LegacyClimate 1.0: a dataset of pollen-based climate reconstructions from 2594 Northern Hemisphere sites covering the last 30 kyr and beyond

Here we describe LegacyClimate 1.0, a dataset of the reconstruction of the 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 Period. Two reconstruction methods, the modern analog 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 in the prediction and reconstruction significance tests. The dataset is beneficial for synthesis studies of proxy-based reconstructions 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.org/10.1594/PANGAEA.930512; Herzschuh et al., 2023a). The R code for the reconstructions is provided at Zenodo (https://doi.org/10.5281/zenodo.7887565; Herzschuh et al., 2023b), including the harmonized open-access modern and fossil datasets used for the reconstructions, so that customized reconstructions can be easily established

Late-Glacial Paleoecology of the Middle Susitna Valley, Alaska: Environmental Context for Human Dispersal

We present here the results of multi-proxy analyses (sediment geochemistry, diatoms, and pollen) from sediment cores collected at four lakes in the middle Susitna Valley, Alaska. These lakes form a transect from the tundra to the boreal forest. The retrieved cores span from ∼12,000 cal yr BP to the present, with age control provided by radiometric dates and tephra deposits, some of which are newly identified. Results indicate that deglaciation occurred before 12,000 cal yr BP and that by that time, the lakes were deep, productive, and surrounded by shrub tundra. The lake with the highest sampling resolution indicates a brief climatic reversal ∼11,500 cal yr BP with decreased diatom-inferred lake level and lowered lake productivity, and reduced shrub presence. During the early to middle Holocene, all of the sedimentary records provide evidence of climatic amelioration with tree expansion and productive lakes. A middle to late Holocene climatic deterioration with reduced trees and a shallower, less productive lake is also indicated. In addition, the prominent Watana tephra at ∼4,000 cal yr BP likely reduced lake productivity and affected the vegetation. Even though the region was relatively productive soon after deglaciation, people did not occupy the region until ∼11,000 cal yr BP, about 1000 years later, and then only sparsely. By the middle and late Holocene, the region was more densely populated and this shift in human occupancy presumably reflects changes in resource abundance, especially caribou. Whether the Watana ashfall influenced caribou abundance and thus people, is still under investigation, but given the tephra’s effect on vegetation and lake productivity, it seems likely

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

Steppe-tundra composition and deglacial floristic turnover in interior Alaska revealed by sedimentary ancient DNA (sedaDNA)

When tracing vegetation dynamics over long timescales, obtaining enough floristic information to gain a detailed understanding of past communities and their transitions can be challenging. The first high-resolution sedimentary DNA (sedaDNA) metabarcoding record from lake sediments in Alaska—reported here—covers nearly 15,000 years of change. It shows in unprecedented detail the composition of late-Pleistocene “steppe-tundra” vegetation of ice-free Alaska, part of an intriguing late-Quaternary “no-analogue” biome, and it covers the subsequent changes that led to the development of modern spruce-dominated boreal forest. The site (Chisholm Lake) lies close to key archaeological sites, and the record throws new light on the landscape and resources available to early humans. Initially, vegetation was dominated by forbs found in modern tundra and/or subarctic steppe vegetation (e.g., Potentilla, Draba, Eritrichium, Anemone patens), and graminoids (e.g., Bromus pumpellianus, Festuca, Calamagrostis, Puccinellia), with Salix the only prominent woody taxon. Predominantly xeric, warm-to-cold habitats are indicated, and we explain the mixed ecological preferences of the fossil assemblages as a topo-mosaic strongly affected by insolation load. At ca. 14,500 cal yr BP (calendar years before C.E. 1950), about the same time as well documented human arrivals and coincident with an increase in effective moisture, Betula expanded. Graminoids became less abundant, but many open-ground forb taxa persisted. This woody-herbaceous mosaic is compatible with the observed persistence of Pleistocene megafaunal species (animals weighing ≥44 kg)—important resources for early humans. The greatest taxonomic turnover, marking a transition to regional woodland and a further moisture increase, began ca. 11,000 cal yr BP when Populus expanded, along with new shrub taxa (e.g., Shepherdia, Eleagnus, Rubus, Viburnum). Picea then expanded ca. 9500 cal yr BP, along with shrub and forb taxa typical of evergreen boreal woodland (e.g., Spiraea, Cornus, Linnaea). We found no evidence for Picea in the late Pleistocene, however. Most taxa present today were established by ca. 5000 cal yr BP after almost complete taxonomic turnover since the start of the record (though Larix appeared only at ca. 1500 cal yr BP). Prominent fluctuations in aquatic communities ca. 14,000–9,500 cal yr BP are probably related to lake-level fluctuations prior to the lake reaching its high, near-modern depth ca. 8,000 cal yr BP

A 14,000-yr paleoenvironmental record from Windmill Lake, central Alaska: late-glacial and Holocene vegetation in the Alaska Range

A 14,000 yr high-resolution pollen and lake-level record from Windmill Lake in central Alaska provides new evidence for the Late Pleistocene and Holocene paleoenvironments of this region. At 14,000 14Cyr BP, sparse herb tundra and low lake-levels indicate a cold, arid environment. About 11,800 14Cyr BP, the vegetation abruptly shifted to a shrub tundra and lake-levels increased, suggesting warmer and more mesic conditions. Ca 10,500-10,200 14Cyr BP, herbaceous taxa increased at the expense of the shrubs, suggesting a transient episode of climatic deterioration nearly contemporaneous with the Younger Dryas chronozone. By 8000 14Cyr BP, spruce was present in the watershed and alder grew locally by 6500 14Cyr BP. The AMS radiocarbon chronology indicates later expansions of Betula, Picea, and Alnus than at most sites in central Alaska, which are conventionally dated

Aquatic Plants in a Thule House at the Rising Whale site, Cape Espenberg Contribution ofCarpology Studies to the Understanding of Thule Plant Use in Northwestern Alaska

International audienceThis poster aims to present the unusual results of a preliminary carpological and archeo-entomogical analyses of a Thule house at The Rising Whale site, located at the tip of Cape Espenberg, in northwestern Alaska. The identification of macrobotanical remains revealed an unusual amount of aquatics plants, including some species of Carex, Comarum palustris, Hippuris vulgaris, Menyanthes trifoliata and Potamogeton sp., inside the floor levels of the house feature. The use of aquatic plants is not attested ethnohistorically.While paleo-entomology and macro-fossil remains are common paleoecological proxies to reconstruct past vegetation, climates, and provide precise temperatures reconstructions, carpological analyzes have been mostly ignored in the archaeological studies of arctic and subarctic hunter-gatherers. Yet, analyzing these remains can provides unique information about the use of space within the house, hygiene practices, the use and management of the locally available resources, and the impact of people on the landscape.In this paper, we discuss the presence and the potential use of aquatics plants by the early Thule inhabitants of house F-21 at The Rising Whale site.First, we summarize the carpological results of two sedimentary column samples representing 7 to 10 stratigraphical levels from two distinct areas of the house: the western burnt area, and the entrance tunnel. Within diverse plant remains the taxonomic identifications indicate a significant amount of aquatic plant species in the main occupation levels of the two areas. Secondly, our poster present preliminary identification of entomological remains as a way to explore further the presence of the aquatic plants. Our goal was to test in these levels, whether the preserved insect species are coherent with the presence of aquatic remains in the sediment. Finally, our discussion focuses on the contribution of archaeo-entomology to the undesrtanding of plant macrofossil remains and to a better interpretation to the atypical presence of aquatic plants on the floor level in two areas of the house. We take into account 1) the large amount of insects associated with aquatic’s plant seeds present in the tunnel, and 2) the ecological niches with which the beetles are associated. Ultimately our goal is to determine whether the aquatic plants were intentionally brought into the house and for what purpose

Palaeoenvironmental records from Siberia and the Russian Far East – contributions from DIMA Network members – Introduction

As concern about the effects of climate change on northern regions increases, an important goal of palaeoenvironmental science is placing events that appear to be unprecedented—such as the severe boreal forest fires of recent years (Witze et al. 2020)—into a long-term context. The boreal forest zone covers a large span of latitude from the permafrost-affected northern treeline to the southern border with steppe and the diverse mixed temperate forest. Over two thirds of the world’s boreal forest and about a third of the northern hemisphere terrestrial carbon pool lies within Russian territory, and much of this is east of the Ural Mountains, in Siberia and the Russian Far East (SRFE) (Kuusela 1992, Stolbovoi 2002). With the awareness of the region’s sensitivity to climate change growing, it is clear that this vast expanse is understudied. Scientific centres, now associated with the Russian Academy of Sciences, have long histories of pioneering research in SRFE, and there continues to be an impressive flow of new data from these institutions, despite complex logistics of working in remote locations. A problem, however, is that a large proportion of this research is not available to the international community, primarily because of language limitations (i.e. the need to publish in English for the international audience and the inability of most of that audience to read papers published in high quality Russian scientific journals). International research cooperation can provide an avenue for greater dissemination of Russian research (for example, the Lake Baikal and Lake El’gygytgyn drilling projects, ICDP 2020a, b), but many other nationally funded projects fall outside these joint ventures

Aquatic Plants in a Thule House at the Rising Whale site, Cape Espenberg Contribution ofCarpology Studies to the Understanding of Thule Plant Use in Northwestern Alaska

International audienceThis poster aims to present the unusual results of a preliminary carpological and archeo-entomogical analyses of a Thule house at The Rising Whale site, located at the tip of Cape Espenberg, in northwestern Alaska. The identification of macrobotanical remains revealed an unusual amount of aquatics plants, including some species of Carex, Comarum palustris, Hippuris vulgaris, Menyanthes trifoliata and Potamogeton sp., inside the floor levels of the house feature. The use of aquatic plants is not attested ethnohistorically.While paleo-entomology and macro-fossil remains are common paleoecological proxies to reconstruct past vegetation, climates, and provide precise temperatures reconstructions, carpological analyzes have been mostly ignored in the archaeological studies of arctic and subarctic hunter-gatherers. Yet, analyzing these remains can provides unique information about the use of space within the house, hygiene practices, the use and management of the locally available resources, and the impact of people on the landscape.In this paper, we discuss the presence and the potential use of aquatics plants by the early Thule inhabitants of house F-21 at The Rising Whale site.First, we summarize the carpological results of two sedimentary column samples representing 7 to 10 stratigraphical levels from two distinct areas of the house: the western burnt area, and the entrance tunnel. Within diverse plant remains the taxonomic identifications indicate a significant amount of aquatic plant species in the main occupation levels of the two areas. Secondly, our poster present preliminary identification of entomological remains as a way to explore further the presence of the aquatic plants. Our goal was to test in these levels, whether the preserved insect species are coherent with the presence of aquatic remains in the sediment. Finally, our discussion focuses on the contribution of archaeo-entomology to the undesrtanding of plant macrofossil remains and to a better interpretation to the atypical presence of aquatic plants on the floor level in two areas of the house. We take into account 1) the large amount of insects associated with aquatic’s plant seeds present in the tunnel, and 2) the ecological niches with which the beetles are associated. Ultimately our goal is to determine whether the aquatic plants were intentionally brought into the house and for what purpose