The Ballast Effect of Terrigenous Lithogenic Particles From Rivers and Its Influence on POC Fluxes in the Ocean

Abstract

Lithogenic materials such as terrigenous lithogenic particles (TLP) can efficiently promote the formation and sinking of mineral-associated marine organic matter, acting as important ballast and potentially playing an important role in the global carbon cycle. To assess the influence of TLP on fluxes of particulate organic carbon (POC) and other biogeochemical cycles, we construct TLP forcing fields based on global riverine suspended sediment data and then apply them to the Community Earth System Model, version 2 (CESM2) modified with the TLP ballasting effect term. Simulations forced by different concentrations of TLP transported in the surface ocean or along the bottom of continental shelves and slopes are conducted. When the TLP transports seaward along the bottom, simulated POC fluxes at 100 and 2,000 m decrease about 11% and 19%, respectively, for the global ocean, and about 9% and 12%, respectively, for the oceanic regions of continental margins. The initial abiotic ballast processes triggered by TLP input increase POC fluxes, causing additional removal and burial of dissolved iron in continental margins. This further enhances the accumulation of macronutrients in the upwelling regions and their advection transport to neighboring subtropical gyres, thus altering regional productivity when simulations reach quasi-equilibrium. When consider the impacts of TLP in simulations, the simulated POC flux exhibits an increase in subtropical gyres but a decrease in tropical Pacific and mid-high latitude regions. The present work highlights the importance of TLP in global biogeochemical cycles, suggesting that the amount of carbon sequestration might be overestimated without TLP in models.