Data-model comparison of marine 13C across Termination I

We use benthic isotope data from 491 sediment cores compiled in the World Atlas of late Quaternary Foraminiferal Oxygen and Carbon Isotope Ratios (Mulitza et al., 2022) to evaluate transient simulations across the last 25 kyr performed with BICYCLE-SE, the solid Earth version of the Box model of the Isotopic Carbon cYCLE (Köhler & Mulitza, 2024), which have been updated by data-based constraints on the deglacial release of ~250 PgC from land via permafrost thaw (Winterfeld et al., 2018), extensive petrogenic organic carbon oxidation (Wu et al., 2022) and biomass burning (Riddell-Young et al., 2025). These additional land carbon fluxes reduce mean ocean δ¹³C by 0.1‰ since the Last Glacial Maximum (LGM). The increase in mean ocean δ¹³C is 0.45‰ since the LGM in both data and model, but the rise started only after Heinrich Stadial 1 in the data, but earlier in the simulations. Abrupt reductions in Atlantic Meridional Overturning Circulation during Greenland stadials as suggested from ¹⁴C (Köhler et al., 2024) lead to simulated anomalies in δ¹³C in most ocean boxes, that are not confirmed by the δ¹³C data. Further model-data offsets suggest that the so far applied assumptions on changes in the Southern Ocean physical and biological carbon pumps during the deglaciation in BICYCLE-SE might need to be revised – or point to the limitations of this simple box model approach.        

References:

Köhler, P. and Mulitza, S.: No detectable influence of the carbonate ion effect on changes in stable carbon isotope ratios (δ¹³C) of shallow dwelling planktic foraminifera over the past 160kyr, Clim. Past, 20, 991–1015, https://doi.org/10.5194/cp- 20-991-2024, 2024.

Köhler, P., Skinner, L. C., and Adolphi, F.: Radiocarbon cycle revisited by considering the bipolar seesaw and benthic ¹⁴C data, Earth Planet. Sc. Lett., 640, 118801, https://doi.org/10.1016/j.epsl.2024.118801, 2024.

Mulitza, S., Bickert, T., Bostock, H. C., Chiessi, C. M., Donner, B., Govin, A., Harada, N., Huang, E., Johnstone, H., Kuhnert, H., Langner, M., Lamy, F., Lembke-Jene, L., Lisiecki, L., Lynch- Stieglitz, J., Max, L., Mohtadi, M., Mollenhauer, G., Muglia, J., Nürnberg, D., Paul, A., Rühlemann, C., Repschläger, J., Saraswat, R., Schmittner, A., Sikes, E. L., Spielhagen, R. F., and Tiedemann, R.: World Atlas of late Quaternary Foraminiferal Oxygen and Carbon Isotope Ratios, Earth Syst. Sci. Data, 14, 2553–2611, https://doi.org/10.5194/essd-14-2553-2022, 2022.

Riddell-Young, B., Lee, J. E., Brook, E. J., Schmitt, J., Fischer, H., Bauska, T. K., Menking, J. A., Iseli, R., and Clark, J. R.: Abrupt changes in biomass burning during the last glacial period, Nature, 637, 91–96, https://doi.org/10.1038/s41586-024-08363-3, 2025.

Winterfeld, M., Mollenhauer, G., Dummann, W., Köhler, P., Lembke-Jene, L., Meyer, V. D., Hefter, J., McIntyre, C., Wacker, L., Kokfelt, U., and Tiedemann, R.: Deglacial mobilization of pre-aged terrestrial carbon from degrading permafrost, Nature Communications, 9, 3666, https://doi.org/10.1038/s41467-018-06080-w, 2018.

Wu, J., Mollenhauer, G., Stein, R., Köhler, P., Hefter, J., Fahl, K., Grotheer, H., Wei, B., and Nam, S.-I.: Deglacial release of petrogenic and permafrost carbon from the Canadian Arctic impacting the carbon cycle, Nature Communications, 13, 7172, https://doi.org/10.1038/s41467-022-34725-4, 2022.