Poleward Shift of Arctic Oceanic CO₂ Uptake From Asymmetric Seasonal Changes Under Climate Warming

The Arctic region plays a disproportionate role in the global carbon cycle by acting as a critical sink for atmospheric CO₂. However, how Arctic air-sea CO₂ fluxes will respond to continued warming regarding their spatial and temporal changes remains poorly understood. Here, using 14 CMIP6 Earth System Models, we find that Arctic CO₂ uptake exhibits nonmonotonic trends over the 21st century, initially increasing and then declining, alongside a pronounced poleward shift in regions with high CO₂ uptake. This shift is driven primarily by sea ice retreat and warming-induced rise in sea surface CO₂ partial pressure (pCO₂) that decreases air-sea pCO₂ difference, which together lead to seasonally asymmetric changes in regional CO₂ uptake. By the end of the 21st Century, the Polar Sea surpasses the Barents Sea and the Arctic Ocean exceeds the Nordic Seas in CO₂ uptake. These findings indicate the importance of accurately simulating Arctic climate processes to assess future carbon-climate feedbacks and their implications for global climate mitigation.