TY - JOUR T1 - Antarctic water tracks: Microbial community responses to variation in soil moisture, pH, and salinity JF - Frontiers in Microbiology Y1 - 2021 A1 - George, Scott F. A1 - Noah Fierer A1 - Joseph S. Levy A1 - Byron Adams KW - Antarctica KW - extremophiles KW - Mars analog KW - microbial ecology KW - water tracks AB -

Ice-free soils in the McMurdo Dry Valleys select for taxa able to cope with challenging environmental conditions, including extreme chemical water activity gradients, freeze-thaw cycling, desiccation, and solar radiation regimes. The low biotic complexity of Dry Valley soils makes them well suited to investigate environmental and spatial influences on bacterial community structure. Water tracks are annually wetted habitats in the cold-arid soils of Antarctica that form briefly each summer with moisture sourced from snow melt, ground ice thaw, and atmospheric deposition via deliquescence and vapor flow into brines. Compared to neighboring arid soils, water tracks are highly saline and relatively moist habitats. They represent a considerable area (∼5–10 km2) of the Dry Valley terrestrial ecosystem, an area that is expected to increase with ongoing climate change. The goal of this study was to determine how variation in the environmental conditions of water tracks influences the composition and diversity of microbial communities. We found significant differences in microbial community composition between on- and off-water track samples, and across two distinct locations. Of the tested environmental variables, soil salinity was the best predictor of community composition, with members of the Bacteroidetes phylum being relatively more abundant at higher salinities and the Actinobacteria phylum showing the opposite pattern. There was also a significant, inverse relationship between salinity and bacterial diversity. Our results suggest water track formation significantly alters dry soil microbial communities, likely influencing subsequent ecosystem functioning. We highlight how Dry Valley water tracks could be a useful model system for understanding the potential habitability of transiently wetted environments found on the surface of Mars.

VL - 12 UR - https://www.frontiersin.org/articles/10.3389/fmicb.2021.616730 JO - Front. Microbiol. ER - TY - JOUR T1 - Episodic basin-scale soil moisture anomalies associated with high relative humidity events in the McMurdo Dry Valleys, Antarctica JF - Antarctic Science Y1 - 2021 A1 - Joseph S. Levy KW - deliquescence KW - hydrology KW - microclimate KW - micrometeorology KW - pedology KW - remote sensing AB -

Outside of hydrologically wetted active layer soils and humidity-sensitive soil brines, low soil moisture is a limiting factor controlling biogeochemical processes in the McMurdo Dry Valleys. But anecdotal field observations suggest that episodic wetting and darkening of surface soils in the absence of snowmelt occurs during high humidity conditions. Here, I analyse long-term meteorological station data to determine whether soil-darkening episodes are present in the instrumental record and whether they are, in fact, correlated with relative humidity. A strong linear correlation is found between relative humidity and soil reflectance at the Lake Bonney long-term autonomous weather station. Soil reflectance is found to decrease annually by a median of 27.7% in response to high humidity conditions. This magnitude of darkening is consistent with soil moisture rising from typical background values of < 0.5 wt.% to 2–3 wt.%, suggesting that regional atmospheric processes may result in widespread soil moisture generation in otherwise dry surface soils. Temperature and relative humidity conditions under which darkening is observed occur for hundreds of hours per year, but are dominated by episodes occurring between midnight and 07h00 local time, suggesting that wetting events may be common, but are not widely observed during typical diel science operations.

UR - https://www.cambridge.org/core/product/identifier/S0954102021000341/type/journal_article ER - TY - JOUR T1 - High-resolution elevation mapping of the McMurdo Dry Valleys, Antarctica, and surrounding regions JF - Earth System Science Data Y1 - 2017 A1 - Andrew G Fountain A1 - Fernandez-Diaz, Juan C. A1 - Maciek K. Obryk A1 - Joseph S. Levy A1 - Michael N. Gooseff A1 - David J. Van Horn A1 - Morin, P A1 - Shrestha, Ramesh AB -

We present detailed surface elevation measurements for the McMurdo Dry Valleys, Antarctica derived from aerial lidar surveys flown in the austral summer of 2014–2015 as part of an effort to understand geomorphic changes over the past decade. Lidar return density varied from 2 to > 10 returns  m−2 with an average of about 5  returns  m−2. Vertical and horizontal accuracies are estimated to be 7 and 3 cm, respectively. In addition to our intended targets, other ad hoc regions were also surveyed including the Pegasus flight facility and two regions on Ross Island, McMurdo Station, Scott Base (and surroundings), and the coastal margin between Cape Royds and Cape Evans. These data are included in this report and data release. The combined data are freely available at https://doi.org/10.5069/G9D50JX3.

VL - 9 UR - https://www.earth-syst-sci-data.net/9/435/2017/essd-9-435-2017.pdf JO - Earth Syst. Sci. Data ER - TY - JOUR T1 - Impacts of permafrost degradation on a stream in Taylor Valley, Antarctica JF - Geomorphology Y1 - 2017 A1 - Sudman, Zachary A1 - Michael N. Gooseff A1 - Andrew G Fountain A1 - Joseph S. Levy A1 - Maciek K. Obryk A1 - David J. Van Horn AB -

The McMurdo Dry Valleys (MDV) of Antarctica are an ice-free landscape that supports a complex, microbially dominated ecosystem despite a severely arid, cold environment (b 5 cm water equivalent/y, − 18 °C mean annual air temperature). Recent observations of permafrost degradation in the coastal zones of the MDV suggest that this region is nearing a threshold of rapid landscape change. In 2012, substantial thermokarst development was observed along several kilometers of the west branch of Crescent Stream in Taylor Valley mostly in the form of bank failures, whereas the adjacent east branch was unaffected. The objective of this study was to quantify the changes to the stream banks of the west branch of Crescent Stream and to determine the impacts on the composition of the stream bed material. Three annually repeated terrestrial LiDAR scans were compared to determine the rates of ground surface change caused by thermokarst formation on the stream bank. The areal extent of the thermokarst was shown to be decreasing; however, the average vertical rate of retreat remained constant. Field measurements of bed materials indicated that the west branch and the reach downstream of the confluence (of east and west branches) consistently contained more fines than the unaffected east branch. This suggests that the finer bed material is a result of the thermokarst development on the west branch. These finer bed material compositions are likely to increase the mobility of the bed material, which will have implications for stream morphology, stream algal mat communities, and downstream aquatic ecosystems.

VL - 285 UR - http://linkinghub.elsevier.com/retrieve/pii/S0169555X16308467 JO - Geomorphology ER - TY - JOUR T1 - Experimental formation of pore fluids in McMurdo Dry Valleys soils JF - Antarctic Science Y1 - 2015 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - W. Berry Lyons A1 - Kathleen A. Welch AB -

The aim of the study was to determine if soil salt deliquescence and brine hydration can occur under laboratory conditions using natural McMurdo Dry Valleys soils. The experiment was a laboratory analogue for the formation of isolated patches of hypersaline, damp soil, referred to as ‘wet patches’. Soils were oven dried and then hydrated in one of two humidity chambers: one at 100% relative humidity and the second at 75% relative humidity. Soil hydration is highly variable, and over the course of 20 days of hydration, ranged from increases in water content by mass from 0–16% for 122 soil samples from Taylor Valley. The rate and absolute amount of soil hydration correlates well with the soluble salt content of the soils but not with grain size distribution. This suggests that the formation of bulk pore waters in these soils is a consequence of salt deliquescence and hydration of the brine from atmospheric water vapour.

VL - 27 UR - http://www.journals.cambridge.org/abstract_S0954102014000479 IS - 02 JO - Antarctic Science ER - TY - JOUR T1 - Patterns and processes of salt efflorescences in the McMurdo region, Antarctica JF - Artic, Antarctic and Alpine Research Y1 - 2015 A1 - Bisson, K. M. A1 - Kathleen A. Welch A1 - Sue Welch A1 - Sheets, J. M. A1 - W. Berry Lyons A1 - Joseph S. Levy A1 - Andrew G Fountain AB -

Evaporite salts are abundant around the McMurdo region, Antarctica (~78°S) due to very low precipitation, low relative humidity, and limited overland flow. Hygroscopic salts in the McMurdo Dry Valleys (MDVs) are preferentially formed in locations where liquid water is present in the austral summer, including along ephemeral streams, ice-covered lake boundaries, or shallow groundwater tracks. In this study, we collected salts from the Miers, Garwood, and Taylor Valleys on the Antarctic continent, as well as around McMurdo Station on Ross Island in close proximity to water sources with the goal of understanding salt geochemistry in relationship to the hydrology of the area. Halite is ubiquitous; sodium is the major cation (ranging from 70%–90% of cations by meq kg−1 sediment) and chloride is the major anion (>50%) in nearly all samples. However, a wide variety of salt phases and morphologies are tentatively identified through scanning electron microscopy (SEM) and X-ray diffraction (XRD) work. We present new data that identifies trona (Na3(CO3)(HCO3)·2H2O), tentative gaylussite (Na2Ca(CO3)2·5H2O), and tentative glauberite (Na2Ca(SO4)2) in the MDV, of which the later one has not been documented previously. Our work allows for the evaluation of processes that influence brine evolution on a local scale, consequently informing assumptions underlying large-scale processes (such as paleoclimate) in the MDV. Hydrological modeling conducted in FREZCHEM and PHREEQC suggests that a model based on aerosol deposition alone in low elevations on the valley floor inadequately characterizes salt distributions found on the surfaces of the soil because it does not account for other hydrologic inputs/outputs. Implications for the salt distributions include their use as tracers for paleolake levels, geochemical tracers of ephemeral water tracks or “wet patches” in the soil, indicators of chemical weathering products, and potential delineators of ecological communities.

UR - http://aaarjournal.org/doi/abs/10.1657/AAAR0014-024 ER - TY - JOUR T1 - Hyperspectral measurements of wet, dry and saline soils from the McMurdo Dry Valleys: soil moisture properties from remote sensing JF - Antarctic Science Y1 - 2014 A1 - Joseph S. Levy A1 - Nolin, Anne A1 - Andrew G Fountain A1 - Head, James W. AB -

Soil moisture is a spatially heterogeneous quantity in the McMurdo Dry Valleys of Antarctica that exerts a large influence on the biological community and on the thermal state of Dry Valleys permafrost. The goal of this project was to determine whether hyperspectral remote sensing techniques could be used to determine soil moisture conditions in the Dry Valleys. We measured the spectral reflectance factors of wetted soil samples from the Dry Valleys under natural light conditions and related diagnostic spectral features to surface layer soil moisture content. Diagnostic water absorption features in the spectra at 1.4 µm and 1.9 µm were present in all samples, including samples doped with high concentrations of chloride salts. The depth of the 1.4 µm absorption is shown to increase linearly with increasing gravimetric water content. These results suggest that airborne hyperspectral imaging of the Dry Valleys could generate soil moisture maps of this environment over large spatial areas using non-invasive remote-sensing techniques.

VL - 26 UR - http://www.journals.cambridge.org/abstract_S0954102013000977 IS - 05 JO - Antarctic Science ER - TY - JOUR T1 - The McMurdo Dry Valleys: A landscape on the threshold of change JF - Geomorphology Y1 - 2014 A1 - Andrew G Fountain A1 - Joseph S. Levy A1 - Michael N. Gooseff A1 - David J. Van Horn AB -

Field observations of coastal and lowland regions in the McMurdo Dry Valleys suggest they are on the threshold of rapid topographic change, in contrast to the high elevation upland landscape that represents some of the lowest rates of surface change on Earth. A number of landscapes have undergone dramatic and unprecedented landscape changes over the past decade including, the Wright Lower Glacier (Wright Valley) — ablated several tens of meters, the Garwood River (Garwood Valley) has incised > 3 m into massive ice permafrost, smaller streams in Taylor Valley (Crescent, Lawson, and Lost Seal Streams) have experienced extensive down-cutting and/or bank undercutting, and Canada Glacier (Taylor Valley) has formed sheer, > 4 meter deep canyons. The commonality between all these landscape changes appears to be sediment on ice acting as a catalyst for melting, including ice-cement permafrost thaw. We attribute these changes to increasing solar radiation over the past decade despite no significant trend in summer air temperature. To infer possible future landscape changes in the McMurdo Dry Valleys, due to anticipated climate warming, we map ‘at risk’ landscapes defined as those with buried massive ice in relative warm regions of the valleys. Results show that large regions of the valley bottoms are ‘at risk’. Changes in surface topography will trigger important responses in hydrology, geochemistry, and biological community structure and function.

VL - 225 UR - http://linkinghub.elsevier.com/retrieve/pii/S0169555X14001780http://api.elsevier.com/content/article/PII:S0169555X14001780?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0169555X14001780?httpAccept=text/plain JO - Geomorphology ER - TY - JOUR T1 - Accelerated thermokarst formation in the McMurdo Dry Valleys, Antarctica JF - Scientific Reports Y1 - 2013 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - Dickson, James L. A1 - Head, James W. A1 - Okal, Marianne A1 - Marchant, David R. A1 - Watters, Jaclyn VL - 3 UR - http://www.nature.com/srep/2013/130724/srep02269/full/srep02269.html?WT.ec_id=SREP-20130730 ER - TY - JOUR T1 - CORRIGENDUM: Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth’s most saline lake and implications for Mars JF - Scientific Reports Y1 - 2013 A1 - Dickson, James L. A1 - Head, James W. A1 - Joseph S. Levy A1 - Marchant, David R. VL - 3 ER - TY - JOUR T1 - Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth's most saline lake and implications for Mars JF - Scientific Reports Y1 - 2013 A1 - Dickson, James L. A1 - Head, James W. A1 - Joseph S. Levy A1 - Marchant, David R. VL - 3 UR - http://www.nature.com/srep/2013/130130/srep01166/full/srep01166.html?WT.ec_id=SREP-704-20130201 ER - TY - JOUR T1 - Garwood Valley, Antarctica: A new record of Last Glacial Maximum to Holocene glaciofluvial processes in the McMurdo Dry Valleys JF - Geological Society of America Bulletin Y1 - 2013 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - O'Connor, J. E. A1 - Kathleen A. Welch A1 - W. Berry Lyons VL - 125 UR - http://bulletin.geoscienceworld.org/content/early/2013/06/07/B30783.1.abstract IS - 9-10 ER - TY - JOUR T1 - How big are the McMurdo Dry Valleys? Estimating ice-free area using Landsat image data JF - Antarctic Science Y1 - 2013 A1 - Joseph S. Levy VL - 25 IS - 01 ER - TY - JOUR T1 - Shallow groundwater systems in a polar desert, McMurdo Dry Valleys JF - Hydrogeology Journal Y1 - 2013 A1 - Michael N. Gooseff A1 - John E. Barrett A1 - Joseph S. Levy VL - 21 UR - http://link.springer.com/article/10.1007%2Fs10040-012-0926-3 IS - 1 ER - TY - JOUR T1 - Understanding Terrestrial Ecosystem Response to Antarctic Climate Change JF - Eos, Transactions American Geophysical Union Y1 - 2013 A1 - Joseph S. Levy A1 - W. Berry Lyons A1 - Byron Adams VL - 94 UR - http://onlinelibrary.wiley.com/doi/10.1002/2013EO030009/abstract IS - 3 ER - TY - JOUR T1 - Water track modification of soil ecosystems in the Lake Hoare basin, Taylor Valley, Antarctica JF - Antarctic Science Y1 - 2013 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - Michael N. Gooseff A1 - John E. Barrett A1 - Robert Vantreese A1 - Kathleen A. Welch A1 - W. Berry Lyons A1 - Uffe N. Nielsen A1 - Diana H. Wall ER - TY - JOUR T1 - Hypersaline “wet patches” in Taylor Valley, Antarctica JF - Geophysical Research Letters Y1 - 2012 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - Kathleen A. Welch A1 - W. Berry Lyons VL - 39 IS - 5 ER - TY - JOUR T1 - Water tracks and permafrost in Taylor Valley, Antarctica: Extensive and shallow groundwater connectivity in a cold desert ecosystem JF - Geological Society of America Bulletin Y1 - 2011 A1 - Joseph S. Levy A1 - Andrew G Fountain A1 - Michael N. Gooseff A1 - Kathleen A. Welch A1 - W. Berry Lyons VL - 123 UR - http://bulletin.geoscienceworld.org/content/123/11-12/2295.short IS - 11-12 ER -