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

measurement of snow density and microstructure using computed tomography in the past two dimensional images of internal snow structure have been obtained through plane surface sections or thin sections these techniques are time consuming and necessarily destroy the snow specimen computed tomography ct allows similar images to be obtained but in a more efficient and non destructive manner to demonstrate the methodology a ct scanner was used to obtain cross sectional images over time of a snow sample undergoing kinetic growth metamorphism densities calculated from the ct images correlated well to density measured using a traditional method a procedure was developed that allows the ct image to be converted to binary in an objective manner employing innovative stereological software the microstructural properties grain diameter bond diameter neck length and intercept length of the snow were then measured from the two dimensional ct images the presented methodology provides significant improvements over previous techniques requiring less time and labor to obtain high quality microstructural data

snow density along the route traversed by the japanese swedish antarctic expedition 2007 08 during the japanese swedish antarctic traverse expedition of 2007 08 we measured the surface snow density at 46 locations along the 2800 km long route from syowa station to wasa station in east antarctica the mean snow density for the upper 1 or 0 5 m layer varied from 333 to 439 kg m 3 over a region spanning an elevation range of 365 3800 m a s l the density variations were associated with the elevation of the sampling sites the density decreased as the elevation increased moving from the coastal region inland however the density was relatively insensitive to the change in elevation along the ridge on the antarctic plateau between dome f and kohnen stations because surface wind is weak in this region irrespective of elevation the wind speed was suggested to play a key role in the near surface densification the results of multiple regression performed on the density using meteorological variables were significantly improved by the inclusion of wind speed as a predictor the regression analysis yielded a linear dependence between the density and the wind speed with a coefficient of 13 5 kg m 3 m s 1 1 this relationship is nearly three times stronger than a value previously computed from a dataset available in antarctica our data indicate that the wind speed is more important to estimates of the surface snow density in antarctica than has been previously assumed

unconformable stratigraphy in east antarctica part i large firn cosets recrystallized growth and model evidence for intensified accumulation unconformable firn stratigraphy exists throughout a 650 km long radar profile that we recorded down flow of megadune fields in the byrd glacier east antarctica catchment profile segments reveal cosets of prograding bedding sequences up to 90 m thick and with lateral along crest dimensions up to tens of kilometers we profiled them in oblique section and nearly parallel to the prevailing wind the prograding snow accumulates on broad low windward slopes located above ice bed depressions which implies long term slope stability the apparent subglacial control implies that the accumulation progrades in balance with ice velocity which we measured at 30 ma 1 the sequences prograde over intensely modified and recrystallized wind glaze firn visible in the profiles as unstratified layers and zones up to several tens of meters thick the intense recrystallization eliminates density stratification and the altered layers appear to thicken into a connected network modeling of coset formation using wind and ice flow reproduces their dimensions and morphology however accumulation rates well above current regional estimates and existing data for megadunes are required because of the measured ice speed and required slope stability the consistent unconformable strata along our traverse show that coset and recrystallized morphology extend far beyond the megadune fields

characterization and formation of melt layers in polar snow observations and experiments from west antarctica author posting international glaciological society 2005 this article is posted here by permission of international glaciological society for personal use not for redistribution the definitive version was published in journal of glaciology 51 2005 307 312 doi 10 3189 172756505781829395

phase center of l band radar in polar snow and ice backscatter from an aggregate of inhomogeneities combine to form an apparent surface reflection particularly in relation to interferometric synthetic aperture radar the depth z of this reflection can reside well below the true surface when the transmissivity at the interface between air and the aggregate is high snow and ice provide good examples for which we calculate z with different accumulation history and physical properties using a 0 5 3 0 ghz ground penetrating radar we acquired our data along transects in antarctica and svalbard we find values of z 40 in low absorbing antarctic firn and 10 meters in glaciers and ice shelves where melt freeze cycles and lateral mass movement lead to an electrically more heterogeneous snow and ice column the heterogeneity reduces dielectric contrast more rapidly with depth thus z is found at shallower depth but still resides several meters beneath the snow surface

snow and firn permeability at siple dome antarctica the nature of air snow exchange processes depends upon both the physical characteristics of the snow and forcing from the atmosphere an understanding of snow air transport processes and models of these processes are important for interpreting ice cores and for predicting remotely sensed snow surface characteristics accurate modeling requires knowledge of the physical characteristics of the snow and firn in this paper measurements of snow and firn permeability from the surface down to 12 m depth at siple dome antarctica are presented the permeability varies greatly as a function of layer and depth generally increasing to approximately 3 m and generally decreasing below that the maximum permeability 280 10 10 1 0 m2 occurs at approximately 3 m depth the lowest permeability in the top 12 m of snow and firn 10 10 10w m2 was measured in the surface wind pack the measurements show that layering and microstructure have large effects on permeability a mathematical expression for the overall variation of permeability with depth is presented it is shown that snow density is a poor indicator of permeability quantitative microscopy may be helpful in relating observed snow characteristics to permeability and useful in modeling firnification and chemical species transport

temperature gradient and initial snow density as controlling factors in the formation and structure of hard depth hoar we investigate how temperature gradient and initial density influence depth hoar growth in snow and seek to better define the range of conditions under which cohesive or hard depth hoar forms samples of 400 kg m 3 sieved snow were exposed to temperature gradients of 20 80 c m 1 and samples of four different densities were exposed to a 40 c m temperature gradient following exposure to temperature gradients penetrometer tests were made on samples to determine the presence of solid and or hard depth hoar grain bond orientation was analyzed in section planes by two dimensional stereological techniques where hard depth hoar developed results indicate that hard cohesive depth hoar forms from rounded grain snow having a density of 400 kg m 3 or greater following exposure to a temperature gradient of 20 c m 1 or greater hard depth hoar appears to consist of solid type depth hoar grains connected by necks with vertically preferred directions of grain elongation and organization of grain to grain chains this work corroborates atikaya s 1974 results but extends his observation of formation of hard depth hoar to weaker temperature gradients for high density snow our results also indicate that hard depth hoar is composed of faceted solid type anhedral grains

ice layer and surface crust permeability in a seasonal snow pack ice layers in snowpacks are thought to retard or obstruct gas and melt water flow through the pack yet there has been little published information on the permeability of ice layers in seasonal snow in this paper investigations of ice layer permeabilities are reported for prominent ice layers 1 to 3 mm thick in a seasonal snowpack for distinct fairly solid ice layers 1 to 3 mm thick permeabilities ranged from 1 to 19 x 10 10 m 2 these values are significantly lower than values for the surrounding snow within 24 h early in the melt season the permeability of the surface crust increased 160 from approximately 70 to 120 x 10 10 m 2 this increase in permeability was accompanied by a small increase in grain size and a decrease in albedo the snow air interface can exhibit dramatic changes in transport properties over relatively short periods of time even without precipitation events these changes driven by the surface meteorology affect transport properties such as permeability as well as albedo

water infiltration underneath single ring permeameters and hydraulic conductivity determination summary a single ring permeameter is suitable for measurement of soil hydraulic conductivity at a large field scale because of its simple structure easy operation portability small amount of recharging water and particularly because of its variable radius the authors established a simple single ring permeameter which consists of a hollow cylinder that is simply inserted into the top soil based on the theories of the philip and nestingen methods for single ring permeameter tests this paper presents new equations for describing 1 d infiltration within the inserted depth of the single ring infiltrometer and 3 d flow beyond the depth under both gravity and soil suction forces the soil hydraulic parameters of hydraulic conductivity and soil suction were optimized based on the declines of the ponded water depth within the single ring cylinder the new method was validated using numerical simulations of the declines of the water column within the cylinder through the variably saturated flow modflow vsf modflow the new method was then successfully applied in laboratory troughs and on a hillslope in huanjiang county northwest guangxi in southwest china the results demonstrate that the hydraulic conductivity determined by the new method is more accurate than those from the 1 d green ampt method and the 3 d nestingen method

three dimensional coordination number from two dimensional measurements a new method la valeur de n 3 moyenne des coordonnees du neve a trois dimensions peut etre estimee a partir de n 2 nombre moyen des mesures a deux dimensions et a partir d une fonction qui depend uniquement du rapport entre le rayon moyen de voisinage et de celui du grain de l echantillon

falling head ponded infiltration with evaporation comment reference ecol article 1994 002doi 10 1016 0022 1694 94 90013 2 url http www elsevier com wps find journaldescription cws home 503343 description description record created on 2005 12 09 modified on 2016 11 26

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

practical estimates of field saturated hydraulic conductivity of bedrock outcrops using a modified bottomless bucket method 1 the bottomless bucket bb approach nimmo et al 2009a is a cost effective method for rapidly characterizing field saturated hydraulic conductivitykfsof soils and alluvial deposits this practical approach is of particular value for quantifying infiltration rates in remote areas with limited accessibility a similar approach for bedrock outcrops is also of great value for improving quantitative understanding of infiltration and recharge in rugged terrain we develop a simple modification to the bb method for application to bedrock outcrops which uses a nontoxic quick drying silicone gel to seal the bb to the bedrock these modifications to the field method require only minor changes to the analytical solution for calculatingkfs on soils we investigate the reproducibility of the method with laboratory experiments on a previously studied calcarenite rock and conduct a sensitivity analysis to quantify uncertainty in our predictions we apply the bb method on both bedrock and soil for sites on pahute mesa which is located in a remote area of the nevada national security site the bedrock bb tests may require monitoring over several hours to days depending on infiltration rates which necessitates a cover to prevent evaporative losses our field and laboratory results compare well to kfs values inferred from independent reports which suggests the modified bb method can provide useful estimates and facilitate simple hypothesis testing the ease with which the bedrock bb method can be deployed should facilitate more rapid in situ data collection than is possible with alternative methods for quantitative characterization of infiltration into bedrock

faceted crystal formation in the northeast greenland low accumulation region snow pit analysis in the low accumulation region in northeast greenland indicated a mean annual accumulation of 12 1 6 cm it also revealed numerous faceted layers that were not related to the summer horizon of previous years in general the faceted crystals were found under a wind crust these crusts appear to originate during the winter snow and air temperature data from automatic weather stations suggest that the katabatic storms are responsible for the formation of the wind crusts and the faceted layers frequent abrupt temperature changes up to 30 c were observed within two days due to turbulent mixing of cold air inversions the near surface air temperature variations are correlated with wind speed the latter leading the former by 6 9 hours for increasing wind and 1 4 hours for decreasing wind because of low accumulation katabatic storms affect the same snow surface for several months causing repeated air temperature fluctuations this leads to strong vapor pressure gradients and faceted crystal growth in the top snow layer on average we found two faceted layers in addition to the summer layer per year for a 4 year record in addition to its climatological significance in the snow record the formation of these layers is especially important to understand for the interpretation of microwave satellite observations of the firn

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

bacterial mediation red matrices diagenesis devonian montagne noire southern france abstract two devonian red carbonate rock sections are studied in the montagne noire at coumiac frasnian famennian and at the pic de vissou eifelian givetian the sediments are grey red mudstones and wackestones rich in pelagic fossils they are characteristic of an outer ramp the coumiac sequence is condensed with numerous hardgrounds and hiatuses the pic de vissou succession is more complete and of shallower origin in both cases the origin of the red coloration of the micritic matrix is probably linked to bacterial activity which produced submicronic hematite both iron and manganese concentrations are low average 0 2 bacteria form ferruginous microstromatolites blisters microtufts hedgehogs filling sponge perforations and thin continuous mineralized films probably biofilms hardgrounds are underlined by ferruginous microstromatolites the origin of the matrix color is probably related to the destruction of these bacterial constructions the submicronic hematite ultimately coating the crystal faces of the calcite mosaic during early lithification microfissures appeared and were invaded by microbial colonies scanning electron microscopy sem shows that these colonies are composed of spheroidal beads this suggests continuity of the bacterial activity during early diagenesis later on these early fissures were cut by burrows subsequently a secondary fissure network transected all the previously mentioned sedimentary structures this late fissure network is characterized by diagenetically remobilized hematite and or calcite the latest alterations are stylolites and ultimate tectonic fractures

the depth of penetration in antarctic firn at 10 ghz measurements taken by an x band pulse radar system in east antarctica in 1987 were analyzed to determine the depth of penetration of radar energy in polar firn a minimum estimate of the penetration depth at 10 ghz for the cold and dry polar plateau region is approximately 4 7 m spatial variations in the amount of signal penetration were observed and are related to latitude surface elevation and mean annual temperature the amount of signal penetration and its spatial variation are important factors that should be considered when processing datasets from microwave remote sensing systems that operate in the polar regions

comment on variable head ponded infiltration under constant or variable rainfall by j r philip keywords time equation reference ecol article 1996 002doi 10 1029 95wr03645 url http www agu org journals wr record created on 2005 12 09 modified on 2016 08 08

controls on ers altimeter measurements over ice sheets footprint scale topography backscatter fluctuations and the dependence of microwave penetration depth on satellite orientation we consider the reliability of radar altimeter measurements of ice sheet elevation and snowpack properties in the presence of surface undulations we demonstrate that over ice sheets the common practice of averaging echoes by aligning the first return from the surface at the origin can result in a redistribution of power to later times in the average echo mimicking the effects of microwave penetration into the snowpack algorithms that assume the topography affects the radar echo shape in the same way that waves affect altimeter echoes over the ocean will therefore lead to biased estimates of elevation this assumption will also cause errors in the retrieval of echo shape parameters intended to quantify the penetration of the microwave pulse into the snowpack using numerical simulations we estimate the errors in retrievals of extinction coefficient surface backscatter and volume backscatter for various undulating topographies in the flatter portions of the antarctic plateau useful estimates of these parameters may be recovered by averaging altimeter echoes recorded by the european remote sensing satellite ers 1 by numerical deconvolution of the average echoes we resolve the depths in the snowpack at which temporal changes and satellite travel direction effects occur both of which have the potential to corrupt measurements of ice sheet elevation change the temporal changes are isolated in the surface backscatter cross section while directional effects are confined to the extinction coefficient and are stable from year to year this allows the removal of the directional effect from measurement of ice sheet elevation change

accumulation of a ferric mineral in the biofilm of montacuta ferruginosa mollusca bivalvia biomineralization bioaccumulation and inference of paleoenvironments abstract infrared absorption spectra of the amorphous and phosphorus rich ferric mineral associated with the biofilm of montacuta ferruginosa a marine bivalve were obtained by applying the kbr disc method phosphate absorption bands due to p o stretching vibrations were observed at 1100 and 1020 cm 1 this result as well as the similarity of spectra with other well known bio minerals suggests that the mineral is an amorphous iron oxyhydroxide gel with phosphate sorbed on its surface rather than a pure ferric phosphate it is suggested that phosphate ions are of microbial origin because phosphate producing enzymes were detected in vivo apart from iron the mineral phase is devoid of other heavy metals despite its similarity with other abiotically precipitated phases it is argued that the mineral is the result of in situ microbial biomineralization processes in the biofilm and not the result of a simple bioaccumulation process this is supported by microscopic observations a geological implication is that the simple presence of such iron minerals in ancient sedimentary environments where microbes have not been fossilized might be considered as an indicator of microorganisms performing biomineralization by comparison with the present day environment of m ferruginosa precise paleoenvironmental conditions may be inferred

infiltration into fractured bedrock experiment performed on fractured ash flow tuff water was released from a 3 4m 2 infiltration plot divided into 12 square subplots with a head of 0 04 m over a period of 800 days this experiment revealed peculiar infiltration patterns not amenable to current infiltration models which were originally developed for infiltration into soils over a short duration in particular we observed that in part of the infiltration plot the infiltration rate abruptly increased a few weeks into the infiltration tests we suggest that these anomalies result from increases in fracture permeability during infiltration which may be caused by swelling of clay fillings and or erosion of infill debris interaction of the infiltration water with subsurface natural cavities lithophysal cavities could also contribute to such anomalies this paper provides a conceptual model that partly describes the observed infiltration patterns in fractured rock and highlights some of the pitfalls associated with direct extension of soil infiltration models to fractured rock over a long period

densification of layered firn of the ice sheet at neem greenland densification of firn at the north greenland eemian ice drilling neem camp is investigated using density surrogates dielectric permittivities v and h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy v h is then examined as a surrogate for the anisotropic geometry of firn its size fluctuations and mutual correlations are investigated in samples taken at depths from the surface to 90m the initial of 0 06appears within the uppermost 0 2 m after that decreases rapidly until 21 26 m depth below this decreases slowly layers with more ions of fluorine chlorine and some cations deposited between the autumn and the subsequent summer deform preferentially during all these stages this layered deformation is explained partly by the textural effects initially formed by the seasonal variation of metamorphism and partly by ions such as fluorine chlorine and ammonium which are known to modulate dislocation movement in the ice crystal lattice insolation sensitive microstructure appears to be preserved all the way to the pore close off within layers of the summer to autumn metamorphism like previous authors we hypothesize that calcium is not the active agent in the reported deformation calcium correlations

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

recent changes in the microwave scattering properties of the antarctic ice sheet time series satellite microwave data are used to monitor and quantify changes in the scattering properties of the antarctic ice sheet daily ers scatterometer escat and special sensor microwave imager ssm i image data acquired since 1992 are analyzed to understand the seasonal and interannual changes over the ice sheet for regions of the ice sheet where azimuthal modulation is negligible seasonal cycles are observed in both the escat amplitude spl sim 0 5 db and ssm i data amplitude spl sim 10 k these cycles are attributed to seasonal changes in surface temperature interannual variability in the time series signatures appears to be associated with accumulation there is also evidence to suggest that shifts in the wind direction can alter the backscatter through azimuthal modulation over the period 1992 97 large trends are observed in the escat 1 k yr sup 1 signatures over several regions in antarctica these changes typically occur over ice shelves and at the margins of the ice sheet where previous melt events have occurred and where accumulation is relatively high 300 mm yr sup 1 it is likely the large changes result from the successive burial of an efficient scattering layer formed by refreezing after a melt event prior to 1992 there is also evidence to suggest that similarly large changes can be observed in the interior of the ice sheet due to the burial of depth hear layers in order to monitor long term change in the properties of the antarctic ice sheet it is necessary to remove the seasonal cycle from time series microwave data such anomaly data can then be used to understand the link between escat and ssm i with accumulation and wind shifts

iron bacterial and fungal mats bajocian stratotype mid jurassic northern normandy france abstract the oolithe ferrugineuse de bayeux formation is located at the historical bajocian stratotype of sainte honorine des pertes north of bayeux normandy the condensed formation ranges from the base of the humphriesianum zone to the parkinsoni zone and is divided into four beds of decimetric scale three main microfacies are present 1 oncoid rudstones 2 ooid bioclastic packstones and 3 silty burrowed wackestones packstones sedimentation took place in a very quiet environment below the photic zone and below or near the storm wave base the general setting is a distal carbonate ramp its lower part characterized by hemipelagic sedimentation indicated by the presence of planktonic foraminifers the inferred depth is around 100 m free oxygen concentration was low dysaerobic conditions are indicated by a scarcity of benthic macrofauna ferruginous structures are numerous in the first two microfacies and absent in the last hematite staining is not uniform and follows many sedimentary patterns among the more widespread fe structures are perforation infillings with endolithic micro organisms microstromatolites oncoids ooids blisters coatings and hardgrounds these structures can be associated and none are mutually exclusive hematite coated filaments of different sizes and shapes are observed in the micrite matrix the walls of various organisms the calcite crystals associated with the fe cortical laminations the perforations and burrow the hardgrounds and microstromatolites petrographical and sem examinations suggest that the laminated crusts oncoids and hardgrounds are formed by microbial iron mats dominated by filamentous bacteria and fungi seven types of microbes are recognized filaments five morphotypes spheroidal bodies and stalked bodies filamentous microfossils of type 1 to 4 resemble the present day filamentous bacteria beggiatoales and cytophagaceae because of their large diameter and their branching nature filaments of type 5 are possibly filamentous fungi another argument in favor of fungi is the presence of stalked and spheroidal bodies that resemble zoosporangia and oogonia of some oomycota in deep calm and dysaerobic waters many interfaces e g between aerobic and dysaerobic waters are present in the sediments the stability of the soluble reduced state of iron fe 2 is higher at such interfaces and many ferric iron encrusted microbial fossils are observed iron could thus serve as an electron donor for microbial iron oxidation processes other microbial iron deposition pathways are also possible it appears that regardless of geological age paleozoic mesozoic and geographical location the same microbiological mechanisms are probably responsible for the red color in calcareous stratified or unstratified bodies the presence of fossilized iron encrusted bacteria and fungi at interfaces may therefore serve as an indicator of anoxic to dysaerobic conditions in various paleo micro environments

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

falling head ponded infiltration it is remarkable that the green ampt or delta function solution for falling head ponded infiltration takes precisely the same functional form as that for constant head infiltration only the values of the constants change falling head infiltration experiments are thus as amenable to green ampt analysis as more complicated constant head experiments

mapping greenland accumulation rates using observations of thermal emission at 4 5 cm wavelength accurate predictions of sea level rise over the coming century will require improved knowledge of the processes controlling accumulation on the great ice sheets the sparsity of accumulation rate observations both temporally and spatially hinder development of this understanding we introduce a new method to observe accumulation rates averaged over roughly a decade using satellite observations of microwave emission at 4 5 cm wavelength focusing in this paper on greenland at this wavelength scattering by the grain fabric in firn is unimportant relative to quasi reflection from density and thus dielectric permittivity stratification we show observationally a strong link between random firn density stratification on scales of millimeters to centimeters and accumulation rate we then show theoretically how the observed density stratification can produce and is consistent with observations of polarization of 4 5 cm wavelength emission we employ observations from the scanning multichannel microwave radiometer smmr and previously published ground observations of accumulation rates in greenland to complete specification of the relationship between accumulation rate and polarization the relationship is sufficiently accurate to serve as a basis for mapping accumulation rate fields we compare our satellite derived maps with previously published maps based on syntheses of ground data we find broad agreement between the two types of maps though the satellite derived map indicates more strongly the importance of topography and prevailing weather patterns in determining detailed accumulation rate patterns finally we discuss possible refinements and the prospects for improved satellite derived maps based on a new generation of sensors about to be launched

seasonal variations of glaciochemical isotopic and stratigraphic properties in siple dome antarctica surface snow six snow pit records recovered from siple dome west antarctica during 1994 are used to study seasonal variations in chemical major ion and h 202 isotopic deuterium and physical stratigraphic properties during the 1988 94 period comparison of d measurements and satellite derived brightness temperature for the siple dome area suggests that most seasonal sd maxima occur within 4 weeks of each 1 january several other chemical species h 2o2 non sea salt nss so 4 2 methanesulfonic acid and no3 show coeval peaks with sd together providing an accurate method for identifying summer accumulation sea salt derived species generally peak during winter spring but episodic input is noted throughout some years no reliable seasonal signal is identified in species with continental sources nssca 2 nss mg 2 nh 4 or nsscl visible strata such as large depth hoar layers 5 cm are associated with summer accumulation and its metamorphosis but smaller hoar layers and crusts are more difficult to interpret a multi parameter approach is found to provide the most accurate dating of these snow pit records and is used to determine annual layer thicknesses at each site significant spatial accumulation variability exists on an annual basis but mean accumulation in the sampled 10 km 2 grid for the 1988 94 period is fairly uniform

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

power series solution for falling head ponded infiltration with evaporation 1 assumptions for many of the derived analytical infiltration models are either a constant infiltration rate or a constant head at the soil surface for many realistic infiltration situations a falling head boundary condition is more appropriate philip showed that both the wetting profiles and the cumulated infiltration in one dimensional infiltration into homogenous soil with constant head at the upper boundary can be written as a power series in t presently it is shown that a power series solution can be applied for falling head infiltration with evaporation when comparing with the constant head solution the falling head solution differs only from the second term i e the sorptivity remains unchanged a result which can be applied to falling head infiltrometer technique the effect of a constant evaporation rate in the falling head scenario appears from the third term in the presented numerical examples the retention model by van genuchten and the hydraulic conductivity model by mualem are applied by comparing the wetting profiles obtained with a fem solution it is shown that the discrepancies between the models are very small also the estimation of the time at which the pond is emptied is concordant the infiltration model is compared with a model by parlange and colleagues and a simple infiltrometer method for determining the saturated hydraulic conductivity is proposed

polar firn densification and grain growth a 50 m firn core from dome c east antarctica was found to consist of coarse firn which comprised 90 to 95 of the core and fine firn coarse firn was characterized by large crystals with a vertical shape orientation near the surface connected to nearest neighbors by relatively large necks in a structure different from closest packing fine firn was of higher density and consisted of smaller more spherical crystals connected by relatively narrow necks in a more nearly closest packed configuration higher surface free energy in fine firn causes crystals and necks to grow more rapidly than in coarse firn however we find that coarse firn densifies more rapidly with time contrary to the predictions of unconfined sintering models load driven densification due to a power law creep mechanism is found to account for the larger coarse firn densification rate however if the exponent in the power law exceeds one then densification rates are predicted to increase with depth due to increasing load contrary to observed behavior we speculate that different mechanisms may control the densification process in fine and coarse firn

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

from black and white to colour in the silurian abstract ironstones and iron rich limestones regularly occur as components of time specific intervals of the palaeozoic as well as in younger times brett et al 2012 this issue silurian sediments deposited at high latitudes along the peri gondwana border are characterized by black and white limestone and graptolitic shale sequences those in the carnic alps southern austria additionally contain colourful pink to red limestones and ironstones laminated structures such as the ferruginous coatings around skeletal fragments mostly trilobites and some cephalopods and echinoderms and stromatolitic features along discontinuity surfaces display dark red green white and brownish colours due to the presence of goethite magnetite hematite chamosite calcite and subordinate apatite confocal laser raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites filaments and coccoids suggesting a microbial role in the colouring of the silurian world of the carnic alps iron concentrations up to 30 that of matrix and surrounding non ferruginous rocks suggest blooms of iron microbe activity in response to the time specific occurrence of chemically charged sea water during global biotic events

the impact of accumulation rate on anisotropy and air permeability of polar firn at a high accumulation site the first three dimensional properties of polar firn obtained by x ray microtomography are used to study the microstructure of snow on a 15 m deep firn core from west antarctica the snow is found to undergo coarsening down to approximately 2 5 m depth before grain growth and densification become the prevalent mechanisms of microstructure change in contrast to previous assumptions distinct anisotropy of the ice and pore geometry is observed throughout the profile with a maximum at 2 5 m depth the air permeability and the degree of anisotropy vary with depth and can be linked to short term changes in accumulation rate via the residence time for which a certain snow layer stays in the uppermost 2 5 m patterns of the degree of anisotropy and air permeability of buried polar firn are relative indicators of past accumulation rates

the connectivity of crystallite agglomerates in low density firn at kohnen station dronning maud land antarctica in this study the three dimensional 3 d microstructure of polar firn is investigated by means of x ray microfocus computer tomography mct basic topological properties including the euler and coordination numbers are derived from the reconstructed 3 d volume images it is shown that sample volumes of about 4 cm 3 are representative for polar firn in terms of their connectivity the connectivity function defined as the change of euler number with structure size is calculated via image processing routines it is used to split the ice phase at small bridges into single crystallite agglomerates the bond size distributions and the mean size of the agglomerates are estimated all mct measurements were carried out on the uppermost 9 m of a shallow firn core b35 drilled during the 2005 06 field campaign at kohnen station dronning maud land dml antarctica the results are compared with estimates from classical two dimensional 2 d surface section observations the 3 d approach confirms the linear relationship between coordination number and density which hitherto has only been derived from 2 d observations layers of buried snow dunes show a stronger connectivity than layers of moderate crystal size and density the formation of agglomerates made of crystallites is a common feature of polar firn in dml it is proposed that the growth of agglomerates leads to reduced critical densities for the transition between the densification regime of grain boundary sliding and plastic deformation

comment on falling head ponded infiltration by j r philip reference ecol article 1995 001doi 10 1029 94wr02565 url http www agu org record created on 2005 12 09 modified on 2016 08 08

falling head ponded infiltration in the nonlinear limit the green and ampt infiltration solution represents only an extreme example of behavior within a larger class of very nonlinear delta function diffusivity soils the mathematical analysis of these soils is greatly simplified by the existence of a sharp wetting front below the soil surface solutions for more realistic delta function soil models have recently been presented for infiltration under surface saturation without ponding after general formulation of the problem solutions for a full suite of delta function soils are derived for ponded surface water depleted by infiltration exact expressions for the cumulative infiltration as a function of time or the drainage time as a function of the initial ponded depth may take implicit or parametric forms and are supplemented by simple asymptotic expressions valid for small times and small and large initial ponded depths as with surface saturation without ponding the green ampt model overestimates the effect of the soil hydraulic conductivity at the opposing extreme a low conductivity model is identified that also takes a very simple mathematical form and appears to be more accurate than the green ampt model for larger ponded depths between these two the nonlinear limit of gardner s soil is recommended as a physically valid first approximation relative discrepancies between different soil models are observed to reach a maximum for intermediate values of the dimensionless initial ponded depth and in general are smaller than for surface saturation without ponding

snow accumulation variability from seasonal surface observations and firn core stratigraphy eastern wilkes land antarctica annual accumulation records were derived from two firn cores drilled at gd03 69 00 s 115 30 e 1835m and gd15 69 00 s 130 48 e 2155m which are separated by 750 km along the 2000 m contour in eastern wilkes land the accumulation records spanning the period 1930 85 show that annual accumulation has increased by 25 from 1960 to 1985 resulting in the highest accumulation rates in the 55 year records annual accumulation layers were identified in the firn cores using a firn stratigraphic model based on the observed characteristics and variability of the seasonal snow surface layer together with seasonal oxygen isotope ratios the accumulation records support other evidence for a similar recent increase across antarctica the greater increase over the long term mean for 1930 85 in eastern wilkes land was observed at gd15 which is located on a northeast aspect slope near terre adelie it is suggested that the increase is the result of changes in the general atmospheric circulation pattern which have produced a higher annual frequency of precipitation events

texture and strength changes of buried surface hoar layers with implications for dry snow slab avalanche release buried layers of surface hoar are the failure plane for many slab avalanches including fatal human triggered avalanches in various mountain regions these layers may persist as weak layers in the snow cover for weeks or months it is therefore essential for operational avalanche forecasters to monitor the evolution of persistent weak layers such as buried surface hoar traditional grain shape observations of isolated grains with a magnifier and crystal screen do not show bonding that is decisive for strength in this study we used in situ microphotography and observations of texture to complement strength measurements from shear frame tests buried layers of surface hoar consist of crystals most of which extend from the layer below to the layer above and may exhibit a columnar or truss like structure observations and measurements show that texture and crystal size change little over periods of up to several months during which the snowpack remains dry under these conditions layer thickness decreases while density and strength increase based on field measurements we argue that the increase in strength is primarily due to penetration of the surface hoar crystals into the adjacent layers especially at the bottom of the buried surface hoar layer where bonding is critical the weak bonding at the bottom implies that shear failure occurs at the lower interface rather than within the weak layer on slopes we find that surface hoar crystals that were initially surface normal are tilted downslope faster than predicted by published shear strain rates for settled snow indicating that shear strain is concentrated in these layers the characteristic texture of buried surface hoar columnar or truss like permits collapsing at the time of fracture the gravitational energy released by the displacement of the slab may contribute to the extensive fracture propagation associated with buried surface hoar layers

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

extreme firn metamorphism impact of decades of vapor transport on near surface firn at a low accumulation glazed site on the east antarctic plateau snow and firn properties control the transport of vapor gases and water between the atmosphere and the underlying strata an understanding of this transport and the properties that control it is important for predicting air snow transfer of chemical species and for interpreting ice cores remote sensing images of east antarctica show large areas of alternating light and dark bands these low amplitude long wavelength features have glazed downwind faces and rough upwind faces and are called megadunes the first linked measurements of the permeability and the associated microstructure for a glazed area within a well defined megadune area are reported in this paper permeability and density were measured along with grain scale properties derived from digital image processing of preserved thick sections at this cold low accumulation glazed site a clear layering pattern exists in the top meter the firn density ranges from 0 24 to 0 50 g cm 3 permeability measurements range from 50 x 10 10 to 200 x 10 10 2 several times greater than corresponding profiles from warmer higher accumulation sites like siple dome antarctica it is shown that buoyancy driven natural convection may be important in post depositional processes in very cold low accumulation sites like this

formation of refrozen snowpack layers and their role in slab avalanche release 1 in a variety of snow climates numerous slab avalanches release over crusts consisting of refrozen snow slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts often within a day weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients these processes create interfaces where differences in grain radii can contribute to weak bonding in western canada layers of faceted crystals facet layers on crusts are most common in early and late winter when thaws and rain are more frequent also thin facet layers occur in spring when surface melting by solar radiation is common shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase the spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer

imaging of firn and bubbly ice in coaxial reflected light a new technique for the characterization of these porous media a new technique for characterizing the structure of firn and bubbly ice is presented this technique based on observation of etched sublimation surfaces in coax ial reflected light enables one to see simultaneously the pore network of the firn or bubbles in the ice and the crystal boundaries at the same time the main stages of image proces sing used to transform the initial photographs into clean binary images are described

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

detection and monitoring of stratigraphic markers and temperature trends at the greenland ice sheet project 2 using passive microwave remote sensing data satellite passive microwave sensors provide a sensitive means of studying ice sheet surface processes that assists ice core interpretation and can extend local observations across regional scales analysis of special sensor microwave imager ssm i brightness temperature tb data supports ice core research in two specific ways first the summer hoar complex layers used to date the holocene portion of the greenland ice sheet project 2 ice core can be defined temporally and spatially by ssm i 37 ghz vertically v and horizontally h polarized b ratio v h trends second comparison of automatic weather station temperatures to ssm i 37 ghz v tb data shows that they are an effective proxy temperature record in this region also the tb data can be correlated with proxy temperature trends from stable isotope ratio 18o and d profiles from snow pits and this allows the assignment of dates to specific snow depths

impacts of an accumulation hiatus on the physical properties of firn at a low accumulation polar site 1 recent field investigations of a megadune region of east antarctica provide evidence that differences in grain size thermal conductivity and permeability across a megadune profile are due to spatial accumulation variability in the absence of significant microclimate variations the megadunes are low amplitude 2 8 m long wavelength 2 5 km bands with perceptible but low accumulation less than 40 mm water equivalent weq yr 1 and accumulation hiatus within several kilometers proximity as determined by remote sensing surface feature classification and ground penetrating radar profiling our hypothesis that accumulation rate impacts the extent of temperature gradient driven metamorphic growth in low accumulation rate sites is supported by measurements of various firn physical properties relatively small differences in accumulation rate less than 40 mm weq yr 1 result in large differences in physical properties including grain size thermal conductivity and permeability which are apparent in satellite based microwave data from both passive and active sensors the differences in physical snow structure between low accumulation areas and accumulation hiatus areas in the near surface are sufficiently distinct that evidence of past accumulation hiatus should be observable in the physical and chemical properties of an ice core record

approximate analysis of falling head lined borehole permeameter the falling head lined borehole permeameter consists of a snugly fitting tube extending to the base of a vertical borehole in unsaturated soil water is suddenly introduced into the tube to standard depth and the subsequent time course of water depth is observed soil water data in the amazon basin has been secured with this instrument we develop an approximate analysis based on a green ampt model with the flow treated as a gravity perturbed spherically symmetrical pressure capillarity driven flow

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

annual layers in polar firn detected by borehole optical stratigraphy 1 we have developed a system called borehole optical stratigraphy which can detect annual layers in boreholes in polar firn borehole optical stratigraphy consists of a downhole camera package and post processing routines which allow us to measure the intensity of light emitted from an on board source and returned from the borehole wall we manually identify the annual layers in this optical signal we used this system at siple dome antarctica in the 2001 2002 austral summer season our results agree well with counts of annual layers detected with two different methods in an ice core recovered 50 meters from our borehole

ice core analysis at site a greenland preliminary results ice core drilling at site a greenland 70 45 n 35 57 5 w 3145m a s l by the polar ice coring office recovered two cores of about 100 m each which are now in storage awaiting further analysis field studies show that visible strata in the cores record both individual storms and individual years a typical year comprises 15 storm deposits pore close off occurs between 75 and 80 m depth the grain growth rate in isothermal firn and ice is about 7 8 x 1o 3 mm 2 a l the 10m temperature is about 29 5 c and the accumulation rate over the last 200 years is about 290 mm a i ice melt events occur about once every 40 years and major events can be correlated between cores separated by 20 m

coupled effects of canal lining and multi layered soil structure on canal seepage and soil water dynamics ponding tests were conducted in the shiyang river basin in northwest china to assess canal leakage characteristics four anti seepage constructions concrete lining pebble lining clay lining plus compacted canal bed compacted canal bed only were performed on four canal sections which were situated in multi layered soils the canal sections were tested using a two stage approach first a stable water level was maintained followed by a stage where the water level in the canal section was permitted to drop the canal seepage rate and the soil water content near the canal bed were monitored during the stable and dropping stages soil texture bulk density and hydraulic conductivity were tested in each canal section and soil layer double ring infiltration tests were performed to investigate infiltration behaviour from the canal sections the saturated unsaturated flow model hydrus 2d was applied to simulate canal seepage and the local soil water response the simulation results compared well with the monitored data indicating that the model can reliably simulate canal seepage under these complex soil structures and different canal liners both experimental results and numerical modelling show that the clay lining plus compacted canal bed provides the best anti seepage performance followed by compacted canal bed only then pebble and concrete lining simulation results also predicted that the soil water content was discontinuous at the interface of distinct soil layers and that the range and form of wetting front varied greatly in the four canal sections with a larger wetted area for the more permeable canals simulations were performed to study the sensitivity on canal seepage of to the permeability of each soil lining layer and the lining effect on canal seepage the results confirmed by double ring infiltration tests indicated that the canal lining is not the only dominant factor affecting canal seepage the soil permeability can also influence the seepage greatly especially where there exists a low permeability layer e g compacted soil layer close to the canal

simple relations for the close off depth and age in dry snow densification a physical model for the snow firn densification process salamatin and others 2006 and martinerie and others 1992 1994 correlation for the firn density at the pore closure are employed to perform a scale analysis and computational experiments in order to deduce simplified relations for the close off depth and ice age in quasi stationary ice formation conditions the critical snow density at which ice grain rearrangement stops is used to take into account variability of snow structures subjected to densification the results obtained are validated on a representative set of ice core data from 22 sites which covers wide ranges of present day temperatures and ice accumulation rates a simple analytical approximation for the density depth profile is proposed