Air bubbles trapped in the Antarctic ice revealed that atmospheric carbon dioxide concentration during glacial time was estimated to be 80–90 ppm lower than the interglacial level. Deep-ocean holds about 60 times as much carbon as the atmosphere and has played a major role in regulating the atmospheric carbon dioxide concentration on glacial-interglacial timescales. This review examines glacial-interglacial variations in ocean circulation. It is likely that cold and salty abyssal water formed in the Southern Ocean distributed in the glacial ocean. Glacial Atlantic meridional overturning circulation was suggested to be weakening but still operating. North Atlantic origin deep water was above ca. 2000 m, exhibiting pronounced hydrographic boundary with underlying southern source abyssal water. The cold and salty abyssal water is expected to be isolated from overlying water masses and to be a carbon reservoir during glacial period. In order to seek the isolated abyssal reservoir with depleted radiocarbon, glacial deep water ventilation has been reconstructed based on radiocarbon age offset between co-existing benthic and planktic foraminifera. However, the reconstructed ventilation records indicated little possibility of the presence of the radiocarbon depleted deep water mass in the glacial ocean. For further study to reconstruct how much old deep water was distributed in the glacial ocean, spatial and temporal change in marine reservoir effect must be constrained.