Intrusions of Kuroshio and Shelf Waters on Northern Slope of South China Sea in Summer 2015

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

“…In June 2015, a cyclonic‐anticyclonic eddy pair was found in the studied region (Figure b). The anticlockwise rotation of the cyclonic eddy in eastern side of our study area carried waters originating from the intruding KW into the slope region, while the low salinity coastal water in the upper 50 m was transported from the shelf to the slope along the intersection (Transect III, stations L9–L12; Figure ) of the two eddies (Chen et al, ; Li et al, ). However, intrusions of the KW to the shelf were also observed beneath 100 m (Chen et al, ).…”

“…The salinity reached its maximum at the core layer (100–120 m) of the subsurface water (SSW) where the nitrate and N 2 O increased rapidly downward. Higher N 2 O (20–30 nM), together with low DO (80–150 μM), low nitrite (around the detection limit), and high nitrate (27–39 μM), was usually observed at the water column below 400 m ( σ θ > 26 kg/m 3 ), which is correspondence to the intermediate water (IW; 400–1,000 m) and deep water (DW; >1,000 m) of KW and SCSW (Li et al, ). The salinity reached its minimum at the core layers (~500 m) of the intermediate waters, while N 2 O maximum (25–30 nM) and DO minimum (~82.5 μM) values occurred at the lower part (700–800 m) of the intermediate water.…”

“…T‐S diagram for measured N 2 O, DO, and DIN concentration for all stations at the shelf and slope region of the SCS during June 2015. The water masses in panel a was classified according to Li et al () and Cheng et al (2014). SSW = shelf surface water; SCSSW = South China Sea surface water, KSW = Kuroshio surface water; SCSW = South China Sea water; KW = Kuroshio water; SSW = subsurface water; IW = intermediate water; DW = deep water).…”

“…However, the N* decrease measured in the subsurface and intermediate water (120–1,000 m) of the SCS are probably not due to in situ water column denitrification since high dissolved oxygen concentrations (>100 μM) were observed but are more likely indicative of the contribution of benthic water coming from the continental shelves. The subsurface and intermediate water of the SCS comes from the subtropical salinity minimum North Pacific IW, which is transported to the SCS via the intrusion of Kuroshio through Luzon Strait (You et al, ; Li et al, ). The intrusive current (<750 m) flow along the slope at the continental margin, which supports sedimentary denitrification to produce and consume N 2 O.…”

“…The intrusive denser waters in the deep layer flow southward along the northern slope and mix with the SCS intermediate water, then form the SCS deep water. Below 1,000 m, the percentage of western North Pacific waters (KW) increased gradually with depth and reached 50% at around 1,500 m (Li et al, ). Hence, the N 2 O concentration in the deep water (1,000–2,300 m) of the SCS is slightly higher than those in the WPS but much lower than those in the subtropical western North Pacific and the North Pacific Intermediate Water (Figure a).…”