Slowly Sinking Particles Underlie Dissolved Iron Transport Across the Pacific Ocean

Continental shelf sediments are an important source of iron (Fe) in the oceans. Observational data suggest that basin-scale transport of sedimentary sourced Fe accompanies the ventilation of the intermediate layer in the North Pacific. Here we use a marine biogeochemical model to explore the Fe transport mechanism with a focus on the role of sinking particles. The lateral penetration of sedimentary sourced Fe was best simulated when we assumed a short desorption and disaggregation length scale of Fe from sinking particles. The simulation results indicated that Fe is laterally transported mainly through interactions with particles with sinking velocities of 180-460 m yr(-1); these velocities are two orders of magnitude slower than typical sinking rates of marine aggregates determined from mass flux measurements. Slowly sinking particles drive the basin-scale transport of Fe by prolonging its residence time and by injecting sedimentary sourced Fe supplied originally to less dense waters into the intermediate layer water across isopycnal surfaces. A large amount of Fe from shelf sediments of the Okhotsk and Bering Seas is exported to the North Pacific through this particle interaction. These results highlight a biogeochemical linkage between the marginal seas and ocean basins that has been overlooked in global ocean models.

Automated summary

Continental shelf sediments are an important source of iron in the oceans, with a large amount of Fe laterally transported mainly through interactions with slowly sinking particles in the North Pacific. This biogeochemical linkage between marginal seas and ocean basins has implications for understanding the global Fe cycle.