The ocean’s biological carbon pump transports organic carbon from the surface to depth via three main pathways: the gravitational sinking of particles, active transport by vertically migrating zooplankton, and mixing and advection of suspended and dissolved organic carbon. Here, we use a global data-assimilated ocean biogeochemical model coupled with a new cyclo-stationary ocean circulation inverse model to diagnose the seasonal variability of carbon export and sequestration by these gravitational, migrant, and mixing pumps. The model reveals various seasonal cycles of the carbon export pathways in different ocean biomes. In subtropical regions, the seasonality of gravitational and migrant pump export is weak, while mixing pump export shows strong seasonality with a peak during spring. Contrastingly, in subpolar regions, export and sequestration by the gravitational and migrant pumps peak in the summer, while the mixing pump strongly opposes this seasonality, reaching a maximum during the winter. The gravitational "e-ratio", or ratio of gravitational carbon export to net primary production, shows strong seasonal variability at high latitudes, with higher values in the summer compared to winter. Resolving seasonality suggests sampling bias toward summer could lead to a more contrasting geographic variability of e-ratio. Moreover, the seasonal model also reconciles previous contradictory latitudinal trend in transfer efficiency of particles. These results demonstrate the importance of seasonal observations and models to understand the processes regulating carbon export and sequestration.

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