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Modern source-to-sink processes in the southern South China Sea (SCS) remain poorly understood. In this study, clay minerals and magnetic properties are used to identify the sources and transport pathways of surface sediments in the southern SCS. The distributions of four clay mineral species in the deep southern SCS are mainly controlled by sediment sources, while clay minerals on the outer Sunda Shelf mostly reflect reworking/recycling of older weathered sediments. Clay mineral analyses indicate that the Mekong River is the predominant contributor of clay minerals to the southern SCS, with minor contributions from Luzon and/or Palawan and northern Borneo. The contribution from the Luzon and/or Palawan arc to the southern SCS is semi-quantitatively evaluated as 20% and is mainly smectite. Most sediments in the southern SCS are magnetically dominated by mixtures of magnetite, hematite and goethite in variable proportions. Concentration-dependent magnetic parameters decrease gradually seaward and then sharply towards the outer deep sea. The grain size of magnetite particles also shows a significant fining trend with distance from the southwestern sources. In addition, the magnetic minerals change from hematite- and goethite-dominated to magnetite-dominated type as going further offshore. These magnetic characteristics suggest that the magnetic minerals in the southern SCS are mainly sourced from the southwest through summer monsoon-driven surface currents. Finally, combining the provenance signature indicated by clay minerals and the transport information revealed by magnetic properties, this study highlights that the Mekong River plays a major role in modern source-to-sink processes in the southern SCS. In brief, our study sets a good example for tracing sediment provenance and transport in other marginal seas worldwide. • Clay minerals and magnetic properties are used to identify the sources and transport pathways. • The Mekong River plays a predominant role in the source-to-sink processes of the SW SCS. • Magnetic minerals are sourced from the southwest through summer monsoon-driven surface currents. • Coupled analyses of clays and magnetic minerals can yield valuable and complementary information. [ABSTRACT FROM AUTHOR]