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Microbial assemblages inhabiting soils sheltered by rocks are widespread in the hyperarid and hypersaline Dalangtan Playa, which could contribute significant ly to the ecological processes in this desert ecosystem. Here, we performed geochemical and metagenomic analyses of soils below and beside rocks in the Dalangtan Playa. Fourier transform infrared (FTIR) spectra show more evident signals of organic aromatic molecules in soils below rocks than in nearby bare soils. Soils below rocks harbor distinct microbial communities and much higher biomass and Cyanobacteria abundance in comparison to soils beside rocks. High-quality genomes recovered by hybrid short- and long-read assembly reveal the previously underappreciated contribution of Actinobacteriota in sheltered soils to the primary production of desert ecosystems. In contrast to bare soil communities, the metabolic versatility of sheltered soil communities indicates their critical roles in carbon, nitrogen, and sulfur cycling in the Dalangtan Playa. Trace gases (CO and H2) could be significant energy sources for the respiration and sometimes carbon fixation of both bare and sheltered soil microorganisms in nutrient-deprived environments. The presence of multiple stress response genes against DNA damage, oxidative stress, and osmotic stress, as well as pathways for the biosynthesis and uptake of compatible solutes in genomes across all samples, reveals their capacity for tolerating polyextreme conditions. IMPORTANCE The hyperarid Dalangtan Playa in the western Qaidam Basin, northwestern China, is a unique terrestrial analog of Mars. Despite the polyextreme environments of this area, habitats below translucent rocks capable of environmental buffering could serve as refuges for microbial life. In this study, the hybrid assembly of Illumina short reads and Nanopore long reads recovered high-quality and high-continuity genomes, allowing for high-accuracy analysis and a deeper understanding of extremophiles in the sheltered soils of the Dalangtan Playa. Our findings reveal self-supporting and metabolically versatile sheltered soil communities adapted to a hyperarid and hypersaline playa, which provides implications for the search for life signals on Mars. [ABSTRACT FROM AUTHOR]

ABSTRACT The lacustrine systems of La Brava and La Punta, located in the Tilopozo sector in the extreme south of Salar de Atacama, are pristine high-altitude Andean lakes found along the central Andes of South America. This shallow ecosystem suffers from permanent evaporation, leading to falling water levels, causing it to recede or disappear during the dry season. This dynamic causes physicochemical changes in lakes, such as low nutrient availability, pH change, and dissolved metals, which can influence the composition of the microbial community. In this study, we used a metataxonomic approach (16S rRNA hypervariable regions V3 to V4) to characterize the sedimentary microbiota of these lakes. To understand how the water column affects and is structured in the microbiota of these lakes, we combined the analysis of the persistence of the water column through satellite images and physicochemical characterization. Our results show a significant difference in abiotic factors and microbiota composition between La Punta and La Brava lakes. In addition, microbiota analysis revealed compositional changes in the ecological disaggregation (main and isolated bodies) and antagonistic changes in the abundance of certain taxa between lakes. These findings are an invaluable resource for understanding the microbiological diversity of high Andean lakes using a multidisciplinary approach that evaluates the microbiota behavior in response to abiotic factors. IMPORTANCE In this study, we analyzed the persistence of the water column through satellite images and physicochemical characterization to investigate the composition and diversity in High Andean Lake Systems in a hyperarid environment. In addition to the persistence of the water column, this approach can be used to analyze changes in the morphology of saline accumulations and persistence of snow or ice; for example, for establishing variable plant cover over time and evaluating the microbiota associated with soils with seasonal changes in plants. This makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. In our case, it was used to study microorganisms capable of resisting desiccation and water restriction for a considerable period and adapting to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration.

Ensuring sustainability of groundwater (GW) resources requires understanding the interplaying factors in the hydrogeochemical evolution of the system (cause and effect relationships), which is the subject of the current work concerning the groundwater resource in a hyperarid region, namely, AdDawadmi, Saudi Arabia. Integration of geographical information system (GIS), statistical, graphical, and geochemical modeling approaches are adopted to achieve the study's design intentions. Slicing the study area on a spatial basis helped yield insights into major constituents' variation trends using the graphical methods that lack spatial representation capabilities, such as Piper, radial, and Durov plots. Localities of higher salinities, NO3−, SO42−, Cl−, Na+, and Ca2+ are remarkable, indicating the effects of localized and point source activities and evaporation-driven concentrating processes rather than lithology supported by the largest regression and correlation coefficients for Cl−, Na+, and SO42. Many interacting processes are identified: evaporation, vicious salinization cycle (VSC), rock weathering, ion exchange, and geomorphological-driven flow. Hydrogeochemical modeling using the Visual MINTEQ program concludes that concentration-driven evaporation might lead to the precipitation of significant SO42− and Ca2+ along with CaCO3 saturation. Such processes, coupled with the ion exchange, would greatly impact the GW chemical composition and affect the aquifer and soil properties such as permeability. Human activities impact the GW system, necessitating remediation plans and protection policies to prevent overexploitation and brook the VSC. Finally, the integration of the adopted approaches was found useful, constraining the findings of one approach, reducing the associated uncertainties, enhancing the confidence level and reliability of the obtained conclusions, and obtaining useful information, enabling understanding of the internally interacting processes otherwise hidden. [ABSTRACT FROM AUTHOR]

The hyperarid Atacama Desert is one of the driest and oldest deserts on Earth, rendering it a valuable climate archive. However, unraveling its past climate is particularly challenging and the few studied paleoclimate records of the region reveal strong temporal and spatial variabilities. To enhance our understanding of these dynamics we investigated a sedimentary record in the Yungay valley located in the southern hyperarid Atacama Desert. We employed paleomagnetic and radiocarbon dating, and for the first time for Atacama Desert sediments, a meteoric 10Be/9Be based method for determining the depositional age. The respective 4.20 m deep profile comprises a lower alluvial fan deposit with a maximum age of 3.8 ± 0.8 Ma, and an upper 1.84 m thick clay pan deposit that has accumulated over the last 19 ka. Different proxies including grain size, salt concentration, and elemental composition indicate an aridity increase around 2.3 Ma ago and repeated dry and wet phases during the late Pleistocene and the Holocene. The latter climatic shifts can be assigned to variabilities of the South American Summer Monsoon and El Niño Southern Oscillation with moisture sources from the Atlantic and the Pacific Ocean, respectively. This study provides deeper insights into the heterogeneous climate of the hyperarid Atacama Desert and underlines the importance of interdisciplinary investigations to decipher climate systems and their effect on potential habitable regions in such an extreme environment. • Paleo record in the hyperarid Atacama Desert: clay pan deposits (~100 m Ma−1) cover alluvial fan deposits (~1 m Ma−1). • First application of 10Be/9Be age dating on terrestrial deposits in the Atacama Desert. • Alluvial fan deposits record an increase of aridity at 2.3 Ma. • Clay pan deposits record multiple wet phases during late Pleistocene and Holocene. • Climate shifts can be linked to variabilities in the South American Summer Monsoon and El Niño Southern Oscillation. [ABSTRACT FROM AUTHOR]

Abstract Background The hyperarid core of the Atacama Desert is an extremely harsh environment thought to be colonized by only a few heterotrophic bacterial species. Current concepts for understanding this extreme ecosystem are mainly based on the diversity of these few species, yet a substantial area of the Atacama Desert hyperarid topsoil is covered by expansive boulder accumulations, whose underlying microbiomes have not been investigated so far. With the hypothesis that these sheltered soils harbor uniquely adapted microbiomes, we compared metagenomes and geochemistry between soils below and beside boulders across three distantly located boulder accumulations in the Atacama Desert hyperarid core. Results Genome-resolved metagenomics of eleven samples revealed substantially different microbial communities in soils below and beside boulders, despite the presence of shared species. Archaea were found in significantly higher relative abundance below the boulders across all samples within distances of up to 205 km. These key taxa belong to a novel genus of ammonia-oxidizing Thaumarchaeota, Candidatus Nitrosodeserticola. We resolved eight mid-to-high quality genomes of this genus and used comparative genomics to analyze its pangenome and site-specific adaptations. Ca. Nitrosodeserticola genomes contain genes for ammonia oxidation, the 3-hydroxypropionate/4-hydroxybutyrate carbon fixation pathway, and acetate utilization indicating a chemolithoautotrophic and mixotrophic lifestyle. They also possess the capacity for tolerating extreme environmental conditions as highlighted by the presence of genes against oxidative stress and DNA damage. Site-specific adaptations of the genomes included the presence of additional genes for heavy metal transporters, multiple types of ATP synthases, and divergent genes for aquaporins. Conclusion We provide the first genomic characterization of hyperarid soil microbiomes below the boulders in the Atacama Desert, and report abundant and highly adapted Thaumarchaeaota with ammonia oxidation and carbon fixation potential. Ca. Nitrosodeserticola genomes provide the first metabolic and physiological insight into a thaumarchaeal lineage found in globally distributed terrestrial habitats characterized by various environmental stresses. We consequently expand not only the known genetic repertoire of Thaumarchaeota but also the diversity and microbiome functioning in hyperarid ecosystems. Video Abstract

ABSTRACT Salar de Atacama is located approximately 55 km south of San Pedro de Atacama in the Antofagasta region, Chile. The high UV irradiation and salt concentration and extreme drought make Salar de Atacama an ideal site to search for novel soil microorganisms with unique properties. Here, we used a metataxonomic approach (16S rRNA V3-V4) to identify and characterize the soil microbiota associated with different surface azonal vegetation formations, including strict hygrophiles (Baccharis juncea, Juncus balticus, and Schoenoplectus americanus), transitional hygrophiles (Distichlis spicata, Lycium humile, and Tessaria absinthioides), and their various combinations. We detected compositional differences among the soil surface microbiota associated with each plant formation in the sampling area. There were changes in soil microbial phylogenetic diversity from the strict to the transitional hygrophiles. Moreover, we found alterations in the abundance of bacterial phyla and genera. Halobacteriota and Actinobacteriota might have facilitated water uptake by the transitional hygrophiles. Our findings helped to elucidate the microbiota of Salar de Atacama and associate them with the strict and transitional hygrophiles indigenous to the region. These findings could be highly relevant to future research on the symbiotic relationships between microbiota and salt-tolerant plants in the face of climate change-induced desertification. IMPORTANCE The study of the composition and diversity of the wetland soil microbiota associated with hygrophilous plants in a desert ecosystem of the high Puna in northern Chile makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. These microorganisms are adapted to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration; they can be applied in various fields, such as biotechnology and astrobiology, and industries, including the pharmaceutical, food, agricultural, biofuel, cosmetic, and textile industries. These microorganisms can also be used for ecological conservation and restoration. Extreme ecosystems are a unique biological resource and biodiversity hot spots that play a crucial role in maintaining environmental sustainability. The findings could be highly relevant to future research on the symbiotic relationships between microbiota and extreme-environment-tolerant plants in the face of climate change-induced desertification.

Summary: The post‐Miocene climatic histories of arid environments have been identified as key drivers of dispersal and diversification. Here, we investigate how climatic history correlates with the historical biogeography of the Atacama Desert genus Cristaria (Malvaceae).We analyze phylogenetic relationships and historical biogeography by using next‐generation sequencing (NGS), molecular clock dating, Dispersal Extinction Cladogenesis and Bayesian sampling approaches. We employ a novel way to identify biogeographically meaningful regions as well as a rarely utilized program permitting the use of dozens of ancestral areas.Partial incongruence between the established taxonomy and our phylogenetic data argue for a complex historical biogeography with repeated introgression and incomplete lineage sorting. Cristaria originated in the central southern part of the Atacama Desert, from there the genus colonized other areas from the late Miocene onwards. The more recently diverged lineages appear to have colonized different habitats in the Atacama Desert during pluvial phases of the Pliocene and early Pleistocene.We show that NGS combined with near‐comprehensive sampling can provide an unprecedented degree of phylogenetic resolution and help to correlate the historical biogeography of plant communities with cycles of arid and pluvial phases. [ABSTRACT FROM AUTHOR]

In this study we aim at refining our understanding of the floristic connectivity of the loma- and precordillera floras of southern Peru and northern Chile and the parameters determining vegetation cover in this region. We used multivariate analyses to test for floristic- and environmental similarity across 53 precordillera and loma locations in Peru and Chile. We propose the use of predictive modeling in estimating the extent of desert vegetation as a complementary method to remote sensing. We created habitat suitability models for the vegetation on the coast and in the precordillera based on a combination of latent bioclimatic variables and additional environmental predictors using Maxent. We found Peruvian and Chilean lomas to be strongly floristically differentiated, as are the Chilean precordillera and lomas. Conversely, there is clear connectivity between both the Peruvian loma- and precordillera floras on the one hand and the Peruvian and Chilean precordillera floras on the other. Divergent environmental conditions were retrieved as separating the precordillera and lomas, while environmental conditions are not differentiated between Peruvian and Chilean lomas. Peruvian and Chilean precordilleras show a gradual change in environmental conditions. Habitat suitability models of vegetation cover retrieve a gap for the loma vegetation along the coast between Peru and Chile, while a continuous belt of suitable habitats is retrieved along the Andean precordillera. Unsuitable habitat for loma vegetation north and south of the Chilean and Peruvian border likely represents an ecogeographic barrier responsible for the floristic divergence of Chilean and Peruvian lomas. Conversely, environmental parameters change continuously along the precordilleras, explaining the moderate differentiation of the corresponding floras. Our results underscore the idea of the desert core acting as an ecogeographic barrier separating the coast from the precordillera in Chile, while it has a more limited isolating function in Peru. We also find extensive potentially suitable habitats for both loma- and precordillera vegetation so far undetected by methods of remote sensing.

Background: The hyperarid core of the Atacama Desert is an extremely harsh environment thought to be colonized by only a few heterotrophic bacterial species. Current concepts for understanding this extreme ecosystem are mainly based on the diversity of these few species, yet a substantial area of the Atacama Desert hyperarid topsoil is covered by expansive boulder accumulations, whose underlying microbiomes have not been investigated so far. With the hypothesis that these sheltered soils harbor uniquely adapted microbiomes, we compared metagenomes and geochemistry between soils below and beside boulders across three distantly located boulder accumulations in the Atacama Desert hyperarid core. Results: Genome-resolved metagenomics of eleven samples revealed substantially different microbial communities in soils below and beside boulders, despite the presence of shared species. Archaea were found in significantly higher relative abundance below the boulders across all samples within distances of up to 205 km. These key taxa belong to a novel genus of ammonia-oxidizing Thaumarchaeota, Candidatus Nitrosodeserticola. We resolved eight mid-to-high quality genomes of this genus and used comparative genomics to analyze its pangenome and site-specific adaptations. Ca. Nitrosodeserticola genomes contain genes for ammonia oxidation, the 3-hydroxypropionate/4-hydroxybutyrate carbon fixation pathway, and acetate utilization indicating a chemolithoautotrophic and mixotrophic lifestyle. They also possess the capacity for tolerating extreme environmental conditions as highlighted by the presence of genes against oxidative stress and DNA damage. Site-specific adaptations of the genomes included the presence of additional genes for heavy metal transporters, multiple types of ATP synthases, and divergent genes for aquaporins. Conclusion: We provide the first genomic characterization of hyperarid soil microbiomes below the boulders in the Atacama Desert, and report abundant and highly adapted Thaumarchaeaota with ammonia oxidation and carbon fixation potential. Ca. Nitrosodeserticola genomes provide the first metabolic and physiological insight into a thaumarchaeal lineage found in globally distributed terrestrial habitats characterized by various environmental stresses. We consequently expand not only the known genetic repertoire of Thaumarchaeota but also the diversity and microbiome functioning in hyperarid ecosystems. 7Emv5x2zFsLcvyRTYGWyYK Video Abstract [ABSTRACT FROM AUTHOR]

Aim: We investigated the biogeographic pattern of the species‐rich genus Psectrascelis (Coleoptera: Tenebrionidae) in the Central Andes and the Chilean Atacama Desert as an example for insect evolution in such a geologically and climatically highly dynamic arid region. The main aim was to test two alternative hypotheses about the main drivers of diversification of biotas from deserts in the region: Andean uplift versus Pleistocene fragmentation/dispersal. Location: South America, Central Andes, Atacama Desert. Taxon: Psectrascelis (Coleoptera: Tenebrionidae). Methods: A phylogenetic tree based on cytochrome oxidase I, 16S and Wg genes was prepared for multiple individuals from 36 populations of the region representing 14 species or subspecies. Divergence times, ancestral ranges and biogeographic events that may have led to the current distribution and species diversity were estimated. Results: The first split within the genus is not directly related to the Andean uplift but began at the time of global cooling at ~3.5 Ma, when the Andes had already reached their current altitude. Further differentiations of Psectrascelis lineages were mostly caused by common and more global drivers resulting in major clusters of diversifications at ~2.6–2.2 Ma, ~1.3–0.7 Ma and several subsequent events during the mid‐ to late Quaternary. Today, the two main clades of Psectrascelis almost meet each other after presumably synchronous range expansions along the Western Cordillera. Main conclusions: Diversification of Psectrascelis has primarily been affected by global climate changes since the mid‐Pliocene and has involved multiple vicariance and jump dispersal events. We hypothesize that jump dispersal events have occasionally been accompanied by adaptation to stronger aridity, which paved the way for range expansion into previously unsuitable habitats and eventually led to synchronous colonizations without spatial overlap along different isohyets in the Western Cordillera during the late Pleistocene. [ABSTRACT FROM AUTHOR]

Ecosystem dry limits have been studied in the context of species biology, fitness, and interactions with biotic and abiotic parameters, but the interactive effects of these parameters remain underexplored. Therefore, information on the putative effects of global climate change on these ecosystems is often lacking.We analyzed the interplay between fine‐scale landscape genetics and biotic and abiotic factors of terrestrial Tillandsia lomas in the hyperarid Atacama Desert, characterized by a fog‐dependent vegetation type almost entirely dominated by one single vascular plant species.We showed that metapopulations of Tillandsia landbeckii are genetically connected over many hundreds of square kilometers, and despite having a large potential for clonal propagation, genetic diversity is regionally and locally structured. At the landscape level, genetic diversity correlates well with fitness parameters such as growth, flowering, and vegetation density. We also observed fine‐scale correlation with a 3‐D landscape model indicating a positive feedback with seasonal fog occurrence and availability. The various interactions of biotic and abiotic factors resulted in regular linear banding patterns of vegetation arranged orthogonally toward the landscape slope. Ex situ growth experiments indicated that T. landbeckii grows at optimal rates in this extreme hyperarid environment, and we can extrapolate mean biomass production for this ecosystem.Synthesis. Our results suggest that the unique ecosystem of terrestrial Tillandsia lomas in the hyperarid Atacama Desert is an evolutionarily balanced and fine‐scaled system. The vegetation itself is composed of long‐lived and persistent modules. We developed a descriptive model of the various interacting factors, thereby also highlighting the severe threat caused by global climate change potentially associated with fog disturbance patterns along the Chilean Pacific coast. [ABSTRACT FROM AUTHOR]

A distinct feature of many of the earliest archaeological sites (13,000-11,200 cal yr BP) at the core of the Atacama Desert is that they lie at or just below the surface, often encased in desert pavements. In this study, we compare these sites and undisturbed desert pavements to understand archaeological site formation and pavement development and recovery. Our results indicate these pavements and their soils are poorly developed regardless of their age. We propose that this is because of sustained lack of rain and extreme physical breakdown of clasts by salt expansion. Thus, the core of the Atacama provides an example of the lower limits of rainfall (<50 mm/yr) needed to form desert pavements. At site Quebrada Maní 12 (QM12), humans destroyed the pavement. After abandonment, human-made depressions were filled with eolian sands, incorporating artifacts in shallow deposits. Small and medium-sized artifacts preferentially migrated upwards, perhaps due to earthquakes and the action of salts. These artifacts, which now form palimpsests at the surface, helped – along with older clasts - to restore surface clast cover. Larger archaeological features remained undisturbed on top of a deeper Byzm horizon. The vesicular A horizons (Av horizons) have not regenerated on the archaeological sites due to extreme scarcity of rainfall during the Holocene. [ABSTRACT FROM AUTHOR]

The Atacama Desert in Chile is known to be one of the driest deserts on Earth, with dominating hyperaridity at least since the Miocene. During recent times, however, especially the southern part of the Atacama repeatedly experienced exceptional precipitation events, like in 2015 and 2017. Locally, these events with high rainfall rates caused catastrophic floods with significant destruction and human fatalities. Although the meteorological drivers of these heavy rains are widely understood, only little is known about the frequency and amplitude of similar events on geological timescales. Here we present the results of a study on an endorheic clay pan at the southern edge of the hyperarid core of the Atacama, an area with a mean precipitation of approx. 5 mm per year. A modern ground-truthing approach combining sediment data, remote-sensing and meteorological data as well as climate-modelling was applied. Our observations indicate that the clay pan reacted very sensitively to local precipitation during the past 30 years, with four events >20 mm total rain causing sufficient surface run-off in the catchment to partially flood the basin. Comparative analyses of the four events illustrate that the amount of run-off is dependent on the maximum rain rate during the events rather than the total rain sum. A 1.88-m long sediment core recovered from the centre of the clay pan records the local hydrological and -environmental history since the Late Pleistocene. Sedimentological, mineralogical, geochemical, and biological core analyses imply strong variations in the amplitude of the recorded rainfall, with a clear shift from enhanced alluvial activity caused by higher-amplitude rain events during the Late Pleistocene to lower-amplitude Holocene events. The Holocene background sedimentation is superimposed by seven severe "Millennial-scale rain events", which imply precipitation maxima on sub-orbital timescales that are potentially driven by changes in the El Niño Southern Oscillation (ENSO). The results of the study shed new light on the glacial-interglacial but also the sub-orbital precipitation variability in the Coastal Cordillera of the Atacama Desert and its potential driving mechanisms, and provide perspectives of the future precipitation development in the region under progressive global warming. • The Paranal clay pan reacts highly sensitively to rain events >20 mm. • Surface run-off in the catchment is controlled by rain sums >20 mm and high rain rates. • Seven "Millennial-scale rain events" during the Holocene exceed historic rain. • Much stronger rain intensity during the Late Pleistocene pluvial phases. • Projections of 21st century point to fewer but stronger heavy rain events. [ABSTRACT FROM AUTHOR]

Over the past 15 years several expeditions by French, American and especially Italian cavers have unveiled over 50 caves in the Cordillera de la Sal (Atacama Desert, Northern Chile). Many of these caves contain a variety of speleothems and minerals, some of which have rarely been observed within karst systems. Most of the secondary deposits in these caves are composed of halite, but also other halide, carbonate, sulphate, nitrate, phosphate, and silicate minerals have been found. Among the sixteen cave mineral species recognized, atacamite, darapskite, blödite, leonite, anhydrite, and especially antarcticite are worth mentioning. In one of the samples an unknown Ca-Sr-bearing chloride mineral has also been discovered, but it has not been possible to carry out detailed mineralogical analyses. These often-rare minerals have formed in this region due to the very extreme hyperarid and salt-rich environment. This research reports the mineralogical results and proposes the genetical mechanisms leading to the formation of antarcticite, powdery anhydrite, and the paragenesis of the halite-darapskite-blödite. This study also shows that Atacama caves may be excellent analogues to study weathering processes and subsurface secondary minerals in hyperarid and hypersaline environments on Mars.

Importance: The hyperarid Dalangtan Playa in the western Qaidam Basin, northwestern China, is a unique terrestrial analog of Mars. Despite the polyextreme environments of this area, habitats below translucent rocks capable of environmental buffering could serve as refuges for microbial life. In this study, the hybrid assembly of Illumina short reads and Nanopore long reads recovered high-quality and high-continuity genomes, allowing for high-accuracy analysis and a deeper understanding of extremophiles in the sheltered soils of the Dalangtan Playa. Our findings reveal self-supporting and metabolically versatile sheltered soil communities adapted to a hyperarid and hypersaline playa, which provides implications for the search for life signals on Mars., Competing Interests: The authors declare no conflict of interest.

Based on a field expedition to the Dalangtan (DLT) saline playa located in a hyperarid region (Qaidam Basin) on the Tibet Plateau and follow-up investigations, we report the mineralogy and geochemistry of the salt layers in two vertical stratigraphic cross sections in the DLT playa. Na-, Ca-, Mg-, KCaMg-sulfates; Na-, K-, KMg-chlorides; mixed (K, Mg)-chloride–sulfate; and chlorate and perchlorate were identified in the collected samples. This mineral assemblage represents the last-stage precipitation products from Na-K-Mg-Ca-Cl-SO4 brine and the oxychlorine formation from photochemistry reaction similar to other hyperarid regions on Earth. The spatial distributions of these salts in both stratigraphic cross sections suggest very limited brine volumes during the precipitation episodes in the Holocene era. More importantly, sulfates and chlorides with a high degree of hydrations were found preserved within the subsurface salt-rich layers of DLT saline playa, where the environmental conditions at the surface are controlled by the hyperaridity in the Qaidam Basin on the Tibet Plateau. Our findings suggest a very different temperature and relative humidity environment maintained by the hydrous salts in a subsurface salty layer, where the climatic conditions at surface have very little or no influence. This observation bears some similarities with four observations on Mars, which implies not only a large humidity reservoir in midlatitude and equatorial regions on Mars but also habitability potential that warrants further investigation. [ABSTRACT FROM AUTHOR]

Abstract The halite-encrusted salt pans (salars) present at low elevations in the hyperarid core of the Atacama Desert in northern Chile are unique features of one of the driest and possibly oldest deserts on Earth. Here we show that these landscapes were shallow freshwater lakes and wetlands during the last glacial period and formed periodically between ∼46.9 ka and 7.7 ka. The moisture appears to have been sourced from increased Andean runoff and most of our chronologies for these deposits were coeval with the Central Andean Pluvial Event (17.5–14.2 ka and 13.8–9.7 ka), but we also find evidence for older as well as slightly younger wet phases. These environments supported a diverse hygrophytic-halophytic vegetation, as well as an array of diatoms and gastropods. Using a regional hydrological model, we estimate that recharge rates from 1.5 to 4 times present were required to activate and maintain these wetlands in the past. Activation in the late Pleistocene was part of a regional enhancement of water resources, extending from the Andes, downstream and through riparian corridors, to the lowest and most arid portions of the desert itself. This fundamentally unique environment was encountered by the earliest human explorers in the region, and most likely facilitated migration and encampments on a landscape that at present lacks macroscopic life on its surface. Highlights • Lakes and wetlands formed in the hyperarid core of the Atacama during the late Quaternary. • Groundwater highstands formed a network of wetlands and paleolakes from the Andes to the Pacific. • Most of our findings are coeval with the Central Andean Pluvial Event (CAPE) 17.5–9.7 ka. • Pre-CAPE enhanced periods of recharge have occurred since ∼46.9 ka. [ABSTRACT FROM AUTHOR]

The hyperarid Atacama Desert of northern Chile may be the driest place on Earth. Plants surviving there have adapted a number of unique strategies to cope with the harsh conditions. Many cacti in arid areas tend to produce reproductive organs in positions that maximize incidence of solar radiation. We sought to determine whether Eulychnia acida, an endemic cactus with an arborescent growth form, follows the same pattern. We conducted a study in two populations of the cactus. One population occurs where average annual precipitation (AAP) is 113 mm; AAP at the other site is 50 mm. We randomly sampled 10 plants at each location, and 300 reproductive structures on those plants. On each plant, we recorded the position of all reproductive organs relative to the center of the plant, and relative to the center of the stems on which they were located. The results of the two populations did not differ significantly, so results of the two populations were combined. Both populations lie south of the Tropic of Capricorn, beyond the point where the sun reaches its southernmost zenith. Hence, the sun is located at to the north all year long. We discovered that the reproductive tissue emerges predominantly on stems found the equatorial (north) side of the plant and on the equatorial (north) side of those stems. As reproduction is energetically expensive, the generation of reproductive organs from vegetative tissue that receives high levels of direct solar radiation minimizes the cost of translocating photosynthates from photosynthetic tissue to non-photosynthetic reproductive tissue, thus begetting energetic efficiency. The strategy appears to be common among many cacti and in some other plants of arid regions worldwide and is especially prevalent at extra-tropical latitudes. In addition to nectar rewards, the strategy may also benefit pollinators by offering a thermal reward, especially on overcast or otherwise cool days, thus improving the odds of successful pollination. [ABSTRACT FROM AUTHOR]

Over the past 15 years several expeditions by French, American and especially Italian cavers have unveiled over 50 caves in the Cordillera de la Sal (Atacama Desert, Northern Chile). Many of these caves contain a variety of speleothems and minerals, some of which have rarely been observed within karst systems. Most of the secondary deposits in these caves are composed of halite, but also other halide, carbonate, sulphate, nitrate, phosphate, and silicate minerals have been found. Among the sixteen cave mineral species recognized, atacamite, darapskite, blödite, leonite, anhydrite, and especially antarcticite are worth mentioning. In one of the samples an unknown Ca-Sr-bearing chloride mineral has also been discovered, but it has not been possible to carry out detailed mineralogical analyses. These often-rare minerals have formed in this region due to the very extreme hyperarid and salt-rich environment. This research reports the mineralogical results and proposes the genetical mechanisms leading to the formation of antarcticite, powdery anhydrite, and the paragenesis of the halite-darapskiteblödite. This study also shows that Atacama caves may be excellent analogues to study weathering processes and subsurface secondary minerals in hyperarid and hypersaline environments on Mars. [ABSTRACT FROM AUTHOR]

The lacustrine systems of La Brava and La Punta, located in the Tilopozo sector in the extreme south of Salar de Atacama, are pristine high-altitude Andean lakes found along the central Andes of South America. This shallow ecosystem suffers from permanent evaporation, leading to falling water levels, causing it to recede or disappear during the dry season. This dynamic causes physicochemical changes in lakes, such as low nutrient availability, pH change, and dissolved metals, which can influence the composition of the microbial community. In this study, we used a metataxonomic approach (16S rRNA hypervariable regions V3 to V4) to characterize the sedimentary microbiota of these lakes. To understand how the water column affects and is structured in the microbiota of these lakes, we combined the analysis of the persistence of the water column through satellite images and physicochemical characterization. Our results show a significant difference in abiotic factors and microbiota composition between La Punta and La Brava lakes. In addition, microbiota analysis revealed compositional changes in the ecological disaggregation (main and isolated bodies) and antagonistic changes in the abundance of certain taxa between lakes. These findings are an invaluable resource for understanding the microbiological diversity of high Andean lakes using a multidisciplinary approach that evaluates the microbiota behavior in response to abiotic factors. IMPORTANCE In this study, we analyzed the persistence of the water column through satellite images and physicochemical characterization to investigate the composition and diversity in High Andean Lake Systems in a hyperarid environment. In addition to the persistence of the water column, this approach can be used to analyze changes in the morphology of saline accumulations and persistence of snow or ice; for example, for establishing variable plant cover over time and evaluating the microbiota associated with soils with seasonal changes in plants. This makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. In our case, it was used to study microorganisms capable of resisting desiccation and water restriction for a considerable period and adapting to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration., Competing Interests: The authors declare no conflict of interest.

The Cenozoic paleoclimate of the Atacama Desert is not well known. We examined 14 early to mid-Miocene paleosols exposed in the El Tesoro Mine, near Calama, Chile. The paleosols developed on an aggrading alluvial fan system, and lie above the mineralized gravel horizons that host a copper ore body. Soil-forming conditions that oscillated between chemical weathering and clay production (humid: analogous to modern Alfisols) to environments favoring the accumulation of pedogenic carbonate (arid to semi-arid: analogous to modern Aridisols) are indicated. In contrast, the region is presently hyperarid, and soils accumulate sulfates, chlorides, and nitrates. While total chemical analyses clearly show the accumulation of Ca by the carbonate-rich paleosols, none of the soils exhibit significant losses of elements by leaching. The δ 18 O values of the carbonates range from -8.79‰ to − 3.16‰ (VPDB). The O isotope data, when combined with published data from the region, reveal a significant divergence in the O isotope composition of precipitation in the eastern and western margins of the Andean plateau since the early Miocene, suggesting that simple interpretations of declining δ 18 O values of carbonate with increasing elevation may not be appropriate. These paleosols clearly indicate that wetter conditions prevailed in what is now the Atacama Desert during the early to mid-Miocene. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of Terrestrial Cosmogenic Nuclides (TCN) from an alluvial section in the Atacama Desert is examined. We reconstruct a burial history for the last ∼10 Ma using 40Ar/39Ar dating of volcanic ash layers interbedded with alluvial sediments; this independent dating allows us to distinguish between the effects of erosion, post-burial subsurface production, and radioactive decay during burial on TCN concentrations. Our TCN results show significant post-burial production, which is the result of the extremely slow sedimentation rate (∼3 m/Ma) and the old age of the sediments. Although distinct differences in TCN concentrations are apparent between the lower and upper parts of the sedimentary section, we show that these differences are most likely related to post-burial production and age, and not to changes in bedrock erosion rates or changes in elevation due to tectonic activity. Our approach provides a test to the applicability of the two-isotope cosmogenic burial dating system (26Al–10Be) in regions of extremely slow sedimentation rates. Our results reveal geomorphic stability in terms of erosion and sedimentation rates for the late Miocene–Pliocene in the Atacama Desert. [Copyright &y& Elsevier]

Salar de Atacama is located approximately 55 km south of San Pedro de Atacama in the Antofagasta region, Chile. The high UV irradiation and salt concentration and extreme drought make Salar de Atacama an ideal site to search for novel soil microorganisms with unique properties. Here, we used a metataxonomic approach (16S rRNA V3-V4) to identify and characterize the soil microbiota associated with different surface azonal vegetation formations, including strict hygrophiles (Baccharis juncea, Juncus balticus, and Schoenoplectus americanus), transitional hygrophiles (Distichlis spicata, Lycium humile, and Tessaria absinthioides), and their various combinations. We detected compositional differences among the soil surface microbiota associated with each plant formation in the sampling area. There were changes in soil microbial phylogenetic diversity from the strict to the transitional hygrophiles. Moreover, we found alterations in the abundance of bacterial phyla and genera. Halobacteriota and Actinobacteriota might have facilitated water uptake by the transitional hygrophiles. Our findings helped to elucidate the microbiota of Salar de Atacama and associate them with the strict and transitional hygrophiles indigenous to the region. These findings could be highly relevant to future research on the symbiotic relationships between microbiota and salt-tolerant plants in the face of climate change-induced desertification. IMPORTANCE The study of the composition and diversity of the wetland soil microbiota associated with hygrophilous plants in a desert ecosystem of the high Puna in northern Chile makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. These microorganisms are adapted to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration; they can be applied in various fields, such as biotechnology and astrobiology, and industries, including the pharmaceutical, food, agricultural, biofuel, cosmetic, and textile industries. These microorganisms can also be used for ecological conservation and restoration. Extreme ecosystems are a unique biological resource and biodiversity hot spots that play a crucial role in maintaining environmental sustainability. The findings could be highly relevant to future research on the symbiotic relationships between microbiota and extreme-environment-tolerant plants in the face of climate change-induced desertification.

Abstract: Some hillslopes in the hyperarid region of the Atacama Desert in northern Chile have surface clasts organized into distinct, contour-parallel bands separated by bare soil. We call the bands “zebra stripes” due to the contrast between the darkly varnished clasts and the light-colored, salt-rich soil. Gravel that comprises the zebra stripes is sorted such that the coarsest clasts are at the downslope front and fine progressively upslope. How and when the zebra stripes formed are perplexing questions, particularly in a region experiencing prolonged hyperaridity. Using GoogleEarth, satellite imagery, and field observations, we report the first quantitative and qualitative observations of zebra stripes in order to test hypotheses of the mechanisms and timing of their formation. We consider soil shrink-swell, seismic shaking, and overland flow as possible formation mechanisms, and find that overland flow is the most likely. Based on cosmogenic 10Be concentrations in surface clasts, salt deposition rates from the atmosphere, and content in the soils, we propose that the salt-rich soils began accumulating ~106 y ago and the zebra stripes formed 103–104 y at the latest. The zebra stripe pattern has been preserved due to the self-stabilization of the clasts within the stripes and the continued absence of life (which would disturb the surface, as seen at a wetter site to the south). We conclude that the occurrence of zebra stripes is diagnostic of a set of distinct characteristics of local and/or regional precipitation, soil, hillslope form, and bedrock type. [Copyright &y& Elsevier]

Abstract: New radiometric and magnetostratigraphic data from Quillagua and Calama basins (Atacama desert) indicate that the stratigraphic record over the last 10Ma includes two hiatuses, lasting approximately 2 and 4 million years respectively. These sedimentary gaps are thought to represent prolonged periods of hyperaridity in the region, with absence of sediment production and accumulation in the central depressions. Their remarkable synchrony with Antarctic and Patagonian glacial stages, Humboldt cold current enhancement and cold upwelling waters lead us to suggest long-term climate forcing. Higher frequency climate (orbital precession and eccentricity) forcing is thought to control the sequential arrangement of the lacustrine units deposited at times of lower aridity. Hyperaridity trends appear to be modulated by the activity of the South American Summer Monsoon, which drives precipitation along the high altitude areas to the east of Atacama. This precipitation increase combined with the eastward enlargement of the regional drainage during the late Pleistocene enabled water transfer from these high altitude areas to the low lying closed Quillagua basin and resulted in the deposition of the last widespread saline lacustrine deposits in this depression, before its drainage was open to the Pacific Ocean. [Copyright &y& Elsevier]

A large fraction of the vital groundwater in the Atacama Desert of northern Chile is likely composed of "fossil" or "ancient" reserves that receive little or no recharge in today's hyperarid climate. Here, we present evidence for latest Pleistocene perennial streamflow in canyons from the hyperarid core of the Atacama Desert in northern Chile. Fluvial terraces in the Pampa del Tamarugal (PdT) basin (21°S) contain widespread fossil wood, in situ roots, and well preserved leaf litter deposits indicative of perennial surface flow currently absent in these channels. Nineteen radiocarbon dates on these deposits from four separate drainages within this endorheic basin indicate ages from 16,380 to 13,740 cal yr BP, synchronous with paleolake Tauca on the Bolivian Altiplano and other regional evidence for wetter conditions during the latest Pleistocene. Groundwater-fed riparian ecosystems and associated fluvial deposits abound today in the absence of direct rainfall in northern Atacama canyons with perennial discharge. Our relict riparian ecosystems from the PdT basin are indicative of conditions similar to these northern canyons. Given that discharge was higher than present during this time, we propose that these deposits represent the most important groundwater recharge events of the last 18,000 years. A lesser recharge event occurred during the Holocene, when phreatophytic trees also grew in these drainages between 1,070 and 700 cal yr BP, during the Medieval Climatic Anomaly. Taken together, our evidence lends further support for gradient changes in the equatorial Pacific as a major driver of hydrologic change in the Atacama on both centennial and millennial time scales. [ABSTRACT FROM AUTHOR]

Although various episodes of wet Quaternary climates have been suggested in studies of the Negev Desert, here we demonstrate that Reg soils, developed on flat alluvial surfaces and sensitive to minor changes in precipitation, indicate that the southern Negev has been permanently hyperarid at least since the middle Pleistocene. The wetter episodes were restricted to the northern Negev, currently mildly arid. Gypsic-saline Reg soils that developed on stable surfaces during >200 k.y. in the southern Negev are cumulative and polygenetic, but none exhibits even the weakest development of calcic horizons. Under current climate conditions in the Negev, calcic soils are widespread in areas with rainfall >80 mm yr-1. The fact that the hyperarid (<50 mm yr-1) southern Negev lacks any calcic horizons indicates that it never experienced an average rainfall of ≥80 mm yr-1 during the middle-late Pleistocene, whereas the northern Negev was wetter. This Negev dichotomy is explained by the main physical features controlling rainfall over the Negev, i.e, the southward-decreasing depth of the atmospheric boundary layer with distance from the Mediterranean, and the altitude of the central Negev Highland (1000 m). The interaction between these two features often prevents the passage of rain clouds into the southern Negev. The Holocene and Pleistocene gypsic-salic soil distribution across the Negev closely matches the current circumstances. We suggest that hyperaridity has prevailed over the southern Negev since the last stages of the uplift of the central Negev Highland in the late Pliocene-early Pleistocene. [ABSTRACT FROM AUTHOR]

Preserved remnants of fluvial activity in deserts constitute evidence for changing boundary conditions. The Atacama Desert of northern Chile is the global end-member for aridity, so the history of relict stream networks in this region is a record of how landscapes develop under extreme conditions. On Pampa de Tana in northern Chile (19.4°S), a series of channel forms that are presently inactive but in the past flowed westward are incised into the surface of a fault bounded, topographically elevated portion of the El Diablo Formation, a regionally extensive, relict pediment. We measure cosmic-ray produced 10Be, 26Al and 21Ne in fluvial deposits to date the timing of abandonment of three channels and couple this with topographic profile information from a SPOT-6 derived, 2 m resolution digital elevation model. We find two of the channels were abandoned approximately >5.6 Myr and 2.0 Myr ago. One channel is still capable of flow and has ages suggesting it was fluvially active within the last few hundred thousand years. Using the paleochannel ages measured here and published ages for the end of aggradation of the El Diablo Formation we estimate the rates of fluvial channel incision before channel abandonment, and uplift rates on the faults after channel abandonment. Maximum uplift rates of ~12 m/Myr over the last 2 Myr are found. In general, while rates of uplift are relatively low they are several-fold more rapid than the rates of fluvial incision prior to channel abandonment. This implies that westward channel flow was interrupted by uplift of topography above a blind NW-SE striking reverse fault that affects the Central Depression, an alluvial forearc basin. We consider also that shrinkage of the upstream catchment area by stream capture, promoted via headward erosion and lateral expansion of adjacent canyons (quebradas) could be a factor in the abandonment of the channels on Pampa de Tana. Our results highlight the polygenetic nature of this landscape and show that relatively minor amounts of fault displacement in hyperarid regions can have implications for stream network evolution. Even subtle topographic uplift upstream should be taken into account when fluvial deposits are used as proxies for long-term environmental conditions. • Slow tectonic uplift can control drainage evolution in hyperarid regions. • Multiple cosmogenic nuclides show long-term surface stability juxtaposed with fluvial channel activity. • Sedimentary records can be influenced by subtle topographic change in hyperarid regions. • Major compressional fault structure identified in the northern Atacama Desert. [ABSTRACT FROM AUTHOR]

We systematically investigated the spatial distribution of sulfates, chlorides, and nitrates in Atacama Desert soils in order to identify their relationship to long-term aridity gradients and to secondary redistribution and phase transformation. Thin surface crusts, powdery surface material and subsurface concretions from up to 40 cm depth were sampled along several latitudinal transects between 19.5–25°S and 68.5–70.5°W. The samples were characterized by total soil chemical analysis (ICP-OES and spectrophotometric analysis) complemented by XRD and thermogravimetric analysis to determine contents of chloride, nitrate, and major elements along with gypsum and anhydrite abundance in Atacama Desert soils. Our results demonstrate that the spatial distribution of gypsum, anhydrite, halite, and nitrates in Atacama Desert soils is indeed linked to aridity gradients, but also sources, and secondary dissolution processes. Nitrates and chlorides are best preserved between 19 and 22°S, which thus may constitute the long-term hyperarid core of the Atacama Desert. Remobilization within the soil is ubiquitous south of 22°S, but generally also occurs on the debris fans prograding from the Precordillera into the Central Depression. A near-constant concentration ratio of Na/Cl = 0.83 – very similar to the sea water ratio – throughout the desert and concentration maxima within the reaches of coastal fog penetration below the altitude of 1200 m reveals that sea spray is the primary source of halite in Atacama Desert soils. Calcium sulfates dominate Atacama Desert soils. Deposition is primarily as gypsum, but anhydrite is abundant in the northern Central Depression between 19 and 22°S. The apparent association of anhydrite with high concentrations of nitrate and chloride may point to a formation by dissolution and secondary reprecipitation from salt-concentrated fluids. The predominance of anhydrite in the Central Depression suggest geomorphology and water availability as additional factors remaining to be determined. • The spatial distribution of soluble salts reflects long-term aridity gradients. • Long-term aridity is most severe in the Central Depression between 19 and 22°S. • Chlorides are dominated by a marine source. • Anhydrite mainly forms by dissolution-reprecipitation in the hyperarid core of the Atacama. [ABSTRACT FROM AUTHOR]

The Atacama Desert is considered one of the driest places on Earth, where the availability of water plays a crucial role in determining the presence of plants. The sparse vegetation is limited to the coastal mountains, where abundant fog provides the main source of water and nutrients for unique Tillandsia landbeckii ecosystems. The apparent retreat of this fog-dependent vegetation over the past decades, however, may relate to changing climatic conditions, in particular increasing aridity. In this study, we used the nitrogen isotopic composition (δ15N) of plant organic matter as a measure of water availability and atmospheric nitrogen input in present and past Tillandsia dune fields. We compiled an extensive data set on δ15N values of living plants and corresponding site factors (latitude, elevation, cloud cover and precipitation) along a coastal transect. We present radiocarbon-based ages of relict T. landbeckii layers preserved in sand dunes that evolved episodically over the past 2500 years. Site-averaged δ15N values range from +2‰ to −16‰, with variations of up to 4‰ observed within one site that can be related to changes in elevation. The spread in δ15N values is surprising and considerably larger than previously reported for T. landbeckii. In contrast, δ15N values of Huidobria fruticosa and Ophryosporus spp. leaves collected mostly below and above the fog zone vary between +4‰ and + 17‰, largely in agreement with global observations from water-limited systems. Comparison with satellite-based meteorological data and modelling results revealed significant correlations between δ15N values of T. landbeckii and total cloud cover (r = −0.90; p <.01), cloud height (r = −0.93; p <.001) and precipitation (r = −0.98; p <.001) along the investigated transect. The gradient in δ15N values further coincides with surface ocean nutrient concentrations in austral summer when ocean primary production is highest suggesting a potential marine source for the large spread in δ15N values. Reconstruction of past changes in fog water supply based on fossil T. landbeckii remains indicate a distinct dry episode that is consistent with a known period of extreme long-lasting droughts during late Medieval times. • δ15N values in Tillandsia ecosystems reflect water availability along latitudinal and elevational gradients • Highly 15N-depleted values in Tillandsia plants are in contrast to what is expected from water-limited ecosystems globally • Nitrogen cycle of Tillandsia differs from C 3 plants which may relate to fog nitrogen inputs and different δ15N dynamics • δ15N signature of fossil Tillandsia plants buried in sand dunes reflect changes in water availability during the late Holocene [ABSTRACT FROM AUTHOR]