Modelled interglacial carbon cycle dynamics during the Holocene, the Eemian and Marine Isotope Stage (MIS) 11

Abstract

Abstract. Trends in the atmospheric concentration of CO 2 during three recent interglacials -the Holocene, the Eemian and Marine Isotope Stage (MIS) 11 -are investigated using an earth system model of intermediate complexity, which we extended with process-based modules to consider two slow carbon cycle processes -peat accumulation and shallowwater CaCO 3 sedimentation (coral reef formation). For all three interglacials, model simulations considering peat accumulation and shallow-water CaCO 3 sedimentation substantially improve the agreement between model results and ice core CO 2 reconstructions in comparison to a carbon cycle set-up neglecting these processes. This enables us to model the trends in atmospheric CO 2 , with modelled trends similar to the ice core data, forcing the model only with orbital and sea level changes. During the Holocene, anthropogenic CO 2 emissions are required to match the observed rise in atmospheric CO 2 after 3 ka BP but are not relevant before this time. Our model experiments show a considerable improvement in the modelled CO 2 trends by the inclusion of the slow carbon cycle processes, allowing us to explain the CO 2 evolution during the Holocene and two recent interglacials consistently using an identical model set-up.

What was the source of the atmospheric CO<sub>2</sub> increase during the Holocene?

“…1e). The land use areas in 1750 CE are in line with the most recent update of the HYDE dataset (Klein Goldewijk et al, 2017), although our interpolation underestimates crop and pasture areas earlier than 1750 CE.…”

What was the source of the atmospheric CO<sub>2</sub> increase during the Holocene?

“…Regarding the land source, experiments demonstrate that natural carbon dynamics lead to increase in the land carbon storage during the first half of the simulation (until 2000 BCE). This is in line with previous simulations performed with intermediate complexity models (e.g., Kaplan et al, 2002;Kleinen et al, 2016). During 6000 to 2000 BCE, the atmospheric CO2 increase is about 2/3 of the estimated 20 ppm increase.…”

“…Hypotheses explaining CO2 growth in the Holocene could be roughly subdivided into ocean-and land-based. The ocean mechanisms include changes in carbonate chemistry as a result of carbonate compensation to deglaciation processes (Broecker et al, 1999;Broecker et al, 2001;Joos et al, 2004), redistribution of carbonate sedimentation from deep ocean to shelves, mostly due to coral reef regrowth (Ridgwell et al, 2003;Kleinen et al, 2016), CO2 degassing due to increase in sea surface temperatures, predominantly in tropics (Indermühle et al, 1999;Brovkin et al, 2008), and decrease in marine soft tissue pump in response to circulation changes (Goodwin et al, 2011). Recent synthesis of carbon burial in the ocean during last glacial cycle suggests excessive accumulation of CaCO3 and organic carbon in the ocean sediments during deglaciation and Holocene (Cartapanis et al, 2018), implicitly supporting the ocean-based mechanism of atmospheric CO2 growth in response to decrease in the ocean alkalinity.…”

Ocean carbon inventory under warmer climate conditions – the case of the Last Interglacial

“…Few model-based studies examine the carbon cycle dynamics for the LIG period with a particular focus on the ability of models to simulate the transient changes in atmospheric CO 2 concentration, which remains relatively stable around 270-280 ppm without displaying any trends (Lourantou et al, 2010;Schneider et al, 2013). Most of these studies provide a better understanding of the land carbon budget, particularly highlighting the importance of temperature changes on the land vegetation and slow processes of CO 2 change such as peatland carbon dynamics and CaCO 3 shallow-water accumulation (Schurgers et al, 2006;Kleinen et al, 2016;Brovkin et al, 2016). Although there are numerous studies that have analyzed the role of the ocean carbon cycle in regulating the atmospheric CO 2 , especially for the interglacial-glacial transition period (Ridgwell, 2001;Sigman and Boyle, 2000;Menviel et al, 2012), to the authors' knowledge there is no study that investigate in details changes in marine carbon and nutrient cycling during the Eemian period of the LIG (125-115 ka).…”