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Climate cycles following the mid-Pleistocene transition include the coldest and longest glaciations of the Quaternary, punctuated by repeated rapid climate oscillations and sharp transitions into exceptionally warm, atmospheric CO₂-rich interglacial intervals. Such dramatic climate shifts reflect major reorganizations of the Earth system, with complex feedbacks between North Atlantic ice sheets and ocean–atmosphere carbon cycling believed to have played a central role in the pacing and amplitude of past climate variability. Yet, the response of the deep-ocean, the Earth’s largest reservoir of exchangeable carbon, to abrupt climate change remains elusive, posing a significant challenge to our understanding of the relationship between deep-ocean circulation and past, present, and future climate changes. The recently recovered sedimentary sequence from International Ocean Discovery Program Site U1587 (37°35′N, 10°22′W, 3479n meters below sea level [mbsl]), positioned in a mixing zone of northernand southern-sourced deep waters, offers a valuable archive for reconstructing orbital- to millennial-scale variations in climate and deepocean structure. This study presents new, high-resolution (~1 kyr) benthic foraminifera δ¹⁸O and δ¹³C records from Site U1587, spanning ~ 800 - 300 ka, with a focus on intense glaciations (Marine Isotope Stage [MIS] 16, 12, 10) and subsequent deglaciations (MIS 15, 11, 9). The U1587 δ¹⁸O record was aligned to the established chronology of the nearby Site U1385 (37°34′N, 10°08′W, 2578 mbsl), providing a refined age model for Site U1587 and enabling calculation of vertical δ¹³C gradients across the water column. Site U1587 consistently recorded more negative δ¹³C than the shallower Site U1385, with an average offset of –0.455‰ overall. The vertical δ¹³C gradient between sites is most pronounced during glacial intervals, reaching –1.64‰ at ~465 ka during MIS 12, and is notably reduced during interglacials, with an average of –0.264‰ in MIS 11. These results suggest enhanced deep-ocean stratification and carbon storage during intense glaciations, while the subsequent gradient collapse during deglaciations underscores the link between abrupt changes in deep-ocean circulation and rapid climate transitions into interglacial states.