A recent study published in Nature Communications finds that Antarctic Bottom Water (AABW) overturning circulation slowed rather than strengthened during the early phase of the last deglaciation, around 17,000 to 15,000 years ago. Using isotope-enabled simulations, the study was led by Sifan Gu with co-author Zhengyu Liu, a principal investigator at the Byrd Polar and Climate Research Center and professor in the Atmospheric Sciences program in the Department of Geography at The Ohio State University. 

Researchers have shown that the long-recognized “radiocarbon ventilation seesaw” between the Southern Ocean and the North Atlantic Deep Water (NADW) is best explained by weakened Antarctic overturning, combined with declining Southern Ocean surface reservoir ages. Their results indicate parallel reductions in both AABW and NADW, driven by sea-ice retreat and buoyancy changes in the Southern Ocean. 

This reinterpretation challenges earlier assumptions that stronger Antarctic circulation released carbon from the deep ocean to the atmosphere during deglaciation and instead highlights the role of sluggish overturning at both poles in shaping global carbon exchange. 

The study employed advanced isotope-enabled ocean simulations that track radiocarbon, water transit times, and the mixing of different water masses, allowing the researchers to reproduce observed patterns and separate the effects of circulation slowdowns from changes in air–sea gas exchange. Sensitivity experiments adjusting atmospheric CO₂, sea ice, and winds further confirmed that the early deglacial ventilation seesaw arose from a combination of weaker Antarctic overturning and younger Southern Ocean reservoir ages, refining the interpretation of radiocarbon records and providing new context for modern ocean changes. View the publication.