two cryogenian glacial successions compared aspects of the sturt and elatina sediment records of south australia abstract two cryogenian glacial sequences the sturt and elatina occur within the adelaide rift complex s australia and are part of an 8 km thick succession recording rodinia fragmentation and subsequent passive margin development we compare and contrast these glacial successions presenting new data including detailed logged sections for both glacial sequences facies analysis reveals a total of six facies associations recording a range of glacial and glacially related processes these are a diamictite facies association ice proximal debris flows a sheet sandstone facies association fluvial deposits a flaser and rhythmically bedded facies association tidal flat a hummocky cross stratified sandstone facies association shoreface to offshore transition zone deposits and an underflow facies association recording offshore deposition a sixth facies association a ferruginous lonestone bearing siltstone is restricted to the top of the elatina formation and records rapid environmental amelioration and emergence from glaciation in the central flinders ranges the sturt succession commences with a glacial erosion surface ges which in agreement with previous workers was probably enhanced by rifting this ges is overlain in ascending order by the pualco tillite holowilena ironstone and wilyerpa formation with the warcowie dolomite member at the base of this latter formation a second ges is preserved within this latter unit and is overlain by a stratigraphic motif that records an alternation of offshore transition zone and offshore deposits significant base level falls within the wilyerpa formation are identified by fluvial deposits sitting disconformably upon offshore deposits in contrast within the elatina formation a single ges is proposed which defines the base of the formation the elatina formation is split into two informal members on the basis of analysis of sediment stacking patterns and the recognition of a sharp stratigraphic surface that divides the formation apart from a locally preserved basal diamictite the lower member consists of fluvial deposits whereas the upper member is dominated by a mixture of tidal flat sediments and debris flow deposits the boundary between these units is therefore interpreted as a hybrid surface recording tidal ravinement in some areas and a glacial advance in others deglaciation left contrasting deposits the sturt deglaciation culminated in deposition of black shale of the tindelpina shale member of the tapley hill formation seemingly as a sheet like deposit over the adelaide rift complex and beyond into the amadeus basin of central australia the elatina deglaciation meanwhile began first with deposition of the sixth facies association ferruginous dropstone bearing siltstone then proceeded with deposition of cap dolostone of the nuccaleena formation

sedimentary challenge to snowball earth evidence from the magnetic field fossilized in sedimentary rocks suggests that more than 600 million years ago ice occupied tropical latitudes a popular explanation for these findings the snowball earth concept envisages a fully frozen earth for millions of years caused by a runaway ice albedo feedback a rapid catastrophic meltback at very high levels of atmospheric carbon dioxide is thought to have ended this extreme climatic state however sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle the sedimentary evidence therefore indicates that despite the severity of glaciation some oceans must have remained ice free significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle the snowball earth concept envisages a fully frozen earth for millions of years several times during the neoproterzoic era between 1 000 and 542 million years ago however the sedimentary evidence suggests that despite the severity of glaciation some oceans must have remained ice free

neoproterozoic iron formation an evaluation of its temporal environmental and tectonic significance article neoproterozoic iron formation nif provides evidence for the widespread return of anoxic and ferruginous ba sins during a time period associated with major changes in climate tectonics and biogeochemistry of the oceans here we summarize the stratigraphic contextof neoproterozoic iron formation and its geographic and temporal dis tribution it is evident that most nif is associated with the earlier cryogenian sturtian glacial epoch although it is possible that some nif may be ediacaran there is no incontrovertible evidence to support this age assignment the paleogeographic distribution of nif is consistent with anoxic and ferruginous conditions occurring in basins within rodinia or in rift basins developed on its margins consequently nif does not require whole ocean anoxia simple calculations using modern day iron fluxes suggest that only models that invoke hydrothermal and or detrital sourcesofiron are capable ofsupplying sufficient ironto account forthe mass of the largernif occurrences this con clusion is reinforced by the available geochemical data that imply nif record is a mixture of hydrothermal and de trital components a common thread that appears to link most if not all nif is an association with mafi cv olcanics

origin of the neoproterozoic fulu iron formation south china insights from iron isotopes and rare earth element patterns abstract in the neoproterozoic era there was widespread deposition of iron formations in close association with global or near glaciations these snowball earth glaciations likely played a key role in iron formation distribution and deposition however the environmental conditions fe sources and formation mechanisms remain debated here we present the rare earth element geochemistry and fe isotope composition of the synglacial iron formation within the neoproterozoic fulu formation south china the fulu iron formation consists of layers of authigenic minerals mainly hematite and detrital components quartz feldspars fe chlorite and minor biotite positive eu anomalies in one of the fulu localities indicate a hydrothermal influence suggesting that fe was mainly sourced from distal hydrothermal systems the bulk rock fe isotope composition of the fulu iron formation shows a large range with 56fe from 0 23 to 1 78 correlation between bulk rock 56fe values and al fe ratios demonstrates that 56fe variability reflects in part varying proportions of authigenic versus detrital components the fe isotope composition of authigenic hematite is calculated by a linear regression and shows 56fe between 0 83 and 2 21 with an average at 1 54 0 50 2 n 41 using a dispersion reaction model the high 56fe values of hematite constrain local dissolved o2 concentrations of the ocean to less than 0 4 nmol l even in the shallow part of the water column this relationship is consistent with highly reducing conditions in the neoproterozoic oceans favored by isolation from the atmosphere by a sea ice we attribute the extremely positive values to partial iron oxidation in waters that were cold relative to modern surface oceans the dominant occurrence of hematite supports an abiotic precipitation pathway given that biological activity would have introduced organic matter to the sediments and led to partial reduction of fe iii oxides and subsequent formation of magnetite and or siderite as is observed in archean and paleoproterozoic iron formations oxic glacial meltwater and or o2 vertical transfer from the atmosphere to the upper ocean linked to ice dynamics is likely to have mediated the abiotic oxidation we propose that vertical transfer of o2 resulted from the deposition of snow that trapped air bubbles at the top of the glacier coupled to a melting of the bottom of the glacier which in combination delivered a limited but continuous amount of o2 to the ocean

elevation changes of ice caps in the canadian arctic archipelago 1 precise repeat airborne laser surveys were conducted over the major ice caps in the canadian arctic archipelago in the spring of 1995 and 2000 in order to measure elevation changes in the region our measurements reveal thinning at lower elevations below 1600 m on most of the ice caps and glaciers but either very little change or thickening at higher elevations in the ice cap accumulation zones recent increases in precipitation in the area can account for the slight thickening where it was observed but not for the thinning at lower elevations for the northern ice caps on the queen elizabeth islands thinning was generally 0 5 m yr 1 which is consistent with what would be expected from the warm temperature anomalies in the region for the 5 year period between surveys and appears to be a continuation of a trend that began in the mid 1980s farther south however on the barnes and penny ice caps on baffin island this thinning was much more pronounced at over 1 m yr 1 in the lower elevations here temperature anomalies were very small and the thinning at low elevations far exceeds any associated enhanced ablation the observations on barnes and perhaps penny are consistent with the idea that the observed thinning is part of a much longer term deglaciation as has been previously suggested for barnes ice cap on the basis of the regional relationships between elevation and elevation change in our data the 1995 2000 mass balance for the archipelago is estimated to be 25 km3 yr 1 of ice which corresponds to a sea level increase of 0 064 mm yr 1 this places it among the more significant sources of eustatic sea level rise though not as substantial as the greenland ice sheet alaskan glaciers or the patagonian ice fields

on the characterization of glacier response by a single time scale glacier response to climate can be characterized by a single time scale when the glacier changes sufficiently slowly then the derivative of volume with respect to area defines a thickness scale similar to that of johannesson and others and the time scale follows from it our version of the time scale is different from theirs because it explicitly includes the effect of surface elevation on mass balance rate which can cause a major increase in the time scale or even lead to unstable response the time constant has a dual role controlling both the rate and magnitude of response to a given climate change data from south cascade glacier washington u s a illustrate the ideas some of the difficulty in obtaining accurate values for the thickness and time scales and the susceptibility of all response models to potentially large errors

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

iron isotopic variations of the cryogenian banded iron formations a new model abstract the fe isotope composition of banded iron formation bif is regarded as a powerful tracer in paleoceanography and the cryogenian banded iron formation associated with snowball earth events provides a precious record of environmental change in the neoproterozoic however fe isotope studies on cryogenian bifs are rare and previous interpretations of cryogenian fe isotope data are problematic here we present a systematic investigation of the fe isotope composition of the cryogenian xinyu bif sections from four localities in the yangtze region south china these bif sections comprise banded magnetite quartzite banded chlorite magnetite quartzite and magnetite bearing chlorite phyllite in stratigraphically ascending order the 56feirmm 014 values of the xinyu bif vary significantly and show an overall increase upsection from ca 0 to ca 1 5 this stratigraphic trend in fe isotope compositions is similar to those reported previously for cryogenian bifs in north america and australia and thus seems to be a common phenomenon we interpret fe isotope variation in cryogenian bif to be essentially controlled by varying degrees of fe precipitation in seawater rather than resulted from a water column fe isotope gradient as proposed previously the variation in the degree of fe precipitation can be controlled by changes of eh and or ph conditions in seawater resulting from transgression or ocean acidification

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

sedimentation associated with antarctic peninsula ice shelves implications for palaeoenvironmental reconstructions of glacimarine sediments abstract recent disintegration of a number of antarctic peninsula ice shelves has given us a unique opportunity to investigate sub ice shelf sediments we characterize three sediment facies associations of two antarctic peninsula ice shelves larsen a and larsen inlet subglacial facies consist mainly of basal till diamicton with high shear strengths deposited under a grounded ice sheet progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition proximal ice shelf glacimarine facies diamicton gravel rich and sand rich facies gravelly mud dropstone mud and sandy muds were deposited by sub ice shelf rain out bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea floor distal ice shelf glacimarine and or open marine facies comprise terrigenous and diatom bearing bioturbated muds and gravelly muds that contain limited ice rafted debris these accumulated after recession of the grounding line to the coast with coarse grained surface sediments possibly documenting most recent ice shelf break up antarctic peninsula ice shelf sediments are more heterogeneous than ice shelf facies deposited elsewhere in antarctica cold polar antarctic ice shelves can be differentiated from temperate and sub polar marine terminated glacial sedimentary systems by the dominance of coarse grained proximal ice shelf glacimarine facies and an absence of subaqueous outwash meltwater sediment facies

relation between the mass balance of western canadian mountain glaciers and meteorological data le bilan de masse les bilans d ete et d hiver et l altitude de la ligne d equilibre de 3 glaciers canadiens sont compares avec les donnees meteorologiques de stations avoisinantes pour la periode 1966 1984 presentation de reconstructions statistiques pour les 3 glaciers sur la base des equations de regression avec les enregistrements meteorologiques depuis 1938

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

subglacial meltwater supported aerobic marine habitats during snowball earth the earth s most severe ice ages interrupted a crucial interval in eukaryotic evolution with widespread ice coverage during the cryogenian period 720 to 635 ma aerobic eukaryotes must have survived the snowball earth glaciations requiring the persistence of oxygenated marine habitats yet evidence for these environments is lacking we examine iron formations within globally distributed cryogenian glacial successions to reconstruct the redox state of the synglacial oceans iron isotope ratios and cerium anomalies from a range of glaciomarine environments reveal pervasive anoxia in the ice covered oceans but increasing oxidation with proximity to the ice shelf grounding line we propose that the outwash of subglacial meltwater supplied oxygen to the synglacial oceans creating glaciomarine oxygen oases the confluence of oxygen rich meltwater and iron rich seawater may have provided sufficient energy to sustain chemosynthetic communities these processes could have supplied the requisite oxygen and organic carbon source for the survival of early animals and other eukaryotic heterotrophs through these extreme glaciations

use of historical elevation data to calculate surface elevation and volume changes of ha iltzuk icefield southwest british columbia canada 1970 to mid 1980s investigations into glacial changes including understanding variations in the rates of glacial volume and surface elevation changes have increased over the past decade this study uses historical glacier elevation data in the form of topographic maps from 1970 and a digital elevation model from the mid 1980s to calculate surface elevation and volume changes for ha iltzuk icefield southwest british columbia canada results indicate that the icefield thinned at an average rate of 0 76 0 25 m a 1 during this period a previous study of ha iltzuk icefield also using the geodetic method found a thinning rate of 1 0 0 20 m a 1 between the mid 1980s and 1999 indicating a slight increase in the amount of icefield thinning within the ablation zone thinning increased with decreasing elevation at a rate of 1 9 0 68 m a 1 km 1 between these two periods 1970 to mid 1980s versus mid 1980s to 1999 analysis of meteorological data suggests that increases in both temperature and rainfall as well as decreases in snowfall likely contributed to the increased thinning rate

global distributions of glacier properties a stochastic scaling paradigm many problems in global climate and earth systems science require knowledge of regional or global scale distributions of glacier properties which includes mass balance ice velocity flux thickness volume and surface area among others with roughly 160 000 glaciers worldwide obtaining information on the global probability distributions of most ice properties is expensive and often infeasible only surface area distributions are relatively easy to measure either by direct observation or remote sensing while other properties are difficult to observe this work shows that scaling relationships from the continuum dynamics of ice can link the distribution of surface areas to the global and regional distributions of any other continuum property some data inventories already exist for constructing reasonable distributions of glacier sizes and this analysis presents theoretical arguments based on glacier network topologies similar in concept to river networks to suggest a power law times an exponential distribution of surface areas in agreement with the data therefore by using existing data or the theoretical distributions of surface areas specific distributions for other glacier properties in any region of the world can be constructed as an example predictions up to a scaling constant are made for the distribution of glacier volumes characteristic thicknesses characteristic velocities and characteristic response times in the alps

present and future states of himalaya and karakoram glaciers a complete glacier inventory of the himalaya and karakoram h k has been created by merging records from the chinese glacier inventory several regional inventories produced by the international centre for integrated mountain development kathmandu nepal and partial inventories from the geological survey of india the only remaining gap the indian part of kashmir has been filled by a reconnaissance inventory based on soviet military maps at 1 200 000 scale representing the late 1970s it contains records for 3526 glaciers covering 9584 km 2 the new h k inventory contains records and outlines for 20 812 glaciers covering 43 178 km 2 the extent of ice in the karakoram is slightly less than in the himalaya but the karakoram glaciers are on average twice as thick 160 m as against 80 m a glacier by glacier analysis relying on estimates of mass balance for the entire mountain range and on an extension of the often used volume area scaling relation suggests that up to about one fifth of the glaciers present in 1985 may have disappeared already if mass loss were to remain constant at the average rate for 1975 2008 from 3000 to 13 000 more glaciers might disappear by 2035 if mass loss were to continue to accelerate as inferred for 1985 2008 only a few thousand to a few hundred glaciers might remain in 2035 total area and total mass would each decrease by about one half constant rate assumption or three quarters constant trend assumption these projections which are uncertain and neglect some possibly important mitigating controls such as variable extents of debris cover and the feedback due to retreat to higher elevations demonstrate the need for more complete analyses to inform public perceptions of and policy decisions relating to the health of h k glaciers

glacier changes in alaska can mass balance models explain grace mascon trends temperature and precipitation data from three weather stations in the st elias mountains of alaska and northwestern canada were used to drive one dimensional 1 d elevation dependent and 0 d degree day mass balance models model outputs were optimized against a 10 day resolution time series of mass variability during 2003 07 obtained from gravity recovery and climate experiment grace mass concentration mascon solutions the models explained 52 60 of the variance in the grace time series modelled mass variations matched the phase of the grace observations and all optimized model parameters were within the range of values determined from conventional mass balance and meteorological observations we describe a framework for selecting appropriate weather stations and mass balance models to represent glacier variations of large regions there is potential for extending these calibrated mass balance models forwards or backwards in time to construct mass balance time series outside of the grace measurement window

elevation and volume changes on the harding icefield alaska airborne surface elevation profiles of the harding icefield south central alaska were made in 1994 and 1996 thirteen glaciers were profiled along with the upper region of the icefield the profiles were compared to u s geological survey topographic maps made in the 1950s to obtain elevation and volume changes comparison of the changes for the different glaciers shows no significant correlation between volume change and the type of glacier or characteristics such as location aspect size slope or terminus changes estimated total volume change for this 43 year period is about 34 km 3 which corresponds to an area average elevation change of 21 m the estimated error in this elevation change of 5 m is mainly due to errors in the maps at higher elevations our measurements provide an accurate baseline against which future determinations of volume change can be made

changes in the elevation and extent of two glaciers along the yanglonghe river qilian shan china we use topographic maps historical data multispectral satellite data and real time kinematic gps data to analyze glacier area length and ice elevation changes of two glaciers in the central qilian shan china between 1956 and 2007 we find that the fronts of yanglonghe glacier no 1 5y432a1 and yanglonghe glacier no 5 5y432a5 have retreated by 266 5 37 1 m 5 2 0 73 m a 1 and 181 4 37 1 m 3 6 0 73 m a 1 respectively and that this retreat accelerated after 1999 during the study period the glacier areas decreased by 4 1 and 15 9 respectively in addition spatially non uniform thinning which averaged 20 2 11 m 0 4 0 22 m a 1 and 16 9 11 m 0 33 0 22 m a 1 in the ablation areas of 5y432a1 and 5y432a5 respectively is observed using digital elevation models constructed using data from 1956 1977 and 2007 the ice volume depletion from 5y432a1 2 91 10 7 m 3 was 2 7 times greater than from the smaller 5y432a5 1 08 10 7 m 3 based on records from nearby tuole weather station increasing annual temperatures are principally responsible for the observed glacier thinning and retreat

pre drill pore pressure modelling and post well analysis using seismic interval velocity and seismic frequency based methodologies a deepwater well case study from mississippi canyon gulf of mexico managing and identifying risk and uncertainly involved in drilling operations in unconventional geologic settings starts with improving and correctly applying pore pressure modelling a relatively new approach which predicts pore pressure by way of seismic frequencies has addressed some of the short comings seen in seismic interval velocity applications with the overall goal of reducing operational drilling risk by utilizing multiple pore pressure modelling strategies a case study will be presented for a near salt field in deepwater gulf of mexico this study will outline the pre drill pore pressure modeling which includes petrophysical seismic interval velocity and seismic frequency based approaches the accuracy of these three approaches will be analyzed both qualitatively and quantitatively for currently existing wells and from a pre drill and post drill standpoint for one prospect well

iron isotopes in an archean ocean analogue abstract iron isotopes have been extensively used to trace the history of microbial metabolisms and the redox evolution of the oceans archean sedimentary rocks display greater variability in iron isotope ratios and more markedly negative values than those deposited in the proterozoic and phanerozoic this increased variability has been linked to changes in either water column iron cycling or the extent of benthic microbial iron reduction through time we tested these contrasting scenarios through a detailed study of anoxic and ferruginous lac pavin france which can serve as a modern analogue of the archean ocean a depth profile in the water column of lac pavin shows a remarkable increase in dissolved fe concentration 0 1 1200 m and 56fe values 2 14 to 0 31 across the oxic anoxic boundary to the lake bottom the largest fe isotope variability is found at the redox boundary and is related to partial oxidation of dissolved ferrous iron leaving the residual fe enriched in light isotopes the analysis of four sediment cores collected along a lateral profile one in the oxic layer one at the redox boundary one in the anoxic zone and one at the bottom of the lake indicates that bulk sediments porewaters and reactive fe mostly have 56fe values near 0 0 0 2 similar to detrital iron in contrast pyrite 56fe values in sub chemocline cores 60 65 and 92 m are highly variable and show significant deviations from the detrital iron isotope composition 56fepyrite between 1 51 and 0 09 average 0 93 importantly the pyrite 56fe values mirror the 56fe of dissolved iron at the redox boundary where near quantitative sulfate and sulfide drawdown occurs suggesting limited iron isotope fractionation during iron sulfide formation this finding has important implications for the archean environment specifically this work suggests that in a ferruginous system most of the fe isotope variability observed in sedimentary pyrites can be tied to water column cycling foremost to the oxidation of dissolved ferrous iron this supports previous suggestions that enhanced iron isotope variability in the archean may record a unique stage in earth s history where partial ferrous iron oxidation in upwelling water masses was a common process probably linked to oxygenic or anoxygenic photosynthesis

source and progression of a submarine landslide and tsunami the 1964 great alaska earthquake at valdez like many subduction zone earthquakes the deadliest aspects of the 1964 m 9 2 alaska earthquake were the tsunamis it caused the worst of these were generated by local submarine landslides induced by the earthquake these caused high runups engulfing several coastal towns in prince william sound in this paper we study one of these cases in detail the port valdez submarine landslide and tsunami we combine eyewitness reports preserved film and careful posttsunami surveys with new geophysical data to inform numerical models for landslide tsunami generation we review the series of events as recorded at valdez old town and then determine the corresponding subsurface events that led to the tsunami we build digital elevation models of part of the pretsunami and posttsunami fjord head delta comparing them reveals a 1500 m long region that receded 150 m to the east which we interpret as the primary delta landslide source multibeam imagery and high resolution seismic reflection data identify a 400 m wide chute with hummocky deposits at its terminus which may define the primary slide path using these elements we run hydrodynamic models of the landslide driven tsunamis that match observations of current direction maximum inundation and wave height at valdez old town we speculate that failure conditions at the delta front may have been influenced by manmade changes in drainage patterns as well as the fast retreat of valdez and other glaciers during the past century

the impact of melting ice on ocean waters abstract ice melts when it is in contact with ocean waters that have temperatures above the in situ freezing point the product is a mixture of meltwater and seawater having properties intermediate between those of the two components density is one of the properties that is affected and this has important implications for how the melt induced changes are eventually manifested although the direct impact of melting is to cool and dilute the ocean subsequent convection can carry the products of melting to parts of the water column where they are comparatively warm and salty these principles are illustrated with a set of observations from the continental shelf of the amundsen sea measurements made near a floating glacier are used to calculate the concentration of meltwater in the water column concentrations approaching 2 are associated with comparatively high temperatures low dissolved oxygen concentrations and negligible stable isotope anomalies the impact of drifting icebergs on the southern ocea

a systematic classification of glacial and periglacial environments facies and deposits abstract several aspects of the deposits formed in the glacial and periglacial environments are presented in order to establish a framework that can be used in various disciplines dealing with sedimentation under glacial and periglacial conditions the almost unlimited number of different deposits are grouped into 37 types that are all described briefly most of them are also illustrated by field examples mainly from poland these 37 types are grouped within 23 facies belonging to 3 continental glacial 3 continental periglacial and 3 marine periglacial subenvironments all environments subenvironments facies and deposits are defined and presented with a hierarchic code that enables unambiguous definition attention is paid to both the general characteristics of the various deposits as they have been described by previous investigators and to specific deposits that have been studied by the present authors the factors influencing peri glacial sedimentation are discussed briefly

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

geochemical signatures of transgressive shale intervals from the 811 ma fifteenmile group in yukon canada disentangling sedimentary redox cycling from weathering alteration abstract despite iron and trace element proxies informing much of our insight into earth s oxygenation history the processes that controlled their accumulation and distribution in ancient sedimentary environments are not fully understood furthermore deciphering between primary depositional signals and oxidative weathering alteration poses a substantial challenge to reconstructing earth s redox history using its sedimentary record here we present a multi proxy geochemical investigation of three transgressive shale intervals from the ca 811 ma reefal assemblage upper fifteenmile group in yukon canada to help resolve these issues systematic stratigraphic trends from low to high fehr fet and fet al compositions across shale intervals represent shoaling of a discrete redoxcline that separated oxygenated surface waters from anoxic ferruginous deep waters during marine transgression in some cases these trends are followed by a symmetric fall which represents a full transgressive regressive cycle of the redoxcline the high proportion of glauconite to total illite indicate short term oscillating redox conditions as the redoxcline migrated across the sediment water interface during relative sea level rise these conditions invigorated dissimilatory iron reduction dir within anoxic sediment pore waters which released fe ii into the overlying water column where it was oxidized to iron oxy hydr oxide and shuttled downslope high rates of dir within sediment replete with highly reactive iron oxy hydr oxide and organic matter removed isotopically light bio available iron rendering the residual sediment depleted in fet al relative to the detrital baseline and enriched in 56fe the low iron content of the detrital flux to the basin fe al 0 3 rendered the sediment susceptible to changes in its bulk 56fe composition by modification of its authigenic components alone and enabled fractionation from dir to drive bulk rock 56fe values up to 0 8 anomalously high concentrations of redox sensitive elements in three samples up to 5792 ppm cr 586 ppm mn 726 ppm mo and 3509 ppm ni and their relative distribution patterns show similarities to co enrichment due to particulate shuttling within a weakly restricted basin however sem eds element maps and large area bse image mosaics show the remains of framboidal pyrite ghosts with secondary enrichment of redox sensitive elements thus these geochemical trends in redox sensitive trace metals most likely reflect mobilization and re accumulation following pyrite dissolution during outcrop weathering the low primary pyrite content and local transformation of pyrite iron to iron oxy hdr oxide suggest that 56fe and fehr fet data were unaltered despite indications of pyrite weathering ultimately this dataset elucidates key aspects of sedimentary redox cycling directly preceding evolutionary milestones and a major perturbation to the global carbon cycle and also provides a template for evaluating the effects of outcrop weathering on commonly used sedimentary redox proxies

evidence for oxygenic photosynthesis half a billion years before the great oxidation event the early earth was characterized by the absence of oxygen in the ocean atmosphere system in contrast to the well oxygenated conditions that prevail today atmospheric concentrations first rose to appreciable levels during the great oxidation event roughly 2 5 2 3 gyr ago the evolution of oxygenic photosynthesis is generally accepted to have been the ultimate cause of this rise but it has proved difficult to constrain the timing of this evolutionary innovation1 2 the oxidation of manganese in the water column requires substantial free oxygen concentrations and thus any indication that mn oxides were present in ancient environments would imply that oxygenic photosynthesis was ongoing mn oxides are not commonly preserved in ancient rocks but there is a large fractionation of molybdenum isotopes associated with the sorption of mo onto the mn oxides that would be retained here we report mo isotopes from rocks of the sinqeni formation pongola supergroup south africa these rocks formed no less than 2 95 gyr ago3 in a nearshore setting the mo isotopic signature is consistent with interaction with mn oxides we therefore infer that oxygen produced through oxygenic photosynthesis began to accumulate in shallow marine settings at least half a billion years before the accumulation of significant levels of atmospheric oxygen

contribution of glacier melt to sea level rise since ad 1865 a regionally differentiated calculation the contribution of glacier melt including the greenland ice sheet to sea level change since ad 1865 is estimated on the basis of modelled sensitivity of glacier mass balance to climate change and historical temperature data calculations are done in a regionally differentiated manner to overcome the inhomogeneity of the global distribution of glaciers a distinction is made between changes in summer temperature and in temperature over the rest of the year our best estimate of the ice melt in the period 1865 1990 in terms of sea level change equivalent is 5 7 cm 2 7 cm for glaciers and 3 0 cm for the greenland ice sheet additional calculations show that simpler methods like using annual or even global mean temperature anomaly give estimates that differ by up to 55 consequently a regionally differentiating approach is advised for making projections of glacier melt with gcm output

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

redox condition in the nanhua basin during the waning of the sturtian glaciation a chromium isotope perspective abstract the neoproterozoic oxygenation event noe is often considered to be synchronously and possibly causally associated with the cryogenian glaciations reconstructing early cryogenian redox conditions is therefore essential for understanding the onset of the noe we analyzed cr isotope compositions 53cr as well as major and rare earth element ree concentrations of the banded iron formations bifs in the basal fulu formation of the xiajiajiang section nanhua basin which are thought to have been deposited during the waning stage of the sturtian glaciation strongly positively fractionated authigenic 53cr values were obtained after detrital correction ranging from 0 64 to 1 22 and averaging at 0 91 0 40 2 n 10 or after detrital evaluation 0 71 this suggests extensive oxidative cr cycling occurred at the earth s surface and implies that the po2 was probably higher than 1 pal during this period the lack of ce anomalies 0 90

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

the mass balance of mccall glacier brooks range alaska u s a its regional relevance and implications for climate change in the arctic mccall glacier has the only long term mass balance record in arctic alaska average annual balances over the periods 1958 72 and 1972 93 were 15 and 33cm respectively recent annual balances 1993 96 are about 60 cm and the mass balance gradient has increased for an arctic glacier with its low mass exchange rate this marks a significant negative trend recently acquired elevation profiles of mccall glacier and ten other glaciers within a 30 km radius were compared with topographic maps made in 1956 or 1973 most of these glaciers had average annual mass balances between 25 and 33 cm while mccall glacier averaged 28 cm for 1956 93 indicating that it is representative of the region in contrast changes in terminus position for the different glaciers vary markedly thus mass balance trends in this region cannot be estimated from fractional length changes at time scales of a few decades we developed a simple degree day accumulation mass balance model for mccall glacier the model was tested using precipitation and radiosonde temperatures from weather stations at inuvik canada and barrow kaktovik and fairbanks alaska and was calibrated with the measured balances the inuvik data reproduce all measured mass balances of mccall glacier well and also reproduce the long term trend towards more negative balances data from the other stations do not produce satisfactory model results we speculate that the arctic front oriented east west in this region causes the differences in model results

airborne and spaceborne dem and laser altimetry derived surface elevation and volume changes of the bering glacier system alaska usa and yukon canada 1972 2006 using airborne and spaceborne high resolution digital elevation models and laser altimetry we present estimates of interannual and multi decadal surface elevation changes on the bering glacier system alaska usa and yukon canada from 1972 to 2006 we find 1 the rate of lowering during 1972 95 was 0 9 0 1 m a 1 2 this rate accelerated to 3 0 0 7 m a 1 during 1995 2000 and 3 during 2000 03 the lowering rate was 1 5 0 4 m a 1 from 1972 to 2003 70 of the area of the system experienced a volume loss of 191 17 km 3 which was an area average surface elevation lowering of 1 7 0 2 m a 1 from november 2004 to november 2006 surface elevations across bering glacier from mcintosh peak on the south to waxell ridge on the north rose as much as 53 m up glacier on bagley ice valley about 10 km east of juniper island nunatak surface elevations lowered as much as 28 m from october 2003 to october 2006 nasa terra modis observations from may to september 2006 indicated muddy outburst floods from the bering terminus into vitus lake this suggests basal englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006

a radar transparent layer in a temperate valley glacier bench glacier alaska radar surveys of bench glacier alaska collected over five field seasons between 2002 and 2006 reveal a surface layer of radar transparent ice in this temperate valley glacier the transparent layer covers the up glacier half of the ablation zone and is defined by a distinct lack of the radar scattering events considered typical of temperate ice radar scattering ice underlies the transparent zone and extends to the surface elsewhere on the glacier we observed the layering in constant offset radar surveys conducted with characteristic frequencies ranging from 5 mhz to 100 mhz the radar transparent layer extends from the surface to 20 m depth on average but up to 50 m in some places bench glacier s transparent layer appears similar to the cold surface layer of polythermal glaciers however observations in over 50 boreholes on bench glacier suggest there is no cold ice corresponding to the radar transparent layer we conclude that spatially extensive radar transparent layers normally used to identify cold ice in polythermal glaciers are present in some temperate glaciers copyright 2009 john wiley sons ltd

a macroscopic approach to glacier dynamics a simple approach to glacier dynamics is explored in which there is postulated to be a relationship between area and volume with three parameters the time for area to respond to changes in volume a thickness scale and an area characterizing the condition of the initial stale this approach gives a good fit to the measurements of cumulative balance and area on south cascade glacier from 1970 97 the area time scale is roughly 8 years the thickness scale about 123 m and the 1970 area roughly 4 larger than required for adjustment with volume combining this relationship with a version of mass continuity expressed in terms of area and volume produces a theory of glacier area and volume response to climate in which another time constant the volume time scale appears area and volume both respond like a damped spring and mass system the damping of the south cascade response is approximately critical and the volume time scale is roughly 48 vexes six times the area time scale the critically damped spring and mass analogy reproduces the time dependence predicted by the more complicated traditional theory of nyc

response time of glaciers as a function of size and mass balance 1 theory a simple interpretation of the traditional definitions of glacier and ice sheet response time e g thickness divided by mass balance rate h b suggests that larger glaciers respond more slowly than small glaciers to a perturbation in climate however with reasonable choices for mass balance behavior a scaling analysis shows that the response time of valley glaciers decreases as a function of increasing size when other variables are held constant in essence this is because larger valley glaciers push further into the ablation zone and ablation increases more rapidly than the thickness so that h b gets smaller ice sheets have different mass balance regimes than valley glaciers and as they grow larger the ablation does not increase faster than the thickness therefore as ice sheets grow in surface area the response time increases for both ice sheets and valley glaciers the response time also depends on a mass balance index which is defined as the slope of the balance curve as a function of horizontal distance along the glacier surface rather than elevation the response time decreases as the balance index increases so for valley glaciers an increase in the balance index and an increase in glacier size have opposite effects on the response time the balance index is typically larger for smaller valley glaciers therefore a small glacier will typically respond faster than a large glacier but this quicker response is because of mass balance considerations and not because of the dynamic characteristics of the glacier arising from its small size as often assumed

the physical basis of glacier volume area scaling ice volumes are known for only a few of the roughly 160 000 glaciers worldwide but are important components of many climate and sea level studies which require water flux estimates a scaling analysis of the mass and momentum conservation equations shows that glacier volumes can be related by a power law to more easily observed glacier surface areas the relationship requires four closure choices for the scaling behavior of glacier widths slopes side drag and mass balance reasonable closures predict a volume area scaling exponent which is consistent with observations giving a physical and practical basis for estimating ice volumes glacier volume is insensitive to perturbations in the mass balance scaling but changes in average accumulation area ratios reflect significant changes in the scaling of both mass balance and ice volume

synchronous retreat and acceleration of southeast greenland outlet glaciers 2000 06 ice dynamics and coupling to climate a large portion of the recent increase in the rate of mass loss from the greenland ice sheet is from increased outlet glacier discharge along its southeastern margin while previous investigations of the region s two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat we examine seasonal and interannual changes in ice front position surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006 while substantial seasonality in front position and speed is apparent nearly all the observed glaciers show net retreat thinning and acceleration with speed up corresponding to retreat the ratio of retreat to the along flow stress coupling length is proportional to the relative increase in speed consistent with typical ice flow and sliding laws this affirms that speed up results from loss of resistive stress at the front during retreat which leads to along flow stress transfer large retreats were often preceded by the formation of a flat or reverse sloped surface near the front indicating that subsequent retreats were influenced by the reversed bed slope many retreats began with an increase in thinning rates near the front in the summer of 2003 a year of record high coastal air and sea surface temperatures this anomaly was driven in part by recent warming suggesting that episodes of speed up and retreat may become more common in a warmer climate

dissolved oxygen variations in alpine glacial meltwaters recent models of chemical weathering in alpine glacial meltwaters suggest that sulphide oxidation is a major source of solute in the distributed component of the subglacial hydrological system this reaction requires o2 and may lower dissolved oxygen levels to below saturation with respect to the atmosphere this should result in an inverse association between so72 and dissolved oxygen saturation however measurements of o2 saturation in bulk meltwaters draining the haut glacier d arolla switzerland show that there is a positive association between so42 and o2 saturation the o2 content of glacial meltwaters depends on the initial content of snow and icemelt which may be controlled by the rate of melting and the kinetic balance between o2 losses e g sulphide oxidation microbial respiration and gains e g diffusion of o2 into solution

a diverse benthic assemblage 100 km from open water under the amery ice shelf antarctica 1 a hot water drill was used to penetrate 480 m of ice to reveal a diverse benthic assemblage dominated by suspension feeding invertebrates under the amery ice shelf east antarctica at a location 100 km from open water and at a depth of 775 m below sea level 840 m below the ice shelf surface this is the first record of a benthic assemblage of this type found at this distance under an ice shelf the few previous reports of life under ice shelves describe assemblages with very different trophic strategies e g sparse assemblages of mobile scavengers or chemotrophs or are in circumstances in which in situ photosynthesis at tide cracks or through the ice cannot be ruled out as a potential source of primary production the physical characteristics of the amery ice shelf and the feeding strategies represented together indicate that the only likely source of primary production to sustain the benthic assemblage is material advected from open water this suggestion is supported by observed current speeds in the vicinity and reported rates of particle settling the observation under an ice shelf of a benthic assemblage that is very similar to those found elsewhere in antarctica in locations dominated by annual sea ice or at depths below the photic zone has implications for the interpretation of sediment paleorecords to represent the history of ice shelf advance and retreat without observations of this living assemblage in situ the remnants of its component species in the sediment record such as sponge spicules echinoderm ossicles and bryozoan fragments could be interpreted reasonably but erroneously to represent open water conditions

alaska tidewater glacier terminus positions 1948 2012 a significant portion of the world s glacier ice drains through tidewater outlets though much remains unknown about the response to recent climate change of tidewater glaciers we present a 64 year record of length change for 50 alaska tidewater glaciers we use u s geological survey topographic maps to provide a base length for glaciers before 1970 using all available cloud free landsat images we manually digitize calving front outlines for each glacier between 1972 and 2012 resulting in a total of more than 10 000 outlines tidewater glacier lengths vary seasonally focusing on the 36 glaciers terminating in tidewater throughout the study period we find a mean standard deviation seasonal variation of 60 85 m a 1 we use these oscillations to determine the significance of interannual changes in glacier length all 36 glaciers underwent at least one period 1 year of significant advance or retreat 28 glaciers underwent at least one period of both significant advance and retreat over the entire period 1948 2012 24 of these glaciers retreated a total uncertainty of 107 95 0 29 km 11 advanced a total of 7 71 0 20 and one chenega glacier did not change significantly retreats and advances are highly variable in time several glaciers underwent rapid short term retreats of a few years duration these retreats occurred after large changes in summer sea surface temperature anomalies further study is needed to determine what triggered these retreats no coherent regional behavior signal is apparent in the length record although two subregions show a coherence similar to recent observations in greenland

width and length scaling of glaciers an analysis of hundreds of mountain and valley glaciers in the former soviet union and the alps shows that characteristic glacier widths scale as characteristic glacier lengths raised to an exponent of 0 6 this is in contrast to most previous analyses which implicitly or explicitly assumed scaling exponents of either 0 or 1 the exponent 0 6 implies that average glacier widths are proportional to average glacier thicknesses although this seems to suggest v shaped glacier valleys the linear width thickness relationship is not inconsistent with parabolic valley cross sections because the characteristic or average width of a glacier depends on many other aspects of channel and glacier morphology including variations in the channel width with distance up and downstream

end of winter snow depth variability on glaciers in alaska a quantitative understanding of snow thickness and snow water equivalent swe on glaciers is essential to a wide range of scientific and resource management topics however robust swe estimates are observationally challenging in part because swe can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes in spring 2013 we measured snow accumulation on several glaciers around the gulf of alaska using both ground and helicopter based ground penetrating radar surveys complemented by extensive ground truth observations we found that swe can be highly variable 40 difference over short spatial scales tens to hundreds of meters especially in the ablation zone where the underlying ice surfaces are typically rough elevation provides the dominant basin scale influence on swe with gradients ranging from 115 to 400 mm 100 m regionally total accumulation and the accumulation gradient are strongly controlled by a glacier s distance from the coastal moisture source multiple linear regressions used to calculate distributed swe fields show that robust results require adequate sampling of the true distribution of multiple terrain parameters final swe estimates comparable to winter balances show reasonable agreement with both the parameter elevation relationships on independent slopes model climate data set 9 36 difference and the u s geological survey alaska benchmark glaciers 6 36 difference all the glaciers in our study exhibit substantial sensitivity to changing snow rain fractions regardless of their location in a coastal or continental climate while process based swe projections remain elusive the collection of ground penetrating radar gpr derived data sets provides a greatly enhanced perspective on the spatial distribution of swe and will pave the way for future work that may eventually allow such projections

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

an extended perfect plasticity method for estimating ice thickness along the flow line of mountain glaciers 1 direct measurement of the thickness of mountain glaciers is difficult over large areas yet knowledge of the thickness is essential for calculating their volumes and future evolution we develop a new method for estimating the ice thickness along glacier flow lines using the perfect plasticity rheological assumption that relates the thickness and surface slope to a yield stress previous studies have used this assumption with the shallow ice approximation to estimate the ice thickness but the standard approach neglects the effect of side drag on glacier stress balance our method addresses this shortcoming and extends the standard method by accounting for the side drag via the glacier width besides the assumed yield stress the inputs for our method are the outline and surface topography of the glacier surface velocity and mass balance data are unnecessary we validated the extended method on five glaciers in northwest china where thickness data are available from radio echo soundings finding that it can reproduce measured thicknesses with a mean absolute error of 11 8 like the standard method moreover for long glacier tongues confined to flow between parallel valley sides this method is found to give more accurate thickness estimates than does the standard method with a mean absolute error of as low as 5 3 sensitivity analysis shows that the estimated ice thickness depends strongly on yield stress and surface slope and less strongly on glacier width because this method is physically more realistic than the standard method and its inputs are easily derivable from remote sensing observations it has the potential to be used for processing large glacier data sets

mass balance of glaciers other than the ice sheets small glaciers appear to have been at equilibrium or shrinking very slightly during 1961 90 according to analysis of an essentially compl ete set of published measurements simple calculations give an average annual mass balance of 195 59 mm a 1 water equivalent but this is too low because of systema tic errors eglect of internal accumulation is respon sible for some tens of millime ters of under esti mate uneven spatial coverage with fewer measurements where mass balances are less negative accounts for about 50 mm a 1 of underestimate this figure derives from spatial interpolati on based on global data on ice extent and on an analysis of correlations between balance time series the eorrelogram shows exponential decay the scale length being about 600 km the largest bias is due to a newly detec ted dependence of mass balance on glacier size among the 231 measured glaciers many arc small and belong to a restricted size range in which balance is negativ e but much of the small glacier extent is accounted for by larger glac iers in a size range where balance is indisti ngui shable from zero correct ing for this size bias increases the average balance to 35 89 mm a i inspection of time series for 1940 95 251 glaciers shows that mass balance was least negative during the 1960s and has varied in broad agreementvith northern hemisphere temperature anomalies smaller small glaciers a 16 km2 appear to be more sensitive than larger small glaciers to changes in thermal forci ng the small glaci er contribution to sea level rise implied by this asse ssment is only 0 06 0 32 mm a i consistent with glaciers in general mak i ng little or no contri bution to sea level change during 1961 90

well constrained seismic estimation of pore pressure with uncertainty the safe drilling of wells for hydrocarbon exploration or production requires that the wellbore pressure be maintained between the formation pore pressure and the maximum pressure the formation can withstand without fracturing this task is made more difficult when drilling in overpressured areas which require a quantitative predrill prediction of pore pressure with uncertainty to be made a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated by offset well data however the uncertainty in velocity is often not quantified this example from the gulf of mexico uses seismic velocities with uncertainty derived by combining seismic velocities with well data den boer et al 2006 parameters in the velocity to pore pressure transform are estimated using seismic velocities density logs pressure information and well velocities derived by inverting time depth pairs from check shots in the area pore pressure and associated uncer

elevation volume and terminus changes of nine glaciers in north america nine glaciers in alaska and washington u s a originally mapped as part of the international geophysical year igy in 1957 58 were re mapped between 1993 and 1996 eight using airborne surface elevation profiling and the ninth using ground based kinematic global positioning system methods elevation volume and terminus changes were determined for the approximately 38 year period between the igy mapping and the profiling all nine glaciers showed substantial thinning at lower elevations seven of the nine thickened at higher elevations none of the glaciers had a significant net volume increase two had close to zero change and the others had a decrease for the eight glaciers for which we could obtain quantitative information the mean thickness change was 10 m with a large scatter 8 m standard deviation the volume and terminus changes had no clear geographic pattern and no simple relationship between volume change and terminus advance or retreat was identified the largest error in the estimated volume changes is due to map errors

a laboratory study of seismic velocity and attenuation anisotropy in near surface sedimentary rocks the laboratory ultrasonic pulse echo method was used to collect accurate p and s wave velocity 0 3 and attenuation 10 data at differential pressures of 5 50 mpa on water saturated core samples of sandstone limestone and siltstone that were cut parallel and perpendicular to the vertical borehole axis the results when expressed in terms of the p and s wave velocity and attenuation anisotropy parameters for weakly transversely isotropic media q q show complex variations with pressure and lithology in general attenuation anisotropy is stronger and more sensitive to pressure changes than velocity anisotropy regardless of lithology anisotropy is greatest over 20 for velocity over 70 for attenuation in rocks with visible clay organic matter laminations in hand specimens pressure sensitivities are attributed to the opening of microcracks with decreasing pressure changes in magnitude of velocity and attenuation anisotropy with effective pressure show similar trends although they can show different signs positive or negative values of q q we conclude that attenuation anisotropy in particular could prove useful to seismic monitoring of reservoir pressure changes if frequency dependent effects can be quantified and modelled

sharply increased mass loss from glaciers and ice caps in the canadian arctic archipelago the canadian arctic archipelago contains one third of the global volume of land ice outside the ice sheets but its contribution to sea level change is largely unknown gardner et al use three independent techniques to reveal that mass loss from the archipelago was 92 12 gigatonnes per year in 2007 09 about three times greater than in 2004 06 and coincident with warmer summer temperatures the record is too short to allow a firm conclusion on longer term trends but it is clear that the canadian arctic archipelago is a significant contributor to sea level rise mountain glaciers and ice caps are contributing significantly to present rates of sea level rise and will continue to do so over the next century and beyond1 2 3 4 5 the canadian arctic archipelago located off the northwestern shore of greenland contains one third of the global volume of land ice outside the ice sheets6 but its contribution to sea level change remains largely unknown here we show that the canadian arctic archipelago has recently lost 61 7 gigatonnes per year gt yr 1 of ice contributing 0 17 0 02 mm yr 1 to sea level rise our estimates are of regional mass changes for the ice caps and glaciers of the canadian arctic archipelago referring to the years 2004 to 2009 and are based on three independent approaches surface mass budget modelling plus an estimate of ice discharge smb d repeat satellite laser altimetry icesat and repeat satellite gravimetry grace all three approaches show consistent and large mass loss estimates between the periods 2004 2006 and 2007 2009 the rate of mass loss sharply increased from 31 8 gt yr 1 to 92 12 gt yr 1 in direct response to warmer summer temperatures to which rates of ice loss are highly sensitive 64 14 gt yr 1 per 1 k increase the duration of the study is too short to establish a long term trend but for 2007 2009 the increase in the rate of mass loss makes the canadian arctic archipelago the single largest contributor to eustatic sea level rise outside greenland and antarctica

a new depositional model for ice shelves based upon sediment cores from the ross sea and the mac robertson shelf antarctica we document the similarity of depositional facies occurring in gravity cores recovered from two disjunct regions of the antarctic continental shelf the ross sea and the mac robertson shelf the facies sequence model is represented in two cores one collected during the 1995 1 cruise of the r v nathaniel r palmer core nbp95 tc 18 and the other collected by the rsv aurora australis during cruise 149 in 1995 core 149 39gc38 both cores show a succession of facies indicative of ice shelf retreat during the late pleistocene to holocene transition distinct lithofacies range in thickness from a few tens of cm to 1 m and consist of from bottom to top a coarse granulated sandy mud laminated silt and clay structureless silly clay poorly sorted sandy siliceous mud and siliceous mud and ooze these facies represent the passage of distinct depositional regimes across the core sites including sub ice shelf beneath a basal debris zone sub ice shell distal to a debris zone calving line transition and open marine this facies model represents an advance in our understanding of glacial marine stratigraphy for the antarctic continental shelf and will provide the basis for more realistic palaeoglacial reconstructions

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

neoproterozoic ice sheets and olistoliths multiple glacial cycles in the kingston peak formation california the kingston peak formation is a diamictite bearing succession that crops out in the death valley region california usa an exceptionally thick 1 5 km outcrop belt in its type area the kingston range provides clear insights into the dynamics of mid cryogenian sturtian ice sheets in laurentia seven detailed logs allow the lateral and vertical distribution of facies associations to be assessed we recognize 1 diamictite facies association ice proximal glacigenic debris flows 2 lonestone bearing facies association ice marginal hemipelagic deposits and low density gravity flows with iceberg rafting 3 pebble to boulder conglomerate facies association ice proximal cogenetic glacigenic debris flows and high density turbidites 4 megaclast facies association olistostrome and hemipelagic sediments subject to ice rafting and 5 interbedded heterolithics facies association low density turbidites and hemipelagic deposits the stratigraphic motif allows three glacial cycles to be inferred across the range ice minimum conditions interrupting the kingston peak succession are associated with the development of an olistostrome complex succeeded by a thick accumulation of boulder conglomerates deposited during ice readvance the data testify to a strong glacial influence on sedimentation within this ancient subaqueous succession and to highly dynamic ice sheet behaviour with clear glacial cycles during the sturtian glaciation

melt regimes stratigraphy flow dynamics and glaciochemistry of three glaciers in the alaska range we used ground penetrating radar gpr gps and glaciochemistry to evaluate melt regimes and ice depths important variables for mass balance and ice volume studies of upper yentna glacier upper kahiltna glacier and the mount hunter ice divide alaska we show the wet percolation and dry snow zones located below 2700ma s l at 2700 to 3900ma s l and above 3900ma s l respectively we successfully imaged glacier ice depths upwards of 480m using 40 100mhz gpr frequencies this depth is nearly double previous depth measurements reached using mid frequency gpr systems on temperate glaciers few holocene length climate records are available in alaska hence we also assess stratigraphy and flow dynamics at each study site as a potential ice core location ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in gpr profiles collected on upper yentna glacier suggest that regions below 2800ma s l are inappropriate for paleoclimate studies because of chemical diffusion through melt flow complexities on kahiltna glacier preclude ice core climate studies minimal signs of melt or deformation and depth age model estimates suggesting 4815years of ice on the mount hunter ice divide 3912ma s l make it a suitable holocene age ice core location

the use of hypsometry to indicate long term stability and response of valley glaciers to changes in mass transfer a simple equation is derived relating the net mass balance and hypsometric curves of a steady state valley glacier it is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions examples are given which show that area based indices e g aar for estimating the equilibrium line altitude ela may be subject to a substantial built in variance because they implicitly rely upon similarity of glacier shape and regimen over a region if accurate topographic maps are available the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass balance gradients alternatively if similar information is available concerning regional glacier regimen disparate extents and responses may be collectively utilized to estimate values of ela or to infer climatic influence taking glacier hypsometry into account

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

glacial changes of five southwest british columbia icefields canada mid 1980s to 1999 this study adjusts and compares digital elevation models dems created from photogrammetric and interferometric synthetic aperture radar techniques to determine volume and surface elevation changes of five icefields in a remote region of southwest british columbia canada between the mid 1980s and 1999 preliminary differences between the dems in ice free and vegetation free areas indicated variable elevation offsets with increasing altitude 11 m km 1 and with increasing slope 2 7 m 108 1 results indicate a surface elevation change of 6 0 2 7 m 0 5 0 2 m a 1 and a total volume loss of 19 4 8 8 km 3 1 5 0 7 km 3 a 1 which represents a potential sea level rise contribution of 0 004 0 002 mm a 1 temperature and snowfall data from four nearby meteorological stations indicate that increased temperatures and decreased snowfall throughout the late 1980s and 1990s are a likely cause of the thinning glacier terminus positions were compared between a historical map 1927 and satellite images 1974 1990 91 and 2000 01 all observed glaciers were in retreat between 1927 and 1974 as well as between 1990 91 and 2000 01 but many glaciers advanced or significantly slowed in their retreat between 1974 and 1990 91

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

altitude variation of glacier mass balance in scandinavia 1 for each of ten glaciers in norway and two in sweden vertical profiles of net balance bn z which are typically published as values at about a dozen altitudes are strongly linear and nearly parallel from year to year separate linear functions fit the bn z from year to year with r2 0 89 over the 12 glaciers a family of parallel lines for each glacier that differ from year to year only by an amount bn constant with altitude has r2 0 85 there is an altitude z on each glacier where the measured balance bn z correlates well with the glacier total bn with r 0 97 over the 12 glaciers a remarkable consequence of this and of the high correlation of bn between many of the glaciers in the region is that measurements on one glacier 1775 meters on hardangerjokulen provide a good estimate of bn at several other glaciers

glacier specific elevation changes in parts of western alaska the meltwater from glaciers in alaska contributes strongly to global sea level rise but accurate determination is challenging as only two comparatively small glaciers have long term measurements of annual mass balance gulkana and wolverine simple upscaling of their values to the entire region is error prone as their representativeness is unknown and might be biased alternatively differencing digital elevation models dems from two epochs provides overall volume changes for a longer period of time that can be converted to mass changes using appropriate density assumptions here we combine outlines from two glacier inventories to determine glacier specific elevation changes over a 50 year period for 3180 glaciers in western alaska using dem differencing this allows us to determine the representativeness of the land terminating gulkana and wolverine glaciers for the entire region and to exclude calving glaciers marine and lacustrine from the sample mean changes for all land terminating lake terminating and tidewater glaciers are 0 23 0 44 0 63 0 40 and 0 64 0 66 m a 1 respectively and 0 7 and 0 6 m a 1 for the two mass balance or benchmark glaciers thus fortuitously their changes better represent calving glaciers and the overall mean 0 63 1 14 m a 1 than the change of land terminating glaciers i e they are not representative for their own type different methods of considering potential dem artefacts provide variable mean changes but the same general result

elevation changes measured during 1966 2010 on the monsoonal temperate glaciers ablation region gongga mountains china abstract temperate glaciers are more sensitive to climate change than are polar or continental glaciers and can drive remarkable runoff variation in local water catchments changes in the glacier area and surface elevation of the three monsoonal temperate glaciers in the gongga mountains china were analyzed using series of remote sensing images and digital elevation model dem data all possible sources of uncertainty were considered in detail the results showed that the total glacier area decreased by 4 3 km 2 6 7 between 1966 and 2010 a comparison of glacier surface elevations using dems derived from dual frequency differential gps dgps surveys in 2010 and from 1966 to 1989 from topographic maps the three glaciers underwent significant mass loss from 1966 to 2010 and the mean surface elevation changes were 0 90 0 45 m y 1 06 0 45 m y and 1 12 0 45 m y for hailuogou hlg dagongba dgb and yanzigou yzg glaciers respectively from 1966 to 2010 analysis of the meteorological data showed that the mean annual air temperature increase was the main reason for the thinning and volume loss thinning of the glacier tongue and volume loss was more intense in the period 1989 2010 than in 1966 89 debris thickness and other factors are also believed to play important roles in differential thinning among different areas and periods