Toward Reconciling Radiocarbon Production Rates With Carbon Cycle Changes of the Last 55,000 Years
Peter Köhler, Florian Adolphi, Martin Butzin, Raimund Muscheler
Abstract
Abstract Since it is currently not understood how changes in 14 C production rate ( Q ), and in the carbon cycle, can be combined to explain the reconstructed atmospheric Δ 14 C record, we discuss possible reasons for this knowledge gap. Reviewing the literature, we exclude that changes in the content of atoms in the atmosphere, which produce cosmogenic 14 C after being hit by galactic cosmic rays, might be responsible for parts of the observed differences. When combining Q with carbon cycle changes, one needs to understand the changes in the atmospheric 14 C inventory, which are partially counterintuitive. For example, during the Last Glacial Maximum, Δ 14 C was ∼400‰ higher compared with preindustrial times, but the 14 C inventory was 10% smaller. Some pronounced changes in atmospheric Δ 14 C do not correspond to any significant changes in the atmospheric 14 C inventory, since CO 2 was changing simultaneously. Using two conceptually different models (BICYCLE‐SE and LSG‐OGCM), we derive hypothetical Q s by forcing the models with identical atmospheric CO 2 and Δ 14 C 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.