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Deep-ocean carbonate ion concentrations ([CO(3)(2-)]) and carbon isotopic ratios (δ(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 δ(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.

Submit to Quaternary Science Reviews as an Article Highlights:  New [CO 3 2-] for the intermediate Atlantic and deep Pacific during 0-160 ka;  [CO 3 2-] records show both temporal and transient changes that differ from  13 C;  The MIS 5c-to-3 [CO 3 2-] rise is consistent with the "coral-reef" hypothesis;  Vertical carbon shifting affects [CO 3 2-] variations at MIS 4 and 2;  Deep water [CO 3 2-] controlled CaCO 3 preservation in the deep Pacific.

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Ice core records show a tight correlation between changes in atmospheric CO 2 65 where k = 0.59 ± 0.01 (1used throughout) ( Supplementary Fig. 1, 2 Fig. 9-10 Atlantic (>~3 km) from MIS 5a to 4 (Fig. 3a-c in the deep Atlantic across the MIS 5a-4 transition ( Supplementary Fig. 11-12 25±13 mol/kg calculated based on [CO 3 2-] reconstructions for the 10 studied cores (Fig. 3a-c ~8,000 years after a weakening or shutdown of NADW ( Supplementary Fig. 15, 19) which is ~38% smaller than the observed DIC change (Fig. 1c). The difference is caused by a 177 ~40 mol/kg ALK increase from NADW to AABW (Fig. 1d) ratio of -0.37 been applied, which empirically includes the ALK changes (Fig. 3c), then our 179 calculated deep Atlantic carbon storage increase would be amplified by a factor of 1.6, and the 180 quantity of carbon sequestration in the deep Atlantic would be comparable within uncertainty to 181 the entire atmospheric CO 2 decline from MIS 5a to MIS 4. Additionally, consideration of larger 182  B/Ca in the western Atlantic, which is currently under sampled (Fig. 3a), would potentially raise (Fig. 4b) 34 , which was previously used to infer global carbon budget 199 change leading an AMOC reorganization 3 , might be caused by air-sea isotopic exchange effects

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