Hourly ground temperature measurements from the highest shallow ground temperature monitoring system on Earth and sedimentological data were used to construct a thermal model at the Ojos del Salado, in the Dry Andes (5830 m a.s.l.). The results were used to investigate daily temperature fluctuations and the phase changes of water in the regolith, where the permafrost and ground ice are present. Model results reveal that the thermal evolution of the ground and the speed of phase changes are determined by the differing thermal properties of liquid and solid water, and change in their vertical distribution over time. At the start of summer, the increasing ratio of liquid water near the surface insulates deeper layers, and thus, melting is delayed and daily temperature fluctuations are damped in the regolith. The approach of the present study includes testing how simple, relatively low processing power required data analysis might be applied for Mars in the future. Periglacial and aeolian landforms were also surveyed, with a focus on thermo- and cryokarstic features, as previous studies have shown that patterned ground structures are rare in the region due to the highly porous nature of the dry regolith. Besides the wealth of aeolian features, gravel mantled megaripples, solifluction lobes, and thermo- and cryokarstic depressions, were found. In the case of the former, a close association with ephemeral ponds-hosting extremophilic microorganisms-was found, highlighting the fact that meltwater percolates horizontally even in this extremely dry environment. The thermo- and cryokarstic depressions also reveal the role of melting and its intricate connection to sublimation. As these features indicate degrading permafrost, closer investigation may provide useful analogs for earlier and contemporary climatic changes on Mars.

Although the martian environment is currently cold and dry, geomorphological features on the surface of the planet indicate relatively recent (<4 My) freeze/thaw episodes. Additionally, the recent detections of near-subsurface ice as well as hydrated salts within recurring slope lineae suggest potentially habitable micro-environments within the martian subsurface. On Earth, microbial communities are often active at sub-freezing temperatures within permafrost, especially within the active layer, which experiences large ranges in temperature. With warming global temperatures, the effect of thawing permafrost communities on the release of greenhouse gases such as carbon dioxide and methane becomes increasingly important. Studies examining the community structure and activity of microbial permafrost communities on Earth can also be related to martian permafrost environments, should life have developed on the planet. Here, two non-psychrophilic methanogens, Methanobacterium formicicum and Methanothermobacter wolfeii, were tested for their ability to survive long-term (similar to 4 year) exposure to freeze/thaw cycles varying in both temperature and duration, with implications both for climate change on Earth and possible life on Mars.

By the land use change analysis and modeling inputs including the plant biomass and soil organic carbon density for carbon sequestration, and the greenhouse gases emissions fluxes, we estimated the total emissions and carbon sequestration of the marshlands in the Sanjiang Plain of the northeast China before conversion and after their conversion to paddy fields (marshlands-paddy) or to uplands (marshlandsuplands). Between 1982 and 2010, it showed that the converted marshlands area occupied 54.8%. And it indicated that the marshlands before conversion had greater contribution to the global warming mitigation than the marshlands conversion to croplands. This study further demonstrated that the marshlands conversion to croplands in the Sanjiang Plain would lead to 64.80 x 10(6) t CO(2)eq/yr of net sequestration loss and may cause the future climate warming. (C) 2014 Elsevier B.V. All rights reserved.

At martian mid-to-high latitudes, the surfaces of potentially ice-rich features, including concentric crater fill, lobate debris aprons, and lineated valley fill, typically display a complex texture known as brain terrain, due to its resemblance to the complex patterns on brain surfaces. In order to determine the structure and developmental history of concentric crater fill and overlying latitude-dependent mantle (LDM) material, brain terrain and polygonally-patterned LDM surfaces are analyzed using HiRISE images from four craters in Utopia Planitia containing concentric crater fill. Brain terrain and mantle surface textures are classified based on morphological characteristics: (1) closed-cell brain terrain, (2) open-cell brain terrain, (3) high-center mantle polygons, and (4) low-center mantle polygons. A combined glacial and thermal-contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill. A similar model, related to thermal contraction cracking and differential sublimation of underlying ice, is proposed for the formation and development of polygonally patterned mantle material. Both models require atmospheric deposition of ice, likely during periods of high obliquity, but do not require wet active layer processes. Crater dating of brain terrain and mantled surfaces suggests a transition at martian mid-latitudes from peak glacial conditions occurring within the past similar to 10-100 My to a quiescent period followed by a cold-desert periglacial period during the past similar to 1-2 My. (C) 2009 Elsevier Inc. All rights reserved.

Permafrost is ground remaining frozen (temperatures are below the freezing point of water) for more than two consecutive years. An active layer in permafrost regions is defined as a near-surface layer that undergoes freeze-thaw cycles due to day-average surface and soil temperatures oscillating about the freezing point of water. A dry active layer may occur in parched soils without free water or ice but significant geomorphic change through cryoturbation is not produced in these environments. A wet active layer is currently absent on Mars. We use recent calculations on the astronomical forcing of climate change to assess the conditions under which an extensive active layer could form on Mars during past climate history. Our examination of insolation patterns and surface topography predicts that an active layer should form on Mars in the geological past at high latitudes as well as on pole-facing slopes at mid-latitudes during repetitive periods of high obliquity. We examine global high-resolution MOLA topography and geological features on Mars and find that a distinctive latitudinal zonality of the occurrence of steep slopes and an asymmetry of steep slopes at mid-latitudes can be attributed to the effect of active layer processes. We conclude that the formation of an active layer during periods of enhanced obliquity throughout the most recent period of the history of Mars (the Amazonian) has led to significant degradation of impact craters, rapidly decreasing the steep slopes characterizing pristine landforms. Our analysis suggests that an active layer has not been present on Mars in the last similar to 5 Ma, and that conditions favoring the formation of an active layer were reached in only about 20% of the obliquity excursions between 5 and 10 Ma ago. Conditions favoring an active layer are not predicted to be common in the next 10 Ma. The much higher obliquity excursions predicted for the earlier Arnazonian appear to be responsible for the significant reduction in magnitude of crater interior slopes observed at higher latitudes on Mars. The observed slope asymmetry at mid-latitudes suggests direct insolation control, and hence low atmospheric pressure, during the high obliquity periods throughout the Amazonian. We formulate predictions on the nature and distribution of candidate active layer features that could be revealed by higher resolution imaging data. (c) 2007 Elsevier Ltd. All rights reserved.

The Antarctic Dry Valleys (ADV) are generally classified as a hyper-arid, cold-polar desert. The region has long been considered an important terrestrial analog for Mars because of its generally cold and dry climate and because it contains a suite of landforms at macro-, meso-, and microscales that closely resemble those occurring on the martian surface. The extreme hyperaridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology and landscape evolution at a range of scales on both planets. The ADV can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime measurements of atmospheric temperature, soil moisture, and relative humidity. Subtle variations in these climate parameters result in considerable differences in the distribution and morphology of: (1) macroscale features (e.g., slopes and gullies); (2) mesoscale features (e.g., polygons, including ice-wedge, sand-wedge, and sublimation-type polygons, as well as viscous-flow features, including solifluction lobes, gelifluction lobes, and debris-covered glaciers); and (3) microscale features (e.g., rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). Equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones. Some equilibrium landforms, such as sublimation polygons, indicate the presence of extensive near-surface ice; identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice. Landforms that today appear in disequilibrium with local microclimate conditions in the ADV signify past and/or ongoing shifts in climate zonation; understanding these shifts is assisting in the documentation of the climate record for the ADV. A similar type of landform analysis can be applied to the surface of Mars where analogous microclimates and equilibrium landforms occur (1) in a variety of local environments, (2) in different latitudinal bands, and (3) in units of different ages. Documenting the nature and evolution of the ADV microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on Mars. (c) 2007 Elsevier Inc. All rights reserved.

1 Recent studies demonstrated the sensitivity of northern forest ecosystems to changes in the amount and duration of snow cover at annual to decadal time scales. However, the consequences of snowfall variability remain uncertain for ecological variables operating at longer time scales, especially the distributions of forest communities. 2 The Great Lakes region of North America offers a unique setting to examine the long-term effects of variable snowfall on forest communities. Lake-effect snow produces a three-fold gradient in annual snowfall over tens of kilometres, and dramatic edaphic variations occur among landform types resulting from Quaternary glaciations. We tested the hypothesis that these factors interact to control the distributions of mesic (dominated by Acer saccharum, Tsuga canadensis and Fagus grandifolia) and xeric forests (dominated by Pinus and Quercus spp.) in northern Lower Michigan. 3 We compiled pre-European-settlement vegetation data and overlaid these data with records of climate, water balance and soil, onto Landtype Association polygons in a geographical information system. We then used multivariate adaptive regression splines to model the abundance of mesic vegetation in relation to environmental controls. 4 Snowfall is the most predictive among five variables retained by our model, and it affects model performance 29% more than soil texture, the second most important variable. The abundance of mesic trees is high on fine-textured soils regardless of snowfall, but it increases with snowfall on coarse-textured substrates. Lake-effect snowfall also determines the species composition within mesic forests. The weighted importance of A. saccharum is significantly greater than of T. canadensis or F. grandifolia within the lake-effect snowbelt, whereas T. canadensis is more plentiful outside the snowbelt. These patterns are probably driven by the influence of snowfall on soil moisture, nutrient availability and fire return intervals. 5 Our results imply that a key factor dictating the spatio-temporal patterns of forest communities in the vast region around the Great Lakes is how the lake-effect snowfall regime responds to global change. Snowfall reductions will probably cause a major decrease in the abundance of ecologically and economically important species, such as A. saccharum.