Ocean circulation crucially affects the global climate on glacial-interglacial timescales. In particular, changes in the Atlantic overturning circulation are thought to facilitate carbon storage in the deep ocean and lower atmospheric CO₂ during the Last Glacial Maximum (LGM). Despite extensive effort, the LGM Atlantic circulation regime remains highly debated. Because deep waters formed in the high-latitude Atlantic have contrasting carbonate chemistry, a change in their mixing would affect deep water acidity and, via dissolution, sedimentary calcium carbonate contents. Here, we reconstruct the LGM Atlantic deep-water mass structure through modeling of published carbonate content data. We show that relatively corrosive southern-sourced water (SSW) largely filled the deep Southwest Atlantic and penetrated into the Equatorial Eastern Atlantic through fracture zones during the LGM. Except for Cape Basin which was affected by very corrosive deep Pacific waters, the LGM East Atlantic was occupied by greater amounts of well saturated northern-sourced waters. Our reconstructed asymmetrical water-mass distribution in the LGM Atlantic places new constraints on the past thermohaline circulation and, hence, global carbon cycle changes.