and in the ocean and across all climate zones. iii Acknowledgements I would like to start by thanking my supervisors, Helen M. Talbot and Thomas Wagner, who have provided technical and scientific support as well as a large amount of encouragement during this project. I would like to thank the European Research Council (ERC) for funding this PhD as part of a starting grant (258734; awarded to H.M.T.). I would also like to acknowledge the International Ocean Discovery Programme (IODP) for providing access to ODP 1075 and to the Wildlife Conservation Society of Congo (WCS-Congo) for logistical support and invaluable local knowledge during the sampling campaigns. Furthermore, I would also like to thank Bienvenu Jean Dinga, John R. Poulsen, Jose N. Wabakanghanzi, Rob Spencer and Paul Mann for collecting and providing access to such an extensive set of samples. I sincerely hope future research continues to reveal the secrets of the Congo. I would like to thank Frances R. Sidgwick, Bernard Bowler, Paul Donohoe, Tracy Thompson, and Philip Green for their technical support and patience during this project. I also thank Melissa Ware, Gail de Blaquiere and Yvonne Hall for making my experience at Newcastle University positive. I also thank members of the AMOprox and Biogeochemistry group for sharing their research and allowing me to think beyond my own narrow field. I would also like to extend my thanks to members of the European Geoscience Union (EGU) Early Career Researcher network and representatives for showing me the wider, social implications of geoscience research and for supporting discussions about diversity and inclusivity within the field. I would also like to thank Enno Schefuß and Erin McClymont for scientific advice and support during this project. I would also like to thank my Viva Voce examiners, Bart van Dongen and Martin P. Cooke for their valuable comments. I would like to thank my friends and family for understanding the commitment a PhD takes and supporting me throughout it. Last, but not least, I would like to thank Liam Pollard who has been my emotional support throughout this process. Thank-you for always putting my PhD-woes into perspective. Thank-you all so much, I could not have done it without you. iv Publication History The following papers have been either been published or are in preparation. Published Spencer-Jones, C.L., Wagner, T., Dinga, B.J., Schefuß, E., Mann, P.J., Poulsen, J.R., Spencer, R.G.M., Wabakanghanzi, J.N., Talbot, H.M. Bacteriohopanepolyols in tropical soils and sediments in the Congo River catchment area. Organic Geochemistry, In Press. Talbot, H.M., Handley, L., Spencer-Jones, C.L., Bienvenu, D.J., Schefuß, E., Mann, P.J., Poulsen, J.R., Spencer, R.G.M., Wabakanghanzi, J.N., Wagner, T., 2014. Variability in aerobic methane oxidation over the past 1.2Myrs recorded in microbial biomarker signatures from Congo fan sediments. Geochimica et Cosmochimica Acta 133, 387-401. In Preparation Spencer-Jones, C.L., Wagner, T., Schefuß, E., Talbot, H.M. High resolution record of terrestrial methane cycling in central Africa during MIS 5 and 11-13. In Preparation. Spencer-Jones, C.L., Schefuß, E., Talbot, H.M. Bacteriohopanepolyol signatures in Congo fan sediments (GeoB 6518-1). In Preparation. Schefuß, E., Eglinton, T.I., Spencer-Jones, C.L., Rullkötter, J., De Pol Holz, R., Talbot, H.M., Grootes, P.M., Schneider, R.R., Hydrologic control of carbon release from tropical wetlands”. In Preparation. v Abbreviations The following abbreviations are commonly used throughout this thesis Aerobic methane oxidation AMO Anaerobic oxidation of methane AOM Bacteriohopanepolyol BHP Branched GDGT br-GDGT Branched vs Isoprenoid tetraether index BIT Glycerol dialkyl glycerol tetraether GDGT Intertropical convergence zone ITCZ Liquid chromatography - Mass spectrometry LC-MS Marine isotope stage MIS Mean annual air temperature MAAT Organic carbon OC Organic matter OM Palaeocene-Eocene thermal maximum PETM Sea surface temperature SST Soil organic matter SOM Sulfate reducing bacteria SRB Terrestrial derived organic carbon OCter Total lipid extract TLE Total organic carbon TOC vi Contents Chapter 1. Introduction and Literature Review .................................................. 2 1.1. Introduction ................................................................................................. 2 1.2. Modern Sources of CH4 .............................................................................. 4 1.2.1. Soils...................................................................................................... 4 1.2.2. Wetlands .............................................................................................. 5 1.2.3. Floodplain Lakes .................................................................................. 7 1.2.4. Marine Sources .................................................................................... 7 1.3. Modern CH4 Cycling and Aerobic/Anaerobic Sinks ..................................... 8 1.3.1. Anaerobic Oxidation of Methane
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