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Deep-ocean carbonate ion concentrations ([CO32-]) and carbon isotopic ratios (δ13C) place important constraints on past redistributions of carbon in the ocean-land-atmosphere system and hence provide clues to the causes of atmospheric CO2 concentration changes. However, existing deep-sea [CO32-] reconstructions conflict with one another, complicating paleoceanographic interpretations. Here, we present deep-sea [CO32-] for five cores from the three major oceans quantified using benthic foraminiferal boron/calcium ratios since the last glacial period. Combined benthic δ 13C and [CO32-] results indicate that deep-sea-released CO2 during the early deglacial period (17.5 to 14.5 thousand years ago) was preferentially stored in the atmosphere, whereas during the late deglacial period (14 to 10 thousand years ago), besides contributing to the contemporary atmospheric CO2 rise, a substantial portion of CO2 released from oceans was absorbed by the terrestrial biosphere. [ABSTRACT FROM AUTHOR]