Climate–Carbon Cycle Model Response to Freshwater Discharge into the North Atlantic

The response of a coupled climate–carbon cycle model to discharge of freshwater into the North Atlantic is investigated with regard to cold reversals caused by meltwater from northern continental ice sheets such as the Younger Dryas during the last deglaciation. The extreme case in which the North Atlantic thermohaline circulation ceases in several decades is discussed. In the preindustrial case, northern severe cooling is reproduced by the collapse of the Atlantic northward heat transport, and land carbon decreases because of a decrease in net primary production (NPP) by the cooling or precipitation decrease, resulting in a decrease in global air temperature and an increase in atmospheric carbon dioxide (CO2) concentration. The atmospheric CO2 increase by the land carbon decrease is consistent with a previous terrestrial vegetation model study and a minimum in ice core δ13CO2 during the Younger Dryas. The atmospheric CO2 increase in this model is less than 10 ppmv, consistent with the paleoclima...