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Surface Ocean and Lower Atmosphere Study—Air-Sea interactions and their climatic and environmental impacts
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Distribution of concentration and stable isotopic composition of N2O in the shelf and slope of the northern South China Sea: Implications for production and emission
P-C4-15
Gui-Ling Zhang* , Ocean University of China
Su-Mei Liu, Ocean University of China
Karen L. Casciotti, Stanford University
Matthew Forbes, Stanford University
Yan-Yan Ren, Ocean University of China
Wen-Jing Zheng, Ocean University of China
Xue-Ji Gu, Ocean University of China
Presenter Email: guilingzhang@ouc.edu.cn |
| Oceans are the second most important natural source of the greenhouse gas nitrous oxide (N2O). The isotopomer signature of N2O provides a useful tool to differentiate the production and consumption processes of N2O in the oceans. Here we present the distribution of concentration and stable isotopic composition of dissolved N2O in the water column of the continental shelf and slope region of the northern South China Sea (SCS) in June 2015. Dissolved N2O concentrations in surface waters ranged from 6.85 to 9.07 nM with an average of 7.72±0.58 nM (136±10% saturation). Higher N2O was found at the region influenced by coastal water entrained by eddies. Vertical profiles of dissolved N2O showed a general increase with depth below the mixed layer and reached a broad peak (23-29 nM) at around 700m coinciding with the nitrate maximum and oxygen minimum. The SP values measured for N2O ranged between 10.18‰and 18.76‰ (14.17±2.53‰, suggesting that dissolved N2O in the water column can be produced from both nitrification (ammonium oxidation) and nitrifier denitrification (nitrite reduction). Nitrification dominants in the intermediate water while nitrifier denitrification dominants in the euphotic zone. The measured δ15N-N2O values (6.28‰-10.29‰, 7.85±1.03‰ indicate that AOA might contribute significantly to the formation of N2O in the studied region. N2O yields from nitrification were estimated to be 0.03% and comparable to those observed at the northwestern Pacific. The sea-to-air fluxes of N2O were estimated to be 7.04±6.10 and 6.94±6.49 μmol m2 d-1 by N2000 and W2014 relationships. N2O emission from continental shelf and slope region of the northern SCS were estimated to be 0.25 Tg N2O yr-1, suggesting this area is an active area to produce and emit N2O to the atmosphere. |
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