Ancient Arctic Ice Pack

   I redid the estimate of the rate of global warming for the oceans more carefully and found a value of 1.57 °C per 1000 years.

Taking into account a mean ocean temperature of 13.9 °C for the 20th Cent. and that seawater freezes at -1.89 °C we find that much of the worlds oceans would have been frozen over about 10,000 years ago. 

So, we have to assume that the Arctic Ice Pack would have been much greater during the last ice age. The land bridges for North America could have been farther south in the Pacific and the Atlantic.