Towards an understanding of the physical and biological controls on the cycling of dimethylsulfide (DMS) in Arctic and Antarctic sea ice by Gauthier Carnat A thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in partial fulfilment of the requirements of the degree of DOCTOR OF PHILOSOPHY Department of Environment and Geography University of Manitoba Winnipeg, Manitoba, Canada Copyright © 2014 by Gauthier Carnat Abstract In the last two decades there has been an increasing interest in the role played by the marine cryosphere in the production and emission of the climate-active gas dimethylsulfide (DMS). This was motivated by observations of high concentrations of the DMS precursor, the intracellular metabolite dimethylsulfoniopropionate (DMSP), in Arctic and Antarctic sea ice. The understanding of the factors driving the cycling of DMS in sea ice is limited. Little is known about the spatio-temporal variability and fate of the sea ice DMS pool. To date, studies have essentially focused on biotic factors, linking the high DMSP concentrations to the high biomass of sympagic communities, and to their physiological adaptations to the low temperatures and high salinities of the brine habitat. In this thesis, an approach integrating both biotic and abiotic factors is presented, and the influence of ice growth processes and brine dynamics on the DMS cycle is investigated. First, the halo-thermodynamic evolution of sea ice and brine dynamics from growth to melt are explored and defined based on a significant data set of ice temperature and salinity collected in the Arctic. A strong desalination phase over a small time window in the spring is identified. Using calculated proxies of permeability (brine volume fraction) and of the intensity of brine convection (Rayleigh number), this phase is shown to correspond to full-depth gravity drainage initiated by restored connectivity of the brine network on warming. This halo-thermodynamic background is then used to investigate the spatio-temporal variability of DMS in Arctic sea ice during a year-round survey in the Amundsen Gulf. The influence of processes such as scavenging and brine convection on the sea ice DMS cycle is shown, and the first combined measurement of DMS, DMSP, and I dimethylsulfoxide (DMSO), a third organosulfur compound acting as both source and sink for DMS through photo-chemical and bacterial processes, is presented. DMSO is shown to largely dominate the dimethylated sulfur pool in surface ice when the snow cover is low. Based on strong relationships with irradiance, it is suggested that this DMSO originates from the photo-chemical oxidation of DMS trapped in impermeable ice. Finally, the spatio-temporal variability of DMS in Antarctic sea ice is investigated during another year-round survey in McMurdo Sound. Platelet crystals growth under the influence of ice shelf waters are shown to favor the incorporation of strong DMSP producers, to increase the environmental stress on the cells in interior ice, and to favor the accumulation of DMS,P by reducing permeability. The increase of permeability on warming is shown to trigger an important release of DMS in the ocean and a vertical redistribution of DMSP concentrations in the ice cover. On the whole, this thesis provides a clear picture of the spatial and seasonal variability of dimethylated sulfur compounds in sea ice, highlighting strong contrasts between both hemispheres, and contributes to a better understanding of some of the biological and physical factors driving the DMS cycle in the polar regions. II Acknowledgments First and foremost, I would like to acknowledge my thesis supervisor, and friend, Tim Papakyriakou for his unlimited patience, trust, and wisdom. You definitely were the cement of this work and your selfless dedication to both my personal and academic development will stay forever engraved in my memory. I was really touched by your compassion and sensitivity towards other people’s problems, a very unique gift. Your contribution towards this thesis extended way beyond scientific guidance. On the same day, we could spend hours building and rebuilding sentences in a manuscript, and hours discussing about politics around a fire where bison meat was roasting. I really hope that our paths will keep crossing in the future. I would like to extend my gratitude to my thesis committee members, Feiyue Wang, Maurice Levasseur, and Mario Tenuta for their untiring assistance and guidance throughout the years. Mario, thank your for bringing your sagacity and enthusiasm to each of my presentations, and for always finding the right words to take my anxiety away. Fei, thank you for teaching me the fundamentals of aquatic chemistry in such bright and inventive ways. I will always keep a piece of chocolate in my pockets to share with my friends. Maurice, I will never forget the trust you placed in a young scientist at the dawn of his career, giving him unconditional access to your most sensitive equipment. Thanks also for the extreme human kindness I could feel every time I talked to you. My interest for polar science was sparked when my life path crossed that of Jean- Louis Tison and his colorful and inspirational slides during my undergraduate years. I could not be prouder of my academic roots. Jean-Louis not only planted the seed, but also provided continuous water and nutrient supply to the tree, with III so much energy and generosity that I long thought he had a twin brother. This twin brother could definitely have been Bruno Delille, who was given wings to cross the oceans many times a year but remained always available to provide fruitful comments on my work. I am eternally grateful to the two of you for the memorable times spent sampling sea ice in comfortable Tyvek suits, for your support, your trust, and your teaching. More than great mentors, I always considered you as good friends and I really hope this thesis honors the time you have invested in me. Field trips to the hostile but magnificent polar regions were the cornerstones of this thesis and will undoubtedly stay in my mind forever. I have tremendous respect for the commitment and professionalism of the talented captains and crews of the CCGS Amundsen and RV Nathaniel B. Palmer, and of the BASC and Scott Base teams. Thanks to these true heroes of polar research who brought me back home safely from these labyrinths of dangers. These field trips lied upon the shoulders of David Barber, Steve Ackley, Hajo Eicken and Tim Haskell, visionary and humble founding fathers who dedicated their life to polar science. I have been fortunate to share endless days and nights of sampling and analyses with great individuals. Thanks to the mercury team, Debbie Armstrong, Alexis Burt, and Monica Pucko for their much appreciated help in the field and in the labs, to my friend Benoît Philippe, the Zinedine Zidane of the poles, to my great sister in science Isabelle Dumont, and to Rodd Laing for the unforgettable times looking for bears in the Alaskan wilderness. I am very grateful to the British Columbia CO 2 contingent, Lisa Miller, Kristina Brown, and the legendary and inexhaustible duo, Keith Johnson and Nes Sutherland, from whom I have learned so much. This thesis would not have been possible without the incredible work of lab technicians. I would like to thank Art Hildebrand who helped me to diagnose the IV many illnesses that can affect the sensitive patients that are gas chromatographs, Emmelia Stainton, Bruce Johnson and Vlad Petrusevich who helped me to order, prepare and ship all the ingredients of a successful scientific trip to the North Pole. I am eternally grateful to Saïda El Amri, the most efficient and dedicated individual I know. Choukrane for the tasty pastries and the teaching of Arabic and astrology; true social oases amid a lonely world of lab instruments. I would also like to acknowledge the staff of CEOS, DSTE and graduate studies for guiding me through the mystifying maze of the university administration, always with a generous smile. Denise Whynot, Gail Yacucha, Linda Chow, David Mosscrop and Claire Lelouchier, you were my Ariadne’s thread through this thesis. My thoughts also go to Pat Gutoski who helped me take my first steps as a graduate student, but unfortunately will not see me cross the finish line. During my thesis, I had the great chance to collaborate with very enthusiastic and skilled scientists from across the world. I have wonderful memories of my time in the lab of Maurice Levasseur in Université Laval, Québec. Martine Lizotte, Myriam Luce, Sarah-Jeanne Royer, Michael Scarratt, and Sonia Michaud, thanks for your hospitality. Many online collaborators generously take their time and energy to help me solve the multifaceted problems of sea ice biogeochemistry, may they all be warmly thanked for their investment. A heartfelt thanks to Martin Vancoppenolle and his sidekick Ivan Grozny for the hours spent computing and interpreting Rayleigh numbers, to Sangeeta Sharma for sharing her secrets on atmospheric DMS sampling, to Janne-Markus Rintala for his detailed observations of the infinitely small world of ice algae, and to Jacqueline Stefels, an indisputable source of inspiration for the DMS community. V This thesis was a long adventure that I was fortunate to share with other graduate and post-graduate students. Thanks to all the CEOS students at UofM for the friendly working atmosphere, and to all my Canadian colleagues for introducing the chocolate eater and soccer addict that I am to the wonderful world of donuts and hockey. Thanks to Alex Hare for sharing his enthusiasm for the mesmerizing Canadian wilderness, to CJ Mundy and Jens Ehn for the fruitful discussions at the beginning of the thesis, to Matthew Asplin for making the tastiest deep dish pizza you will find on Earth, and to Ryan Galley, the living proof that scientific excellence and a great sense of humour are not incompatible.