The Younger Dryas (YD, dated between 12.7}11.6 ky BP in the GRIP ice core, Central Greenland) is a distinct cold period in the North Atlantic region during the last deglaciation. A popular, but controversial hypothesis to explain the cooling is a reduction of the Atlantic thermohaline circulation (THC) and associated northward heat #ux as triggered by glacial meltwater. Recently, a CH # -based synchronization of GRIP ###O and Byrd CO # records (West Antarctica) indicated that the concentration of atmospheric CO # (CO### # ) rose steadily during the YD, suggesting a minor in#uence of the THC on CO### # at that time. Here we show that the CO### # change in a zonally averaged, circulation-biogeochemistry ocean model when THC is collapsed by freshwater #ux anomaly is consistent with the Byrd record. Cooling in the North Atlantic has a small e!ect on CO### # in this model, because it is spatially limited and compensated by far-"eld changes such as a warming in the Southern Oce...