Lead (Pb) is primarily introduced into the marine environment through atmospheric deposition and is transported into the ocean interior via deep-water formation and circulation. As anthropogenic Pb emissions decline and their isotope compositions shift over time, the oceanic Pb signature also evolves. To investigate Pb sources, distribution, and influence of circulation on Pb in the Ulleung Basin, East/Japan Sea, seawater samples were collected in March 2019 and March 2024, and analyzed for Pb concentrations and Pb isotope ratios (²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb).
 Vertical profiles show maximum Pb concentrations at the surface with rapid decrease at depth. These surface levels are comparable to those in the Northwest Pacific but significantly higher than the western Philippine Sea, a discrepancy attributed to the basin’s downwind proximity to East Asian emission centers. In the surface layer (e.g., East Sea Surface Water; ESSW), Pb isotope ratios align closely with Northern Chinese coal, identifying coal combustion as the predominant anthropogenic source.
 In the intermediate layer, distinct isotopic fingerprints characterize regional water masses. On the continental shelf and slope, the North Korea Cold Water (NKCW) exhibited the lowest Pb concentrations at shallow depths, while the East Sea Intermediate Water (ESIW) showed unradiogenic Pb isotope signatures, which may have been influenced by Pb input from coastal freshwater sources. Within the basin, ESIW remains hydrographically distinct based on T-S properties but shows isotopic similarities to East Sea Central Water (ESCW). Pb isotope in ESCW appears as a mixed relationship with ESIW-related Pb, Pb of Russian leaded gasoline which associated with deep-water masses, and potentially Chinese coal, as it shares the adjacent formation area (PGB or west of 131°E) to those water masses.
 In the deep layer, East Sea Deep Water (ESDW) and East Sea Bottom Water (ESBW) possess unique signatures distinct from ESCW and sediments. A linear mixing relationship using Pb isotopes within the deep layer indicates the mixing of Pb from Russian coals and Russian leaded gasoline. Notably, a temporal shift was observed between 2019 and 2024, reflecting the mixing or dilution with background seawater over time. This temporal shift of Pb origin in the deep layer indicates that Pb isotopes can be used as a new oceanographic tracer for evaluating deep-water ventilation and water mass aging in the East/Japan Sea.

Deep-water ventilation,Stable Pb isotopes,Ulleung Basin,Water masses,Pb sources