Submesoscale Physics and Biophysical coupling Affect DOC export in the North Atlantic*

Dissolved organic matter is the largest oceanic carbon reservoir, yet key discrepancies remain in its mechanisms of cycling and sequestration. While dissolved organic carbon (DOC) is thought to accumulate in the surface over the year and mix into the deeper ocean during winter and large-scale mixing, submesoscale dynamics (including submesoscale eddies, fronts, and filamentary structures) likely drive unaccounted DOC flux throughout the year. We investigate how submesoscale dynamics shape DOC fluxes using the Massachusetts Institute of Technology General Circulation Model in two setups: one couples the circulation to a biogeochemical model that explicitly represents heterotrophic bacterial processes and DOC dynamics, and the other only includes a simple passive DOC tracer. Preliminary experiments show that 3-D physics reshape the annual cycles of DOC and net community production, and that active biological coupling increases DOC export beyond mixing or reaction-time effects from DOC lability and causes different in-eddy spatial patterns in DOC. These findings challenge the view that DOC export is driven mainly by seasonal and large-scale mixing and highlight the need to resolve fine-scale physical–biogeochemical interactions to predict ocean carbon sequestration.