Differential scavenging behavior of anthropogenic Pb revealed by sediment traps in the northern South China Sea basin

Trace metals emitted from human activities may have penetrated into the deep seas, and the underlying control mechanisms remain poorly understood. Sinking particles collected by moored time-series sediment traps from the northern South China Sea (NSCS) basin showed significant enrichment of anthropogenic aerosol Pb relative to lithogenic Fe. Total mass flux was primarily driven by seasonal primary production, and significant positive correlations were found between Pb/Fe flux and major biogenic components, indicating the crucial role of the biological pump in Pb/Fe scavenging in the water column. Notably, Pb exhibited 30–50 times higher affinity to biogenic components than Fe. A comparison was made between the enrichment factors of Fe and Pb in aerosols, euphotic particles, and sinking particles, which revealed that Pb exhibited significantly higher particle reactivity than Fe. This higher particle reactivity may encompass processes such as adsorption/desorption, bioaccumulation and decomposition release. The differential scavenging behavior of Pb suggested that the majority of Pb was rapidly scavenged in the euphotic zone and was preferentially released for accumulation in the twilight zone. This accumulation may further outflow through the Luzon Strait and result in the high dissolved Pb concentration observed in the subsurface water columns in both the NSCS and western Pacific Ocean. The rest of anthropogenic Pb in sinking particles tended to penetrate into deeper water layers and continue to be released below the twilight zone. These findings provide new insights into the biogeochemical cycling of trace metals originating from anthropogenic aerosols in marginal seas and serve as an example of the fate of other anthropogenic atmospheric pollutants.