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We build on previous work which explained the origin of myriad gullies and incised channels on the dry, sandy uplands of northern Lower Michigan by invoking widespread permafrost. Indicators of permafrost (ice-wedge casts and patterned ground) are known from many sites across the region. Our study area, within an extensive reentrant of the retreating Laurentide Ice Sheet, had been particularly well positioned, geographically, for permafrost. Our goal was to characterize the geomorphic characteristics of the gullies on 72 large ridges, to address the hypothesis that they had formed in association with permafrost. Across the study area, thousands of dry, narrow channels and gullies occur in dense networks, typically with channels aligned directly downslope, in parallel drainage patterns. Most of the gullies exhibit only a minimal amount of incision (ca. 2–3 m), a nearly straight longitudinal profile, and lack a clear depositional fan at their mouth. Even where small fans are present, they are subtle and exhibit little down-fan textural sorting, as would be present in larger, more mature fluvial systems. Gully morphologies did not exhibit strong morphological differences as a function of aspect, as we would have expected for an erosional, periglacial system forming on fairly steep slopes. Nonetheless, in these sandy/gravelly sediments, we could find no other scenario that would have allowed for runoff and gully formation, except ice-rich permafrost that limited infiltration and promoted saturation of the active layer, and eventually, runoff. We conclude that the gullies formed via thermo-erosion into ice-rich permafrost, involving mostly fluvial processes but also some slope failure. Even though thermo-erosion can rapidly form deep gullies, our study area has mainly weak gully forms, perhaps because: (1) permafrost existed here only briefly, (2) the landscape was so cold and the permafrost so ice-rich that runoff was rare, (3) the permafrost on the sandy slopes remained somewhat permeable, limiting runoff, and/or (4) the paleoclimate was so dry that little water was available for sediment transport. We could find no evidence that the gullies developed within preexisting polygonal networks, as is happening today in polar regions under a warming climate. Thus, our study has implications for areas of the Arctic and Antarctic that are, today, experiencing rapid hydrological changes. • The dry, sandy uplands of northern Lower Michigan house thousands of fluvial-incised gullies. • The gullies are shallow, narrow, and have nearly linear longitudinal profiles. • The gullies formed when postglacial permafrost rendered slopes nearly impermeable. • Despite their likely periglacial origins, gully morphologies vary on different slope aspects. • Gully formation likely involved thermo-erosion, possibly along former water tracks. [ABSTRACT FROM AUTHOR]

• Groundwater flow modeling was conducted for an Arctic watershed. • Supra-permafrost aquifer hydro-stratigraphy was based on extensive observations. • Water table gradients were defined by topography (DEM) • Input parameter uncertainty was quantified through statistical methods. • Modeled groundwater flow and DOC flux overlapped with those of the river. Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predict the long-term fate of recently thawed carbon in permafrost environments. Here, we used distributed Darcy's Law calculations to quantify groundwater and DOC fluxes into Imnavait Creek, Alaska, a representative headwater stream in a continuous permafrost watershed. We developed a statistical ensemble approach to model the parameter variability and range of potential contributions of steady-state groundwater flow to the creek. We quantified the model prediction uncertainty using statistical sampling of in-situ, active-layer soil hydro-stratigraphy (water table, ice table, and soil stratigraphy), high-resolution topography data, and DOC data. Moreover, the predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season were also considered given the potential variability in saturation. The model predictions were similar to and span most of the observed range of Imnavait Creek streamflow, especially during recession periods, and also during saturation excess overland flow. As the Arctic warms and supra-permafrost aquifers deepen, groundwater flow is expected to increase. This increase is expected to impact stream, river, and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach. [ABSTRACT FROM AUTHOR]

Key Points: Dissolved organic carbon (DOC) from thawed permafrost had high biodegradability, with an average of 21.7% loss over a 28‐day incubationThe biodegradability of permafrost‐derived DOC was larger than or equal to that in active‐layer across 72% of sampling sitesSpatial and vertical variations in DOC biodegradability were jointly determined by vegetation types, soil properties, and DOC composition Dissolved organic carbon (DOC) plays an important role in permafrost carbon cycle. However, substantial uncertainties remain about what determines the biodegradability of permafrost‐derived DOC and how the biodegradability varies between permafrost and active‐layer soils at a regional scale. Here, we conducted an incubation experiment with DOC leached from permafrost and active‐layer soils along a ~1,000‐km permafrost transect on the Tibetan Plateau. Our results showed that permafrost‐derived DOC had high biodegradability, with an average of 21.7% loss of DOC over a 28‐day incubation. The biodegradability of DOC leached from permafrost soils was larger than or equal to that in active‐layer within 72% of sampling sites. Our results also revealed that variation in DOC biodegradability in permafrost soils and its difference with that in active‐layer soils were jointly determined by vegetation types, soil properties, and related DOC composition. The biodegradability of permafrost‐derived DOC in alpine steppe and meadow was lower than that in swamp meadow. It also declined with the decreasing soil carbon: nitrogen ratio, increasing pH, clay content, DOC molecular weight, and its degradation degree. Similarly, the variability in the difference of DOC biodegradability between permafrost and active‐layer soils also resulted from the differences of three types of above‐mentioned factors between the two layers. These results suggest that permafrost thawing‐induced DOC release could intensify permafrost carbon‐climate feedback due to its vulnerability to microbial decomposition, with its impact depending on vegetation, soil, and substrate properties. Plain Language Summary: When permafrost thaws, a portion of the organic matter within permafrost can be dissolved into water and transported as dissolved organic carbon (DOC). If permafrost DOC is easily broken down by microbes, it could accelerate carbon loss from permafrost, reinforcing climate warming. Permafrost DOC is traditionally regarded as more biodegradable than DOC from active‐layer (seasonally frozen) soils, but it is unknown how general this pattern is since these differences are usually observed within a small geographic area. In this study, we measured DOC biodegradability in 25 sites across the Tibetan alpine permafrost region and observed that permafrost‐derived DOC biodegradability was not always higher than active‐layer soils, but 72% of sampling sites had higher DOC biodegradability in permafrost layer than or equal to that in the active layer. We also found that vegetation types, soil properties, and related DOC composition explained the variation of permafrost‐released DOC biodegradability and its difference between permafrost and active‐layer soils. This work highlights that permafrost‐derived DOC is vulnerable to microbial decomposition upon thaw, potentially intensifying the permafrost carbon‐climate feedback. [ABSTRACT FROM AUTHOR]

The response of active-layer thickness and the ground thermal regime to climatic conditions on the Ulu Peninsula (James Ross Island, northeastern Antarctic Peninsula) in 2011-13 is presented. The mean air temperature over this period was -8.0°C and ground temperature at 5 cm depth varied from -6.4°C (2011-12) to -6.7°C (2012-13). The active-layer thickness ranged between 58 cm (January 2012) and 52 cm (February 2013). Correlation analyses indicate that air temperature affects ground temperature more significantly on snow-free days (R2 = 0.82) than on snow cover days (R2 = 0.53). Although the effect of snow cover on the daily amplitude of ground temperature was observable to 20 cm depth, the overall influence of snow depth on ground temperature was negligible (freezing n-factor of 0.95-0.97). Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Active-layer thickness's distribution is a key parameter for permafrost area studies. In the past, the factors of vegetation, soil water content usually were employed to forecast the spatial distribution of active-layer thickness. But in coarse material distribution area, the above method is often unsatisfactory due to the failure in accurate acquisition of biomass and soil water content. In this paper, a simple method was recommended to be used for calculating of active layer thickness distribution, which is suitable for all kinds of soil texture. Our study analyzed the relationship between ground surface layer permittivity and the thawing depth of the active layer in a permafrost area that was undisturbed by subsurface water flow or local melting. Ground surface layer permittivity is confirmed as having a strong correlation with soil moisture content and biomass of the vegetation cover. We used the direct ground wave velocities from GPR detecting results to compute the dielectric permittivity. Our conclusion is that in our specific study area, a power function relationship existed between the ground surface layer permittivity and the thawing depth of the active layer. [ABSTRACT FROM AUTHOR]

In permafrost regions, the thaw depth strongly controls shallow subsurface hydrologic processes that in turn dominate catchment runoff. In seasonally freezing soils, the maximum expected frost depth is an important geotechnical engineering design parameter. Thus, accurately calculating the depth of soil freezing or thawing is an important challenge in cold regions engineering and hydrology. The Stefan equation is a common approach for predicting the frost or thaw depth, but this equation assumes negligible soil heat capacity and thus exaggerates the rate of freezing or thawing. The Neumann equation, which accommodates sensible heat, is an alternative implicit equation for calculating freeze-thaw penetration. This study details the development of correction factors to improve the Stefan equation by accounting for the influence of the soil heat capacity and non-zero initial temperatures. The correction factors are first derived analytically via comparison to the Neumann solution, but the resultant equations are complex and implicit. Explicit equations are obtained by fitting polynomial functions to the analytical results. These simple correction factors are shown to significantly improve the performance of the Stefan equation for several hypothetical soil freezing and thawing scenarios. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Transparent high-performance ZnO TFTs have been fabricated via low-temperature hydrothermal method. The dip of H3PO4 solution prior to the hydrothermal process can form the under-cut AZO seed layer and benefit for the control of ZnO growth. While the use of under-cut AZO seed layer with proper design of channel length, the lateral ZnO growth can be artificially controlled in the desired location to make a continuous active-layer and nearly single one vertical grain boundary cross to the current flow in the channel region. ZnO TFTs indicate the behavior of n-channel enhancement-mode devices. The optimum design of channel length (i.e. L=10μm) can provide enough space for the lateral growth of large ZnO grains with less channel defects and bring about the advanced device characteristics (i.e. the positive threshold voltage of 3.0V, mobility of 9.03cm2/V·s, on/off current ratio >106, gate leakage of <1nA with less fluctuation, and extremely high drain current >500μA). [Copyright &y& Elsevier]

Abstract: Dramatic warming of the climate over the last several decades has influenced the properties and distribution of permafrost in the Antarctic Peninsula region. Five approaches were used to estimate the distribution of permafrost in the region: (1) correlation of permafrost distribution with mean annual air temperature isotherms, (2) mapping the distribution of periglacial features indicative of permafrost, (3) summarizing data from shallow excavations and boreholes, (4) detection of permafrost from geophysical techniques, and (5) application of models to predict the occurrence of permafrost. Whereas permafrost is continuous in the South Orkney Islands (60–61°S) and along the eastern Antarctic Peninsula (63–65°S), it is discontinuous in the South Shetland Islands (62–63°S), and occurs only sporadically in the Palmer Archipelago and Biscoe Islands along the western Antarctic Peninsula (64–66°S). Permafrost then becomes continuous on Alexander Island (71–74°S) along the western Antarctic Peninsula as the maritime climate shifts to a more continental climate. Reports prior to 1980 mention the presence of permafrost at depths of 25 to 35cm in ice-free areas near Palmer Station (64°46′S; 64°04′W), where the mean annual air temperature from extrapolation of data from the nearby Vernadsky Station has increased 3.4°C and the mean winter temperature has increased 6°C since 1950. Recent measurements suggest that permafrost is absent or close to 0°C in the upper 14m of the highest ice-free areas (67ma.s.l.) near Palmer Station. Permafrost temperatures elsewhere along the western Antarctic Peninsula region range from −0.4 to −1.8°C in the South Shetland Islands (62–63°S) to −3.1°C at Adelaide Island (67°34′S). Permafrost at this temperature is susceptible to thawing, which has resulted in historic increases in active-layer thicknesses and in thermokarst features such as debris flows, and active-layer detachment slides. [Copyright &y& Elsevier]