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

Abstract 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.