environmental factors controlling the δ13c and δ18o variations of recent fluvial tufas a 12 year record from the monasterio de piedra natural park ne iberian peninsula abstract a 12 year study 2000 2012 of the stable isotopes of recent fluvial tufas has been performed in the monasterio de piedra natural park river piedra ne iberian peninsula an area of mediterranean climate with intense tufa deposition since the pleistocene the biannual monitoring of the tufa calcite 13c and 18o signatures and of the water 18o value has demonstrated a clear seasonal pattern for the tufa calcite oxygen isotope composition with less negative values for cool periods which is consistent with regional temperature oscillations the tufa calcite 13c values only occasionally exhibit a pattern which is inconclusive and opposite to the 18o clear pattern the water 18o signature has a distinct seasonal pattern also opposite to the tufa calcite 18o clear pattern the temperature calculations from the tufa calcite 18o values and average water 18o values agree with the seasonal pattern of measured water temperatures with a mean difference of 2 3 c between the calculated and measured temperatures the anomalous values recorded for both the water and the tufa calcite oxygen isotope composition during a two year period are characterized by smoothing of the seasonal variations of the tufa calcite and by reversal of the water pattern there is also an increase in the differences between the measured and estimated temperatures the detected anomaly is roughly synchronous with a change in the isotopic signature of the regional precipitation 18o values this contribution demonstrates that tufas in this depositional and climatic context are good indicators of seasonal temperature oscillations and that tufas can also record other interannual environmental changes such as variations in the isotopic composition of precipitation these results can be extrapolated to ancient tufa systems developed in similar contexts which would expand the potential of tufas as high resolution records of paleoenvironmental conditions

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

microbes and mineral precipitation miette hot springs jasper national park alberta canada at miette hot springs so42 h2s ca2 sr2 and co32 rich waters with a mean temperature of 51 2 c are ejected from three spring vents and several minor seeps near the floor of sulphur creek valley runoff channels from the springs are colonized by cyanobacteria oscillatoria phormidium gloeocapsa synechococcus xenococcus that grow in resistant mats and as loose filaments within 0 5 m of the spring vents diatom assemblages cymbella mastagloia brachysira sellaphora rhopalodia nitzschia navicula pinnularia that dominate the flow paths 0 5 2 0 m from the vents and microbial mats with cyanobacteria and diatoms in the distal flow paths sulphate reducing bacteria and green algae are also present gypsum elemental sulphur and lesser quantities of calcite and strontianite precipitate from the spring waters microbial populations influence accumulation of mineral precipitates by i forming mats close to the spring vents on which crystals grow ii forming mats alongside the flow paths t

deeply incised submarine glacial valleys beneath the greenland ice sheet the bed topography beneath the greenland ice sheet controls the flow of ice and its discharge into the ocean a combination of sparse radar soundings of ice thickness and high resolution ice motion data suggest that many submarine ice covered valleys extend significantly deeper below sea level and farther inland than thought

dielectric properties of lava flows west of ascraeus mons mars 1 the sharad instrument on the mars reconnaissance orbiter detects subsurface interfaces beneath lava flow fields northwest of ascraeus mons the interfaces occur in two locations a northern flow that originates south of alba patera and a southern flow that originates at the rift zone between ascraeus and pavonis montes the northern flow has permittivity values estimated from the time delay of echoes from the basal interface between 6 2 and 17 3 with an average of 12 2 the southern flow has permittivity values of 7 0 to 14 0 with an average of 9 8 the average permittivity values for the northern and southern flows imply densities of 3 7 and 3 4 g cm 3 respectively loss tangent values for both flows range from 0 01 to 0 03 the measured bulk permittivity and loss tangent values are consistent with those of terrestrial and lunar basalts and represent the first measurement of these properties for dense rock on mars

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

analysis of co2 leakage through low permeability faults from natural reservoirs in the colorado plateau east central utah the numerous co 2 reservoirs in the colorado plateau region of the united states are natural analogues for potential geologic co 2 sequestration repositories to better understand the risk of leakage from reservoirs used for long term underground co 2 storage we examine evidence for co 2 migration along two normal faults from a reservoir in east central utah co 2 charged springs geysers and a hydrocarbon seep are localised along these faults these include natural springs that have been active for long periods of time and springs that were induced by recent drilling the co 2 charged spring waters have deposited travertine mounds and carbonate veins the faults cut siltstones shales and sandstones and the fault rocks are fine grained clay rich gouge generally thought to be barriers to fluid flow the geologic and geochemical data are consistent with these faults being conduits for co 2 to the surface consequently the injection of co 2 into faulted geologic reservoirs including faults with clay gouge must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere

diagenesis or dire genesis the origin of columnar spar in tufa stromatolites of central greece and the role of chironomid larvae two greek pleistocene tufa stromatolites were examined petrographically and with stable isotope geochemistry to determine whether calcite spar is of primary or diagenetic origin the younger ca 100 ka tufa from zemeno primarily is micritic with primary columnar calcite spar restricted to areas immediately above chironomid larval tubes this relationship suggests that chironomid larval feeding behaviour is responsible for the development of zemeno tufa columnar calcite probably involving biological substances smeared onto the tufa surface most micritic crystals are not suitably oriented to allow later post depositional growth resulting in columnar fabrics the older ca 1 ma predominantly sparry tufa from nemea contains some chironomid tubes and organic cyanobacterial filaments preserved in crystal fans but also contains many fabrics found in primary speleothem spar columnar spar here is unlikely to be the result of post depositional crystal growth a comparison of stable isotopic trends between the two tufa deposits suggests that both contain interpretable seasonal trends and implies little or minor post depositional alteration of either tufa consequently there is no basis for the common assumption that sparry tufa fabrics must be of diagenetic origin

effect of in stream physicochemical processes on the seasonal variations in δ13c and δ18o values in laminated travertine deposits in a mountain stream channel abstract travertines are potential archives of continental paleoclimate records of stable carbon and oxygen isotopic composition 13 c and 18 o in laminated travertine deposits from endogene spring waters show regular cyclic patterns which may be due to seasonal change in climate determinants such as temperature and rainfall in this study 13 c and 18 o measurements of three travertine specimens that grew naturally over the eight years 2004 2011 at upstream middle and downstream sites in a canal at baishuitai sw china are presented they exhibit clear seasonal variations that generally correlate with biannual laminations specifically 13 c and 18 o values show significant positive correlation with each other for the three travertine specimens with the correlation coefficients increasing downstream along the canal to reveal the factors governing the seasonal and spatial variations in 13 c and 18 o values newly formed travertines precipitated on plexiglas substrates are also examined both 13 c and 18 o of the substrate travertines are low in the summer rainy season and high in the winter dry season showing a great consistency with the patterns in the natural travertines spatially isotope values increase downstream in both seasons with higher increase rates in winter that are related to removal of larger fractions of dissolved inorganic carbon dic from the solution and stronger kinetic isotopic fractionation in winter due to in stream physicochemical processes including caco 3 precipitation and the associated degassing of co 2 seasonal changes in 13 c and 18 o in the travertines are amplified by two times between the upstream and downstream sites this is opposite to trends for epigene meteogene tufas whose seasonal changes in stable isotope compositions are reduced downstream we suggest in stream physicochemical processes are a potential reason for underestimation of annual temperature ranges that are inferred from epigene tufa 18 o data

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

high resolution records of rainfall events from clay bands in tufa individual rainfall events are recorded as thin clay bands in annually laminated freshwater carbonate tufa runoff from rainfall events entrains clay that then adheres to the tufa surface a specimen collected from southwest japan exhibits 100 clay bands formed during a 15 yr period from 1988 to 2002 the chronology of the clay bands was determined by using the temperature dependent cycle of oxygen isotope ratios in the carbonate and the clay content was quantified by electron probe microanalysis si x ray strength the obtained si x ray strength curve and actual rainfall record follow a nearly identical pattern the clay content of each band correlates with rainfall amount rainfall of 50 mm week produced sufficient amounts of suspended cave clay to produce clay bands in the tufa because the clay bands survive postdepositional alteration this new method can be applied to ancient tufa deposits and has great potential as a high resolution rainfall record for use in climate studies

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

multiple weather regimes over the north atlantic analysis of precursors and successors abstract the algorithm developed by vautard and legras is applied to a series of 37 winter of 700 mb geopotential height observations in order to identify quasi stationary patterns occurring over the extratropical north atlantic area weather regimes are obtained as solutions of a act of nine nonlinear statistical equations giving the balance of the large scale average tendency four regime patterns are found the first one exhibits the typical european blocking dipole the second one is an enhanced zonal flow the third one consists of a positive anomaly over greenland and the last one is characterized by a ridge over the eastern atlantic ocean the role played by the transient small scales in the maintenance of thew four regimes is discussed next the backward and forward memory times of the different weather regimes are established evidence is brought that the atmosphere keeps its memory of regime occurrences into the medium range 10 20 days backward memory times are shorter 5 10 days showin

dynamics and mass balance of taylor glacier antarctica 1 geometry and surface velocities 1 taylor glacier antarctica exemplifies a little studied type of outlet glacier one that flows slowly through a region of rugged topography and dry climate this glacier in addition connects the east antarctic ice sheet with the mcmurdo dry valleys a region much studied for geomorphology paleoclimate and ecology here we report extensive new measurements of surface velocities ice thicknesses and surface elevations acquired with insar gps and gpr the latter two were used to construct elevation models of the glacier s surface and bed ice velocities in 2002 2004 closely matched those in 2000 and the mid 1970s indicating negligible interannual variations of flow comparing velocities with bed elevations shows that along much of the glacier flow concentrates in a narrow axis of relatively fast flowing ice that overlies a bedrock trough the flow of the glacier over major undulations in its bed can be regarded as a cascade it speeds up over bedrock highs and through valley narrows and slows down over deep basins and in wide spots this pattern is an expected consequence of mass conservation for a glacier near steady state neither theory nor data from this taylor glacier study support the alternative view recently proposed that an outlet glacier of this type trickles slowly over bedrock highs and flows fastest over deep basins

stratigraphic restriction of stromatolites in a middle and upper ordovician foreland platform succession ottawa embayment eastern ontario stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in middle darriwilian and upper lower turinian ordovician strata of the laurentian foreland interior in the ottawa embayment eastern ontario these lithostratigraphic markers coincide with rapid tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow peritidal subtidal marine reworking of terrestrial or nutrient rich coastal systems the remaining chatfieldian edenian foreland platform succession represents deeper water deposition in response to elevated subsidence rates along the laurentian margin stromatolites are absent in this higher energy setting but microbial calcite is preserved as coccoid like microencrustations on skeletal debris stromatolites of darriwilian age are dolomitic occur in the carillon formation and are part of a regional 200 km onlap of peritidal sediment during onset of taconic orogenesis

factors controlling present day tufa dynamics in the monasterio de piedra natural park iberian range spain depositional environmental settings sedimentation rates and hydrochemistry the tufa record and hydrochemical characteristics of the river piedra in the monasterio de piedra natural park ne spain were studied for 6 years the mean discharge of this river was 1 22 m3 s the water was supersaturated with calcium carbonate the hco3 ca2 and tdic concentrations decreased along the 0 5 km long studied stretch whereas the calcite si showed no systematic downstream or seasonal variation over the same stretch several sedimentary subenvironments exist in which four broad types of tufa facies form 1 dense laminated tufa stromatolites 2 dense to porous massive tufa 3 porous coarsely laminated tufa with bryophytes and algae and 4 dense hard laminated deposits in caves the half yearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls and lower in slow flowing or standing river areas and in spray and splash areas mechanical co2 outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls but this process does not explain the seasonal changes in depositional rates the deposition rates showed a half yearly period pattern recorded in all fluvial subenvironments persistent over time 5 26 mm 0 86 g cm2 in warm periods 2 26 mm 0 13 g cm2 in cool periods mass balance calculations showed higher calcite mass values in warm 21 58 mg l than in cool 13 68 mg l periods this biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity tufa sedimentation was therefore controlled by both physicochemical and biological processes the results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi arid conditions in particular in the quaternary

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

trends in δ18o and δ13c values in lacustrine tufa mounds palaeohydrology of searles lake california four tufa facies have been identified in abundant tufa mounds that accumulated in searles lake california usa during the pleistocene covariance of 18 o and 13 c values within the tufa facies has been analysed and correlated with palaeo lake history this study demonstrates that characteristics of 18 o and 13 c values are different in each of the tufa facies and can be related to palaeo lake stages the first facies of tufa formation p has relatively low average 18 o and 13 c values 18 o 27 and 13 c 12 n 14 these low values are attributed to rapid increases in the lake volume this increase was followed by higher average 18 o and 13 c values of both the nodular n facies 18 o 18 and 13 c 41 n 24 and the columnar c facies 18 o 06 and 13 c 40 n 7 these higher values are interpreted to record a decrease in lake volume due to high evaporation and increased biogenic productivity following formation of facies c the lake was essentially dry during formation of the finely laminated lc facies facies lc formed subaerially as spring water flowed up through the central conduit of the mounds and cascaded down their periphery the relatively high 18 oa nd 13 c values for this facies 18 o 14 and 13 c 44 n 12 are due to evaporation and fast co2 degassing although covariant trends are well displayed variations in lake chemistry alter some of these trends due to periods of hyper alkalinity this study confirms the utility of stable isotopic analyses of lacustrine tufa facies to determine palaeo lake history

shrub morpho types as indicator for the water flow energy tivoli travertine case central italy abstract travertines from tivoli area central italy possess abundant shrub like fabrics that are laterally continuous over hundreds of square meters they occur dominantly in horizontal layers with aggradational and progradational stacking patterns their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the pre salt reservoirs offshore brazil and angola with huge oil accumulations petrographic and micro computer tomography analyses allowed the identification of six shrub morpho types i e narrow dendriform wide dendriform fili dendriform arborescent arbustiform and pustular dendriform shrubs are the most common lithotype in tivoli area and three different subtypes could be distinguished according to the arrangement of their branches the shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite ranging in average from 1 to 3 cm in height the shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas changing laterally into a slope system with crusts as the main lithotype changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho types making them very variegated shrub morphologies likely reflect specific micro environments that are controlled by water flow rates evaporation and microbial activity the latter processes influenced shrub fabric and morphology under high flow conditions co 2 degassing is the main process leading to carbonate precipitation consequently denser and tightly packed morphologies will precipitate composing mainly the crust lithotype in this scenario microbes are less dominant dendriform shrubs with narrow wide and fili morphologies are interpreted to occur in moderate to low energy water flows narrow dendriform shrubs reflect faster flowing conditions with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs slow to very slow flowing waters are more characteristic for the arborescent arbustiform and pustular shrubs that possibly are highly influenced by evaporation a decrease of water flow likely allows higher microbial activity and consequently shrub morphologies become more fragile and enriched in peloidal micritic aggregate fabrics

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

subsurface investigation of a rock glacier using ground penetrating radar implications for locating stored water on mars 1 the discovery of rock glacier like features on mars suggests the presence of flowing or once flowing ice rock mixtures these landforms which include lobate debris aprons concentric crater fill and lineated valley fill hold significant promise as reservoirs of stored water ice that could be used as fuel sources for human exploration of mars and provide a frozen record of the climatic history of the planet to understand the deformation and distribution of ice within these landforms fundamental descriptions of their internal structure and development are required to this end a ground penetrating radar investigation was initiated using rock glaciers in the san juan mountains of colorado as surrogates for similar martian landforms results obtained from one of these rock glaciers show that the interior of the landform is composed of a layered permafrost matrix of ice sediment and ice lenses that comprise thicker depositional units formed through high magnitude debris falls folds in the uppermost layers correspond to the surface expression of ridges and furrows suggesting that compressive stresses originating in the accumulation zone are transmitted downslope through the rock glacier rock glacier features on mars may also consist of layered permafrost which would suggest a history of development involving seasonal frost accumulation and or water influx from below in terms of water storage within martian analogs consideration must include the possibility that some water ice may be stored in relatively pure form within lenses and vein networks such as observed in the surrogate rock glacier of this study

sublimation and surface energy budget of taylor glacier antarctica taylor glacier an outlet of the east antarctic ice sheet flows through the transantarctic mountains and terminates in the dry valleys understanding how this glacier fluctuates is important for studies of glacial geology paleoclimate ice dynamics and ecology sublimation is the primary mass loss process for most of the glacier four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cma 1 we used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate calculated and measured ablation rates agree to within uncertainties indicating that wind speed and vapour pressure gradient a function of temperature and humidity are the governing variables as expected from theory measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier on average sublimation is about two times faster in summer than winter rapid sublimation occurs during storms and katabatic wind events but such periods contribute less to the annual total than do slow persistent losses spatially sublimation reaches a maximum midway along the glacier where descending surface air currents are focused by the topography of the aptly named tributary windy gully

age and isotopic constraints on pleistocene pluvial episodes in the western desert egypt abstract north africa has undergone drastic climatic changes over the past several hundred thousand years the timing of humid intervals called pluvials was investigated by uranium series disequilibrium dating of travertines from the kurkur oasis western desert egypt the youngest and best dated travertines 70 160 ka are found in wadi kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces travertines having an age of approximately 191 220 ka are exposed by differential erosion as linear mounds produced by spring systems over fracture zones in ancient wadis the oldest travertines having ages 260 ka are extensive cap limestone units above the oasis and were deposited in paludal and lacustrine environments oxygen isotope ratios were measured for the wadi travertines 18o values ranging from 16 7 to 19 1 smow and for spring mound travertines 18 5 20 5 equilibrium oxygen isotope fractionation calculations indicate that the kurkur travertines were deposited from waters having 18o values similar to ancient western desert groundwaters 11 sonntag et al 1978a b thorweithe 1990 sultan et al 1996 the ages of the travertines correspond to times of monsoonal maxima eustatic sea level high stands and interglacial maxima rainfall producing these groundwaters and travertines was significantly fractionated during atmospheric transport in contrast to modern meteoric waters 2 09 joseph et al 1992 implying a distant source for the pluvial waters increased precipitation recharge of western desert groundwaters and resultant travertine deposition are interpreted to be consequences of milankovitch insolation cycle forcing through enhanced atlantic and indian ocean monsoons during interglacial time periods

assessing the paleoenvironmental potential of pliocene to holocene tufa deposits along the ghaap plateau escarpment south africa using stable isotopes the tufa deposits of the ghaap plateau escarpment provide a rich yet minimally explored geological archive of climate and environmental history coincident with hominin evolution in south africa this study examines the sedimentary and geochemical records of ancient and modern tufas from buxton norlim limeworks groot kloof and gorrokop to assess the potential of these sediments for providing reliable chronologies of high resolution paleoenvironmental information chronometric dating demonstrates that tufa formation has occurred from at least the terminal pliocene through to the modern day the stable isotope records show a trend toward higher more variable 18o and 13c values with decreasing age from the end of the pliocene onwards the long term increase in 18o values corresponds to increasingly arid conditions while increasing 13c values reflect the changing proportion of c3 c4 vegetation in the local environment analysis of the thabaseek tufa in particular provides valuable evidence for reconstructing the depositional and chronological context of the enigmatic taung child australopithecus africanus collectively the results of the present study demonstrate the potential of these deposits for developing high precision records of climate change and ultimately for understanding the causal processes relating climate and hominin evolution

high resolution ice thickness mapping in south greenland airborne radar sounding is difficult in south greenland because of the presence of englacial water which prevents the signal from reaching the bed data coverage remains suboptimal for traditional methods of ice thickness and bed mapping that rely on geostatistical techniques such as kriging because important features are missing here we apply two alternative approaches of high resolution 300 m ice thickness mapping that are based on the conservation of mass to two regions of south greenland 1 qooqqup sermia and kiattuut sermiat and 2 ikertivaq these two algorithms solve optimization problems for which the conservation of mass is either enforced as a hard constraint or as a soft constraint for the first region very few measurements are available but there is no gap in ice motion data whereas for ikertivaq more ice thickness measurements are available but there are gaps in ice motion data we show that mass conservation algorithms can be used as validation tools for radar sounding we also show that it is preferable to apply mass conservation as a hard constraint rather than a soft constraint as it better preserves elongated features such as glacial valleys and ridges

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

actively growing siliceous oncoids in the waiotapu geothermal area north island new zealand oncoids that are actively growing in some of the shallow water pools around champagne pool waiotapu new zealand are formed of amorphous silica opal a with minor amounts of native sulphur the growth of these oncoids is being mediated by a high diversity microbial biota that achieves optimal growth in waters that have a temperature of 35 42 c and ph of 6 6 6 9 although this biota is dominated by coccoid bacilliform and filamentous cyanobacteria sulphur oxidizing bacteria are common in the cortical laminae of some oncoids in addition diatoms and silicified pollen grains are present in some cortical laminae the silicified microbes are superbly preserved with their three dimensional form and some of their internal structures being apparent including the sites of sulphur globules in the sulphur oxidizing bacteria the microbes probably acted as templates for silica precipitation and thereby mediated the growth of the oncoids some cortical laminae are formed entirely of silicified pollen grains that came from the pinus radiata that grow in the exotic pine plantations around champagne pool by using these laminae as a record of the annual pollination event typically in september november it can be shown that many of the oncoids are

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

mn and fe rich black travertine shrubs bacterially and nanobacterially induced precipitates abstract black shrubs i e arborescent forms are present within hot water travertine deposits from morocco the shrubs are commonly a few centimeters high and laterally grouped along individual laminae other than in mineral composition the black shrubs closely resemble the calcite shrubs from other hot water travertine deposits e g bagni di tivoli italy and mammoth hot springs yellowstone national park they are composed of a variety of minerals that are mn rich and also have a significant fe oxide component similar mn and fe rich shrub like forms have been described from desert varnish deep sea mn nodules and marine carbonates frutexites sem analyses show that bacterial bodies are densely packed within the mn rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae the bacterial bodies range in shape and size from rods commonly 0 8 m long by 0 1 m in diameter to spherical forms commonly 0 3 m in diameter that form chains up to 1 m long to nanobacterial spheres 150 to 200 nm in diameter that make up densely packed chains commonly 15 m in length it is well documented within the microbiological literature that not only do bacteria have the ability to induce the precipitation of mn and fe they can concentrate mn in mineral precipitates from waters with very low to essentially undetectable concentrations of mn the black mn rich shrubs within the moroccan travertines other hot water travertines and related features such as desert varnish deep sea mn nodules and frutexites are postulated to also be the result of bacterially induced precipitation

the calcareous tufa in the tadrart acacus mt sw fezzan libya an early holocene palaeoclimate archive in the central sahara article i nfo the palaeoclimatic signi cance of calcareous tufa deposits found in the presently hyperarid tadrart acacus massif central sahara sw libya is discussed on the basis of u th datings stable isotope analyses and the regional hydrogeological context these deposits formed mostly between c 9600 and 8100 yr bp the isotopic signature 18 o and 13 c of this tufa indicates that the water forming these carbonates originated as isotopically depleted rainwater as a result of the northward expansion of the sw african monsoon system during the early holocene carbonate sedimentation in the tadrart acacus decreased shortly before c 8000 yr bp attributed to a drop in precipitation in the course of the well known 8 2 kyr event a correlation between tufa development and climate change in n and e africa and in the mediterranean basin during the early holocene is discussed the effect of early holocene climate change on both the landscape and the dwellers living in the tadrart acacus region is also evaluated

differences in the delta 18 o and delta 13 c signatures of seasonal laminae comprising travertine stromatolites abstract alternation of sparry and micritic laminae in modern nonmarine travertine stromatolites from creeks in the arbuckle mountains of oklahoma and from eocene hot water deposits in the palm park formation of new mexico represent seasonal accumulations the sparry laminae with upright biogenic structures represent spring summer accumulations whereas the micritic laminae with flat lying microbial remains represent fall winter accumulations the 18o values of the modern creek waters average 5 04 spring summer and 5 25 fall winter smow and calcite precipitated in equilibrium with these waters should have 18o values of approximately 6 4 and 5 2 pdb for spring summer and fall winter precipitates respectively 18o values for calcite which precipitated during three month periods on test objects in the creek waters average 6 5 for spring summer and 4 9 for fall winter the sparry and micritic laminae comprising the naturally occurring modern stromatolites from these creeks average 6 4 for sparry spring summer and 5 2 for micritic fall winter laminae thus the agreement between 18o values for precipitates which formed in isotopic equilibrium with the creek water composition precipitates on test objects and the sparry and micritic laminae comprising naturally occurring modern stromatolites confirm the seasonal origin of the laminae the 13c values for the creek waters the test objects and the naturally occurring laminae of the stromatolites are higher in the sparry spring summer than the micritic fall winter deposits the 18o values obtained as a result of lamina by lamina analyses of the eocene hot water travertine stromatolites of new mexico do not display a seasonal trend but the 13c values are consistently higher in the sparry laminae than in the micritic laminae in addition increased concentrations of trace elements occur in the sparry relative to the micritic laminae of the hot water stromatolites the lamina by lamina stable isotopic and trace elemental analyses provide confirmation of the seasonal origin of the sparry spring summer and micritic fall winter laminae comprising the ancient stromatolites

microbial silica interactions in icelandic hot spring sinter possible analogues for some precambrian siliceous stromatolites silicified deposits such as sinters occur in several modern geothermal environments but the mechanisms of silicification and crucially the role of microorganisms in their construction are still largely unresolved detailed examination of siliceous sinter in particular sections of microstromatolites growing at the krisuvik hot spring iceland reveals that biomineralization contributes a major component to the overall structure with approximately half the sinter thickness attributed to silicified microorganisms almost all microorganisms observed under the scanning electron microscope sem are mineralized with epicellular silica ranging in thickness from 5 lm coatings on individual cells to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick within the overall profile there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite microbial layers are predominantly consisting of filamentous intact vertically aligned biomineralized cyanobacteria identified as calothrix and fischerella sp and weakly laminated silica layers which appear to be devoid of any microbial component the microbial layers commonly have a sharply defined base overlying the weakly laminated silica and a gradational upper surface merging into the weakly laminated silica these cyclic laminations are probably explained by variations in microbial activity active growth during spring summer allows the microorganisms to keep pace with silicification with the cell surfaces facilitating silicification while during their natural slow growth phase in the dark autumn winter months silicification exceeds the bacteria s ability to compensate i e grow upwards at this stage the microbial colony is probably not essential to microstromatolite formation with silicification presumably occurring abiogenically when conditions once again become favourable for growth recolonization of the solid silica surface by free living bacteria occurs cell motility is not responsible for the laminations we have also observed that microbial populations within the microstromatolite some several mm in depth appear viable i e they still have their pigmentation the trichomes are not collapsed cell walls are unbroken cytoplasm is still present and they proved culturable this suggests that the bulk of silicification occurred rapidly probably while the cells were still alive surprisingly however measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light pal only transmitted through the uppermost 2 mm therefore the deeper microbial

orbital radar imagery and atmospheric modeling reveal an aeolian origin for abalos mensa mars 1 icy deposits surrounding planum boreum mars contain crucial information for deciphering paleoclimate and past geologic processes at the martian north pole one such deposit abalos mensa is an enigmatic wedge of material located near the 1 km high rupes tenuis its unique location and lobate morphology have fostered formation hypotheses that assume either fluvial or aeolian erosion of a once larger ice deposit the aeolian scenario posed previously requires impact shielding of ancient basal unit material to provide an erosional remnant which seeds later deposition while the fluvial hypotheses invoke cryovolcanism beneath the younger north polar layered deposits npld and associated outflow to erode the adjacent chasmata here we combine newly available radar sounding data high resolution imagery digital elevation models and atmospheric modeling to examine internal structure and infer both the mechanisms for and timing of abalos mensa formation from this integrative approach we conclude that abalos mensa formed as a distinct feature via atmospheric deposition following erosion of rupes tenuis and grew concurrently with the rest of planum boreum as the npld accumulated the required processes are consistent with those observed today no exotic phenomena cryovolcanism fluvial activity or impact shielding appear necessary to explain the formation of abalos mensa

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

large tufa mounds searles lake california mounds that have formed around spring vents occur in a variety of environmental settings many at sites generally difficult or inaccessible for sampling in contrast over 500 tufa mounds occur in the dry bed of searles lake california the mounds range from minor features to 45 m in height most are 5 to 12 m high these mounds composed of calcite and aragonite formed associated with spring vents in the pleistocene lake bottom thus analyses of these mounds in searles lake provide a model with regard to the origin and architecture of tufa mounds the mounds consist of four distinctive tufa facies the initial deposits consist of porous tufa including the innermost porous 1 and the outermost porous 2 deposits followed by nodular tufa then columnar tufa and laminated crusts there are two simple sequences of tufa deposition the first sequence is from porous 1 to nodular to laminated crusts and finally to porous 2 a second sequence consists of porous 1 to columnar to laminated crusts and lastly to porous 2 facies changes are a response to changes in environmental conditions from deep water porous 1 facies to an essentially dry lake phase during and after the formation of laminated crusts facies to deep water porous 2 facies and at the present time totally dry the primary constituents that comprise the tufa deposits include thin laminae pisoids spherulites peloids and stromatolite like crusts on the microscopic scale these constituents dominantly make up nano spheres micro rods and rod like crystals as well as other calcified bodies these constituents are interpreted to be the calcified remains of bacterial bodies these findings suggest that microbial participation in the construct of other mounds should be a major concern of investigation both for terrestrial and extraterrestrial spring fed mounds