Electrochemical methods for autonomous monitoring of chemicals (oxygen and phosphate) in seawater: Application to the Oxygen Minimum Zone Justyna Elzbieta Jonca To cite this version: Justyna Elzbieta Jonca. Electrochemical methods for autonomous monitoring of chemicals (oxygen and phosphate) in seawater: Application to the Oxygen Minimum Zone. Analytical chemistry. Uni- versité Paul Sabatier - Toulouse III, 2012. English. tel-00776773 HAL Id: tel-00776773 https://tel.archives-ouvertes.fr/tel-00776773 Submitted on 16 Jan 2013 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TTHHÈÈSSEE En vue de l'obtention du DOCTORAT DE L’UNIVERSITÉ DE TOULOUSE Délivré par l’Université Paul Sabatier III Discipline ou spécialité : Chimie-Océanographie Présentée et soutenue par Justyna Elżbieta Jońca Le 1 Octobre 2012 Titre : Méthodes électrochimiques pour la surveillance autonome des espèces chimiques (oxygène et phosphate) dans l’eau de mer : Application aux Zones de Minimum d’Oxygène JURY V. Garçon – Directrice de Recherches, CNRS, LEGOS, Toulouse, France M. Comtat – Professeur, Université Paul Sabatier Toulouse III, France D. Connelly – Senior Research Scientist, National Oceanography Center, Royaume-Uni G. W. Luther III – Professeur, Université de Delaware, États-Unis J.-L. Marty – Professeur, Université de Perpignan, France N. P. Revsbech – Professeur, Université d’Aarhus, Danemark M. Trojanowicz – Professeur, Université de Varsovie, Pologne Ecole doctorale : SDU2E Unité de recherche : Laboratoire d’Etudes en Géophysique et Océanographie Spatiales Directeur(s) de Thèse : Véronique Garçon Co-directeur de Thèse : Maurice Comtat 1 2 I dedicate this work to my beloved mother. Niniejszą pracę dedykuję mojej ukochanej mamie. 3 4 Acknowledgments Working on the Ph.D. has been a wonderful experience. It is hard to say whether it has been grappling with the topic itself which has been the real learning experience, or grappling with how to write papers, give talks, work in a group, and stay focussed to the late night hours...In any case, I am indebted to many people for making the time working on my Ph.D. an unforgettable experience. First of all, I am deeply grateful to my advisor Véronique Garçon for introducing me into the fascinating world of oceanography. Working with her has been a real pleasure to me. She has oriented and supported me with care, and has always been patient and encouraging in times of new ideas and difficulties. Her ability to select and approach compelling research problems, her high scientific standards, and her hard work set an example. Despite many responsibilities, she always had a moment to correct my manuscripts and prepare me for conferences. Above all, she made me feel friend, which I appreciate from my heart. I will forever be thankful to my co-advisor Maurice Comtat for his scientific advice and knowledge and many insightful discussions and suggestions. He was my primary resource for getting my electrochemical questions answered. I am also grateful for our long discussions about french cooking and wines. I also thank my scientific advisor Niels Peter Revsbech from Aarhus University in Denmark for choosing a very interesting topic for my secondment in his laboratory and for helping me achieve excellent results in a very short period of time. I also have to thank the members of my PhD committee: George Luther III, Douglas Connelly, Niels Peter Revsbech, Marek Trojanowicz and Jean-Louis Marty for their helpful suggestions and hard questions. Thank you all for having accepted this additional work. During my PhD studies I was supported by an Initial Training Network Marie Curie within the SENSEnet project (grant agreement N° 237868). The SENSEnet project gave me this tremendous opportunity to collaborate with research institutes across Europe and to work with the best scientists within the marine chemistry science. I will be forever grateful for all SENSEnet meetings, field courses and other workshops full of scientific discussions and presentations. All that was possible thanks to an excellent project management and I have to thank for that Carla Sands and Douglas Connelly. In this place I would like to thank also all SENSEnet students for effective brainstorming during our workshops and for great time we had together during informal meetings. 5 I also thank people who were working with me during my 3 years journey at LEGOS laboratory. I will be forever thankful to Danièle Thouron for her tinkering abilities which were crucial in my work and for her constant dialogue with me in french which forced me to learn french faster. I would like to thank Carole Barus, William Giraud, Ludovic Lesven and Margeaux Gourdal for all scientific and non-scientific discussions. I thank Nicolas Striebig and Marcel Belot for designing and manufacturing my measurement electrochemical cell. Many thanks to Aurélien Paulmier for sharing with me his huge knowledge on Peruvian waters and for his help in preparing the oceanographic cruise offshore Peru in October 2010. In this place I would like to also thank officers, scientists and crew of Pelagico 1011-12-BIC OLAYA cruise aboard R/V Jose Olaya Balandra for their assistance in the collection of water samples and to IMARPE laboratory for organization of the cruise. I would also like to thank the administrative staff from the laboratory (Nadine, Martine, Brigitte) for their so precious help. I thank my family because I would not have gone so far without them. I wished my mum had lived longer for my graduation. She sacrificed her life for my sister and brothers and myself and provided unconditional love and care. The memory of her will be with me for the rest of my life. Special thanks to my sister Agnieszka, my brothers Krzysztof and Piotr for being supportive when times were rough and for long phone conversations about everything and nothing. I thank my best friend Agata for having faith in me and my intellect and for our long “intelligent” discussions on Skype. Finally, I would like to thank my boyfriend and soul-mate Wojtek for sharing with me the passion for science and for his love and support during my good and bad times. 6 SUMMARY General introduction 11 Introduction générale (français) 15 CHAPTER I: Introduction on ocean biogeochemistry and on Oxygen Minimum Zones 19 1. Introduction on ocean biogeochemistry 21 1.1. The role of ocean in the global carbon cycle 21 1.1.1. The physical and biological carbon pumps 24 1.1.2. Human impact on ocean CO2 uptake 27 1.1.3. Oceanic circulation and global warming 28 1.2. The components of the biological carbon pump 29 1.2.1. Phytoplankton and primary production 29 1.2.2. Role of nutrients and iron in the biological carbon pump 32 1.3. The phosphate in the ocean 33 1.3.1. Chemistry of phosphate 33 1.3.2. The cycle of phosphate in the ocean 34 2. Introduction on Oxygen Minimum Zones (OMZs) 38 2.1. Oxygen in the ocean 38 2.2. Formation, distribution and stability of OMZ 40 2.3. The role of OMZ in the global climate change 42 2.3.1. Influence of OMZ on the biogeochemical cycles and greenhouse gases budget 42 2.3.2. Biotic response to OMZ 43 3. Summary 44 CHAPTER II: Fundamentals of electrochemical techniques 47 1. Basic concepts 49 1.1. Electrolytes and the electrode-solution interface 49 1.2. The electrode reactions 50 1.3. Galvanic cell and Nernst equation 51 1.4. Electrolysis cell and non-equilibrium processes 53 1.5. Electrochemical methods and apparatus 53 2. Electrochemical kinetics 56 2.1. Faraday’s law and Butler-Volmer’s law 57 2.2. Fick’s diffusion law 60 2.2.1. First case: transport by pure diffusion 61 2.2.2. Second case: transport by convective diffusion 63 3. Electrochemical methods used in this work 64 3.1. Diffusion controlled methods: Cyclic voltammetry 64 3.1.1. First case: reversible system 66 3.1.2. Second case: irreversible system 67 3.1.3. Third case: quasi-reversible system 67 3.2. Modulated voltammetric techniques-differential pulse voltammetry 67 3.3. Methods controlled by forced convection: hydrodynamic methods 69 3.3.1. Levich’s equation 70 3.3.2. Koutecky-Levich’s equation 70 3.5. Chronoamperometry 71 7 4. Influence of adsorption on electrochemical signals 71 5. Electrochemical reactions coupled with chemical reaction 72 5.1. CrEr mechanism 74 5.2. ErCi mechanism 75 6. Summary 76 CHAPTER III: In situ phosphate and oxygen monitoring 79 1. Ocean observing systems 81 2. Sensor characteristics for long term ocean monitoring 84 3. Sensors for oxygen in situ measurements 85 3.1. Clark-type oxygen microsensors 89 3.1.1. Construction and functioning 89 3.1.2. Characteristics of Clark-type sensors 91 3.2. STOX sensor as an improved Clark-type sensor 93 3.2.1. Construction and principle of functioning 94 3.2.2. Sensor characteristic 95 3.2.3. In situ applications of STOX sensor 96 3.2.4. Advantages and disadvantages 99 3.3. Optical vs amperometric microsensors 100 4. Methods for phosphate monitoring in seawater 102 4.1. Autonomous phosphate analyzers based on wet chemistry and spectrophotometry 102 4.1.1. Principle of phosphate measurements 102 4.1.2. ANAIS-Autonomous Nutrient Analyzer In Situ 104 4.1.3. Other spectrophotometric analyzers 107 4.2.