Also, the Red Earth people had an extensive trade system in the Arctic at about the same time.
Both of these observations are consistent with a lowering of sea level during a warmer than Present segment of time.
Isotope studies of the Greenland and Antartic Ice Cores include assumptions that are consistent with Ocean waters periodically being as much as 9 degrees Celcius warmer than the Present.
There is NO evidence that CO2 was a SIGNIFICANT cause of ANY of these temperature and Ocean Level cycles.
How did the ocean water levels get to be lower during warmer times?