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Perchlorate has been observed in many environments on Earth and Mars but its sources remain poorly quantified. In this study, we use a global three‐dimensional chemical transport model to simulate perchlorate's gas‐phase photochemical production, atmospheric transport, and deposition on Earth's surface. Model predictions are compared to newly compiled observations of atmospheric concentrations, deposition flux, and oxygen isotopic composition of perchlorate. We find that the modeled gas‐phase production of perchlorate is consistent with reported stratospheric observations. Nevertheless, we show that this mechanism alone cannot explain the high levels of perchlorate observed at many near‐surface sites (aerosol concentrations >0.1 ng m−3 and deposition fluxes >10 g km−2 yr−1) or the low 17O‐excess observed in perchlorate sampled from pristine environments (<+18.4‰). We discuss four hypotheses to explain the model‐observation discrepancies and recommend laboratory and field observations to address key uncertainties in atmospheric sources of perchlorate. Plain Language Summary: Perchlorate (ClO4−) pollution is an environmental issue because excessive exposure can affect the thyroid and disrupt hormonal balance, especially for infants. Perchlorate on Earth has both human and natural sources. Industrial perchlorate is used for explosives and rocket fuels. Perchlorate also occurs naturally and accumulates in many deserts on Earth and in the soil of Mars. Atmospheric chemistry has long been considered a source of natural perchlorate, but its contribution remains uncertain. In this study, we use a 3‐D atmospheric model to estimate how much of the perchlorate occurrence on Earth can be explained by known and plausible reactions between gases containing chlorine and oxygen. We find that these reactions can explain the abundance of stratospheric perchlorate. However, they cannot explain many tropospheric observations of perchlorate, especially those in Antarctica and urban areas. Our analysis of oxygen isotopic anomalies also suggests that stratospheric chemistry alone cannot account for all the natural perchlorate found in deserts. We discuss four possible explanations for the differences between observations and model predictions. We recommend some future research that can reduce the uncertainties in the sources of atmospheric perchlorate and improve our understanding of the occurrence of natural perchlorate in planetary atmospheres. Key Points: We conduct the first global simulation of atmospheric perchlorate using a three‐dimensional chemical transport modelGas‐phase production of perchlorate in the stratosphere and its subsequent transport cannot explain observations at many surface sitesAnalysis of modeled and observed 17O excess suggests that non‐stratospheric sources are important for the occurrence of natural perchlorate [ABSTRACT FROM AUTHOR]

Previous studies have established links between biodiversity and soil geochemistry in the McMurdo Dry Valleys, Antarctica, where environmental gradients are important determinants of soil biodiversity. However, these gradients are not well established in the central Transantarctic Mountains, which are thought to represent some of the least hospitable Antarctic soils. We analyzed 220 samples from 11 ice-free areas along the Shackleton Glacier (∼ 85 ∘ S), a major outlet glacier of the East Antarctic Ice Sheet. We established three zones of distinct geochemical gradients near the head of the glacier (upper), its central part (middle), and at the mouth (lower). The upper zone had the highest water-soluble salt concentrations with total salt concentrations exceeding 80 000 µ g g -1 , while the lower zone had the lowest water-soluble N:P ratios, suggesting that, in addition to other parameters (such as proximity to water and/or ice), the lower zone likely represents the most favorable ecological habitats. Given the strong dependence of geochemistry on geographic parameters, we developed multiple linear regression and random forest models to predict soil geochemical trends given latitude, longitude, elevation, distance from the coast, distance from the glacier, and soil moisture (variables which can be inferred from remote measurements). Confidence in our random forest model predictions was moderately high with R2 values for total water-soluble salts, water-soluble N:P , ClO 4- , and ClO 3- of 0.81, 0.88, 0.78, and 0.74, respectively. These modeling results can be used to predict geochemical gradients and estimate salt concentrations for other Transantarctic Mountain soils, information that can ultimately be used to better predict distributions of soil biota in this remote region. [ABSTRACT FROM AUTHOR]

Previous studies have established links between biodiversity and soil geochemistry in the McMurdo Dry Valleys, Antarctica, where environmental gradients are important determinants of soil biodiversity. However, these gradients are not well established in the Central Transantarctic Mountains, which are thought to represent some of the least hospitable Antarctic soils. We analyzed 220 samples from 11 ice-free areas along the Shackleton Glacier (~85 °S), a major outlet glacier of the East Antarctic Ice Sheet. We established three zones of distinct geochemical gradients near the head of the glacier (upper), central (middle), and at the mouth (lower). The upper zone had the highest water-soluble salt concentrations with total salt concentrations exceeding 80,000 μg g-1, while the lower zone had the lowest water-soluble N:P ratios, suggesting that, in addition to other parameters (such as proximity to water/ice), the lower zone likely represents the most favorable ecological habitats. Given the strong dependence of geochemistry with geographic parameters, we established multiple linear regression and random forest models to predict soil geochemical trends given latitude, longitude, elevation, distance from the coast, distance from the glacier, and soil moisture (variables which can be inferred from remote measurements). Confidence in our model predictions was moderately high, with R2 values for total water-soluble salts, water-soluble N:P, ClO4-, and ClO3- of 0.51, 0.42, 0.40, and 0.28, respectively. These modeling results can be used to predict geochemical gradients and estimate salt concentrations for other Transantarctic Mountain soils, information that can ultimately be used to better predict distributions of soil biota in this remote region. [ABSTRACT FROM AUTHOR]

Future exploration of the Moon will require access to the subsurface and acquisition of samples for scientific analysis and ground truthing of water-ice and mineral reserves for in situ resource utilization purposes. The LunarVader drill described in this paper is a 1-m class drill and cuttings acquisition system enabling subsurface exploration of the Moon. The drill employs rotary-percussive action, which reduces the weight on bit and energy consumption. This drilling approach has been successfully used by previous lunar missions, such as the Soviet Luna 16, 20, and 24, and United States Apollo 15, 16, and 17. These missions and drilling systems are described in detail. The passive sample acquisition system of the LunarVader drill delivers cuttings directly into a sample cup or an instrument inlet port. The drill was tested in a vacuum chamber and penetrated various formations, such as a water-saturated lunar soil simulant (JSC-1A) at −80°C, water-ice, and rocks to a depth of 1 m. The system was also field tested in the lunar analog site on Ross Island, Antarctica, where it successfully penetrated to 1-m depth and acquired icy samples into a sample cup. During the chamber and field testing, the LunarVader demonstrated drilling at the 1-1-100-100 level; that is, it penetrated 1 m in approximately 1 h with roughly 100-W power and less than 100-N weight on bit. This corresponds to a total drilling energy of approximately 100 Whr. The drill system achieved high enough technology readiness to be considered as a viable option for future lunar missions, such as the South Pole-Aitken Basin Sample Return and Geophysical Network missions recently recommended by the Decadal Survey of the National Research Council, and commercial missions, such as Google Lunar X-Prize missions. [ABSTRACT FROM AUTHOR]

Abstract: We measured chlorate (ClO3 −) and perchlorate (ClO4 −) concentrations in ice covered lakes of the McMurdo Dry Valleys (MDVs) of Antarctica, to evaluate their role in the ecology and geochemical evolution of the lakes. ClO3 − and ClO4 − are present throughout the MDV Lakes, streams, and other surface water bodies. ClO3 − and ClO4 − originate in the atmosphere and are transported to the lakes by surface inflow of glacier melt that has been differentially impacted by interaction with soils and aeolian matter. Concentrations of ClO3 − and ClO4 − in the lakes and between lakes vary based on both total evaporative concentration, as well as biological activity within each lake. All of the lakes except the East lobe of Lake Bonney support biological reduction of ClO3 − and ClO4 − either in the anoxic bottom waters or sediment. The younger less saline lakes (Miers and Hoare), have surface ClO3 − and ClO4 − concentrations, and ratios of ClO3 −/Cl− and ClO4 −/Cl−, similar to source streams, while Lake Fryxell has concentrations similar to input streams but much lower ClO3 −/Cl− and ClO4 −/Cl− ratios, reflecting the influence of a large Cl− source in bottom sediments. ClO3 − and ClO4 − in Lake Bonney are the highest of all the lakes reflecting the lake’s greater age and higher concentration of Cl−. ClO4 − appears to be stable in the East Lobe and its concentration is highly correlated with Cl− concentration suggesting that some ClO4 − at depth is a remnant of the initial seawater that formed Lake Bonney. ClO3 − and ClO4 − concentrations provide a simple and sensitive means to evaluate microbial activity in these lakes due to their relatively low concentrations and lack of biological sources, unlike NO3 −, NO2 −, and SO4 −2. [Copyright &y& Elsevier]