Cretaceous-Palaeogene experiments in Biogeochemical Resilience

Abstract:

Human activity is altering biogeochemical cycles in the ocean. While ultimately anthropogenic forcings may be brought under control, it is still unclear whether tipping points may exist beyond which human-induced changes to biogeochemical cycles become irreversible. We use the Late Cretaceous and the Cretaceous-Palaeogene (K-Pg) boundary interval as an informative case study. Over this interval, two carbon cycle perturbations (gradual flood basalt volcanism and abrupt bolide impact) occurred within a short time window, allowing us to investigate the resilience of biogeochemical cycles to different pressures applied to the same initial boundary conditions on very different time scales. We demonstrate that relatively gradual emission of CO₂ from the Deccan large igneous province was efficiently mitigated within the limits of existing biogeochemical processes. However, the rapid extinction of pelagic calcifying organisms at the K-Pg boundary due to the Chicxulub bolide impact had more profound effects, and caused lasting (> 1 million years) changes to biogeochemical cycles. By combining sedimentological observations with boron isotope-based pH reconstructions over these events, we document two potentially useful partial analogues for best and worst case scenarios for anthropogenic global change. We suggest that if current ocean acidification results in the mass extinction of marine pelagic calcifiers, we may cause profound changes to the Earth system that will persist for 100,000s to millions of years.