Principal role of fungi in soil carbon stabilization during early pedogenesis in the high Arctic.

Climate warming is causing widespread deglaciation and pioneer soil formation over glacial deposits. Melting glaciers expose rocky terrain and glacial till sediment that is relatively low in biomass, oligotrophic, and depleted in nutrients. Following initial colonization by microorganisms, glacial till sediments accumulate organic carbon and nutrients over time. However, the mechanisms driving soil nutrient stabilization during early pedogenesis after glacial retreat remain unclear. Here, we traced amino acid uptake by microorganisms in recently deglaciated high-Arctic soils and show that fungi play a critical role in the initial stabilization of the assimilated carbon. Pioneer basidiomycete yeasts were among the predominant taxa responsible for carbon assimilation, which were associated with overall high amino acid use efficiency and reduced respiration. In intermediate- and late-stage soils, lichenized ascomycete fungi were prevalent, but bacteria increasingly dominated amino acid assimilation, with substantially decreased fungal:bacterial amino acid assimilation ratios and increased respiration. Together, these findings demonstrate that fungi are important drivers of pedogenesis in high-Arctic ecosystems that are currently subject to widespread deglaciation from global warming.

Seasonal environmental transitions and metabolic plasticity in a sea-ice alga from an individual cell perspective.

Sea-ice microalgae are a key source of energy and nutrient supply to polar marine food webs, particularly during spring, prior to open-water phytoplankton blooms. The nutritional quality of microalgae as a food source depends on their biomolecular (lipid:protein:carbohydrate) composition. In this study, we used synchrotron-based Fourier transform infra-red microspectroscopy (s-FTIR) to measure the biomolecular content of a dominant sea-ice taxa, Nitzschia frigida, from natural land-fast ice communities throughout the Arctic spring season. Repeated sampling over six weeks from an inner (relatively stable) and an outer (relatively dynamic) fjord site revealed high intra-specific variability in biomolecular content, elucidating the plasticity of N. frigida to adjust to the dynamic sea ice and water conditions. Environmental triggers indicating the end of productivity in the ice and onset of ice melt, including nitrogen limitation and increased water temperature, drove an increase in lipid and fatty acids stores, and a decline in protein and carbohydrate content. In the context of climate change and the predicted Atlantification of the Arctic, dynamic mixing and abrupt warmer water advection could truncate these important end-of-season environmental shifts, causing the algae to be released from the ice prior to adequate lipid storage, influencing carbon transfer through the polar marine system.

Comparison of Yamuna (India) and Mississippi River (United States of America) bacterial communities reveals greater diversity below the Yamunotri Glacier.

The Yamuna River in India and the Mississippi River in the United States hold significant commercial, cultural, and ecological importance. This preliminary survey compares the bacterial communities sampled in surface waters at 11 sites (Yamuna headwaters, Mississippi headwaters, Yamuna River Yamunotri Town, Mississippi River at Winona, Tons River, Yamuna River at Paonta Sahib, Yamuna River Delhi-1, Yamuna River Delhi-2, Yamuna River before Sangam, Sangam, Ganga River before Sangam). Bacterial 16S rDNA analyses demonstrate dominance of Proteobacteria and Bacteroidetes phyla. Actinobacteria were also dominant at sites near Sangam in India and sites in Minnesota. A dominance of Epsilonbacteraeota were found in Delhi, India. Principal component analysis (PCA) using unique operational taxonomic units (OTUs) resulted in the identification of 3 groups that included the Yamuna River locations in Delhi (Delhi locations), Yamuna headwaters and Yamuna River at Yamunotri (Yamuna River locations below the Glacier) and Mississippi, Ganga, Tons, and other Yamuna River locations. Diversity indices were significantly higher at the Yamuna River locations below the Glacier (Simpson D = 0.986 and Shannon H = 5.06) as compared (p value <0.001) to the Delhi locations (D = 0.951 and H = 4.23) and as compared (p value < 0.001) to Mississippi, Ganga, Tons, and other Yamuna River locations (D = 0.943 and H = 3.96). To our knowledge, this is the first survey to compare Mississippi and Yamuna River bacterial communities. We demonstrate higher diversity in the bacterial communities below the Yamunotri glacier in India.

Declining lake ice in response to climate change can impact spending for local communities.

Lake ice is an important socio-economic resource that is threatened by climate change. The cover and duration of lake ice are expected to decline as air temperatures warm in the coming decades, disrupting a previously reliable source of income for many activities dependent on lake ice. The economic consequences of climate-induced lake ice loss remain unexplored, creating a significant research gap. The purpose of this study was to quantify the monetary spending associated with lake ice and how climate change may impact that value. Using a series of General Circulation Models (GCMs), greenhouse gas emissions scenarios, and models for lake ice cover, we predicted changes in lake ice by the end of the 21st century for the Northern Hemisphere. We also synthesized examples of spending associated with lake ice activities and discussed the potential implications expected with declining ice cover. We found that lake ice will decrease in area by 44,000-177,000 km2 and shorten in duration by 13-43 days by 2100. Using 31 examples of revenue from lake ice, we found that lake ice generates spending of over USD 2.04 billion to local communities and economies. We also found that countries predicted to experience the greatest ice loss by the end of the century are those that currently have the largest GDP, highest greenhouse gas emissions, and are most dependent on freshwater withdrawal. Our findings confirm predicted losses in lake ice that are expected because of climate change and quantify some of the potential consequences for local communities. Here we highlight lake ice as another casualty of human-caused climate change that will have profound socio-economic implications.

The diversity and risk of potential pathogenic bacteria on the surface of glaciers in the southeastern Tibetan Plateau.

Glaciers, which constitute the world's largest global freshwater reservoir, are also natural microbial repositories. The frequent pandemic in recent years underscored the potential biosafety risks associated with the release of microorganisms from the accelerated melting of glaciers due to global warming. However, the characteristics of pathogenic microorganisms in glaciers are not well understood. The glacier surface is the primary area where glacier melting occurs that is often the main subject of research on the dynamics of pathogenic microbial communities in efforts to assess glacier biosafety risks and devise preventive measures. In this study, high-throughput sequencing and quantitative polymerase chain reaction methods were employed in analyses of the composition and quantities of potential pathogenic bacteria on the surfaces of glaciers in the southeastern Tibetan Plateau. The study identified 441 potential pathogenic species ranging from 215 to 4.39 × 1011 copies/g, with notable seasonal and environmental variations being found in the composition and quantity of potential pathogens. The highest level of diversity was observed in April and snow, while the highest quantities were observed in October and cryoconite. Host analysis revealed that >70 % of the species were pathogens affecting animals, with the highest proportion of zoonotic pathogens being observed in April. Analysis of aerosols and glacial meltwater dispersion suggested that these microbes originated from West Asia, primarily affecting the central and southern regions of China. Null model analysis indicated that the assembly of potential pathogenic microbial communities on glacier surfaces was largely governed by deterministic processes. In conclusion, potential pathogenic bacteria on glacier surfaces mainly originated from the snow and exhibited significant temporal and spatial variation patterns. These findings can be used to enhance researchers' ability to predict potential biosafety risks associated with pathogenic bacteria in glaciers and to prevent their negative impact on populations and ecological systems.

Pengzhenrongella frigida sp. nov., isolated from a glacier.

A Gram-stain-positive, rod-shaped bacterium, designated as HLT2-17T, was isolated from soil sample taken from the Hailuogou glacier in Sichuan province, PR China. Strain HLT2-17T was capable of growing at 4-25°C and in NaCl concentrations ranging from 0 to 2% (w/v). The highest level of 16S rRNA gene sequence similarity was observed with Pengzhenrongella phosphoraccumulans M0-14T (98.3 %) and Pengzhenrongella sicca LRZ-2T (98.2 %). The average nucleotide identity and digital DNA-DNA hybridization values between strain HLT2-17T and its closest relatives, P. phosphoraccumulans M0-14T and P. sicca LRZ-2T, were 80.0-84.0 % and 23.3-27.7 %, respectively. Phylogenomic analysis indicated that strain HLT2-17T clustered together with strains P. phosphoraccumulans M0-14T and P. sicca LRZ-2T. Strain HLT2-17T contained C16 : 0 and anteiso-C15 : 0 as the major fatty acids, and MK-9(H4) as the menaquinone. Therefore, based on a polyphasic approach, we propose that strain HLT2-17T (=CGMCC 1.11116T= NBRC 110443T) represents a novel species of the genus Pengzhenrongella and suggest the name Pengzhenrongella frigida sp. nov.

Ecological "Windows of opportunity" influence biofilm prokaryotic diversity differently in glacial and non-glacial Alpine streams.

In glacier-fed streams, the Windows of Opportunity (WOs) are periods of mild environmental conditions supporting the seasonal development of benthic microorganisms. WOs have been defined based on changes in biofilm biomass, but the responses of microbial diversity to WOs in Alpine streams have been overlooked. A two year (2017-2018) metabarcoding of epilithic and epipsammic biofilm prokaryotes was conducted in Alpine streams fed by glaciers (kryal), rock glaciers (rock glacial), or groundwater/precipitation (krenal) in two catchments of the Central-Eastern European Alps (Italy), aiming at testing the hypothesis that: 1) environmental WOs enhance not only the biomass but also the α-diversity of the prokaryotic biofilm in all stream types, 2) diversity and phenology of prokaryotic biofilm are mainly influenced by the physical habitat in glacial streams, and by water chemistry in the other two stream types. The study confirmed kryal and krenal streams as endmembers of epilithic and sediment prokaryotic α- and ß-diversity, with rock glacial streams sharing a large proportion of taxa with the two other stream types. Alpha-diversity appeared to respond to ecological WOs, but, contrary to expectations, seasonality was less pronounced in the turbid kryal than in the clear streams. This was attributed to the small size of the glaciers feeding the studied kryal streams, whose discharge dynamics were those typical of the late phase of deglaciation. Prokaryotic α-diversity of non-glacial streams tended to be higher in early summer than in early autumn. Our findings, while confirming that high altitude streams are heavily threatened by climate change, underscore the still neglected role of rock glacier runoffs as climate refugia for the most stenothermic benthic aquatic microorganism. This advocates the need to define and test strategies for protecting these ecosystems for preserving, restoring, and connecting cold Alpine aquatic biodiversity in the context of the progressing global warming.

Ice-inhabiting species of Bdelloidea Rotifera reveal a pre-Quaternary ancestry in the Arctic cryosphere.

Historical climate data indicate that the Earth has passed through multiple geological periods with much warmer-than-present climates, including epochs of the Miocene (23-5.3 mya BP) with temperatures 3-4°C above present, and more recent interglacial stages of the Quaternary, for example, Marine Isotope Stage 11c (approx. 425-395 ka BP) and Middle Holocene thermal maximum (7.5-4.2 ka BP), during which continental glaciers may have melted entirely. Such warm periods would have severe consequences for ice-obligate fauna in terms of their distribution, biodiversity and population structure. To determine the impacts of these climatic events in the Nordic cryosphere, we surveyed ice habitats throughout mainland Norway and Svalbard ranging from maritime glaciers to continental ice patches (i.e. non-flowing, inland ice subjected to deep freezing overwinter), finding particularly widespread populations of ice-inhabiting bdelloid rotifers. Combined mitochondrial and nuclear DNA sequencing identified approx. 16 undescribed, species-level rotifer lineages that revealed an ancestry predating the Quaternary (> 2.58 mya). These rotifers also displayed robust freeze/thaw tolerance in laboratory experiments. Collectively, these data suggest that extensive ice refugia, comparable with stable ice patches across the contemporary Norwegian landscape, persisted in the cryosphere over geological time, and may have facilitated the long-term survival of ice-obligate Metazoa before and throughout the Quaternary.

Remote-sensing monitoring of colored dissolved organic matter in the Arctic Ocean.

In the Arctic Ocean, variations in the colored dissolved organic matter (CDOM) have important value and significance. This study proposed and evaluated a novel method by combining the Google Earth Engine with a multilayer back-propagation neural network to retrieve CDOM concentration. This model performed well on the testing data and independent validation data (R2 = 0.76, RMSE = 0.37 m-1, MAPD = 35.43 %), and it was applied to Moderate Resolution Imaging Spectroradiometer (MODIS) images. The CDOM distribution in the Arctic Ocean and its main sea areas was first depicted during the ice-free period from 2002 to 2021, with average CDOM concentration in the range of 0.25 and 0.31 m-1. High CDOM concentration appeared in coastal areas affected by rivers on the Siberian side. The CDOM concentration was highly correlated with salinity (r = -0.92) and discharge (r > 0.68), while melting sea ice diluted seawater and CDOM concentration.

Habitat changes due to glacial freezing and melting reshape microbial networks.

The phenomenon of glacial freezing and thawing involves microbial sequestration, release, and colonization, which has the potential to impact ecosystem functioning through changes in microbial diversity and interactions. In this study, we examined the structural features of microbial communities of the Dongkemadi glacier, including bacteria, fungi, and archaea, in four distinct glacial environments (snow, ice, meltwater, and frontier soil). The sequestration, release, and colonization of glacial microbes have been found to significantly impact the diversity and structure of glacial microbial communities, as well as the complexity of microbial networks. Specifically, the complexity of bacterial networks has been observed to increase in a sequential manner during these processes. Utilizing the Inter-Domain Ecological Network approach, researchers have further explored the cross-trophic interactions among bacteria, fungi, and archaea. The complexity of the bacteria-fungi-archaea network exhibited a sequential increase due to the processes of sequestration, release, and colonization of glacial microbes. The release and colonization of glacial microbes led to a shift in the role of archaea as key species within the network. Additionally, our findings suggest that the hierarchical interactions among various microorganisms contributed to the heightened complexity of the bacteria-fungi-archaea network. The primary constituents of the glacial microbial ecosystem are unclassified species associated with the Polaromonas. It is noteworthy that various key species in glacial ecosystems are influenced by the distinct environmental factors. Moreover, our findings suggest that key species are not significantly depleted in response to abrupt alterations in individual environmental factors, shedding light on the dynamics of microbial cross-trophic interactions within glacial ecosystems.

Physical constraints during Snowball Earth drive the evolution of multicellularity.

Molecular and fossil evidence suggests that complex eukaryotic multicellularity evolved during the late Neoproterozoic era, coincident with Snowball Earth glaciations, where ice sheets covered most of the globe. During this period, environmental conditions-such as seawater temperature and the availability of photosynthetically active light in the oceans-likely changed dramatically. Such changes would have had significant effects on both resource availability and optimal phenotypes. Here, we construct and apply mechanistic models to explore (i) how environmental changes during Snowball Earth and biophysical constraints generated selective pressures, and (ii) how these pressures may have had differential effects on organisms with different forms of biological organization. By testing a series of alternative-and commonly debated-hypotheses, we demonstrate how multicellularity was likely acquired differently in eukaryotes and prokaryotes owing to selective differences on their size due to the biophysical and metabolic regimes they inhabit: decreasing temperatures and resource availability instigated by the onset of glaciations generated selective pressures towards smaller sizes in organisms in the diffusive regime and towards larger sizes in motile heterotrophs. These results suggest that changing environmental conditions during Snowball Earth glaciations gave multicellular eukaryotes an evolutionary advantage, paving the way for the complex multicellular lineages that followed.

Himalayas is barrier for transportation of light-absorbing particles from South Asia to inner Third Pole.

Through a comprehensive investigation into the historical profiles of black carbon derived from ice cores, the spatial distributions of light-absorbing impurities in snowpit samples, and carbon isotopic compositions of black carbon in snowpit samples of the Third Pole, we have identified that due to barriers of the Himalayas and remove of wet deposition, local sources rather than those from seriously the polluted South Asia are main contributors of light-absorbing impurities in the inner part of the Third Pole. Therefore, reducing emissions from residents of the Third Pole themselves is a more effective way of protecting the glaciers of the inner Third Pole in terms of reducing concentrations of light-absorbing particles in the atmosphere and on glaciers.

Pengzhenrongella phosphoraccumulans sp. nov., isolated from high Arctic glacial till, and emended description of the genus Pengzhenrongella.

A yellow pigmented, Gram-stain-positive, motile, facultatively anaerobic and irregular rod-shaped bacteria (strain M0-14T) was isolated from a till sample collected from the foreland of a high Arctic glacier near the settlement of Ny-Ålesund in the Svalbard Archipelago, Norway. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that M0-14T formed a lineage within the family Cellulomonadaceae, suborder Micrococcineae. M0-14T represented a novel member of the genus Pengzhenrongella and had highest 16S rRNA gene sequence similarity to Pengzhenrongella sicca LRZ-2T (97.3 %). Growth occurred at 4-25 °C (optimum 4-18 °C), at pH 6.0-9.0 (optimum pH 7.0), and in the presence of 0-5 % (w/v) NaCl. The predominant menaquinone was MK-9(H4) and the major fatty acids were anteiso-C15 : 0, C16 : 0 and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c). The major polar lipids were phosphatidylglycerol, phosphatidylinositol mannosides, phosphatidylinositol, one undefined phospholipid and five undefined phosphoglycolipids. The cell-wall diamino acid was l-ornithine whereas rhamnose and mannose were the cell-wall sugars. Polyphosphate particles were found inside the cells of M0-14T. Polyphosphate kinase and polyphosphate-dependent glucokinase genes were detected during genomic sequencing of M0-14. In addition, the complete pstSCAB gene cluster and phnCDE synthesis genes, which are important for the uptake and transport of phosphorus in cells, were annotated in the genomic data. According to the genomic data, M0-14T has a metabolic pathway related to phosphorus accumulation. The DNA G+C content of the genomic DNA was 70.8 %. On the basis of its phylogenetic relationship, phenotypic properties and chemotaxonomic distinctiveness, strain M0-14T represents a novel species of the genus Pengzhenrongella, for which the name Pengzhenrongella phosphoraccumulans sp. nov. is proposed. The type strain is M0-14T (= CCTCC AB 2012967T = NRRL B-59105T).

Giant viral signatures on the Greenland ice sheet.

BACKGROUND: Dark pigmented snow and glacier ice algae on glaciers and ice sheets contribute to accelerating melt. The biological controls on these algae, particularly the role of viruses, remain poorly understood. Giant viruses, classified under the nucleocytoplasmic large DNA viruses (NCLDV) supergroup (phylum Nucleocytoviricota), are diverse and globally distributed. NCLDVs are known to infect eukaryotic cells in marine and freshwater environments, providing a biological control on the algal population in these ecosystems. However, there is very limited information on the diversity and ecosystem function of NCLDVs in terrestrial icy habitats. RESULTS: In this study, we investigate for the first time giant viruses and their host connections on ice and snow habitats, such as cryoconite, dark ice, ice core, red and green snow, and genomic assemblies of five cultivated Chlorophyta snow algae. Giant virus marker genes were present in almost all samples; the highest abundances were recovered from red snow and the snow algae genomic assemblies, followed by green snow and dark ice. The variety of active algae and protists in these GrIS habitats containing NCLDV marker genes suggests that infection can occur on a range of eukaryotic hosts. Metagenomic data from red and green snow contained evidence of giant virus metagenome-assembled genomes from the orders Imitervirales, Asfuvirales, and Algavirales. CONCLUSION: Our study highlights NCLDV family signatures in snow and ice samples from the Greenland ice sheet. Giant virus metagenome-assembled genomes (GVMAGs) were found in red snow samples, and related NCLDV marker genes were identified for the first time in snow algal culture genomic assemblies; implying a relationship between the NCLDVs and snow algae. Metatranscriptomic viral genes also aligned with metagenomic sequences, suggesting that NCLDVs are an active component of the microbial community and are potential "top-down" controls of the eukaryotic algal and protistan members. This study reveals the unprecedented presence of a diverse community of NCLDVs in a variety of glacial habitats dominated by algae.

Holed up, but thriving: Impact of multitrophic cryoconite communities on glacier elemental cycles.

Cryoconite holes (water and sediment-filled depressions), found on glacier surfaces worldwide, serve as reservoirs of microbes, carbon, trace elements, and nutrients, transferring these components downstream via glacier hydrological networks. Through targeted amplicon sequencing of carbon and nitrogen cycling genes, coupled with functional inference-based methods, we explore the functional diversity of these mini-ecosystems within Antarctica and the Himalayas. These regions showcase distinct environmental gradients and experience varying rates of environmental change influenced by global climatic shifts. Analysis revealed a diverse array of photosynthetic microorganisms, including Stramenopiles, Cyanobacteria, Rhizobiales, Burkholderiales, and photosynthetic purple sulfur Proteobacteria. Functional inference highlighted the high potential for carbohydrate, amino acid, and lipid metabolism in the Himalayan region, where organic carbon concentrations surpassed those in Antarctica by up to 2 orders of magnitude. Nitrogen cycling processes, including fixation, nitrification, and denitrification, are evident, with Antarctic cryoconite exhibiting a pronounced capacity for nitrogen fixation, potentially compensating for the limited nitrate concentrations in this region. Processes associated with the respiration of elemental sulfur and inorganic sulfur compounds such as sulfate, sulfite, thiosulfate, and sulfide suggest the presence of a complete sulfur cycle. The Himalayan region exhibits a higher potential for sulfur cycling, likely due to the abundant sulfate ions and sulfur-bearing minerals in this region. The capability for complete iron cycling through iron oxidation and reduction reactions was also predicted. Methanogenic archaea that produce methane during organic matter decomposition and methanotrophic bacteria that utilize methane as carbon and energy sources co-exist in the cryoconite, suggesting that these niches support the complete cycling of methane. Additionally, the presence of various microfauna suggests the existence of a complex food web. Collectively, these results indicate that cryoconite holes are self-sustaining ecosystems that drive elemental cycles on glaciers and potentially control carbon, nitrogen, sulfur, and iron exports downstream.

Tibetan terrestrial and aquatic ecosystems collapsed with cryosphere loss inferred from sedimentary ancient metagenomics.

Glacier and permafrost shrinkage and land-use intensification threaten mountain wildlife and affect nature conservation strategies. Here, we present paleometagenomic records of terrestrial and aquatic taxa from the southeastern Tibetan Plateau covering the last 18,000 years to help understand the complex alpine ecosystem dynamics. We infer that steppe-meadow became woodland at 14 ka (cal BP) controlled by cryosphere loss, further driving a herbivore change from wild yak to deer. These findings weaken the hypothesis of top-down control by large herbivores in the terrestrial ecosystem. We find a turnover in the aquatic communities at 14 ka, transitioning from glacier-related (blue-green) algae to abundant nonglacier-preferring picocyanobacteria, macrophytes, fish, and otters. There is no evidence for substantial effects of livestock herding in either ecosystem. Using network analysis, we assess the stress-gradient hypothesis and reveal that root hemiparasitic and cushion plants are keystone taxa. With ongoing cryosphere loss, the protection of their habitats is likely to be of conservation benefit on the Tibetan Plateau.

One-third of Southern Ocean productivity is supported by dust deposition.

Natural iron fertilization of the Southern Ocean by windblown dust has been suggested to enhance biological productivity and modulate the climate1-3. Yet, this process has never been quantified across the Southern Ocean and at annual timescales4,5. Here we combined 11 years of nitrate observations from autonomous biogeochemical ocean profiling floats with a Southern Hemisphere dust simulation to empirically derive the relationship between dust-iron deposition and annual net community production (ANCP) in the iron-limited Southern Ocean. Using this relationship, we determined the biological response to dust-iron in the pelagic perennially ice-free Southern Ocean at present and during the last glacial maximum (LGM). We estimate that dust-iron now supports 33% ± 15% of Southern Ocean ANCP. During the LGM, when dust deposition was 5-40-fold higher than today, the contribution of dust to Southern Ocean ANCP was much greater, estimated at 64% ± 13%. We provide quantitative evidence of basin-wide dust-iron fertilization of the Southern Ocean and the potential magnitude of its impact on glacial-interglacial timescales, supporting the idea of the important role of dust in the global carbon cycle and climate6-8.

Trajectory of increased iceberg kill-off in West Antarctica's shallows.

Compared with low latitude coasts, many polar latitudes are still little impacted by intense and direct anthropogenic stressors. Climate forcing is now bringing rapid physical change to nearshore polar realms. In the shallow coastal waters adjacent to the United Kingdom's Rothera Research Station in the West Antarctic Peninsula (WAP), 225 seabed markers at 5-25 m depth have been surveyed and replaced every year from 2002-2023 (75 markers at each of 5, 10 and 25 m). This is one of the longest continuously running marine disturbance experiments in the world, in one of Earth's fastest changing environments. Different categories of sea ice are recorded (including when the sea surface freezes into fast ice) at Rothera since the 1980s, and losses of marine ice in both polar regions are one of the striking responses to a warming planet1. Five to ten years of seabed marker hit rate data (marker broken or moved) showed that reduced sea ice cover is correlated with disturbance and mortality on the seabed2,3.

Hot spring oases in the periglacial desert as the Last Glacial Maximum refugia for temperate trees in Central Europe.

Northern glacial refugia are a hotly debated concept. The idea that many temperate organisms survived the Last Glacial Maximum (LGM; ~26.5 to 19 thousand years) in several sites across central and northern Europe stems from phylogeographic analyses, yet direct fossil evidence has thus far been missing. Here, we present the first unequivocal proof that thermophilous trees such as oak (Quercus), linden (Tilia), and common ash (Fraxinus excelsior) survived the LGM in Central Europe. The persistence of the refugium was promoted by a steady influx of hydrothermal waters that locally maintained a humid and warm microclimate. We reconstructed the geological and palaeohydrological factors responsible for the emergence of hot springs during the LGM and argue that refugia of this type, allowing the long-term survival and rapid post-LGM dispersal of temperate elements, were not exceptional in the European periglacial zone.