LegacyClimate 1.0: A dataset of pollen-based climate reconstructions from 2594 Northern Hemisphere sites covering the late Quaternary

Here we describe the LegacyClimate 1.0, a dataset of the reconstruction of mean July temperature (TJuly), mean annual temperature (Tann), and annual precipitation (Pann) from 2594 fossil pollen records from the Northern Hemisphere spanning the entire Holocene with some records reaching back to the Last Glacial. Two reconstruction methods, the Modern Analogue Technique (MAT) and Weighted-Averaging Partial-Least Squares regression (WA-PLS) reveal similar results regarding spatial and temporal patterns. To reduce the impact of precipitation on temperature reconstruction and vice versa, we also provide reconstructions using tailored modern pollen data limiting the range of the corresponding other climate variables. We assess the reliability of the reconstructions using information from the spatial distributions of the root-mean squared error of prediction and reconstruction significance tests. The dataset is beneficial for climate proxy synthesis studies and to evaluate the output of climate models and thus help to improve the models themselves. We provide our compilation of reconstructed TJuly, Tann, and Pann as open-access datasets at PANGAEA (https://doi.pangaea.de/10.1594/PANGAEA.930512; Herzschuh et al., 2021). R code for the reconstructions is provided at Zenodo (https://doi.org/10.5281/zenodo.5910989; Herzschuh et al., 2022), including harmonized open-access modern and fossil datasets used for the reconstructions, so that customized reconstructions can be easily established

Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp

Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the “arctic greening”) will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species

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

Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic)

Ice Complex deposits (locally known as the Buchchagy Ice Complex) are exposed at both coasts of the East Siberian Dmitry Laptev Strait and preserved below the Yedoma Ice Complex that formed during MIS3 and MIS2 (Marine Isotope Stage) and lateglacial-Holocene thermokarst deposits (MIS1). Radioisotope disequilibria (Th-230/U) of peaty horizons date the Buchchagy Ice Complex deposition to 126 + 16/-13 kyr and 117 + 19/-14 kyr until 98 +/- 5 kyr and 89 +/- 5 kyr. The deposit is characterised by poorly sorted medium-to-coarse silts with cryogenic structures of horizontal ice bands, lens-like, and lens like reticulated segregation ice. Two peaty horizons within the Buchchagy Ice Complex and syngenetic ice wedges (2-4 m wide, up to 10 m high) are striking. The isotopic composition (delta O-18, delta D) of Buchchagy ice-wedge ice indicates winter conditions colder than during the MIS3 interstadial and warmer than during MIS2 stadial, and similar atmospheric winter moisture sources as during the MIS2 stadial. Buchchagy Ice Complex pollen spectra reveal tundra-steppe vegetation and harsher summer conditions than during the MIS3 interstadial and rather similar vegetation as during the MIS2 stadial. Short-term climatic variability during MIS5 is reflected in the record. Even though the regional chronostratigraphic relationship of the Buchchagy Ice Complex to the Last Interglacial remains unclear because numerical dating is widely lacking, the present study indicates permafrost (Ice Complex) formation during MIS5 sensu lato, and its preservation afterwards. Palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern Siberia are deduced from the record. (C) 2015 Elsevier Ltd. All rights reserved

Evolution of thermokarst in East Siberian ice-rich permafrost: A case study

Thermokarst lakes and basins are major components of ice-rich permafrost landscapes in East Siberian coastal lowlands and are regarded as indicators of regional climatic changes. We investigate the temporal and spatial dynamics of a 7.5 km2, partly drained thermokarst basin (alas) using field investigations, remote sensing, Geographic Information Systems (GIS), and sediment analyses. The evolution of the thermokarst basin proceeded in two phases. The first phase started at the Pleistocene/Holocene transition (13 to 12 ka BP) with the initiation of a primary thermokarst lake on the Ice Complex surface. The lake expanded and persisted throughout the early Holocene before it drained abruptly about 5.7 ka BP, thereby creating a > 20 m deep alas with residual lakes. The second phase (5.7 ka BP to present) is characterized by alternating stages of lower and higher thermokarst intensity within the alas that were mainly controlled by local hydrological and relief conditions and accompanied by permafrost aggradation and degradation. It included diverse concurrent processes like lake expansion and stepwise drainage, polygonal ice-wedge growth, and the formation of drainage channels and a pingo, which occurred in different parts of the alas. This more dynamic thermokarst evolution resulted in a complex modern thermokarst landscape. However, on the regional scale, the changes during the second evolutionary phase after drainage of the initial thermokarst lakes were less intense than the early Holocene extensive thermokarst development in East Siberian coastal lowlands as a result of a significant regional change to warmer and wetter climate conditions

An approach for spatial analysis on the medieval Ust-Voikar settlement (subarctic Western Siberia) using macroremains and non-pollen palynomorphs

<p>The settlement of Ust-Voikar is one of the unique multilayered archaeological sites of north-west Siberia. The settlement was inhabited in the late Middle Ages and the early modern period by the Ob Ugrian or northern Khanty ethnographic group. Due to the presence of a frozen cultural layer ruins of wooden residential buildings and other organic materials are well preserved. Plant macroremain, pollen and non-pollen palynomorph (NPP) analyses were applied to samples of the cultural layer from different parts of buildings and from space between them to establish the vegetation cover, plants used by the population, and differences between functional zones in the buildings. For the first time, the NPP analysis combined with statistical methods were used to clarify the settlement planning and human economic activity. Plant communities around the Ust-Voikar settlement were typical for the northern taiga subzone, some settlement's areas were overgrown with weed vegetation. Residents did not engage in agriculture and used local plant resources for construction, medicinal and food purposes. According to macroremain and NPP data were reconstructed (i) the use of spruce branches and cereal bedding indoors and outdoors on wet sites; (ii) the careful use of fire indoors; (iii) the presence of animals indoors; and (iv) whipworm infection. The cluster analysis and principal component analysis of NPPs helped to clarify the planning affiliations of several samples with the unclear origin and to suggest ways in which archaeological objects were used by the inhabitants.</p&gt

Hill coefficients from different sources of sediment core from Lake Bayan Nuur

Estimating aquatic and pollen-assemblages, and community diversity. Comparison of multivariate datasets of bioproxies. To evaluate the similarity or dissimilarity of aquatic (lacustrine) and pollen assemblages, and their response to environmental changes, different datasets were compared using the statistical methods applied in modern species ecology. The richness and diversity of all bioproxies (pollen, diatoms, cladoceran, and chironomids) were calculated as the effective taxon numbers N0, N1, and N2 proposed by Hill (1973, doi:10.2307/1934352). Investigators using Hill numbers should report, at least, the diversity of all species (q0), of ''typical'' species (q1), and dominant species (q2) (Chao et al., 2014, doi:10.1890/13-0133.1). where S is the number of taxa in the sample count and the ith taxon has a relative abundance pi. The parameter q determines how sensitive the estimate is to taxon frequencies, where q = 0 is simply the total number of taxa in a community (Hill N0, 0D), q = 1 is the number of common taxa represented by the exponential of the Shannon-Wiener diversity index (Hill N1, 1D), and q = 2 is the number of dominant taxa represented by the inverse of Simpson's diversity index (Hill N2, 2D) (Chao et al., 2014, doi:10.1890/13-0133.1). These measures give easily interpretable numbers and provide information at three different levels based on how rare and abundant taxa are weighted. Diversity analyses for pollen, diatom, chironomid, and cladoceran (original counts) were conducted using the iNEXT package version 2.0.12 for R. Integrated curves that allow rarefaction and extrapolation were used to standardize samples based on sample size or sample completeness, and facilitate the comparison of biodiversity data; and the Hill numbers (N0, N1, and N2) were calculated using a non-asymptotic approach. A comparison of multivariate datasets can be performed using Procrustes rotation, which assesses the overall degree of correlation between two or more ordination results, and finds an optimal superimposition that maximizes their fit. PROTEST performs a random permutation test and assesses the degree of concordance between two matrices, producing the significance of the Procrustes fit as an r value with an associated p-value to indicate the likelihood of the relationship occurring by chance (Jackson, 1995, doi:10.1080/11956860.1995.11682297); and this approach has been employed in evaluating the similarities among different proxies or between environmental signals and their driving factors. We evaluated the similarity in temporal evolutions among pollen, diatom, chironomid, and cladoceran using Procrustes rotation and tested the significance of any relationship found with the associated PROTEST permutation test for the non-metric multidimensional scaling (NMDS) results of these datasets. Preliminarily to NMDS, Procrustes analyses, and PROTEST, all datasets were temporally standardized for each 100-year interval between 2850 and 50 cal yr BP. The NMDS, Procrustes analyses and PROTEST were carried out using the vegan package version 2.5-2, and linear interpolation was achieved by interp.dataset function in the rioja package version 0.9-15.1. Evenness (E) was calculated as the N2/N0 ratio. Evenness is a measure of the relative frequency of species in the community (sample). If evenness is at maximum, then all species are likely to be represented in a sample comprising only a few per cent of the individuals of the community. In contrast, if evenness is very low only a fraction of the species present in the entire population is likely to be found in even a large sample comprising almost half the individuals of the community. Interpretations of fossil assemblages in terms of evenness dynamics prove more rewarding than studies of past species richness (N0). Detrended canonical correspondence analysis (DCCA), the direct form of DCA, with species assemblage changes constrained to sediment age as the sole environmental variable, was used to develop quantitative estimates of compositional turnover, scaled in standard deviation (SD) units for each taxonomic group. The analysis is performed in CANOCO 5. Pollen percentages were square-root transformed. No down weighting of rare species was selected in this study because of the many rare pollen taxa present in our data. The change in weighted average (WA) sample scores reflects compositional change or turnover in standard deviation (SD) units along the temporal gradient

Reconstruction of the amount of annual precipitation (PANN; mm/year) for Lake Bayan Nuur

The modern pollen data from arid central Asia (Bordon et al., 2009, doi:10.1016/j.quaint.2008.05.014) and our newly completed modern pollen data from southwest Siberia (unpublished) was homogenized and combined into the modern pollen dataset (Cao et al., 2014, doi:10.1016/j.revpalbo.2014.08.007). In this study, the 808 modern pollen sites 1000-km around Bayan Nuur were selected to establish pollen-climate calibration-sets. PANN was selected as the target climatic variable for past climate 206 reconstruction. The model performance of cross-validation for the pollen-PANN calibration-set has high R2 (0.79) and low RMSEP (71 mm). A quantitative PANN reconstruction was performed using the WAPLS function in rioja package version 0.7-3 (Juggins, 2012) for R with square-root transformed pollen data

The link between climate change and biodiversity of lacustrine inhabitants and terrestrial plant communities of the Uvs Nuur Basin (Mongolia) during the last three millennia

In August 2016 the lacustrine sediment core was obtained from lake Bayan Nuur one of the northern lakes in the Great Lake Depression of Mongolia. Exact location of coring site (50.01072 N, 93.9745 E; 932 m a.s.l.) was in a water depth of 29 m at the deepest part of the lake. Corning was performed by small platform using a 60-mm gravity corer UWITEC. A 112-cm-long sediment core (BN2016-1) was studied by number of proxies including: radiocarbon dating, geochemical, pollen, diatoms and cladocera analyses. Acquired data were used for numerical analyses such as biomization, reconstruction of annual precipitation rate based on pollen data and reconstruction mean July temperature based on chironomid data, additionally was evaluated past biodiversity of the lake's microflora and microfauna using Hill numbers (Hill, 1973) based on all bioproxies data (pollen, diatoms, cladoceran, and chironomids). Six AMS radiocarbon measurements for bulk sediment samples were used for calibration and the age modeling. The average sediment accumulation rate is estimated at 0.37 mm/year. The reservoir effect calculated as 736 years was subtracted from the age-depth model. Core BN2016-1 covers the last 2885 cal. years BP