Large-scale effects of eddies on ocean biological carbon pump

Estimates of the ocean biological carbon pump – the transfer of organic carbon from the surface to the ocean interior - are limited by uncertainties in the physical injection of particulate and dissolved organic carbon. A major challenge is to evaluate the integrated effect of these physical pumps at small spatial and temporal scales. We used a submesoscale permitting (2 km) biophysical model covering a subpolar and a subtropical gyre that successfully simulates intense eddy‐driven subduction hotspots comparable to what has been observed in nature. These eddy‐driven subduction events are able to transfer carbon below the mixed‐layer, but contribute little to the annual export, due to strong compensation between upward and downward fluxes. In contrast, we show that small‐scale heterogeneities of the mixed layer intermittently export large amounts of both particulate and dissolved organic carbon (POC and DOC). This suggests that the traditional view of the mixed-layer pump (wintertime export of DOC) should be expanded to include the downward mixing of plankton associated with springtime short-lived de-stratification events. High resolution measurements of export flux, such as the one undertaken by the NASA EXPORTS program, are needed to test models such as this one, and improve our mechanistic understanding of the biological pump.