observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

thermochronometry reveals headward propagation of erosion in an alpine landscape glacial erosion of mountain ranges produces spectacular alpine landscapes and by linking climate with tectonics influences a broad array of geophysical phenomena although the resultant landforms are easily identified the timing and spatial pattern of topographic adjustment to pleistocene glaciations remain poorly known we investigated topographic evolution in the archetypal glacial landscape of fiordland new zealand using u th he thermochronometry we find that erosion during the past 2 million years removed the entire pre pleistocene landscape and fundamentally reshaped the topography erosion focused on steep valley segments and propagated from trunk valleys toward the heads of drainage basins a behavior expected if subglacial erosion rate depends on ice sliding velocity the fiordland landscape illustrates complex effects of climate on earth s surface morphology

rapid soil accumulation in a frozen landscape polygonal patterned ground is a dominant geomorphic feature in the mcmurdo dry valleys antarctica in central beacon valley polygons are considered to be ancient expressions of stagnant surface processes and are thought to be stable for millions of years however the actual rate at which these polygons form and alter is not known we describe a detailed cross section of a polygon make several depth profiles of meteoric 10be along this cross section and use optically stimulated luminescence to date a few key samples at the center of this polygon while confirming conclusions of previous studies that the polygon shoulders are stable on a 100 k y time scale and experience little vertical sediment mixing our results also give clear evidence of eolian transport to the polygon center leading to a sediment accumulation rate of 3 cm k y 1 over the past 15 k y moreover the data suggest that the accumulated material is locally derived and hence surface erosion of the polygon shoulders must exist that cannot be recorded by meteoric 10be we conclude that polygon modification and soil accumulation under the apparent frozen conditions of beacon valley is an active and ongoing process

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

bet surface area distributions in polar stream sediments implications for silicate weathering in a cold arid environment abstract bet surface area values are critical for quantifying the amount of potentially reactive sediments available for chemical weathering and ultimately prediction of silicate weathering fluxes bet surface area values of fine grained 2 g of surface area values samples from one delta stream taylor valley of the four sampled stream transects exhibit high values up to 70 6 m 2 g which greatly exceed surface area values from three temperate proglacial streams 0 3 12 1 m 2 g only clark stream in wright valley exhibits a robust trend with distance wherein surface area systematically decreases and particle size increases in the mud fraction downstream interpreted to reflect rapid dissolution processes in the weathering environment the remaining transects exhibit a range in variability in surface area distributions along the length of the channel likely related to variations in eolian input to exposed channel beds adjacent snow drifts and to glacier surfaces where dust is trapped and subsequently liberated during summer melting additionally variations in stream discharge rate which mobilizes sediment in pulses and influences water rock ratios the origin and nature of the underlying drift material and the contribution of organic acids may play significant roles in the production and mobilization of high surface area sediment this study highlights the presence of sediments with high surface area in cold based glacier systems which influences models of chemical denudation rates and the impact of glacial systems on the global carbon cycle

the sound and speed of ice wedge cracking arctic canada rifle like sounds produced by ice wedge cracking although seldom heard have been reported in the permafrost literature for a century the sounds similar to those produced by the rapid cracking of lake ice indicate a high speed of crack propagation the speed of ice wedge crack propagation has been measured at two field sites for the 1966 1989 period no evidence of rapid crack propagation has been detected at these sites the fracture patterns of ribs as seen on vertical crack faces and the numerous short interacting cracks as seen in plan view suggest slow rates of cracking enquiries made of many northern residents indicate that rifle like sounds are uncommon along the mainland coast from the alaska yukon boundary eastward to coppermine n w t but are heard more frequently in the arctic islands high speeds of crack propagation appear associated with sharp drops in temperature windblown sites and long straight ice wedges as a preliminary estimate crack propagation rates exceeding about 200

evolution of polygonal patterns in stratified mud during desiccation the role of flaw distribution and layer boundaries detailed analysis of diagnostic surface morphologies of fractures in natural mud indicates that mud cracks systematically nucleate at the bottom of the mud and propagate vertically upward toward the free surface and laterally outward toward adjacent cracks earlier generations of mud cracks rupture the set of desiccated layers altogether forming polygonal patterns that are similar throughout the mud sequence later generations of mud cracks subdivide each layer separately forming markedly different polygonal patterns within individual mud layers a simple mechanical model draws an analog between cooling of granular materials and drying of mud it shows that subfact defects at grain boundaries near the base may become critical before defects associated with fine particles at the top even though the stress profile due to drying is usually more tensile at the top thin section analysis and sieving method indicate that grain boundaries at the bottom are several times longer than at the top of the mud due to the natural sorting of grains illustrating the validity of the model this study suggests that stress variations with depth are less important for pattern evolution of mud cracks than previously theorized however nonuniform flaw distribution and surface discontinuities play a fundamental role during mud crack nucleation and growth these results have significance for several subjects including experimental studies of cracking induced by desiccation the previously suggested analogy between natural mud fracturing and basalt fracturing and the use of mud cracks in stratigraphic interpretation

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

spatial and temporal distribution of soil organic carbon in nonsorted striped patterned ground of the high arctic 1 the role of periglacial processes on soil carbon distribution is examined at a high arctic site in northwest greenland a 16 m trench dug across a series of nonsorted stripes at thule air base revealed sand rich wedges underlying striped vegetated troughs and organic rich soil horizons buried at depth the site has sparse prostrate vegetation and is estimated to contain 9 4 kg m 2 of soil organic carbon soc in the active layer the distribution of carbon is variable with nearly half 49 stored in the sand wedges which only account for 10 of the trench area additionally 62 of the total soc was found below 25 cm highlighting the significant role of cryoturbation and physical redistribution of carbon in permafrost affected soils carbon in the active sand rich wedges dates from modem at the surface 65 35 radiocarbon years to 2695 40 radiocarbon years at depth and carbon turnover time appears to be 450 years buried organic horizons found at 50 70 cm depth have radiocarbon ages of 27 480 31 900 bp a conceptual model is proposed in which the active sand wedges have developed in an approximately 30 ka surface containing buried soils preserved in permafrost or under a cold based glacier as the ice retreated and soils warmed soil development and active cryoturbation resumed forming nonsorted stripes in the modern surface

origin and evolution of polygonal cracks in hydrous sulphate sands white sands national monument new mexico the nucleation and propagation of polygonal cracks in hydrous sulphate dunes at white sands national monument new mexico are affected by water availability transport through the sand and exchange with the atmosphere these gypsum sands are cohesive enough to crack due to capillary forces and gypsum cements formed during evaporation surface cracks form five sided polygons with a variety of triple junction angles cracks extend down to variable depths and polygons increase in size with depth showing a maturation similar to experimentally produced polygonal columns in drying corn starch results from two years of monitoring crack geometries temperature and humidity demonstrate that cracks form when water is lost to the atmosphere through the transport of water vapour subsurface relative humidity below 5 to 10 cm is almost always maintained at 100 by the evaporation and condensation of water in thin films on grains the amplitude of daily temperature and thus absolute humidity changes decreases with depth consistent with lower evaporation and condensation rates with increasing depth changes in absolute humidity and the contrast between humidity in pore spaces versus the overlying atmosphere result in significant water loss from the dunes except during times of precipitation and frost dew condensation this water loss allows cracks to nucleate and propagate into the dunes this study hypothesizes that crack tips propagate into sand to the depth at which thin films of water on grains are drying and that this depth varies from the surface of the dune during precipitation events to depths greater than 45 cm when dunes are drier

possible closed system pingo and ice wedge thermokarst complexes at the mid latitudes of utopia planitia mars abstract on earth hydrostatic or closed system pingos csps are perennial ice cored mounds formed by the freeze thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation the mounds vary in shape from circular or sub circular to elongate are sub kilometre in their long axes and may reach decametres in height often the mounds show summit depressions radial fractures and single tiers or benches as the csps degrade small scale debris flows or slumps occur end stage degradation typically exhibits debris laden ramparts elevated metres above the surrounding terrain typically the csps originate and develop where deep and continuous permafrost is ice rich i e infused with excess ice as it is in the tuktoyaktuk coastlands of northern canada mid to northern alaska and northeast russia in these areas or regions the terrain often is populated by a thermokarst lakes and alases thermokarst lake basins absent of water b fields of small scale ice wedge polygons either low centred or high centred relative to the polygon margins and c melt water filled or emptied polygon margin troughs or corner pits individual troughs and pits connected by means of the local topographical gradient comprises beaded stream systems or networks here we report describe and discuss a suite of candidate csps at the mid latitudes of utopia planitia up 35 50 n 80 115 e the morphologies scale and height of the martian mounds as well as the surface textures and characteristics landscape features and spatially associated landforms are consistent with the csps observed in ice rich regions on earth the up mounds are nested in or reside adjacent to flat floored possibly thermokarstic depressions small scale polygons some of which exhibit low or high centres relative to their margins and connected polygon margin depressions or pits that mirror beaded stream systems in ice rich terrain on earth the size frequency distribution of craters in our study region precludes a surface younger than 100 ma thus the csp like mounds in up and the pre mound periglacial revisions of the landscape presented by us may be markers of freeze thaw cycling that occurred much earlier in the amazonian epoch than most of the current discussions about periglaciation in up suggest

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars 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

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

late cenozoic paleoenvironment in southern victoria land antarctica based on a polar glaciolacustrine deposit in western victoria valley situated in the transantarctic mountains western victoria valley is in a key position to test the late cenozoic stability of the east antarctic ice sheet as well as that of the surrounding landscape surface victoria drift which covers most of western victoria valley represents a peculiar yet common type of deposit in the region the sedimentology of victoria drift is dominated by loose sorted material which preserves lacustrine algae quite unlike tills in the dry valleys ridges characterize its morphology extraordinarily old ridges and mounds as well as fresh features and unweathered and perched boulders occur without apparent order accelerator mass spectrometry ams radiocarbon dates of algae from within victoria drift range from 11 th054 95 to 45 th000 14 c yr b p and are not arrayed in chronological order across the drift sheet resting on a miocene erosion surface victoria drift is the only widespread deposit in western victoria valley younger than ca 14 ma one hypothesis is that the drift consists of moraines the strength of this hypothesis is that it explains the arcuate form of many ridges however it does not explain the sedimentology weathering characteristics or radiocarbon dates a second hypothesis is that victoria drift is a unique polar glaciolacustrine sediment facies deposited by a lake ice conveyer the morphologic features sedimentology weathering characteristics and radiocarbon dates of the drift are all consistent with deposition in a perennially ice covered lake this second hypothesis implies polar glacial conditions during deposition of the drift sheet in order to maintain a permanently ice covered proglacial lake

the first 20 years 1978 1979 to 1998 1999 of ice wedge growth at the illisarvik experimental drained lake site western arctic coast canada in august 1978 a large tundra lake was drained to study the aggradation of permafrost into newly exposed lake bottom sediments ice wedge growth which started in the first winter following drainage had ceased in most of the lake bottom within about twelve years the gradual cessation of thermal contraction cracking can be attributed to rapid vegetation growth snow entrapment an increase in winter ground temperatures and a decrease in the linear coefficient of thermal contraction associated with freeze thaw consolidation of the initially saturated lake bottom sediments the tilt and separation of markers in the active layer revealed gradual convergence towards the troughs even after ice wedge growth had ceased for the first few years the ice wedge growth rate was up to 3 cm a as determined by excavation drilling separation of the bottoms of benchmarks installed into permafrost and divergence of free floating inductance coils placed on the sides of ice wedges well below the bottom of the active la

the direction of ice wedge cracking in permafrost downward or upward field studies have been carried out along the western arctic coast of canada in an attempt to determine whether all ice wedge cracks originate at the ground surface and therefore propagate downward or whether some cracks originate near the top of permafrost and then propagate both upward and downward the field studies have been concentrated upon 1 low and high centred tundra polygons a few thousand years old and 2 ice wedges growing for the first time on the bottom of a lake experimentally drained in 1978 the field instrumentation has included electronic crack direction indicators electronic elapsed timers and continuous temperature measurements the field studies reveal that many of the ice wedge cracks originated near the top of permafrost and then propagated upward to the ground surface as well as downward into ice wedge ice for the 1974 1982 period the field observations showed that about 57 of the ice wedges cracked from the ground surface downward and 43 cracked both upward and downw

hydraulic conductivity of active layer soils in the mcmurdo dry valleys antarctica geological legacy controls modern hillslope connectivity abstract spatial variability in the hydraulic and physical properties of active layer soils influences shallow groundwater flow through cold desert hydrological systems this study measures the saturated hydraulic conductivity and grain size distribution of 90 soil samples from the mcmurdo dry valleys mdv antarctica primarily from taylor valley to determine what processes affect the spatial distribution of saturated hydraulic conductivity in a simple mineral soil dominated natural hillslope laboratory we find that the saturated hydraulic conductivity and the grain size distribution of soils are organized longitudinally within taylor valley soils sampled down valley near the coast have a higher percentage of fine sized sediments fine sand silt clay and lower saturated hydraulic conductivities than soils collected up valley near taylor glacier 1 3 10 2 vs 1 2 10 1 cm s soils collected mid valley have intermediate amounts of fines and saturated hydraulic conductivity values consistent with a hydrogeologic gradient spanning the valley from high inland to low near the coast these results suggest the organization of modern soil properties within taylor valley is a relict signature from past glaciations that have deposited soils of decreasing age toward the mouth of the valley modified by fluvial activity acting along temporal and microclimate gradients

luminescence dating of paleolake deltas and glacial deposits in garwood valley antarctica implications for climate ross ice sheet dynamics and paleolake duration the formation of perched deltas and other lacustrine deposits in the mcmurdo dry valleys of antarctica is widely considered to be evidence of valley filling lakes dammed by the grounded ross sea ice sheet during the local last glacial maximum with lake drainage interpreted as a record of grounding line retreat we used luminescence dating to determine the age of paleolake deltas and glacial tills in garwood valley a coastal dry valley that opens to the ross sea luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years results suggest that late holocene delta deposition into paleolake howard in garwood valley persisted until ca 3 5 ka this is significantly younger than the date when grounded ice is thought to have retreated from the ross sea our evidence suggests that the local stranded ice cored till topography in garwood valley rather than regional ice sheet dynamics may have controlled lake levels for some mcmurdo dry valleys paleolakes age control from the supraglacial ross sea drift suggests grounding and up valley advance of the ross sea ice sheet into garwood valley during marine oxygen isotope stage mis 4 71 78 ka and the local last glacial maximum 9 10 ka this work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation glacial position and stream discharge in response to climate change

polygon pattern geomorphometry on svalbard norway and western utopia planitia mars using high resolution stereo remote sensing data abstract polygonal systems formed by thermal contraction cracking are complex landscape features widespread in terrestrial periglacial regions the manner in which cracking occurs is controlled by various environmental factors and determines dimension shape and orientation of polygons analogous small scale features are ubiquitous in martian mid and high latitudes and they are also inferred to originate from thermal contraction cracking we studied the geomorphometry of polygonally patterned ground on svalbard to draw a terrestrial analogy to small scale polygonal structures in scalloped terrain in martian mid latitudes we performed a comparative quantitative terrain analysis based on high resolution stereo remote sensing data hrsc ax and hirise in combination with terrestrial field data and multivariate statistics to determine the relationship of polygon geomorphometry to local environmental conditions results show that polygonal structures on svalbard and in utopia planitia on mars are similar with respect to their size and shape a comparable thermal contraction cracking genesis is likely polygon evolution however is strongly related to regional and local landscape dynamics individual polygon dimensions and orthogonality vary according to age thermal contraction cracking activity and local subsurface conditions based on these findings the effects of specific past and current environmental conditions on polygon formation on mars must be considered on both earth and mars the smallest polygons represent young recently active low centered polygons that formed in fine grained ice rich material small low centered martian polygons show the closest analogy to terrestrial low centered ice wedge polygons the formation of composite wedges could have occurred as a result of local geomorphological conditions during past martian orbital configurations larger polygons reflect past climate conditions on both earth and mars the present degradation of these polygons depends on relief and topographical situation on svalbard the thawing of ice wedges degrades high centered polygons in contrast the present appearance of polygons in utopia planitia is primarily the result of contemporary dry degradation processes

thermokarst lakes and ponds on mars in the very recent late amazonian past the history of water is fundamental to understanding the geological evolution of mars and to questions concerning the possible development of life on the red planet today mars is cold and dry it

modeling vapor diffusion within cold and dry supraglacial tills of antarctica implications for the preservation of ancient ice abstract we modeled water vapor diffusion within mullins till a relatively dry supraglacial till in southern victoria land antarctica that rests directly on mullins glacier purportedly one of the oldest alpine glaciers in the world like most supraglacial tills in cold desert environments mullins till contains three characteristic facies a weathered facies representing the oxidation of iron bearing minerals and the physical disintegration of surface rocks a sand wedge facies representing the episodic infill of thermal cracks associated with contraction crack polygons and an underlying fresh facies representing the addition of englacial debris sourced from rockfall as overlying ice sublimes using a one dimensional model for fickian vapor diffusion through porous media we show that the rate of subsurface ice sublimation varies by 5 5 beneath till facies and that over timescales of 10 5 years diffusion through porous sand wedges contributes to the development of deep troughs surrounding high centered polygons applying site specific meteorological data collected over a four year period we show that ice loss at the stagnant terminus of mullins glacier is 6 6 10 5 m a 1 a value that although low and assuming an ice thickness of 150 m is consistent with complete ice loss under current environmental forcing in 2 5 ma our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of 6 4 c or an increase in atmospheric relative humidity from 44 to 75 both of which could arise from an increase in cloud cover over mullins glacier sublimation responses to meteorological forcing are not uniform across mullins glacier a summer increase in soil temperature of 2 c results in negligible change in ice sublimation at mullins terminus but a 27 increase in ice loss in upper mullins valley the key factor is the thickness of mullins till which is greater near the glacier terminus for till thicknesses exceeding 25 cm non linear variations in soil temperature result in downward vapor fluxes capable of producing thin cm scale lenses of secondary pore that cap the surface of buried glacier ice this downward vapor flow sourced from modern snowfall and or elevated atmospheric relative humidity is one of the key factors that enable long term preservation of buried glacier ice overall our results highlight the subtle relations among changes in till texture till thickness and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi million year old ice can exist beneath thin supraglacial tills

an enhanced model of the contemporary and long term 200 ka sublimation of the massive subsurface ice in beacon valley antarctica a massive ice body buried under several decimeters of dry regolith in beacon valley antarctica is believed to be more than 1 ma old and perhaps over 8 1 ma however vapor diffusion models suggest that subsurface ice in this region is not stable under current climate conditions to better understand the controls on sublimation rates and stability of this massive ice we have modeled vapor diffusion using 12 years of climate and soil temperature data from 1999 to 2011 including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of ground ice sublimation the model is then extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures estimated from ice core data from nearby taylor dome and a relationship between atmospheric temperature and humidity derived from our meteorological records the model quantifies the impact of episodic snow events they account for a nearly 30 reduction in the massive ice loss the sublimation rate of ground ice averages 0 11 mm a 1 between 1999 and 2011 in beacon valley parameterized with past environmental conditions and assuming the same regolith thickness the modeled sublimation rate of ground ice in beacon valley averages 0 09 mm a 1 for the last 200 ka comparable to the long term average rate estimated independently from various studies based on cosmogenic isotopes this study provides a realistic estimate of the long term sublimation history and supports the inference that the buried ice in beacon valley is older than 1 ma

cold and dry processes in the martian arctic geomorphic observations at the phoenix landing site and comparisons with terrestrial cold desert landforms 1 we analyze surface stereo imager observations of rocks sediments and permafrost related landforms in the vicinity of the phoenix lander comparing the imaged features to analogous examples of physical weathering and periglacial processes observed in the antarctic dry valleys observations at the phoenix landing site of pitted rocks puzzle rocks undergoing in situ breakdown perched clasts and thermal contraction crack polygon morphologies strikingly similar to terrestrial sublimation polygons all strongly suggest that stable non churning permafrost processes dominate the phoenix landing site morphological evidence suggests that cold desert processes in the absence of wet active layer cryoturbation and largely driven by sublimation of buried ice either pore ice excess ice or both are shaping the landscape

rb sr isochron ages magmatic 87sr 86sr initial ratios and oxygen isotope geochemistry of the proterozoic lava flows and intrusions of the east arm of great slave lake northwest territories canada two rb sr isochrons from the oldest wilson island group and one of the youngest pearson formation proterozoic volcanic units in the east arm of great slave lake give dates and initial ratios of 1810 19 ma 0 7051 0 0008 and 1809 30 ma 0 7089 0 0004 respectively these dates restrict the great slave supergroup entirely to the aphebian the pearson formation date is interpreted as magmatic but it is considered to be rapidly followed by a significant metamorphic and tectonic event within the area both the above suites and the volcanic formations of intermediate age have undergone metamorphism up to and including epidote amphibolite facies a study of remnant clinopyroxene grains from these formations has indicated general increases in 18o of whole rocks during epidote actinolite facies metamorphism of 0 4 2 0 the tholeiitic volcanic rocks and intrusions all indicated 18o values typical of modern continental tholeiites 5 9 7 0 the highest 18o came from those suites that were suspecte

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

co evolution of polygonal and scalloped terrains southwestern utopia planitia mars abstract thermal contraction crack polygons and scalloped depressions two of the most common landforms found in utopia planitia mars have previously been linked to the presence of ice rich deposits in the subsurface although the formation and evolution of these features individually are relatively well understood little to no effort has been directed towards elucidating possible interactions that occur between them during their development thus the overarching goal of this research was to investigate if there is an evolutionary link between polygonal and scalloped terrains by correlating metrics representing polygon and scallop maturity a variety of statistical analyses were performed using hirise and mola datasets to quantify interactions between four sets of polygonal and scalloped terrains our results demonstrate the existence of a negative relationship between polygonal subdivision and surface elevation indicating that polygon networks become more evolved as the surface subsides these results suggest that the permafrost landscape in utopia planitia may once have been extremely ice rich and that multiple geomorphic processes may be responsible for its evolution ultimately this work demonstrates that landscape reconstruction is more complete when a system approach is followed quantifying interactions between landforms as opposed to examining an individual landform in isolation

meter scale thermal contraction crack polygons on the nucleus of comet 67p churyumov gerasimenko we report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67p churyumov gerasimenko using images acquired by the osiris camera onboard rosetta between august 2014 and march 2015 they are found in consolidated terrains and grouped in localized networks they are present at all latitudes from north to south and longitudes head neck and body sometimes on pit walls or following lineaments about 1 5 of the observed surface is covered by polygons polygons have an homogeneous size across the nucleus with 90 of them in the size range 1 5 m and a mean size of 3 0 1 4 m they show different morphologies depending on the width and depth of their trough they are found in networks with 3 or 4 crack intersection nodes the polygons observed on 67p are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard mpa and consolidated sintered layer of water ice located a few centimeters below the surface our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment with more evolved polygons i e deeper and larger troughs where the temperature and the diurnal and seasonal temperature range are the highest thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67p in the inner solar system typically 100 000 years ago and could be as young as a few orbital periods following the decreasing of its perihelion distance in 1959 from 2 7 to 1 3 a u meter scale thermal contraction crack polygons should be common features on the nucleus of jupiter family comets

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

underlying structural control of small scale faults and fractures in west candor chasma mars 1 orientations of small scale faults and fractures within the interior layered deposits of west candor chasma were measured to investigate what information about the geologic history of valles marineris they can contribute deformational features were separated into six categories based on morphology and their orientations were analyzed the elevations at which the deformational features formed are recorded as a proxy for stratigraphic level deformational features occur over a continuous range of elevations and display regionally consistent preferred orientations indicating their formation was controlled by a regional stress regime the two most abundant preferred orientations of 35 and 110 are approximately parallel to the chasma walls and the inferred underlying normal faults the alignment of three populations of small faults at 140 consistent with the morphology of release faults indicates a large scale fault underlying the southeastern border of ceti mensa the preferred orientations imply these small scale deformational features formed from a continuation of the same imposed stresses responsible for the formation of valles marineris indicating these stresses existed past the formation of the interior layered deposits the origins of a fourth preferred orientation of 70 is less clear but suggests the study area has undergone at least two periods of deformation

micro relief development in polygonal patterned ground in the dry valleys of antarctica polygonal patterned ground in polar regions of both earth and mars has received considerable attention in comparison with the size shape and arrangement of the polygons the diverse micro relief and topography termed here simply relief of polygonal patterned ground have been understudied and yet the relief reflects important conditions and processes occurring directly below the ground surface and it can be observed readily in the field and through remote sensing herein we describe the relief characteristic of the simplest and relatively young form of patterned ground in the dry valleys of antarctic we also develop a numerical model to examine the generation of relief due to subsurface material being shouldered aside contraction cracks by incremental sand wedges growth and to down slope creep of loose granular material on the surface we model the longterm subsurface deformation of ice cemented permafrost as a non linear viscous material our modeling is guided and validated using decades of field measurements of surface displacements of the permafrost and relief this work has implications for assessing the activity of surfaces on earth and mars and much larger scale potential manifestations of incremental wedging in icy material namely the distinct paired ridges on europa

seasonal variations of polygonal thermal contraction crack patterns in a south polar trough mars we present observations of seasonal variations in polygonal crack patterns located in a polar trough on the south polar cap of mars previously there was no direct observation showing that these patterns change polygonal patterns on mars are attributed to thermal contraction cracking which is commonly observed in periglacial environments on earth in this paper we discuss observations based upon the high resolution image data of the mars orbiter camera and focus on the reconstruction of the seasonal development the image based observations are further supported by temperature data we show that the south polar trough pattern is located in an active geologic unit which undergoes seasonal variations and annual crack formation furthermore there are strong indications showing these contraction crack processes take place in a thin layer that might be composed of water ice and is located beneath the seasonal carbon dioxide ice cover

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

probing supraglacial debris on mars 1 sources thickness and stratigraphy abstract geomorphic and geophysical evidence supports a debris covered glacier origin for a suite of landforms at the mid latitudes of mars including lobate debris aprons lda lineated valley fill lvf and concentric crater fill ccf these large reservoirs of ice and their near surface structure provide a rich record for understanding the planet s climate and history of global volatile exchange over the past billion years lda lvf and ccf are also potential sites for future robotic and human missions but the accessibility of glacial ice for direct sampling and in situ resource utilization depends largely on the geotechnical properties of the surface debris supraglacial debris including its thickness grain sizes and density structure the physical properties of this supraglacial debris layer have been poorly constrained we use images of morphology digital elevation models thermal inertia data and radar sounding data to probe the near surface of lda lvf and ccf in deuteronilus mensae in order to place constraints on the sources grain sizes thickness and stratigraphy of supraglacial debris we find evidence for at least a two layer stratigraphy layered mantle consisting of atmospherically emplaced dust and ice superposes boulder rich sediment sourced by rockfalls glacially transported downslope high thermal inertia boulder rich termini and debris bands reminiscent of medial moraines are found throughout the study region supporting a rockfall origin for at least a fraction of the debris exposed at the surface this supraglacial debris layer would have thickened with time from sublimation of glacial ice and liberation of englacial sediment and dust at present the entire supraglacial debris package is a minimum of a few meters in thickness and is likely tens of meters in thickness in many locations possibly thinning regionally at lower latitudes and locally thinning toward the headwalls the lack of terracing or interior structures in craters formed within lda lvf and ccf and the absence of near surface reflectors in sharad radar data further suggest that no strong contrasts in permittivity or strength occur at the interface of the layers

fast growing till over ancient ice in beacon valley antarctica we analyze published cosmogenic 3he depth profiles through the till that covers relict glacier ice in beacon valley antarctica in order to derive rigorous constraints on the till thickness history and on the amount and rate of ice loss by sublimation the till is a residue of debris laden ice that sublimed the 3he profiles show that the lower 80 of the till formed in the past 310 43 k y under sublimation rates averaging 7 m m y 1 meters per million years such rapid recent growth of the till contradicts previous interpretations that it is older than 8 1 ma at an adjacent site where it encloses volcanic ash of this age we question whether the ash provides a valid age constraint for the ice cosmogenic nuclide analysis of the till where the ash was collected for dating should resolve this question

low altitude remote sensing and gis based analysis of cropmarks classification of past thermal contraction crack polygons in central western poland abstract the examination of low altitude aerial photographs reveals the presence of more than 400 polygonal nets in central western poland polygons range from 5 to almost 70 m in diameter based on the polygons diameter and intersection angles we identified seven main types of nets geometry based on ground verification we interpreted them as past thermal contraction cracks filled mostly with sand i e sand wedge casts as favourable weather conditions and a proper land cover i e cultivated land are necessary for identifying polygonal nets the observed number of polygons is probably much underestimated the broad occurrence of former thermal contraction cracks polygons indicates that continuous permafrost was widespread in central western poland after the termination of the last glacial maximum lgm preliminary dating of the cracks infilling as well as polygon geometry suggest that thermal contraction cracking occurred in several different phases and that a time frame of a few thousand years is sufficient to form complex mature nets

origin and significance of decameter scale polygons in the lower peace vallis fan of gale crater mars abstract decameter scale polygons are extensively developed in the bedded fractured bf unit of the lower peace vallis fan the polygons occur in a likely extension of the gillespie lake member north of yellowknife bay the section first drilled by the mars science laboratory msl mission we examine hypotheses for the origin of these polygons to provide insight into the history of gale crater the polygons are 4 30 m across square to rectangular and defined by 0 5 4 m wide generally straight troughs with orthogonal intersections polygon networks are typically oriented orthogonal systems with occasional nearly circular patterns hundreds of meters across potential origins include cooling of lava and for sedimentary units syneresis unloading weathering desiccation impact processes and cold climate thermal contraction cold climate thermal contraction is the hypothesis most consistent with the sedimentary nature of the bf unit and the polygon morphology geometry networks and apparent restriction to the coarse grained gillespie lake member a periglacial setting further provides the best analogs for the circular networks and is consistent with geologic context and msl data most of the decametric polygons appear to be ancient they are confined to the hesperian bf unit and only a few of their bounding fractures extend into younger or recently exposed units in this regard they differ from the majority of proposed thermal contraction polygons on mars as those are generally thought to be young features and accordingly the history of formation preservation and reactivation of the decametric polygons is likely to be more complex than that of any proposed young polygons on mars the decametric polygons in the bf unit may represent landforms developed in a cold but still comparatively wet interlude between a clement early mars and the much drier and colder planet of today

resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground 1 to help interpret the polygonal patterned ground on mars we present recent findings about a similar form of patterned ground in a particularly cold and arid region on earth the dry valleys of antarctica in this region distinct arrays of interconnected polygons which we refer to herein simply as patterned ground characterize many surfaces reflecting a subsurface network of interconnected subvertical wedges of sand that grow incrementally as sand progressively fills soil fractures the fractures form initially as thermoelastic stresses arise during periods of rapid cooling of frozen ground and they continue to open and close in response to thermal cycles we describe the initiation and maturation of the patterned ground using data for the growth of sand wedges and for the evolution of crack patterns and microrelief over time scales ranging up to 106 years

regolith transport quantified by braking block mcmurdo dry valleys antarctica abstract the mcmurdo dry valleys of antarctica are today a hyper arid polar desert prior work has identified several in situ volcanic ashes 6 11 myr old resting on the surface regolith that suggests the persistent stability of the regolith surfaces and climate however our field observations of characteristic regolith bulges above and cavities below boulders that are lodged in the hillslope braking blocks contradict the apparent preservation of the regolith surfaces to quantify the regolith mobility we modeled the downslope regolith transport around large boulders in the dry valleys using a finite difference regolith transport model to guide our modeling effort we surveyed the detailed topography around one large boulder in the field model results fit the observed topography well and allow for the calculation of the minimum volume of regolith per unit width of slope that was mobilized 4 m3 1 m width to assess the general applicability of the braking block analysis on random boulders on hillslope we surveyed the topographic characteristics adjacent to 997 boulders on 10 separate hillslopes the bulge cavity development appears to be sensitive to 1 the adjacent obstructions that restrict the free movement of the regolith around the given boulder and 2 the inherent surface roughness even though theoretically boulders of all sizes should have a cavity bulge pair surrounding them the signal to noise ratio prevented us from extracting such measurements reliably on boulders whose diameter was smaller than about 1 m on boulders that sat on bedrock covered by a thin veneer of regolith and on boulders that were part of an actively aggrading talus the limiting minimum topographic diffusivity was found to be 10 6 m2 yr over time periods of millions of years this is enough to rework the surfaces and highlights the intriguing contradiction between the preserved ashes and the observed regolith transport

volumetric estimates of ancient water on mount sharp based on boxwork deposits gale crater mars while the presence of water on the surface of early mars is now well known the volume distribution duration and timing of the liquid water have proven difficult to determine this study makes use of a distinctive boxwork rich sedimentary layer on mount sharp to map fluid based cementation from orbital imagery and estimate the minimum volume of water present when this sedimentary interval was formed the boxwork structures on mount sharp are decameter scale light toned polygonal ridges that are unique compared to previous observations of martian fractured terrain because they are parallel sided ridges with dark central linear depressions this texture and the sedimentary setting strongly imply that the ridges are early diagenetic features formed in the subsurface phreatic groundwater zone high resolution orbital imagery was used to map the volume of light toned cemented ridges based on the cemented volume a minimum of 5 25 105 m 3 of cement was deposited within the fractures using a brine composition based on observations of other martian cements and modeling the degree of evaporation each volume of cement requires 800 6700 pore volumes of water so the mapped boxwork ridge cements require a minimum of 0 43 km 3 of water this is a significant amount of groundwater that must have been present at the 3620 m level 1050 m above the current floor of gale crater providing both a new constraint on the possible origins of mount sharp and a possible future science target for the curiosity rover where large volumes of water were present and early mineralization could have preserved a once habitable environment

differential frost heave model for patterned ground formation corroboration with observations along a north american arctic transect 1 frost boils in the arctic are a manifestation of patterned ground in the form of nonsorted circles active frost boils involve convection of water through the soil that can bring basic salts from depth to the surface as such active frost boils can mitigate acidification and thereby strongly influence the type of vegetation supported by arctic soils the presence or absence of active frost boils is thought to play a pivotal role in establishing the sharp demarcation between moist nonacidic tundra mnt and moist acidic tundra mat in the arctic the focus of this paper is to corroborate the predictions of a mathematical model that relates observable patterned ground features to ecosystem parameters with observations at the field sites along the north american arctic transect naat established by the biocomplexity of patterned ground ecosystems project model predictions indicate that recurrent one dimensional frost heave can become unstable and evolve into multidimensional differential frost heave dfh a laboratory frost heave simulation produced a 28 cm pattern in an active layer of 10 cm which agrees with linear stability theory predictions a finite element solution predicts three dimensional patterns with approximately 3 m spacing develop in a 1 0 m active layer with a surface n factor of 0 35 which agrees well with field observations from the naat the lack of significant frost boil activity in the mat is a result of suppression of dfh owing to denser surface vegetation characterized by low n factors prominent active frost boils are observed in the mnt at higher latitudes with more sparse vegetation characterized by higher n factors that promote dfh however at the northernmost field sites frost boils cannot be generated even though the n factors are relatively high owing to very rapid freezing conditions that mitigate dfh

depth and seasonal variations in the thermal properties of antarctic dry valley permafrost from temperature time series analysis 1 we present the first dedicated study of the thermal properties of perennially frozen ice cemented subsurface dry valley permafrost from time series analysis of 14 months temperature measurements we resolve depth and seasonal variations in the thermal properties at two nearby sites at table mountain with different origin composition and polygonal ground patterning we determine apparent thermal diffusivity atd profiles directly from thermistor array measurements at 13 5 cm depth intervals and 4 hour time intervals in the top 2 m we treat the system as purely conductive year round due to the cold temperatures and compare the performance of several common analysis schemes with a graphical finite difference method that we present in detail this comparison is facilitated by one site showing strong depth variations including an abrupt twofold increase in atd across a sharp compositional boundary we characterize the composition of the inhomogeneous ground from recovered cores and estimate an ice fractiondependent heat capacity in the range c 1 7 0 1 to 1 8 0 1 mj m 3 c 1 we calculate apparent thermal conductivity profiles that correlate very well with the core compositions the conductivity generally lies in the range 2 5 0 5 w m 1 c 1 but is as high as 4 1 0 4 w m 1 c 1 for a quartose sirius sandstone unit at one site the seasonal variation in the atd is consistent with its expected temperature dependence index terms 3299 mathematical geophysics general or miscellaneous 5134 physical properties of rocks thermal properties 5194 physical properties of rocks instruments and techniques keywords dry valleys antarctica thermal properties of frozen ground permafrost

million year old ice found under meter thick debris layer in antarctica cosmogenic nuclide measurements associated with buried glacier ice in ong valley in the transantarctic mountains suggest the preservation of ancient ice there are three glacial tills on the valley floor which have formed from the concentration of regolith contained within sublimating glacier ice two tills are less than 1 m thick and underlain by ice measurements of cosmogenic 10be 26al and 21ne show that i the youngest buried ice unit and corresponding till are at least 11 13 ka ii another ice unit and corresponding intermediate age till are at least 1 1 ma old under any circumstances and most likely older than 1 78 ma and iii the oldest till is at least 1 57 ma and most likely greater than 2 63 ma these observations highlight the longevity of ice under thin debris layers and the potential to sample ancient ice for paleoclimate paleoatmosphere information close to the present land surface

the frequency of ice wedge cracking 1967 1987 at garry island western arctic coast canada the frequency of ice wedge cracking has been studied at garry island northwest territories for the 1967 1987 period sites have included low centre polygons intermediate centre polygons and polygons that do not fit any classification system analyses of crack frequency have included trough characteristics polygon characteristics and ice wedge types the results show that crack frequencies are highly variable within one site and also between two adjacent sites the correlation between crack frequency and a low air temperature is poor crack frequencies for a site with 59 wedges ranged from 8 to 42 between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75 between 1967 and 1987 in view of the wide range in crack frequencies at a given site the use of mean ice wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous the data show that the common twofold classification into active and inactive wedges is difficult to apply be

excess ground ice of condensation diffusion origin in university valley dry valleys of antarctica evidence from isotope geochemistry and numerical modeling abstract this study investigates the origin and age of ground ice in the uppermost 1 m of permafrost in university valley one of the upper valleys in the mcmurdo dry valleys of antarctica in contrast to other regions in the mdv mean daily air and soil temperatures at the coring sites are always below 0 c which allows for unique cryogenic processes to occur in the two cores that were analyzed excess ground ice was measured throughout ranging between 23 and 85 isotope geochemical trends in the ice rich permafrost indicate that the ground in core 5 65 cm long and the uppermost 52 cm of core 7 originated from condensation diffusion of water vapor whereas the ground ice between 57 90 cm in core 7 originated from freezing of liquid water using numerical modeling we show that the excess ground ice of condensation diffusion origin formed by the long term thermal contraction expansion of the cryotic sediments which allowed for the ice content to exceed pore filling capacity absolute age estimates of the sandy loam sediments based on optically stimulated luminescence dating indicate that soils have been accreting at the site for at least the last 170 36 ka years and this places an upper limit to the age of the ground ice absolute soil ages allowed us to link the change in ground ice origin in core 7 which took place around 152 12 ka years with shifts in climate conditions since marine isotope stage 5e interglacial period our findings offer a new process of ground ice emplacement in sediments in cold dry environments and allow an alternative explanation regarding the enigmatic origin of excess ground ice identified by mars odyssey and phoenix in the northern martian plain which is that overfilled pore ice can form by vapor deposition and repeated thermal cycling without the presence of melt water

clastic polygonal networks around lyot crater mars possible formation mechanisms from morphometric analysis polygonal networks of patterned ground are a common feature in cold climate environments they can form through the thermal contraction of ice cemented sediment i e formed from fractures or the freezing and thawing of ground ice i e formed by patterns of clasts or ground deformation the characteristics of these landforms provide information about environmental conditions analogous polygonal forms have been observed on mars leading to inferences about environmental conditions we have identified clastic polygonal features located around lyot crater mars 50 n 30 e these polygons are unusually large 100 m diameter compared to terrestrial clastic polygons and contain very large clasts some of which are up to 15 metres in diameter the polygons are distributed in a wide arc around the eastern side of lyot crater at a consistent distance from the crater rim using high resolution imaging data we digi tised these features to extract morphological information these data are compared to existing terrestrial and martian polygon data to look for similarities and differences and to inform hypotheses concerning possible formation mechanisms our results show the clastic polygons do not have any morphometric features that indicate they are similar to terrestrial sorted clastic polygons formed by freeze thaw processes they are too large do not show the expected variation in form with slope and have clasts that do not scale in size with polygon diameter however the clastic networks are similar in network morphology to thermal contraction cracks and there is a potential direct martian analogue in a sub type of thermal contraction polygons located in utopia planitia based upon our observations we reject the hypothesis that polygons located around lyot formed as freeze thaw polygons and instead an alternative mechanism is put forward they result from the infilling of earlier thermal contraction cracks by wind blown material which then became compressed and or cemented resulting in a resistant fill erosion then leads to preservation of these polygons in positive relief while later weathering results in the fracturing of the fill material to form angular clasts these results suggest that there was an extensive area of ice rich terrain the extent of which is linked to ejecta from lyot crater

atmospheric 10be in an antarctic soil implications for climate change 1 concentrations of 10be 9be and salt in a soil profile from the lower wright valley reveal two distinct climatic regimes in the upper horizon of the soil profile a thin gravel lag overlies the hart ash 3 9 0 3 ma and this sits on the surface of a well developed paleosol which makes up the lower horizon of the profile the surface lag has a smaller inventory of 10be than predicted from the fallout rate at nearby taylor dome below the gravel the hart ash is virtually devoid of 10be and the calculated erosion rate for the gravel ash horizon is 2 8 m ma 1 the paleosol which has been sealed by the overlying ash has a relatively high inventory of 10be and this gives it a significantly lower erosion rate 0 5 m ma 1 than the gravel ash horizon beryllium 10 migrates into a soil profile either by solution transport or by fine particle translocation the lack of 10be in the hart ash indicates that neither of these processes have been active at this site for the past 3 9 ma however enrichment of 10be in the paleosol indicates they were active prior to deposition of the ash the most likely reason these processes were active is that there was more water which could translocate fine particles with attached 10be thus the gravel ash horizon developed in climatic conditions similar to the present while the paleosol developed in wetter and possibly warmer conditions during the early pliocene and possibly before that time

chronology of taylor glacier advances in arena valley antarctica using in situ cosmogenic 3he and 10be abstract in situ produced cosmogenic nuclides provide a new technique for constraining exposure ages of glacial deposits in situ3he and 10be in quartz sandstone boulders from arena valley southern victoria land antarctica provide chronological constraints for a sequence of moraines taylor ii ivb moraines related to expansions of taylor glacier and the east antarctic ice sheet mean 3he ages are 113 000 45 000 yr 208 000 67 000 yr 335 000 187 000 yr and 1 2 0 2 myr for taylor ii iii iva and ivb moraines respectively mean 1 corresponding mean 10be ages for taylor ii and ivb moraines are 117 000 51 000 yr and 2 1 0 1 myr for the older deposits the 3he ages are probably lower limits due to diffusive loss although the exposure ages appear consistent with the few previous age estimates particularly with an isotope stage 5 age for taylor ii each moraine exhibits a broad age distribution the distribution probably results from a variety of factors which may include prior exposure to cosmic rays 3he loss erosion postdepositional boulder movement and radiogenic production of 3he nonetheless the exposure ages provide direct chronological constraints for the moraine sequence and suggest a maximum thickening of taylor glacier relative to the present ice surface of 500 m since the late pliocene early pleistocene

subaqueous shrinkage cracks in the sheepbed mudstone implications for early fluid diagenesis gale crater mars the sheepbed mudstone yellowknife bay formation gale crater represents an ancient lakebed now exhumed and exposed on the martian surface the mudstone has four diagenetic textures including a suite of early diagenetic nodules hollow nodules and raised ridges and later diagenetic light toned veins that crosscut those features in this study we describe the distribution and characteristics of the raised ridges a network of short spindle shaped cracks that crosscut bedding do not form polygonal networks and contain two to four layers of isopachous erosion resistant cement the cracks have a clustered distribution within the sheepbed member and transition laterally into concentrations of nodules and hollow nodules suggesting that these features formed penecontemporaneously because of the erosion resistant nature of the crack fills their three dimensional structure can be observed cracks that transition from subvertical to subhorizontal orientations suggest that the cracks formed within the sediment rather than at the surface this observation and comparison to terrestrial analogs indicate that these are syneresis cracks cracks that formed subaqueously syneresis cracks form by salinity changes that cause sediment contraction mechanical shaking of sediment or gas production within the sediment examination of diagenetic features within the sheepbed mudstone favors a gas production mechanism which has been shown to create a variety of diagenetic morphologies comparable to the raised ridges and hollow nodules the crack morphology and the isopachous layered cement fill show that the cracks were filled in the phreatic zone and that the sheepbed mudstone remained fluid saturated after deposition and through early burial and lithification

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

high resolution imaging science experiment hirise observations of glacial and periglacial morphologies in the circum argyre planitia highlands mars 1 the landscape of the argyre planitia and adjoining charitum and nereidum montes in the southern hemisphere of mars has been heavily modified since formation of the argyre impact basin this study examines morphologies in the argyre region revealed in images acquired by the high resolution imaging science experiment hirise camera and discusses the implications for glacial and periglacial processes distinctive features such as large grooves semicircular embayments in high topography and streamlined hills are interpreted as glacially eroded grooves cirques and whalebacks or roche moutonnee respectively large boulders scattered across the floor of a valley may be ground moraine deposited by ice ablation glacial interpretations are supported by the association of these features with other landforms typical of glaciated landscapes such as broad valleys with parabolic cross sections and stepped longitudinal profiles lobate debris aprons interpreted as remnant debris covered glaciers or rock glaciers and possible hanging valleys aligned boulders observed on slopes may also indicate glacial processes such as fluting alternatively boulders aligned on slopes and organized in clumps and polygonal patterns on flatter surfaces may indicate periglacial processes perhaps postglaciation that form patterned ground at least portions of the argyre region appear to have been modified by processes of ice accumulation glacial flow erosion sediment deposition ice stagnation and ablation and perhaps subsequent periglacial processes the type of bedrock erosion apparent in images suggests that glaciers were at times wet based the number of superposed craters is consistent with geologically recent glacial activity but may be due to subsequent modification

zebra stripes in the atacama desert fossil evidence of overland flow abstract some hillslopes in the hyperarid region of the atacama desert in northern chile have surface clasts organized into distinct contour parallel bands separated by bare soil we call the bands zebra stripes due to the contrast between the darkly varnished clasts and the light colored salt rich soil gravel that comprises the zebra stripes is sorted such that the coarsest clasts are at the downslope front and fine progressively upslope how and when the zebra stripes formed are perplexing questions particularly in a region experiencing prolonged hyperaridity using googleearth satellite imagery and field observations we report the first quantitative and qualitative observations of zebra stripes in order to test hypotheses of the mechanisms and timing of their formation we consider soil shrink swell seismic shaking and overland flow as possible formation mechanisms and find that overland flow is the most likely based on cosmogenic 10 be concentrations in surface clasts salt deposition rates from the atmosphere and content in the soils we propose that the salt rich soils began accumulating 10 6 y ago and the zebra stripes formed 10 3 10 4 y at the latest the zebra stripe pattern has been preserved due to the self stabilization of the clasts within the stripes and the continued absence of life which would disturb the surface as seen at a wetter site to the south we conclude that the occurrence of zebra stripes is diagnostic of a set of distinct characteristics of local and or regional precipitation soil hillslope form and bedrock type

echo source discrimination in single pass airborne radar sounding data from the dry valleys antarctica implications for orbital sounding of mars the interpretation of radar sounding data from mars where significant topographic relief occurs will require echo source discrimination to avoid the misinterpretation of surface echoes as arising from the subsurface this can be accomplished through the identification of all radar returns from the surface in order to positively identify subsurface echoes we have developed general techniques for this using airborne radar data from the dry valleys of antarctica these data were collected in a single pass including taylor glacier ice covered lake bonney and an ice free area of taylor valley the pulsed radar 52 5 67 5 mhz was coherently recorded our echo discrimination techniques included a radar simulator using a digital elevation model dem to predict the location and shape of surface echoes in the radar data real and simulated echo strengths were used to calculate a signal to clutter ratio this was complemented by the cross track migration of radar echoes onto the surface these migrated echoes were superimposed on the dem and imagery in order to correlate with surface features using these techniques enabled us to identify a number of echoes in the radar data as arising from the surface and to identify subsurface echoes including a continuous reflector under the main trunk of taylor glacier and multiple reflectors beneath the terminus of taylor glacier surface based radar confirms the thickness of the glacier at three crossing points the results illustrate the importance of using complementary techniques the usefulness of a dem and the limitations of single pass radar sounding data

possible ice wedge polygons and recent landscape modification by wet periglacial processes in and around the argyre impact basin mars abstract the argyre basin and associated rim materials in the southern hemisphere of mars are ancient having been formed by the impact of a large body 4 gya this notwithstanding the regional landscape continues to be altered by a multiplicity of geological and geomorphological processes three landforms whose close spatial association is identified in a new geological map of the argyre region 290 360 e 30 72 s feature prominently in the list of very late amazonian epoch alterations a small sized 20 m in diameter and unsorted polygons that exhibit metre to sub metre elevated margins or shoulders giving them a low centred appearance in wet permafrost environments on earth low centred polygons lcps often are underlain by ice wedges b gullies seemingly formed by wet flow s and incised by the lcps c a putative possibly ice rich latitude dependent mantle ldm that underlies the lcps and spatially convergent wet gullies in all of our observations these landforms occur from the middle to the high near polar latitudes of the region and overlie geological units of all ages hitherto the presence of the lcps has been reported only fleetingly in the literature and only in as much as they have been observed on the walls of a few scalloped depressions in mid utopia planitia by contrast we report the ubiquitous occurrence of the lcps in and around the argyre impact basin on gully margins and adjacent slopes as well as on relatively flat inter crater terrain on the basis of three separate but related lines of reasoning we hypothesise that ice wedges could be present beneath lcp margins in our study region if we are correct then these lcp sites are geomorphological expressions of boundary conditions that were relatively warm and wet in the recent past first substantial ice wedging in permafrost environments on earth requires the availability of meltwater if as some researchers propose the formation of some wet gullies at the martian mid latitudes is induced by the localised slope side and crater wall thaw of the underlying ldm at the gully sites themselves then meltwater also should be available for ice wedging and the formation of lcps at these sites interestingly lcps are observed on gully channel walls as expected if meltwater is associated with gully formation however in some instances the lcps are also observed on the slope side terrain that extends for hundreds of metres beyond the channel walls and even above the gully alcoves this suggests that the distribution of icy terrain affected by thaw could be much more substantial than has been suggested hitherto second lcps that are identical in shape and scale to the slope side lcps are observed on relatively flat inter crater terrain also underlain by the ldm that is distal from the wet gullies by contrast here their distribution extends for kilometres this too could be indicative of meltwater being more extensive in the regional landscape than most workers have thought possible third on earth the dryness or the wetness of a permafrost environment determines whether lcp margins are underlain by sand or by ice when the observed lcps and major deposits of sand in the study region are plotted on our new map of the argyre impact basin we see that these deposits are rarely proximal on the other hand the ldm underlies the lcps in all instances and if modified by thaw seems to be a likelier source of margin fill for the lcps than sand

possible pingos and a periglacial landscape in northwest utopia planitia hydrostatic closed system pingos are small elongate to circular ice cored mounds that are perennial features of some periglacial landscapes the growth and development of hydrostatic pingos is contingent upon the presence of surface water freezing processes and of deep continuous ice cemented permafrost other cold climate landforms such as small sized polygonal patterned ground also may occur in the areas where pingos are found on mars landscapes comprising small elongate to circular mounds and other possible periglacial features have been identified in various areas including utopia planitia where water is thought to have played an important role in landscape evolution despite the importance of the martian mounds as possible markers of water most accounts of them in the planetary science literature have been brief and or based upon viking imagery we use a high resolution mars orbiter camera image eo300299 and superposed mars orbiter laser altimeter data tracks to describe and characterise a crater floor landscape in northwest utopia planitia 64 8 n 292 7 w the landscape comprises an assemblage of landforms that is consistent with the past presence of water and of periglacial processes this geomorphological assemblage may have formed as recently as the last episode of high obliquity a similar assemblage of landforms is found in the tuktoyaktuk peninsula of northern canada and other terrestrial cold climate landscapes we point to the similarity of the two assemblages and suggest that the small roughly circular mounds on the floor of the impact crater in northwest utopia planitia are hydrostatic pingos like the hydrostatic pingos of the tuktoyaktuk peninsula the origin of the crater floor mounds could be tied to the loss of ponded local water permafrost aggradation and the evolution of a sub surface ice core

landscape evolution of the dry valleys transantarctic mountains tectonic implications there are different views about the amount and timing of surface uplift in the transantarctic mountains and the geophysical mechanisms involved our new interpretation of the landscape evolution and tectonic history of the dry valleys area of the transantarctic mountains is based on geomorphic mapping of an area of 10 000 km2 the landforms are dated mainly by their association with volcanic ashes and glaciomarine deposits and this permits a reconstruction of the stages and timing of landscape evolution following a lowering of base level about 55 m y ago there was a phase of rapid denudation associated with planation and escarpment retreat probably under semiarid conditions eventually downcutting by rivers aided in places by glaciers graded valleys to near present sea level the main valleys were flooded by the sea in the miocene during a phase of subsidence before experiencing a final stage of modest upwarping near the coast there has been remarkably little landform change under the stable cold polar conditions of the last 15 m y it is difficult to explain the sirius group deposits which occur at high elevations in the area if they are pliocene in age overall denudation may have removed a wedge of rock with a thickness of over 4 km at the coast declining to 1 km at a point 75 km inland which is in good agreement with the results of existing apatite fission track analyses it is suggested that denudation reflects the differences in base level caused by high elevation at the time of extension due to underplating and the subsequent role of thermal uplift and flexural isostasy most crustal uplift 2 4 km is inferred to have occurred in the early cenozoic with 400 m of subsidence in the miocene followed by 300 m of uplift in the pliocene

climate and material controls on periglacial soil processes toward improving periglacial climate indicators one of the distinguished efforts of a l washburn was to reconstruct mean annual air temperature using periglacial features as climate indicators this paper reviews existing periglacial indicators and proposes a strategy to improve their thermal resolution based on recent periglacial process studies with a focus on solifluction and thermal contraction cracking and associated landforms structures landforms resulting from solifluction reflect both the depth subjected to freeze thaw and the thickness of frost susceptible soils the thickness of a solifluction structure can be used to infer the dominant freeze thaw regime and minimum seasonal frost depth ice wedge pseudomorphs have limited potential as a climate indicator because 1 they mainly reflect extreme winter temperatures 2 their thermal thresholds depend on the host material and 3 they need to be distinguished from frost wedges of other origin produced under different thermal and or material conditions monitoring studies of currently active ice wedges suggest that ice wedge cracking requires a combination of low temperature and large temperature gradients in the frozen active layer further field monitoring of periglacial processes and their controlling factors under various climate conditions and in various materials are needed however to improve the resolution of periglacial paleoclimate indicators

the first 7 years 1978 1985 of ice wedge growth illisarvik experimental drained lake site western arctic coast a large lake measuring 600 m 300 m and with a depth of nearly 5 m was artificially drained on 13 august 1978 observations on the formation width and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature the first winter s cracks had box like profiles with surface widths to 10 cm and depths to 2 5 m some cracks continued to widen and deepen once opened in early winter and then narrowed or even closed completely in summer mean growth rates for the ice wedges for the first few years have been as much as 3 5 cm year temperature gradients at the time of first cracking have been in the range of 10 15 c m the growth rate of young ice wedges is site specific and temperature dependent varying with factors such as the temperature gradient vegetation and snow cover so an estimate of the age of an ice wedge from its width will usually be impossible a study of crack w

new constraints on equatorial temperatures during a late neoproterozoic snowball earth glaciation intense glaciation during the end of cryogenian time 635 million years ago marks the coldest climate state in earth history a time when glacial deposits accumulated at low tropical paleolatitudes the leading idea to explain these deposits the snowball earth hypothesis predicts globally frozen surface conditions and subfreezing temperatures with global climate models placing surface temperatures in the tropics between 20 c and 60 c however precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined here we make new geologic observations of tropical periglacial aeolian and fluvial sedimentary structures formed during the end cryogenian marinoan glaciation in south australia these observations allow us to constrain ancient surface temperatures we find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith the wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2 4 m below the ground surface these observations paired with a model of ground temperature forced by solar insolation constrain the local mean annual surface temperature to within a few degrees of freezing this temperature constraint matches well with our observations of fluvial deposits which require temperatures sufficiently warm for surface runoff although this estimate coincides with one of the coldest near sea level tropical temperatures in earth history if these structures represent peak marinaon glacial conditions they do not support the persistent deep freeze of the snowball earth hypothesis rather surface temperatures near 0 c allow for regions of seasonal surface melting atmosphere ocean coupling and possible tropical refugia for early metazoans if instead these structures formed during glacial onset or deglaciation then they have implications for the timescale and character for the transition into or out of a snowball state

the periglacial landscape at the phoenix landing site 1 the mars scout mission phoenix landed in the northern high latitudes of mars in an area thought to be dominated by subsurface ground ice and has provided a unique detailed examination of periglacial morphology and topography that is not visible from orbit the landing site and surrounding terrain is dominated by polygonal patterned ground typical of the martian northern plains the polygons exhibit a gentle u shaped trough and rounded mound topography with an average trough depth of 17 cm and an average surface slopes of only 6 7 polygons an average 4 3 m across form a pattern superimposed on all other geologic landforms including larger 20 25 m polygons and kilometer long linear ridges the polygon morphology and the predominance of subsurface ice cemented soil are consistent with the formation of subsurface sand wedges in a permanently frozen arid climate small scale soil furrows and cracks into the ice cemented soil indicate that the thermal contraction process responsible for the formation of the polygons is active today rocks appear to be sorted within the polygon troughs indicating a process of cryoturbation within the permanently frozen polygons the complexity of the patterns crosscutting relations and rock distributions indicate advanced maturity of the polygon networks and shifting crack patterns possibly facilitated by crack and wedge annealing during times of low obliquity

desiccation cracks provide evidence of lake drying on mars sutton island member murray formation gale crater mars science laboratory msl curiosity rover data are used to describe the morphology of desiccation cracks observed in ancient lacustrine strata at gale crater mars and to interpret their paleoenvironmental setting the desiccation cracks indicate subaerial exposure of lacustrine facies in the sutton island member of the murray formation in association with ripple cross stratification and possible eolian cross bedding these facies indicate a transition from longer lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure the transition from perennial to episodically exposed lacustrine environments provides evidence for local to regional climate change that can help constrain mars climate models

fractal analysis of cracking in a clayey soil under freeze thaw cycles abstract under extreme climate conditions clayey soils experience not only seasonal drying and wetting but also frequent freezing and thawing cracking would also occur in clayey soils under freeze thaw cycles but now less academic attention has been paid on this issue in this study a series of laboratory tests were conducted on a clayey soil to investigate the cracking behaviors under freeze thaw cycles water loss surface crack initiation and propagation processes were monitored after each freeze thaw cycle by using the image processing technique the crack patterns were described and then quantitatively analyzed on the basis of the fractal dimension concept it was found that for the tested clayey soil subjected to freeze thaw cycles the surface crack pattern slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi hexagonal one and the water loss closely related to the sample thickness plays a significant role in the process of the clay cracking upon cyclic freezing thawing the fractal dimension is well correlated to the surface crack ratio in a logarithmic equation fractal dimension concept can offer a new perspective on the quantitative understanding of cracking initiation and propagation in clayey soils under freeze thaw cycles

ground ice recharge via brine transport in frozen soils of victoria valley antarctica insights from modeling δ18o and δd profiles abstract soils in the mcmurdo dry valleys antarctica contain ice and considerable amounts of salt ice often occurs at shallow depth throughout the dry valleys and other areas of hyperarid permafrost notably on mars this common occurrence of shallow ice is enigmatic however since according to published sublimation models it should disappear relatively quickly at rates of order 0 1 mm a 1 due to vapor loss to the atmosphere this loss may be offset by recharge from snowmelt infiltrating and freezing in the soil herein we present a first quantitative estimate of this recharge based on measured vertical profiles of d and 18 o that reveal considerable detail about the sources and sinks of ice we model these profiles taking into account the salt content and a soil temperature record along a 1 6 m depth profile of 10 ka old ice cemented soils in victoria valley antarctica the stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement 20 cm depth both d and 18 o values plotted against depth exhibit a concave upward curve at depth the isotope composition is similar to that of lake victoria and modern meteoric water the concave shape of the isotope profile is suggestive of downward advection dispersion of snowmelt water enriched in heavy isotopes into the ice cement our advection dispersion model coupled with field data enables us to quantify the advective flux and dispersion of melt water into the ice the advective velocity and dispersion coefficient depend on the time since advection began and the ice to brine ratio they are respectively of the order of 10 11 10 10 m s 1 and 10 12 10 11 m 2 s 1 these values suggest that over the 10 ka time period a total of 190 mm water infiltrated into the ice cemented ground the isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system rayleigh fractionation to develop the isotopic signature of the upper ice cement requires evaporation of 95 of the snowmelt water based on 190 mm brine infiltrating into the soil requires an initial total of 4 m of snowmelt water this corresponds to 0 4 mm a 1 suggesting that under the current climate condition water from snowmelt is sufficient to compensate modeled sublimation rates and therefore conserve ground ice in victoria valley