Ice Age people in boats in the Mediterranean

This story comes from www.pasthorizons.com/index.php/archives/08/2011/obsidian-artifacts-point… and it seems that mariners may have been sailing the Mediterranean before the end of the Pleistocene – according to new evidence. Their mission, to find volcanic rock to make sharp cutting tools, namely obsidian (a volcanic glass). Obsidian was being extracted as early as 15,000 years ago, it is being said, between the end of the Ice Age and the beginning of the Younger Dryas event. This clarifies the date as the article says Ice Age mariners and this is not strictly true. Obsidian artifacts, it turns out, have been found in a cave on the Peloponnese which had an origin on the island of Melos – but was it an island during the Late Pleistocene? According to a Greek archaeologist, one of the co-authors of a paper in the September 2011 upcoming issue of the Journal of Archaeological Science, these people were sailors, island hopping around the Aegean. The trade appears to have continued into the Mesolithic period too as other obsidian artifacts from the cave have been dated back to 8500BC (or 10,500 years ago) – using a novel mass spectrometry dating technique. The importance of the discovery is that boats were being used in the Late Pleistocene and early Holocene – so why not during the Late Palaeolithic as a whole?