Continuous permafrost is present across the McMurdo Dry Valleys of southern Victoria Land, Antarctica. While summer active-layer thaw is common in the low-elevation portions of the Dry Valleys, active layers have not significantly thickened over time. However, in some locations, coastal Antarctic permafrost has begun to warm. Here, based on soil and meteorological measurements from 1993 to 2023, we show that wintertime soil temperatures have increased across multiple sites in the Dry Valleys, at rates exceeding the pace of summer soil warming. Linear warming trends over time are significant (P < 0.05) at six of seven soil monitoring sites. Winter warming is strongly correlated with increased numbers of down-valley wind events (Foehn/katabatics), but it may also be driven by increased incident longwave radiation at some stations (although winter longwave increase is not significant over time). While down-valley wind events increase winter warming, when down-valley wind events are excluded from the record, winter soil warming remains persistent and significant, suggesting that Antarctic soils are experiencing less cold winters over time in response to regional warming. Together, these observations suggest that some Antarctic permafrost may be approaching a transition to discontinuous permafrost in some regions as winter freezing intensity is reduced over time.

Ongoing studies conducted in northern polar regions reveal that permafrost stability plays a key role in the modern carbon cycle as it potentially stores considerable quantities of greenhouse gases. Rapid and recent warming of the Arc-tic permafrost is resulting in significant greenhouse gas emissions, both from physical and microbial processes. The po-tential impact of greenhouse gas release from the Antarctic region has not, to date, been investigated. In Antarctica, the McMurdo Dry Valleys comprise 10 % of the ice-free soil surface areas in Antarctica and like the northern polar regions are also warming albeit at a slower rate.The work presented herein examines a comprehensive sample suite of soil gas (e.g., CO2, CH4 and He) concentrations and CO2 flux measurements conducted in Taylor Valley during austral summer 2019/2020. Analytical results reveal the presence of significant concentrations of CO2, CH4 and He (up to 3.44 vol%, 18,447 ppmv and 6.49 ppmv, respec-tively) at the base of the active layer. When compared with the few previously obtained measurements, we observe increased CO2 flux rates (estimated CO2 emissions in the study area of 21.6 km2 approximate to 15 tons day-1). We suggest that the gas source is connected with the deep brines migrating from inland (potentially from beneath the Antarctic Ice Sheet) towards the coast beneath the permafrost layer. These data provide a baseline for future investigations aimed at monitoring the changing rate of greenhouse gas emissions from Antarctic permafrost, and the potential origin of gases, as the southern polar region warms.

The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analysed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60cm depth. The sediments are characterised as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments. Copyright (c) 2017 John Wiley & Sons, Ltd.

The McMurdo Dry Valleys of Antarctica are a climate-sensitive ecosystem, where future projected climate warming will increase liquid water availability to release soil biology from physical limitations and alter ecosystem processes. For example, many studies have shown that CO2 flux, an important aspect of the carbon cycle, is controlled by temperature and moisture, which often overwhelm biotic contributions in desert ecosystems. However, these studies used either single-point measurements during peak times of biological activity or diel cycles at individual locations. Here, we present diel cycles of CO2 flux from a range of soil moisture conditions and a variety of locations and habitats to determine how diel cycles of CO2 flux vary across gradients of wet-to-dry soil and whether the water source influences the diel cycle of moist soil. Soil temperature, water content and microbial biomass significantly influenced CO2 flux. Soil temperature explained most of the variation. Soil CO2 flux moderately increased with microbial biomass, demonstrating a sometimes small but significant role of biological fluxes. Our results show that over gradients of soil moisture, both geochemical and biological fluxes contribute to soil CO2 flux, and physical factors must be considered when estimating biological CO2 flux in systems with low microbial biomass.

The McMurdo Dry Valleys (MDVs), Antarctica, exist in a hyperarid polar desert, underlain by deep permafrost. With an annual mean air temperature of -18 A degrees C, the MDVs receive < 10 cm snow-water equivalent each year, collecting in leeward patches across the landscape. The landscape is dominated by expansive ice-free areas of exposed soils, mountain glaciers, permanently ice-covered lakes, and stream channels. An active layer of seasonally thawed soil and sediment extends to less than 1 m from the surface. Despite the cold and low precipitation, liquid water is generated on glaciers and in snow patches during the austral summer, infiltrating the active layer. Across the MDVs, groundwater is generally confined to shallow depths and often in unsaturated conditions. The current understanding and the biogeochemical/ecological significance of four types of shallow groundwater features in the MDVs are reviewed: local soil-moisture patches that result from snow-patch melt, water tracks, wetted margins of streams and lakes, and hyporheic zones of streams. In general, each of these features enhances the movement of solutes across the landscape and generates soil conditions suitable for microbial and invertebrate communities.

Two 30-m deep permafrost temperature-monitoring boreholes were installed in bedrock, one at Marble Point and one in the Wright Valley, in the Ross Sea region of Antarctica. A soil climate-monitoring station in till is located near each borehole. The ground surface temperature (GST) was highly correlated with the air temperature at both sites in 2008. Thermal offsets were small (< 1 degrees C) in the till and negligible in the boreholes. The active layer was thicker in the boreholes than in the till, presumably because of the higher thermal diffusivity of the rock. The measured depth of zero annual temperature amplitude was around 27 m at Wright Valley and 25 m at Marble Point. Permafrost thickness was estimated at about 680 m at Wright Valley and 490 m at Marble Point. The GST history, reconstructed using an inversion procedure, suggests a slight cooling from 1998 to 2003 followed by a slight warming to 2008. Longer temperature records or deeper boreholes would be required to establish if long-term climate change has occurred. Copyright (c) 2011 John Wiley & Sons, Ltd.

We modeled the sensitivity of six ice-cemented slope deposits from the western McMurdo Dry Valleys, Antarctica to failure by shallow, thaw-induced planar sliding. The deposits examined have purportedly remained physically stable, without morphologic evidence for downslope movement, for millions of years. Could they fail in the near future from greenhouse-induced warming? To address this question, we first prescribed various increases in mean summertime soil surface temperature (MSSST) and modeled numerically the resultant changes in soil thaw depths using a one-dimensional heat diffusion equation (including the effects of latent heat of fusion). Second, we calculated the minimum thaw depths required to facilitate failure by shallow planar sliding for each deposit, for all numerical simulations, we maintained present soil-moisture conditions and used a Mohr-Coulomb-based equation of safety factor. Third, we calculated the rate of subsurface meltwater flow assuming Darcy's Law. Our results show that although most deposits contain sufficient subsurface ice to induce sliding upon thawing, lateral rates of water flow of as much as similar to 40 m/day for some colluvial deposits prohibit the build-up of requisite pore pressures for failure. On the other hand, silty deposits, that contain gravimetric water >= 15%, occur on slopes > 20 degrees, and possess low hydraulic conductivities (similar to 30-60 cm/day), common in the Dry Valleys region, could fail if MSSST, and by inference mean summertime atmospheric temperatures, increase by 4 to 9 degrees C. This temperature increase is similar to that predicted to occur from greenhouse-induced wart-ning in Antarctica over the next century. (c) 2007 Elsevier B.V. All rights reserved.