Dissolved Lead in the East China Sea With Implications for Impacts of Marginal Seas on the Open Ocean Through Cross-Shelf Exchange

The distribution of lead (Pb) in the ocean is influenced by human activities. During a cruise in the East China Sea (ECS) in August 2013, we investigated six representative stations and gave the first systematic description of dissolved lead (DPb) distributions after the phasing out of leaded gasoline in China. The DPb concentration in the ECS ranged from 23.8 to 96.7 pmol/kg, with the highest concentrations observed at the surface of the middle shelf, while the lowest concentrations were determined to be in deep samples collected at the shelf break. Vertical profiles of DPb vary with geographic locations, seawater turbidity, hypoxic conditions, atmospheric deposition, and hydrographic regimes. As one of the most important western boundary currents, Kuroshio receives an additional 10–20 pmol/kg of DPb from the ECS shelf through a cross-shelf exchange process, and approximately (1.1–1.7) × 10⁹ g/yr of DPb was exported through the shelf break area, which will directly join the North Pacific circulation based on a preliminary box model. In addition, the ECS shelf exported another 1.4 × 10⁹ g/yr of DPb from the Tsushima/Korea Strait, which has the potential to influence the northwestern Pacific Ocean as well as the Sea of Japan/East Sea. A residence time of 2–3 months for DPb in the ECS was inferred.