The deep ocean as a major sink for terrestrial organic carbon

Abstract Rivers transport ~200 Tg of particulate organic carbon (POC) to the global ocean annually, of which 30% is known to be buried in continental‐shelf sediments. The fate of the remaining “missing” terrestrial POC (POC terr ) remains uncertain, with proposed explanations including rapid remineralization or transport to the remote deep ocean. Here, based on δ 13 C and 234 Th tracers, we show that the vertical fluxes of POC terr to the deep sea (~2.7 Tg C yr −1 ) account for the “missing” portion in the northwestern Pacific marginal seas. The East China Sea and East/Japan Sea are ideal for testing this hypothesis, given substantial POC terr inputs and extensive shelf areas connected to a semi‐enclosed deep sea. We found that sediment resuspension and the refractory nature of POC terr facilitate its effective transport to the deep sea, which serves as its major sink. These findings provide crucial insights into the fate of POC terr in the global ocean.