The role of land–sea fluxes during deglacial flooding in ocean biogeochemistry and CO₂ exchange remains poorly constrained due to the lack of climate models that consider such fluxes. We implement the terrestrial organic matter fluxes into the ocean at a transiently changing land–sea interface in MPI-ESM and investigate their effect during the last deglaciation. Most of the terrestrial carbon goes to the ocean during flooding events of Meltwater Pulse 1a, which leads to regional CO₂ outgassing.