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The timing, context and nature of the first people to enter Sahul is still poorly understood owing to a fragmented archaeological record. However, quantifying the plausible demographic context of this founding population is essential to determine how and why the initial peopling of Sahul occurred. We developed a stochastic, age-structured model using demographic rates from hunter-gatherer societies, and relative carrying capacity hindcasted with LOVECLIM's net primary productivity for northern Sahul. We projected these populations to determine the resilience and minimum sizes required to avoid extinction. A census founding population of between 1,300 and 1,550 individuals was necessary to maintain a quasi-extinction threshold of ≲0.1. This minimum founding population could have arrived at a single point in time, or through multiple voyages of ≥130 people over ~700-900 years. This result shows that substantial population amalgamation in Sunda and Wallacea in Marine Isotope Stages 3-4 provided the conditions for the successful, large-scale and probably planned peopling of Sahul.

A continental-scale model of Holocene Australian hunter-gatherer demography and mobility is generated using radiocarbon data and geospatial techniques. Results show a delayed expansion and settlement of much of Australia following the termination of the late Pleistocene until after 9,000 years ago (or 9ka). The onset of the Holocene climatic optimum (9-6ka) coincides with rapid expansion, growth and establishment of regional populations across ~75% of Australia, including much of the arid zone. This diffusion from isolated Pleistocene refugia provides a mechanism for the synchronous spread of pan-continental archaeological and linguistic attributes at this time (e.g. Pama-Nyungan language, Panaramitee art style, backed artefacts). We argue longer patch residence times were possible at the end of the optimum, resulting in a shift to more sedentary lifestyles and establishment of low-level food production in some parts of the continent. The onset of El Niño - Southern Oscillation (ENSO; 4.5-2ka) restricted low-level food production, and resulted in population fragmentation, abandonment of marginal areas, and reduction in ranging territory of ~26%. Importantly, climate amelioration brought about by more pervasive La Niña conditions (post-2ka), resulted in an intensification of the mobility strategies and technological innovations that were developed in the early- to mid-Holocene. These changes resulted in population expansion and utilization of the entire continent. We propose that it was under these demographically packed conditions that the complex social and religious societies observed at colonial contact were formed.

Reliable chronological frameworks for archaeological sites are essential for accurate interpretations of the past. Geochronology represents the core of interdisciplinary research because it allows integration of diverse data on a common timeline. Since the radiocarbon revolution in Australian archaeology in the 1950s, thousands of ages have been produced across Sahul (combined landmass of Australia and New Guinea). Methods such as thermoluminescence (TL) and optically stimulated luminescence (OSL) have also been used on Australian archaeological deposits and enabled the study of the deep past beyond the limits of radiocarbon dating. After seven decades, these geochronological methods no longer provide just a 'date', but instead, the geochronological community is focussed on providing the most reliable, precise, and reproducible ages. These aspects of age estimation are central to the framework of the SahulArch geochronological database. SahulArch is a new publicly available continental-scale dataset in which context and quality assurance criteria of each dated sample are considered as important as the age itself. SahulArch contains a total of 10,717 ages (9,504 radiocarbon, 973 OSL, and 240 TL) from 2,318 sites across the Sahul landmass. We describe the structure of SahulArch, types of auxiliary data collected, and provide a summary of the data in SahulArch. [ABSTRACT FROM AUTHOR]

Reconstructing past sea levels can help constrain uncertainties surrounding the rate of change, magnitude, and impacts of the projected increase through the 21st century. Of significance is the mid-Holocene relative sea-level highstand in tectonically stable and remote (far-field) locations from major ice sheets. The east coast of Australia provides an excellent arena in which to investigate changes in relative sea level during the Holocene. Considerable debate surrounds both the peak level and timing of the east coast highstand. The southeast Australian site of Bulli Beach provides the earliest evidence for the establishment of a highstand in the Southern Hemisphere, although questions have been raised about the pretreatment and type of material that was radiocarbon dated for the development of the regional sea-level curve. Here we undertake a detailed morpho- and chronostratigraphic study at Bulli Beach to better constrain the timing of the Holocene highstand in eastern Australia. In contrast to wood and charcoal samples that may provide anomalously old ages, probably due to inbuilt age, we find that short-lived terrestrial plant macrofossils provide a robust chronological framework. Bayesian modelling of the ages provide improved dating of the earliest evidence for a highstand at 6,880±50 cal BP, approximately a millennium later than previously reported. Our results from Bulli now closely align with other sea-level reconstructions along the east coast of Australia, and provide evidence for a synchronous relative sea-level highstand that extends from the Gulf of Carpentaria to Tasmania. Our refined age appears to be coincident with major ice mass loss from Northern Hemisphere and Antarctic ice sheets, supporting previous studies that suggest these may have played a role in the relative sea-level highstand. Further work is now needed to investigate the environmental impacts of regional sea levels, and refine the timing of the subsequent sea-level fall in the Holocene and its influence on coastal evolution. [ABSTRACT FROM AUTHOR]

Drawing on the recent synthesis of Australian palaeoclimate by the OZ-INTIMATE group (Reeves et al., 2013a), we consider the effects of climate systems on past human settlement patterns and inferred demography. We use 5044 radiocarbon dates from ∼1750 archaeological sites to develop regional time-series curves for different regions defined in the OZ-INTIMATE compilation as the temperate, tropics, interior and Southern Ocean sectors to explore human–climate relationships in Australia over the last 35,000 years. Correlations undertaken with improved palaeoclimatic data and archaeological records indicate that the regional time-series curves are robust, and can be used as a proxy for human behaviour. However, interrogation of the datasets is essential with artificial peaks and taphonomic over-correction being critical considerations. The time-series curves are interpreted as reflecting population growth, stasis and even decline in phase with terminal Pleistocene/early Holocene climatic fluctuations. This coupling, however, decreases during the last 5000 years, most likely due to increased population levels, greater territoriality, technological solutions to stress, and social and ideational innovation. Curves from all sectors show exponential population growth over the last 5000 years. We identify future research priorities, highlighting the paucity of archaeological records across several parts of Australia (<1 dated site/4,000 km 2 ), especially around the fringes of the arid zone, and the need for improved taphonomic correction techniques. Finally, we discuss how these time-series curves represent a first-order framework, not dissimilar to global climate models, which researchers can continue to test and refine with local, regional and continental records. [ABSTRACT FROM AUTHOR]

Abstract: A number of models, developed primarily in the 1980s, propose that Aboriginal Australian populations contracted to refugia – well-watered ranges and major riverine systems – in response to climatic instability, most notably around the Last Glacial Maximum (LGM) (∼23–18 ka). We evaluate these models using a comprehensive continent-wide dataset of archaeological radiocarbon ages and geospatial techniques. Calibrated median radiocarbon ages are allocated to over-lapping time slices, and then K-means cluster analysis and cluster centroid and point dispersal pattern analysis are used to define Minimum Bounding Rectangles (MBR) representing human demographic patterns. Exploring data between 25 and 12 ka, we find a refugia-type hunter-gatherer response during the LGM (∼23–18 ka) and again during the Antarctic Cold Reversal (ACR) (∼14.5–12.5 ka), with expansion in the intervening period. Several refugia persist between 25 and 12 ka, including (by Interim Biogeographic Regionalisation for Australia areas) Gulf Plains/Einasleigh Uplands, Brigalow Belt South, Murray Darling Depression, and Tasmanian Central Highlands. Others appear sporadically through the same period. These include South Eastern Highlands, NSW South Western Slopes, Sydney Basin, Warren, Murchison, Gascoyne, Central and Northern Kimberley, Ord Victoria Plain, Arnhem Plateau, MacDonnell Ranges and Central Ranges. The Pilbara may also have been a refugium during the LGM, but geospatial results are problematic for this region. Areas devoid of human activity (‘barriers’) include the main desert regions, especially in the south and west of the continent, although some of these may be the result of an absence of archaeological fieldwork. Point dispersal pattern analysis indicates a reduction in occupied territory of nearly 80% during the LGM. A reduction of close to 50% was also evident during the ACR. A large number of the refugia were in close proximity to glaciated areas during the LGM, and probably benefitted from increased summer snowmelt along the major river systems. The remaining refugia are likely the result of a range of local environmental and resource factors. We identify areas for future research, including a focus on regional studies to determine possible cryptic or idiosyncratic refugia emerging in phlyogeographic studies. [Copyright &y& Elsevier]

A radiocarbon-dated multiproxy palaeoenvironmental record from the Lower Thames Valley at Hornchurch Marshes has provided a reconstruction of the timing and nature of vegetation succession against a background of Holocene climate change, relative sea level movement and human activities. The investigation recorded widespread peat formation between c. 6300 and 3900 cal. yr BP (marine ‘regression’), succeeded by evidence for marine incursion. The multiproxy analyses of these sediments, comprising pollen, Coleoptera, diatoms, and plant and wood macrofossils, have indicated significant changes in both the wetland and dryland environment, including the establishment of Alnus (Alder) carr woodland, and the decline of both Ulmus (Elm; c. 5740 cal. yr BP) and Tilia (Lime; c. 5600 cal. yr BP, and 4160–3710 cal. yr BP). The beetle faunas from the peat also suggest a thermal climate similar to that of the present day. At c. 4900 cal. yr BP, Taxus (L.; Yew) woodland colonised the peatland forming a plant community that has no known modern analogue in the UK. The precise reason, or reasons, for this event remain unclear, although changes in peatland hydrology seem most likely. The growth of Taxus on peatland not only has considerable importance for our knowledge of the vegetation history of southeast England, and NW Europe generally, but also has wider implications for the interpretation of Holocene palaeobotanical records. At c. 3900 cal. yr BP, Taxus declined on the peatland surface during a period of major hydrological change (marine incursion), an event also strongly associated with the decline of dryland woodland taxa, including Tilia and Quercus, and the appearance of anthropogenic indicators. [ABSTRACT FROM PUBLISHER]

Abstract: Using a database of Australian archaeological radiocarbon dates (n = 2996), this paper explores three key methodological issues associated with the use of summed probability plots of radiocarbon data: 1) the minimum sample size needed for a statistically reliable plot; 2) the effect of radiocarbon calibration on the structure of these plots; and 3) the application of a taphonomic correction to such time-series data. The results identify several protocols, recommended as best-practice when using summed probability plots: 1) a minimum sample size of 500 radiocarbon dates should be used, and the sample size and the mean of the standard deviations of the radiocarbon dates (ΔT) in the sample should both be reported; 2) a moving average trendline of 500–800 years should be used to offset the effects of the calibration process; and 3) Surovell et al. “Correcting temporal frequency distributions for taphonomic bias” [Journal of Archaeological Science 36 (2009) 1715–1724] is explored, with modifications and temporal limits (<25,000 cal years BP) proposed. Correction of time-series data using theoretical taphonomic correction curves is useful as a heuristic tool but can obscure real trends if applied routinely. Comparison between summed probability plots and other occupation data is presented and shows good correlation. However it is recommended that plots are supplemented by other archaeological indices and the cross-comparison of such multiple proxies will strengthen identification of occupation trends. [Copyright &y& Elsevier]

Reconstructing the patterns of Homo sapiens expansion out of Africa and across the globe has been advanced using demographic and travel-cost models. However, modelled routes are ipso facto influenced by migration rates, and vice versa. We combined movement 'superhighways' with a demographic cellular automaton to predict one of the world's earliest peopling events — Sahul between 75000 and 50000 years ago. Novel outcomes from the superhighways-weighted model include (i) an approximate doubling of the predicted time to continental saturation (∼10,000 years) compared to that based on the directionally unsupervised model (∼5000 years), suggesting that rates of migration need to account for topographical constraints in addition to rate of saturation; (ii) a previously undetected movement corridor south through the centre of Sahul early in the expansion wave based on the scenarios assuming two dominant entry points into Sahul; and (iii) a better fit to the spatially de-biased, Signor-Lipps-corrected layer of initial arrival inferred from dated archaeological material. Our combined model infrastructure provides a data-driven means to examine how people initially moved through, settled, and abandoned different regions of the globe. • We combined movement 'superhighways' with a demographic model to predict the initial peopling of Sahul. • The combined model doubled the predicted time to continental saturation (∼10,000 years) compared to previous estimates. • The model revealed a previously undetected movement corridor south through the centre of Sahul. • The combined model provided a better fit to archaeological material than models not weighted by superhighways. • The model infrastructure can be applied to the initial movement of people in different regions of the globe. [ABSTRACT FROM AUTHOR]