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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