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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. • MIS4 lowstand exposed a vast archipelago off the northwest coast of Sahul. • The island environment likely enabled staged human dispersal from Wallacea to Sahul. • The NW Shelf contained a mosaic of habitable fresh and saltwater environments. • Modelling reveals the drowned shelf could have supported between 50,000 and 500,000 people. • Retreat ahead of sea level rise drove increasing occupation and new rock art styles. [ABSTRACT FROM AUTHOR]

The peopling of Sahul (the combined landmass of New Guinea and Australia) is a topic of much debate. The Kimberley region of Western Australia holds many of Australia's oldest known archaeological sites. Here, we review the chronological and archaeological data available for the Kimberley from early Marine Isotope Stage 3 to the present, linking episodes of site establishment and the appearance of new technologies with periods of climatic and sea-level change. We report optical ages showing human occupation of Widgingarri 1, a rockshelter located on the Kimberley coast of northwest Australia, as early as 50,000 years ago, when the site was located more than 100 km from the Late Pleistocene coastline. We also present the first detailed analysis of the stone artefacts, including flakes from ground stone axes, grinding stones and ground haematite recovered from the deepest excavated layer. The high proportion of flakes from ground axe production and resharpening in the earliest occupation phase emphasises the importance of this complex technology in the first peopling of northern Sahul. Artefact analyses indicate changes in settlement patterns through time, with an increase in mobility in the terminal Pleistocene and a shift to lower mobility during the late Holocene. The optical ages for Widgingarri 1 mean that the Kimberley now contains the greatest number of sites in Sahul with earliest occupation dated to more than 46,000 years ago, overlapping with the time of initial occupation of sites in other regions across the continent. • Redating of Widgingarri 1 using OSL reveals occupation of the site began ∼50,000 years ago. • The Kimberley region now contains the most archaeological sites dated to this period in Sahul. • Widgingarri 1 contains some of the oldest evidence for ground stone axe manufacture in Sahul. • Kimberley-wide peopling and occupation patterns linked to periods of climate and sea level change. • Updated Bayesian age models of oldest sites in Sahul show high degree of overlap in first occupation. [ABSTRACT FROM AUTHOR]