Riverine lithogenic material (RLM) may play an important role in the global carbon cycle for promoting particulate organic carbon sinking through “ballast effect”, but it is rarely represented in Earth system models (ESMs). We therefore compiled the global riverine sediment input data, and generated simplified RLM forcing fields. By applying them to the improved Community Earth System Model, version 2(CESM2) with ballast effect of RLM and considering the seaward transportation of RLM with different modes and intensities, we identified the potential influence of riverine lithogenic ballasting on POC flux and other biogeochemical parameters in global estuarine regions, global marginal seas and global ocean. We assess two types of seaward transmission: surface forcing and lateral forcing,corresponding to the transport of RLM at the surface ocean or along the bottom of shelf and slope, respectively.

We find that the global pattern of POC export and downward transfer changes is, when the model reaches quasi-equilibrium, decreasing in the tropical Pacific, East Pacific coastal zone and subploar ocean but increasing in the subtropical oligotrophic gyres regardless of the transport scenario of RLM inputs. This may be because the RLM inputs led to the removal of sediment-derived iron from the shelf, thus affecting the iron limited degree of the subpolar and tropical upwelling regions as well as the productivity of neighboring subtropical gyres. The final result is that the global POC export and transfer are significantly decreased, which reflect the important contribution of sediment-derived iron to the model. In the continental marginal seas the impact of RLM on POC export depends on regional nutrient limitation. The effect is generally negative in areas that is originally Fe-limited, and positive in areas that is not Fe-limited. The POC downward transfer of marginal seas increases under the surface forcing, indicating that the role of lithogenic ballasting in the middle and deep oceans is more important than the changes in primary production caused by the addition of RLM. The total annual POC export and its transfer to the deep in the global estuarine regions increased significantly after considering RLM inputs. This supports the view that lithogenic minerals can stimulate the increase of POC flux through abiotic processes. However, the variations of phytoplankton biomass in the eutrophic zone from top to bottom, firstly increase and then decrease or vice versa, result from nutrient limitation and light intensity changes in the water column caused by different transport modes of RLM.