Geobiology of the stratified central Baltic Sea water column Dissertation zur Erlangung des mathematisch-naturwissenschaftlichen Doktorgrades „Doctor rerum naturalium“ der Georg-August-Universität Göttingen im Promotionsprogramm Geowissenschaften der Georg-August University School of Science (GAUSS) vorgelegt von Christine Berndmeyer aus Cloppenburg Göttingen, 2014 Betreuungsausschuss Prof. Dr. Volker Thiel, GZG, Abteilung Geobiologie Dr. Martin Blumenberg, Bundesanstalt für Geowissenschaften und Rohstoffe Mitglieder der Prüfungskomission Referent: Prof. Dr. Volker Thiel, GZG, Abteilung Geobiologie Korreferent: Dr. Martin Blumenberg, Bundesanstalt für Geowissenschaften und Rohstoffe weitere Mitglieder der Prüfungskomission: Prof. Dr. Joachim Reitner, GZG, Abteilung Geobiologie Prof. Dr. Daniel Jackson, Courant Research Center Geobiology Dr. Steffen Kiel, GZG, Abteilung Geobiologie Dr. Oliver Schmale, Leibnizinstitut für Ostseeforschung Warnemünde Tag der mündlichen Prüfung: 20. August 2014 Acknowledgments Working in this project was a great experience and although Göttingen is not necessarily famous for its maritime flair, my work here allowed me keeping my marine background. First of all, I cordially thank Martin Blumenberg for the opportunity to work in this Baltic Sea project, for his patient and diligent mentoring and his support during all stages of this thesis. I furthermore thank Volker Thiel for his scientific support, good advice, the hours spent for proofreading, and critical questions. I thank Joachim Reitner, Daniel Jackson, Steffen Kiel, and Oliver Schmale for being members of my thesis committee. In addition, I thank Oliver Schmale for help with sampling and onboard ship, and for constructive discussions. I am very thankful to my co-doctoral candidate Gunnar Jakobs for the nice times spent onboard ships, the scientific discussions and exchange of ideas, the non- scientific discussions and the mutual support. Thomas Bode and Nadine Schäfer have always been helpful with any PC problems. For help in laboratory and analytical support, I thank Cornelia Conradt, Lukas Kammel, Birgit Röhring, Andreas Reimer, Tobias Licha, Karsten Nödler and Jens Dyckmans. Thanks to my colleagues Jan Bauermeister, Juliane Germer, Ines Herlitze, Jennifer Hohagen, Tim Leefmann, Eva-Maria Sadowski, and Leyla Seyfullah for lunch breaks, chats on the roof, and help with this work. Special thanks to Jan-Peter Duda for all his support during years of study in Bremen and the current support for our “double-finish”. I am very grateful to my family for never ending support, help, encouragement, and interest in what I am doing. I am especially indebted to Timo Köhnsen who always supported my work but steadily reminds me what is really important. This thesis was written as a part of the DFG research project “Aerobic and anaerobic methane consumption in the central Baltic Sea water column”. This thesis is dedicated to Anette and Klaus Berndmeyer. Preface The following papers and manuscripts are part of this doctoral thesis: Berndmeyer, C., Thiel, V., Blumenberg, M., 2014. Test of microwave, ultrasound and Bligh & Dyer extraction for quantitative extraction of bacteriohopanepolyols (BHPs) from marine sediments. Organic Geochemistry 68, 90-94. Berndmeyer, C., Thiel, V., Schmale, O., Blumenberg, M., 2013. Biomarkers for aerobic methanotrophy in the water column of the stratified Gotland Deep (Baltic Sea). Organic Geochemistry 55, 103-111. Berndmeyer, C., Thiel, V., Schmale, O., Wasmund, N., Blumenberg, M., 2014b. Biomarkers in the stratified water column of the Landsort Deep (Baltic Sea). Biogeosciences Discussions 11, 9853-9887. Under review. Blumenberg, M., Berndmeyer, C., Moros, M., Muschalla, M., Schmale, O., Thiel, V., 2013. Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea. Biogeosciences 10, 2725- 2735. Schmale, O., Blumenberg, M., Kießlich, K., Jakobs, G., Berndmeyer, C., Labrenz, M., Thiel, V., Rehder, G., 2012. Microbial methane oxidation at the redoxcline of the Gotland Deep (Baltic Sea). Biogeosciences 9, 4969-4977. Contents Abstract 1 Chapter 1 - Introduction 3 1.1 Molecular biomarkers 4 1.2 Stratified water columns 7 1.3 Geobiology of stratified water columns 10 1.4 Holocene development of the Baltic Sea and the present situation 11 1.5 Sampling and analytical methods 16 1.6 Introduction to the following chapters 18 References 19 Chapter 2 – “Test of microwave, ultrasound and Bligh & Dyer extraction for quantitative extraction of bacteriohopanepolyols (BHPs) from marine sediments” 27 2.1 Abstract 27 2.2 Introduction 27 2.3 Methods 28 2.4 Results 30 2.5 Discussion 31 2.6 Conclusions 34 Acknowledgments 34 References 35 Chapter 3 – “Biomarkers in the stratified water column of the Landsort Deep (Baltic Sea)” 41 3.1 Abstract 41 3.2 Introduction 42 3.3 Material and methods 43 3.4 Results 46 3.5 Discussion 53 3.6 Conclusions 59 Acknowledgments 60 References 61 Chapter 4 – “Aerobic methanotrophy within the pelagic redox-zone of the Gotland Deep” 73 4.1 Abstract 73 4.2 Introduction 74 4.3 Methods 76 4.4 Results and discussion 79 4.5 Conclusions 85 Acknowledgments 86 References 86 Chapter 5 – “Biomarkers for aerobic methanotrophy in the water column of the stratified Gotland Deep (Baltic Sea)” 95 5.1 Abstract 95 5.2 Introduction 96 5.3 Methods 98 5.4 Results 101 5.5 Discussion 105 5.6 Conclusions and outlook 110 Acknowledgments 111 References 111 Chapter 6 – “Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea” 121 5.1 Abstract 121 5.2 Introduction 122 5.3 Study site and core stratigraphy 124 5.4 Materials and methods 126 5.5 Results 127 5.6 Discussion 130 5.7 Conclusions 137 Acknowledgments 137 References 138 Chapter 7 – Summary and conclusions 145 Curriculum Vitae 149 Abstract Abstract The central Baltic Sea water column is permanently density stratified leading to stagnating bottom waters and a zonation into an oxic, suboxic and anoxic zone. The anoxic zone of the central Baltic Sea is characterized by strong methane gradients that indicate methane consumption in the suboxic zone. This thesis comprises five papers that are based on investigations of water column and sediment samples from the central Baltic Sea. The aim of these investigations was to assess the geobiology of this stratified system using biomarkers with a focus on bacteriohopanepolyols (BHPs). First, three different extraction methods were compared with respect to BHP yields. Microwave, ultrasound, and Bligh & Dyer extraction revealed similar results for total extracted BHPs and studies were continued using microwave extraction. In the Landsort Deep, biomarkers were used to assess the geobiology in the whole water column. They mirrored the water column stratification and revealed different microbial communities. An initial multidisciplinary study including biomarker analysis revealed the presence of type I aerobic methanotrophic bacteria in the suboxic zone of the Gotland Deep. A following detailed investigation of Gotland Deep biomarkers in the oxic and suboxic zone and the underlying sediment showed high BHP concentrations in the suboxic zone and suggested that this zone is an important source layer for these compounds. The BHP signal found in the suboxic zone is also mirrored in the surface sediments. Subsequently, the Holocene geological record of BHPs was analyzed in a Gotland Deep sediment core covering all stages of the Baltic Sea development. BHPs reflected the onset of the stratification during Littorina stage and are of particular abundance during periods of pronounced anoxia. The studies presented in this thesis demonstrate biomarkers to be a versatile tool to assess microbial communities in present and past stratified environments and contribute to the general knowledge on the geobiology of stratified water columns. 1 2 Chapter 1 – Introduction 1 Introduction Geobiology is the science of the interactions between the non-living geosphere and the living biosphere. Much like the geosphere has an influence on the development and distribution of life, life, inversely, is able to change and shape the geosphere. Numerous topics such as early life environments, the photosynthetic oxygenation of the atmosphere, microbial mineral precipitation, or nutrient cycles are of geobiological interest. This thesis, however, is focused on the geobiology of the central Baltic Sea stratified water column, i.e. the distribution of microbial life in physicochemically differing water layers. A permanent pycnocline divides the present central Baltic Sea water column into an oxic, suboxic and anoxic zone. The resulting chemocline supports numerous microbial metabolisms, including the aerobic oxidation of methane. This thesis was written in the context of the multidisciplinary project “Aerobic and anaerobic methane consumption in the central Baltic Sea water column” conducted by the geobiology group of the Georg-August-University of Göttingen and the working group “trace gases” of the Leibniz Institute for Baltic Sea Research Warnemünde (IOW). Methane is known to be a highly effective greenhouse gas that is amongst others produced in marine sediments. Microbial methane oxidation in the sediments and in the water column removes large amounts of the produced methane before it can reach the atmosphere and affects climate. Little was known about the microbial key players in methane oxidation, the