Holocene carbon cycle dynamics

We are investigating the late Holocene rise in CO 2 by performing four experiments with the climate‐carbon‐cycle model CLIMBER2‐LPJ. Apart from the deep sea sediments, important carbon cycle processes considered are carbon uptake or release by the vegetation, carbon uptake by peatlands, and CO 2 release due to shallow water sedimentation of CaCO 3 . Ice core data of atmospheric CO 2 between 8 ka BP and preindustrial climate can only be reproduced if CO 2 outgassing due to shallow water sedimentation of CaCO 3 is considered. In this case the model displays an increase of nearly 20 ppmv CO 2 between 8 ka BP and present day. Model configurations that do not contain this forcing show a slight decrease in atmospheric CO 2 . We can therefore explain the late Holocene rise in CO 2 by invoking natural forcing factors only, and anthropogenic forcing is not required to understand preindustrial CO 2 dynamics.