Atlantic Meridional Overturning Circulation during the Last Glacial and Deglacial: Inferences from the Atlantic Tropical Thermocline Temperature and Seawater Radiocarbon Activity

This thesis aims to investigate variations of the last glacial and deglacial Atlantic Ocean circulation, with emphasize on the Atlantic deepwater ventilation rate during the Last Glacial Maximum (LGM). The highlights of the thesis are as the followings: (1) the modern frontal zone between the North Atlantic and the South Atlantic central waters off NW Africa shifted to the south during the last glacial and deglacial time periods. (2) The radiocarbon-based circulation age of the deep Atlantic (> 1500 m) was estimated to be less than 400 years during the LGM, which was equal to or less than its pre-bomb value. Therefore, the LGM deep Atlantic was inferred to be well ventilated. (3) The abyssal Atlantic (below 2500 m) prior to the LGM was more depleted in radiocarbon activities by 400 per mil than the contemporary atmosphere. A significant change in the structure of the carbon cycle could have importantly contributed to extremely high atmospheric radiocarbon activities prior to the LGM.