Readers of this website may well have been intrigued by the thesis in 'hidden history' author Graham Hancock's 2002 book Underworld: The Mysterious Origins of Civilization - that during the last Ice Age, sea levels were much lower, and so many traces of ancient cultures may have been lost when coastal areas were submerged when the 'big thaw' occurred. Though many academics have taken issue with the conclusions in Underworld, Hancock certainly was prescient in bringing focus to this aspect of our history, at a time when very few archaeologists were thinking along these lines.
However, in recent years more and more attention has been placed on the search for cultural traces beneath the waves. In 2009 the research network SPLASHCOS was funded "to coordinate and promote research on the underwater landscapes and archaeology of the continental shelf drowned by the sea level rise at the end of the Last Glacial.":
For most of human history on this planet — about 90 per cent of the time — sea levels have been substantially lower than at present, exposing large tracts of territory for human settlement. Europe alone would have had a land area increased by 40 per cent at the maximum sea level regression. Although this has been recognised for many decades, archaeologists have resisted embracing its full implications, barely accepting that most evidence of Palaeolithic marine exploitation must by definition be invisible, believing that nothing has survived or can be found on the seabed, and preferring instead to emphasise the opportunities afforded by lower sea level for improved terrestrial dispersal across land bridges and narrowed sea channels.
In the past decade, opinions have begun to change in response to a number of factors: evidence that marine exploitation and seafaring have a much deeper history in the Pleistocene than previously recognised; the steady accumulation of new underwater Stone Age sites and materials, amounting now to over 3000 in Europe, and often with unusual and spectacular conditions of preservation; availability of new technologies and research strategies for underwater exploration; and the growth of targeted underwater research.
Above all, it has become ever clearer that coastal regions generally support larger concentrations of population than hinterlands, with greater ecological diversity, better groundwater supplies, more equable climatic conditions, more productive conditions for plant and animal life on land, and the availability of marine resources. Since most of the great transformations of world prehistory took place when the sea level was lower than at present—including the global dispersal of archaic and anatomically modern humans, the origins of fishing and seafaring, the origins and dispersal of early farming economies, and the roots of the earliest civilisations such as those of Mesopotamia and the Aegean—it follows that existing syntheses of world prehistory are likely to be seriously incomplete.
Read more about the recent discoveries at Antiquity: "Submerged Prehistoric Archaeology and Landscapes of the Continental Shelf".
Also, for those interested, Graham Hancock's 2002 documentary, Underworld: Flooded Kingdoms of the Ice Age: