Decoupled Antarctic and Subarctic export productivity under intensified Southern Hemisphere westerlies during the...

The Last Interglacial (128-113 ka B.P.) provides key insights into climate-carbon interactions under warm, high-CO₂ conditions. While Antarctic temperature-driven Southern Ocean ventilation has been proposed to modulate atmospheric CO₂, role of Southern Hemisphere westerlies (SHW) remains unclear. Here we synthesize 15 Antarctic and 5 subarctic Pacific export productivity records over two glacial-interglacial cycles. We find that Antarctic and subarctic productivity generally tracked Antarctic temperature and atmospheric CO₂, but decoupled during Marine Isotope Stage 5, notably the Last Interglacial: high Antarctic productivity and CO₂ persisted despite reduced subarctic productivity and over 6 °C Antarctica cooling. We suggest that poleward-intensified SHW strengthened upwelling of Circumpolar Deep Water, sustaining Antarctic productivity and atmospheric CO₂, while altered Southern Ocean deep-water supply to the subarctic Pacific likely suppressed upwelling, limiting CO₂ release. These findings identify SHW as key in polar ocean dynamics and carbon cycling, with implications for future climate under projected SHW intensification.