the occurrence and significance of biogenic opal in the regolith abstract biogenic opal produced by vascular plants diatoms and siliceous sponges have been found in soils and terrestrial sediments of all continents except antarctica since the middle of the 19th century the opal particles range in size from fine silt to fine sand almost all soils contain detectable opal up to levels of 2 3 and a significant number contain values in excess of 5 even higher values have been found from soils and sediments of all continents in a wide range of soil types the most important factor is poor soil drainage and seasonal to permanent water logging this encourages the proliferation of silica producing organisms such conditions have been found in the soils and aquatic sediments of the monsoonal tropics tropical rain forests temperate forests tropical savanna tropical islands semi arid grasslands and savanna and temperate woodland and grassland the presence of a volcanic substrate also appears favourable in some cases but is not necessary biogenic opal preferentially collects in the a horizon of soils and to a lesser extent in the b horizon this preferential distribution facilitates identification of palaeosols in stacked soil sequences biogenic opal is also a component of windblown dust even in arid environments biogenic opal is significant to regolith processes in a number of ways firstly as in the case in marine environments it is likely to be important in silica cycling and storage because of its greater lability compared to quartz secondly dissolution and reprecipitation of opal a as opal ct or micro quartz may play a role in cementation and silicification of regolith to form silica hardpans and silcrete thirdly the organisms that form biogenic opal can have considerable palaeoenvironmental significance and be valuable in reconstructing regolith evolution finally some forms of biogenic silica in particular sponge spicules can present a health hazard their high abundance in some soils and sediments needs to be considered when assessing the health implications of airborne dust

dissolution of biogenic silica from land to ocean role of salinity and ph the dissolution rates of diatom frustules phytoliths two diatomaceous lake sediments a siliceous ooze from the southern ocean a diatomite deposit and a synthetic amorphous silica were measured in flow through reactors supplied with either seawater or freshwater although the rates varied by more than one order of magnitude among the different siliceous materials for any given solid the rate was systematically higher in seawater than freshwater on average by a factor of five flow through reactor experiments with the diatom frustules and synthetic silica using mixtures of freshwater and seawater indicated that most of the rate increase occurred for seawater fractions between 0 and 50 the observed rate enhancement is attributed to the higher ph of seawater and the catalytic effect of seawater cations on the hydrolysis of siloxane bonds at the silica surface because of their abundance in seawater na and mg2 are mainly responsible for the salinity induced rate increase the large difference in dissolution kinetics between freshwater and seawater helps explain the very efficient recycling of biogenic silica in marine environments compared with freshwater lakes enhanced dissolution at the land ocean transition of biogenic silica produced by terrestrial plants and freshwater diatoms may represent a significant but largely overlooked source of nutrient silicon for estuarine and nearshore marine ecosystems

the fracture of water ice ih a short overview this paper presents a short overview of the fracture of water ice ih topics include the ductile to brittle transition tensile and compressive strength compressive failure under multiaxial loading compressive failure modes and brittle failure on the geophysical scale arctic sea ice cover europa s icy crust emphasis is placed on the underlying physical mechanisms where appropriate comment is made on the formation of high latitude impact craters on mars

biological uptake and accumulation of silica on the amazon continental shelf abstract water column and seabed samples were obtained from 92 stations on the amazon continental shelf during october of 1979 uptake of silica near and southeast of the river mouth began at a salinity of 8 and accounted for 17 of the riverine silica flux to this region uptake northwest of the river mouth began at a salinity of 20 and resulted in 33 removal of the riverine silica flux examination of filtered suspended solids revealed abundant diatoms in the surface waters including coscinodiscus skeletonema synedra and thalassiosira the biological uptake of silica appears to be dependent on three factors turbidity turbulence and nutrient availability there was no evidence of abiological removal of silica in the amazon estuary 75 to 88 of the silica removed from surface waters by diatoms dissolves prior to accumulation in the seabed based on the mean biogenic silica content of shelf sediment 0 25 and estimates of rates of sediment accumulation the biogenic silica accumulation rate on the shelf is 2 1012 g yr which represents only 4 of the dissolved silica supplied by the amazon river biological uptake of silica in estuarine surface waters may not accurately reflect permanent removal of biogenic silica to the seabed because of dissolution which occurs in bottom waters and near the sediment water interface

the fracture of ice on scales large and small arctic leads and wing cracks from observations and calculations of crack patterns in ice it is suggested that a similar mechanism may account for cracking over a wide range of scales

silica dynamics in a pampean lake lake chascomus argentina abstract silica dynamics in a pampean lake lake chascomus chaco pampa plain argentina is described pampean lakes are shallow alkaline ecosystems with circulation pattern corresponding to polymictic lakes due to the nearly continuous vertical mixing that promotes a high concentration of suspended particulate matter and low transparency a silica budget was calculated in lake chascomus in 1999 2000 using a one box model that constitutes the first one for a shallow pampean lake in general terms the dissolved silica in lake chascomus contributed by streams and groundwater the latter responsible for 70 of the incoming dissolved silica was able to support the diatom production development however in the algal bloom period spring and summer the winter input contributed by the streams and groundwater was insufficient and therefore an extra source of dissolved silica was necessary dissolution of silicate mineral phases or silica desorption from metallic oxides might provide the dissolved silica needed for the seasonal increase in diatom abundance

silica diatoms and a freshwater productivity maximum in atlantic coastal plain estuaries chesapeake bay abstract monthly data collected in 1981 from the james york and rappahannock rivers show that dissolved silica silicic acid exhibits two distinct types of longitudinal distributions in these estuaries during the year conservative behavior was observed during winter or when river discharge was high the second distribution occurs when uptake by planktonic diatoms reduces concentrations below the levels attributable to dilution by seawater in all three systems the non conservative behavior is characterized by rapid uptake of silicic acid in the tidal freshwater portion just upstream of the limit of salt intrusion and corresponds to a chlorophyll maximum shown to contain bloom densities of diatoms silicic acid is exhausted below detectable concentrations in the vicinity of the diatom maximum representing more than 98 removal of the riverine source non conservative distributions of total silica silicic acid biogenic silica in this same region indicate deposition of biogenic silica to the sediments at the same time the riverine source is depleted by the diatoms in the freshwater reaches silicic acid is resupplied to the water column in the oligohaline portion of the estuaries this resupply is shown to be significant nearly equal to the amount of silicic acid entering the estuary in river input suggesting complete mineralization of biogenic silica produced in the freshwater zone the spatial distributions described above were observed regularly in all three systems indicating that enhanced phytoplankton production and nutrient regeneration in the vicinity of the transition zone is a natural feature of these partially mixed estuarine rivers possible mechanisms contributing to the accumulation of phytoplankton biomass and the enhanced cycling of silicon are discussed

a model for co isotopic signatures of evolving ground ice in the cold dry environments of earth and mars abstract the basics of the model rego are summarized including diffusive water vapor transport ice content adsorption and the isotopic ratios of the various water species inclusion of a temperature and stress strain solution is also described as are the effects of cracking when the tensile breaking strengths are exceeded cracking is viewed as a multi scale phenomena whereby the larger cracks are produced by chaining together smaller ones after some validation the model is applied to the upper university valley antarctic dry valleys data and to the phoenix landing site at lat 69n on mars for the university valley the model when forced by measured diurnal temperature cycles and known relative humidity reproduces some of the complex the ice content and isotope structure found in the upper university valley ground ice cores the model takes a few hundred years to fill the pores just under the ice table the excess ice observed in the university valley cores can be produced by thermal cracking combined with the diurnal temperature cycle time taken to achieve the observed excess ice content is of order 10 4 years there is limited subsurface data for the phoenix site but there are measured ice table depths surface thermal properties and met variables there is enough to do diurnal and seasonal runs of the rego model as with the university valley the upper few tens of centimeters icing are controlled by the diurnal temperatures largely in the warmer part of the year the observed ubiquitous pore full ice right at the ice table could be produced from a dry soil in about 10 3 a and the nearly pure ice patches could be produced by the cracking diffusion mechanism in about million years if shear stresses are included emplacement of ice down to 10 m is possible using the seasonal temperature cycle and cracking excess ice in the upper meter could produced by the model in about 6 10 6 a if the temperature at the phoenix site was 10 20 deg warmer

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

stability of massive ground ice bodies in university valley mcmurdo dry valleys of antarctica using stable o h isotope as tracers of sublimation in hyper arid regions abstract to date studies of the stability of subsurface ice in the mcmurdo dry valleys of antarctica have been mainly based on climate based vapor diffusion models in university valley 1800 m a small glacier is found at the base of the head of the valley and adjacent to the glacier a buried body of massive ice was uncovered beneath 20 40 cm of loose cryotic sediments and sandstone boulders this study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable o h isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends the results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period the contrasting 18 o profiles and regression slope values between the uppermost 6 cm of the buried massive ice upward convex 18 o profile and s d 18o 5 1 and that below it progressive increase in 18 o and s d 18o 6 4 suggest independent post depositional processes affected the isotope composition of the ice the upward convex 18 o profile in the uppermost 6 cm is consistent with the ice undergoing sublimation using a sublimation and molecular diffusion model and assuming that diffusion occurred through solid ice the sublimation rate needed to fit the measured 18 o profile is 0 2 10 3 mm yr 1 a value that is more similar to net ice removal rates derived from 3 he data from cobbles in beacon valley till 7 0 10 3 mm yr 1 than sublimation rates computed based on current climate 0 1 0 2 mm yr 1 we suggest that the climate based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters particularly the nature and thermo physical properties of the overlying sediments i e temperature humidity pore structure and ice content grain size

silicon isotope compositions of dissolved silicon and suspended matter in the yangtze river china abstract silicon isotope compositions of main channel samples of the yangtze river were systematically investigated along with their chemical compositions the concentration of suspended matter in the yangtze river tends to decrease from the upper reaches to the lower reaches corresponding to settling of the sediments in the lakes and reservoirs due to reduction of the velocity of water flow the silica contents of suspended matter vary from 52 1 to 56 9 and their 30si values vary from 0 to 0 7 both similar to those of shales from the upper to lower reaches the silica contents of suspended matter tend to increase whilst their 30si values tend to decrease both trends reflect the increase of clay minerals and decrease of carbonates in suspended matter the concentrations of dissolved silicon vary from 97 to 121 mol l and their 30si values vary over a wide range from 0 7 to 3 4 from the upper to lower reaches dissolved silica concentrations tend to decrease and their 30si values tend to increase these trends mainly reflect the change of chemical and isotopic characteristics of the tributaries from the upper to lower reaches the major factors responsible for these changes may be the high meteoric precipitation and significant silicon absorption by grass in wetlands and rice in paddy fields in drainage areas of the middle and lower reaches there is no correlation between 30si of dissolved silicon and that of suspended matter the 30sidiss spm values vary over a wide range of 1 0 3 7 indicating that 1 they are out of isotopic equilibrium 2 dissolved silicon and the associated suspended matter do not belong to one physico chemical system and 3 isotopic exchange rate between them is very slow the 30si value of dissolved silicon output from the yangtze river to the east sea is estimated to be 3 0 much higher than the values reported for the amazon and congo rivers this increases the 30si range of dissolved silicon in the world s rivers from 0 4 1 2 to 0 4 3 4

early diagenesis of biogenic silica in the amazon delta alteration authigenic clay formation and storage deltaic environments are commonly assumed to be relatively minor sites of biogenic silica burial because of the small quantities of opaline silica detected by most operational analytical techniques rapid conversion of biogenic silica into authigenic silicates is also often discounted as a significant control on oceanic silica budgets a variety of evidence for extensive early diagenetic alteration of biogenic silica in rapidly accumulating amazon delta sediments indicates that both of these general assumptions are unjustified apparent lack of significant biogenic silica storage in deltaic environments particularly in the tropics may be largely an artifact of operational definitions that do not include early diagenetic products of biogenic silica biogenic silica particles buried in suboxic amazon delta deposits can be unaltered partially dissolved covered with aluminosilicate or metal rich coatings or completely reconstituted into authigenic k fe rich aluminosilicate minerals pore water k mg f si and solid phase distributions direct observations of particles laboratory experiments and depositional context indicate that authigenic clays form rapidly 1 yr in the seasonally reworked surface layer 0 5 2 m of the delta topset and are disseminated during sediment remobilization fe al oxide rich debris derived from the tropical drainage basin is an abundant reactant and thus the supply of biogenic silica is a major control on the amount of clay formed the mild 1 na2co3 alkaline leach procedure commonly used to estimate biogenic silica was modified to include an initial mild leach step with 0 1n hcl to remove metal oxide coatings and to activate poorly crystalline authigenic phases for alkaline dissolution well crystallized clays are not significantly affected by this modification nor is bulk amazon river bed sediment the two step procedure indicates that 90 of the biogenic silica originally present in deposits is converted to clay or otherwise altered raising the effective quantity of biogenic silica stored from 33 to 296 mol si g 1 1 8 sio2 biogenic si stored in the delta increases away from the river mouth across shelf and along the dispersal system where primary production is highest the k si ratio of labile authigenic material is 0 19 mol mol 1 far higher than amazon river suspended matter 0 07 mol mol 1 diagenetic models indicate formation rates in the mobile sediment layer of 2 8 mol k g 1 yr 1 16 mol si g 1 yr 1 inclusion of authigenic alteration products of biogenic silica in estimates of reactive si burial increases the deltaic storage of riverine si to 22 of the amazon river input the rapid formation of aluminosilicates from biogenic sio2 seawater solutes and remobilized fe al oxides represents a form of reverse weathering rapid reverse weathering reactions in tropical muds and deltaic deposits the largest sediment depocenters on earth confirms the general importance of these processes in oceanic elemental cycles

biogenic silica in wetlands and their relationship with soil and groundwater biogeochemistry in the southeastern of buenos aires province argentina although phytoliths constitute part of the wetland suspended load there are few studies focused on the quantification of them in the biogenic silica bsi pool so the aim of this paper is both to determine bsi content diatoms and phytoliths and its relationship with dissolved silica in surface waters and the influence of soil and groundwater si biogeochemistry in los padres wetland buenos aires province argentina in the basin of the los padres wetland dissolved silica dsi concentration is near 840 232 mol l and 211 83 275 92 mol l in groundwaters and surface waters respectively bsi represents an 5 6 22 1 of the total suspension material and 8 34 of the total mineralogical components of the wetland bottom sediments dsi and bsi vary seasonally with highest bsi content diatoms specifically during the spring summer in correlation to the lowest dsi concentration dsi 660 917 5 mol l and phytolith 3 35 5 84 concentrations in the inflow stream are higher than in the wetland and its outflow stream 19 1 113 mol l 0 45 3 2 respectively probably due to the high phytolith content in soils the high silica concentration in the soil solution and the groundwater inflow diatom content 5 16 8 in the wetland and its outflow stream is higher than in the inflow stream 0 45 1 97 controlling dsi in this system the understanding of the groundwater surface water interaction in an area is a significant element for determining the different components and the role that they play on the local biogeochemical cycle of si

magmatic lithospheric heating and weakening during continental rifting a simple scaling law a 2 d thermomechanical rifting model and the east african rift system 1 continental rifting is accompanied by lithospheric thinning and decompressional melting after extraction melt is intruded at shallower depth thereby heating and weakening the lithosphere in a feedback mechanism this weakening may assist rifting and melt production a one dimensional kinematic lithospheric thinning model is developed including decompressional melting and intrusional magma deposition the intrusional heating effect is determined as a function of thinning rate and amount melting parameters potential temperature and the depth range of emplacement the temperature increases approximately proportionally to the square root of the thinning rate and to the square of the supersolidus potential temperature simple scaling laws are derived allowing predicting these effects and the surface heat flux for arbitrary scenarios two dimensional thermomechanical extension models are carried out for a multicomponent crust mantle two phase melt matrix system with a rheology based on laboratory data including magmatic weakening in good agreement with the 1 d kinematic models it is found that the lithosphere may heat up by several 100 k this heating enhances viscous weakening by one order of magnitude or more in a feedback mechanism rifting is dynamically enforced leading to a significant increase of rift induced melt generation including the effect of lateral focusing of magma toward the rift axis the laws are applied to different segments of the east african rift system the amount of intrusional heating increases with maturity of the rift from o 10 k to up to 200 k or 400 k at the afar rift depending on the depth range of the magmatic emplacement

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

paleosols on late cainozoic loessic sequences in the northeastern side of tandilia range buenos aires argentina abstract the purpose of this work is to describe and characterize paleosols from late cainozoic loessic sequences in the northeastern flank of tandilia range pedological and non pedological levels are described considering the vertical thickness color texture and structure and horizontal lateral pattern development mineralogical grain size physico chemical features are analyzed in type profiles this study recognizes two groups of paleosols associated with distinct paleoenvironmental conditions i paleosols which are regionally continuous and extensive related to moisture conditions wetter than the present ones showing truncated and superimposed profiles ii paleosols related to water bodies showing uneven distribution which are mainly topographically controlled sediments that have undergone pedogenesis are identified by their morphological physico chemical textural and mineralogical characteristics and bioturbation features the history of pedogenesis and erosion is related to the alternating humid arid climatic cycles that have affected the region since the plio pleistocene to the present

temperature response of mars to milankovitch cycles 1 on mars annual mean surface temperature near 60 latitude varies predominately with precession and is not closely related to annual mean insolation based on the last few million years of orbital history the precession cycle dominates in a narrow latitude range 54 65 in which the margins of the two ice rich permafrost layers in each hemisphere happen to lie while mean annual temperature at other latitudes is controlled by the obliquity cycle the phenomenon already exists on an airless uniform body in mars orbit where this latitude range shifts to 62 74 on both hemispheres and is closely related to temperature amplitude dependent reradiation into space

deuteronomy a puzzle of deuterium and oxygen on mars mars is covered by channels that were likely formed by liquid water sometime in its past among the very few available clues to a wetter and warmer ancient climate on mars are the isotopic signatures left by processes that have modified its atmosphere over time in their research commentary yung and kass discuss two sets of results in the same issue krasnopolsky et al have used the hubble space telescope to detect the presence of deuterium in the upper atmosphere of mars and farquhar et al report measurements of the martian meteorite alh84001 showing that the oxygen isotopes in the carbonate are fractionated with respect to silicate minerals the findings suggest the presence of chemical processes operating in mars atmosphere that have yet to be fully understood

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

terrestrial ecosystems and the global biogeochemical silica cycle 1 most research on the global si cycle has focused nearly exclusively on weathering or the oceanic si cycle and has not explored the complexity of the terrestrial biogeochemical cycle the global biogeochemical si cycle is of great interest because of its impact on global co2 concentrations through the combined processes of weathering of silicate minerals and transfer of co2 from the atmosphere to the lithosphere a sizable pool of si is contained as accumulations of amorphous silica or biogenic silica bsi in living tissues of growing plants known as phytoliths and after decomposition of organic material as remains in the soil the annual fixation of phytolith silica ranges from 60 200 tmol yr 1 and rivals that fixed in the oceanic biogeochemical cycle 240 tmol yr 1 internal recycling of the phytolith pool is intense with riverine fluxes of dissolved silicate to the oceans buffered by the terrestrial biogeochemical si cycle challenging the ability of weathering models to predict rates of weathering and consequently changes in global climate consideration must be given to the influence of the terrestrial bsi pool on variations in the global biogeochemical si cycle over geologic time and the influence man has had on modifying both the terrestrial and aquatic biogeochemical 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

distribution and state of h2o in the high latitude shallow subsurface of mars abstract a quantitative model of the state distribution and migration of water in the shallow martian regolith is presented reported results are confined to the region of the planet greater than 40 lat the calculations take into account 1 expected thermal variations at all depths latitudes and times resulting from seasonal and astronomically induced insolation variations 2 variations in atmospheric ph2o and pco2 resulting from polar insolation variations and regolith adsorptive equilibria 3 feedback effects related to latent heat and albedo variations resulting from condensation of atmospheric constituents 4 two possible regolith mineralogies 5 variable total h2o content of the regolith 6 kinetics of h2o transport through the martian atmosphere and regolith and 7 equilibrium phase partitioning of h2o between the condensed adsorbed and vapor phases results suggest that the adsorptive capacity of the regolith is important in controlling the state and distribution of high latitude h2o unweathered mafic silicates favor the development of shallow ground ice at all temperate and polar latitudes while heavily weathered clay like regolith materials leads to a deeper ground ice interface and far more extensive quantities of adsorbed h2o the capacity of the high latitude regolith for storage of h2o and the total mass of h2o exchanged between the atmosphere polar cap and subsurface over an obliquity cycle is found to be relatively independent of mineralogy the maximum exchanged volume is found to be 3 0 104 km3 of ice per cycle implications for the history of the polar caps and the origin of the layered terrain are discussed results also suggest that seasonal thermal waves act to force adsorbed h2o into the solid phase over a wide variety of latitude obliquity conditions seasonal phase cycling of regolith h2o is most common at high latitudes and obliquities such phase behavior is highly dependent on regolith mineralogy in a highly weathered regolith adsorbed h2o is annually forced into the solid phase at all latitudes 40 at obliquities greater than approximately 25 seasonal adsorption freezing cycles which are predicted here may produce geomorphologic signatures not unlike those produced by terrestrial freeze thaw cycles