reading the climate record of the martian polar layered deposits abstract the martian polar regions have layered deposits of ice and dust the stratigraphy of these deposits is exposed within scarps and trough walls and is thought to have formed due to climate variations in the past insolation has varied significantly over time and caused dramatic changes in climate but it has remained unclear whether insolation variations could be linked to the stratigraphic record we present a model of layer formation based on physical processes that expresses polar deposition rates of ice and dust in terms of insolation in this model layer formation is controlled by the insolation record and dust rich layers form by two mechanisms 1 increased summer sublimation during high obliquity and 2 variations in the polar deposition of dust modulated by obliquity variations the model is simple yet physically plausible and allows for investigations of the climate control of the polar layered deposits pld we compare the model to a stratigraphic column obtained from the north polar layered deposits npld fishbaugh k e hvidberg c s byrne s russel p s herkenhoff k e winstrup m kirk r 2010a geophys res lett 37 l07201 and show that the model can be tuned to reproduce complex layer sequences the comparison with observations cannot uniquely constrain the pld chronology and it is limited by our interpretation of the observed stratigraphic column as a proxy for npld composition we identified however a set of parameters that provides a chronology of the npld tied to the insolation record and consistently explains layer formation in accordance with observations of npld stratigraphy this model dates the top 500 m of the npld back to 1 million years with an average net deposition rate of ice and dust of 0 55 mm a 1 the model stratigraphy contains a quasi periodic 30 m cycle similar to a previously suggested cycle in brightness profiles from the npld laskar j levrard b mustard f 2002 nature 419 375 377 milkovich s head j w 2005 j geophys res 110 but here related to half of the obliquity cycles of 120 and 99 kyr and resulting from a combination of the two layer formation mechanisms further investigations of the non linear insolation control of pld formation should consider data from other geographical locations and include radar data and other stratigraphic datasets that can constrain the composition and stratigraphy of the npld layers

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

genesis of altered conway granite grus in new hampshire usa abstract increased pedologic interest in grus has created a need for better understanding of geologic and pedogenic processes producing such materials progress in this area is hindered by the incomplete understanding of pedogenic processes as well as the fact that some of the properties of grus may be created through any of several pathways hydrothermal alteration is one important example of a geologic process which may produce characteristics similar to those created by pedogenesis this process is not often considered by soil scientists because of their unfamiliarity with the geologic environments which engender such conditions and the petrographic evidence specific to these processes this study uses petrographic evidence of microfracturing silicification and sericitization indicative of hydrothermal alteration in conjunction with igneous structural geology to enhance traditional pedologic assessments of weathering and soil genesis in the conway granite grus this interdisciplinary approach led to the interpretation that the grus was a product of hydrothermal alteration rather than paleopedogenesis as had been proposed previously more importantly this study demonstrates that interpretations of soil weathering paleosol occurrences and grus genesis in a variety of locations can be enhanced by such considerations

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

hirise observations of recurring slope lineae rsl during southern summer on mars abstract recurring slope lineae rsl are active features on mars that might require flowing water most examples observed through 2011 formed on steep equator facing slopes in the southern mid latitudes they form and grow during warm seasons and fade and often completely disappear during colder seasons but recur over multiple mars years they are recognizable by their incremental growth relatively low albedo and downhill orientation we examined all images acquired by hirise during l s 250 10 slightly longer than southern summer l s 270 360 of mars years 30 31 03 2011 10 2011 and supplemented our results with data from previous studies to better understand the geologic context and characteristics of rsl we also confirmed candidate and likely sites from previous studies and discovered new rsl sites we report 13 confirmed rsl sites including the 7 in mcewen et al mcewen et al 2011 science 333 6043 740 743 the observed seasonality latitudinal and slope orientation preferences and themis brightness temperatures indicate that rsl require warm temperatures to form we conclude that rsl are a unique phenomenon on mars clearly distinct from other slope processes that occur at high latitudes associated with seasonal co 2 frost and episodic mass wasting on equatorial slopes however only 41 82 out of 200 of the sites that present apparently suitable conditions for rsl formation steep equator facing rocky slopes with bedrock exposure in the southern mid latitudes 28 60 s contain any candidate rsl with confirmed rsl present only in 7 13 sites of those locations significant variability in abundance size and exact location of rsl is also observed at most sites indicating additional controls such as availability of water or salts that might be playing a crucial role

mineralogical changes during intense chemical weathering of sedimentary rocks in bangladesh abstract bangladesh is situated in a subtropical to tropical climatic zone a recently weathered crust has developed on sedimentary bedrock sandstone siltstone shale and claystones of tertiary quaternary age weathered samples were collected from 16 sections totaling 68 samples and were analyzed mineralogically the main primary minerals identified in the weathered crust of sedimentary rocks are quartz plagioclase k feldspar biotite muscovite sparse carbonate and epidote the secondary minerals are kaolinite illite chlorite gibbsite and goethite weathering initiated along the grain boundaries and cleavage planes of the minerals forming small cloudy materials which were very difficult to identify in the advanced stage of weathering these cloudy materials have turned into secondary minerals in region 1 high rain fall 7100 mm yr and monsoonic climate resulted in a kaolinite gibbsite goethite suite through the weathering of feldspars and biotite the occurrence of gibbsite in the relatively elevated lands of sylhet and fe kaolinite throughout the study areas is indicative of a humid tropical climate during formation of the weathered crust

the imprint of time on canadian soil landscapes abstract the imprint of time on canadian soil landscapes reflects the strong influence of repeated quaternary glaciations with most soils having formed on late pleistocene glacial sediments and to a lesser extent holocene non glacial sediments soil chronosequences in these youthful landscapes seldom span the full holocene and have been documented principally in areas of coastal isostatic uplift and shoreline evolution as well as on recessional moraine sequences in the cordillera these chronosequences have placed quantitative constraints on rates of podzolization in environments ranging from coastal temperate rainforest to subarctic longer sequences involving soils and relict paleosols on pleistocene morainal and glaciofluvial surfaces in the central yukon territory record more complex legacies of pedogenesis and landscape evolution but with much coarser time control and many potentially confounding influences of climatic change and disturbance processes older weathered bedrock and regolith can make significant contributions to soil parent materials in several settings 1 in favoured locations where local conditions protected these materials from glacial erosion in southern canada 2 beyond the maximum limits of glaciation principally in northwestern canada and 3 in the arctic where cold based non erosive ice allowed preservation of these materials closer collaborations between pedologists and other quaternary scientists will be needed to ensure a more complete understanding of these complex pedogenic legacies in canadian landscapes

driven by excess climatic implications of new global mapping of near surface water equivalent hydrogen on mars abstract we present improved mars odyssey neutron spectrometer mons maps of near surface water equivalent hydrogen weh on mars that have intriguing implications for the global distribution of excess ice which occurs when the mass fraction of water ice exceeds the threshold amount needed to saturate the pore volume in normal soils we have refined the crossover technique of feldman et al 2011 by using spatial deconvolution and gaussian weighting to create the first globally self consistent map of weh at low latitudes our new maps indicate that weh exceeds 15 in several near equatorial regions such as arabia terra which has important implications for the types of hydrated minerals present at low latitudes at high latitudes we demonstrate that the disparate mons and phoenix robotic arm ra observations of near surface weh can be reconciled by a three layer model incorporating dry soil over fully saturated pore ice over pure excess ice such a three layer model can also potentially explain the strong anticorrelation of subsurface ice content and ice table depth observed at high latitudes at moderate latitudes we show that the distribution of recently formed impact craters is also consistent with our latest mons results as both the shallowest ice exposing crater and deepest non ice exposing crater at each impact site are in good agreement with our predictions of near surface weh overall we find that our new mapping is consistent with the widespread presence at mid to high martian latitudes of recently deposited shallow excess ice reservoirs that are not yet in equilibrium with the atmosphere

the evolution of exposed ice in a fresh mid latitude crater on mars abstract recent observations of the surface of mars have shown several fresh mid latitude craters some of these craters show exposed ice byrne s et al 2009 science 325 1674 1676 in some craters albedo of ice slowly decreases while in others it remains nearly constant we attempt to determine influence of the regolith structure on the rate of sublimation of ice for this purpose we performed numerical simulations describing evolution of the exposed ice in model craters located at middle latitudes we consider a new model for the structure and evolution of the material at and beneath the crater floors in contrast to the previous study by dundas and byrne dundas c m byrne s 2010 icarus 206 716 728 we do not investigate sublimation of dirty ice and the related formation of a sublimation lag instead we consider sublimation of a pure ice layer on top of layered regolith in our model the observed reflectivity decreases due to the sublimation driven changes of the optical properties of thinning clean ice this offers an alternative to the deposition of the dust embedded in ice sublimation lag we have shown that in our model among many parameters affecting ice sublimation rate volumetric fraction of water ice in the subsurface beneath the crater has the strongest influence hence observed darkening of the ice patch on the crater floor might be sufficient to determine the content of water ice in the subsurface our calculations show that an albedo decrease of fresh ice patches in mid latitude craters can be explained by either strong dust sedimentation or if this is excluded by sublimation of a thin layer of water ice from the regolith with large thermal inertia this is consistent with a large volumetric fraction of water ice beneath the crater floor and contributes to evidence for an extended subsurface water reservoir on mars the overall conclusion of our work is that a thin post impact surface ice coating over ice rich ground beneath the crater floors is consistent with the observations

an ice age recorded in the polar deposits of mars layered ice deposits at the poles of mars record a detailed history of accumulation and erosion related to climate processes radar investigations measure these layers and provide evidence for climate changes such as ice advance and retreat we present a detailed analysis of observational data showing that 87 000 cubic kilometers of ice have accumulated at the poles since the end of the last ice age 370 000 years ago this volume is equivalent to a global layer of 60 centimeters the majority of the material accumulated at the north pole these results provide both a means to understand the accumulation history of the polar deposits as related to orbital milankovitch cycles and constraints for better determination of mars past and future climates

changes in blast zone albedo patterns around new martian impact craters abstract blast zones bzs around new martian craters comprise various albedo features caused by the initial impact including diffuse halos extended linear and arcuate rays secondary craters ejecta patterns and dust avalanches we examined these features for changes in repeat images separated by up to four mars years here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time such changes are most likely due to airfall of high albedo dust restoring darkened areas to their original albedo the albedo of adjacent non impacted surfaces although some sites show drastic changes over short timescales nearly half of the sites show no obvious changes over several mars years albedo changes are more likely to occur at higher latitude sites lower elevation sites and at sites with smaller central craters no correlation was seen between amount of change and dust cover index relative halo size or historical regional albedo changes quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features the average lifetime among sites with measurable fading is 15 mars years the median is 8 mars years for a linear brightening however at approximately half of sites with three or more repeat images a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior this would predict even longer lifetimes the predicted lifetimes of bzs are comparable to those of slope streaks and considered representative of fading by global atmospheric dust deposition they last significantly longer than dust devil or rover tracks albedo features that are erased by different processes these relatively long lifetimes indicate that the measurement of the current impact rate by daubar et al daubar i j et al 2013 icarus 225 506 516 http dx doi org 10 1016 j icarus 2013 04 009 does not suffer significantly from overall under sampling due to blast zones fading before new impact sites can be initially discovered however the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

ice sublimation as a geomorphic process a planetary perspective abstract sublimation plays a role in the shaping of landforms of planetary surfaces where ice is present as frost as polar caps or in the subsurface this review is focused primarily on the geomorphologic consequences of sublimation a summary of the suite of landforms that have been observed on the surface of various planetary bodies and whose formation is attributed to sublimation is presented this includes the sublimation of a range of different ices that are found on planetary bodies water ice carbonic ice etc at least four groups of landforms are distinguishable independent of the planetary body i residual lags that are depleted in ice which form after sublimation loss such residual lags isolate deeper ice from sublimation and thus can have an important impact on planetary volatile cycles ii landforms due to differential sublimation resulting from enhanced sublimation in low albedo warmer areas of the planet and preservation of ice in the high albedo regions iii landforms due to differential sublimation initiated by fractures or ground heterogeneities for example sublimation enhanced polygonal cracks iv pitted terrains that occur in a relatively homogeneous ice bearing subsurface or as an effect of local ice enrichment or segregation in the ground

characteristics of residual and colluvial soils developed on granite and of the associated pre wisconsin landforms in north central new brunswick an area in north central new brunswick of approximately 20 km2 where tors are common was found to be undisrupted by glaciation the soils in this area are developed on grus and appear to be of pr

cenozoic weathering covers in buchan scotland and their significance isolated occurrences of chemically weathered rock or saprolite are common in many formerly glaciated areas around the north atlantic1 6 these pockets of saprolite are widely regarded as remnants of cenozoic deep weathering covers which existed before the first extensive northern hemisphere glaciations at 2 4 myr ref 7 and their apparent survival has long been used as evidence for the local ineffectiveness of glacial erosion2 4 8 9 however the scarcity of correlative deposits means that the age and significance of these fragmented saprolites are uncertain i report here the results of a detailed survey which shows that in buchan scotland a combination of cenozoic tectonic stability and extremely limited pleistocene glacial erosion has allowed the preservation of deep weathering covers of probable miocene to early pleistocene age on a scale not previously reported from any other formerly glaciated area

vertical distribution of hydrogen at high northern latitudes on mars the mars odyssey neutron spectrometer 1 neutron leakage currents measured using the mars odyssey neutron spectrometer are used to develop a two layer model of the distribution of hydrogen here parameterized as water equivalent hydrogen weh at high northern latitudes the weh abundance in the upper layer wup was found to range between 1 and about 5 the maximum value of the apparent thickness d of this upper layer peaks at about 60 latitude giving the appearance of zonal bands of enhanced d in both hemispheres this maximum is consistent with an expected transition from weh contained solely in hydrous minerals at lower latitudes to weh contained both in the forms of water ice and water of hydration at high latitudes a strong anti correlation between the weh concentration in the lower layer and apparent depth d at high latitudes is observed and may provide clues to the origin of these deposits

the role of sublimation for the formation of the northern ice cap results from the mars orbiter laser altimeter abstract the evolutionary history of the martian ice caps is practically unknown and the caps are key to understanding the climatic history of mars sublimation and ice flow are two hypotheses that have recently been suggested to explain the observed form of the northern ice cap here we present a sublimation model and compare the shape of the cap obtained from this model with mars orbiter laser altimeter mola observations of the north polar region this model can reproduce the shape of the cap and individual troughs sublimation is an important process as are flow and wind erosion we were able to constrain the time scales of sublimation only to about two orders of magnitude 1 100 million years this estimate depends on many unknown parameters such as friction velocity and wind speed over the ice caps these can be determined only by direct measurement over the surface

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

effect of mars atmospheric loss on snow melt potential in a 3 5 gyr mars climate evolution model post noachian martian paleochannels indicate the existence of liquid water on the surface of mars after about 3 5 gya irwin et al 2015 palucis et al 2016 in order to explore the effects of variations in co2 partial pressure and obliquity on the possibility of surface water we created a zero dimensional surface energy balance model we combine this model with physically consistent orbital histories to track conditions over the last 3 5 gyr of martian history we find that melting is allowed for atmospheric pressures corresponding to exponential loss rates of dp dt t 3 73 or faster but this rate is within 0 5 of the rate calculated from initial measurements made by the mars atmosphere and volatile evolution maven mission if we assume all the escaping oxygen measured by maven comes from atmospheric co2 lillis et al 2017 tu et al 2015 melting at this loss rate matches selected key geologic constraints on the formation of hesperian river networks assuming optimal melt conditions during the warmest part of each mars year irwin et al 2015 stopar et al 2006 kite et al 2017a b the atmospheric pressure has a larger effect on the surface energy than changes in mars s mean obliquity these results show that initial measurements of atmosphere loss by maven are consistent with atmospheric loss being the dominant process that switched mars from a melt permitting to a melt absent climate jakosky et al 2017 but non co2 warming will be required if 2 gya paleochannels are confirmed or if most of the escaping oxygen measured by maven comes from h2o

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

new paleomagnetic data for the triassic guichon batholith of south central british columbia and their bearing on terrane i tectonics the 198 ma guichon batholith outcrops in the southern end of the intermontane belt or composite terrane i of the western north american cordillera thermal demagnetization of specimens from 19 sites at 200 450 and 560 c isolates a stable primary component at 560 c in 13 sites giving a pole position of 347 w 52 n p 5 m 9 these data support earlier results obtained by the author that indicate the batholith has undergone a clockwise rotation about a vertical axis of 43 7 they also show that the batholith has undergone northward motion of 13 6 which supports recent arguments that the terrane underwent 14 2 of northward translation between late cretaceous and pre miocene time

properties and genesis of a soil and the underlying gibbsite bearing saprolite cape breton island canada brownish yellow saprolite derived from granite gneiss is exposed beneath 1 2 m of reddish brown till along a roadcut in the cape breton highlands the strongly acid soil is similar to other podzolic soils of the region except for the presence of gibbsite in the silt and clay fractions in the saprolite feldspar and biotite have weathered to poorly crystalline kaolinite gibbsite and a minor component of iron oxide the poorly crystalline kaolinite does not occur in the overlying till the evidence presented is consistent with the view that the area was covered either by cold based or by stagnant warm based glaciers that eroded the pre quaternary surface only slightly and deposited a thin discontinuous veneer of till derived mainly from local bedrock and saprolite weathering products from the saprolite are probably incorporated commonly in tills of the area during the formation of soils in these tills the poorly crystalline kaolinite and most of the gibbsite are either transformed to other minerals

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

chaos terrain storms and past climate on mars 1 we model the atmospheric response to a chaos forming event at juventae chasma north of valles marineris mars using the mars regional atmospheric modeling system mrams interactions between lake driven convergence topography and the regional wind field steer lake induced precipitation to the southwest mean snowfall reaches a maximum of 0 9 mm h water equivalent peak snowfall 1 7 mm h water equivalent on the sw rim of the chasm more than 80 of vapor released by the lake is trapped in or next to the lake as snow radiative effects of the thick cloud cover raise mean plateau surface temperature by up to 18 k locally we find that the area of maximum modeled precipitation corresponds to the mapped juventae plateau channel networks at echus chasma modeled precipitation maxima also correspond to mapped plateau channel networks this is consistent with the earlier suggestion that valles marineris plateau layered deposits and interbedded channel networks result from localized precipitation however snowpack thermal modeling shows temperatures below freezing for the 12 mbar co2 atmosphere used in our mrams simulations this is true even for the most favorable orbital conditions and whether or not the greenhouse effect of the lake storm is included moderately higher co2 pressures or non co2 greenhouse forcing is very likely required for melting and plateau channel network formation under a faint young sun required warming is 10 k global temperatures need not be higher than today in these localized precipitation scenarios the rest of the planet remains dry

initiation and growth of martian ice lenses abstract water ice in the upper meters of the martian regolith is a major volatile reservoir although the geographic extent burial depth and thermal stability of this shallow ice are well understood its origin history and stratigraphy are not over the past decade a growing body of observational evidence has indicated that shallow ground ice exceeds the pore volume of its host soil over large regions of both martian hemispheres this is confounding given that 1 the physical theory that accurately predicts the location of ground ice also assumes that ice should be pore filling in the upper meter of regolith and 2 the phoenix spacecraft uncovered far more pore filling ice than excess ice at its landing site in the northern hemisphere the development of ice lenses by low temperature in situ segregation analogous to the processes that generate frost heave on earth has been hypothesized to explain shallow excess ice on mars we have developed a numerical model of ice lens initiation and growth in the martian environment and used it to test this hypothesis for the first time we carried out a large suite of numerical simulations in order to place quantitative constraints on the timing and location of ice lens initiation and on the magnitude of ice lens growth in a variety of host soils we find that ice lens initiation is a ubiquitous process in the martian high latitudes but the ultimate magnitude of lens growth or frost heave is sensitive to the properties of the host soil depending on the specific properties of martian soils in situ segregation may be a very slow process sufficient to explain the excess ice observed in the dodo goldilocks trench at the phoenix landing site but without regionally significant effects alternatively if clay sized particles or perchlorate salts are present in situ segregation may be a vigorous process that has significantly affected the stratigraphy of ground ice in the upper meter of regolith throughout the high latitudes

a granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins abstract a review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation if present this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated these blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the quaternary based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields other regoliths in periglacial settings and regoliths from non periglacial settings a fingerprint of chemical weathering in periglacial landscapes was identified a mobile regolith origin under at least seasonal periglacial conditions is indicated where clay 0 5 silt 8 across a sample batch this contrasts with a mobile regolith origin under non periglacial conditions which is indicated where clay 0 5 silt 6 across a sample batch with clay 0 5 silt 8 in at least one sample a range of secondary minerals which frequently includes interstratified minerals and indicates high local variability in leaching conditions is also commonly present in regoliths exposed to periglacial conditions during their formation clay silt ratios display a threshold response to temperature related to the freezing point of water but there is little response to precipitation or regolith residence time lithology controls clay and silt abundances which increase from felsic through intermediate to mafic compositions but does not control clay silt ratios use of a sedigraph or coulter counter to determine regolith granulometry systematically indicates lower clay abundances and intra site variability than use of a pipette or hydrometer in contrast to clay silt ratios secondary mineral assemblages vary according to regolith residence time temperature and or precipitation a microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges according to the fingerprint of chemical weathering in periglacial landscapes there is generally no evidence of blockfield origins under warm neogene climates nearly all blockfields appear to be a product of quaternary physical and chemical weathering a more dominant role for periglacial processes in further bevelling elevated low relief non glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated

modeling sublimation of ice exposed by new impacts in the martian mid latitudes abstract new impacts in the martian mid latitudes have exposed near surface ice this ice is observed to slowly fade over timescales of months in the present martian climate exposed surface ice is unstable during summer months in the mid latitudes and will sublimate we model the sublimation of ice at five new impact sites and examine the implications of its persistence even with generally conservative assumptions for most reasonable choices of parameters it is likely that over a millimeter of sublimation occurred in the period during which the ice was observed to fade the persistence of visible ice through such sublimation suggests that the ice is relatively pure rather than pore filling such ice could be analogous to the nearly pure ice observed by the phoenix lander in the dodo goldilocks trench and suggests that the high ice contents reported by the mars odyssey gamma ray spectrometer at high latitudes extend to the mid latitudes our observations are consistent with a model of the martian ice table in which a layer with high volumetric ice content overlies pore filling ice although other structures are possible

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

characteristics and significance of two pre late wisconsinan weathering profiles adirondacks usa and miramichi highlands canada abstract the properties of two weathering profiles developed from granitic rocks and covered by deposits of wisconsinan age were studied in order to characterize saprolites and non saprolite residuum of the glaciated area of northeastern north america the warrensburg profile adirondacks new york is more than 9 m thick and formed on a hornblende granitic gneiss total chemical analysis of the sandy saprolite shows slight losses compared to bedrock kaolinite is the main weathering product in the

geologic context of recurring slope lineae in melas and coprates chasmata mars one of the major mars discoveries of recent years is the existence of recurring slope lineae rsl which suggests that liquid water occurs on or near the surface of mars today these dark and narrow features emerge from steep rocky exposures and incrementally grow fade and reform on a seasonal basis and are detected in images from the high resolution imaging science experiment camera rsl are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another one major exception is the steep low albedo slopes of melas and coprates chasmata in valles marineris where rsl are detected among diverse geologic surfaces e g bedrock and talus and landforms e g inselbergs and landslides new images show topographic changes including sediment deposition on active rsl slopes midwall locations in coprates and melas appear to have more areally extensively abundant rsl and related fans as compared with other rsl sites found on mars water budget estimates for regional rsl are on the order of 105 to 106 m3 of fluid for depths of 10 to 100 mm and suggest that a significant amount of near surface water might be present many rsl are concentrated near local topographic highs such as ridge crests or peaks which is challenging to explain via groundwater or ice without a recharge mechanism collectively results provide additional support for the notion that significant amounts of near surface water can be found on mars today and suggest that a widespread mechanism possibly related to the atmosphere is recharging rsl sources

ice processes and surface ablation in a shallow thermokarst lake in the central qinghai tibetan plateau the qinghai tibetan plateau qtp is characterized by a cold climate and a large number of lakes the long ice season necessitates study of the widespread ice covers in the region an unprecedented multidisciplinary field campaign was conducted on lake ice processes in the central qtp during the period 2019 13 the study lake generally froze up in late october or early november and broke up in mid or late april with a maximum ice thickness of 50 70 cm the mass balances at both ice surface and bottom were measured continuously significant ice surface sublimation ablation was detected and accounted for up to 40 of the whole ice thickness over the ice season a simple heat transfer model was developed for the surface ice loss the calculated values were in good agreement with the observations they also indicated that atmospheric conditions including low air humidity and prevailing strong winds are the primary drivers of the ice surface sublimation

glacigenic rafting of weathered granite charlie lake new brunswick glaciation in the area of charlie lake new brunswick has produced a granitic till very similar in appearance to weathered bedrock portions of weathered granite were moved intact and redeposited as imbricated rafts under basal till the rafts vary from 0 3 to 2 m in thickness over a 10 m wide exposure and show deep weathering zones and brittle deformation despite the fact that they are highly friable the rafts are separated by glacigenic fault planes defined by lenses of diamict and rare clasts of distant origin they are recognizable only in excavations where fault planes can be seen to delineate slabs of rock imbricated mainly upglacier surface weathering features including core stones were preserved during movement over short distances

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

weathering characteristics of arctic islands in northern norway the arctic islands of the lofoten vesteralen archipelago in northern norway have a wide distribution of weathered land surfaces commonly located above 250 m with several apparent similarities in order to investigate the characteristics of deep weathering in this region northern langoya and hadseloya were chosen for in depth analyses eight weathering profiles were excavated from various surfaces and the stratigraphies were logged in detail material was collected throughout the weathering horizons and all samples were subsequently analysed for clay mineralogy 40 000 years of subaerial conditions considering the steady surface erosion this figure should be viewed as an absolute minimum age estimate mapping of the superficial sediments and geomorphological features of the study areas has revealed several common morphological features which indicate dominance of glacial and periglacial processes in the areas lying below the lower boundary of blockfields c 250 m the weathering mantles are not a periglacial end product but rather a relict tertiary landform that were modulated by permafrost processes as well as biological processes at later stages the regolith cover constrain the vertical extension of warmbased quaternary ice sheets challenging the notion of a parabolic ice mass consuming every mountain top of lofoten and vesteralen

gasa impact crater mars very young gullies formed from impact into latitude dependent mantle and debris covered glacier deposits abstract the mode of formation of gullies on mars very young erosional depositional landforms consisting of an alcove channel and fan is one of the most enigmatic problems in martian geomorphology major questions center on their ages geographic and stratigraphic associations relation to recent ice ages and if formed by flowing water the sources of the water to cause the observed erosion deposition gasa 35 72 s 129 45 e a very fresh 7 km diameter impact crater and its environment offer a unique opportunity to explore these questions we show that gasa crater formed during the most recent glacial epoch 2 1 0 4 ma producing secondary crater clusters on top of the latitude dependent mantle ldm interpreted to be a layered ice dust rich deposit emplaced during this glacial epoch high resolution images of a pre gasa impact crater 100 km northeast of gasa reveal that portions of the secondary crater covered ldm have been removed from pole facing slopes in crater interiors near gasa gullies are preferentially located in these areas and channels feeding alcoves and fans can be seen to emerge from the eroding ldm layers to produce multiple generations of channel incision and fan lobes we interpret these data to mean that these gullies formed extremely recently in the post gasa impact time period by melting of the ice rich ldm stratigraphic and topographic relationships are interpreted to mean that under favorable illumination geometry steep pole facing slopes and insolation conditions melting of the debris covered ice rich mantle took place in multiple stages most likely related to variations in spin axis orbital conditions closer to gasa in the interior of the 18 km diameter ldm covered host crater in which gasa formed the pole facing slopes display two generations of gullies early somewhat degraded gullies have been modified by proximity to gasa ejecta emplacement and later fresh appearing gullies are clearly superposed cross cut the earlier phase and show multiple channels and fans interpreted to be derived from continued melting of the ldm on steep pole facing slopes thus we conclude that melting of the ice rich ldm is a major source of gully activity both pre gasa crater and post gasa crater formation the lack of obscuration of gasa secondary clusters formed on top of the ldm is interpreted to mean that the gasa impact occurred following emplacement of the last significant ldm layers at these low latitudes and thus near the end of the ice ages this interpretation is corroborated by the lack of ldm within gasa however gasa crater contains a robustly developed set of gullies on its steep pole facing slopes unlike other very young post ldm craters in the region how can the gullies inside gasa form in the absence of an ice rich ldm that is interpreted to be the source of water for the other adjacent and partly contemporaneous gullies analysis of the interior floor and walls of the host crater suggest that prior to the gasa impact the pole facing walls and floor were occupied by remnant debris covered glaciers formed earlier in the amazonian which are relatively common in crater interiors in this latitude band we suggest that the gasa impact cratering event penetrated into the southern portion of this debris covered glacier emplaced ejecta on top of the debris layer covering the ice and caused extensive melting of the buried ice and flow of water and debris slurries on the host crater floor inside gasa the impact crater rim crest and wall intersected the debris covered glacier deposits around the northern pole facing part of the gasa interior we interpret this exposure of ice rich debris covered glacial material in the crater wall to be the source of meltwater that formed the very well developed gullies along the northern pole facing slopes of gasa crater

rounded cobbles that have not travelled far incorporation of corestones from saprolites in the south mountain area of southern nova scotia canada saprolitic palaeosurfaces occur at several localities on the granitoid rocks of the south mountain batholith of nova scotia there are three ages of saprolites within the study area pre pleistocene pre triassic and pre carboniferous within these in place weathered horizons there are remnant ellipsoidal blocks of unweathered granitoid referred to as corestones these corestones are isolated rounded pods of relatively unweathered material surrounded by rotted granitoid saprolitic material the weathered material which surrounds these corestones is poorly consolidated and easily eroded the erosion of these horizons produces a lag deposit that contains many rounded corestones which can be incorporated into subsequent sedimentary units the rounded boulders cobbles and pebbles of granite within many of the pleistocene glacial deposits in southern nova scotia are probably related to the incorporation of these saprolite related structures given the locally derived within 400 m of the source nature of the tills the presence of saprolites at unconformities of various ages on the south mountain granitoid rocks suggests that incorporation of saprolitic material probably occurred along a number of palaeosurfaces in the past the recognition of this process has implications for the interpretation of rounded granite clast conglomerates and quartz rich sandstones of various ages within the stratigraphic record of eastern canada similar palaeosurfaces elsewhere in the world also have related saprolite derived sedimentary rocks associated with them in summary well rounded spherical pebbles cobbles and boulders of granitoid material incorporated in sedimentary strata need not have travelled far from source nor are they necessarily recycled from older conglomerates

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

history and anatomy of subsurface ice on mars abstract ice buried beneath a thin layer of soil has been revealed by neutron spectroscopy and explored by the phoenix mars lander it has also been exposed by recent impacts this subsurface ice is thought to lose and gain volume in response to orbital variations milankovitch cycles we use a powerful numerical model to follow the growth and retreat of near surface ice as a result of regolith atmosphere exchange continuously over millions of years if a thick layer of almost pure ice has been deposited recently it has not yet reached equilibrium with the atmospheric water vapor and may still remain as far equatorward as 43 n where ice has been revealed by recent impacts a potentially observable consequence is present day humidity output from the still retreating ice we also demonstrate that in a sublimation environment subsurface pore ice can accumulate in two ways the first mode widely known is the progressive filling of pores by ice over a range of depths the second mode occurs on top of an already impermeable ice layer subsequent ice accumulates in the form of pasted on horizontal layers such that beneath the ice table the pores are completely full with ice most or all of the pore ice on mars today may be of the second type at the phoenix landing site where such a layer is also expected to exist above an underlying ice sheet it may be extremely thin due to exceptionally small variations in ice stability over time

profiles of elemental concentrations in precambrian paleosols on basaltic and granitic parent materials abstract profiles of elemental concentrations are interpreted for four precambrian paleosols two developed on basalt and two on granodiorite all four paleosols appear to be the erosional remnants of originally thick soil saprolite regoliths the granitic paleosols are in south africa where they underlie the 2 9 3 0 ga pongola supergroup and the 2 8 2 9 ga dominion reef conglomerate one of the basaltic paleosols also occurs in south africa where it caps the ventersdorp basalt and underlies the 2 3 ga black reef quartzite the other basaltic paleosol underlies sandstone of the 2 7 ga timiskaming group in the abitibi belt of the canadian shield all four paleosols exhibit pronounced upward loss of sodium but no consistent loss of the heavier alkali elements rubidium and cesium iron decreases upward above iron rich basaltic parent rocks but there is no consistent loss of iron above iron poor granitic parents the rare earth elements are less fractionated than during intensive modern weathering uranium locally has been fractionated from thorium possibly due to oxidative dissolution during precambrian weathering

paleoweathered surfaces on granitoids of southern nova scotia paleoenvironmental implications of saprolites in addition to minor postglacial weathering effects a complex history of three distinct weathering events has been identified within the granitoids of the south mountain batholith of southwestern

a prelanding assessment of the ice table depth and ground ice characteristics in martian permafrost at the phoenix landing site 1 we review multiple estimates of the ice table depth at potential phoenix landing sites and consider the possible state and distribution of subsurface ice a two layer model of ice rich material overlain by ice free material is consistent with both the observational and theoretical lines of evidence results indicate ground ice to be shallow and ubiquitous 2 6 cm below the surface undulations in the ice table depth are expected because of the thermodynamic effects of rocks slopes and soil variations on the scale of the phoenix lander and within the digging area which can be advantageous for analysis of both dry surficial soils and buried ice rich materials the ground ice at the ice table to be sampled by the phoenix lander is expected to be geologically young because of recent climate oscillations however estimates of the ratio of soil to ice in the ice rich subsurface layer suggest that that the ice content exceeds the available pore space which is difficult to reconcile with existing ground ice stability and dynamics models these high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity initially high porosity soils or the migration of water along thin films measurement of the d h ratio within the ice at the ice table and of the soil to ice ratio as well as imaging ice soil textures will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable

implications of using broadband photometry for compositional remote sensing of icy objects water ice has such a low absorption coefficient at visual wavelengths 0 01 cm 1 that a very small amount of particulate material can significantly darken an icy surface a variety of ice plus particle mixtures were studied to show that particulate contaminations of 1 by weight even 0 1 or less in some cases in ice or frosts result in reflectance levels close to that of the contaminants in a very clear ice no bubbles it is plausible to have a reflectance 0 05 for particulate contaminations 10 7 by weight for submicron dark particles such as carbon lampblack scattering conditions compete for domination with contaminants for control of visual reflectance implying that the apparent reflectivity level and color of a surface is a poor indicator of ice content a dark surface e g albedo 0 05 does not necessarily imply that there us very little water ice present infrared jhk colors of water ice and other minerals including ice mineral mixtures show that some orthopyroxenes can have jhk colors very similar to fine grained water frosts in general it is possible that the jhk colors of an ice plus particulate mixture can fall anywhere in the classical j h versus h k diagram thus the diagram cannot be used to distinguish a predominately rock surface from one which is predominantely ice for one specific case an important exception is the case where both the j h and h k colors are 0 2 it appears that such colors indicate a relatively pure icy surface in some cases the diagram might be used as a statistical tool to distinguish between the compositions of surfaces within a class of objects but the validity of such comparisons decreases for different classes such as the main belt asteroids when compared to outer solar system satellites where water ice is more stable

redistribution of water in terrestrial soils at subfreezing temperatures a review of processes and their potential relevance to mars 1 any study of water behavior in the martian regolith should begin with an examination of our current understanding of subsurface water in terrestrial cold regions the terrestrial analog provides a wealth of readily available information to help formulate and test new ideas about possibilities on mars this paper discusses the major mechanisms driving the phenomenal ability of capillary media to redistribute moisture when freezing it examines both thermally induced and freezing induced redistribution of moisture the magnitude of which can vastly exceed the transport expected from fickian diffusion alone if the martian crust is truly water rich then these processes in response to transient thermal disturbances caused by impacts volcanic and magmatic activity changes in climate and potential future human activities may induce substantial changes in the local distribution of subsurface ice

h2o grain size and the amount of dust in mars residual north polar cap in mars north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and h2o grains of comparable size and abundance however metamorphism of such material will gradually lower its albedo by increasing the size of the h2o grains only if the cap is undergoing net annual sublimation as inferred from water vapor observations late summer observations should be of old ice with h2o grain sizes of 100 microns or more ice of this granularity containing 30 percent fine dust has a reflectivity similar to that of dust alone the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less the brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by viking and aged for thousands of years the residual cap surface cannot be old dirty ice it could be old coarse and clean or it could be young fine and dirty this brings into question both the source of the late summer water vapor and the formation rate of laminated terrain

chemical weathering studies in relation to geomorphological research in southeastern canada abstract although chemical weathering provides fundamental information relevant to geomorphology the subject has been overlooked during the 20th century in canada this paper provides an overview of the current state of canadian research on chemical weathering in southeastern canada and takes into account three spatial and temporal contexts 1 the formation of bedrock morphology by chemical weathering 2 occurrences characteristics and age of saprolites and 3 contemporary chemical denudation rates long term geomorphological evolution of southeastern canadian landscapes shows that chemical weathering has played an important role an example is taken from the laurentide region of the canadian shield north of montreal quebec the present topography resulted from the stripping of the former weathering mantle and from the probable subsequent modification of the weathering front first by the action of hillslope processes and rivers and then by glaciers before and during plio pleistocene times the present landscape reflects the timing of the formation of erosion surfaces and of the stripping of the paleozoic cover rocks and exposure of the shield since the late seventies several isolated occurrences of saprolite soil profiles have been discovered in eastern canada and prompted a renewal of the study of these materials about the cenozoic evolution of these regions one of the problems in this field of research is the dating of saprolites and their inclusion in a chronostratigraphic framework along with the other cenozoic surficial deposits and landforms because of the multiple factors involved in the development of secondary minerals in saprolites during the course of weathering it is preferable to distinguish the dating of saprolites from the study of their mineralogical and geochemical evolution fortunately several new techniques are becoming available for the absolute dating of surficial deposits and saprolites including the use of cosmogenic radionuclides saprolites provide a strong potential field of research for our understanding of the geological evolution of eastern canada during the cenozoic contemporary weathering and erosion rates are fields of research that have gained increasing interest recently since modeling landscape geochemical response can be applied to various environmental stress situations such as acidification by rain and forest harvesting rock type may be the main factor explaining the large differences between watersheds in fact variability of cation removal in the temperate zone is probably most closely related to flow paths of water investigations at different scales from entire watersheds to slopes to individual pedons highlight the problem in the catamaran brook watershed new brunswick water chemistry is explained by a mix of groundwater and soil solution from the horizons at the base of the floodplain soils geochemical mass balances based on net outputs give little information on the weathering reactions of primary minerals the weathering products or on the nature of the weathering processes that provide the dissolved load of streams mineralogic and petrographic analysis of selected soil pedons are necessary to determine weathering reactions and their role as sources or sinks for bases silica aluminum and iron in the various compartments through which water percolates before it reaches the stream

distribution of mid latitude ground ice on mars from new impact craters new impact craters at five sites in the martian mid latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice near infrared spectra of the largest example confirm this composition and repeated imaging showed fading over several months as expected for sublimating ice thermal models of one site show that millimeters of sublimation occurred during this fading period indicating clean ice rather than ice in soil pores our derived ice table depths are consistent with models using higher long term average atmospheric water vapor content than present values craters at most of these sites may have excavated completely through this clean ice probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars