Abstract: The onset of Northern Hemisphere Glaciation (NHG, ~2.7 Ma) marks a pivotal transition in late Cenozoic climate, which was closely linked to global ocean circulation reorganization and marine carbon reservoir evolution. Understanding their interplay can provide critical insights into climate-carbon cycle feedbacks. We combined recent high-resolution paleoceanographic records (e.g., δ¹³C, CO₃²⁻, εNd) from the Atlantic, Southern Ocean, and Pacific to explore deep water circulation changes and carbon cycle responses during NHG. We proposed that the Antarctic Sea ice expansion probably initiated the Southern Ocean circulation shifts, and thus triggered global ocean teleconnections. In the Atlantic, North Atlantic Deep Water formation was weakened and Antarctic Bottom Water intrusion was enhanced, which altered the deep-carbon storage patterns, and modulated the latitudinal carbon sequestration efficiency. The strengthened Southern Ocean stratification and biological pump efficiency jointly suppressed deep CO₂ release, providing positive feedback for ice-sheet growth. In contrast, Pacific deep-water dynamics remain debated, particularly the role of Pacific Meridional Overturning Circulation and North Pacific Deep Water, requiring further evidence. Future studies shall integrate higher-resolution paleo-proxies and climate modeling to quantify inter-basin coupling mechanisms. Resolving the cascading effects of high-latitude Southern Hemisphere ice expansion and cross-basin feedbacks will refine our understanding of late Cenozoic climate transition and inform projections of modern deep-ocean carbon sink sensitivity.