The oceanic physical injection pump of particulate organic carbon

Abstract

The contribution of the ocean biological carbon pump to the export of organic carbon at depth has predominantly been assessed by considering sinking particulate matter and vertically migrating organisms. Despite growing recognition of the importance of dynamical pathways that export carbon through upper ocean mixing and advection, observation-based estimates of their global impact are still lacking. In this study, we leverage a 4D data-driven time series (1997-2018) of particulate organic carbon concentration (POC) and ocean circulation to quantify the physical injection pump. We dissect the roles of entrainment and horizontal/vertical advection across mesoscale to large scales. Our findings indicate that, on average, the physical injection pump exports 0.086±0.030 Pg POC yr⁻¹. This value diminishes to less than one-third when using climatological POC values instead of weekly estimates, highlighting the critical coupling between the POC annual cycle and upper layer dynamics in determining net export. Observed interannual variations are linked to a linear combination of the El Niño–Southern Oscillation and Southern Annular Mode, suggesting a dynamic connection to intermediate/mode water-mass formation in the Southern Ocean.