Role of the Amazon River Estuary in Land-to-Ocean Carbon and Nutrients Exchanges

Estuaries are biogeochemical hotspots that regulate the balance of carbon and nutrients delivered to the ocean. In the absence of land-to-ocean models, estuarine processes are overlooked in the global carbon budget. Here, we connected the watershed (Global NEWS 2), reactive transport estuary (C-GEM), and ocean-biogeochemical (ECCO-Darwin) models to quantify the estuarine contribution to carbon and nutrient exchanges across the Lower Amazon. The remineralization of organic carbon drives substantial CO2 outgassing (27 Tg C yr-1) along the estuary and reduces the organic carbon delivered to the ocean (-62%). However, the resulting increase in lateral fluxes of inorganic nutrients enhances primary production in the river plume region (+150%). The estuary enhances CO2 uptake in the river plume and the tropical Atlantic (+8 and +7.1 Tg C yr-1, respectively) and improves simulated air-sea CO2 fluxes in ECCO-Darwin. Our coupled model approach advances the implementation of models that reduces the uncertainty associated with land-to-ocean processes in the global carbon budget.