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We report 3 years of data from one meteorological and three smaller stations in University Valley, a high-elevation (1677 m) site in the Dry Valleys of Antarctica with extensive dry permafrost. Mean air temperature was -23.4°C. Summer air temperatures were virtually always < 0°C and were consistent with the altitude lapse rate and empirical relationships between summer temperature, distance from the coast and elevation. The measured frost point (-22.5°C) at the 42 cm deep ice table is equal to the surface frost point and above the atmospheric frost point (-29.6°C), providing direct evidence that surface conditions control ground ice depth. Observed peak surface soil temperatures reach 6°C for ice-cemented ground > 15 cm deep but stay < 0°C when it is shallower. We develop an energy balance model tuned to this rocky and dry environment. We find that differences in peak soil surface temperatures are primarily due to the higher thermal diffusivity of ice-cemented ground compared to dry soil. Sensitivity studies show that expected natural variability is insufficient for melt to form and significant excursions from current conditions are required. The site's ice table meets the criteria for a Special Region on Mars, with 30% of the year > -18°C and water activity > 0.6. [ABSTRACT FROM AUTHOR]

The origin and stability of ground ice in the stable uplands of the McMurdo Dry Valleys remains poorly understood, with most studies focusing on the near-surface permafrost. The 2016 Friis Hills Drilling Project retrieved five cores reaching 50 m depth in mid-Miocene permafrost, a period when Antarctica transitioned to a hyper-arid environment. This study characterizes the cryostratigraphy of arguably the oldest permafrost on Earth and assesses 15 Myr of ground ice evolution using the REGO model. Four cryostratigraphic units were identified: 1) surficial dry permafrost (0–30 cm), 2) ice-rich to ice-poor permafrost (0.3–5.0 m) with high solute load and δ18O values (-16.2 ± 1.8‰) and low D-excess values (-65.6 ± 4.3‰), 3) near-dry permafrost (5–20 m) and 4) ice-poor to ice-rich permafrost (20–50 m) containing ice lenses with low solute load and δ18O values (-34.6 ± 1.2‰) and D-excess of 6.9 ± 2.6‰. The near-surface δ18O profile of ground ice is comparable to other sites in the stable uplands, suggesting that this ice is actively responding to changing surface environmental conditions and challenging the assumption that the surface has remained frozen for 13.8 Myr. The deep ice lenses probably originate from the freezing of meteoric water during the mid-Miocene, and their δ18O composition suggests mean annual air temperatures ~7–11°C warmer than today. [ABSTRACT FROM AUTHOR]

Climate change is impacting lakes and ponds in Antarctica. To that end, we investigated the distribution and chemical composition of ice-covered ponds in Untersee Oasis, East Antarctica. Thirty-nine ponds were inventoried, and the thirteen sampled ponds have low total dissolved solutes (TDS) with a Ca(Na)-SO4 or Na-Cl geochemical facies. Tritium and radiocarbon measurements of the total inorganic carbon (TIC) suggest that the ponds are recharged by modern snowmelt. Hierarchical cluster analysis grouped the ponds based on the amount of potential incoming solar radiation reaching their surface. Ponds receiving higher insolation develop moats or completely lose their ice cover during summer, have lower pH, and higher TDS, δ18O, total inorganic carbon, and δ13CTIC,which suggest CO2 availability is not limiting benthic photosynthetic activity. The ponds that receive lower insolation retain their full ice cover and remain well-sealed to direct exchanges with the atmosphere, have high pH, and lower TDS and TIC, and likely host a CO2-starved benthic microbial ecosystem. Therefore, the state of the ponds' ice cover evolved their hydrochemistry along different trajectories. The findings can be used to predict the trajectory of the chemical composition of the ponds and effect on biological productivity as the phenology of their ice cover shifts under a warming climate. [ABSTRACT FROM AUTHOR]

Lake Untersee is one of the largest perennially ice-covered lakes in Dronning Maud Land. We investigated the energy and water mass balance of Lake Untersee to understand its state of equilibrium. The thickness of the ice cover is strongly correlated with sublimation rates; variations in sublimation rates across the ice cover are largely determined by wind-driven turbulent heat fluxes and the number of snow-covered days. Lake extent and water level have remained stable for the past 20 years, indicating that the water mass balance is in equilibrium. The lake is damned by the Anuchin Glacier and mass balance calculation suggest that subaqueous melting of terminus ice contributes 40–45% of the annual water budget; since there is no evidence of streams flowing into the lake, the lake must be connected to a groundwater system that contributes 55–60% in order to maintain the lake budget in balance. The groundwater likely flows at a rate of ~8.8 × 10−2 m3 s−1, a reasonable estimate given the range of subglacial water flux in the region. The fate of its well-sealed ice cover is likely tied to changes in wind regime, whereas changes in water budget are more closely linked to the response of surrounding glaciers to climate change. [ABSTRACT FROM AUTHOR]

This study compares the relations between solar radiation and air and ground temperatures in the Quartermain Mountains of the McMurdo Dry Valleys of Antarctica with those in ice-free Victoria Land and Arctic Canada. The surface offset is near 0°C at all sites in the Quartermain Mountains and other sites in coastal Victoria Land, whereas the thermal offset is near 0°C at shallow ice table depths (< 20 cm) and near 1°C for ice tables deeper than the depth of diurnal temperature variation. The surface and thermal offsets in Victoria Land differ markedly from those in Arctic Canada, which are generally characterised by a positive surface offset and a negative thermal offset. These important differences highlight the effects of a lack of vegetation, surface organic layer, snow cover and moisture content in near-surface soils on the direction and magnitude of surface and thermal offsets. Summer ground surface temperatures in the Quartermain Mountains correlate strongly with incoming solar radiation. Based on measured ground surface temperatures and modelled potential incoming solar radiation, two zones with distinct ground surface temperatures are defined in the Quartermain Mountains: (i) perennially cryotic zones (PCZs) characterised by ground surface temperatures always below 0°C; and (ii) seasonally non-cryotic zones (NCZs) characterised by ground surface temperatures > 0°C for at least a few hours. Soils in the PCZs experience water exchange through vapour diffusion, whereas soils in the NCZs contain features associated with liquid water activity, such as increased soil moisture and frozen ponds recharged by snow/glacier meltwater. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20–40cm of loose cryotic sediments and sandstone boulders. This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O–H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting δ18O profiles and regression slope values between the uppermost 6cm of the buried massive ice (upward convex δ18O profile and S D-18O =5.1) and that below it (progressive increase in δ18O and S D-18O =6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex δ18O profile in the uppermost 6cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured δ18O profile is 0.2 ⋅ 10−3 mm yr−1, a value that is more similar to net ice removal rates derived from 3He data from cobbles in Beacon Valley till (7.0 ⋅ 10−3 mm yr−1) than sublimation rates computed based on current climate (0.1–0.2mm yr−1). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size). [Copyright &y& Elsevier]

Ice-free areas occupy <0.5% of Antarctica and are unevenly distributed across the continent. Terrestrial ecosystem dynamics in ice free areas are strongly influenced by permafrost and the associated active layer. These features are the least studied component of the cryosphere in Antarctica, with sparse data from permanent study sites mainly providing information related to the ground thermal regime and active layer thickness (ALT). One of the most important results of the International Polar Year (IPY, 2007/08) was an increase in ground thermal regime monitoring sites, and consequently our knowledge of Antarctic permafrost dynamics. Now, 15 years after the IPY, we provide the first comprehensive summary of the state of permafrost across Antarctica, including the sub-Antarctic Islands, with analyses of spatial and temporal patterns of the dominant external factors (climate, lithology, biota, and hydric regime) on the ground thermal regime and active layer thickness. The mean annual ground temperatures of the active layer and uppermost part of the permafrost in Antarctica remain just below 0 °C in the warmest parts of the Antarctic Peninsula, and were below −20 °C in mountainous regions of the continent. The ALT varies between a few cm in the coldest, mountainous, parts of the Transantarctic Mountains up to >5 m in bedrock sites in the Antarctic Peninsula. The deepest and most variable ALTs (ca. 40 to >500 cm) were found in the Antarctic Peninsula, whereas the maximum ALT generally did not exceed 90 cm in Victoria Land and East Antarctica. Notably, found that the mean annual near-surface temperature follows the latitudinal gradient of −0.9 °C/deg. (R2 = 0.9) and the active layer thickness 3.7 cm/deg. (R2 = 0.64). The continuous permafrost occurs in the vast majority of the ice-free areas in Antarctica. The modelling of temperature on the top of the permafrost indicates also the permafrost presence in South Orkneys and South Georgia. The only areas where deep boreholes and geophysical surveys indicates discontinuous or sporadic permafrost are South Shetlands and Western Antarctic Peninsula. • Permafrost is widespread in the vast majority of ice-free areas in Antarctica. • Active layer thickness in Antarctica ranges from <5 cm to >500 cm. • Ground temperature and active layer thickness variations follow latitudinal gradient. [ABSTRACT FROM AUTHOR]