Pathways of anthropogenic carbon subduction in the global ocean

Abstract The oceanic uptake of anthropogenic carbon is tightly coupled to carbon subduction, i.e., the physical carbon transfer from the well‐ventilated surface ocean to its interior. Despite their importance, pathways of anthropogenic carbon subduction are poorly understood. Here we use an ocean carbon cycle model to quantify the mechanisms controlling this subduction. Over the last decade, 90% of the oceanic anthropogenic carbon is subducted at the base of the seasonally varying mixed layer. Vertical diffusion is the primary mechanism of this subduction (contributing 65% of total subduction), despite very low local fluxes. In contrast, advection drives the spatial patterns of subduction, with high positive and negative local fluxes. Our results suggest that vertical diffusion could have a leading role in anthropogenic carbon subduction, which highlights the need for an accurate estimate of vertical diffusion intensity in the upper ocean to further constrain estimates of the future evolution of carbon uptake.