| Summary: | Atmospheric CO2 reconstructions beyond ice core records are based on geochemical proxies, which bear proxy-specific intrinsic uncertainties. Here, we use the global carbon cycle box model BICYCLE-SE and explore possible changes in the carbon cycle during the last 4 Myr in order to improve existing interpretation of proxy-based CO2 reconstructions with focus on δ11B. Simulating the full marine carbon cycle the results can be compared with various variables of interest, and which are necessary within the context of the δ11B-based CO2 proxy. In detail, these are pH, dissolved inorganic carbon, total alkalinity, and pCO2 within the surface equatorial Atlantic or equatorial Pacific, the areas in which the sediment records are located, that are used for atmospheric CO2 reconstructions. In addition, simulated mean ocean δ13C is compared with various available data. The model is forced with changing physical boundary conditions, mainly changes in temperature and sea level, which are taken from a new data compilation. Simulated changes in surface and deep ocean carbonate ion and the depth of the calcite saturation horizons are further model ouput that can be used for evaluation of results. Finally, simulated / assumed solid Earth carbon fluxes (volcanic CO2 outgassing, carbonate and silicate weathering, coral reef growth, carbonate accumulation in the sediment and the net ocean-to-sediment fluxes) are included here.
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