What was the source of the atmospheric CO2 increase during the Holocene?

Abstract. The atmospheric CO2 concentration increased by about 20 ppm from 6000 BCE to the pre-industrial period (1850 CE). Several hypotheses have been proposed to explain mechanisms of this CO2 growth based on either ocean or land carbon sources. Here, we apply the Earth system model MPI-ESM-LR for two transient simulations of climate 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, stagnates afterwards, and decreases from 1 CE, while the ocean continuously takes CO2 out of the atmosphere after 4000 BCE. This leads to a missing source of 166 Pg of carbon in the ocean–land–atmosphere system by the end of the simulation. In the second experiment, we applied a CO2 nudging technique using surface alkalinity forcing to follow the reconstructed CO2 concentration while keeping the carbon cycle interactive. In that case the ocean is a source of CO2 from 6000 to 2000 BCE due to a decrease in the surface ocean alkalinity. In the prescribed CO2 simulation, surface alkalinity declines as well. However, it is not sufficient to turn the ocean into a CO2 source. The carbonate ion concentration in the deep Atlantic decreases in both the prescribed and the interactive CO2 simulations, while the magnitude of the decrease in the prescribed CO2 experiment is underestimated in comparison with available proxies. As the land serves as a carbon sink until 2000 BCE due to natural carbon cycle processes in both experiments, the missing source of carbon for land and atmosphere can only be attributed to the ocean. Within our model framework, an additional mechanism, such as surface alkalinity decrease, for example due to unaccounted for carbonate accumulation processes on shelves, is required for consistency with ice-core CO2 data. Consequently, our simulations support the hypothesis that the ocean was a source of CO2 until the late Holocene when anthropogenic CO2 sources started to affect atmospheric CO2.

[1]  M. Toohey,et al.  Global temperature modes shed light on the Holocene temperature conundrum , 2020, Nature Communications.

[2]  V. Brovkin,et al.  The Global Methane Budget 2000–2017 , 2016, Earth System Science Data.

[3]  P. Köhler.  Interactive comment on “What was the source of the atmospheric CO2 increase during the Holocene?” by Victor Brovkin et al. , 2019 .

[4]  E. Galbraith,et al.  Carbon burial in deep-sea sediment and implications for oceanic inventories of carbon and alkalinity over the last glacial cycle , 2018, Climate of the Past.

[5]  G. Hugelius,et al.  Extensive loss of past permafrost carbon but a net accumulation into present-day soils , 2018, Nature.

[6]  W. Ruddiman.  Geographic evidence of the early anthropogenic hypothesis , 2017 .

[7]  M. Lachniet,et al.  Holocene warming in western continental Eurasia driven by glacial retreat and greenhouse forcing , 2017 .

[8]  T. Ilyina,et al.  Incorporating a prognostic representation of marine nitrogen fixers into the global ocean biogeochemical model HAMOCC , 2017 .

[9]  F. Joos,et al.  Holocene peatland and ice-core data constraints on the timing and magnitude of CO2 emissions from past land use , 2017, Proceedings of the National Academy of Sciences.

[10]  E. Stehfest,et al.  Anthropogenic land use estimates for the Holocene – HYDE 3.2 , 2016 .

[11]  V. Brovkin,et al.  Modelled interglacial carbon cycle dynamics during the Holocene, the Eemian and Marine Isotope Stage (MIS) 11 , 2016 .

[12]  C. Heinze,et al.  Ocean carbon cycling during the past 130 000 years – a pilot study on inverse palaeoclimate record modelling , 2016 .

[13]  T. Ilyina,et al.  Impacts of artificial ocean alkalinization on the carbon cycle and climate in Earth system simulations , 2016 .

[14]  V. Brovkin,et al.  Comparative carbon cycle dynamics of the present and last interglacial , 2016 .

[15]  V. Brovkin,et al.  Strong dependence of CO2 emissions from anthropogenic land cover change on initial land cover and soil carbon parametrization , 2015 .

[16]  E. Rohling,et al.  Deep ocean carbonate chemistry and glacial-interglacial atmospheric co2 changes , 2014 .

[17]  Kuno M. Strassmann,et al.  Past and future carbon fluxes from land use change, shifting cultivation and wood harvest , 2014 .

[18]  Tobias Stacke,et al.  Impact of the soil hydrology scheme on simulated soil moisture memory , 2013, Climate Dynamics.

[19]  F. Joos,et al.  A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception , 2013 .

[20]  S. Eggins,et al.  Responses of the Deep Ocean Carbonate System to Carbon Reorganization During the Last Glacial-Interglacial Cycle , 2013 .

[21]  V. Brovkin,et al.  Representation of natural and anthropogenic land cover change in MPI‐ESM , 2013 .

[22]  B. Stevens,et al.  Climate and carbon cycle changes from 1850 to 2100 in MPI‐ESM simulations for the Coupled Model Intercomparison Project phase 5 , 2013 .

[23]  Hongmei Li,et al.  Global ocean biogeochemistry model HAMOCC: Model architecture and performance as component of the MPI‐Earth system model in different CMIP5 experimental realizations , 2013 .

[24]  Katja Lohmann,et al.  Characteristics of the ocean simulations in the Max Planck Institute Ocean Model (MPIOM) the ocean component of the MPI‐Earth system model , 2013 .

[25]  B. Stevens,et al.  Atmospheric component of the MPI‐M Earth System Model: ECHAM6 , 2013 .

[26]  Shaun A Marcott,et al.  A Reconstruction of Regional and Global Temperature for the Past 11,300 Years , 2013, Science.

[27]  Zicheng Yu.  Northern peatland carbon stocks and dynamics: a review , 2012 .

[28]  C. Timmreck,et al.  Impact of an extremely large magnitude volcanic eruption on the global climate and carbon cycle estimated from ensemble Earth System Model simulations , 2012 .

[29]  Thomas F. Stocker,et al.  Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores , 2012, Science.

[30]  F. Joos,et al.  Toward explaining the Holocene carbon dioxide and carbon isotope records: Results from transient ocean carbon cycle-climate simulations , 2012 .

[31]  T. Lenton,et al.  Observational constraints on the causes of Holocene CO2 change , 2011 .

[32]  E. Stehfest,et al.  Harmonization of land-use scenarios for the period 1500–2100: 600 years of global gridded annual land-use transitions, wood harvest, and resulting secondary lands , 2011 .

[33]  Jed O. Kaplan,et al.  Holocene carbon emissions as a result of anthropogenic land cover change , 2011 .

[34]  M. Claussen,et al.  Coupled climate–carbon simulations indicate minor global effects of wars and epidemics on atmospheric CO2 between ad 800 and 1850 , 2011 .

[35]  S. Solanki,et al.  Towards a long-term record of solar total and spectral irradiance , 2009, 0911.4002.

[36]  V. Brovkin,et al.  The effect of a dynamic background albedo scheme on Sahel/Sahara precipitation during the mid-Holocene , 2010 .

[37]  C. Timmreck,et al.  Sensitivity of a coupled climate-carbon cycle model to large volcanic eruptions during the last millennium , 2010 .

[38]  F. Joos,et al.  Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core , 2009, Nature.

[39]  Victor Brovkin,et al.  Global biogeophysical interactions between forest and climate , 2009 .

[40]  U. Cubasch,et al.  Mid- to Late Holocene climate change: an overview , 2008 .

[41]  V. Brovkin,et al.  A lowering effect of reconstructed Holocene changes in sea surface temperatures on the atmospheric CO2 concentration , 2008 .

[42]  Jens Kattge,et al.  Will the tropical land biosphere dominate the climate–carbon cycle feedback during the twenty-first century? , 2007 .

[43]  W. Broecker,et al.  Is the magnitude of the carbonate ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric CO2 content , 2007 .

[44]  C. Hensen,et al.  Organic carbon content in surface sediments—defining regional provinces , 2004 .

[45]  Gerrit Lohmann,et al.  North Pacific and North Atlantic sea-surface temperature variability during the Holocene , 2004 .

[46]  Kenji Kawamura,et al.  Evidence for substantial accumulation rate variability in Antarctica during the Holocene, through synchronization of CO 2 in the Taylor Dome, Dome C and DML ice cores , 2004 .

[47]  Paul J. Valdes,et al.  Transient simulations of Holocene atmospheric carbon dioxide and terrestrial carbon since the Last Glacial Maximum , 2004 .

[48]  W. Berger,et al.  Increase of atmospheric CO2 during deglaciation: Constraints on the coral reef hypothesis from patterns of deposition , 2004 .

[49]  M. Maslin,et al.  Implications of coral reef buildup for the controls on atmospheric CO2 since the Last Glacial Maximum , 2003 .

[50]  W. Ruddiman,et al.  The Anthropogenic Greenhouse Era Began Thousands of Years Ago , 2003 .

[51]  Sandy P. Harrison,et al.  Climate change and Arctic ecosystems: 1. Vegetation changes north of 55°N between the last glacial maximum, mid‐Holocene, and present , 2003 .

[52]  Victor Brovkin,et al.  Carbon cycle, vegetation, and climate dynamics in the Holocene: Experiments with the CLIMBER‐2 model , 2002 .

[53]  P. Valdes,et al.  Modeling the dynamics of terrestrial carbon storage since the Last Glacial Maximum , 2002 .

[54]  W. Broecker,et al.  What caused the atmosphere's CO2 content to rise during the last 8000 years? , 2001 .

[55]  D. Jolly,et al.  Mid‐Holocene and glacial‐maximum vegetation geography of the northern continents and Africa , 2000 .

[56]  W. Broecker,et al.  Evidence for a reduction in the carbonate ion content of the deep sea during the course of the Holocene , 1999 .

[57]  Martin Wahlen,et al.  Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica , 1999, Nature.

[58]  Christoph Heinze,et al.  A global oceanic sediment model for long‐term climate studies , 1999 .

[59]  David Archer,et al.  A data-driven model of the global calcite lysocline , 1996 .

[60]  L. David Meeker,et al.  A 110,000-Yr Record of Explosive Volcanism from the GISP2 (Greenland) Ice Core , 1996, Quaternary Research.

[61]  J. Foley.  The sensitivity of the terrestrial biosphere to climatic change: A simulation of the Middle Holocene , 1994 .

[62]  A J Gow,et al.  Record of Volcanism Since 7000 B.C. from the GISP2 Greenland Ice Core and Implications for the Volcano-Climate System , 1994, Science.

[63]  J. C. Walker,et al.  Return of the coral reef hypothesis: basin to shelf partitioning of CaCO3 and its effect on atmospheric CO2. , 1992, Geology.

[64]  K. Hasselmann,et al.  Transport and storage of CO2 in the ocean ——an inorganic ocean-circulation carbon cycle model , 1987 .

[65]  David M. Karl,et al.  VERTEX: carbon cycling in the northeast Pacific , 1987 .

[66]  André Berger,et al.  Long-term variations of daily insolation and Quaternary climatic changes , 1978 .