Reconstructed late-Pleistocene CO2 fluxes reveal a shift in carbon cycling since the Mid-Brunhes transition

Ice cores provide constraints on past carbon cycling and associated atmospheric CO2 and mean surface temperature variations1,2, revealing systematic shifts between glacial and interglacial climate states3,4. However, poor quantification of surface source and sink CO2 fluxes hinders understanding of the drivers and feedbacks behind such climate variability. Correlated atmospheric CO₂ and temperature variations over the past ~800 kyr are largely due to orbital forcing, but the intensification of glacial-interglacial cycles since ~430 ka, following the so-called Mid-Brunhes Transition (MBT)5, cannot be explained by orbital parameters alone6. This suggests the activation of interacting mechanisms within the Earth system, the nature of which remains debated. We apply a new Bayesian inversion algorithm7 to the Dome C (Antarctica) CO₂ and temperature record3,4 to generate unprecedented reconstructions of surface CO₂ source and sink fluxes. Results reveal systematic pulses of CO₂ source fluxes during glacial maxima and deglaciations, preceding peaks in CO₂ sink fluxes, with all pulses first appearing post-MBT. Wavelet coherence and cross-correlation analyses suggest that post-MBT climate variability was amplified by feedbacks linking sea-level change, ice-sheet dynamics, and volcanic CO₂ emissions8,9. Our findings underscore the influence of the solid Earth on late-Pleistocene carbon cycling and climate and offer critical constraints for models of past and future climates.