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Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
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Isotope constraints on the forming mechanism of Primary Nitrite Maximum (PNM) in the South China Sea
P-M5-08-S
Siqi Wu* , State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Shuh-ji Kao, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Presenter Email: wusiqi@stu.xmu.edu.cn |
| Nitrogen (N), as a biologically important nutrient element, plays an important role in the ocean, modulating primary production and carbon cycle in the euphotic zone. Among N species, nitrite (NO2-) with N of intermediate valence state, is an important intermediate connecting with a number of biological N processes. Since NO2- is chemically metastable, it has fast turnover rate and its concentration is usually under detection limit except a ubiquitous layer at the bottom of the euphotic zone where NO2- accumulates to considerable concentration, named Primary Nitrite Maximum (PNM). Given that PNM layer is close to the deep chlorophyll maximum (DCM) and ammonium maximum layer, various accumulation mechanisms (e.g., dominated by ammonium oxidation or phytoplankton nitrate reduction) of the metastable NO2- and its forcing factor (e.g., light or temperature) determining the location of PNM had been long proposed yet remains debatable to date. In this study, we presume that combined light and temperature effects on NO2- related processes determines PNM¡¯s location and formation. To test this hypothesis, stations with different water mass characteristics were chosen for manipulation experiment, which combined light (~100 mol photons m-2 s-1, ~30 mol photons m-2 s-1(~1% PAR), dark) and temperature (in situ temperature and in situ temperature ¡À5oC) with multiple tracer addition (15N-NH4+, 15N-NO2-, 15N-NO3-). Our incubation experiment contains total 9 light and temperature combination potentially to resolve the synergistic effect. Further, combining molecular biological information such as genetic information on NO2- source and sink processes and plankton community structure, our results might give new insights into the universal forming mechanism of PNM and the response of PNM to the global change such as enhanced stratification and global warming. |
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