recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

persistence in intra annual snow depth distribution 1 measurements and topographic control 1 terrestrial and airborne laser scanning tls and als techniques have only recently developed to the point where they allow wide area measurements of snow distribution in varying terrain in this paper we present multiple tls measurements showing the snow depth development for a series of precipitation events we observe that the pattern of maximum accumulation is similar for the two years presented here correlation up to r 0 97 storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms based on the strong link between accumulation patterns and terrain we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns this approach of winstral et al 2002 which describes wind exposure and shelter was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance furthermore a high sensitivity to the local wind direction was demonstrated we suggest that winstral et al s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

pattern recognition of air photographs for estimation of snow reserves a certain snow covered area determined from air photographs in different years can contain different volumes of snow the pattern recognition of snow fields reveals whether the snow reserves are relatively high or low for the given snow coverage it also signals a short terra increase of the snow covered area by summer snowfall

integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the mekong delta abstract arsenic is contaminating the groundwater of holocene aquifers throughout south and southeast asia to examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of as within soils sediments in the mekong river delta a 50 km2 field site was established near phnom penh cambodia where aqueous as concentrations are dangerously high and where groundwater retrieval for irrigation is minimal dissolved as concentrations vary spatially ranging up to 1300 g l in aquifer groundwater and up to 600 g l in surficial clay pore water groundwaters with high as concentrations are reducing with negligible dissolved o2 and high concentrations of fe ii nh 4 and dissolved organic c within near surface environments these conditions are most pronounced in sediments underlying permanent wetlands often found within oxbow channels near the mekong river there labile c co deposited with as bearing fe hydr oxides under reducing conditions drives the reductive mobilization inclusive of fe and as reduction of as here conditions are described under which as is mobilized from these sediments and near surface as release is linked to aquifer contamination over long time periods 100s to 1000s of years site biogeochemistry is coupled with extensive hydrologic measurements and accordingly a comprehensive interpretation of spatial as release and transport within a calibrated hydraulic flow field is provided of an as contaminated aquifer that is representative of those found throughout south and southeast asia

geomorphic controls on groundwater arsenic distribution in the mekong river delta cambodia natural arsenic contamination of groundwater is a severe public health crisis affecting nearly 60 million people in south asia and southeast asia alone contamination is spatially heterogeneous and results from the coupled microbial decomposition of organic matter and reductive dissolution of arsenic bearing iron minerals here we demonstrate that elevated arsenic concentrations arise in regions of recent organic matter deposition and thus are controlled by fluvial geomorphic processes arsenic contamination is best expressed within recent geomorphic features such as docked islands scroll bars and avulsions within these features the deposition of rapidly buried reactive organic matter facilitates microbial iron reduction and arsenic release ultimately the organic matter supply is exhausted and the conditions necessary for soluble arsenic to persist diminish

an analysis of snow cover patterns in a small alpine catchment snow cover patterns in a 9 4 km2 basin in the austrian alps are examined during spring and summer 1989 digital mono plotting from oblique aerophotographs is used for mapping on the basis of a square grid with 25 m spacing snow cover as mapped during nine surveys is analysed as a function of elevation and slope during winter conditions the snow cover is found to be much better related to these terrain features than during the late ablation period

estimating the mean areal snow water equivalent by integration in time and space by modelling the snow accumulation process in time and space as sums of random gamma distributed variables the mean areal snow water equivalent swe can be estimated in the methodology we make use of the fact that sums of gamma distributed variables with a certain set of parameters also are gamma distributed variables with parameters being functions of the original and the number of summations the measured snow swe at a point and at a certain time t can thus be seen as the accumulation or the sum of snowfall events from the beginning of the snowfall season up to t the integration of these points over an area can be seen as another summation from snow pillows and precipitation gauges the value of daily accumulated precipitation snow has been found to be well represented by a two parameter gamma distribution this distribution has been found to be representative for large areas the number of events where the precipitation was accumulated can be estimated from snow pillows situated in the area the mean snow coverage over an area which represents the summation of the individual points over an area can be derived from satellite images represented in a gis the methodology is tested for two nested catchments of size 4723 km 2 and 19 832 km 2 in a mountainous area in southern norway for ten satellite scenes the results are compared with simulated snow reservoirs using a rainfall runoff model and found to agree well large discrepancies in the snow reservoirs reservoirs using a rainfall runoff model and found to agree well large discrepancies in the snow reservoirs between the proposed method and the rainfall runoff model are found in late spring and are probably due to errors in the estimated mean snow coverage derived from the satellite images

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

hopane sterane and n alkane distributions in shallow sediments hosting high arsenic groundwaters in cambodia the presence of elevated as in ground waters exploited for drinking water and irrigation in south east asia is causing serious impacts on human health a key mechanism that causes the mobilization of as in these waters is microbially mediated reductive transformation of as bearing fe iii hydrated oxides and the role of degradable organic matter om in this process is widely recognized a number of different types of om that drive as release in these aquifers have been suggested including petroleum derived hydrocarbons naturally seeping into shallow sediments from deeper thermally mature source rocks however the amount of information on the characteristics of the om in south east asian aquifers is limited here the organic geochemical analyses of the saturated hydrocarbon fractions and radiocarbon analysis of two additional sites in se asia are reported the results show that the om in a given sedimentary horizon likely derives from multiple sources including naturally occurring petroleum the importance of naturally occurring petroleum as one of the sources was clearly indicated by the n alkane cpi of approximately 1 the presence of an unresolved complex mixture and hopane dominated by 17 h 21 h hopanes and sterane distribution patterns the results also indicate that the om in these aquifers varies tremendously in content character and potential bioavailability furthermore the presence of petroleum derived om in sediments at both sites doubles the number of locations where their presence has been observed in association with as rich shallow aquifers suggesting that the role of petroleum derived om in microbially mediated as release might occur over a wider range of geographical locations than previously thought

redox control of arsenic mobilization in bangladesh groundwater abstract detailed hydrochemical measurements 34sso4 and 3h analyses were performed on 37 groundwater samples collected during february 1999 january and march 2000 from 6 locations in eastern and southeastern bangladesh to examine redox processes that lead to as mobilization in groundwater the study sites were chosen based on available nation wide as surveys to span the entire spectrum of as concentrations in bangladesh groundwater and to represent 3 of 5 major geological units of the ganges brahmaputra delta uplifted pleistocene terrace fluvial flood plain and delta plain arsenic was found to be mobilized under fe reducing conditions in shallow aquifers 50 g l or 0 7 m were always accompanied by high dissolved hco3 4 mm and were close to saturation with respect to calcite groundwater enriched in as 200 800 g l or 2 7 10 7 m and phosphate 30 100 m but relatively low in dissolved fe 5 40 m probably resulted from re oxidation of reducing as and fe enriched water this history was deduced from isotopic signatures of 34sso4 and 3h2o 3h to delineate the nature of redox changes for some of the reducing groundwaters in contrast as is not mobilized in presumed pleistocene aquifers both shallow 30 60 m and deep 150 270 m because conditions were not reducing enough due to lack of sufficient o2 demand

initiation of the mekong river delta at 8 ka evidence from the sedimentary succession in the cambodian lowland abstract modern deltas are understood to have initiated around 7 5 9 ka in response to the deceleration of sea level rise this episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea level rises the initial stage of the mekong river delta one of the world s largest deltas is well recorded in cambodian lowland sediments this paper integrates analyses of sedimentary facies diatom assemblages and radiocarbon dates for three drill cores from the lowland to demonstrate holocene sedimentary evolution in relation to sea level changes the cores are characterized by a tripartite succession 1 aggrading flood plain to natural levee and tidal fluvial channel during the postglacial sea level rise 10 8 4 ka 2 aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea 8 4 6 3 ka and 3 a prograding fluvial system on the delta plain 6 3 ka to the present the maximum flooding of the sea occurred at 8 0 0 1 ka 2000 years before the mid holocene sea level highstand and tidal flats penetrated up to 20 50 km southeast of phnom penh after a period of abrupt 5 m sea level rise at 8 5 8 4 ka the delta progradation then initiated as a result of the sea level stillstand at around 8 7 5 ka another rapid sea level rise at 7 5 7 ka allowed thick mangrove peat to be widely deposited in the cambodian lowland and the peat accumulation endured until 6 3 ka since 6 3 ka a fluvial system has characterized the delta plain and the fluvial sediment discharge has contributed to rapid delta progradation the uppermost part of the sedimentary succession composed of flood plain to natural levee sediments reveals a sudden increase in sediment accumulation over the past 600 1000 years this increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the mekong as with other asian rivers

distributed snow process modelling an image processing approach an approach to spatially distribute a snow process model by segmenting images of land cover terrain and snow properties is reported a small 1 7 ha study area with an existing database was selected for this preliminary evaluation the methodology was carried out over a relatively flat valley bottom at camp grayling michigan meteorological measurements on two sides of the area showed only small differences so uniform meteorological variables were assumed over the site initial snow cover conditions were reconstructed and were distributed over the area using snow maps and sparse snow pit measurements one metre resolution terrain soil vegetation and snow type maps were individually processed into class maps these layers were then combined to produce a segmented class map where the attributes from the data layers were known for each class a one dimensional model of snow processes was run for each class then the results were mapped back into images shallow snow conditions provided high sensitivity of ablation patterns to meteorological conditions over a 72 h period the model performance was assessed by comparing predicted and observed ablation patterns the error in total snow covered area was less than 9 however the location errors were greater predicted snow where no snow was observed and observed snow where no snow was predicted extensive error analysis was not justified because of the lack of multiple point measurements of snow properties

tracing organic matter composition and distribution and its role on arsenic release in shallow cambodian groundwaters biogeochemical processes that utilize dissolved organic carbon are widely thought to be responsible for the liberation of arsenic from sediments to shallow groundwater in south and southeast asia the accumulation of this known carcinogen to hazardously high concentrations has occurred in the primary source of drinking water in large parts of densely populated countries in this region both surface and sedimentary sources of organic matter have been suggested to contribute dissolved organic carbon in these aquifers however identification of the source of organic carbon responsible for driving arsenic release remains enigmatic and even controversial here we provide the most extensive interrogation to date of the isotopic signature of ground and surface waters at a known arsenic hotspot in cambodia we present tritium and radiocarbon data that demonstrates that recharge through ponds and or clay windows can transport young surface derived organic matter into groundwater to depths of 44 m under natural flow conditions young organic matter dominates the dissolved organic carbon pool in groundwater that is in close proximity to these surface water sources and we suggest this is likely a regional relationship in locations distal to surface water contact dissolved organic carbon represents a mixture of both young surface and older sedimentary derived organic matter ground surface water interaction therefore strongly influences the average dissolved organic carbon age and how this is distributed spatially across the field site arsenic mobilization rates appear to be controlled by the age of dissolved organic matter present in these groundwaters arsenic concentrations in shallow groundwaters 20 m groundwaters we suggest that while the rate of arsenic release is greatest in shallow aquifer sediments arsenic release also occurs in deeper aquifer sediments and as such remains an important process in controlling the spatial distribution of arsenic in the groundwaters of se asia our findings suggest that any anthropogenic activities that alter the source of groundwater recharge or the timescales over which recharge takes place may also drive changes in the natural composition of dissolved organic carbon in these groundwaters such changes have the potential to influence both the spatial and temporal evolution of the current groundwater arsenic hazard in this region

topographic meteorologic and canopy controls on the scaling characteristics of the spatial distribution of snow depth fields 1 in this study lidar snow depths bare ground elevations topography and elevations filtered to the top of vegetation topography vegetation in five 1 km 2 areas are used to determine whether the spatial distribution of snow depth exhibits scale invariance and the control that vegetation topography and winds exert on such behavior the one dimensional and mean two dimensional power spectra of snow depth exhibit power law behavior in two frequency intervals separated by a scale break located between 7 m and 45 m the spectral exponents for the low frequency range vary between 0 1 and 1 2 for the one dimensional spectra and between 1 3 and 2 2 for the mean twodimensional power spectra the spectral exponents for the high frequency range vary between 3 3 and 3 6 for the one dimensional spectra and between 4 0 and 4 5 for the mean two dimensional spectra such spectral exponents indicate the existence of two distinct scaling regimes with significantly larger variations occurring in the larger scale regime similar bilinear power law spectra were obtained for the fields of vegetation height with crossover wavelengths between 7 m and 14 m further analysis of the snow depth and vegetation fields together with wind data support the conclusion that the break in the scaling behavior of snow depth is controlled by the scaling characteristics of the spatial distribution of vegetation height when snow redistribution by wind is minimal and canopy interception is dominant and by the interaction of winds with features such as surface concavities and vegetation when snow redistribution by wind is dominant

scaling properties and spatial organization of snow depth fields in sub alpine forest and alpine tundra this paper reports on a study analysing the spatial distribution functions the correlation structures and the power spectral densities of high resolution lidar snow depths 1 m in two adjacent 500 m 500 m areas in the colorado rocky mountains one a sub alpine forest the other an alpine tundra it is shown how and why differences in the controlling physical processes induced by variations in vegetation cover and wind patterns lead to the observed differences in spatial organization between the snow depth fields of these environments in the sub alpine forest area the mean of snow depth increases with elevation while its standard deviation remains uniform in the tundra subarea the mean of snow depth decreases with elevation while its standard deviation varies over a wide range the two dimensional correlations of snow depth in the forested area indicate little spatial memory and isotropic conditions while in the tundra they indicate a marked directional bias that is consistent with the predominant wind directions and the location of topographic ridges and depressions the power spectral densities exhibit a power law behaviour in two frequency intervals separated by a break located at a scale of around 12 m in the forested subarea and 65 m in the tundra subarea the spectral exponents obtained indicate that the snow depth fields are highly variable over scales larger than the scale break while highly correlated below based on the observations and on synthetic snow depth fields generated with one and two dimensional spectral techniques it is shown that the scale at which the break occurs increases with the separation distance between snow depth maxima in addition the breaks in the forested area coincide with those of the corresponding vegetation height field while in the tundra subarea they are displaced towards larger scales than those observed in the corresponding vegetation height field

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

interior structure and seasonal mass redistribution of mars from radio tracking of mars pathfinder doppler and range measurements to the mars pathfinder lander made using its radio communications system have been combined with similar measurements from the viking landers to estimate improved values of the precession of mars pole of rotation and the variation in mars rotation rate the observed precession of 7576 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition the estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps

modelling snow melt and snowcover depletion in a small alpine cirque canadian rocky mountains spatial and temporal patterns of areal snowcover depletion scd were studied over a small 0 6 km 2 alpine cirque within the canadian rocky mountains using a combined approach of daily acquisition of remotely sensed imagery together with meteorological observations and snowmelt modelling digital terrestrial photographs were georeferenced using a novel software tool together with a high resolution digital elevation model and used to derive measurements of fractional snowcovered area sca over the cirque manual snow surveys carried out in the pre melt period were used to describe the initial frequency distribution of snow water equivalent swe values over the cirque and indicated a lognormal distribution of swe when surveys were stratified by terrain features rates of snowmelt were simulated using a physically based snowmelt energy balance model snobal driven by observed meteorological conditions at a nearby station which were adjusted for slope orientation and exposure by making corrections to observed incoming shortwave and longwave radiation components in the cold regions hydrological model platform simulated melt rates were then applied to the approximated swe distributions to model the decline in sca over the spring the model was found to perform well for the simulation of snowmelt based on point observations of swe at the meteorological station and produced a close correspondence between simulated and observed scd curves representing two opposing slopes within the cirque the results show that both the pre melt distributions of swe and the spring melt rates exhibit considerable spatial variability between distinct slope units within the cirque and that this variability has a significant impact on simulated scd assuming a unimodal pre melt frequency distribution and conditions of spatially uniform snowmelt over complex terrain such as this can lead to large errors in the simulation results it is suggested that modelling applications intended to represent snowmelt dynamics and areal scd in similar alpine environments consider the effects of spatial variation in swe distribution and melt energetics between slopes

release of arsenic to deep groundwater in the mekong delta vietnam linked to pumping induced land subsidence deep aquifers in south and southeast asia are increasingly exploited as presumed sources of pathogen and arsenic free water although little is known of the processes that may compromise their long term viability we analyze a large area 1 000 km2 of the mekong delta vietnam in which arsenic is found pervasively in deep pliocene miocene age aquifers where nearly 900 wells at depths of 200 500 m are contaminated there intensive groundwater extraction is causing land subsidence of up to 3 cm y as measured using satellite based radar images from 2007 to 2010 and consistent with transient 3d aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988 we propose a previously unrecognized mechanism in which deep groundwater extraction is causing interbedded clays to compact and expel water containing dissolved arsenic or arsenic mobilizing solutes e g dissolved organic carbon and competing ions to deep aquifers over decades the implication for the broader mekong delta region and potentially others like it across asia is that deep untreated groundwater will not necessarily remain a safe source of drinking water

impact basin relaxation as a probe for the thermal history of pluto we investigate viscoelastic impact basin relaxation on pluto for a variety of thermal evolution scenarios encompassing both convective and conductive ice shells basins smaller than 200 km in diameter do not relax appreciably while relaxation fractions can be up to 60 for large impact basins the main control on basin relaxation is the amount of radiogenic heat produced in the rocky core our results are insensitive to the formation time of the basin the ice reference viscosity adopted and the presence absence of a subsurface ocean other volatiles such as co2 or nh3 if present in the ice shell in sufficient quantities could increase the predicted relaxation fraction of basins relaxation causes extensional stresses interior to the basin the orientation of the resulting tectonic features is controlled by the effective elastic thickness beneath the basin future observations of the relaxation states and tectonics of impact basins are therefore likely to provide a key constraint on pluto s thermal history

snow control on active layer thickness in steep alpine rock walls aiguille du midi 3842 m a s l mont blanc massif since the early 2000s a remarkable amount of rockfalls has been observed in permafrost areas of the mid latitude mountain ranges concurrently to hot summers this study explores the seasonal thaw st in permafrost rock walls of the aiguille du midi site 3842 m a s l mont blanc massif we first analyse six years of temperature records in three 10 m deep boreholes against air temperature at and a four year time series of pictures showing the snow conditions on two rock faces then we test the sensitivity of the active layer against eight snow fall scenarios using the 1 d surface energy balance and heat conduction model cryogrid 3 forced by in situ measurements from a vertical face snow falls occur all the year round at this elevation and play an important role for the active layer thickness alt but the snow cover and its control are highly heterogeneous a long lasting of a snow cover during spring early summer delays the st and reduces the alt the thicker and the more spatially continuous is the snow cover the stronger are the delay and alt reduction convective clouds could also reinforce this pattern the summer at and heat waves are the dominant controlling factors of the alt but summer snow falls can sometimes persist for several days on the rock surface and reduce the effect of the heat waves active layer can thicken during the early fall except if the snow starts to accumulate on the rock surface and favours the refreezing the timing of the snow fall is the most critical parameter to determine the snow effect on the alt this study suggests that the characteristics of the bedrock and snow accumulation steepness surface roughness and sun exposure must be taken into account to better understand the formation and changes of the active layer and its possible implications for rockfall triggering

snow accumulation distribution inferred from time lapse photography and simple modelling the spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments many snow redistribution processes such as avalanching slushflow or wind drift are controlled by topography but their modelling remains challenging in situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution in this respect time lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access in this paper the snow accumulation distribution of an alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography the comparison of the resulting end of winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements on average over the ablation season the observed melt out pattern can be reproduced correctly in 93 of the area visible from the fixed camera the relations between inferred snow accumulation distribution and topographic variables indicate large scatter however a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation copyright 2010 john wiley sons ltd

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

tidally induced surface displacements external potential variations and gravity variations on mars abstract we have used and extended roosbeek s tidal potential for mars to calculate tidal displacements gravity variations and external gravitational potential variations the tides on mars are caused by the sun and to a lesser degree by the natural satellites phobos 8 relative to the sun and deimos 0 08 relative to the sun to determine the reaction of mars to the tidal forcing the love numbers h l and k and the gravimetric factor were calculated for interior models of mars with different state density and radius of the core and for models which include mantle anelasticity the latitude dependence and frequency dependence of the love numbers have been taken explicitly into account the love numbers are about three times smaller than those for the earth and are very sensitive to core changes e g a difference of about 30 is found between a model with a liquid core and an otherwise similar model with a solid core tidal displacements on mars are much smaller than on earth due to the smaller tidal potential but also due to the smaller reaction of mars smaller love numbers for both the tidal diplacement and the tidal external potential perturbations the tidal signal is at the limit of detection and is too small to permit properties of mars s interior to be inferred on the other hand the phobos tidally induced gravity changes which are subdiurnal with typical periods shorter than 12 h can be measured very precisely by the very broad band seismometer with thermal control of the seismological experiment seis of the upcoming netlander mission it is shown that the phobos induced gravity tides could be used to study the martian core

redox controls on arsenic enrichment and release from aquifer sediments in central yangtze river basin abstract more than 100 million people in asia are presently exposed to groundwater with arsenic as concentrations exceeding the world health organization standard of 10 g l 1 arsenic contaminated groundwater within basins of the central portion of the yangtze river has recently been reported but the processes controlling arsenic concentrations have yet to be resolved we examined the hydrologic and geochemical factors controlling arsenic within the jianghan plain an inland sedimentary basin of the yangtze river where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing schaefer et al 2016 hydrologic fluctuations alter redox conditions in the aquifer leading to oscillations between arsenic iron reduction and oxidation here we investigate the depth distribution of solid and aqueous phase iron and arsenic species and through a series of laboratory manipulations constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations in sediment incubations from 20 m below the surface where solid phase arsenic concentrations exceed 100 mg kg 1 both unamended and glucose amended sediment samples result in arsenic release to the aqueous phase in situ carbon was capable of promoting as release in the sediment in contrast sediment batch incubations from other depths resulted in limited as release solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods in sediments below the as enriched zone glucose amendment resulted in arsenic reduction but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the jianghan plain aquifer leads to rapid release of as to groundwater arsenic release from sediments at 20 m depth is sufficient to explain arsenic concentrations throughout the aquifer and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater

interannual persistence of the seasonal snow cover in a glacierized catchment knowledge of the spatial snow distribution and its interannual persistence is of interest for a broad spectrum of issues in cryospheric sciences in this study snow depths derived from airborne laser scanning are analyzed for interannual persistence of the seasonal snow cover in a partly glacierized mountain area 36 km2 at the end of five accumulation periods the snow covered area varied by 16 of its temporal mean mean snow depth of the total area ranged by a factor of two 1 31 2 58 m with a standard deviation of 0 42 m interannual correlation coefficients of snow depth distribution were in the range 0 68 0 84 of the investigated area 75 was found to be interannually persistent the remaining area showed variable snow cover from year to year caused by occasional avalanches and changes in surface topography as a result of glacier retreat snow cover underwent a change from a homogeneous distribution on the former glacier surface to a more heterogeneous snow cover in the recently deglaciated terrain a geostatistical analysis shows interannual persistence in scaling behavior of snow depth in ice free terrain with scale break distances at 20 m scale invariant behavior of snow depth is indicated over 100 m on smooth glacier surfaces

mars time variable gravity and its determination simulated geodesy experiments 1 the seasonal carbon dioxide co2 cycle on mars results in a time variable global redistribution of mass these large scale variations are associated with changes in the gravity field mainly in the two zonal gravity coefficients and which have been recently evaluated from doppler tracking data of the mars global surveyor mgs spacecraft in the present study we calculated these variations from the mass redistribution obtained from outputs of two general circulation models gcm as well as from co2 thickness measurements by the high energy neutron detector hend instrument on board the mars odyssey spacecraft and compared them to the observations tracking observations provide one of the most direct measures of the global scale atmospheric mass cycle however the associated uncertainties are relatively large partly because the low degree zonals obtained from a single orbiter tracking analysis are contaminated by higher degree harmonics which are shown to have nonnegligible seasonal variations thus we investigated possibilities to improve the determination of the time variable gravity field by means of simulated geodesy experiments additional radio tracking of a second spacecraft with suitable orbital characteristics was shown to be able to separate the higher degree geodetic signatures radio links between landers on the martian surface and a near polar orbiter can further better estimate especially the even zonals

crab burrows as conduits for groundwater surface water exchange in bangladesh groundwater recharge affects water budgets and groundwater quality on the deltas and floodplains of south and southeast asia rain and flooding rivers recharge groundwater during the monsoon irrigated rice fields and surface water bodies recharge aquifers during the dry season groundwater throughout the region is severely contaminated by arsenic and recent research suggests that quantifying and characterizing recharge is important to understand whether recharge flushes or mobilizes arsenic from aquifers at a field site in bangladesh we found that burrows of terrestrial crabs short circuit low permeability surface sediments providing the primary conduit for recharge we combine field observations along with a model that couples isotope and water balances to quantify the effect of crab burrows on aquifer recharge given the wide distribution of burrowing crabs and the surficial geology we suggest that crab burrows provide widespread conduits for groundwater recharge

a new approach to computing accurate gravity time variations for a realistic earth model with lateral heterogeneities we have developed a new elasto gravitational earth model able to take into account lateral variations deviatoric pre stresses and topographies as a first application we assume an el lipsoidal earth with hydrostatic pre stresses and validate and discuss our numerical model by comparison with previous studies on the m 2 body tide we then study the response of the ellipsoidal earth to zonal atmospheric loads and find that global lateral variations within the earth such as ellipticity have a weak impact about 1 per cent on the elasto gravitational deformations induced by atmospheric loading at low frequencies the earth is deformed mainly by luni solar tides and by surface loads including ocean atmosphere ice volumes and post glacial rebound in this work we focus our attention on the earth s body tides and atmospheric loadings the most accepted earth body tide models presently deal with an ellipsoidal rotating earth containing a liquid core and an anelastic mantle with hydrostatic pre stresses wahr 1981 wahr bergen 1986 the earth however is not an exact ellipsoid but presents lateral variations and deviatoric pre stresses there are long wavelength density anomalies within the mantle as shown by geoid anomalies and tomography studies e g romanowicz gung 2002 wang 1994 and dehant et al 1999 studied the influence of lateral heterogeneities on earth tides and showed that this effect is small but not necessarily negligible they did not however take into account possible deviatoric pre stresses these effects on the earth s body tides are totally unknown in addition to tidal forces mass changes in the atmosphere also cause deformation and mass redistribution inside the planet involving both local and global surface motions and variations in the gravity field which may be observed in geodetic experiments for several decades satellite geodesy has provided information on the temporal variation of the earth s geopotential and especially on the low degree zonal harmonics j 2 j 3 gegout cazenave 1993 which are essentially controlled by surface loads these hydrological atmospheric or oceanic effects on the earth s gravity field are usually modelled assuming a spherical earth with hydro static pre stress e g farrell 1972 wahr et al 1998 with the advent of the new generation of gravity measurements one of the challenges of the coming decade will be to provide more realistic earth models that show the variation of gravity with time in particular global studies based on gravity data from satellites such as grace goce and future grace goce follow on ones require accurate body tide deformation models more realistic gravity variation models are also needed for local and ground measurements particularly for the very accurate superconducting gravimeters and the associated gravimetric observatory network such as the global geodynamic project crossley et al 1999 the formalism developed to compute this elasto gravitational model is usually based on spherical harmonic analysis the addition of lateral variations leads to couplings between spherical harmonics i e to a more complex formalism that requires a large numerical effort e g wang 1994 plag et al 1996 we develop here a new approach for a non radially symmetrical earth model using a finite element method known as the spectral element method the efficiency of this method is less dependent on the shape of the lateral heterogeneities than the spherical harmonic method our method is therefore well adapted to studying the impact of global and local lateral variations on the earth deformation we solve the elasto gravitational equations taking into consideration the lateral variations within the earth by using a first order perturbation theory smith 1974 dahlen tromp 1998 this new model allows us to take into account lateral variations of density and rheological parameters deviatoric pre stresses and interface topography in order to validate our calculations we tackle a well known problem the impact of the hydrostatic ellipticity on the earth body tides an analytical solution for this problem can be derived for a simple model in which the earth is assumed to be homogeneous and incompressible the gravitational potential and the vertical displacement on the surface of the deformed ellipsoid were first derived by love 1911 and then corrected by wang 1994 we have recently extended these analytical results to the tangential surface displacement greff lefftz et al 2005 we first validate our model with our analytical solutions and then compare our results with

depositional facies and radiocarbon ages of a drill core from the mekong river lowland near phnom penh cambodia evidence for tidal sedimentation at the time of holocene maximum flooding abstract the depositional facies and radiocarbon ages of a long holocene sediment core ks from cambodia are reported here to clarify the sedimentary environments of the mekong river delta system at the time of holocene maximum flooding by the sea the 30 7 m long ks core from the upper mekong river lowland about 20 km southeast of phnom penh penetrated five depositional facies a to e in ascending order facies a is cross laminated fluvial sand facies b is laminated very fine sand with mud drapes facies c to e are salt marsh flood plain and natural levee deposits characterized by a succession of peat organic clay and reddish brown silt facies b dates to 9 0 7 5 ka and is interpreted as aggradational tidal deposits 16 5 m thick deposited during a rapid rise of sea level these deposits became overlain by an accumulation of salt marsh and flood plain deposits during the subsequent period of slowly rising and then falling sea level the maximum flooding surface lies in the facies b interval the presence of tidal deposits implies that the core site about 230 km inland from the present river mouth was near the shoreline and experienced strong tidal influences during the early holocene

perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in west bengal india excess of 4600 m gk g 1 stable isotope ratios of waters from constructed perennial ponds indicate the ponds are chiefly recharged during the summer monsoon and subsequently undergo extensive evaporation during the dry winter season in contrast groundwaters with high as concentrations plot along the local meteoric water line lmwl near where the annual volume weighted mean precipitation values for d 2 ha ndd 18 o would plot the stable isotope data demonstrate that groundwaters are directly recharged by local precipitation without significant evaporation and thus are not recharged by nor mixed with the pond waters furthermore reactive transport modeling indicates that dissolved organic matter dom derived from pond waters does not fuel microbial respiration and as mobilization at depth in the underlying aquifer because travel times for pond derived dom exceed groundwater ages by thousands of years instead organic matter within the aquifer sediments must drive dissimilatory iron reduction and as release to groundwaters citation datta s a w neal t j mohajerin t ocheltree b e rosenheim c d white and k h johannesson 2011 perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in west bengal india geophys res lett 38 l20404 doi 10 1029 2011gl049301

linking organic matter deposition and iron mineral transformations to groundwater arsenic levels in the mekong delta cambodia enriched as in drinking water wells in south and southeast asia has increased the risk of cancer for nearly 100 million people this enrichment is generally attributed to the reductive dissolution of fe oxides however the complex expression of as enrichment in these areas is not yet well understood here the coupled sedimentological and geochemical factors that contribute to the extent and spatial distribution of groundwater as concentrations in the mekong river delta cambodia in an avulsed scroll bar sequence are examined x ray absorption spectroscopy xas was used to determine fe and as speciation in redox preserved sediment collected from drilled cores dissolved as fe and s solution concentrations in existing and newly drilled wells cores differed considerably depending on their source sedimentology the rapid burial of organic matter in the scroll bar sequence facilitated the development of extensive fe reducing conditions and as release into the aquifer in older features organic c levels are high enough to sustain extensive fe reduction and provide ample so4 which is reduced to sulfide this s reduction impacts as levels as is sequestered in sulfide minerals outside of the scrollbar sequence decreasing pore water concentrations in contrast as is depleted in sediments from the scroll sequence and associated with elevated pore water aqueous concentrations the concentration and form of organic c in the scrollbar sequence is related to depositional environment and can facilitate fe and s mineral transformations distinct sedimentary environments explain a portion of the inherent heterogeneity of aquifer as concentrations

the first mars thermospheric general circulation model the martian atmosphere from the ground to 240 km 1 the martian general circulation model gcm at the laboratoire de meteorologie dynamique lmd has been extended up to approximately 240 km and it is now the first gcm to fully simulate the martian atmosphere from the ground up to the thermosphere in this paper we summarize the processes that have been added and give a first simple study of the effects of parameterized orographic gravity waves on the zonal mean fields this first study clearly emphasizes the coupling between the different atmospheric regions and notes the importance of having fully coupled models to simulate the atmosphere of mars

hysteretic dynamics of seasonal snow depth distribution in the swiss alps 1 the dynamics of the spatial snow distribution is a key feature when investigating a seasonal snow cover on the catchment scale this study explores the spatial variability of snow depth during the course of snow accumulation and depletion based on daily data from 77 weather stations in the swiss alps during 6 consecutive seasons we derive a statistical description of the snow cover dynamics by analyzing temporal trajectories in plots of the standard deviation over mean where xi is a set of snow depth measurements on one particular day the analysis reveals that the evolution of closely follows a power law 0 84 0 01 during the accumulation period for all 6 winters however during snowmelt the trajectory of displays a clearly different path as with classical hysteresis phenomena surprisingly a simplistic model of uniform melting describes this path reasonably well we believe that the conceptual framework outlined in this study is helpful in describing important characteristics of the dynamics of seasonal snow depth spatial variability future studies could apply the methodology introduced here to incorporate stochastic means in modeling snow distribution even for a broader range of length scales and different alpine terrain

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

use of lithium tracers to quantify drilling fluid contamination for groundwater monitoring in southeast asia abstract drilling is widely used in groundwater monitoring and many other applications but has the inherent problem of introducing some degree of external contamination into the natural systems being monitored contamination from drilling fluid is particularly problematic for i wells with relatively low water flow rates which are difficult to flush and for ii hydrogeochemical research studies of groundwaters hosted by incompletely consolidated shallow sediments which are widely utilized as sources of drinking water and irrigation water across many parts of asia here we develop and evaluate a method that can be simply used to quantify the extent of drilling fluid contribution to a water sample either to optimize sample collection for reduced contamination or to allow a correction for contamination to be made we report the utility of lithium chloride tracers using both field and laboratory analytical techniques to quantitatively evaluate and correct for drilling fluid contamination of casing waters through an investigation of 15 sites in kandal province cambodia high analytical errors limit the practicality and resolution of field based lithium ion selective electrode measurements for purposes other than broad estimates of gross contamination however when laboratory analysis is integrated with the method e g via inductively coupled plasma atomic emission spectrometry analysis lithium tracers can provide a robust and accurate method for evaluating drilling related contamination if appropriate samples are collected casing water is susceptible to contamination from drilling fluid which was shown to be significantly reduced within two to three well volumes of flushing but can still persist above background for greater than seven well volumes of flushing a waiting period after drilling and prior to water sampling was shown to further decrease contamination due to dilution from the surrounding aquifer particularly in more permeable wells contamination values were generally

peat formation concentrates arsenic within sediment deposits of the mekong delta abstract mekong river delta sediment bears arsenic that has been released to groundwater under anaerobic conditions over the past several thousand years the oxidation state speciation and distribution of arsenic and the associated iron bearing phases are crucial determinants of as reactivity in sediments peat from buried mangrove swamps in particular may be an important host source or sink of arsenic in the mekong delta the total concentration speciation and reactivity of arsenic and iron were examined in sediments in a mekong delta wetland by x ray fluorescence spectrometry xrf x ray absorption spectroscopy xas and selective chemical extractions total solid phase arsenic concentrations in a peat layer at a depth of 6 m below ground increased 10 fold relative to the overlying sediment extended x ray absorption fine structure exafs spectroscopy revealed that arsenic in the peat was predominantly in the form of arsenian pyrite arsenic speciation in the peat was examined further at the micron scale using xrf and x ray absorption near edge structure xanes spectroscopy coupled with principal component analysis the multiple energy xrf mapping and xanes routine was repeated for both iron and sulfur phase analyses our xrf xanes analyses confirm arsenic association with pyrite a less reactive host phase than iron hydr oxides under anaerobic conditions the arsenian pyrite likely formed upon deposition formation of the peat in a past estuarine environment 5 5 ka bp a process that is not expected under current geochemical conditions presently arsenian pyrite is neither a detectable source nor a sink for aqueous arsenic in our sediment profile and under present geochemical conditions represents a stable host of as under the reducing aquifer conditions of the mekong delta furthermore organic carbon within the peat is unable to fuel fe iii reduction as noted by the persistence of goethite which can be reduced microbially with the addition of glucose

mapping snow distribution in the alaskan arctic using aerial photography and topographic relationships a method is presented for mapping the end of winter snow distribution in the arctic using vertical aerial photographs taken during the melt the photos show a limited number of distinctive snowmelt patterns that arise reliably year after year data and results from an energy balance melt model indicate that the patterns are not caused by differential melt but instead represent areas of distinctive end of winter snow depth a map of these snowmelt patterns is thus a map of the end of winter snow distribution because wind transport of snow is common the patterns are closely related to the topography rules based on this pattern topography relationship are developed and used to map the snow cover directly from topographic maps for three areas covering 220 km2 of the kuparuk basin in northern alaska analysis of the snow maps suggests that about 75 of the area was mapped correctly applicability reliability and limitations of this mapping approach are discussed

heavy rain on snow cover heavy ram on snow often leads to disastrous damages in torrent water sheds injanuary 1998 a project was started to investigate runoltand infiltration character isties ofdilyerent alpine soil vegetation units under snow cover one aim was to determine the runoff rates from snow eovered rlifferently eultivated snil vegetation units pastures dwarf shrub stands forests espeeially under eonditions of sparse snow eover and frozen soil differenees in runoffformation between artifieially snowed skiing areas and plots with natural snow eover were also of interest heavy ram intensity 100 mm h was simulated on four plots by using a transportable spray irrigation installation the investigations showed runoff eoeffieients of 0 4 0 7 the lowest runoff values were found where the soil under snow eover was not frozen hut even on these stands the runoffeoeffieient exeeeded 0 4 snow depth and runoffdelay are strongly eorrelated r 0 8 an inerement in snow of 10 cm is followed by a runoffdelay of 3 6 min divergences from this coherence are due to the eomposition ofthe snowpaek espeeially in ease ofartificial snow this result is enenuraged by runoffsimulations performed for tbe irrigated plots by use ofa hydrological model

phase transitions in the martian mantle implications for partially layered convection abstract numerical simulations of mantle convection in mars using an axisymmetric spherical shell model show partial layering caused by the two exothermic olivine spinel phase transitions an extended boussinesq approximation has been used in which viscous dissipation adiabatic heating and cooling and latent heat are included the rayleigh number ra has been varied between 5 105 and 108 the partial layering with the vertical velocity at the exothermic phase transitions varying strongly in space and time is the result of two opposing effects the enhanced buoyancy of the phase boundaries by thermal anomalies and the impeding influences from the latent heat release or consumption the effect of the latent heat is stronger in mars than the earth because of the comparatively low pressure gradient in the martian mantle and the smaller excess temperature of upwellings and downwellings the time series of the mean vertical mass transport across the phase transitions show oscillations between blocking and acceleration of the flow the amplitude and the oscillations in the time series increase with increasingra because of the partial layering the planet will cool more slowly and less uniformly than suggested by thermal evolution models with parameterized convection in addition the number of strong mantle plumes is reduced to only a few upwellings such a pattern is suggested for mars by the existence of two pronounced volcanic centers tharsis and elysium this could also cause a strong time dependence in the martian volcanic activity the latent heat release causes the mantle temperature to increase across each transition by about 50 k and produces a hot lower mantle and a liquid core we have tested the case of a 85 350 km thick perovskite layer at the core mantle boundary a layer thicker than about 300 km would convect separately and induce leaking to the mantle above at a significantly smaller rate compared to the layers induced by the olivine spinel phase boundaries for a perovskite layer smaller than about 300 km the convective vigor near the core mantle boundary decreases with the layer thickness

thick shell tectonics on one plate planets applications to mars a theory for stress distributions in thick lithospheric shells on one plate planets is developed based on the zero frequency equations of a self gravitating elastic spherical shell overlying a strengthless fluid stress distributions in lithospheres are reviewed for both the compensated and flexural modes in the former case surface stresses only depend on surface topography while for the latter case it is shown for long wavelengths that stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties computational analyses are carried out for mars and it is found that isostatically compensated models correctly predict the graben structure in the immediate tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding tharsis a three stage model is hypothesized for the evolution of tharsis isostasy with north south graben formation on tharsis followed by flexural loading and radial graben formation on the perimeter of tharsis followed by a last stage of loading with little or no regional deformation this model is consistent with the martian lithosphere monotonically thickening over geologic time

natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of west bengal and its worldwide implications in order to investigate the mechanism of as release to anoxic ground water in alluvial aquifers the authors sampled ground waters from 3 piezometer nests 79 shallow 80 m wells in an area 750 m by 450 m just north of barasat near kolkata calcutta in southern west bengal high concentrations of as 200 1180 mug l 1 are accompanied by high concentrations of fe 3 13 7 mgl 1 and po4 1 6 5 mg l 1 ground water that is rich in mn 1 5 3 mg l 1 contains 50 mug l 1 of as the composition of shallow ground water varies at the 100 m scale laterally and the metre scale vertically with vertical gradients in as concentration reaching 200 mug l 1 m 1 the as is supplied by reductive dissolution of feooh and release of the sorbed as to solution the process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit in well waters thermotolerant coliforms a proxy for faecal contamination are not present in high numbers 10 cfu 100 ml in 85 of wells showing that faecally derived organic matter does not enter the aquifer does not drive reduction of feooh and so does not release as to ground water arsenic concentrations are high much greater than50 mug l 1 where reduction of feooh is complete and its entire load of sorbed as is released to solution at which point the aquifer sediments become grey in colour as feooh vanishes where reduction is incomplete the sediments are brown in colour and resorption of as to residual feooh keeps as concentrations below 10 mug l 1 in the presence of dissolved fe sorbed as released by reduction of mn oxides does not increase as in ground water because the as resorbs to feooh high concentrations of as are common in alluvial aquifers of the bengal basin arise because himalayan erosion supplies immature sediments with low surface loadings of feooh on mineral grains to a depositional environment that is rich in organic mater so that complete reduction of feooh is common c 2004 published by elsevier ltd

mantle lateral variations and elastogravitational deformations ii possible effects of a superplume on body tides summary the body tides response deformation and gravity of the earth is generally computed assuming radial symmetry in stratified earth models at the hydrostatic equilibrium we present in this paper numerical experiments with the aim to evaluate the impact of very large mantle heterogeneities of density on body tides in a companion paper we have developed a new earth elasto gravitational deformation model able to take into account the heterogeneous structure of the mantle we use this model to calculate the theoretical perturbation induced by three types of spherical heterogeneities in the mantle on m2 body tides response the heterogeneities are 1 our limit case a heterogeneity of 1000 km of radius in the lower mantle 2 a heterogeneity of 500 km of radius at the bottom of the lower mantle and 3 a heterogeneity of 285 km of radius in the upper mantle the density variation has been set to 50 kg m 3 f or each experiment we first calculate the equilibrium state of the earth when it contains a heterogeneity including non hydrostatic prestresses dynamical topography and lateral variation of density then we compute the m2 tidal perturbation we find that the surface tidal displacement perturbation is smaller than 1 mm and that the gravity perturbation has a maximum amplitude of 525 nanogal ngal regarding to the present precision in position measurement the displacement is too small to be detected the gravity perturbation should be measurable with superconducting gravimeters which have a ngal instrumental precision in experiment 2 the maximum gravity perturbation is about 120 ngal and in experiment 3 the maximum perturbation is about 33 ngal finally we investigate the maximum theoretical impact of the pacific and the african superplumes on the m2 body tide the superplumes have been modelled as two spherical heterogeneities with a radius of 1000 km in the lower mantle we find that these superplumes induce a maximum perturbation in gravity of about 370 ngal with a large part corresponding to a mean variation of gravity we conclude that we can expect to have a gravity perturbation of body tide with an order of magnitude of about hundred of ngal induced by the biggest mantle heterogeneities of density this perturbation in gravity should be measurable with superconducting gravimeters if all other contributions in the signal could be extracted with a sufficient precision

predicting groundwater arsenic contamination in southeast asia from surface parameters arsenic contamination of groundwater resources threatens the health of millions of people worldwide particularly in the densely populated river deltas of southeast asia although many arsenic affected areas have been identified in recent years a systematic evaluation of vulnerable areas remains to be carried out here we present maps pinpointing areas at risk of groundwater arsenic concentrations exceeding 10 g l 1 these maps were produced by combining geological and surface soil parameters in a logistic regression model calibrated with 1 756 aggregated and geo referenced groundwater data points from the bengal red river and mekong deltas we show that holocene deltaic and organic rich surface sediments are key indicators for arsenic risk areas and that the combination of surface parameters is a successful approach to predict groundwater arsenic contamination predictions are in good agreement with the known spatial distribution of arsenic contamination and further indicate elevated risks in sumatra and myanmar where no groundwater studies exist arsenic contamination of groundwater resources threatens the health of millions of people worldwide particularly in the densely populated river deltas of southeast asia maps of areas at risk of groundwater arsenic concentrations have been produced by combining geological and surface soil parameters in a logistic regression model they show that holocene deltaic and organic rich surface sediments are key indicators for arsenic risk areas and indicate elevated risks in sumatra and myanmar where no groundwater studies exist

space time structure of rain rate fields information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems in this study rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of taylor s hypothesis for relating their spatial and temporal statistics weather radar derived rain rate maps were employed to obtain one and two dimensional spatial power spectra azimuthally averaged two dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two dimensional turbulence driven by the input of energy over a narrow band of wave numbers one dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data temporal spectra from the gage time series were nearly identical in shape to the one dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate themore temporal and spatial scales for spectra corresponding to longer durations a match could not be made less

geochemistry of aquifer sediments and arsenic rich groundwaters from kandal province cambodia abstract elevated as is well known to be present in aquifers utilised for drinking water and irrigation in west bengal and bangladesh this problem has also more recently been discovered in other parts of asia including vietnam cambodia inner mongolia and the middle ganges plain analysis of groundwaters in kandal province of cambodia found waters with comparable geochemistry to the as rich groundwaters of the west bengali delta similarities included high but heterogeneous as distributions predominantly in the form as iii high fe moderate to high hco 3 circumneutral ph low so 4 2 and geochemical components indicative of reducing conditions good positive correlations between as fe hco 3 and nh 4 and dissolved organic c is consistent with as release predominantly via microbially mediated reductive dissolution of as bearing fe iii oxides further evidence for such a process is found from correlations between as fe and organic matter from analysis of aquifer sediments by the presence of goethite in the finer fractions and from the association of as with amorphous poorly crystalline and well crystallised hydrous fe oxides the presence of several high as but low fe wells implies that microbes could have a more direct role in mediating as release via the direct utilisation of fe iii or as v as electron acceptors the presence of elevated as in waters with short aquifer residence times as indicated by their geochemical signature highlights the possible vulnerability of these aquifers to the influx of surface derived waters providing an additional source of labile organic c that could exacerbate as release by stimulating microbial activity

groundwater flow in an arsenic contaminated aquifer mekong delta cambodia abstract to advance understanding of hydrological influences on as concentrations within groundwaters of southeast asia the flow system of an as rich aquifer on the mekong delta in cambodia where flow patterns have not been disturbed by irrigation well pumping was examined monitoring of water levels in a network of installed wells extending over a 50 km2 area indicates that groundwater flow is dominated by seasonally variable gradients developed between the river and the inland wetland basins while the gradient inverts annually net groundwater flow is from the wetlands to the river hydraulic parameters of the aquifer k 10 4 ms 1 and overlying clay aquitard k 10 8 ms 1 were determined using grain size permeameter and slug test analyses when coupled with observed gradients they indicate a net groundwater flow velocity of 0 04 0 4 ma 1 downward through the clay and 1 13 ma 1 horizontally within the sand aquifer producing aquifer residence times on the order 100 1000 a the results of numerical modeling support this conceptual model of the flow system and when integrated with observed spatial trends in dissolved as concentrations reveal that the shallow sediments upper 2 10 m of fine grained material are an important source of as to the underlying aquifer

martian global scale co2 exchange from time variable gravity measurements 1 the martian co2 cycle causes variations in the gravity field that can be detected by an orbiting spacecraft the time variable c20 and c30 reported from the radio tracking analysis of mars global surveyor are used to calculate the seasonal changes in the polar cap masses as well as in the global atmospheric pressure the results show a good agreement with the model dependent solutions of general circulation models and co2 thickness observations of the high energy neutron detector on board mars odyssey

evidence for postglacial signatures in gravity gradients a clue in lower mantle viscosity abstract the earth s surface was depressed under the weight of ice during the last glaciations glacial isostatic adjustment gia induces the slow recession of the trough that is left after deglaciation and is responsible for a contemporary uplift rate of more than 1 cm yr around hudson bay the present day residual depression an indicator of still ongoing gia is difficult to identify in the observed topography which is predominantly sensitive to crustal heterogeneities according to the most widespread gia models which feature a viscosity of 2 3 10 21 pa s on top of the lower mantle the trough is approximately 100 m deep and cannot explain the observed gravity anomalies across north america these large anomalies are therefore usually attributed to subcontinental density heterogeneities in the tectosphere or to slab downwelling in the deep mantle here we use observed gravity gradients gg to show that the uncompensated gia trough is four times larger than expected and that it is the main source of the north american static gravity signal we search for the contribution to these ggs from mantle mass anomalies which are deduced from seismic tomography and are mechanically coupled to the global mantle flow this contribution is found to be small over laurentia and at least 82 of the ggs are caused by gia such a contribution from gia in these gg observations implies a viscosity that is greater than 10 22 pa s in the lower mantle our conclusions are a plea for gia models with a highly viscous lower mantle which confirm inferences from mantle dynamic models any change in gia modelling has important paleoclimatological and environmental implications encouraging scientists to re evaluate the past ice history at a global scale these implications in turn affect the contribution of bedrock uplift to the contemporaneous mass balance over antarctica and greenland and thus the present day ice melting rate as deduced from the grace space mission additionally studies of the thermo chemical structure of the lithosphere crust under north america that exploit gravity or geodetic data should be corrected for a gia model which is not the case today

a transect of groundwater and sediment properties in araihazar bangladesh further evidence of decoupling between as and fe mobilization a new sampling device was used to obtain 8 detailed profiles of groundwater and associated sediment properties to 30 m depth in a 4 km 2 area of bangladesh that is characterized by high spatial variability in groundwater as concentrations of dissolved as fe and mn ranged from b0 1 to 600 g l b0 1 to 18 mg l and b0 1 to 4 mg l respectively voltammetric measurements conducted in the field indicate that n95 of the dissolved arsenic was as iii the proportion of fe ii in the hot leachable iron fraction of the sediment ranged from 0 2 to 0 9 the concentration of phosphate extractable as in aquifer sands ranged from b0 1 to 1 1 mg kg although the highest dissolved as concentration was measured at the site where the highest groundwater fe and mn concentrations were also observed the dissolved as maximum was located several meters below the dissolved fe and mn maxima fe ii fe ratios and p extractable as concentrations in the solid phase were particularly elevated at the same site though again the profiles of these properties did not consistently match that of groundwater as concentrations a 500 m section composed of 5 vertical profiles confirms that whereas low as concentrations are broadly associated with low dissolved fe and mn concentrations as well as low fe ii fe ratios in the solid phase the spatial distributions of these properties in the subsurface do not follow a simple relationship in combination with other observations from the area the results suggest that elevated local recharge in areas where the permeability of surface soils is high prevents as from accumulating in groundwater conversely dissolved as concentrations tend to be high in areas where local recharge is restricted by a surface cover of low permeability the data demonstrate that further investigation of the mechanisms underlying as mobilization is likely to require sampling at lateral scales b1 km 2006 elsevier b v all rights reserved

electrical resistivity tomography determines the spatial distribution of clay layer thickness and aquifer vulnerability kandal province cambodia despite being rich in water resources many areas of south east asia face difficulties in securing clean water supply this is particularly problematic in regions with a rapidly growing population in this study the spatial variability of the thickness of a clay layer controlling surface groundwater interactions that affect aquifer vulnerability was investigated using electrical resistivity tomography ert data were acquired along two transects showing significant differences in the imaged resistivities borehole samples were analyzed regarding particle density and composition and linked to their resistivity the obtained relationships were used to translate the field electrical resistivities into lithologies those revealed considerable variations in the thickness of the clay layer ranging from 0 m up to 25 m geochemical data highlighting zones of increased ingress of surface water into the groundwater confirmed areas of discontinuities in the clay layer which act as preferential flow paths the results may guide urban planning of the phnom penh city expansion in order to supply the growing population with safe water the presented approach of using geophysics to estimate groundwater availability accessibility and vulnerability is not only applicable to kandal province cambodia but also to many other areas of fast urbanization in south east asia and beyond

groundwater arsenic concentrations in vietnam controlled by sediment age arsenic contamination of groundwater threatens the health of millions of people in southeast asia measurements in an arsenic contaminated aquifer in vietnam point to sediment age as a key determinant of groundwater arsenic concentrations

self similarity in glacier surface characteristics catchment wide information on glacier snow cover depth surface albedo and surface roughness is important input data for distributed models of glacier energy balance in this study we investigate the small scale mm to 100 m spatial variability in these properties with a view to better simulating this variability in such models data were collected on midre lovenbreen a 6 km 2 valley glacier in northwest svalbard the spatial variability of all three properties was found to be self similar over the range of scales under investigation snow depth and albedo exhibit a correlation length within which measurements were spatially autocorrelated late winter and summer properties of snow depth differed with smaller depths in summer due to melt and shorter correlation lengths similar correlation lengths for snow depth and surface albedo may suggest that snow depth variation is an important control on the small scale spatial variability of glacier surface albedo for surface roughness the data highlight a possible problem in energy balance studies which use microtopographic surveys to calculate aerodynamic roughness in that the scale of the measurements made affects the calculated roughness value this suggests that further investigations of the relationships between surface form and aerodynamic roughness of glacier surfaces are needed

influence of a variable thermal conductivity on the thermochemical evolution of mars 1 the influences of variations in thermal conductivity due to composition temperature and pressure in mantle and crust on the thermochemical evolution of mars have been examined with parameterized convection models we use a temperature and pressure dependent thermal conductivity in the mantle and column averaged values between 1 5 and 4 wm 1k 1 for the crust with 2 wm 1k 1 as the representative value for a basaltic crust the major characteristic of the models is a slower cooling of the upper mantle with a long existing global partial melt zone and a stronger crustal production late in the evolution compared to earlier models which assume a constant thermal conductivity of 4 wm 1k 1 to explain the observed crustal thickness and the early crustal formation on mars the formation of an enriched primordial crust is required recent volcanism can be explained by lateral temperature variations that are caused by thickness variations of the low conducting crust these melt zones which occur underneath thicker than average crust may be the source region for the observed longstanding volcanism in tharsis and elysium instead of plumes rising from the core mantle boundary the evolution of the elastic lithosphere is characterized by a transition at which the elastic strength is first provided by the crust and later also by the upper mantle this finding may explain the estimated elastic lithosphere thickness of less than 16 km in the noachian and more than 100 km in the hesperian and amazonian

characterisation of organic matter in a shallow reducing arsenic rich aquifer west bengal abstract elevated arsenic in groundwaters extensively exploited for irrigation and drinking water in west bengal and bangladesh is causing serious impacts on human health a key mechanism for the genesis of arsenic as in these waters is microbially mediated reductive transformation of arsenic bearing fe iii hydrated oxides the role of organic c in this process whether from in situ organic matter om i e om from within the sediment or from other sources is widely recognised despite this there is a paucity of data about the characteristics of om in these as rich aquifers extraction and analysis of the polar and apolar fractions from seven different sediments from a known groundwater as hotspot in west bengal revealed om characteristic of the original terrestrial depositional environment however this was overprinted by abundant hydrocarbons with thermally mature e g petroleum distributions these hydrocarbons included abundant high molecular weight n alkanes and unresolved complex mixtures ucms as well as thermally mature distributions of hopanes and steranes additionally at certain depths surface sands 8 and 13 m deeper sands 25 m the om appeared to be biodegraded with the preferential removal of petroleum sourced n alkanes suggesting that indigenous microbes within the aquifer can utilise this carbon source the presence of this previously unreported source of bioavailable organic carbon is of importance as it has the potential to promote microbial activity and subsequent as release in the aquifers

potential of time lapse photography of snow for hydrological purposes at the small catchment scale time lapse photography provides an attractive source of information about snow cover characteristics especially at the small catchment scale the objective of this study was to design and test a monitoring system which allows multi resolution observations of snow cover characteristics the main aim was to simultaneously investigate the spatio temporal patterns of snow cover snow depth and snowfall interception in the area very close to the camera and the spatio temporal patterns of snow cover in the far range the multi resolution design was tested at three sites in the eastern part of the austrian alps hochschwab rax region digital photographs were taken at hourly time steps between 6 00 and 18 00 in the period november 2004 to december 2006 the results showed that the time lapse photography allows effective mapping of the snow depths at high temporal resolution in the region close to the digital camera at many snow stake locations it is possible to process a large number of photos by using an automatic procedure for accurate snow depth readings the digital photographs can also be used to infer the settling characteristics of the snow pack and snow interception during the day although it is not possible to directly estimate the snow interception mass the photos may indeed give very useful information on the snow processes on and beneath the forest canopy the main advantage of using time lapse photography in the far range of the digital camera is to observe the spatio temporal patterns of snow cover over different landscape configurations the results illustrate that digital photographs can be very useful for parameterising processes such as sloughing on steep slopes snow deposition in gullies and snow erosion on mountain ridges in a distributed snow model copyright 2011 john wiley sons ltd

mountain snow distribution governed by an altitudinal gradient and terrain roughness 1 the heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer the snow distribution affects water resources natural hazards such as avalanches and ecology while a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone we present a model of the mean snow depth in topographic control units as a function of two terrain parameters the conventional elevation plus a fractal roughness parameter for this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner the model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation this unusually simple relationship holds for clusters of the snow depths of small topographical units by applying fractal analysis we describe the roughness of the terrain and use this parameter for the prediction of snow deposition rougher terrain holds less snow than smoother terrain this finding is important not only for avalanche warning or eco hydrological applications but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions

snow depth structure fractal behavior and interannual consistency over haut glacier d arolla switzerland snow depth patterns over glaciers are controlled by precipitation snow redistribution due to wind and avalanches and the exchange of energy with the atmosphere that determines snow ablation while many studies have advanced the understanding of ablation processes less is known about winter snow patterns and their variability over glaciers we analyze snow depth on haut glacier d arolla switzerland in the two winter seasons 2006 2007 and 2010 2011 to 1 understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas and 2 investigate the snow pattern consistency over the two accumulation seasons we perform this analysis on a data set of high resolution lidar derived snow depth using variograms and fractal parameters our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior with a scale break around 20 m after which the fractal dimension increases indicating more autocorrelated structure before the scale break than after second this behavior is consistent over the two years with fractal parameters and their spatial variability almost constant in the two seasons we also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment with longer correlation distances on the tongue in the direction of the main winds suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples

arsenic contaminated groundwater from parts of damodar fan delta and west of bhagirathi river west bengal india influence of fluvial geomorphology and quaternary morphostratigraphy arsenic contamination in groundwater affecting west bengal india and bangladesh is a serious environmental problem contamination is extensive in the low lying areas of bhagirathi ganga delta located mainly to the east of the bhagirathi river a few isolated as contaminated areas occur west of the bhagirathi river and over the lower parts of the damodar river fan delta the damodar being a peninsular indian river the arsenic problem is not restricted to himalayan rivers alone arsenic contamination in the bengal delta is confined to the holocene younger delta plain and the alluvium that was deposited around 10 000 7 000 years bp under combined influence of the holocene sea level rise and rapid erosion in the himalaya further contaminated areas are often located close to distribution of abandoned or existing channels swamps which are areas of surface water and biomass accumulation extensive extraction of groundwater mainly from shallow aquifers cause recharge from nearby surface water bodies infiltration of recharge water enriched in dissolved organic matter derived either from recently accumulated biomass and or from sediment organic matter enhanced reductive dissolution of hydrated iron oxide that are present mainly as sediment grain coatings in the aquifers enhancing release of sorbed arsenic to groundwater

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

upper atmosphere of mars up to 120 km mars global surveyor accelerometer data analysis with the lmd general circulation model 1 mars global surveyor mgs aerobraking accelerometer density measurements are analyzed with the use of the general circulation model gcm at the laboratoire de meteorologie dynamique lmd mgs constant altitude density data are used obtaining longitudinal wavelike structures at fixed local times which appear to be dominated by low zonal wave number harmonics comparisons with simulated data for different seasons and latitudinal bands at constant altitude are performed excellent agreement is obtained between the simulated and observational data for low latitudes with accuracy in both mean and zonal structure higher latitudes show a reduction in agreement between gcm results and mgs data comparisons that result in good agreement with the observational data allow for the study of wave composition in the mgs data in particular the excellent agreement between the simulations and the data obtained at 115 km during areocentric longitude ls 65 allows the extraction of the major contributors to the signature with the eastward propagating diurnal waves of wave numbers one to three being the major players significant contributions are also obtained for eastward propagating semidiurnal waves of wave numbers two three and five and diurnal wave number five a sensitivity study is performed to delineate the effects of the near ir tidal forcing of the upper atmosphere on the wave content at those heights simulations without this forcing yield reduced amplitudes for diurnal eastward propagating waves two and three along with a more latitudinally symmetric response for these two components as well as for diurnal eastward propagating wave number one

self similarity and multifractality of topographic surfaces at basin and subbasin scales self similarity of fluvial erosion topography manifests itself through statistical renormalization properties of drainage networks and river profiles results based on these renormalization properties are often inconsistent with those from spectral or variogram analysis of linear transects we show that the inconsistency is due to two factors 1 network and transect analyses are based on different self similarity conditions and 2 elevation along transects depends on the hillslopes where self similarity either does not apply or applies with different parameters as a result transect methods produce misleading results when the topography has finite hillslopes we also consider whether self similarity is sufficient to describe the scaling invariance of natural river basin topography or more sophisticated multifractal conditions should be used the conclusion of multifractality reached in recent studies was based on the use of gradient amplitudes rather than elevation increments the gradient amplitude method is found to produce spurious multifractality also in cases when the surface is known to be self similar when more appropriate methods are used topography shows little evidence of multifractality we support our conclusions through numerical analysis of synthetic and natural river basins

characterisation of organic matter and microbial communities in contrasting arsenic rich holocene and arsenic poor pleistocene aquifers red river delta vietnam abstract high concentrations of geogenic as in the groundwaters of south and se asia which are used as drinking waters are causing severe health impacts to the exposed human populations it is widely accepted that as mobilisation from sediments into these shallow reducing groundwaters requires active metal reducing microbes and electron donors such as organic matter om although om in such holocene aquifers has been characterised there is a dearth of data on pleistocene aquifers from the same areas reported here are preliminary studies of om and microbial communities present in two aquifers one of pleistocene and one of holocene age with contrasting concentrations of as viz pleistocene low as

a top down origin for martian mantle plumes the two main volcanic centers on mars tharsis and elysium are often interpreted in terms of mantle plume hotspots even though there are several problems with the plume hypothesis for mars we present results of 2d cylindrical shell numerical mantle convection experiments in which we try to ascertain whether flushing of the hot lower mantle could provide a mechanism for the generation of a small number of plume like features i e localized upwelling of hot material in this scenario the formation of hot upwellings is driven from the top by cold downwellings rather than from a hot thermal boundary layer at the cmb first we construct a range of mars interior structure models consistent with observations in order to demonstrate that the presence of a thin lower mantle in the martian interior is a viable scenario then we use a series of numerical convection experiments to investigate the effects of solid state phase transitions different stratified and temperature dependent viscosity models and the presence of a thick southern hemisphere crust on the operation of such a mechanism our results show that it is possible to generate hot strong localized upwellings from top down dynamics if the lithosphere is thin or actively involved in the convective pattern the presence of a thick immobile insulating southern hemisphere crust reduces the number of upwellings and the perovskite phase transition causes a focusing of the upwellings further experiments demonstrate that an initial 500 myr phase of mobile lid is sufficient to start this process create an upwelling which is stable for billions of years

the interior structure of mars implications from snc meteorites two end member models of mars present interior structure are presented the first model is optimized to satisfy the geochemical data derived from the snc meteorites in terms of the bulk chondritic ratio fe si 1 71 while the second model is optimized to satisfy the most probable maximum value c 0 366 x m p r p 2 of the polar moment of inertia factor hydrostatic equilibrium and stationary heat transfer are assumed and the basic differential equations for the mechanical and thermal structure are solved numerically together with an isothermal murnaghan birch type equation of state truncated in eulerian strain at forth order we obtain the radial distribution of mass hydrostatic pressure gravity temperature and heat flow density along with the corresponding density stratification viscosity profiles and the global seismic velocity structure of model mars the first model being consistent with the geochemical requirement produces c 0 357 x m p r p 2 whereas the second model commensurate with the geophysical constraint gives fe si 1 35 the calculated central pressure is about 40 gpa in both models and the central temperature is in the 2000 to 2200 k range the model calculations suggest a fe ni fes core a little less than one half of the planetary radius in size surrounded by a silicate mantle subdivided into lower spinel and upper olivine layers and overlain by a 100 to 250 km thick basaltic crust and a surface heatflow density of 25 to 30 mw m 2 in both models the pressure in the mantle is not sufficient for the spinel to perovskite transition to occur the present thermal lithosphere is estimated to be about 500 km thick and to be subdivided into a 300 km thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection given the core sulfur content of 14 wt as derived from snc meteorites the martian core is found to be entirely molten implying the nonoperation of a self sustained dynamo due to the absence of sufficiently vigorous convection

co2 snow depth and subsurface water ice abundance in the northern hemisphere of mars observations of seasonal variations of neutron flux from the high energy neutron detector hend on mars odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the mars orbiter laser altimeter mola on mars global surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide the observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil the lower ice rich layer contains between 50 and 75 weight water indicating that the shallow subsurface at northern polar latitudes on mars is even more water rich than that in the south

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

seasonal and static gravity field of mars from mgs mars odyssey and mro radio science abstract we present a spherical harmonic solution of the static gravity field of mars to degree and order 120 gmm 3 that has been calculated using the deep space network tracking data of the nasa mars missions mars global surveyor mgs mars odyssey ody and the mars reconnaissance orbiter mro we have also jointly determined spherical harmonic solutions for the static and time variable gravity field of mars and the mars k 2 love numbers exclusive of the gravity contribution of the atmosphere consequently the retrieved time varying gravity coefficients and the love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of mars respectively we obtain a mars love number k 2 of 0 1697 0 0027 3 the inclusion of mro tracking data results in improved seasonal gravity field coefficients c 30 and for the first time c 50 refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic c 30 for 1 5 solar cycles 16 years this gravity model shows improved correlations with mola topography up to 15 larger at higher harmonics l 60 80 than previous solutions

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

distribution of groundwater arsenic in xinjiang p r china although potential contamination of groundwater as is expected to occur in xinjiang p r china few data are available for the regional distribution of groundwater as in this study the spatial distribution of groundwater as was investigated in the chepaizi cpz n and shihezi shz n areas of northern xinjiang the balikun yiwu basin by e in eastern xinjiang and the tarim trm s and yanqi yq s basins in southern xinjiang arsenic concentrations greater than 10 g l were found in 12 of analyzed groundwaters all groundwater samples collected in cpz n had as concentrations greater than 10 g l 25 185 g l 30 in shz n 10 g l was found in the eastern and southern trm s and yq s distribution of groundwater as showed a tremendous spatial variability which greatly varied over a short distance horizontally arsenic concentration generally increased with increasing sampling depth the spatial distribution of groundwater as would be regulated by as source and hydrogeochemical processes higher ph and or lower orp values were generally observed in high as groundwater 10 g l in comparison with low as groundwater 10 g l arsenic mobility in shz n and cpz n may result from as desorption under relatively high ph conditions and more tentatively from reductive dissolution of fe iii oxides in by e and trm s however detailed mechanisms of as mobilization in these regions need further investigation

the effect of the internal structure of mars on its seasonal loading deformations abstract mars is continuously subjected to surface loading induced by seasonal mass changes in the atmosphere and ice caps due to the co2 sublimation and condensation process it results in surface deformations and in time variations of gravity large wavelength annual and semi annual variations of gravity particularly zonal coefficients j n have been determined using present day geodetic satellite measurements however loading deformations have been poorly studied for a planet like mars in this paper we compute these deformations and their effect on spacecraft orbiting around mars loading deformations of terrestrial planet are typically investigated assuming a spherical planet radially symmetric the mean radial structure of mars is not well known in particular the radius of the liquid or solid core remains not precisely determined one may then wonder what is the effect of these uncertainties on loading deformations moreover mars presents a strong topography and probably large lateral variations of crustal thickness relative to the earth the paper answer the questions of what is the effect of such lateral heterogeneities on surface deformations and is the classical way to calculate loading deformation well adapted for a planet like mars in order to answer these questions we have investigated theoretically loading deformations of mars like planets we first investigated classical load love numbers we show that for degrees inferior to 10 the load love numbers mainly depend on the radius of the core and on its state and that for degree greater than 10 they depend on the mean radius of mantle crust interface using a general circulation model gcm of atmosphere and ice caps dynamics we show that loading vertical displacements have a 4 5 cm magnitude and present a north south pattern with periodic transitions finally we investigated the effect of lateral variations of the crustal thickness on these loading deformations we show that thickness heterogeneities perturb the deformations and the time variation of gravity at about 0 5 however this perturbation on j n is only about 1 due to main direct attraction of surface fluid layers we conclude that lateral variations of crustal thickness are today negligible however observation of load love numbers would bring information on the radial internal structure of the planet particularly on the core radius j n study would permit to infer the load love number k n particularly for degree 2 and 3 knowing surface fluid layer dynamics however k n load love numbers are quite small about 0 05 and despite the present good agreement between gcm and j n observations will only be estimated in the near future when a slightly better precision in observation and modeling will make it possible to infer these numbers the investigation of load love number h n which are larger than k n numbers would be particularly interesting it would permit to study degree 1 contribution of atmosphere and ice caps dynamics which is the most important component of surface fluid dynamics on mars surface displacement measurements would be necessary on a few places near the pole regions which may be possible in the future with a project involving precise positioning of a lander on the surface of mars