Model results and newly developed model code for time-slice carbon cycle simulations with CESM1.2

Three time-slice carbon-cycle simulations for the last glacial maximum (LGM) constrained by the CO2 concentration in the atmosphere and the amount of carbon stored in the deep ocean were carried out with a fully-coupled comprehensive climate model CESM1.2 (the Community Earth System Model version 1.2). Although the three modeled LGM ocean states had remarkably different physical features, all of them were compatible with the pre-industrial (PI) state in terms of the global ocean carbon inventory considering the presumed transfers of carbon among the various reservoirs during the evolution from the LGM to PI. The increase in the total alkalinity required to simulate ocean states that is deemed appropriate for the LGM was quantitatively in line with the scenario of post-glacial shallow water deposition of calcium carbonate, suggesting that the reconstructed estimates of the glacial deep-ocean carbon inventory and those of the amount of carbonate deposition on shelves are in agreement with each other. On the other hand, comparisons between the simulated distributions of paleoceanographic tracers and corresponding reconstructions clearly distinguished the different geometry of ocean-circulation cells and favored a shallower Atlantic meridional overturning circulation (AMOC) for the LGM compared to PI.