This Beringia info is really fascinating. Actually, the article said this is the oldest DNA recovered, and perhaps at the time it was, but I seem to recall 9,000 year old DNA recovered from a peat bog in Britain, and they were able to trace related DNA in a modern man living nearby. Once people find a good place to live it seems some chose never to move away.
Regarding the "sudden" raise/fluctuation in sea levels between 18kya and 8kya. These changes might have occurred over decades or over several centuries. During those periods, while there might have been an initial tsunami, such as when Lake Agassiz (sp?) rushed into the Atlantic, that would have caused injury, death and destruction, the main problem would have been that as people moved uphill ahead of the slowly rising water, they would not have had time to reproduce their original level of material culture before they would have had to move again. Decades or centuries of repeated displacement would have significantly reduced any groups level of advanced civilization. This would have occurred weather it was the Americas, the Mediterranean, the Persian Gulf, India, South East Asia or China and Japan. Thus when sea levels finally stabilized, there would have been a significantly degraded base to build from
That was Mr Targett and Cheddar Man. (...and my wife used to say that I never went anywhere)
Descendent Of Stone Age Skeleton Found (Cheddar Man - 9,000 Years-Old)