Distribution of Dissolved Aluminum in the Northern South China Sea in Summer: Roles of Terrestrial Inputs, Kuroshio Intrusion and Mesoscale Eddies

Abstract To better understand the biogeochemical cycling of dissolved aluminum (dAl) in the northern South China Sea (NSCS) during summer, we compile dAl data from four cruises in three years (2015, 2017, and 2018) to discuss the effects of terrestrial inputs and Kuroshio intrusion on dAl distributions in the NSCS. Results reveal a distinct cross‐shelf pattern, with significantly higher dAl concentrations on the shelf‐slope (18.8 ± 9.2 nmol/L) than in the basin (7.5 ± 5.5 nmol/L). DAl exhibited non‐conservative behavior on the continental shelf of SCS. In contrast, a relatively conservative relationship with salinity was observed in the subsurface waters between the shelf break and the central basin, indicating that physical water‐mass mixing is the dominant controlling process in this offshore region. The Pearl River plume facilitates the offshore transport of terrigenous materials exceeding 420 km seaward, above the 23.0 isopycnal surface. Concurrently, sediment resuspension at the shelf break supplies dAl to subsurface waters, with subsequent lateral dispersion extending up to 192 km along the 25.0 isopycnal surface. Considering water mass properties and dAl concentrations, the distributions of dAl in the subsurface water (24.2–25.0 kg/m 3 ) of the region between the shelf break and central SCS were controlled by the mixing of South China Sea Water, Kuroshio Water, and Shelf Mixing Water. Although the Kuroshio intrusion is weak in summer, a significantly enhanced Kuroshio intrusion in summer 2017, facilitated by mesoscale eddies in the Luzon Strait, reduced subsurface dAl by nearly 34% compared to other years.