Upwelling systems and their associated oxygen minimum zones (OMZs) represent hotspots of N₂O production in the ocean. The Benguela Upwelling System (BUS) is one of the most productive regions worldwide, and an important, yet variable, source of N₂O to the atmosphere. The exact environmental controls on microbial N₂O production pathways are still uncertain, as is our understanding of how marine N₂O production changes in relation to global change. Questions remain, in particular, regarding the relative importance of nitrification versus denitrification as key N₂O production processes, and their regulation by different environmental factors. To identify key metabolic pathways of N₂O production in the BUS, and to assess the microbial players involved, we combined N₂O production rate measurements, and analysis of natural abundance isotope composition of N₂O with microbial diversity analysis of nitrifying and denitrifying microbial communities. We demonstrate that nitrification and denitrification contribute equally to the accumulation of N₂O in low-O₂ waters. Yet, in the same waters we also verified a high potential for N₂O reduction to N₂. We identified Thioglobus ponitus and Nitrosopumilus sp. as the potentially major microbial drivers of N₂O production. In light of expected changes in upwelling intensities and the expansion of the OMZ, understanding the dynamics that likely modulate the balance between reductive and oxidative N₂O production will be a prerequisite for estimating future changes in N₂O emissions from the BUS.

Primary Presenter: Gabriela Dangl, Leibniz Insitute for Baltic Sea Research Warnemuende (gabriela.dangl@gmail.com)

Authors:

Gabriela Dangl, Leibniz Institute for Baltic Sea Research Warnemuende  ()

Claudia Frey, University of Basel, Department of Environmental Sciences  ()

Christiane Hassenrück, Leibniz Institute for Baltic Sea Research Warnemuende  ()

Bita Sabbaghzadeh, Leibniz Institute for Baltic Sea Research Warnemuende  ()

Janine Wäge-Recchioni, Leibniz Institute for Baltic Sea Research Warnemuende  ()

Moritz Lehmann, University of Basel, Department of Environmental Sciences  ()

Martin Ley, University of Basel, Department of Environmental Sciences  ()

Gregor Rehder, Leibniz Institute for Baltic Sea Research Warnemuende  ()

Klaus Jürgens, Leibniz Institute for Baltic Sea Research Warnemuende  ()