Post-glacial adaptations: 18,000-10,000 years ago

The climatic cooling trend that had led to the LGM peaked around 22,000 years bp, and after that time global warming and consequent sea-level rise gradually began. Sea-level rise accelerated dramatically in the millennium between 19,000 and 18,000 years ago, with a rise of more that 15 metres in ocean levels (>1-2 cm p.a.), as millions of cubic kilometres of ice in the Northern Hemisphere were released into the oceans.

In the north coastlines retreated southwards more than 1,000 kilometres as the gently sloping continental shelf was inundated. The diverse habitats that existed on the exposed shelf, including the huge brackish Lake Carpentaria, vanished as the oceans flowed onto the shelf and flooded the region.^[602] Although the loss of land elsewhere around Sahul was not as great, it was often still substantial. Whole territories were drowned, forcing people into the lands already occupied by other groups, and demanding territorial restructuring and re-conceptualization. The result was not only a landmass almost one-third smaller but a transformed coastline. Rapid sea-level rise prevented the formation of stable inshore ecosystems in many localities, reducing the supply of food resources accessible along the shore. For example, in northeastern Australia it was not until sea level began to stabilize about 3,000-4,000 years ago that ecosystems rich in mangroves as well as sandy shores formed and abundant shoreline foods such as molluscs and crustaceans became available.

One example of developing coastal economies is the island-creation in the Whitsunday region on the northeast coast. There sea-level rise flooded low- lying areas of the continental shelf to leave a long peninsula of high ground, and then as the ocean continued to rise the peninsula was progressively cut into a series of islands. Throughout this process constant changes in sea level prevented the development of fringing mangroves and shoreline foods, and at the same time the diversity and abundance of terrestrial fauna reduced as land was broken into small islands, leaving the islands themselves as limited sources of food. Archaeological deposits preserved in large rockshelters on some islands document that the foragers in this landscape were frequently fishing, often in deep water, and at least occasionally capturing large marine mammals such as dugong and turtles. Hunting and fishing on the open seas provided significant supplements to the diet that could be obtained through terrestrial foraging, and required a specific and reliable toolkit. Sound water­craft are demonstrated not only by the capture of large marine mammals that rarely or never come ashore but also by the regular and large-scale transpor­tation of stone artefacts between islands at the end of this period.^[603] People made large, regularly shaped artefacts with sharp edges and blunt backs and transported these widely within the islands - possibly as a technological device to help them explore and exploit the region at a time of resource uncertainty and change.^[604]

At the southern extremity of Sahul sea-level rise inundated the Bassian Plain, creating the 200-kilometre-wide Bass Strait about 14,000 years ago and isolating humans in the newly created Island of Tasmania. A number of subsequent shifts in economic practices, social life and demography have been inferred and often interpreted as long-term consequences of the phys­ical isolation of Tasmania. Such responses can be seen as yet another example of cultural diversification, a process that has operated throughout the human history of Australasia.