Modelled dispersal patterns for wood and grass charcoal are different: implications for paleofire reconstruction

Sedimentary charcoal records provide useful perspectives on the long-term controls and behavior of fire in the Earth system. However, a comprehensive understanding of the nuances, biases, and limitations of charcoal as a fire proxy is necessary for reliable paleofire interpretations. Here, we use a charcoal dispersal model to answer the following questions: (1) How does the dispersal of wood and grass charcoal particles differ? (2) Do traditional conceptual models of charcoal dispersal reliably characterize grass charcoal dispersal? We find that small differences in shape (L:W) and density of grass and wood charcoal can cause substantial differences in particle dispersal and source area. Whereas the modelled dispersal of wood charcoal shows a localized deposition signal which decays with distance, grass charcoal shows more diffuse deposition lacking a localized center (for both >125 µm and >60 µm). Although paleofire research has typically not distinguished between fuel types, we show that the dispersal of charcoal derived from different fuels is unlikely to be uniform. Because differences in localization, production, and preservation could bias aggregate charcoal accumulation, caution should be taken when interpreting wood and grass-derived charcoal particles preserved in the same record. Additionally, we propose an alternative, dual background conceptual model of grass charcoal dispersal, as the traditional, two-component (peak and background) conceptual model does not accurately characterize the modelled dispersal of grass charcoal. Lastly, this mismatch of conceptualizations of dispersal mechanics implies that grass charcoal may not fit the criteria necessary for peak analysis techniques

Holocene Climatic Changes in the Alaskan Arctic as Inferred from Oxygen-Isotopic Analysis

Reconstructions of Holocene climate in the Alaskan Arctic allow for better understanding of how the region may respond to future climate changes. However, long-term records from the region are scarce. We conducted lithological and isotopic analyses at Wahoo Lake (69º 4.612, -146º 55.676) to infer Holocene climate variability in northern Alaska. Isotopic composition of modern water from this large, open-basin lake in the northern foothills of the Brooks Range suggests that winter precipitation dominates inputs to the lake. Isotopic composition of Pisidium exhibits large variations throughout the past 11,800 years, with δ18O values ranging between 11.6 and 14.2‰ (VSMOW) and δ13C between -2.3 and -7.1‰ (VPDB). Loss-on-ignition (LOI) shows high carbonate content (8.1-50.9%) in the subbasin sediments between 11.8-6.3 kcal BP, transitioning to lower carbonate (1.3-25.3%) and increased organic content (11.7-65.2%) between 6.3-1.4 kcal BP. High carbonate and elevated δ18O values (13.0-14.0‰) from 11.5-8.5 kcal BP likely reflect lower lake level and possibly evaporative enrichment of lake water, suggesting warm, dry summers during the early Holocene. The disappearance of Pisidium, paired with a decrease in calcite deposition at ~6.5 kcal BP, suggests increasing lake-level in the mid-Holocene, which is supported by a basal date of 5.3 kcal BP from a core of the shallow shelf of the lake. This increase coincided with lake-level increases in interior Alaska and likely resulted from enhanced regional effective moisture. The shelf sediments exhibit a marked increase in carbonate content at ~3.5 kcal BP and δ18O values generally rose from 12.4‰ at 3.5 kcal BP to 13.2‰ at 2.0 kcal BP (range = 11.6-14.2‰), suggesting increasing annual temperatures during this period. After 2.0 kcal BP, δ18O values fluctuate between 11.9-13.3‰, but generally decline until 1.0 kcal BP, suggesting dramatic temperature fluctuations in the late Holocene. These Holocene variations in δ18O values at Wahoo Lake generally correspond to fluctuations in total solar irradiance, suggesting that solar variability may have played an important role in Holocene climate change of the Alaskan Arctic. Understanding the role of solar irradiance on natural variability of climate in this region provides a framework for evaluating climatic response and sensitivity to anthropogenic forcing.Ope

Beringia and the peopling of the Western Hemisphere

Did Beringian environments represent an ecological barrier to humans until less than 15 000 years ago or was access to the Americas controlled by the spatial–temporal distribution of North American ice sheets? Beringian environments varied with respect to climate and biota, especially in the two major areas of exposed continental shelf. The East Siberian Arctic Shelf (‘Great Arctic Plain’ (GAP)) supported a dry steppe-tundra biome inhabited by a diverse large-mammal community, while the southern Bering-Chukchi Platform (‘Bering Land Bridge’ (BLB)) supported mesic tundra and probably a lower large-mammal biomass. A human population with west Eurasian roots occupied the GAP before the Last Glacial Maximum (LGM) and may have accessed mid-latitude North America via an interior ice-free corridor. Re-opening of the corridor less than 14 000 years ago indicates that the primary ancestors of living First Peoples, who already had spread widely in the Americas at this time, probably dispersed from the NW Pacific coast. A genetic ‘arctic signal’ in non-arctic First Peoples suggests that their parent population inhabited the GAP during the LGM, before their split from the former. We infer a shift from GAP terrestrial to a subarctic maritime economy on the southern BLB coast before dispersal in the Americas from the NW Pacific coast

Assessing changes in global fire regimes

PAGES, Past Global Changes, is funded by the Swiss Academy of Sciences and the Chinese Academy of Sciences and supported in kind by the University of Bern, Switzerland. Financial support was provided by the U.S. National Science Foundation award numbers 1916565, EAR-2011439, and EAR-2012123. Additional support was provided by the Utah Department of Natural Resources Watershed Restoration Initiative. SSS was supported by Brigham Young University Graduate Studies. MS was supported by National Science Centre, Poland (grant no. 2018/31/B/ST10/02498 and 2021/41/B/ST10/00060). JCA was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 101026211. PF contributed within the framework of the FCT-funded project no. UIDB/04033/2020. SGAF acknowledges support from Trond Mohn Stiftelse (TMS) and University of Bergen for the startup grant ‘TMS2022STG03’. JMP participation in this research was supported by the Forest Research Centre, a research unit funded by Fundação para a Ciência e a Tecnologia I.P. (FCT), Portugal (UIDB/00239/2020). A.-LD acknowledge PAGES, PICS CNRS 06484 project, CNRS-INSU, Région Nouvelle-Aquitaine, University of Bordeaux DRI and INQUA for workshop support.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.Peer reviewe

Polar bears and ice: cultural connotations of Arctic environments that contradict the science of climate change

In spite of overwhelming agreement between scientists and scientific agencies around the world that anthropogenic climate change is currently occurring, many American citizens and politicians alike continue to doubt its validity. In this article, we examine 21st-century media reporting and 20th-century cinematic examples that provide possible reasons for why this is the case, especially foregrounding Western cultural perceptions and connotations of the Arctic region, which have constructed an intellectual framework that resists scientific findings of anthropogenic forcing of climate change

Peak analysis of sedimentary charcoal records: some underlying assumptions and potential pitfalls

Fire histories are derived from sedimentary charcoal sequences using a suite of statistical techniques that has become increasingly complex. Here we outline the various assumptions that underpin these methods, and highlight potential sources of error that must be considered. We hope to spur debate on the circumstances in which such methods are appropriate, and highlight areas needing further research

A Meta‐Analysis of Studies Attributing Significance to Solar Irradiance

Abstract The relationship between solar irradiance and climate is greatly debated. This inferred relationship is often characterized via the statistical analysis of paleoclimate data. REDFIT is a commonly used statistical tool that overcomes uneven sampling to identify significant periodicities of variability in proxy data. We critically examine the use of REDFIT to identify solar signals in these data. By conducting a literature review, we show the REDFIT significance thresholds used by researchers to analyze paleoclimate data vary considerably. As there is some subjectivity and practicality involved in any statistical analysis, some variability is to be expected. However, we observe that the bulk of the significance thresholds used in the literature are less stringent than the critical false‐alarm level outlined by REDFIT's creators. We reexamine periodicities deemed “significant” in a published data set to show that using this more stringent, more objective critical false‐alarm threshold likely eliminates the previously inferred significance of solar signals in proxy data. Likewise, we address a lack of consideration of age model uncertainty on REDFIT's reliability in identifying solar periodicities. Overall, we show that the relationship between solar irradiance and climate, as identified by REDFIT analyses, may not be as robust as previous work might suggest

Paleoenvironment and archaeology provide cautionary tales for climate policymakers

Federal climate policy in the United States is still in its infancy and is in large part characterized by efforts to reach a consensus on the very existence and causality of climate change. This has stemmed from a sociopolitical rift within the country, with the objectivity and usefulness of science attacked by detractors. Scientists who are most qualified to defend their methods and provide information to policymakers rarely have an institutional incentive to share this knowledge, but should be encouraged to communicate their findings to the public, especially those who receive public funding. By not doing so, they are effectively 1) keeping data and their interpretations within the academy alone, despite their importance to the public welfare, 2) losing public support through inactivity, and 3) potentially harming the future availability of research support in what has rapidly become a politically polarized funding atmosphere. Archaeologists and geoscientists in particular, as repositories of past ecological knowledge established through one method (Western academic) of empirical examination, are well positioned to broadcast to the public a variety of societal responses to long-term environmental change as well as the repercussions of political reorganization in the wake of resource shortage-induced societal collapse. This paper summarizes a few promising public outreach engagements on environment and climate change, and suggests further venues for institutional change at the university level. As an example of how multi-causal socio-ecological processes can be concisely packaged for consumption by the public and policymakers without oversimplifying data, we present a synthesis of regional case studies from the New and Old Worlds. Case studies are connected through anthropological processes of cooperation versus exclusion, subsistence shifts, sociopolitical (re)organization and hierarchy, violence, and disease in a preliminary attempt a) to identify the emotional and anecdotal psychology of our own society when it comes to the changing global environment, b) to discuss the issue of scalar differences between ancient and modern ecology, and c) to call on academics to introspectively alter our own attitudes and systems of incentives at the university level. © 2018 by Gamma Theta Upsilon

Climate exceeded human management as the dominant control of fire at the regional scale in California’s Sierra Nevada

The societal impacts of recent, severe fires in California highlight the need to understand the long-term effectiveness of human fire management. The relative influences of local management and climate at centennial timescales are controversial and poorly understood. This is the case in California’s Sierra Nevada, an actively managed area with a rich history of Native American fire use. We analyzed charcoal preserved in lake sediments from Yosemite National Park and spanning the last 1400 years to reconstruct local and regional area burned. Warm and dry climates promoted burning at both local and regional scales. However, at local scales fire management by Native Americans before 850 and between ca. 1350 and 1600 CE and, subsequently, Yosemite park managers from ca. 1900 to 1970 CE, decoupled fire extent dictated by regional climate scenarios. Climate acts as a top-down, broader scale control of fire, but human management serves a bottom-up, local control. Regional area burned peaked during the Medieval Climate Anomaly and declined during the last millennium, as climate became cooler and wetter and Native American burning declined. This trend was accentuated by 20th century fire suppression policies, which led to a minimum in burned area relative to the last 1400 years. In light of projected anthropogenic greenhouse gas emissions and predicted climate changes in California, our data indicate that although active management can mitigate local fire activity, broader regional burning may become more spatially extensive than has been observed in the last century