avalanche grainflow on a simulated aeolian dune 1 avalanches maintain the slipface of aeolian dunes which alters their airflow characteristics and sediment dynamics and results in the development of grainflow cross bedding we report on a series of experiments in which avalanches were observed on a 1 1 replica of a small 1 2 m brink height transverse dune in the dune simulation wind tunnel under wind velocities of 8 11 m s 1 changes in slipface topography were observed photographically and measured utilizing a 3 d laser scanner with 1 mm2 spatial resolution avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced changes in local slope confirm that the steep pre avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand 32 over all involved portions of the slipface avalanche volumes are measured and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed this independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

interaction between aeolian fluvial and playa environments in the permian upper rotliegend group uk southern north sea the permian upper rotliegend group in offshore uk quadrants 42 43 47 and 48 comprises a sequence of mixed aeolian fluvial playa deposits these deposits are up to 300 m thick and contain a record of the interaction between desert fluvial systems and adjacent aeolian and playa environments the relative dominance of water vs wind transport and deposition in this stratigraphic package was a function of fluctuations in the discharge of ephemeral fluvial systems and changes in water table playa level driven by a combination of climatic change and syndepositional tectonics the rotliegend sedimentary record is punctuated by numerous surfaces recording erosion by wind and water the origin of these surfaces is mostly climatic with periods of increased runoff resulting in fluvial incision especially near active faults during periods of reduced runoff wind erosion of fluvial deposits occurred with fluvially derived sand being reworked into expanding aeolian dune fields wind erosion also occurred as a rising water table isolated dunes from their sediment supply resulting in deflation of dunes down to the water table these surfaces formed in a basin that was subsiding thus even in a background of overall increasing accommodation space climatically driven falls in the water table allowed for periods of erosion the occurrence of significant erosion especially near syndepositional fault zones resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations

mapping the interactions between rivers and sand dunes implications for fluvial and aeolian geomorphology article i nfo the interaction between fluvial and aeolian processes can significantly change earth surface morphology when riversandsanddunes meet theinteractionofsedimenttransportbetweenthetwosystemscanleadtochangein eitherorboth systems however these two systemsare usuallystudied independently which leavesmanyques tions unresolved in terms of how they interact this paper carries out a global inventory using satellite imagery to identify 230 sites where there are significant fluvial aeolian interactions at each location key attributes such as wind river direction net sand transport direction fluvial aeolian meeting angle dune type and river channel pattern were identifiedand relationshipsbetween each factorwere analysed from thesedata six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems results from this classification confirm that only certain types of interaction were significant the meeting angle and dunetype themeeting angle and interaction type and finally thechannel pattern andinteraction type however the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

large wind ripples on mars a record of atmospheric evolution wind blowing over sand on earth produces decimeter wavelength ripples and hundred meter to kilometer wavelength dunes bedforms of two distinct size modes observations from the mars science laboratory curiosity rover and the mars reconnaissance orbiter reveal that mars hosts a third stable wind driven bedform with meter scale wavelengths these bedforms are spatially uniform in size and typically have asymmetric profiles with angle of repose lee slopes and sinuous crest lines making them unlike terrestrial wind ripples rather these structures resemble fluid drag ripples which on earth include water worked current ripples but on mars instead form by wind because of the higher kinematic viscosity of the low density atmosphere a reevaluation of the wind deposited strata in the burns formation about 3 7 billion years old or younger identifies potential wind drag ripple stratification formed under a thin atmosphere

a review of prokaryotic populations and processes in sub seafloor sediments including biosphere geosphere interactions article i nfo sub seafloor biosphere marine microbiology prokaryotic diversity dark energy biosphere geosphere interactions a general review of the sub seafloor biosphere is presented this includes an update and assessment of prokary otic cell distributions within marine sediments current deepest 1922 m and the impact of this on global sub seafloor biomass estimates these global estimates appear relatively robust to different calculation approaches and our updated estimate is 5 39 10 29 cells taking into consideration new data from very low organic matter south pacific gyre sediments this is higher than other recent estimates which is justified as several sediments such as gas hydrate deposits and oil reservoirs can have elevated cell concentrations the proposed relationship between elevated cell concentrations and milankovitch cycles in sequential diatom rich layers at some sites demonstratesnotonlyadynamicdeepbiosphere butalsothatthedeepbiosphereisanintegralpartofearthsys tem processes over geological time scales cell depth distributions vary in different oceanographic provinces and this is also reflected in contrasting biodiversity despite this there are some clear common sub seafloor prokary otes for bacteria these are the phyla chloroflexi gammaproteobacteria planctomycetes and the candidate phylum js1 and for archaea uncultivated lineages within the phylum crenarchaeota miscellaneous crenarchaeotal group and marine benthic group b euryarchaeota sagmeg marine benthic group d thermoplasmatales associated groups and thaumarchaeota marine group i in addition spores viruses and fungi have been detected but their importance is not yet clear consistent with the direct demonstration of active prokaryotic cells prokaryotes have been enriched and isolated from deep sediments and these reflect a subset of the total diversity including spore formers that are rarely detected in dna analyses activities are generally low in deep marine sediments 10 000 times lower than in near surface sediments however depth integrated activity calculations demonstrate that sub surface sediments can be responsible for the majority of sediment activity up to 90 and hence are biogeochemically important unlike near surface sediments competitive metabolisms can occur together and metabolism per cell can be 1000 times lower than

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

origin of abundant moonmilk deposits in a subsurface granitic environment subsurface granitic environments are scarce and poorly investigated a multi disciplinary approach was used to characterize the abundant moonmilk deposits and associated microbial communities coating the granite walls of the 16th century paranhos spring water tunnel in porto city north west portugal it is possible that this study is the first record of moonmilk in an urban subsurface granitic environment the morphology and texture mineralogical composition stable isotope composition and microbial diversity of moonmilk deposits have been studied to infer the processes of moonmilk formation these whitish secondary mineral deposits are composed of very fine needle fibre calcite crystals with different morphologies and density calcified filaments of fungal hyphae or bacteria were distinguished by field emission scanning electron microscopy stable isotope analysis revealed a meteoric origin of the needle fibre calcite with an important contribution of atmospheric co2 soil respiration and hco3 from weathering of ca bearing minerals the dna based analyses revealed the presence of micro organisms related to urban contamination including actinobacteria mainly represented by pseudonocardia hispaniensis thaumarchaeota and ascomycota dominated by cladosporium this microbial composition is consistent with groundwater pollution and contamination sources of the overlying urban area including garages petrol stations and wastewater pipeline leakage showing that the paranhos tunnel is greatly perturbed by anthropogenic activities whether the identified micro organisms are involved in the formation of the needle fibre calcite or not is difficult to demonstrate but this study evidenced both abiotic and biogenic genesis for the calcite moonmilk in this subsurface granitic environment this article is protected by copyright all rights reserved

coastal sabkha and salt pan deposition of the lower clear fork formation permian texas abstract middle permian leonard series evaporites carbonates and red beds of the lower clear fork formation in the texas panhandle display many features common to modern coastal and continental sabkha facies similarities among lithofacies patterns and sequences sedimentary structures and anhydrite halite textures and fabrics of both the lower clear fork formation and modern sabkha facies permit construction of a model of halite deposition in coastal sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins inferred coastal sabkha and marine inner shelf environments and lithofacies recognized in the lower clear fork formation are largely based upon analogous modern depositional se tings and include the following 1 red siltstone to mudstone deposited in a wadi or desert alluvial eolian plain and inner sabkha mud flats both passing basinward into 2 chaotic mudstone halite of an inner sabkha saline mud flat which flanked 3 inner sabkha salt pans bearing banded to massive halite and laminated anhydrite and 4 nodular nodular mosaic and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments salt pans may have formed in the inner sabkha as a result of displacive gypsum anhydrite growth and jacking up of the marginal sabkha surface which impeded seaward drainage of floodwater off the sabkha modern process sediment analogs include alluvial fans saline mud flats and salt pans of the coastal sabkhas in baja mexico the trucial coast and kutch india evaporites and terrigenous clastics in bristol dry lake california exhibit many features analogous with the permian suggesting that this setting though strictly continental serves as a process analog bromide values in lower clear fork halite average 40 ppm which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis upward decreasing values in the lower clear fork upper cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

displacive halite hoppers from the dead sea some implications for ancient evaporite deposits abstract large hopper shaped halite cubes up to 10 cm on a side grow displacively within holocene sediments near the southern end of the dead sea under conditions of high temperatures ionic concentrations and rapid rates of crystallization two theories of formation are presented downward diffusion of ions versus upward diffusion and evaporative pumping both alternatives are considered possible and the correct choice probably depends upon the location of the sediments at the time of precipitation whether subaqueous or subaerial a choice indeterminate at present because of human disturbance to the sediments prior to collection displacively formed halite crystals similar in morphology to the dead sea cubes are common in evaporite bearing carbonate rocks of many regions such as the salina fm u silurian michigan basin the kirkham mudstone u triassic cumbria england and the u miocene gessoso solfifera fm of sicily these are believed to have formed under conditions analogous to those in the present dead sea these observations taken together with those of other authors may now be used for the facies interpretation of ancient halite deposits

sand supply to the algodones dunefield south eastern california usa in an effort to gain a better understanding of the relationship between climate sand supply and aeolian sand deposition an investigation was undertaken in the algodones dunefield of south eastern california to determine 1 the source of the sand and 2 the mode of sand supply to the algodones dunefield textural geochemical and mineralogical analyses show that the dune sands were mainly derived from colorado river sands during episodes when the colorado river drained west to the salton basin instead of south to the gulf of california a model is presented which relates episodic aeolian deposition in the algodones dunefield to the growth of the resulting lake under a persistent intense north westerly wind regime and to subsequent desiccation of the lake following diversion of the colorado river to the gulf of california late holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south western united states these conditions are likely to have been the cause of intensified north westerly winds which coincided with high stands of lake cahuilla although diversion of the colorado river to the salton basin occurred at least three times during the late holocene it is evident that the river did not change its course in response to the majority of the floods it appears that the critical control on diversion of the river was the difference in gradient between courses leading to the salton basin and gulf of california which in turn was influenced by fluvial deposition and tectonic activity flooding was able to cause diversion of the colorado river to the salton basin only when the difference in gradient between the two courses was relatively small

a new ice thickness and bed data set for the greenland ice sheet 2 relationship between dynamics and basal topography new data sets of bed and surface elevation have been combined with balance velocities bed topography and radar reflectivity to investigate the relationship between ice flow and bed conditions it has been found that the bed topography affects the local driving stresses and initiates the onset of streaming flow in specific areas where there are large undulations this onset region only appears significantly inland in three areas the northeast greenland ice stream kangerdlugssuaq gletscher and a region in the southwest associated with abnormally low driving stresses and an apparently unnamed but active glacier bed reflectance values below the northeast ice stream suggest that basal melting could be occurring along its length and it seems likely therefore that the enhanced flow observed inland from the onset of streaming may be due in part to basal sliding

a microbial driver of chemical weathering in glaciated systems glaciological processes under ice sheets provide sustainable ecosystems for microbes forming an aquatic environment through basal melting and providing nutrients and energy from bedrock microbes facilitate solute production in most earth surface environments but the balance of biotic and abiotic weathering in subglacial environment is presently unknown this study demonstrates an up to eightfold increase in dissolved major cations in biotic relative to abiotic weathering experiments using glacial sediments and meltwater this conclusion greatly expands our view of earth s biogeochemically active weathering zone by incorporating the large wet based portions of glaciated continents both at present and during earth s history the profound environmental significance is that microbial processes have the ability to maintain terrestrial chemical weathering rates in cooling climates during glacial advance

multiple applications of dipmeter curves for analyzing evaporite formations examples from paleogene of bresse trough france the microresistivity curves recorded by dipmeters give much diverse information about evaporitic formations because these curves have a fine vertical resolution approximately 1 cm and show the very high contrast in resistivity between evaporites with high resistivity and clay and carbonate rocks which are porous and conductive examples are taken from the paleogene salt sequence and its overlying formations of the bresse trough in southeastern france the consistency of the 4 to 8 dipmeter curves allows clear recognition of different salt facies primary salt secondary salt and mixed patches of clay and carbonate within displacive halite layers and sulfate facies massive anhydrite nodular anhydrite etc the correlation of thin continuous carbonate and clastic beds using resistivity curves discloses with a high degree of precision the geometry of the various formations between wells examples show the detection of small magnitude halite dissolution a few meters vertically and the lateral effect of anhydrite hydration in this paper a method is proposed for determining structural dip of salt beds by computing dip angle and azimuth of thin conductive beds within the salt using the dualdip computer program a frequency distribution plot of these dip angles and azimuths gives a good indication of the dip of the salt beds

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone white canyon southern utah usa the permian cedar mesa sandstone represents the product of at least 12 separate aeolian erg sequences each bounded by regionally extensive deflationary supersurfaces facies analysis of strata in the white canyon area of southern utah indicates that the preserved sequences represent erg centre accumulations of mostly dry though occasionally water table influenced aeolian systems each sequence records a systematic sedimentary evolution enabling phases of aeolian sand sea construction accumulation deflation and destruction to be discerned and related to a series of underlying controls sand sea construction is signalled by a transition from damp sandsheet ephemeral lake and palaeosol deposition through a phase of dry sandsheet deposition to the development of thin chaotically arranged aeolian dune sets the onset of the main phase of sand sea accumulation is reflected by an upward transition to larger scale ordered sets which represent the preserved product of climbing trains of sinuous crested transverse dunes with original downwind wavelengths of 300 400 m regularly spaced reactivation surfaces indicate periodic shifts in wind direction which probably occurred seasonally compound co sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger slipfaceless draa each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio eustatic origin that characterize many permo carboniferous age successions sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level the main sand supply being former shallow marine shelf sediments that lay to the north west sand sea deflation and destruction would have commenced at or shortly after the time of maximum aridity as the available sand supply became exhausted restricted episodes of non aeolian accumulation would have occurred during humid interglacial phases accumulation and preservation being enabled by slow rises in the relative water table subsidence analysis within the paradox basin together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the cedar mesa erg sequences could be the product of 413 000 years so called long eccentricity cycles by contrast annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the cedar mesa succession was reserved for supersurface development

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

stable isotope evidence for microbial sulphate reduction at the bed of a polythermal high arctic glacier glacier beds may be host to a range of microbial communities which drive oxic waters towards anoxia along certain hydrological flowpaths chemical and isotopic signatures in meltwaters from finsterwalderbreen a polythermal glacier on sedimentary bedrock in svalbard show clear evidence for anoxia at the glacier bed increases in 34s and 18o of sulphate indicate that microbial sulphate reduction has resulted in significant decreases in sulphate concentration the 13c of the dissolved inorganic carbon dic is isotopically light 13c 8 which is consistent with the use of bedrock kerogen and or the necromass of sulphide oxidising bacteria as organic substrates for the sulphate reducing bacteria calculated rates of organic carbon mineralisation correspond to 10 of the total annual dic flux of the glacial meltwaters this microbial ecosystem is chemoautotrophically based ultimately being sustained by the kerogen and or bacterial necromass and sulphides in the bedrock this work suggests that glacier beds can be refugia for life when climatic and or atmospheric conditions are otherwise inclement and also supports the contention that microbial life is present in subglacial lake vostok

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

rock comminution as a source of hydrogen for subglacial ecosystems microbes live under glaciers that have persisted for millions of years without a clear energy supply analyses of crushed rocks suggest that interactions of glaciers with the rocks beneath can produce enough h2 to support methanogenic bacteria substantial parts of the beds of glaciers ice sheets and ice caps are at the pressure melting point1 the resulting water harbours diverse subglacial microbial ecosystems2 3 capable of affecting global biogeochemical cycles4 5 such subglacial habitats may have acted as refugia during neoproterozoic glaciations6 however it is unclear how life in subglacial environments could be supported during glaciations lasting millions of years because energy from overridden organic carbon would become increasingly depleted7 8 here we investigate the potential for abiogenic h2 produced during rock comminution to provide a continual source of energy to support subglacial life we collected a range of silicate rocks representative of subglacial environments in greenland canada norway and antarctica and crushed them with a sledgehammer and ball mill to varying surface areas under an inert atmosphere in the laboratory we added water and measured h2 production with time h2 was produced at 0 c in all silicate water experiments probably through the reaction of water with mineral surface silica radicals formed during rock comminution h2 production increased with increasing temperature or decreasing silicate rock grain size sufficient h2 was produced to support previously measured rates of methanogenesis under a greenland glacier we conclude that abiogenic h2 generation from glacial bedrock comminution could have supported life and biodiversity in subglacial refugia during past extended global glaciations

the differing biogeochemical and microbial signatures of glaciers and rock glaciers glaciers and rock glaciers supply water and bioavailable nutrients to headwater mountain lakes and streams across all regions of the american west here we present a comparative study of the metal nutrient and microbial characteristics of glacial and rock glacial influence on headwater ecosystems in three mountain ranges of the contiguous u s the cascade mountains rocky mountains and sierra nevada several meltwater characteristics water temperature conductivity ph metals nutrients complexity of dissolved organic matter dom and bacterial richness and diversity differed significantly between glacier and rock glacier meltwaters while other characteristics ca fe sio2 concentrations reactive nitrogen and microbial processing of dom showed distinct trends between mountain ranges regardless of meltwater source some characteristics were affected both by glacier type and mountain range e g temperature ammonium nh4 and nitrate no3 concentrations and bacterial diversity due to the ubiquity of rock glaciers and the accelerating loss of the low latitude glaciers our results point to the important and changing influence that these frozen features place on headwater ecosystems

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

windblown desert sands in coeval shallow marine deposits a key for the recognition of coastal ergs in the mid cretaceous iberian basin spain introductionthe action of the wind in ancientsedimentary records is commonlybased on the direct observations ofdune and interdune deposits within ahierarchy of aeolian bounding surfa ces a direct observation of ancientaeolian systems is not always possibleas they are prone to erosion and to theremoval of sand into other uvial andmarine systems although the aeoliandeposits may no longer be present their former existence can be inferredon the basis of grain size characteris tics and aeolian features on grainsurfaces aeolian sediments indeedconstitute an important source formarine deposits kukal and saadal lah 1973 fryberger et al 1983 widespread ne grained very well sorted quartz sandstones characterizeshallow marine facies in the mid cre taceous of the eastern spain iberianbasin the good sorting and round ness of the grains hint at the presenceof a nearby erg system suggestive ofan arid climatic zone along the west ern tethyan margin during the mid cretaceous geological settingthe mesozoic iberian basin along thewestern tethyan margin has one ofthe more complete lower middle cre taceous sedimentary records in eur ope the iberian range is a nw sestriking intraplate fold belt generatedby the tectonic inversion of theiberian basin during the palaeogene fig 1a b salas and casas 1993 capote et al 2002 this basin wasformed by crustal thinning duringthe late permian triassic and latejurassic early cretaceous rift stages salas and casas 1993 arche andlo pez go mez 1996 during thesecond rift stage extensional sub basins were formed as part of thelarger maestrazgo basin i e the east ern sector of the iberian basin fig 1b soria 1997 sands of boththe last synrift unit of these sub basins the escucha formation and of the rst post rift unit of the iberian basin the utrillas formation were depos ited across the estuarine deltaic and uvial environments fig 1c quer ol et al 1992 the sands are domi nantly ne grained show excellentsorting and as they consist almostpurely of quartz they are mineralog ically very mature the escucha and the utrillasformationsthe upper aptian middle albian es cucha formation aguilar et al 1971 sole de porta et al 1994 fig 1c was formed during the last phases ofthe second rift stage that a ected theiberian basin salas and casas 1993 it is a tidally in uenced heterolithicunit dominated by very well sorted ne sand and clay with coal bearingdepositsinitslowerpart andlocallyinthe basal part coarse grained siliciclas tic levels it lies upon the limestonesand marls of the urgonian platform aptian and is covered by sandstonesof the utrillas formation fig 1c pardo 1979 querol 1990 the es cucha formation was interpreted as adeltaic estuarine succession querolet al 1992 with a barrier island sys tem in the northern part of the olietesub basin rodri guez lo pez et al 2005 it was deposited in extensionalsub basins bounded by palaeogeo graphic thresholds produced by listricand block rotation faults the utrillasformation overlies the escucha for mation and is late albian early cen omanian in age and represents uvialdeposits pardo 1979 however theabstract

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

ants as a powerful biotic agent of olivine and plagioclase dissolution the biotic enhancement of ca mg silicate weathering has helped maintain earth s habit ability over geological time scales by assisting in the gradual drawdown of atmospheric co 2 25 years of in situ measurements of ca mg silicate mineral dissolution by ants termites root mats bare ground and a control reveals ants to be one of the most powerful biotic weathering agents yet recognized six sites in arizona and texas usa indicate that eight different ant species enhance mineral dissolution by 50 300 over controls a comparison of extracted soil at a 50 cm depth in ant colonies and adjacent bare ground shows a gradual accumulation of caco 3 content for all eight ant species over 25 yr ants thus have potential to provide clues on how to enhance contemporary carbon sequestration efforts to transform ca mg sili cates and co 2 into carbonate given that ants underwent a great diversification and biomass expansion over the cenozoic a speculative implication of this research is that ant enhance ment of ca mg silicate dissolution might have been an influence on cenozoic cooling

sedimentological modal analysis and geochemical studies of desert and coastal dunes altar desert nw mexico sedimentological compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the altar desert sonora mexico grain size distributions of the desert dune sands are influenced by the colorado river delta sediment supply and wind selectiveness the desert dune sands are derived mainly from the quartz rich colorado river delta sediments and sedimentary lithics the dune height does not exert a control over the grain size distributions of the desert dune sands the quartz enrichment of the desert dune sands may be due to wind sorting which concentrates more quartz grains and to the aeolian activity which has depleted the feldspar grains through subaerial collisions the desert dune sands suffer from little chemical weathering and they are chemically homogeneous with chemical alteration indices similar to those found in other deserts of the world the desert sands have been more influenced by sedimentary and granitic sources this is supported by the fact that ba and sr concentration values of the desert sands are within the range of the ba and sr concentration values of the colorado river quartz rich sediments the sr values are also linked to the presence of ca bearing minerals the zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes the golfo de santa clara and puerto penasco coastal dune sands are influenced by long shore drift tidal and aeolian processes coarse grains are found on the flanks whereas fine grains are on the crest of the dunes high tidal regimens long shore drift and supply from colorado delta river sediments produce quartz rich sands on the beach that are subsequently transported into the coastal dunes outcrops of quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands the chemical index of alteration cia values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous the trace element values for the coastal dune sands are similar to those found for the desert dune sands however an increase in sr content in the coastal dune sands may be due to more caco3 of biogenic origin as compared to the desert dune sands correlations between the studied parameters show that the dune sands are controlled by sedimentary sources e g colorado river delta sediments since heavy minerals are present in low percentages in the dune sands probably due to little heavy mineral content from the source sediment grain sizes in the dune sands are coarser than those in which heavy minerals are found and or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune a cluster analysis shows that the el pinacate group is significantly different from the rest of the dune sands in terms of the grain size parameters due to longer transport of the sands and the long distance from the source sediment whereas the puerto penasco coastal dune sands are different from the rest of the groups in terms of their geochemistry probably caused by their high caco3 content and slight decrease in the cia value copyright 2006 john wiley sons ltd

sedimentology and evaporite genesis in a holocene continental sabkha playa basin bristol dry lake california bristol dry lake a 155 km2 continental sabkha playa basin in the mojave desert of south eastern california is filled with at least 300 m of interbedded terrigenous clastics gypsum anhydrite and halite evaporite facies conform approximately to a bull s eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite transects through bristol dry lake from the alluvial fan to the centre of the playa reveal 1 crudely bedded alluvial fan clastics interfingering with 2 playa margin sand flat and wadi sand and silt followed by 3 gypsum anhydrite chaotic mud halite and clay of the saline mud flat and 4 salt pan halite beds terrigenous clastics were deposited in bristol dry lake by sheetflow and by suspension settling from ponded floodwater some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin thin nodular like beds of anhydrite and several types of gypsum occur across most of the playa giant hopper shaped halite cubes are suspended in saline mud flat facies suggesting that they grew displacively in brine soaked sediment just below the surface thick beds 4 m of halite in the playa centre may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods intense evaporation and brine level lowering and capillary discharge of brines the stratigraphy in the playa centre is cyclic an ideal cycle consists of 1 chaotic mud halite at the base overlain by 2 green to red clay with abundant giant hoppers and at the top 3 red clay gypsum and anhydrite with flaser to wavy bedded sand and silt this type of cycle probably records a gradual progradation of mud flat facies over salt pans bristol dry lake sediments are nearly identical to some of the permian evaporites of the permian basin region u s a and they can serve as modern analogues for ancient sabkha facies analysis

dune migration and slip face advancement in the rabe crater dune field mars 1 eight overlapping images of a dune slip face in rabe crater 35 e 44 s from the mars global surveyor mars orbiter camera show changes interpreted to be multiple grainflow events that would indicate present day sand saltation and dune migration new occurrences of these features appear sporadically throughout late southern summer and early fall and then no further changes occur throughout winter by the following summer the pattern of old streaks had been almost completely covered by new dark streaks assuming that this activity is typical from year to year migration rates are estimated to be on the order of 1 2 cm per martian year produced by south to southeasterly winds that blow mostly during the southern spring and early summer this slow migration rate is consistent with a present day sediment state that is either transport or availability limited

climbing zibars of the algodones abstract zibars are coarse grained low relief slipfaceless eolian bedforms that occur on sand sheets and within interdune corridors of many eolian sand seas zibar surface features consist exclusively of wind ripples and local shadow and shrub coppice dunes associated with vegetation a study of zibars located on the southwestern margin of the algodones dune field california shows that zibars and their associated interzibar areas are migrating features oriented transverse to oblique to the resultant sand transport direction zibars leave deposits formed by deposition on the zibar lee face the zibar shape modifies the near surface airflow to produce a subtle grain size change across the zibar interzibar surface flow expansion not separation leeward of the zibar crest causes the lee face deposits those preserved upon bedform migration to have the finest grain size on the zibar interzibar surface sediment coarser than that deposited on the zibar lee face is transported more slowly and less frequently and thus becomes concentrated on the zibar stoss slope and ultimately becomes interzibar deposits migration of zibars and interzibar areas can produce two characteristic depositional sequences depending upon the angle of climb for low angles of climb a sequence of stacked amalgamated interzibar deposits is preserved zibar deposits are absent amalgamated interzibar deposits consist of low angle usually less than 5 wind ripple laminae of medium to coarse sand given higher angles of climb deposits of both the entire interzibar and zibar lower lee face are preserved low angle interzibar deposits of medium to coarse sand are overlain tangentially by finer grained fine to medium sand wind ripple laminae dipping less than 15 of the zibar lee face lee face wind ripple laminae are sharply truncated and overlain by the succeeding set of interzibar wind ripple deposits this zibar interzibar sequence is distinctive and allows for the detailed interpretation of some ancient sand sheet deposits as left by migrating zibars a possible example of ancient zibar deposits is present in the entrada sandstone jurassic of southwestern colorado

sedimentary record of erg migration the sedimentary record of erg eolian sand sea migration consists of an idealized threefold division of sand sea facies sequences the basal division here termed the fore erg is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment these sand bodies consist of eolian strata deposited by small dune complexes zibars and sand sheets the fore erg represents the downwind leading edge of the erg and records the onset of eolian sedimentation basin subsidence coupled with erg migration places the medial division termed the central erg over the fore erg strata the central erg represented by a thick accumulation of large scale cross stratified sandstone is the product of large draa complexes eolian influence on regional sedimentation patterns is greatest in the central erg and most of the sand transported and deposited in the erg is contained within this region reduction in sand supply and continued erg migration will cover the central erg deposits with a veneer of back erg deposits this upper division of the erg facies sequence resembles closely the fore erg region similar types of eolian strata are present and organized in sand bodies encased in sediments of the upwind flanking depositional environment s back erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration or they may be completely absent because of great susceptibility to postdepositional erosion tectonic climatic and eustatic influences on sand sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence the resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western north america europe southern africa and south america

solute sources and geochemical processes in subglacial lake whillans west antarctica national science foundation nsf grants opp 0838933 1346250 and 1439774 italian national antarctic program barbante graduate fellowships from the nsf integrative graduate education and research traineeship program 0654336 and nsf center for dark energy biosphere investigations dissertation grant from the american association of university women

a preliminary study of the dynamics of a modern draa algodones southeastern california usa a transverse crescentic draa in the algodones dune field california was monitored for a year using surface process mapping aerial photography and supplemental wind measurement the draa is oriented by the long term resultant wind whereas its superimposed features are in equilibrium with the bedform modified secondary airflow surface airflow and the movement of superimposed bedforms is typically oblique or parallel to the draa brinkline particularly on the lee slope comparison of measurements of draa movement and sand deposition on the lee slope with expected rates calculated from wind data and draa size confirm that there is a significant component of sand flow parallel to the draa brinkline the internal structure being generated at the base of the draa lee slope is inferred from the surface processes active there within the space of a kilometer two types of compound cross strata separated by an area of simple cross strata are being produced this has significant implications for interpretations of ancient aeolian strata variations in internal structure types found in lateral sequence may be generated by one complex bedform and these cross strata may be simple or compound second order bounding surface orientations indicate resultant primary palaeowind directions compound cross strata dip directions indicate secondary flow conditions the existence of cross strata dip directions oblique or perpendicular to the second order surface indicates longitudinal secondary flow on the lee face but not necessarily a longitudinal or oblique draa without further detailed knowledge about various draa configurations and behaviour stratification attributed to draas can be used only to interpret activity on the lower draa lee face

lithological and hydrological controls on water composition evaporite dissolution and glacial weathering in the south central andes of argentina 33 34 s lithological and hydrological influence on fluvial physical and chemical erosion was studied in a glacierized sedimentary basin with high evaporite presence suspended particulate matter spm total dissolved solids tds and major ion concentrations were analysed for 2 years of different hydrologic condition i 2009 2010 q 100 average and ii 2010 2011 q 60 average annual hydrograph was simple regime type with one peak in summer related to snow melting the intra annual spm and tds variations were directly and inversely associated to q respectively snow chemistry showed continental influence na ca2 0 17 and atmospheric input of tds was 1 of the total exported flux river water was highly concentrated in ca2 and so42 4 mmol l 1 and in na and cl 3 mmol l 1 ca2 so42 and na cl molar ratios were 1 and related to q directly and inversely respectively major ion relationships suggest that river chemistry is controlled by evaporite gypsum and halite dissolution having a summer input from sulfide oxidation and carbonate dissolution and a winter input from subsurface flow loaded with silicate weathering products this variation pattern resulted in nearly chemostatic behaviour for ca mg2 and so42 whereas na cl and sio2 concentrations showed to be controlled by dilution concentration processes during the 2009 2010 hydrological year the fluxes of water spm and tds registered in the snow melting high q season were respectively 71 92 and 67 of the annual total whereas for equal period in 2010 2011 56 of water 86 of spm and 54 of tds annual fluxes were registered the spm fluxes for 2009 2010 and 2010 2011 were 1 19 106 and 0 79 106 t year 1 whereas tds fluxes were 0 68 106 and 0 55 106 t year 1 respectively export rates for 2009 2010 were 484 t km2 year 1 for spm and 275 t km2 year 1 for tds these rates are higher than those observed in glacierized granite basins and in non glacierized evaporite basins suggesting a synergistic effect of lithology and glaciers on physical and chemical erosion copyright 2014 john wiley sons ltd

an empirical model of aeolian dune lee face airflow airflow data gathered over dunes ranging from 60 m tall complex crescentic dunes to 2 m tall simplecrescentic dunes were used to develop an empirical model of dune lee face airflow for straight crested dunes the nature of lee face flow varies and was found to be controlled by the interaction of at least three factors dune shape the incidence angle between the primary wind direction and the dune brinkline and atmospheric thermal stability three types of lee face flow separated attached and deflected along slope or attached and undeflected were found to occur separated flows characterized by a zone of low speed 0 3o of crestal speed back eddy flow typically occur leeward of steep sided dunes in transverse flow conditions unstable atmospheric thermal stability also favours flow separation attached flows characterized by higher flow speeds up to 84 of crestal speed that are a cosine function of the incidence angle typically occur leeward of dunes that have a lower average lee slope and are subject to oblique flow conditions depending on the slope of the lee face attached flow may be either deflected along slope lee slopes greater than about 20 or have the same direction as the primary flow lee slopes less than about 20 neutral atmospheric thermal stability also favours flow attachment as each of the three types of lee face flow is defined by a range of wind speeds and directions the nature of lee face flow is intimately tied to the type of aeolian depositional process i e wind ripple or superimposed dune migration grainflow or grainfall that occurs on the lee slope and the resulting pattern of dune deposits therefore the model presented in this paper can be used to enhance the interpretation of palaeowind regime and dune type from aeolian cross strata

physical and chemical controls on habitats for life in the deep subsurface beneath continents and ice the distribution of life in the continental subsurface is likely controlled by a range of physical and chemical factors the fundamental requirements are for space to live carbon for biomass and energy for metabolic activity these are inter related such that adequate permeability is required to maintain a supply of nutrients and facies interfaces invite colonization by juxtaposing porous habitats with nutrient rich mudrocks viable communities extend to several kilometres depth diminishing downwards with decreasing porosity carbon is contributed by recycling of organic matter originally fixed by photosynthesis and chemoautotrophy using crustal carbon dioxide and methane in the shallow crust the recycled component predominates as processed kerogen or hydrocarbons but abiotic carbon sources may be significant in deeper metamorphosed crust hydrogen to fuel chemosynthesis is available from radiolysis mechanical deformation and mineral alteration activity in the subcontinental deep biosphere can be traced through the geological record back to the precambrian before the colonization of the earth s surface by land plants a geologically recent event subsurface life probably dominated the planet s biomass in regions of thick ice sheets the base of the ice sheet where liquid water is stable and a sediment layer is created by glacial erosion can be regarded as a deep biosphere habitat this environment may be rich in dissolved organic carbon and nutrients accumulated from dissolving ice and from weathering of the bedrock and the sediment layer

siderophore promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater river and ocean water abstract the rare earth elements ree are a group of trace elements that have short marine residence times and that in river lake and marine surface waters are typically associated with organic and inorganic particles explosive volcanic eruptions such as the 2010 eruptions of eyjafjallajokull volcano in iceland produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms to become bioavailable however this iron needs to be solubilized by complexing agents such as siderophores a well studied example of such a chelator is the biogenic siderophore desferrioxamin b dfob based on results from incubation experiments with glacial meltwater rich river waters from southern iceland which are rich in suspended volcanic ash and that had been incubated with and without dfob respectively we here show that siderophores not only enhance the release of iron but also promote the mobilization of ree from these particles in the presence of dfob partial dissolution of volcanic ash and presumably other lithic particles produces a flux of dissolved ree into ambient waters that is characterized by depletion of the light ree over the middle ree and by selective enrichment of cerium due to the formation of dissolved ce iv dfob complexes in siderophore rich environments this siderophore bound ree flux has the potential to modify the concentrations and distribution of the dissolved ree and of the isotopic composition of dissolved nd in glacial meltwaters river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater which are assumed to account for the missing nd flux to seawater thermodynamic data further suggest that siderophore promoted element mobilization could also be important for other polyvalent trace elements such as hf

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

influence of bedrock mineral composition on microbial diversity in a subglacial environment microorganisms in subglacial environments drive the chemical weathering of bedrock however the influence of bedrock mineralogy on the composition and activity of microbial assemblages in such environments is poorly understood here using a combination of in situ mineral incubation and dna fingerprinting techniques we demonstrate that pyrite is the dominant mineralogical control on subglacial bacterial community structure and composition in addition we show that the abundance of fe in the incubated minerals influences the development of mineral associated biomass the ubiquitous nature of pyrite in many common bedrock types and high so 4 2 concentrations in most glacial meltwaters suggest that pyrite may be a dominant lithogenic control on microbial communities in many subglacial systems mineral based energy may therefore serve a fundamental role in sustaining subglacial microbial populations and enabling their persistence over glacial interglacial time scales

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

conditions favourable for the formation of warm climate aeolian sand sheets aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent sand sheets are ubiquitous to modern warm climate sand seas generally occurring marginal to dune fields although they may exist within the interior of a sand sea or independent of a dune field sand sheet deposits are recognized in ancient aeolian sequences where they may account for significant accumulations of low angle aeolian stratification we suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets a study of six modern sand sheets in north america located at great sand dunes gran desierto dumont algodones padre island and colorado river delta indicates that the factors favourable for sand sheet development are 1 a high water table 2 surface cementation or binding 3 periodic flooding 4 a significant coarse grained sediment population and 5 vegetation these factors are reflected in the nature of stratification and the accessory features of sand sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the triassic dolores and pennsylvanian permian rico formations

variability in the chemical composition of in situ subglacial meltwaters meltwaters collected from boreholes drilled to the base of the haut glacier d arolla switzerland have chemical compositions that can be classified into three main groups the first group is dilute whereas the second group is similar to though generally less concentrated in major ions than contemporaneous bulk glacial runoff the third group is more concentrated than any observed bulk runoff including periods of flow recession waters of the first group are believed to represent supraglacial meltwater and ice melted during drilling limited solutes may be derived from interactions with debris in the borehole the spatial pattern of borehole water levels and borehole water column stratification combined with the chemical composition of the different groups suggest that the second group represent samples of subglacial waters that exchange with channel water on a diurnal basis and that the third group represent samples of water draining through a distributed subglacial hydraulic system high no 3 concentrations in the third group suggest that snowmelt may provide a significant proportion of the waters and that the residence time of the waters at the bed in this particular section of the distributed system is of the order of a few months the high no 3 concentrations also suggest that some snowmelt is routed along different subglacial flowpaths to those used by icemelt the average so2 4 hco 3 so2 4 ratio of the third group of meltwaters is 0 3 suggesting that sulphide oxidation and carbonate dissolution which gives rise to a ratio of 0 5 cannot provide all the hco 3 to solution hence carbonate hydrolysis may be occurring before sulphide oxidation or there may be subglacial sources of co2 perhaps arising from microbial oxidation of organic c in bedrock air bubbles in glacier ice or pockets of air trapped in subglacial cavities the channel marginal zone is identified as an area that may influence the composition of bulk meltwater during periods of recession flow and low diurnal discharge regimes 1997 by john wiley sons ltd

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

influence of glaciation on mechanisms of mineral weathering in two high arctic catchments in order to investigate the effect of glaciation on mineral weathering the stream water chemistry and the bacterial community composition were analysed in two catchments containing nominally identical sedimentary formations but which differed in the extent of glaciation the stream waters were analysed for major ions 34s 18oso4 and 18oh2o and associated stream sediments were analysed by 16s rrna gene tagged sequencing sulphate comprised 72 86 and 35 45 of the summer anion budget in meq in the unglaciated and glaciated catchments respectively this indicates that sulfuric acid generated from pyrite weathering is a significant weathering agent in both catchments based on the relative proportions of cations sulphate and bicarbonate the stream water chemistry of the unglaciated catchment was found to be consistent with a sulphide oxidation coupled to silicate dissolution weathering process whereas in the glaciated catchment both carbonates and silicates weathered via both sulfuric and carbonic acids stable isotope measurements of sulphate together with inferences of metabolic processes catalysed by resident microbial communities revealed that the pyrite oxidation reaction differed between the two catchments no 34s fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions in contrast 34s and 18oso4 values were positively correlated in the glaciated catchment and were positively offset from pyrite this was interpreted to reflect pyrite oxidation under anoxic conditions with loss of s intermediates this study suggests that glaciation may alter stream water chemistry and the mechanism of pyrite oxidation through an interplay of biological physical and chemical factors

iron and manganese speciation and cycling in glacially influenced high latitude fjord sediments west spitsbergen svalbard evidence for a benthic recycling transport mechanism abstract glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high latitude regions little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in smeerenburgfjorden kongsfjorden and van keulenfjorden along western svalbard solid phase iron and manganese speciation determined by sequential chemical extraction could be linked to the compositions of the local bedrock and hydrological weathering conditions below the local glaciers the concentration and sulfur isotope composition of chromium reducible sulfur crs in kongs and van keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers the varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords high reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of fresh organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron up to 800 m and manganese up to 210 m concentrations in kongsfjorden and van keulenfjorden sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords on going benthic recycling of glacially derived dissolved iron into overlying seawater where partial re oxidation and deposition occurs facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters such iron dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond by contrast low delivery of reducible iron oxyhydr oxide phases and elevated organic carbon mineralization rates driven by elevated input of fresh marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer smeerenburgfjorden sites which may limit iron fluxes to the water column

aeolian stratification and facies association in desert sediments arran basin permian scotland abstract permian aeolian sediments on the island of arran are divisible into dune including draa and interdune deposits both types display a distinctive and unusually wide variation in grain size the dominant features of the dune deposits are grainfall lamination sandflow lamination and inverse graded lamination associated with ripple form lamination and normal graded lamination the flat lying aeolian interdune deposits are characterised by granule and sand ripples horizontal lamination in coarse sand and granules plane bed lamination and inverse graded lamination associated structures include ripple form lamination and deflation lags three types of trace fossil associated with completely bioturbated horizons occur in some low angle dune and interdune deposits the aeolian facies interfinger with alluvial fan deposits giving rise to three recognizable facies belts marginal aeolian deposits are associated with fluvial conglomerates and are dominated by interdune deposits and occasionally very thin barchan deposits set height 3 37 cm intermediate aeolian deposits are characterized by interbedded crescentic dune small draa dune set height 5 cm 4 5 m and interdune deposits and rare fluvial and lake sediments basinal aeolian deposits are dominated by draa deposits dune set height 0 2 28 m associated with rare interdune sediments transverse dunes and draas were moved by north eastern palaeowinds towards the foot of the alluvial fans the aeolian sediments were deposited in a fault bounded desert basin

microbial sulphate reduction during neoproterozoic glaciation port askaig formation uk the neoproterozoic port askaig formation contains widespread pyrite within many diamictite beds across scotland and ireland the quantity of pyrite is anomalous for coarse grained rocks especially in rocks deposited at a time when seawater contained low sulphate levels owing to a continental ice cover which inhibited weathering sulphur isotope compositions evolve from lightest values down to 3 1 at the base of the formation to highly positive compositions in the overlying bonahaven dolomite mean 44 8 this trend is consistent with progressive utilization of available sulphate by closed system microbial sulphate reduction together with records from other contemporary diamictite successions there emerges a picture of global microbial activity during neoproterozoic snowball earth glaciation supplementary material details of the sulphur isotopic composition are given at https doi org 10 6084 m9 figshare c 3768959

development of spatially diverse and complex dune field patterns gran desierto dune field sonora mexico the pattern of dunes within the gran desierto of sonora mexico is both spatially diverse and complex identification of the pattern components from remote sensing images combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns age bracketing by optically stimulated luminescence osl indicates that the simple patterns represent relatively short lived aeolian constructional events since 25 ka the simple dune patterns consist of i late pleistocene relict linear dunes ii degraded crescentic dunes formed at 12 ka iii early holocene western crescentic dunes iv eastern crescentic dunes emplaced at 7 ka and v star dunes formed during the last 3 ka recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern palaeowind reconstructions based upon the rule of gross bedform normal transport are largely in agreement with regional proxy data the sediment state over time for the gran desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment ancestral colorado river sediment and contemporaneous influx from the lower colorado river valley and coastal influx from the bahia del adair inlet aeolian constructional events are triggered by climatic shifts to greater aridity changes in the wind regime and the development of a sediment supply the rate of geomorphic change within the gran desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

algodones dune field of southeastern california case history of a migrating modern dune field the algodones dune field of southeastern california is one of the largest active dune fields in north america the dune field is migrating in an easterly direction oblique to the resultant sand flow direction s 24 e the migration of the algodones results from an interaction between regional winds and the dune field this interaction generates a localized secondary flow that has caused the dune field to migrate in a direction oblique to the resultant sand flow direction four lines of evidence suggest that the algodones has migrated in an easterly direction 1 a ramp interpreted as the trailing edge of the dune field 35 m thick and 500 m wide composed of aeolian deposits that borders the western edge of the dune field no similar deposits are found on the eastern leading edge margin of the dune field 2 leading edge sand sheet deposits are exposed in interdune areas within the dune field these deposits are west of the modern leading edge sand sheet 3 across the breadth of the dune field sands are consistently coarser and more poorly sorted in the west and finer and better sorted in the east this observation suggests that sand is transported from west to east 4 eastward migration of a large compound complex crescentic dune if the dune field continues to migrate it will deposit a vertical sequence consisting of a basal sand sheet deposit consisting of wind and water ripple laminae small scale aeolian cross strata and ephemeral stream wadi deposits aeolian dune deposits consisting of medium scale aeolian compound cross strata small scale simple sets of aeolian cross strata with highly variable dip directions a sand sheet containing low angle wind ripple cross strata capped by a coarse sand lag super bounding surface

basal temperature evolution of north american ice sheets and implications for the 100 kyr cycle 1 we simulate three dimensional ice temperature fields to examine spatial temporal history of the subglacial thermal environment during the last glacial cycle model results suggest that 60 80 of the laurentide ice sheet was cold based frozen to the bed at the lgm and therefore unable to undergo large scale basal flow the fraction of warm based ice increases significantly through the ensuing deglaciation with only 10 20 of the laurentide ice sheet frozen to the bed by 8 kyr bp this basal thermal evolution a function of both climatic and ice sheet history could enable a dynamical switch to widespread basal flow through the deglacial period because basal flow has the capacity to evacuate large amounts of ice from the interior of continental ice sheets creating thin and climatically vulnerable ice masses this switch in flow regime may have played a significant role in glacial terminations and the 100 kyr glacial cycle

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

rates of chemical denudation and co2 drawdown in a glacier covered alpine catchment solute fluxes from a glacier covered alpine catchment are partitioned into components derived from sea salt acid aerosol dissolution of atmospheric co2 and crustal weathering the bulk of solute is crustally derived coupled sulfide oxidation and carbonate dissolution so cd and carbonation of carbonate minerals generate approximately equal amounts of solute chemical denudation constitutes 1 5 of solid denudation but is significantly higher than the continental average co2 drawdown by weathering reactions varies directly with discharge and suspended sediment load and inversely with meltwater p co2 if it is generally true that flushing rates control co2 drawdown in glacier covered catchments then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial interglacial time scales

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd