Over the last 800 ka, significant climatic events such as the Mid-Brunhes Transition (MBT, 430 ka) have profoundly impacted Earth's climate system. The Atlantic Meridional Overturning Circulation (AMOC) and deep-water formation rates around Antarctica have been invoked as vital factors in these climatic events. The MBT marks an increase in the intensity and frequency of glacial-interglacial (G-IG) cycles. Long-term changes in deep-water variability may have played a critical role in providing positive feedback that amplified orbital effects on climate by regulating the ventilation of CO2 in the Southern Ocean through atmospheric and oceanic connections. This study presents a new 770 ka benthic foraminifera δ13C record from sediment core GL-854 retrieved from the western South Atlantic at 2200 m water depth. We compared this record to published δ13C data from the eastern South Atlantic to investigate the zonal δ13C gradient variability (∆δ13Cw-e) of North Atlantic Deep Water (NADW). Our results reveal that ∆δ13Cw-e G-IG variability responds to a “deep-water seesaw” driven by increased influence of Antarctic Bottom Water (AABW) at mid-depths promoted by a shallower AMOC during intense glacial stages. RAMPFIT analysis of the ∆δ13Cw-e record shows an oscillation between four AMOC modes controlled by orbitally-triggered variations in Antarctic sea ice extent, which promoted NADW intensification in particular after 300 ka. Spectral power in the obliquity and eccentricity domains identified in our record suggests that the orbital forcing on Antarctic sea ice extent is propagated toward subtropical regions through controls over the deep-water seesaw. Our interpretation proposes a framework connecting sea-ice and ocean-atmosphere dynamics to deep-water geometry within the South Atlantic basin, which ultimately contributed to the climate changes during the Late Pleistocene.