late quaternary paleoenvironments and growth of intrusive ice in eastern beringia eagle river valley northern yukon canada in this study the sediments exposed in a fluvial terrace and in the headwall of a thaw slump in the eagle river valley northern yukon provide new data about the timing of flooding of glacial lake old crow the formation of massive ground ice bodies and the vegetation and the fauna in eastern beringia during the late quaternary the stratigraphy and radiocarbon ages establish the following chronology of events 1 a gravel fluvial terrace was deposited by an overflow from glacial lake hughes into glacial lake old crow 2 a carbonate silty clay was deposited during the maximum level of glacial lake old crow at 15 120 14c year bp 3 permafrost and large intrusive ice bodies aggraded through the glaciolacustrine and underlying sediments following the drainage of glacial lake old crow from the site 4 at 11 290 14c year bp a shrub sedge tundra colonized an uneven surface deformed by the bodies of ground ice 5 a thaw lake drained at 6730 14c year bp after flooding the site 6 during the early h

a two phase approach to the simulation of the combined isotope salinity signal of marine ice a modified boundary layer box diffusion model is used to simulate the production of the combined oxygen isotope salinity signal of a body of marine ice the final signal is considered to be the result of fractionation and segregation processes occurring first upon the formation of frazil crystals in suspension and second during their accumulation and consolidation due to the advancement of a freezing front the model results are compared to oxygen isotope and salinity values in a 45 m marine ice core from the nansen ice shelf antarctica parameters more suitable to the modeling of marine ice as opposed to sea ice are introduced and conclusions are drawn on the origin of the impurity characteristics of marine ice including the still unresolved question of its anomalously low salinity

sedimentological constraints on hydrometeor enhanced particle deposition 1992 eruptions of crater peak alaska abstract water is a dominant component of volcanic clouds and has fundamental control on very fine particle deposition particle size characteristics of distal tephra fall 100s km from source volcano have a higher proportion of very fine particles compared to predictions based on single particle settling rates in this study sedimentological analyses of fallout from for the 18 august and 16 17 september 1992 eruptions of crater peak alaska are combined with satellite observations and cloud trajectory and microphysics modeling to investigate meteorological influences on particle sedimentation total grain size distributions of tephra fallout were reconstructed for both crater peak eruptions and indicate a predominance of fine particles 2 g m 3 based on an estimated cloud thickness of 1000 m from trajectory modeling hydrometeor formation on particles in the volcanic cloud and subsequent sublimation may induce a cloud base instability that leads to rapid bulk en masse sedimentation of very fine particles through a mammatus like mechanism

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

segregated intrusive ice of subglacial meltwater origin in retrogressive thaw flow headwalls richardson mountains nwt canada abstract extensive beds of icy sediments are exposed in the headwalls of active retrogressive thaw flows which developed on the aklavik plateau richardson mountains nwt sedimentary and isotopic characteristics defined two units debris rich ice overlain by icy diamicton these units originated from the same glacial sediment deposited during the late wisconsin westward expansion of the laurentide ice sheet the icy diamicton is a result of the development of thaw flows and mass movement processes during the early holocene warm interval which reworked the sediments the ice in the diamicton is characterized by average 18o and d values of 22 6 1 8 and 181 15 respectively which are similar to the modern isotropic composition of precipitation for that area the debris rich ice is more depleted in 18o and d with 18o ranging from 30 to 27 and d ranging from 230 to 210 air bubbles enclosed in the ice have 13c values ranging between 24 and 19 and a co2 concentration nine times higher than the expected concentration of air entrapped in modern glacier ice but similar to that of soil co2 both physical and isotopic properties of the debris rich ice suggest that it is segregated intrusive ice that formed after the retreat of the laurentide ice sheet during permafrost aggradation as sediment laden subglacial meltwater moved through a proglacial talik this article discusses the mechanism involved in the formation of massive segregated intrusive ice and how it differs from both buried glacier ice and holocene massive intrasedimental ice

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

weertman regelation multiple refreezing events and the isotopic evolution of the basal ice layer a simple model is developed to s imulate the isotopic fractionation which accompanies weertman regelation at the bed of temperate based glaciers the fractionation equations of jouzel and souchez 1 982 are applied to multiple refreezing events over measured glacier bed profiles and mass balance is maintained as the basal ice and meltwater produced at one bedrock hummock enter the next s imulation results indicate that undeformed regelation ice layers are on the order of millimetres to centimetres thick often being completely melted at the stoss face of certain hummocks and exceptionally reaching a thickness in excess of 1 0 cm neither the internal morphology nor the isotopic composition of these layers is constant but both vary down glacier in accordance with bedrock configuration a glacier wide fractionation process is identified whereby heavy isotopes are preferentially removed fro m the basal meltwater film and incorporated into the basal ice this process might go some way to explaining the anomalously light isotopic composition measured in base flow waters leaving some glaciers vertical isotope profiles through undeformed basal ice layers are reconstructed and show that significant isotopic excursions can occur at a scale of millimeteres while the range of isotopic compositions within such m ulti layered regelation ice is greater than that which would occur in ice produced by a single refreezing event in circumstances where the regelation system is disrupted by removal of film waters into a network of linked cavities i t is found that the remaining basal ice may be significantly enriched in heavy isotopes relative to the composition of the initial mass inputs to the system heavy isotope enrichment of this m agnitude and consideration of the thickness of the basal ice layers concerned may explain the absence of recorded basal ice samples heavy enough to h ave been formed in equilibrium with subglacial precipitates sampled at one of the sites glacier de tsanfleuron and reported in an earlier paper

composition and origin of amber ice and its influence on the behaviour of cold glaciers in the mcmurdo dry valleys antarctica this paper examines the basal ice sequence of rhone glacier a cold based glacier in the mcmurdo dry valleys antarctica using isotopic and solute chemistry data three different ice facies are identified englacial amber and stratified the englacial facies is clean bubbly ice of meteoric origin and is underlain by an amber facies amber ice is a characteristic of cold alpine glaciers in the mcmurdo dry valleys and is distinctive for its high solute concentrations and much higher strain rates compared with the overlying englacial ice and the underlying stratified ice analysis of the stratified facies reveals an isotopic signature indicative of melt then refreeze processes and it is most likely associated with apron entrainment at the margin by contrast the amber facies has a co isotopic slope of 8 and plots on a meteoric waterline the inclusion of impurities in the amber ice reveals prolonged contact with the bed and its depleted isotopic signature is consistent with ice formed during a cooler period comparison of the basal sequence of rhone glacier with other cold based glaciers in the mcmurdo dry valleys reveals strong similarities between valley side glaciers e g meserve and rhone glaciers whereas valley floor glacier basal sequences e g suess glacier are characterized by structurally complex amalgamations of ice and debris

the buildup of the ice sheet in central greenland a study of the isotopic and gas composition of the basal silty ice recovered by the greenland ice core project grip core indicates that local ice formed in the absence of the greenland ice sheet is still preserved at summit such ice developed most probably within a peat deposit in a permafrost environment this local ice was subsequently intimately mixed with glacier ice from an advancing ice sheet progressing on the site this is in agreement with the highland origin and windward growth hypothesis for ice sheet development not for an in situ or regional growth from snowbanks the basal ice from the grip core possibly dates back to the original buildup of the greenland ice sheet 2 4 million years ago

characterization of dissolved organic matter dom from glacial environments using total fluorescence spectroscopy and parallel factor analysis aquatic dissolved organic matter dom is a major reservoir of reduced organic carbon and has a significant influence on heterotrophic biological productivity and water quality in marine and freshwater environments although the forms and transformations of dom in temperate aquatic and soil environments have been studied extensively this is not the case for glacial environments in this study fluorescent excitation emission matrices eems parallel factor analysis parafac and cluster analysis were used to characterize the fluorescing components of dom in ice and water samples from supraglacial englacial subglacial and proglacial environments of seven glaciers in the canadian arctic norway and antarctica at least five significant fluorescent dom fractions were identified which accounted for 98 2 of the variance in the dataset these included four protein like components and one humic like component the predominantly proteinaceous character of dom from these glaciers is very different from the more humic character of dom described previously from lacustrine fluvial estuarine and marine environments dom from the sampled glaciers is broadly similar in character despite their geographically distinct locations different thermal regimes and inter and intra site differences in potential organic matter sources glacier ice samples had a relatively low ratio of humic like protein like fluorescence while meltwater samples had a higher ratio

lirad observations of tropical cirrus clouds in mctex part ii optical properties and base cooling in dissipating storm anvil clouds abstract during the maritime continent thunderstorm experiment mctex several decaying storm anvils were observed the anvil clouds exhibited typical patterns of fallout and decay over a number of hours of observation the anvil bases were initially very attenuating to lidar pulses and continued that way until anvil breakup commenced during that time the anvil base reached some characteristic altitude 7 km below which the cloud particles had evaporated fully some typical tongues of fallout below such levels also occurred millimeter radar showed the storm anvil cloud tops to be much higher than detected by lidar until the anvil was well dissipated the infrared properties of the anvils were calculated in three of the four anvils studied the calculated emittance never exceeded 0 8 0 85 in the remaining case the cloud emittance approached unity only in the period before the anvil had descended appreciably radiative transfer calculations showed that the infrared emission originated mostly fro

case study a 3d resistivity and induced polarization imaging from downstream a waste disposal site in brazil a contaminated site from a downstream municipal solid waste disposal site in brazil was investigated by using a 3d resistivity and induced polarization ip imaging technique this investigation purpose was to detect and delineate contamination plume produced by wastes the area was selected based on previous geophysical investigations and chemical analyses carried out in the site indicating the presence of a contamination plume in the area resistivity model has successfully imaged waste presence 31 mv v water table depth and groundwater flow direction a higher chargeability zone m 31 mv v outside wastes placement and following conductive anomaly was interpreted as a contamination plume normalized chargeability mn m confirmed polarizable zone which could be an effect of a salinity increase contamination plume and the clay presence in the environment

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

the effect of refreezing on the isotopic composition of melting snowpack the isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack the slope of the d 18o line for the liquid phase is found to be lower than for the solid phase this is proved to be due to the isotopic fractionation occurring in the melt freeze mass exchange within the snowpack melting of the snowpack has no clear impact on the d 18o line for the solid phase but the slope of the d 18o line for the liquid shows an overall slight decrease in the melting period when the snowpack is refrozen the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases thus the slope of the solid would become lower and lower as the diurnal melt freeze episodes cycle throughout the melting season this effect is then demonstrated by looking into the isotopic composition changes of glacier firn the extent of the effect depends on the snowpack properties and environmental conditions the slope changes also result in a decreasing trend in deuterium excess copyright 2007 john wiley sons ltd

multisensor characterization of mammatus abstractmultisensor observations of anvil mammatus are analyzed in order to gain a more detailed understanding of their spatiotemporal structure and microphysical characterization remarkable polarimetric radar signatures are detected for the pentecost 2014 supercell in northrhine westfalia germany and severe storms in oklahoma along their mammatus bearing anvil bases radar reflectivity at horizontal polarization zh and cross correlation coefficient hv decrease downward toward the bottom of the anvil while differential reflectivity zdr rapidly increases consistent with the signature of crystal depositional growth the differential reflectivity zdr within mammatus exceeds 2 db in the pentecost storm and in several oklahoma severe convective storms examined for this paper observations from a zenith pointing ka band cloud radar and a doppler wind lidar during the pentecost storm indicate the presence of a supercooled liquid layer of at least 200 300 m depth near the anvil base at temperatures between

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

pleistocene ice at the bottom of the vavilov ice cap severnaya zemlya russian arctic the vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments in contrast to the overlying glacier ice the basal ice is composed of different ice layers with a variable debris load the stable isotope composition of these layers shows values much lower than everywhere else in the core or in the vavilov ice cap this is most probably the signature of a remnant of pleistocene ice which for the first time is shown to occur in the russian arctic

insights into hydrological regime of lake vostok from differential behavior of deuterium and oxygen 18 in accreted ice 1 we use isotopic data deuterium and oxygen 18 of the recently recovered deepest vostok ice core section down to 3650 m depth to study processes leading to the formation of lake ice and the hydrological regime of subglacial lake vostok the significant variability of the lake ice isotopic content implies fluctuations in physical conditions of ice formation mainly volume and or growth rate of frazil ice crystals as well as variations of the isotope composition of the freezing water the latter implies a poor mixing of the source waters glacier melt and hydrothermal water with the water of the main lake body poor mixing within the lake may have important consequences for the lake s chemical and gas balance and particularly for its microbiological content a poorly mixed lake may provide ecological niches where microbial life can hide from high oxygen concentrations likely typical for the lake we also show that the isotopic content of the main lake s input meltwater significantly differs from that of the output lake ice which can be explained by the contribution of an additional hydrothermal source this latter conclusion is supported by the observed noncovariant behavior of deuterium and oxygen 18 isotopes in the lake ice

some characteristics of thunderstorms over bathurst and melville islands near darwin australia a study defining the occurrence structure and evolution of maritime continent island thunderstorms over bathurst and melville islands near darwin australia is presented satellite data for the november december pre monsoon transition season show unambiguous records of island thunderstorms on at least 65 of days over the period 1978 1986 storms develop most commonly between 1230lst and 1530lst and radar data indicate a mean lifetime of 2 5 h non occurrence was found on only 7 of the days examined and was associated with a return to dry flow typical of the early transition season with middle level subsidence or suppressed conditions in the wake of previous convective activity environmental sounding data indicated that these maritime continent thunderstorms develop in a regime with moderate cape low to moderate shear and high moisture the dynamic regime is characteristic of multicellular storms examination of the evolution of the storms indicates the existence of a typical lifecycle but with considerable variability in detail initially the lifecycle is consistent with the multicellular storm concept but the developing storms tend to aggregate to form one or more mesoscale systems which in turn may develop into propagating squall lines in the mature stage the developing storms have preferred geographic regions of genesis and intensification over the islands and while motion of the storms is variable it is generally consistent with the mean surface to 700mb pressure weighted flow

physical and biogeochemical properties in landfast sea ice barrow alaska insights on brine and gas dynamics across seasons 1 the impacts of the seasonal evolution of sea ice physical properties on ice ocean biogeochemical exchanges were investigated in landfast ice at barrow alaska from january through june 2009 three stages of brine dynamics across the annual cycle have been identified based on brine salinity brine volume fraction and porous medium rayleigh number ra these are sea ice bottom layer convection full depth convection and brine stratification we further discuss the impact of brine dynamics on biogeochemical compounds in sea ice stable isotopes of water d 18o nutrients no3 po43 nh4 microalgae chlorophyll a and inert gas argon in general full depth convection events favor exchanges between sea ice and seawater while brine stratification limits these exchanges however argon responds differently to brine dynamics than the other biogeochemical compounds analyzed in this study this contrast is attributed to the impact of bubble nucleation on inert gas transport compared to the other biogeochemical compounds we present a scenario for argon bubble formation and evolution in sea ice and suggest that a brine volume fraction approaching 7 5 10 is required for inert gas bubbles to escape from sea ice to the atmosphere

stratigraphy stable isotopes and salinity in multi year sea ice from the rift area south george vi ice shelf antarctic peninsula results from a detailed profile in a 5 54m multi year sea ice core from the rift area in the southern part of george vi ice shelf are presented stratigraphy stable isotopes and na content are used to investigate the growth processes of the ice cover and to relate them to melting processes at the bottom of the ice shelf the thickest multi year sea ice in the sampling area appears to be second year sea ice that has survived one melt season combined salinity stable isotope analyses show large scale sympathetic fluctuations that can be related to the origin of the parent water brackish ice occurs between 450 and 530cm in the core it is demonstrated that this results from the feezing of brackish water formed by mixing of normal sea water with melted basal shelf ice with dilution percentages of maximum 80 fresh water from authors

doppler radar observations of mammatus abstract observations of mammatus like cloud features associated with a convective rain shower were obtained using a vertically pointing 8 mm wavelength doppler radar the radar s excellent sensitivity and resolution allowed even very weak finescale features of the cloud to be resolved the mammatus were located 3 5 km above ground along the underneath side of an anvil like stratiform region of the storm cloud and preceded the arrival of precipitation both reflectivity and velocity exhibited strongly periodic patterns with larger downward motions and larger reflectivities occurring together the mammatus lobes were separated by about 90 s or approximately 1 km horizontally the mammatus features could be traced more than 500 m upward into the cloud echo interior where the amplitude of the vertical velocity oscillations was greatest the measured vertical velocities of particle motions ranged from 0 5 to 3 0 m s 1 the observed reflectivity and velocity patterns suggest that although evaporation was

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

mechanisms of basal ice formation in polar glaciers an evaluation of the apron entrainment model 1 previous studies of polar glaciers have argued that basal ice can form when these glaciers override and entrain ice marginal aprons that accumulate adjacent to steep ice cliffs to test this idea we have studied the morphology structure composition and deformation of the apron and basal ice at the terminus of victoria upper glacier in the mcmurdo dry valleys which are located on the western coast of the ross sea at 77 si n southern victoria land antarctica our results show that the apron has two structural elements an inner element that consists of strongly foliated ice that has a steep up glacier dip and an outer element that lacks a consistent foliation and has a down glacier slope parallel dip although strain measurements show that the entire apron is deforming the inner element is characterized by high strain rates whereas relatively low rates of strain characterize the outer part of the apron co isotopic analyses of the ice together with analysis of solute chemistry and sedimentary characteristics show that the apron is compositionally different from the basal ice our observations show that aprons may become deformed and partially entrained by advancing glaciers however such an ice marginal process does not provide a satisfactory explanation for the origin of basal ice observed at the ice margin our interpretation of the origin of basal ice is that it is formed by subglacial processes which are likely to include deformation and entrainment of subglacial permafrost

an alternative methodology for the analysis of electrical resistivity data from a soil gas study the aim of this paper is to present an alternative method for the analysis of resistivity data the methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills the main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores field measurements of electrical resistivity static chamber gas flux and weather data were collected at a landfill in helsingborg sweden the resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 x20 m the abem lund imaging system provided vertical and horizontal resistivity profiles every second hour the data were inverted in res3dinv using l 1 norm based optimization method with a standard least squares formulation each horizontal soil layer was then represented as a linear interpolated raster model different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer and the vertical extension of the zones could be followed at greater depths in deeper layer models the average resistivity values of the defined areas were calculated and plotted on a time axis to provide graphs of the variation in resistivity with time in a specific section of the ground residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data the resulting residual resistivity graphs were compared with field data of soil moisture precipitation soil temperature and methane flux the results of the study were qualitative but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found even though more research and better data quality is necessary for verification of the results presented here we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application

isotope geochemistry of frost blister ice north fork pass yukon canada oxygen 18 and deuterium abundances vary with depth in ice from a frost blister at a spring site near north fork pass yukon they indicate that the ice was formed by continuous downward freezing under nearly ideal closed system conditions in a water filled cavity weighted mean values of 18o and 2h for the ice samples indicate that the frost blister ice was formed from groundwater similar to that of nearby springs the slope of the regression line 5 1 for the 18o and 2h data of the frost blister ice suggests that nonequilibrium fractionation conditions existed during freezing tritium concentrations in the ice show irregular variations with depth the weighted mean 3h concentration for the ice is however similar to that of the spring water

δd δ18o relationships and the thermal history of basal ice near the margins of two glaciers in lyngen north norway les resultats des mesures combinees d et 18 o pour 2 glaciers en norvege du nord sont rapportes ainsi que leurs implications pour l histoire thermique de la glace et les variations observees dans l entrainement des debris

stable isotope behavior during cave ice formation by water freezing in scărisoara ice cave romania 1 recently a series of studies have targeted the stable isotopic composition of cave ice as a possible source of paleoclimatic information but none presented an explanation for the way in which the external climatic signal is transferred to cave ice while the relation between the stable isotopic composition of precipitation and drip water can be relatively easily determined a more complex problem arises i e the possible alteration of the primary climatic signal recorded by the oxygen and hydrogen stable isotopes during the freezing of water to form cave ice here we report the results of the first detailed investigations of the oxygen and hydrogen stable isotope behavior during the formation of ice in sc risoara ice cave samples of ice align on a straight line with a slope lower than 8 in a 18o 2h plot characteristic for ice formed by the freezing of water a model is presented for the reconstruction of the initial isotopic composition of water despite the complexity induced by kinetic effects during early stages of freezing these results are consistent with ice that forms by the downward freezing of a stagnant pool of water under kinetic conditions in the initial stages of the process and isotopic equilibrium thereafter as ice caves are described in many parts of the world otherwise poorly represented in ice based paleoclimatology the results of this study could open a new direction in paleoclimatic research so that an array of significant paleoclimate data can be developed on the basis of their study

a parameterization of the visible extinction coefficient of ice clouds in terms of the ice water content abstract this article describes a parameterization of the visible extinction coefficient of cirrus and frontal ice cloud in terms of the ice water content the parameterization is based on the discovery that the ice cloud particle size spectra from a particular dataset tended to fall into three separate well defined regions these regions were a marshall palmer distribution covering particles with dimensions larger than between 100 and 1400 m depending on the cloud temperature a heymsfield platt type power law distribution for the smaller particles dimensions from 20 m to somewhere between 100 and 800 m and a different spectrum of the smallest particles of sizes less than 20 m the dataset chosen had been obtained from aircraft in situ observations of cloud particle size spectra in ice clouds and covered the entire spectral range from 2 to 3000 m thus allowing a study of every important spectral region part of this dataset was used originally in a previous study by heymsfield and platt the da

environmental setting micro morphologies and stable c o isotope composition of cold climate carbonate precipitates a review and evaluation of their potential as paleoclimatic proxies abstract given the growing interest in carbonate deposits from polar regions as paleoclimatic proxies this review paper first provides a classification of the various types of cold climate carbonate precipitates followed by a summary of the 13 c and 18 o composition of the carbonate deposits and parent water from which the carbonates precipitated the cold climate carbonate precipitates were classified into three broad categories powders crusts and speleothem the carbonate powders include those that precipitated in relation to aufeis aggradation cryogenic aufeis calcite and in relation to the growth of various annual perennial ice formations in freezing caves cryptocrystalline calcite and calcite pearls the carbonate crusts can be further subdivided based on their lithic environment those that precipitated on the upper surface of bedrock clasts i e subglacially precipitated calcite and evaporative calcite crusts those that are located on the underside of clasts i e pedogenic carbonates and those that precipitated in rock outcrop fissures i e endostromatolites the cold climate carbonate precipitates have a highly variable isotopic composition with 18 o values ranging between 6 5 and 28 vsmow and 13 c values in the 10 20 vpdb range however each type of carbonate precipitates has a specific 13 c and 18 o range suggesting that their environmental setting and the mechanism by which they formed controls their 13 c and 18 o signature it was found that carbonate deposits that precipitated under equilibrium physico chemical conditions had a 13 c value that is in equilibrium with that of the parent water while its 18 o composition was more variable as it is in part controlled by the temperature of reaction and by the 18 o and calcite saturation state of the parent water by contrast the 18 o composition of biologically precipitated carbonate deposits endostromatolites reflect that of the parent water while its 13 c composition was enriched over that of the parent water due to bacterial methanogenesis in the case of kinetically precipitated carbonate deposits the 18 o and 13 c values are out of equilibrium relative to that of the parent water due to the faster rate of reaction

biogeochemical impact of snow cover and cyclonic intrusions on the winter weddell sea ice pack sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean however proper understanding of its annual impact on exchanges and therefore potentially on the climate notably suffer from the paucity of autumnal and winter data sets here we present the results of physical and biogeochemical investigations on winter antarctic pack ice in the weddell sea r v polarstern awecs cruise july august 2013 which are compared with those from two similar studies conducted in the area in 1986 and 1992 the winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southwards from the open southern ocean these conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover brine tubes favoring relatively high chlorophyll a chl a concentrations we discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions large scale sea ice model simulations also suggest a context of increasingly deep snow warm ice and large brine fractions across the three observational years despite the fact that the model is forced with a snowfall climatology this lends support to the claim that more severe antarctic sea ice conditions characterized by a longer ice season thicker and more concentrated ice are sufficient to increase the snow depth and somehow counter intuitively to warm the ice

trapping of aeolian sediments and build up of the ice cover of a dry based antarctic lake among the perennially frozen lakes of the dry valleys of south victoria land antarctica some are dry based i e frozen to the bottom one of these is studied here by a multiparametric investigation isotopic composition in da nd 18 o ions gas and ice texture analyses a sediment layer about 10 cm thick appearing at a depth of 3 5m is also studied by grain size x ray diffraction and scanning electron microscope analyses the information retrieved indicates that this ice block lake results from a build up in two steps and explains how aeolian sediments were included as a layer into the ice copyright 2002 john wiley sons ltd

high resolution airborne radar observations of mammatus abstract high resolution doppler radar observations of mammatus clouds coupled with soundings of the preanvil and anvil environments provide a unique opportunity to examine previously reported observations of and evaluate various hypotheses of mammatus formation these observations confirm the general hypothesis for mammatus formation advanced by ludlam and scorer and provide detail of the cloud interior structure specifically the radar observations indicate that mammatus elements are reminiscent of eddy circulations with a weak downdraft core flanked by horizontal convergence and divergence at the top and base of the cloud respectively doppler spectral width measurements however yielded values of only 2 3 m s 1 indicating only weak turbulent motions within individual mammatus elements reflectivity analyses of mammatus elements indicate a firm link to the parent anvil a dual doppler analysis of the parent anvil indicates that the larger scale environment where the mammatus exist is characteriz

late proterozoic glacial carbonates in northeast spitsbergen new insights into the carbonate tillite association carbonate rich glacial deposits from two discrete vendian glacial periods are described the older is represented by the 24 40 m thick petrovbreen member e2 of the elbobreen formation which contains abundant detrital dolomite clasts in e2 and their possible source rocks have positive 13 c and negative 18 o pdb values in contrast the carbonate mud fraction of e2 sediments has different cathodoluminescence characteristics from clasts slightly negative 13 c values and higher fe and mn concentrations than clasts oxygen isotopes vary from 2 5 to 4 5 pdb thought to be related to various seawater meltwater mixtures in the depositional environment preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy ostwald s ripening and coinciding with sulphate reduction the younger glaciation is represented by the wilsonbreen formation 170 m which has a distinctive glaciolacustrine middle carbonate member w2 w2 contains precipitated periglacial carbonates with high mn fe ratio both limestone rhythmitic and stromatolitic and dolostone rhythmites stromatolites and dolomite rich sandstones which are compared with carbonates in modern antarctic lakes evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values up to 10 5 pdb high na concentration and evidence for dissolved evaporites high mn concentration in detrital dolostones in w2 is suggestive of syn sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones the carbonate tillite association ultimately arises from the erosion of underlying carbonates which originated in this case under radically different climatic conditions glacial depositional waters then became carbonate saturated as a result of dissolution of detrital carbonate massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis in glacial lakes carbonate precipitated in response to evaporation or photosynthesis carbonate precipitation as the result of seawater freezing or in warm interglacial conditions is not yet established oxygen isotope value are inconsistent too heavy with the presence of high latitude meltwaters implying that glaciation extended to low latitudes as proposed by harland

transverse englacial debris rich ice bands at kviarjokull southeast iceland thick exposures of debris rich ice at various icelandic glaciers are central to the debate over the prevalence of glacial sediment transfer by glaciohydraulic supercooling we present physical analyses of ice and debris at kviarjokull a temperate glacier in southeast iceland with a terminal glacier bed overdeepening where stratified debris rich ice forms up to metre thick transverse englacial bands our results are not consistent with debris rich ice formation predominantly by supercooling because 1 137cs was absent from sediment filtered from debris rich ice 2 isotopic analysis d and 18o demonstrated no clear pattern of isotopic enrichment of debris rich ice with respect to englacial ice and 3 melt out debris from debris rich ice included large striated clasts from both fluvial and basal sources we support transverse englacial debris rich ice band formation by the thickening and elevation of basal materials in a region of longitudinally compressive ice flow situated between the reverse slope of the overdeepening and the base of an ice fall debris band form and distribution are likely to be controlled by thrusting along transverse englacial foliae associated with the formation of band ogives on the glacier surface

seasonal growth bands in pingo ice field studies of pingo ice show that alternating clear and bubble bands may grow when water freezes at the top of a subpingo water lens a study of the banding at one excellent exposure of pingo ic

integrated earth resistivity tomography ert and multilevel sampling gas a tool to map geogenic and anthropogenic methane accumulation on brownfield sites soil gas emissions of methane and carbon dioxide on brownfield sites are usually attributed to anthropogenic activities however geogenic sources of soil gas are often not considered during site investigation and risk management strategies this paper presents a field study at a redeveloped brownfield site on a flood plain to identify accumulations of methane biogas trapped in underlying sediments the investigation is based on a multidisciplinary approach using direct multi level sampling measurements and earth resistivity tomography resistivity imaging was applied to evaluate the feasibility of identifying the size and spatial continuity of soil gas accumulations in anthropogenic and naturally occurring deposits as a result biogas accumulations are described within both anthropogenic deposits and pristine organic sediments this result is important to identify the correct approaches to identify and manage risks associated with soil gas emissions on brownfield and pristine sites the organic rich sediments in quaternary fluvial environments of sao paulo basin in particular the tiete river biogas reservoirs can be generated and trapped beneath geogenic and anthropogenic layers potentially requiring the management of brownfield developments across this region

entrainment at cold glacier beds here we present measurements of the gas content and isotopic composition of debris rich basal layers of a polar glacier meserve glacier antarctica which has a basal temperature of 17 c these measurements show that debris entrainment has occurred without alteration of the glacial ice and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers without bulk freezing of water entrainment at subfreezing temperatures may have formed the u shaped trough containing meserve glacier in addition to possibly allowing some cold based glaciers to be important geomorphic agents entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets which are rheologically distinct and can limit the time span of ice core analyses furthermore accumulating evidence suggests that geomorphologists should abandon the assumption that cold based glaciers do not slide and abrade their beds