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Ethnographic observations suggest that Indigenous peoples employed a distinct regime of frequent, low-intensity fires in the Australian landscape in the past. However, the timing of this behaviour and its ecological impact remain uncertain. Here, we present detailed analysis of charcoal, including a novel measure of fire severity using Fourier transform infrared (FTIR) spectroscopy, at a site in eastern Australia that spans the last two glacial/interglacial transitions between 135–104 ka and 18–0.5 ka BP (broadly equivalent to Marine Isotope Stage (MIS) 6-5 and 2-1, respectively). The accumulation of charcoal and vegetation composition was similar across both periods, correlating closely with Antarctic ice core records, and suggesting that climate is the main driver of fire regimes. Fire severity was lower over the past 18,000 years compared to the penultimate glacial/interglacial period and suggests increasing anthropogenic influence over the landscape during this time. Together with local archaeological records, our data therefore imply that Indigenous peoples have been undertaking cultural burning since the beginning of the Holocene, and potentially the end of the Last Glacial Maximum. We highlight the fact that this signal is not easily discernible in the other proxies examined, including widely used charcoal techniques, and propose that any anthropogenic signal will be subtle in the palaeo-environmental record. While early Indigenous people's reasons for landscape burning were different from those today, our findings nonetheless suggest that the current land management directions are based on a substantive history and could result in a reduction in extreme fire events. [ABSTRACT FROM AUTHOR]

The timing and duration of the coldest period in the last glacial stage, often referred to as the last glacial maximum (LGM), has been observed to vary spatially and temporally. In Australia, this period is characterised by colder, and in some places more arid, climates than today. We applied Monte-Carlo change point analysis to all available continuous proxy records covering this period, primarily pollen records, from across Australia (n = 37) to assess this change. We find a significant change point occurred (within uncertainty) at 28.6 ± 2.8 ka in 25 records. We interpret this change as a shift to cooler climates, associated with a widespread decline in biological productivity. An additional change point occurred at 17.7 ± 2.2 ka in 24 records. We interpret this change as a shift towards warmer climates, associated with increased biological productivity. We broadly characterise the period between 28.6 (± 2.8) – 17.7 (± 2.2) ka as an extended period of maximum cooling, with low productivity vegetation that may have occurred as a combined response to reduced temperatures, lower moisture availability and atmospheric CO2. These results have implications for how the spatial and temporal coherence of climate change, in this case during the LGM, can be best interrogated and interpreted. [ABSTRACT FROM AUTHOR]

The Riverine Plain in south‐eastern Australia contains numerous palaeochannels that are much larger than the present rivers and provide evidence about past hydrological conditions. Previous research suggested optima in fluvial activity both before and after the peak of the Last Glacial Maximum (LGM; 21 ± 3 ka), and, in some cases, throughout the LGM. In this study, we revisit palaeochannel remnants of the Gum Creek and Yanco palaeochannel systems along the Murrumbidgee River, which drains the high‐elevation catchments of the Australian Alps in south‐eastern Australia. We date fluvial and aeolian sediments using single‐grain optically stimulated luminescence (OSL) and apply thermoluminescence (TL) dating to a subset of samples. We compare the OSL ages to new and previously published TL ages and investigate reasons for age discrepancies between these methods, possible effects of partial bleaching and other factors that may affect luminescence ages. We propose a new OSL‐based chronology for the Gum Creek and Yanco palaeochannel systems and assign periods of enhanced fluvial activity for the Tombullen and Yanco phases to 41–29 and 29–18 ka, respectively. Importantly, we infer that conditions of increased sediment and water discharge persisted for the Murrumbidgee River at the time of the LGM. [ABSTRACT FROM AUTHOR]

Abstract: Human disturbance induces significant geomorphic changes to river systems. In eastern Australia, land‐use practices such as clearance of forests and riparian vegetation, and removal of wood from channels in the 19th and 20th centuries induced widespread geomorphic impacts. However, since the 1970s, there has been a noticeable shift in the geomorphic condition of many rivers in eastern New South Wales (NSW). This transition to a recovery trajectory reflects a reduction in land‐use pressures and improved farming practices on the one hand and adoption of recovery enhancement approaches to river conservation and rehabilitation by management authorities on the other. Monitoring and tracking changes in condition by state government agencies involves identifying when geomorphic recovery is occurring so that decision‐support frameworks can determine whether river management is required, where, when, and how much to intervene to enhance river recovery and when to opt‐out of management because the system requires little (or no) intervention. Here, we document procedures that are used to manage process‐based, recovery enhancement in NSW. Following a brief review of river change in eastern NSW since European settlement, we outline an approach to identify and measure key geomorphic indicators of river recovery for different river types. We use case studies to demonstrate examples of geomorphic river recovery, prior to showing how state government agencies in NSW are monitoring trajectories and rates of recovery. Broader implications of this ‘good news story’ are discussed. [ABSTRACT FROM AUTHOR]

The filling of Kati Thanda-Lake Eyre (KT-LE), Australia's 'inland sea' has captured scientific and cultural interest for over a century and a half. However, despite the presence of multiple shorelines around the modern playa at or near the modern maximum lake-filling levels, no quantitative estimates of major late-Holocene filling events have ever been documented. We develop a preliminary chronological data set using single-grain optically stimulated luminescence (OSL) on lake shoreline samples in order to determine the timing of large lake-filling events (equivalent to 1974 Common Era (CE) as Australia's wettest year on record) for KT-LE, Australia's largest lake basin. Despite quartz grains with very low natural dose luminescence (Ln) signal, we derive palaeodoses from geologically recent deposits (decades to centuries) using standard rejection criteria and highlight no signs of partial bleaching but occasional bioturbation in modern deposits. Major modern filling episodes, such as the1974 and 1949/1950 filling events, are successfully captured in the geochronological record, as are two major lake-filling episodes in 1854 ± 21 CE years and 1598-1654 CE. Two additional periods of potential lake-filling events have been identified at 1.2 ± 0.09 and 1.9 ± 0.14 ka, but stratigraphic control on these events is less robust. These chronostratigraphic records, while discontinuous, provide important hydrological evidence for extreme pluvial events akin to 1974 or 1949/1950, and the approach holds promise for identifying climate extremes and landscape response over the late Holocene. [ABSTRACT FROM AUTHOR]

Williams Point is an iconic late Quaternary sedimentary sequence exposed at the southern margin of Madigan Gulf at Kati Thanda – Lake Eyre (KT-LE), Australia's largest lake. The ∼15 m high cliff outcrop includes 6 m of aeolian sediments, capping a ∼0.5 m beach/shoreline facies containing abundant Coxiella (aquatic gastropod) unconformably overlying 5–6 m of fluvio-lacustrine facies. The base of the outcrop and the playa floor comprises shallow and deeper water laminated lacustrine sediments. We re-examine the stratigraphic sequence using detailed excavations, micromorphological analysis and geochemical characterisation (X-ray fluorescence, X-ray diffraction, palaeoecology, stable isotope analysis of gypsum hydration water and biogenic carbonates, rare earth element analysis) and present a revised chronology using single-grain optically stimulated luminescence (OSL) within a Bayesian framework. Our new chronostratigraphic data generally supports previous interpretations for Williams Point, but crucially refines the timing of several of the key sedimentological units. The deeper-water lacustrine facies on the lake floor, unconformably overlying the Miocene Etadunna Formation, were deposited 206 ± 13 ka (232–169 ka, 95% credible interval; C.I.). A palaeoplaya, or oxidised shallow lake deposits, formed at 153 ± 11 ka (175–131 ka, 95% C.I.) and the uppermost shallow water lacustrine facies at the base of the cliff was deposited at 131 ± 9 ka (150–113 ka, 95% C.I.). An unconformity separates these sediments from the overlying fluvio-lacustrine phase, securely constrained (with eight OSL samples) to 86 ± 4 ka (95–78 ka, 95% C.I.). The isotopic composition of the palaeo-lake water (δ18O and δD), reconstructed from the hydration water of syndepositional gypsum formed in-situ in these fluvio-lacustrine sediments, indicates wetter conditions at 95–78 ka than at ca. 232–131 ka. Based on the provenance analysis these fluvio-lacustrine and lacustrine sediments were sourced from the northern catchments within the Lake Eyre basin but with an additional contribution from the northern Flinders Ranges. An erosional unconformity separates this sedimentary unit from the overlying Coxiella beach facies, which itself dates to 71 ± 4 ka (79–63 ka; 95% C.I.). This beach facies is interpreted to represent a regressional shoreline or near-shore deposit formed during Marine Isotope Stage [MIS] 4. This is the most reliable palaeolake level indicator in the sequence and indicates a maximum water depth of 12 m. The overlying Williams Point aeolian unit (WPAU) dates to 49 ± 4 ka (56–41 ka, 95% C.I.), slightly younger than previous estimates. The modelled age for WPAU overlaps with (and is within uncertainty of) the last KT-LE megalake phase, which reached +5 m AHD at 48 ± 2 ka. However, considering its elevation (−3 to +3 m AHD), the age of this gypsiferous aeolian unit demands that it accreted as KT-LE was entering a playa phase with lengthy periods of exposed lake floor. In turn, this means that the putative Genyornis newtoni (a megafaunal flightless bird) which laid its eggs in the gypsiferous dunes, went extinct during a time of hydrological transformation. These results bring fresh perspectives to a site that has held a heavy sway over previous views of the Quaternary history of Australia's arid zone. • Williams Point, at Kati Thanda- Lake Eyre shows episodic sedimentation in a lacustrine setting from 230 to 131 ka and fluvio-lacustrine deposition at 86 ka. • Coxiella beach facies were deposited at 71 ka, showing water depths of 12 m. • Rare earth elements show northern catchments supplied water and discharge in MIS 7–4. • Gypsiferous aeolian sedimentation occurred at 49 ka contemporaneously with the last mega lake highstand. • Genyornis newtoni (a megafaunal flightless bird) went extinct during a time of hydrological transformation. [ABSTRACT FROM AUTHOR]

Central to the debate over the extinction of many of Australia's last surviving megafauna is the question: Was climate changing significantly when humans arrived and megafauna went extinct? Here we present a new perspective on variations in climate and water resources over the last glacial cycle in arid Australia based on the study of the continent's largest lake basin and its tributaries. By dating paleoshorelines and river deposits in the Lake Eyre basin, we show that major hydrological change caused previously overflowing megalakes to enter a final and catastrophic drying phase at 48 ± 2 ka just as the giant bird, Genyornis newtoni, went extinct (50-45 ka). The disappearance of Genyornis and other megafauna has been previously attributed to "ecosystem collapse" coincident with the spread of fire-wielding humans. Our findings suggest a climate-driven hydrological transformation in the critical window of human arrival and megafaunal extinction, and the results call for a re-evaluation of a human-mediated cause for such extinctions in arid Australia. [ABSTRACT FROM AUTHOR]

The standardised growth curve (SGC) procedure is a technique that can facilitate rapid D e estimation. In this study, we apply a least-squares (LS) normalisation procedure to single grains of quartz from multiple sites across Australia to test its applicability for establishing common SGCs for individual quartz grains from the same continent. Seventy-two samples from 18 sites were divided into two groups: (1) forty samples were used to construct common SGCs for Australian quartz, and (2) thirty-two samples were used to blind test the reliability of single-grain dating, based on the continental SGCs. Individual grains of quartz from different sites exhibit significant variability in their OSL decay curves, inherent signal intensities and dose response curves (DRCs) constructed using the single-aliquot regenerative dose (SAR) procedure. Application of a LS-normalisation procedure can largely reduce between-grain variability in the shape of the DRCs, allowing for the establishment of a suite of continental SGCs for Australian quartz. For radiation doses below 50 Gy, all investigated grains share a single, common SGC. At higher doses, the DRCs can be divided into six groups, with each group represented by a common SGC. The proportion of grains belonging to each group shows no discernable dependence on OSL properties, but varies significantly among the different sites. The single-grain D e values determined using the continental SGCs are consistent at 2σ with those obtained from their individual DRCs. Likewise, the single-grain D e distributions obtained using the SGCs and the individual DRCs are similar for most of the blind-test samples. Discrepancies for a small number of samples can be explained by the inclusion in the SGC D e dataset of a few outlying values associated with aberrant or saturated grains. Our results show that the establishment of a group of continental SGCs can significantly reduce the machine time required for single-grain OSL measurements, enabling more samples and/or more grains to be measured per unit time. Continental SGCs also yield single-grain D e estimates with comparable accuracy and precision to those obtained from individual DRCs constructed using the full SAR procedure. • Standardised growth curves (SGCs) are obtained for single grains of Australian quartz. • The SGC procedure is applied to quartz grains from 72 samples from 18 sites. • A single SGC is established for doses <50 Gy and six SGCs for doses >50 Gy. • SGC D e distributions are similar to those obtained using the full SAR procedure. • Final D e values of most samples are consistent for the SGC and full SAR procedures. [ABSTRACT FROM AUTHOR]

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]

Eastern Australia has a climate characterised by extreme variability and the occurrence of multiple years of drought conditions. Arguably one of the severest droughts on record - the Big Dry ended in many areas with the La Niña of 2009/2010. A succession of subsequent dry years brought a return to drought conditions across much of eastern Australia in 2018 and 2019, ending with the catastrophic fires of 2019/2020. An analysis of river gauges in eastern Australia demonstrates that unregulated rivers have been subject to reduced monthly and total annual flow for far longer than the recent multi-year droughts. A breakpoint regression model on the annual streamflow data shows statistically significant declines in total annual flow (by up to a factor of three) since 1992/93 on the far South coast of New South Wales (NSW). In the monthly data, fifteen of the nineteen gauges analysed exhibit modelled breakpoints, but with statistically significant differences in monthly mean discharge between consecutive periods only occurring in three of these gauges (occurring between 1972 and 1993 in both the North and South coast). The trend toward reduced flow over the last few decades has, for many rivers, coincided with land use and river management changes resulting in increases in woody riparian vegetation. To show this we use a remote sensing technique and estimate the magnitude of vegetation change along all major rivers and their tributaries on the eastern seaboard of NSW (28 catchments with total river length assessed of 19,750 km) using a normalized difference vegetation index (NDVI) analysis of woody vs non-woody riparian vegetation extent. Predicted vegetation change between 1987 and 2020 is spatially variable across catchments but the mean increase in woody riparian vegetation across all catchments is 9-51% (0.2 and 0.1 NDVI increases). Such increases are perhaps the largest biogeomorphic change the SE Australian drainage network has experienced since the initial clearance of vegetation associated with European colonisation in the late 18th and early 19th centuries., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)