Biomarker evidence for anammox in the oxygen minimum zone of the Eastern Tropical North Pacific |
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| Institution: | 1. State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou 570228, China;2. Shenzhen Marine Environment Monitoring Center Station, State Oceanic Administration, Shenzhen 518067, China;3. State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China;4. Marine Science Institute and Guangdong Provincial Key Laboratory of Marine Biotechnology College of Science, Shantou University, Shantou 515063, China;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. Guangxi Key Laboratory of Marine Disaster in the Beibu Gulf, Beibu Gulf University, Qinzhou 535011, China;3. Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Ministry of Natural Resources, Guangzhou 510760, China;1. Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Lab of Submarine Geosciences and Prospecting Techniques, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China;4. MLR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China;5. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | Anaerobic oxidation of ammonium (anammox) is an important process in the marine N cycle. It has been estimated to contribute up to 50% of N loss from the ocean and is especially prevalent within the oxygen minimum zone (OMZ). We studied the presence and distribution of anammox in the extended OMZ of the Eastern Tropical North Pacific (ETNP) using ladderane fatty acids (FAs), specific biomarkers for anammox bacteria. The validity of ladderane FAs as a proxy for anammox bacteria was demonstrated by their excellent correspondence with anammox 16S rRNA functional gene abundances and their expression and intact polar ladderane lipid concentrations in suspended particulate matter (SPM) from the Arabian Sea. In the ETNP, SPM was collected from various water depths at four stations along a northwest to southeast cruise transect and ladderane FAs were analysed at each station. In all SPM samples where ladderanes were detected, C18 ladderane FAs were on average fivefold more abundant than C20 ladderane FAs. Maximum ladderane FA concentrations (1.1–2.3 ng l?1) were recorded at 400–600 m, often corresponding to the depth of the secondary nitrite maximum. At one of the four stations, a second maximum in concentration was noted at a shallower depth (85 m), coinciding with higher nitrite availability at this depth. This suggests that nitrite, along with oxygen, may be a limiting factor for anammox activity in the ETNP. Anammox lipids were abundant within the OMZ at all stations and concentrations were comparable to those in other OMZs, suggesting that anammox may be responsible for a significant loss of N from the OMZ of the ETNP. |
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