We are investigating the late Holocene rise in CO2 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 CaCO3. Ice core data of atmospheric CO2 between 8 ka BP and preindustrial climate can only be reproduced if CO2 outgassing due to shallow water sedimentation of CaCO3 is considered. In this case the model displays an increase of nearly 20 ppmv CO2 between 8 ka BP and present day. Model configurations that do not contain this forcing show a slight decrease in atmospheric CO2. We can therefore explain the late Holocene rise in CO2 by invoking natural forcing factors only, and anthropogenic forcing is not required to understand preindustrial CO2 dynamics.

Four experiments were performed: AO (Atmosphere-Ocean), AOV (Atmosphere-Ocean-Vegetation), AOVP (Atmosphere-Ocean-Vegetation-Peat), and AOVPC (Atmosphere-Ocean-Vegetation-Peat-Coral). All experiments were transient experiments from 8 ka BP to present day, initialised from 8 ka BP conditions, driven by orbital forcing. For exact experiment description, see reference.Transient output is provided for all four experiments, time resolution is 50-year average values every 50 years.Each experiment output consists of 8 files, with filenames preceded by the experiment code.This publication and supplement is a result of sub-project "Comparison of climate and carbon cycle dynamics during late Quaternary interglacials using a spectrum of climate system models, ice-core and terrestrial archives" (COIN, web page archived at hdl:10013/epic.37020.d001).

Supplement to: Kleinen, Thomas; Brovkin, Victor; von Bloh, Werner; Archer, David E; Munhoven, Guy (2011): Holocene carbon cycle dynamics. Geophysical Research Letters, 37, L02705, 5 pp