Biogeosciences, 16, 2543–2555, 2019 https://doi.org/10.5194/bg-16-2543-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. What was the source of the atmospheric CO2 increase during the Holocene? Victor Brovkin1, Stephan Lorenz1, Thomas Raddatz1, Tatiana Ilyina1, Irene Stemmler1, Matthew Toohey2, and Martin Claussen1,3 1Max-Planck Institute for Meteorology, Hamburg, Germany 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany 3Meteorological Institute, University of Hamburg, Hamburg, Germany Correspondence: Victor Brovkin (
[email protected]) Received: 22 February 2019 – Discussion started: 4 March 2019 Revised: 7 June 2019 – Accepted: 12 June 2019 – Published: 2 July 2019 Abstract. The atmospheric CO2 concentration increased by face alkalinity decrease, for example due to unaccounted for about 20 ppm from 6000 BCE to the pre-industrial period carbonate accumulation processes on shelves, is required for (1850 CE). Several hypotheses have been proposed to ex- consistency with ice-core CO2 data. Consequently, our sim- plain mechanisms of this CO2 growth based on either ocean ulations support the hypothesis that the ocean was a source or land carbon sources. Here, we apply the Earth system of CO2 until the late Holocene when anthropogenic CO2 model MPI-ESM-LR for two transient simulations of climate sources started to affect atmospheric CO2. and carbon cycle dynamics during this period. In the first simulation, atmospheric CO2 is prescribed following ice- core CO2 data. In response to the growing atmospheric CO2 concentration, land carbon storage increases until 2000 BCE, 1 Introduction stagnates afterwards, and decreases from 1 CE, while the ocean continuously takes CO2 out of the atmosphere after The recent interglacial period, the Holocene, began in 4000 BCE.