Premium
Distribution of Concentration and Stable Isotopic Composition of N 2 O in the Shelf and Slope of the Northern South China Sea: Implications for Production and Emission
Author(s) -
Zhang GuiLing,
Liu SuMei,
Casciotti Karen L.,
Forbes Matthew S.,
Gu XueJi,
Ren YanYan,
Zheng WenJing
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc014947
Subject(s) - denitrification , nitrous oxide , photic zone , water column , nitrification , nitrate , ammonium , saturation (graph theory) , seawater , environmental chemistry , nitrogen , surface water , chemistry , environmental science , oceanography , geology , environmental engineering , nutrient , phytoplankton , mathematics , organic chemistry , combinatorics
Oceans are an important natural source of the greenhouse gas nitrous oxide (N 2 O). The isotopomer signature of N 2 O provides a useful tool to differentiate the production processes of N 2 O in the oceans. Here we present the distribution of the concentration and stable isotopic composition of dissolved N 2 O in the water column of the shelf and slope region of the northern South China Sea (SCS) in June 2015. Dissolved N 2 O concentrations in surface waters ranged from 6.9 to 9.1 nM with an average of 7.7 ± 0.6 nM (136 ± 10% saturation). Higher N 2 O was found at the region influenced by coastal water entrained by eddies. Vertical profiles of dissolved N 2 O showed a general increase with depth below the mixed layer and reached a broad peak (23–29 nM) at around 700 m coinciding with the nitrate maximum and oxygen minimum. The SP values measured for N 2 O ranged between 10.2‰ and 18.8‰, suggesting that dissolved N 2 O in the water column had been produced from both nitrification (ammonium oxidation) and nitrifier denitrification (nitrite reduction). Nitrification dominated in the intermediate water (120–1,000 m) while nitrifier denitrification dominated in the euphotic zone. The sea‐to‐air fluxes of N 2 O were estimated to be 7.0 ± 6.1 and 6.9 ± 6.5 μmol m −2 day −1 using two different gas transfer relationships. N 2 O emissions from the shelf and slope regions of the northern SCS were estimated to be 0.25 Tg N 2 O year −1 , suggesting that coastal areas like the SCS are net sources of N 2 O to the atmosphere.