Zusammenfassung: Onset of Quaternary glaciations and the role of the oceans and CO2:
The final closure of the Central American Seaways near Panama (CAS), which stopped the inflow of Pacific low-salinity water into the Carribean was probably the crucial event for the onset of Quaternary cold climates.
As many models and studies show the increased salinity in the Carribean Sea induced a profound rise in heat and salt transport into the North Atlantic, thereby enhancing the meridional overturning circulation and reducing, in turn, the atmospheric CO2 level.
Also, the closing caused a slight rise in the poleward atmospheric moisture transport to northwest Eurasia. Models and data also show that the final closure of the CAS led to a major decrease in sea-sea surface salinity and a stronger stratification and steric height of the subarctic North Pacific. Consequently, CO2 outgassing was barred and the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC) at least doubled.
This led to an increased sea-ice cover in the Arctic Ocean, thus enhancing surface albedo, a crucial positive feedback, which allowed the build-up of continental ice sheets.