As world sea level dropped during the ice cap advances of the last Ice Age, the exit straits of the Sea of Japan one by one dried and closed. There is controversy as to whether or not in each ice cap advance the world sea level fell low enough for the deepest, the western channel of the Korea Strait, to dry and close, turning the Sea of Japan into a huge cold inland lake with a surface layer of fresh water, freezing over in the winters.
As world sea level dropped during the ice cap advances of the last Ice Age the exit straits of the Sea of Japan one by one dried and closed There is controversy as to whether or not in each ice cap advance the world sea level fell low enough for the deepest the western channel of the Korea Strait to dry and close turning the Sea of Japan into a huge cold inland lake with a surface layer of fresh water freezing over in the winters