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Abstract

We used an ocean carbon cycle model that was imposed on the output of the climate model MIROC 4m to explore the mechanisms of transient changes in the ocean carbon cycle during the last deglaciation. Transient ocean carbon cycle modeling showed millennial-scale changes in atmospheric partial pressure of carbon dioxide (pCO2) caused by climate change including drastic changes in the Atlantic meridional overturning circulation (AMOC) during the last deglaciation. To elucidate the factors contributing to the change in atmospheric pCO2, we focused on changes in the partial pressure of pCO2 at the sea surface, which controls atmospheric pCO2 through the gas-exchange between the atmosphere and ocean. During the Heinrich stadial 1, increases in sea surface temperature (SST) controlled the rise in atmospheric pCO2. During the Bølling-Allerød and Younger Dryas, changes in pCO2 solubility and distribution of carbonate compounds combined to change atmospheric pCO2. The increase in alkalinity of the surface North Atlantic associated with the AMOC resumption contributed most to the decrease in atmospheric pCO2 during the Bølling-Allerød, while during the Younger Dryas, the increase in SST in the Southern Ocean contributed most to the increase in atmospheric pCO2. We present that changes in SST and alkalinity as well as dissolved inorganic carbon associated with changes in AMOC are important factors controlling the rise in atmospheric pCO2 during the deglaciation.