Traditionally, trace metals in coastal tidal systems have been considered to be efficiently removed through particle scavenging driven by high suspended particle loads. Recent studies, however, have challenged this view, suggesting that tidal processes, including periodic tidal fluctuations and submarine groundwater discharge (SGD), may facilitate the release and offshore transport of trace metals to adjacent coastal seas. To better understand the fate of trace metals in these environments, we investigated the distributions and sources of dissolved trace metals (Fe and Mn) across the subtidal zones of the Yellow Sea (YS), one of the world's largest macrotidal continental shelves. Seawater samples were collected during two cruises in June and August 2024, together with measurements of ²²²Rn and ²³⁴Th activities as tracers of SGD and particle scavenging, respectively. During both sampling periods, dissolved trace metal concentrations in the surface layer were elevated along the western coast of Korea, coinciding with high ²²²Rn activities. In addition, dissolved trace metal concentrations increased with depth by up to two orders of magnitude, despite rapid particle scavenging rates (~0.2 d⁻¹) in the YS coastal waters. This pattern cannot be explained by riverine inputs and in situ remineralization alone but suggests substantial benthic inputs. The dissolved trace metals were enriched relative to Al compared with the upper continental crust values, inconsistent with lithogenic inputs as the dominant source. Instead, the elevated trace metal concentrations accompanied by Ce/Ce* values approaching unity (~1) suggest that the observed trace metal enrichment may be associated with reductive dissolution in sediment pore waters. The estimated SGD rates (0.2–1.2 cm d⁻¹) during the sampling periods further support the transport of sediment-derived trace metals to the overlying water column via SGD. Collectively, these results suggest that macrotidal systems can act as significant sources of dissolved trace metals to adjacent coastal seas.

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