168 / 2024-09-10 15:35:42

Evaluating the role of enhanced weathering in marine carbon dioxide removal under high emission pathway

mCDR,Enhanced Weathering,Efficacy

Among many proposed geoengineering methods, ocean alkalinity enhancement (OAE) is the only one that can synchronically enhance oceanic carbon uptake and abate ocean acidification. However, its efficacy and side-effect has yet to be fully determined. Previous model studies applied OAE uniformly at the basin or global scale, which is unfeasible in practice and neglected the effect of nutrient-release accompanied with OAE. To test efficacy of a more practical OAE method and fill the knowledge gap of accompanying nutrient effect along with OAE, we applied OAE at the mouths of global rivers by increasing alkalinity flux in the form of bicarbonate by 5-fold, and by simultaneously increasing fluxes of nutrients and alkalinity by 5-fold in a fully coupled Earth System Model under the high emission scenario (SSP585). We find that the alkalinity enhancement and simultaneous nutrient and alkalinity enhancement respectively increase pH by 0.025 and 0.030, CO₂ influx by 300 and 350 mmol m^-2 yr^-1, oceanic inventory of dissolved inorganic carbon (DIC) by 5.49 and 6.18 Pmol, and decrease the atmospheric CO₂ by 30 and 40 ppmv. The most significant response to the enhancement of alkalinity and nutrients are found in coastal regions, the Indian, and the North Atlantic oceans. Nutrient-induced biological activity also enhances alkalinity further in the Subpolar Atlantic Ocean and India Ocean, and decrease alkalinity in the Southern Ocean and tropical/subtropical Atlantic and Pacific. Our simulation suggests that the simultaneous enhancement of alkalinity and nutrients is more effective in modulating climate change than adding 'pure' alkalinity.