Sea level rise drowned a vast habitable area of north-western Australia driving long-term cultural change

For most of the period of human occupation of Sahul (the combined Pleistocene landmass of Australia and New Guinea), lower sea levels exposed an extensive area of the northwest of the Australian continent, connecting the Kimberley and Arnhem Land into one vast area. Our analysis of high-resolution bathymetric data shows this now-drowned region existed as an extensive archipelago in Marine Isotope Stage 4, transforming in Marine Isotope Stage 2 into a fully exposed shelf containing an inland sea adjacent to a large freshwater lake. These were encircled by deep gorges and escarpments that likely acted as important resource zones and refugia for human populations at that time. Demographic modelling shows the shelf had a fluctuating potential carrying capacity through Marine Isotope Stages 4–2, with the capability to support 50–500 k people at various times. Two periods of rapid global sea level rise at 14.5–14.1 ka (Meltwater Pulse 1A), and between 12 ka and 9 ka, resulted in the rapid drowning of ∼50% of the Northwest Shelf. This likely caused a retreat of human populations, registering as peaks in occupational intensity at archaeological sites. We contend that the presence of an extensive archipelago on the Northwest Shelf in Marine Isotope Stage 4 facilitated the successful dispersal of the first maritime explorers from Wallacea, creating a familiar environment for their maritime economies to adapt to the vast terrestrial continent of Sahul.