Exploring the differing CO2 response to Dansgaard-Oeschger and Heinrich events

Dansgaard-Oeschger (DO) and Heinrich (H) events are ubiquitous features of glacial climates involving abrupt and large changes in climate over the North Atlantic region, extending also to the Southern Hemisphere through the bipolar seesaw mechanism. Ice core data also indicate that the DO and H events are accompanied by pronounced changes in atmospheric CO₂ concentration, but their origin remains uncertain. Here, we use simulations with the fast Earth system model CLIMBER-X, which produces self-sustained DO events as internal variability, to explore the processes involved in the atmospheric CO₂ response. While the DO events are internally generated in the model, the Heinrich events are mimicked by adding a freshwater flux of 0.05 Sv over 1000 years in the latitudinal belt between 40°N and 60°N in the North Atlantic.
The simulated Greenland temperature varies by ~7-8°C between stadials and interstadials, with only small differences between H and DO stadials, while Antarctic temperature responds substantially stronger to H than to DO events, broadly in agreement with observations. In the CLIMBER-X simulations, atmospheric CO₂ varies by ~5 ppm during DO events, but by ~15 ppm during H events, comparable with ice core data. The peak in CO₂ concentrations is delayed by several centuries relative to both the stadial-interstadial transition and the peak in Antarctic temperature. The CO₂ rise during the H stadial is driven by ocean outgassing. In contrast, the rapid CO₂ increase after the transition to the interstadial results from soil carbon release from high NH latitudes originating from substantial warming.