The ocean is a vast store of anthropogenic and natural carbon, the former from manmade CO₂ emissions absorbed at the surface and the latter produced in the interior from remineralization of sinking biogenic particles. On the one hand, climate change is projected to decrease uptake, while on the other it is predicted to increase accumulation of regenerated carbon. However, for how long this carbon will remain sequestered in the ocean under a warming climate remains poorly constrained. With support from this tokutei kadai project, I have quantified for the first time the impact of climate change on the sequestration efficiency of the ocean. My results show that a projected slowdown in the global ocean circulation due to global warming lengthens by centuries to thousands of years the time for which carbon remains sequestered. Moreover, this increase in storage time is evident even under low emission, high mitigation scenarios, and is accompanied by a shift in circulation pathways that further enhances the dominance of the Southern Ocean as the location at which the accumulated carbon remerges at the surface. These results highlight the potential long-term impact of global warming-induced changes in the marine carbon cycle on climate. I will present these results at the European Geosciences Union and Japan Geoscience Union conferences in Vienna and Chiba, respectively, in May 2026. A manuscript is also under preparation for submission to Nature Geoscience. Funding from this project was used to purchase supercomputing time on the Tokyo University Wisteria system to perform simulations, and for travel to meet research collaborators and attend conferences and workshops.