Global maps of silicate, nitrate, and carbon export and resupply fluxes from Biogeochemical Argo observations

The redistribution of nutrients and carbon from the surface ocean to the ocean interior regulates marine productivity and climate, yet global observation-based estimates of export and resupply fluxes remain poorly constrained because most existing estimates rely on fixed stoichiometric assumptions. Here, we develop a hybrid multiple-linear-regression and neural-network framework to reconstruct silicate, nitrate, and dissolved inorganic carbon from hydrographic observations and apply it to 106,905 Biogeochemical Argo profiles collected between 2003 and 2021. This approach produces the first observation-based global maps of annual downward export and upward resupply fluxes of silicate, nitrate, and carbon. The maps reveal pronounced regional decoupling among silicon, nitrogen, and carbon cycling. Silicic acid (Si(OH)₄; hereafter referred to as silicate) export exhibits substantially greater spatial variability than nitrate export, with the highest silicate:nitrate export ratios occurring in the Southern Ocean and decreasing northward across the Indo-Pacific, whereas much of the Atlantic is characterized by silicate:nitrate export ratios below 1. The Southern Ocean south of 45° S accounts for approximately 30% of both global biologically mediated carbon export and net carbon removal to the ocean interior. These observation-based global maps provide a new baseline for investigating nutrient–carbon coupling and its response to future climate change.