Deep-ocean carbonate ion concentrations ([CO(3)(2-)]) and carbon isotopic ratios (delta(13)C) place important constraints on past redistributions of carbon in the ocean-land-atmosphere system and hence provide clues to the causes of atmospheric CO(2) concentration changes. However, existing deep-sea [CO(3)(2-)] reconstructions conflict with one another, complicating paleoceanographic interpretations. Here, we present deep-sea [CO(3)(2-)] for five cores from the three major oceans quantified using benthic foraminiferal boron/calcium ratios since the last glacial period. Combined benthic delta(13)C and [CO(3)(2-)] results indicate that deep-sea-released CO(2) 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 CO(2) rise, a substantial portion of CO(2) released from oceans was absorbed by the terrestrial biosphere.