C01_04

Toward Reconciling Radiocarbon Production Rates With

Carbon Cycle Changes of the Last 55,000 Years

Köhler P¹, Adolphi F¹, Butzin M¹, Muscheler R²

¹Alfred Wegener Institute Helmholtz Centre For Polar And Marine Research, Bremerhaven, Germany, ²Department of Geology, Lund University, Lund, Sweden

Since it is currently not understood how changes in ¹⁴C production rate (Q), and in the carbon cycle, can be combined to explain the reconstructed atmospheric Δ¹⁴C record, we discuss possible reasons for this knowledge gap. When combining Q with carbon cycle changes, one needs to understand the changes in the atmospheric ¹⁴C inventory, which are partially counterintuitive. For example, during the Last Glacial Maximum, Δ¹⁴C was ∼400‰ higher compared with preindustrial times, but the ¹⁴C inventory was 10% smaller. Some pronounced changes in atmospheric Δ¹⁴C do not correspond to any significant changes

in the atmospheric ¹⁴C inventory, since CO₂ was changing simultaneously. Using two conceptually different models (BICYCLE-SE and LSG-OGCM), we derive hypothetical Qs by forcing the models with identical atmospheric CO₂ and Δ¹⁴C data. Results are compared with the most recent data-based estimates of Q derived from cosmogenic isotopes. Millennial-scale climate change connected to the bipolar seesaw is missing in the applied models, which might explain some, but probably not all, of the apparent model-data disagreement in Q. Furthermore, Q based on either data from marine sediments or ice cores contains offsets, suggesting an interpretation deficit in the current data-based approaches.