<jats:title>Abstract</jats:title> <jats:p>During the last deglaciation, the opposing patterns of atmospheric CO<jats:sub>2</jats:sub> and radiocarbon activities (Δ<jats:sup>14</jats:sup>C) suggest the release of <jats:sup>14</jats:sup>C-depleted CO<jats:sub>2</jats:sub> from old carbon reservoirs. Although evidences point to the deep Pacific as a major reservoir of this <jats:sup>14</jats:sup>C-depleted carbon, its extent and evolution still need to be constrained. Here we use sediment cores retrieved along a South Pacific transect to reconstruct the spatio-temporal evolution of Δ<jats:sup>14</jats:sup>C over the last 30,000 years. In ∼2,500–3,600 m water depth, we find <jats:sup>14</jats:sup>C-depleted deep waters with a maximum glacial offset to atmospheric <jats:sup>14</jats:sup>C (ΔΔ<jats:sup>14</jats:sup>C=−1,000‰). Using a box model, we test the hypothesis that these low values might have been caused by an interaction of aging and hydrothermal CO<jats:sub>2</jats:sub> influx. We observe a rejuvenation of circumpolar deep waters synchronous and potentially contributing to the initial deglacial rise in atmospheric CO<jats:sub>2</jats:sub>. These findings constrain parts of the glacial carbon pool to the deep South Pacific.</jats:p>