Abstract
Abstract. Despite intense efforts, the mechanisms that drive glacial–interglacial changes in atmospheric pCO2 are not fully understood. Here, we aim at quantifying the potential contribution of aeolian dust deposition changes to the atmospheric pCO2 drawdown during the Last Glacial Maximum (LGM). To this end, we use the Max Planck Institute Ocean Model (MPIOM) and the embedded Hamburg Ocean Carbon Cycle model (HAMOCC), including a new parameterization of particle ballasting that accounts for the acceleration of sinking organic soft tissue in the ocean by higher-density biogenic calcite and opal particles, as well as mineral dust. Sensitivity experiments with reconstructed LGM dust deposition rates indicate that the acceleration of detritus by mineral dust played a small role in atmospheric pCO2 variations during glacial–interglacial cycles – on the order of 5 ppmv, compared to the reconstructed ∼80 ppmv rise in atmospheric pCO2 during the last deglaciation. The additional effect of the LGM dust deposition, namely the enhanced fertilization by the iron that is associated with the glacial dust, likely played a more important role; although the full iron fertilization effect can not be estimated in the particular model version used here due to underestimated present-day non-diazotroph iron limitation, fertilization of diazotrophs in the tropical Pacific already leads to an atmospheric pCO2 drawdown of around 10 ppmv.
Highlights
According to ice core data (Lüthi et al, 2008; Marcott et al, 2014; Köhler et al, 2017), the atmospheric CO2 concentration during the Last Glacial Maximum (LGM, ∼ 21 000 years ago) was about 80 ppmv lower than during the early Holocene
To simulate a reasonably realistic carbon cycle with atmosphere–ocean CO2 fluxes comparable to observations and to create a mean state with particle ballasting that is very close to the mean state of the standard set-up, it is important to adjust Hamburg Ocean Carbon Cycle model (HAMOCC) to the substantially modified particle sinking speeds that result from the particle ballasting parameterization
We estimate the potential effect of aeolian dust deposition changes on glacial–interglacial atmospheric pCO2 variations by computing the sensitivity of the atmosphere– ocean CO2 fluxes to LGM dust deposition
Summary
According to ice core data (Lüthi et al, 2008; Marcott et al, 2014; Köhler et al, 2017), the atmospheric CO2 concentration during the Last Glacial Maximum (LGM, ∼ 21 000 years ago) was about 80 ppmv lower than during the early Holocene. Model simulations show that the reduced atmospheric CO2 concentration caused a global cooling and, combined with orbital effects on Earth’s climate, allowed the Laurentide, Cordilleran, British, and Scandinavian ice sheets to build up (Abe-Ouchi et al, 2007; Heinemann et al, 2014; Ganopolski and Brovkin, 2017). It is still a matter of active discussion, which of the many potential climate and carbon cycle changes in response to the orbital forcing caused how much of the atmospheric pCO2 drawdown Constrained simulations of the global dust cycle have suggested that dust production and deposition rates were at least twice as large during the LGM compared to the Holocene and present due to (1) enhanced desert dust production and (2) enhanced glacigenic dust production
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