Aerobic ammonium oxidation in the oxycline and oxygen minimum zone of the eastern tropical South Pacific off northern Chile (∼20°S) |
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| Institution: | 1. Departamento de Oceanografía and Centro de Investigación Oceanográfica en el Pacífico Sur-Oriental (FONDAP-COPAS), Universidad de Concepción, Casilla 160-C, Concepción, Chile;2. Programa de Postgrado, Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, Concepción, Chile;1. Department of Oceanography & Center for Oceanographic Research in the eastern South Pacific University of Concepcion PO Box 160-C, Concepcion, Chile;2. Department of Oceanography & Center for Oceanographic Research in the eastern South Pacific University of Concepcion PO Box 160-C, Concepcion, Chile;1. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China;2. College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China;3. Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China;4. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China;5. Key Laboratory for Ecological Environment in Coastal Areas (State Oceanic Administration), National Marine Environmental Monitoring Center, Dalian 116023, China;1. Microbiogeochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany;2. Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany;3. Senckenberg am Meer, Marine Research Department, Suedstrand 40, 26382 Wilhelmshaven, Germany;1. Department of Earth Sciences (Geochemistry), Faculty of Geosciences, Utrecht University, The Netherlands;2. Baltic Nest Institute, Stockholm University, SE-106 91 Stockholm, Sweden;1. School of Civil Engineering and Geosciences, Drummond Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK;2. Groupe de Recherche en Sciences Exactes et Naturelles (GRSEN/DGRST), Ministere de la Recherche Scientifique, Brazzaville, Congo;3. MARUM – Center for Marine Environmental Sciences, University of Bremen, D-28359 Bremen, Germany;4. Northumbria University, Department of Geography, Newcastle Upon Tyne, UK;5. Nicholas School of the Environment, Duke University, P.O. Box 90328, Durham, NC 27708, USA;6. Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA 02540, USA;7. Department of Soil Physics and Hydrology, Congo Atomic Energy Commission, P.O. Box 868, Kinshasa XI, Democratic Republic of the Congo;1. Microbial Ecophysiology group, Faculty of Biology/Chemistry and MARUM, University of Bremen, Bremen, Germany;1. Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD, USA;2. College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA |
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| Abstract: | Aerobic NH4+ oxidation rates were measured along the strong oxygen gradient associated with the oxygen minimum zone (OMZ) of the eastern tropical South Pacific off northern Chile (∼20°S) during 2000, 2003, and 2004. This process was examined by comparing NH4+ rates of change during dark incubations, with and without the addition of allylthiourea, a classical inhibitor of the ammonia monooxygenase enzyme of ammonium-oxidizing bacteria. The contribution of aerobic NH4+ oxidation in dark carbon fixation and NO2− rates of change were also explored. Thirteen samples were retrieved from the oxycline (252 to ⩽5 μM O2; 15 to ∼65 m depth) and three from the oxygen minimum core (⩽5 μM O2; 100–200 m depth). Aerobic NH4+ oxidation rates were mainly detected in the upper part (15–30 m depth) of the oxycline, with rates ranging from 0.16 to 0.79 μM d−1, but not towards the oxycline base (40–65 m depth). In the oxygen minimum core, aerobic NH4+ oxidation was in the upper range and higher than in the upper part of the oxycline (0.70 and 1.0 μM d−1). Carbon fixation rates through aerobic NH4+ oxidation ranged from 0.18 to 0.43 μg C L−1 d−1 and contributed between 33% and 57% of the total dark carbon fixation, mainly towards the oxycline base and, in a single experiment, in the upper part of the oxycline. NO2− consumption was high (up to 10 μM d−1) towards the oxycline base and OMZ core, but was significantly reduced in experiments amended with allylthiourea, indicating that aerobic NH4+ oxidation could contribute between 8% and 76% of NO2− production, which in turn could be available for denitrifiers. Overall, these results support the important role of aerobic NH4+ oxidizers in the nitrogen and carbon cycling in the OMZ and at its upper boundary. |
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