A coupled climate model study indicates the paleoclimate record of glacial thermohaline circulation (THC) and reversed deep-sea temperature-salinity (T-S) distribution in the Atlantic can be explained largely by lower glacial atmospheric CO2 alone. The reduced CO2 leads to increased Southern Ocean wintertime sea-ice cover and salinity, increased production of dense Antarctic Bottom Water (AABW), enhanced cold and saline AABW penetration into the deep North Atlantic, increased oceanic vertical stability, and reduced North Atlantic Deep Water (NADW) circulation. The dominant role of CO2 forcing during the glacial implies a positive feedback between the Southern Ocean regulated THC and the glacial global carbon cycle.