Recent global fire activity has highlighted the importance of understanding fire dynamics across time and space, with records of past fire (palaeofire) providing valuable insights to inform us on current and future management challenges. New records from the recent increase in palaeofire studies from Australia and surrounds have not been captured in any database for broader comparisons, and Australasia is poorly represented in current international databases used for global modelling of palaeofire trends. These problems are addressed by SahulCHAR, a new collection of sedimentary charcoal and black carbon records from Sahul (Australia, New Guinea, and offshore islands) and Aotearoa / New Zealand. Data are stored in the OCTOPUS relational database platform, with a structure designed for compatibility with the existing Global Paleofire Database. Metadata are captured at the site level and observation level, with observations including age determinations and charcoal or black carbon data. SahulCHAR version 1 contains 687 records of charcoal or black carbon, including digitized data, unchanged and modified records from the Global Paleofire Database, and original author-submitted data. SahulCHAR is a much-needed update to past regional palaeofire compilations that will also provide greater representation of records from Sahul and Aotearoa / New Zealand in future global syntheses.

Background The global human footprint has fundamentally altered wildfire regimes, creating serious consequences for human health, biodiversity, and climate. However, it remains difficult to project how long-term interactions among land use, management, and climate change will affect fire behavior, representing a key knowledge gap for sustainable management. We used expert assessment to combine opinions about past and future fire regimes from 99 wildfire researchers. We asked for quantitative and qualitative assessments of the frequency, type, and implications of fire regime change from the beginning of the Holocene through the year 2300. Results Respondents indicated some direct human influence on wildfire since at least ~ 12,000 years BP, though natural climate variability remained the dominant driver of fire regime change until around 5,000 years BP, for most study regions. Responses suggested a ten-fold increase in the frequency of fire regime change during the last 250 years compared with the rest of the Holocene, corresponding first with the intensification and extensification of land use and later with anthropogenic climate change. Looking to the future, fire regimes were predicted to intensify, with increases in frequency, severity, and size in all biomes except grassland ecosystems. Fire regimes showed different climate sensitivities across biomes, but the likelihood of fire regime change increased with higher warming scenarios for all biomes. Biodiversity, carbon storage, and other ecosystem services were predicted to decrease for most biomes under higher emission scenarios. We present recommendations for adaptation and mitigation under emerging fire regimes, while recognizing that management options are constrained under higher emission scenarios. Conclusion The influence of humans on wildfire regimes has increased over the last two centuries. The perspective gained from past fires should be considered in land and fire management strategies, but novel fire behavior is likely given the unprecedented human disruption of plant communities, climate, and other factors. Future fire regimes are likely to degrade key ecosystem services, unless climate change is aggressively mitigated. Expert assessment complements empirical data and modeling, providing a broader perspective of fire science to inform decision making and future research priorities.

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.

The drivers of fire regimes prior to the European occupation of Australia are still contentious, with some advocating regimes dominated by anthropogenic ignitions and others advocating a climate source or mixture of these elements. Here, we examine an 850-year history of fire regimes at Lake Werri Berri in south-east Australia, prior to and following European occupation. Macroscopic charcoal and FTIR spectroscopy were used to infer broad changes of the fire regime in proximity to the lake. We found little change through much of the 850-year period and most interesting, no apparent change following the initial displacement of Indigenous peoples and the introduction of farming and woodcutting to the region by Europeans. From the mid-20th Century onwards, there was an increase in both area burnt and fire severity or intensity, likely the result of increased fuel load and connectivity following an extended period of increased precipitation and heavier recreational land usage, which likely led to an increase in anthropogenic ignitions.

This study examined the effects of commonly used oxidants in sedimentary macroscopic charcoal analysis on two sediment cores from Thirlmere Lakes National Park, Southeast Australia. The cores, from Lake Werri Berri (WB3) and Lake Couridjah (LC2), span ~900 years and 135,000 years, respectively. The Charcoal Accumulation Rate (CHAR) for both charcoal area and count was quantified using four different chemical treatments and compared to a control using only water. We also quantified the Charring Intensity (CI) of isolated charcoal fragments, a proxy for the severity/intensity of fire, determined using the FTIR spectral characteristics of the remaining charcoal after each treatment. We found significant differences in both the area and number of particles across all treatments in both cores. Significantly, we found substantial differences in CI between treatments, with few charcoal particles formed in low-severity fire (e.g., below ~400 °C or 3.0 °C.s.106) in groups treated with an oxidant. In contrast, the control group displayed a wider range of CI values and contained lightly pyrolyzed particles. This suggests that methods using an oxidant to concentrate sedimentary charcoal are potentially biasing records towards high-intensity or -severity fires. We suggest that consideration should be used when choosing laboratory methods based on the hypotheses being tested.

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a consid-erable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary pro-ductivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates.

This study investigated the effects a dilute solution of bleach (4% sodium hypochlorite), has on charcoal. We were particularly interested in considering if charcoal formed under different conditions of pyrolysis was differentially affected by this treatment, which is commonly used for the quantification of charcoal in sediments. We first produced a series of charcoal samples, under laboratory conditions (at temperatures between 250°C and 800°C and under oxygen limited conditions) and then measured total surface area of charcoal before and after treatment in a solution of 4% bleach. We found that charcoal formed ⩽400°C showed nearly complete bleaching after 24 h, while high temperature charcoal (>400°C) was much more resistant. These results indicate this treatment bleaches charcoal formed at lower temperatures: this means particles charred at low temperature may not be quantified in common optical counting or image analysis methods. This could have serious ramifications for sediment-based paleofire research as low intensity fire may be lost from a record, and the resulting fire history biased towards high intensity (high temperature) fires. Our findings suggest the need for a new, non-destructive method for extracting charcoal from sediment.

The widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using C-14 and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment delta C-13 values (-34 to -26 parts per thousand) suggests that C-3 vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0-1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20-40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low delta C-13 and delta N-15 values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5-10%), is relatively higher in delta C-13 and delta N-15, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using C-13-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in delta C-13, delta N-15 and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e-d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one. (C) 2020 Elsevier Ltd. All rights reserved.

This study describes a multivariate statistical model (derived using partial least squares regression, PLS-R) that derives charring intensity (reaction temperature and duration) from the attenuated total reflectance (ATR) Fourier Transform Infrared (FTIR) spectra of charcoal. Data for the model was obtained from a library of charcoal samples produced under laboratory conditions at charring intensities (CI) relevant to wildfires and a series of feedstocks representing common tree species collected from Australia. The PLS-R model developed reveals the potential of FTIR to determine the charring intensity of charcoal. Though limited by the differences between laboratory-produced charcoal and the more heterogeneous and less-structured charcoal produced in a wildfire, the method was tested against fossil charcoal from a well-dated sediment core collected from Thirlmere Lakes National Park, Australia and showed a distinct change in CI that can be related to other climatic and environmental proxies. We suggest that the method has the potential to offer insights into the conditions under which natural charcoal is formed including the modelling of charring intensities of fossil charcoal samples isolated from sediments, archaeological applications or characterisation of contemporary fire events from charcoal in soils.

Quaternary Research is an international journal devoted to the advancement of the interdisciplinary understanding of the Quaternary Period.We aim to publish articles of broad interest with relevance to more than one discipline, and that constitute a signifi cant new contribution to Quaternary science.

AbstractWe present a multiproxy record using pollen, magnetic susceptibility, carbon isotopic composition, carbon/nitrogen ratio, and particle size of mid- to late Holocene environmental changes based on a sediment core from the Pomaeho lagoon on the east coast of Korea. The records indicate that climate deteriorations around 6400 cal yr BP and 4000 cal yr BP caused rapid vegetation changes in the study area, which were presumably attributable to low sunspot activity and strong El Niño–like conditions, respectively. These two cooling events were likely modulated by different climate mechanisms, as El Niño–Southern Oscillation activity began to strengthen around 5000 cal yr BP. These events may have had a substantial impact on ancient societies in the study area. Combining our results with archaeological findings indicated that climate deterioration led to drastic declines in local populations around 6400 cal yr BP, 4400 cal yr BP, and 4000 cal yr BP. Because of its high population, coastal East Asia (e.g., eastern China, Japan, and Korea) is particularly vulnerable to potential cooling events in the future. Therefore, there is a strong need for detailed paleoclimate information in this region.