The Late Miocene Carbon Isotope Shift driven by synergetic terrestrial processes: A box-model study

As the most significant carbon isotope excursion in the past ∼10 Ma, the Late Miocene Carbon Isotope Shift (LMCIS, ∼7.65 to 6.5 Ma) offers a great opportunity to investigate the carbon-climate dynamics in a warmer-than-today world. However, the driving mechanisms of the LMCIS remain controversial. In this study, we used a 7-box biogeochemical model to simulate the long-term sea water δ¹³C and atmospheric CO₂ changes during the late Miocene. Based on quantitative parameterization of two terrestrial processes (C₄-grasses expansion and enhanced weathering input) during the late Miocene, our results show that the synergy between the two terrestrial processes may ultimately result in the LMCIS via the perturbation of the land-sea carbon fluxes. Moreover, our results reveal that the re-partitioning of alkalinity and nutrients between the land and the ocean may have influenced the long-term atmospheric CO₂ change during the late Miocene.