Glob. Biogeochem. Cycles (2013)

Physical processes, such as the advection of surface waters to depth, draw carbon into the ocean interior. Model simulations suggest that the physically induced flux of carbon across the upper ocean exceeds that of other fluxes, such as the sedimentation of organic matter, by an order of magnitude.

Marina Levy, of LOCEAN-IPSL, France, and colleagues used a global sea-ice ocean-circulation model to quantify the physically induced flux of carbon into and out of the mixed layer of the upper ocean in pre-industrial times. According to their simulations, vertical advection led to the net subduction of dissolved inorganic carbon to depth in temperate, mid-latitude waters, whereas horizontal advection resulted in the net enrichment of mixed-layer waters with dissolved inorganic carbon in the tropics. Overall, physical processes led to an annual export of 264.5 Pg of dissolved inorganic carbon out of the mixed layer, and the annual injection of 275.5 Pg into the mixed layer, globally. Furthermore, 2.1 Pg of organic carbon was exported out of the mixed layer due to physical processes, equivalent to 20% of the total flux of organic matter to depth.

Although the ultimate fate of the carbon exported to the oceanic interior remains uncertain, the findings suggest that the physical transfer of carbon is a key component of the marine carbon cycle.