the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

cassini imaging of titan s high latitude lakes clouds and south polar surface changes 1 cassini s imaging science subsystem iss has been observing titan since april 2004 compiling a nearly global surface map and monitoring the surface and atmosphere for activity early images of the south polar region revealed numerous dark surface features and contemporaneous convective cloud systems suggesting the presence of hydrocarbon lakes similar to those later detected at titan s north pole intriguingly repeated south polar imaging by iss revealed differences consistent with ponding of hydrocarbon liquids on the surface due to precipitation from a large storm more recent iss images of high northern latitudes illustrate the full extents 500 000 km2 of hydrocarbon seas sections of which have been observed by cassini s radar these observations demonstrate dynamic processes at work on titan and that the poles harbor liquid hydrocarbon reservoirs the extents of which differ from pole to pole and which may be coupled to seasonally varying circulation

surface water and groundwater contaminations and the resultant hydrochemical evolution in the yongxiu area west of poyang lake china major ion and stable hydrogen and oxygen isotopic compositions were employed in this study of surface water and groundwater contaminations and their impacts on intrinsic hydrochemical evolution in the yongxiu area west of poyang lake south china a total of 36 samples were collected from surface water and groundwater in the study area where water pollution risk is high due to the fertilizer use for farmland and the waste drainage from a nearby silicon industry site the results show that the surface water bodies have been badly polluted and are characterized by low ph values minimum 2 85 and high concentrations of chemical compounds such as cl na nh4 n no3 n and tds groundwater has also been polluted with the similar specific contaminates as both surface water and groundwater may have similar contamination sources and groundwater is recharged from the precipitation infiltration and surface water leakage as indicated by oxygen 18 and deuterium compositions due to the thin unsaturated zone in the area the acidification and the intrusion of contamination further lead to hydrogeochemical reactions and changed hydrochemical type of groundwater from ca mg hco3 to ca mg na cl the data evaluation methods and results of this study could be useful to the water sustainable usage management in this area and other environmental vulnerable areas

titan radar mapper observations from cassini s t3 fly by cassini s titan radar mapper imaged the surface of saturn s moon titan on its february 2005 fly by denoted t3 collecting high resolution synthetic aperture radar and larger scale radiometry and scatterometry data these data provide the first definitive identification of impact craters on the surface of titan networks of fluvial channels and surficial dark streaks that may be longitudinal dunes here we describe this great diversity of landforms we conclude that much of the surface thus far imaged by radar of the haze shrouded titan is very young with persistent geologic activity

surface water groundwater interactions in an alluvial plain chemical and isotopic systematics our work on the loire river forms part of a french national research program dedicated to wetlands and aims to better understand the global functioning of the system from the hydrological geochemical ecological and sociological aspects the present study using a coupled hydrological and geochemical stable and sr isotopes approach focuses on the soulangy site with its secondary anastomosing channels just below the confluence of the loire and allier rivers and also on the dorna nt site with two unconnected oxbow lakes 50 km upstream of the confluence the stable isotopes of water 18o 2h show that the alluvial or riverbank aquifer feeds the loire river during the summer but is not recharged by the river during flood periods in the winter the alluvial groundwater thus has a purely local origin from precipitation the major elements reveal an anthropogenic input of cl and more importantly of no3 especially near farms the 87sr 86sr isotopes identify different groundwater layers in the alluvium i e an upper and a lower alluvial aquifer and a perched aquifer at dornant that have relatively complex relationships with the surface water the two main rivers loire and allier present distinct geochemical characteristics reflecting the different lithologies that they drain upstream in addition the secondary channels lying parallel to the loire main stream at the soulangy site give different geochemical signatures which shows that they are not fed by the same overflows of the loire they are more or less well connected to the upper level of the alluvial plain and a longitudinal study of one of these channels has revealed a loire river influence progressively replaced by a water contribution from the upper alluvial aquifer similarly the two oxbow lakes at the dornant site are not supplied by the same water during the summer months a conceptual scheme of the loire hydrosystem based on 18o and 87sr 86sr suggests that the isotopic variations of the loire river can be related to a massif central surface water supply for the loire and allier main streams and to a groundwater supply from the alluvial plains

stable isotope 2h 18o and 87sr 86sr and hydrochemistry monitoring for groundwater hydrodynamics analysis in a karst aquifer gran sasso central italy this paper deals with chemical and isotope analyses of 21 springs which were monitored 3 times in the course of 2001 the monitoring program was focused on the groundwater of the gran sasso carbonate karst aquifer central italy typical of the mountainous mediterranean area based on the hydrogeological setting of the study area 6 groups of springs with different groundwater circulation patterns were distinguished the hydrogeochemistry of their main components provided additional information about groundwater flowpaths confirming the proposed classification the spatial distribution of their ion concentrations validated the assumptions underlying the hydrogeological conceptual model showing diverging groundwater flowpaths from the core to the boundaries of the aquifer geochemical modelling and saturation index computation elucidated water carbonate rock interaction contribution by alluvial aquifers at the karst aquifer boundaries as well as impacts of human activities the analysis of 18o 16o and 2h h values and their spatial distribution in the aquifer substantiated the hydrogeology based classification of 6 groups of springs making it possible to trace back groundwater recharge areas based on mean isotope elevations the latter were calculated by using two rain monitoring stations 87sr 86sr analyses showed seasonal changes in many springs in winter spring the changes are due to inflow of new recharge water infiltrating into younger rocks and thus increasing 87sr 86sr values in summer autumn when there is no recharge and spring discharge declines changes are due to base flow groundwater circulating in more ancient rocks with a subsequent drop in 87sr 86sr values the results of this study stress the contribution that spatio temporal isotope monitoring can give to the definition of groundwater flowpaths and hydrodynamics in fissured and karst aquifers taking into account their hydrogeological and hydrogeochemical setting

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

hydrogeochemical interpretation of water seepage through a geological barrier at a reservoir boundary a geological barrier such as a mountain ridge surrounding a large reservoir generally plays some part in preventing water leakage from the reservoir but water flows out naturally according to the hydraulic gradient because the reservoir water level is typically higher than that outside the hydrogeological geochemical and isotopic properties of water in the daechung dam area were analysed to characterize the source and the phenomenon of the groundwater flowing through the geological barrier our geochemical analysis showed that the concentrations of anions and cations tended to increase due to the longer residence time of the water as the distance between the sampling site and reservoir increased elevation differences calculated using oxygen and hydrogen isotopes between the highest and lowest sampling sites ranged between 350 and 420 m based on the altitude effect on isotope concentration but the actual difference was only 35 m these results including analysis of the rate of water seepage from the reservoir ca 2 3 to 14 4 of natural recharge indicate the possibility that groundwater in the study area originated from reservoir water that was derived from upstream water and rainfall in the high mountainous area of the upper watershed copyright 2013 john wiley sons ltd

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

processes of water rock interaction in the turonian aquifer of oum er rabia basin morocco possible water rock interaction processes in the moroccan basin of oum er rabia were discussed by a geochemical study of groundwater from the turonian limestone aquifer the most important water resource in the region different types of water according to the classification of piper were defined waters have shown an evolution from dominant cho3 ca mg type through mixed to so4 cl ca mg type the use of geochemical diagrams and chemical speciation modeling method has shown that water rock interaction is mainly controlled by carbonate and anhydrite dissolution ion exchange and reverse ion exchange processes water rock equilibrium conditions are favorable for the precipitation of calcite dolomite kaolinite and magnesian smectite

high precision al mg systematics of forsterite bearing type b cais from cv3 chondrites abstract in order to further elucidate possible temporal relationships between different varieties of calcium aluminum rich inclusions cais we measured the aluminum magnesium isotopic systematics of seven examples of the rare type known as forsterite bearing type b fob inclusions from four different cv3 carbonaceous chondrites allende efremovka nwa 3118 and vigarano the primary phases forsterite al ti rich diopside spinel melilite and anorthite in each inclusion were analyzed in situ using high precision secondary ion mass spectrometry sims in all cases minerals with low al mg ratios all except anorthite yield well defined internal al mg isochrons with a range of initial 26al 27al ratios 26al 27al 0 ranging from 5 30 0 22 10 5 down to 4 17 0 43 10 5 anorthite in all cases is significantly disturbed relative to the isochrons defined by the other phases in the same cais and in several cases contains no resolved excesses of radiogenic 26mg 26mg even at 27al 24mg ratios greater than 1000 the fact that some fobs preserve 26al 27al 0 of 5 2 10 5 close to the canonical value of 5 23 0 13 10 5 inferred from bulk magnesium isotope measurements of cv cais b jacobsen et al 2008 demonstrates that fobs began forming very early contemporaneous with other more refractory cais the range of 26al 27al 0 values further shows that fobs continued to be reprocessed over 200 000 years of nebular history consistent with results obtained for other types of igneous cais in cv chondrites the absence of any correlation between of cai fob formation or reprocessing times with bulk composition or cai type means that there is no temporal evolutionary sequence between the diverse cai types the initial 26mg value in the most primitive fob sj101 is significantly lower than the canonical solar system value of 0 040 0 029

understanding the salinisation process for groundwater in an area of south eastern australia using hydrochemical and isotopic evidence abstract increases in groundwater salinity down gradient are a common occurrence in catchments throughout australia exacerbating the effects of dryland salinisation in discharge areas groundwater hydrochemical and isotopic data from the willaura catchment in south eastern australia which is affected by both primary natural and secondary human induced salinity allowed the factors that cause the down gradient trend in salinisation within this catchment to be determined the overall salinity of the groundwater 0 8 70 ms cm is controlled by evapotranspiration which concentrates cyclic salts in the unsaturated zone greatly increasing the salinity of the soil water to 3700 6400 mg l cl the progressive addition of this saline soil water to fresher groundwaters recharged on the catchment margins causes a gradual increase in salinity down gradient the groundwater stable isotope compositions show that most recharge occurs in winter and spring groundwater salinities increase around the saline lakes of the discharge zone due to direct evaporation from shallow watertables and minor dissolution of halite as indicated by cl br ratios mineral water interactions within the aquifers cause a slight overall reduction in salinity conversion of kaolinite to smectite and illite and cation exchange of na for ca2 on smectites cause na cl mg2 cl k cl si cl and hco3 cl ratios to progressively decline and ph to gradually increase down gradient oxidation of organic matter causes a strong decrease in the redox potential of the groundwaters down gradient the groundwater ages increase from modern containing tritium on the catchment margins to 8000 years based on 14c dating at the end of the 25 km flow path the older groundwaters are isotopically heavier than the younger waters probably due to recharge during a wetter climate in the early holocene the groundwater ages show clearly that the progressive addition of saline soil water causing groundwaters to become more saline down gradient has occurred throughout the holocene and may explain the occurrence of primary salinisation within many australian catchments

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

estimates of fluvial erosion on titan from sinuosity of lake shorelines 1 titan has few impact craters suggesting that its surface is geologically young titan s surface also has abundant landforms interpreted to be fluvial networks here we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes a scarcity of detailed topographic data makes it difficult to measure fluvial incision on titan but images of drowned fluvial features around the lake margins where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys offer a constraint on the topography we mapped the shorelines of several lakes to obtain topographic contours that trace the fluvially dissected topography we then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity which reflects the extent of fluvial valley incision and cumulative erosion we confirmed this relationship by analyzing a partially dissected surface adjacent to the minnesota river usa comparison of the mapped titan contours with the sinuosity erosion relationship suggests that cumulative fluvial erosion around the margins of titan s polar lakes including ligeia mare kraken mare and punga mare in the north and ontario lacus in the south ranges from 4 to 31 of the initial relief additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery suggesting that fluvial erosion is not the only major resurfacing mechanism operating in titan s polar regions

a comparison of general circulation model predictions to sand drift and dune orientations the growing concern over climate change and decertification stresses the importance of aeolian process prediction in this paper the use of a general circulation model to predict current aeolian features is examined a gcm developed at nasa goddard space flight center was used in conjunction with white s aeolian sand flux model to produce a global potential aeolian transport map surface wind shear stress predictions were used from the output of a gcm simulation that was performed as part of the atmospheric model intercomparison project on 1979 climate conditions the spatial resolution of this study as driven by the gcm is 4 degrees x 5 degrees instantaneous 6 hourly wind stress data were saved by the gcm and used in this report a global map showing potential sand transport was compared to drift potential directions as inferred from landsat images from the 1980s for several sand seas and a coastal dune field generally results show a good correlation between the simulated sand drift direction and the drift direction inferred for dune forms discrepancies between the drift potential and the drift inferred from images were found in the north american deserts and the arabian peninsula an attempt to predict the type of dune that would bemore formed in specific regions was not successful the model could probably be further improved by incorporating soil moisture surface roughness and vegetation information for a better assessment of sand threshold conditions the correlation may permit use of a gcm to analyze open quotes fossil close quotes dunes or to forecast aeolian processes 48 refs 8 figs less

hydrocarbon lakes on titan distribution and interaction with a porous regolith from 10 to more than 100 000 km 2 the size and location of lakes provide constraints on parameters associated with subsurface transport using porous media properties inferred from huygens probe observations timescales for flow into and out of observed lakes are shown to be in the tens of years similar to seasonal cycles derived timescales are compared to the time between collocated sar observations in order to considertheroleofsubsurfacetransportintitan shydrologic cycle citation hayes a et al 2008 hydrocarbon lakes on titan distribution and interaction with a porous regolith geophys res lett 35 l09204 doi 10 1029 2008gl033409

dissolution on titan and on earth toward the age of titan s karstic landscapes titan s polar surface is dotted with hundreds of lacustrine depressions based on the hypothesis that they are karstic in origin we aim at determining the efficiency of surface dissolution as a landshaping process on titan in a comparative planetology perspective with the earth as reference our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies the model depends on the solubility of solids in liquids the density of solids and liquids and the average annual net rainfall rates we compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over titan and earth timescales we then investigate the denudation rates of a superficial organic layer in liquid methane over one titan year at this timescale such a layer on titan would behave like salts or carbonates on earth depending on its composition which means that dissolution processes would likely occur but would be 30 times slower on titan compared to the earth due to the seasonality of precipitation assuming an average depth of 100 m for titan s lacustrine depressions these could have developed in a few tens of millions of years at polar latitudes higher than 70 n and s and a few hundreds of million years at lower polar latitudes the ages determined are consistent with the youth of the surface 1 gyr and the repartition of dissolution related landforms on titan

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

comparison of titan s north polar lakes with terrestrial analogs 1 the discovery of hydrocarbon lakes in the polar regions of titan offers a unique opportunity to compare terrestrial lakes with those in an extraterrestrial setting we selected 114 terrestrial lakes formed by different processes as analogs for comparison with the 190 titanian lakes that we had mapped in our previous study using the shuttle radar topography mission srtm c band backscatter data and the srtm water body data swbd we carried out an assessment of manual mapping versus existing automated mapping techniques and found the automated techniques to produce as good representations of the lake shorelines as the manual mapping in the terrestrial dataset we then calculated and compared terrestrial and titanian shoreline statistical parameters including fractal dimension shoreline development index and an elongation index we found different lake generation mechanisms on earth produce statistically different shorelines however we cannot identify any one mechanism or set of mechanisms to be responsible for forming the depressions enclosing the lakes on titan on the basis of our statistical analyses

identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the palar and cheyyar river basins southern india the palar and cheyyar river basins in tamil nadu state of southern india are characterised by different geological formations and groundwater is the major source for domestic agricultural and other water related activities hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality groundwater samples were collected once a month from 43 groundwater wells in this area from january 1998 to july 1999 sampling procedures and chemical analysis were carried out as per the standard methods chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality the chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river which is explained by a mixing mechanism in addition weathering of silicate minerals controls the concentration of major ions such as sodium calcium magnesium and potassium in the groundwater of this area further the activity ratios indicate that the groundwater is in equilibrium with kaolinite smectite and montmorrillonite the reverse ion exchange process controls the concentration of calcium magnesium and sodium in hard rock formations and dissolution of carbonate minerals and accessory minerals is the source of ca and mg in addition to cation exchange in the sedimentary formations in general the chemical composition of the groundwater in this area is influenced by rock water interaction dissolution and deposition of carbonate and silicate minerals ion exchange and surface water interactions

15n isotope biogeochemistry and natural denitrification process in groundwater application to the chalk aquifer of northern france the use of 15n natural isotope tracing in an aquifer contained within chalk rocks in northern france indicates that under certain hydrogeological conditions major denitrification occurs at the boundary where the aquifer becomes confined the nitrate concentrations decrease in the direction of groundwater flow accompanied by an exponential increase in 15n expressed in 15n of the residual nitrate this is characteristic of kinetic isotope effects which accompany the reduction of the nitrate ion during denitrification hydrogeochemical and bacteriological observations confirm this process natural isotope tracing also permits this process to be distinguished from local dilution with nitrate free surface water which would entail a major drop in nitrate values without 15n isotopic enrichment a model is proposed to explain the relatively small observed magnitude of the isotopic fractionation effect

global pattern of titan s dunes radar survey from the cassini prime mission 1 we present a map of the orientation and extent of titan s sand dunes derived from the complete radar imaging dataset from the cassini prime mission the 16 000 dune segments we have mapped cover 8 of the titan s surface suggesting a total coverage of 20 are confined within 30 of the equator and show local and regional deviations of dune orientation of up to about 40 from due eastwards there is no obvious global longitudinal pattern although some divergence with latitude is apparent the most striking pattern is one of collimation by and divergence around bright and or high terrain obstacles 100 300 m high obstruct dunes when the local slope is 1 50 or steeper while slopes 1 200 or shallower cause dunes to thin out as they climb or to deviate around the obstacles

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

internal 26al 26mg isotope systematics of a type b cai remelting of refractory precursor solids high precision sims 26 al 26 mg isotope analyses were performed for a pristine type b1 cai leoville 3535 1 on multiple mineral phases that include aluminum rich zoned melilite mantle ak20 ak60 magnesium rich melilite ak70 fassaite spinel and anorthite in the core the data yield a well defined internal isochron with an inferred initial 26 al 27 al ratio of 5 002 0 065 10 5 which is lower than those of bulk cais and pristine fine grained cais assuming homogeneous dis tribution of 26 al in the early solar system leoville 3535 1 formed 50 ka after the time corresponding to the bulk cai iso chron one anorthite analysis near the grain boundary adjacent to melilite shows sub lm scale heterogeneous magnesium distribution though the 26 al 26 mg data plot on the isochron regression thus the internal 26 al 26 mg system of the cai remained closed since the last melting event that crystallized anorthite high precision magnesium isotope analyses of magnesium rich minerals fassaite magnesium rich melilite and spinel show a small amount of scatter from the regression line 0 1 beyond analytical uncertainties most spinel and some fassa ite data are systematically displaced below and above the regression line respectively it is likely that spinel remained unmelted at the time of the last melting event while fassaite and anorthite crystallized from a partial melt the regression line made by fassaite and anorthite data shows an initial 26 al 27 al ratio indistinguishable from that using all data mass dependent fractionation of magnesium isotopes in spinel is the same as those in melilite and fassaite d 25 mg 5 indicating that magnesium isotope fractionation presumably from evaporative magnesium loss predated the last melting event thus a majority of the cai appears to have escaped magnesium isotope exchange with nebular gas during the last melting event except for the outer rim of the melilite mantle that shows slightly lower d 25 mg values the 26 al 26 mg systematics of this leoville type b cai suggest it experienced a final melting event at 50 ka after the initial al mg fractionation event this may correspond to melting during the active protostar stage known as class i during which sporadic high temperature heating events repeatedly affected refractory solids in the solar nebula 2012 elsevier ltd all rights reserved

astrophysics of cai formation as revealed by silicon isotope la mc icpms of an igneous cai silicon isotope ratios of a typical cai from the leoville carbonaceous chondrite obtained in situ by laser ablation mc icpms together with existing 25 mg 24 mg data reveal a detailed picture of the astrophysical setting of cai melting and subsequent heating models for the chemical and isotopic effects of evaporation of the molten cai are used to produce a univariant relationship between ph2 and time during melting the result shows that this cai was molten for a cumulative time of no more than 70 days and probably less than 15 days depending on temperature the object could have been molten for an integrated time of just a few hours if isotope ratio zoning was eliminated after melting by high subsolidus temperatures e g n1300 k for 500 yr in all cases subsolidus heating sufficient to produce diffusion limited isotope fractionation at the margin of the solidified cai is required these stable isotope data point to a two stage history for this igneous cai involving melting for a cumulative timescale of hours to months followed by subsolidus heating for years to hundreds of years the thermobarometric history deduced from combining si and mg isotope ratio data implicates thermal processing in the disk perhaps by passage through shockwaves following melting this study underscores the direct link between the meaning of stable isotope ratio zoning or lack thereof and the inferred astrophysical setting of melting and subsequent processing of cais 2007 elsevier b v all rights reserved

rb sr chronology of volatile depletion in differentiated protoplanets babi ador and all revisited abstract a strong depletion in moderately volatile elements is a characteristic feature of many planetary bodies in the inner solar system and either reflects the rapid accretion of planetesimals from an incompletely condensed solar nebula or is the result of energetic collisions during planetary accretion to better constrain the origin and timescales of this volatile depletion we have precisely measured sr isotope compositions in angrites eucrites and ca al rich inclusions cai angrites have an initial 87sr 86sr ador 0 698978 0 000004 which is indistinguishable from 87sr 86sr babi 0 698970 0 000028 obtained for eucrites in agreement with earlier studies we find that angrites and eucrites have higher initial 87sr 86sr ratios than cai at face value corresponding to model timescales for volatile loss of several millions of years however all the investigated cai are characterized by elevated 84sr 86sr ratios compared to angrites and eucrites which we interpret to reflect an excess of r process sr in the cai if this is correct then the nucleosynthetic sr isotope anomalies in the cai require an upward correction of their measured 87sr 86sr after this correction cai have an initial 87sr 86sr cai 0 698975 0 000008 which is indistinguishable from ador and babi this implies volatile loss from the angrite and eucrite parent bodies within less than 1 ma after formation of cai the volatile depleted nature of these differentiated protoplanets thus most likely reflects their rapid accretion from volatile poor dust in an incompletely condensed solar nebula

a long duration of the 16 o rich reservoir in the solar nebula as recorded in fine grained refractory inclusions from the least metamorphosed carbonaceous chondrites abstract oxygen isotope ratios and corresponding 26 al 26 mg isotope systematics of refractory inclusions from the least metamorphosed carbonaceous chondrites acfer 094 c ungrouped 3 00 and yamato 81020 co3 05 were measured with an ion microprobe most of the samples are fine grained refractory inclusions which are considered as condensates from high temperature solar nebular gas the refractory inclusions consistently exhibit 16 o enriched signatures among their interior phases spinel melilite and high ca pyroxene as well as phases within their rim structures spinel high ca pyroxene and adjacent anorthite this observation indicates that aggregated refractory condensates and the formation of rim structures occurred in the same 16 o rich environment evidence for mass dependent isotopic fractionation in oxygen and magnesium which would indicate a later flash heating process was not observed in rims all oxygen isotope data from fine grained cais are distributed between the carbonaceous chondrite anhydrous mineral ccam line and the primitive chondrule mineral pcm regression line based on oxygen isotope data from the acfer 094 chondrules the inferred initial 26 al 27 al ratios 26 al 27 al 0 of spinel melilite rich cais are 4 08 0 75 10 5 to 5 05 0 18 10 5 errors are 2 which are slightly lower than the canonical value of 5 25 10 5 as there is no petrologic evidence for re melting after condensation the lower 26 al 27 al 0 values of these cais indicate either they formed up to 0 3 ma after canonical cais or they formed before 26 al was homogeneously distributed in the solar nebula a pyroxene anorthite rich cai g92 has an 16 o rich signature like other cais but also has an order of magnitude less 26 mg excess in anorthite corresponding to a 26 al 27 al 0 of 5 21 0 54 10 6 as there is no evidence for a later mg isotopic disturbance g92 anorthite is interpreted to have formed by interaction with 16 o rich nebular gas at 2 3 ma after cai formation with the observation that 16 o rich refractory inclusions relatively 16 o poor chondrules and extremely 16 o poor cosmic symplectites within acfer 094 all plot on the pcm line it suggests that 16 o rich nebular gas and extremely 16 o poor primordial volatiles represent mass independent fractionated endmembers in the early solar system and that the pcm line represents a mixing line of these two endmembers

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

isostatic compensation of equatorial highlands on venus abstract spherical harmonic models for venus global topography and gravity incorporating magellan data are used to test isostatic compensation models in five 30 30 regions representative of the main classes of equatorial highlands the power spectral density for the harmonic models obeys a power law scaling with spectral slope 2 brown noise for the topography and 3 kaula s law for the geoid similar to what is observed for earth the venus topography spectrum has lower amplitudes than earth s which reflects the dominant lowland topography on venus observed degree geoid to topography ratios gtrs on venus are significantly smaller than degree gtrs for uncompensated topography indicative of substantial compensation assuming a global airy compensation most of the topography is compensated at depths greater than 100 km suggesting a thick lithosphere on venus for each region considered we obtain a regional degree of compensation c from a linear regression of bouguer anomaly versus bouguer gravity data geoid anomaly n versus topography variation h data for each sample were compared in the least squares sense to theoretical correlations for pratt airy and thermal thinning isostasy models yielding regional gtr zero elevation crustal thickness h and zero elevation thermal lithosphere thickness y l 0 respectively we find the regional compensation to be substantial c 52 90 and the h n data correlations in the chosen areas can be explained by isostasy models applicable on the earth and involving variations in crustal thickness airy and or lithospheric thermal thinning thickness however a thick crust and lithosphere y l 0 300 km must be assumed for venus compensation mechanisms are distributed as follows for the high plateaus of ovda gtr 9 m km and thetis gtr 11 m km mainly airy isostasy with h 50 60 km for the chasmata area sample gtr 15 m km airy with perhaps a thermal component finally a very strong thermal component for the broad swells of beta gtr 32 m km and atla gtr 25 m km with the lithosphere thinned to 100 km aphrodite terra which shows a marked eastward increase in pratt and airy model parameter values could be a candidate for thermal isostasy decay from east to west

hydrogeochemistry and quality of groundwater of coastal unconfined aquifer in amol ghaemshahr plain mazandaran province northern iran groundwater of the unconfined aquifer 1 100 sq km of a two tier coastal aquifer located in the amol ghaemshahr plain mazandaran province northern iran is classified into fresh and brackish water types fresh groundwater fgw samples n 36 are characterized by ca2 na mg2 k and hco3 cl so4 2 no3 spearman s rank correlation coefficient matrices factor analysis data values of the c ratio av 0 89 and cai and values of the molar ratios of ca2 hco3 ca2 so4 2 mg2 hco3 and mg2 so4 2 indicate that the ionic load in the fgw is derived essentially from carbonic acid aided weathering of carbonates and aluminosilicates saline sea water trapped in the aquifer sediments now admixed with the groundwater and ion exchange reactions values of the cai and na cl molar ratio suggest that the part of the ca2 mg2 content in 23 fgw samples is derived from clay minerals of the aquifer matrix and part of the na content in 20 12 and 3 fgw samples is derived respectively from alkali feldspar weathering clay minerals of the aquifer matrix and rain water and or halite brackish groundwater bgw samples n 4 contain cl as the dominant anion and their average total ionic concentration 38 65 meq l is 1 79 times higher than that of the fgw samples 21 50 meq l bgw pockets were generated by non conservative mixing of fgw with the upconed saline water from the underlying saline groundwater zone of the semi confined aquifer along bore wells involved in excessive extraction of groundwater from the unconfined aquifer groundwater belongs essentially to high salinity low sodium irrigation water class

relative rates of fluvial bedrock incision on titan and earth 1 observations of likely fluvial channels on the surface of titan along with titan s geologically youthful surface motivate this study of comparative fluvial erosion rates on titan and the earth the roles of bedload abrasion suspended load abrasion plucking and cavitation are considered despite orders of magnitude differences in some of the physical parameters that control fluvial incision on titan and the earth incision rates on titan are likely to be similar to terrestrial rates given similar conditions of slope discharge and sediment supply

al mg isotopic evidence for episodic alteration of ca al rich inclusions from allende textures mineral assemblages and al mg isotope systematics indicate a protracted episodic secondary mineralization history for allende ca al rich inclusions cais detailed observations from one type b1 cai one b2 one compact type a cta and one fluffy type a fta indicate that these diverse types of cais are characterized by two distinct textural and mineralogic types of secondary mineralization 1 grossular rich domains concentrated along melilite grain boundaries in cai interiors and 2 feldspathoid bearing domains confined mostly to cai margins just interior to the wark lovering rim sequence the al mg isotopic compositions of most secondary minerals in the type b1 cai and some secondary minerals in the other cais show no resolvable excesses of 26mg whereas the primary cai phases mostly yield correlated excesses of 26mg with increasing al mg corresponding to canonical initial 26al 27al 4 55 10 5 these secondary minerals formed at least 3 ma after the primary cai minerals all but two analyses of secondary minerals from the fluffy type a cai define a correlated increase in 26mg 24mg with increasing al mg yielding 26al 27al 0 4 9 2 8 10 6 the secondary minerals in this cai formed 1 8 3 2 ma after the primary cai minerals in both cases the timing of secondary alteration is consistent with but does not necessarily require alteration in an asteroidal setting one grossular from the type b2 cai and several grossular and secondary feldspar analyses from the compact type a cai have excesses of 26mg consistent with initial 26al 27al 4 5 10 5 especially in the compact type a cai where 26mg 24mg in grossular correlates with increasing al mg these 26mg excesses are almost certainly due to in situ decay of 26al they indicate a nebular setting for formation of the grossular the preservation of these diverse isotopic patterns indicates that heating on the allende parent body was not pervasive enough to reset isotopic systematics of fine grained secondary minerals secondary mineralization clearly was not restricted to a short time interval and at least some alteration occurred coincident with cai formation and melting events chondrule formation in the nebula this observation supports the possibility that alteration followed by melting affected the compositional evolution of cais

the decay of the spectrum of the gravitational potential and the topography for the earth summary the spectrum of the earth s gravitational potential and topography as represented by spherical harmonic expansions to degree 180 have been computed modelling the decay in the form of al values of a and for several degree l ranges were computed for degree range 5 180 was 2 54 for the potential and 2 16 for equivalent rock topography the potential decay was somewhat slower than that i e 3 implied by kaula s rule however at high degree ranges the values were larger 3 20 for degrees 101 180 agreeing better with recent determinations from terrestrial gravity data and geoid undulations implied by satellite altimetric data the values imply that the potential decays faster at higher l values the values of for topography were fairly uniform around 2 which agrees with a suggestion made by vening meinesz in 1951 we also found that the value for the earth s potential agrees well with the value implied by the topography with airy isostatic compensation with the depth of compensation equal to 30 km however the magnitude of the power implied by the topographic isostatic potential was approximately one third of the observed potential

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

high precision al mg isotopic systematics in usnm 3898 the benchmark all for initial 87sr 86sr in the earliest solar system abstract the allende cai usnm 3898 is the basis for all the lowest measured initial 87sr 86sr value in any solar system material including other cais gray et al 1973 if the value all is correct debated then usnm 3898 must be 1 2 million years older than other cais podosek et al 1991 this would require in turn that it have a much higher initial 26al 27al value than other cais on the order of 4 10 4 podosek et al 1991 showed that this is not the case with initial 26al 27al 4 5 0 7 10 5 but their mg isotopic data had large error bars and there was clear isotopic disturbance in the data having the highest 27al 24mg without the latter data the slope of their isochron is higher 5 10 1 19 10 5 and within large error of being supracanonical we used high precision sims to re determine the initial 26al 27al in this cai and obtained a value of 5 013 0 099 10 5 with an intercept 26 mg 0 008 0 048 and mswd 1 3 this value is indistinguishable from that measured in many other cais and conclusively shows that usnm 3898 is not uniquely ancient we also confirmed evidence of later isotopic disturbance similar to what podosek et al found indicating a re melting and evaporation event some 200 000 years after initial cai solidification

microwave dielectric constant of liquid hydrocarbons application to the depth estimation of titan s lakes 1 cassini radar reveals the surface of titan since flyby ta acquired on october 2004 the radar instrument discovered volcanic structures craters dunes channels lakes and seas in particular flyby t16 realized in july 2006 imaged tens of radar dark features close to titan s north pole they are interpreted as lakes filled with liquid hydrocarbons mainly methane a key material in the geologic and climatic history of titan in order to perform quantitative analysis and modeling of the radar response of titan s lakes the dielectric constant of liquid hydrocarbons is a crucial parameter in particular to estimate the radar wave attenuation we present here first measurements of the dielectric constant of lng liquefied natural gas mainly composed of methane at ku band 10 13 ghz we obtained a value 1 75 0 002j this value is used to model the radar backscattering of lakes observed during t16 flyby using a two layer scattering model we derive a relationship that is used to estimate a minimum depth for titan s lakes the proposed relationship is also coherent with the observation that the larger and then the deeper lakes are also the darker in radar images

tectonic climatic and lithologic influences on landscape fractal dimension and hypsometry implications for landscape evolution in the san gabriel mountains california east west variation in tectonic activity and strong north south climatic gradients provide a unique opportunity to study tectonic climatic and lithologic influences on landscape evolution in the san gabriel mountains california the competing tendencies of constructive tectonic and degradational climatic effects act against lithologic resistance to influence fluvial systems and thus the nature of adjacent and nested drainage basins landscape fractal dimension d a measure of surface roughness over a variety of scales and the hypsometric integral i a measure of the distribution of landmass volume above a reference plane are useful measures of altitudinal variation with scale as such they may provide clues as to the relative influences of tectonism climate and rock type topographic analyses of the san gabriel mountains clearly indicate that tectonism strongly influences d at range wavelength scales while rock type variation apparently influences d and i at smaller scales tectonism is also shown to influence i across the mountain piedmont junction at all scales investigated tectonic activity shows strong negative correlation with both i and d because tectonically active portions of the mountain front do not allow time for much landscape dissection by lower order streams three dimensional topographic modeling suggests climatic parameters exert a stronger influence on d than does tectonism this modeling also suggests an inverse correlation between range scale d and i with varying climate and uplift rate a positive correlation is observed in the san gabriel mountains we suggest this difference results from 1 differences in uplift style between the san gabriel mountains and the models and or 2 variation in rock type erodibility present in the san gabriel mountains but which was not modeled we postulate that the interaction of tectonic climatic and lithologic parameters influences the stable i and d to which a landscape evolves key questions remaining include 1 the time required to reach a stable i or d after a climatic or tectonic change 2 what does the fractal nature of topography tell us about the scaling characteristics of major landforming processes 3 how does climate influence range scale i and both range and small scale d and 4 what are the effects on i and d of range scale lithologic variation both in the models and in real landscapes

mountains on titan observed by cassini radar abstract the cassini titan radar mapper has observed elevated blocks and ridge forming block chains on saturn s moon titan demonstrating high topography we term mountains summit flanks measured from the t3 february 2005 and t8 october 2005 flybys have a mean maximum slope of 37 and total elevations up to 1930 m as derived from a shape from shading model corrected for the probable effects of image resolution mountain peak morphologies and surrounding diffuse blankets give evidence that erosion has acted upon these features perhaps in the form of fluvial runoff possible formation mechanisms for these mountains include crustal compressional tectonism and upthrusting of blocks extensional tectonism and formation of horst and graben deposition as blocks of impact ejecta or dissection and erosion of a preexisting layer of material all above processes may be at work given the diversity of geology evident across titan s surface comparisons of mountain and blanket volumes and erosion rate estimates for titan provide a typical mountain age as young as 20 100 million years

constraints on titan s topography through fractal analysis of shorelines titan s north polar hydrocarbon lakes offer a unique opportunity to indirectly characterize the statistical properties of titan s landscape the complexity of a shoreline can be related to the complexity of the landscape it is embedded in through fractal theory we mapped the shorelines of 290 of the north polar titanian lakes in the cassini synthetic aperture radar dataset out of these we used a subset of 190 lake shorelines for our analysis the fractal dimensions of the shorelines were calculated via two methods the divider ruler method and the box counting method at length scales of 1 10 km and found to average 1 27 and 1 32 respectively the inferred power spectral exponent of titan s topography from theoretical and empirical relations is found to be 2 which is lower than the values obtained from the global topography of the earth or venus some of the shorelines exhibit multi fractal behavior different fractal dimensions at different scales which we interpret to signify a transition from one set of dominant surface processes to another we did not observe any spatial variation in the fractal dimension with latitude however we do report significant spatial variation of the fractal dimension with longitude a systematic difference between the dimensions of orthogonal sections of lake shorelines is also noted which signifies possible anisotropy in titan s topography the topographic information thus gleaned can be used to constrain landscape evolution modeling to infer the dominant surface processes that sculpt the landscape of titan

the methane cycle on titan despite titan s cold temperatures about 93 7 k at the equator fluvial and atmospheric processes are active on this moon of saturn with methane playing a similar role to water on earth however titan lacks a global methane ocean and rainfall appears to be episodic saturn s moon titan is the second largest natural satellite in the solar system and the only one that possesses a substantial atmosphere with a surface temperature of 93 7 k at the equator titan s water is almost completely frozen out of the atmosphere water ice comprises between 35 and 45 of the mass of titan depending on the interior model but methane seems to play many of the roles on titan that water does on earth clouds have been observed fluvial and dendritic features have been imaged suggesting episodic heavy rainfall and there is compelling but circumstantial evidence for near polar lakes or seas of methane and its atmospheric photochemical product ethane however whereas earth possesses a massive global ocean of water titan lacks a global methane ocean and on titan low latitude rainfall appears to be an occasional process limited by the small amount of available solar energy compared with that of earth titan is therefore distinct from the earth but is also different from venus in retaining an active cycle of precipitation and evaporation and from mars in the preponderance of active fluvial and pluvial processes in the present day

groundwater origins and mixing pattern in the multilayer aquifer system of the gafsa south mining district a chemical and isotopic approach major ion geochemistry and environmental isotopes were used to identify the origins and the mineralisation processes of groundwater flowing within the three aquifer levels of the multilayer system of the gafsa south mining district southwestern tunisia it has been demonstrated that groundwaters are characterised by a ca mg so4 water type geochemical pattern is mainly controlled by the dissolution of halite gypsum and or anhydrite as well as by the incongruent dissolution of dolomite 18o and 2h values are much lower than the isotopic signature of regional precipitation and fall close to the meteoric water lines indicating that groundwaters have not been significantly affected by evaporation or mineral water reactions the distribution of stable and radiogenic isotopes 18o 2h 13c and 14c within the aquifer levels suggests that the deep confined aquifer receives a significant modern recharge at higher altitudes while the shallow unconfined aquifer has been mainly recharged under cooler paleoclimatic condition likely during late pleistocene and early holocene humid periods however waters from the intermediate confined unconfined aquifer have composite isotopic signatures highlighting that they are derived from a mixture of the two first end members

environmental isotopes and hydrochemical study applied to surface water and groundwater interaction in the awash river basin an environmental isotope and hydrochemical study was carried out to conceptualize the surface water and groundwater interaction and to explore the groundwater flow pattern in relation to the geological setting more emphasis is given to the afar depression where groundwater is a vital source of water supply conventional field hydrogeological study and river discharge records support the isotope and hydrochemical analysis the region is tectonically active comprising rift volcanic terrain bordered by highlands the result revealed that recent meteoric water is the major source of recharge three distinct groundwater zones were identified associated with the highlands transitional escarpment and the rift towards the rift the ionic concentration and isotopic enrichment 2h and 18dego increases following the groundwater flow paths which is strongly controlled by axial rift faults the groundwater flow converges to the seismically active volcano tectonic depressions with internal drainage and to the awash river within the afar depression at least four groundwater regimen are identified 1 fresh and shallow groundwater associated with alluvial deposits ultimately recharged by isotopically depleted recent highland rainfall and the evaporated awash river 2 cold and relatively younger groundwater within localized fractured volcanics showing mixed origin in axial fault zones 3 old groundwater with very high ionic concentration and low isotopic signature localized in deep volcanic aquifers and 4 old and hot saline groundwaters connected to geothermal systems the study demonstrated that dependable groundwater can only be obtained from the first two aquifer types in aerially restricted zones in flat plains following river courses local wadis and volcano tectonic depressions the conventional hydrogeological survey and discharge records indicate substantial channel losses from the awash river which becomes a more dominant source of recharge in central and lower awash valleys copyright 2007 john wiley sons ltd

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan