| Summary: | We use the box model BICYCLE-SE to simulate the effect of a much shallower Greenland-Scotland-Ridge, as it has been during the Eocene and Oligocene, on the global carbon cycle. Applying the boundary conditions (geometry of boxes, water fluxes, salinity) connected with a lagoonal Eocene setting of the Arctic Ocean increases atmospheric CO2 concentration by 200 ppm. A further 60 ppm increase is caused by the effect of the long-term changes in mean oceanic concentration of magnesium and calcium. Depending on the assumed Eocene or Oligocene temperatures atmospheric CO2 concentration of 450–770 ppm can thus be simulated. Furthermore, in our simulations the calcite saturation horizon in the Eocene Arctic Ocean is much shallower than today. The fraction of calcite in the sedimentary mixed layer as function of water depth in the Arctic, Atlantic, and Pacific are analysed for the regional to global effects of these changes in the carbon cycle.
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