flow dynamics of the rutford ice stream ice drainage basin west antarctica from radar stratigraphy rutford ice stream west antarctica drains a catchment of 45 000 km 2 into the ronne ice shelf through a 26 km wide 2 4 km deep subglacial trough adjacent to the ellsworth mountains forty two per cent of its catchment boundary is common with pine island glacier where rapid change to ice dynamics is currently underway these changes may eventually affect adjacent catchments such as rutford radar sounding data were acquired over the rutford ice drainage basin that show the internal structure in particular distinctive reflector groups were identified that mark the boundaries between four different flow elements the flow margin reflector groups include curvilinear events that cross cut isochrones and are therefore likely to be post depositional these reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin one of the sectors of the ice drainage basin supplies the largest share 38 of the ice volume flux through the main trunk of rutford ice stream this sector may be preferentially affected by continuing surface lowering in the pine island glacier catchment

grounding line movement and ice shelf buttressing in marine ice sheets 1 understanding the dynamics of marine ice sheets is integral to studying the evolution of the antarctic ice sheet in both the short and long terms an important component of the dynamics grounding line migration has proved difficult to represent in numerical models and most successful attempts have made use of techniques that are only readily applicable to flow line models however to capture the stress transmission involved in another important component the buttressing of a marine ice sheet by its ice shelf the transverse direction must also be resolved we introduce a model that solves the time dependent shelfy stream equations and makes use of mesh adaption techniques to overcome the difficulties typically associated with the numerics of grounding line migration we compare the model output with a recent benchmark for flow line models and show that our model yields an accurate solution while using far less resources than would be required without mesh adaption we also show that the mesh adapting techniques extend to two horizontal dimensions experiments are carried out to determine how both ice shelf buttressing and ice rises affect the marine instability predicted for an ice sheet on a foredeepened bed we find that buttressing is not always sufficient to stabilize such a sheet but collapse of the grounded portion is still greatly delayed we also find that the effect of an ice rise is similar to that of narrowing the ice shelf

lgm ice sheet extent in the weddell sea evidence for diachronous behavior of antarctic ice sheets abstract inaccessibility due to harsh weather conditions and perennial sea ice has resulted in the weddell sea being one of the more under studied regions of antarctica re examination of existing cores and unpublished multibeam bathymetric data provide new insight into the lgm configuration of the ice sheet in the region sediment cores from the eastern continental shelf where the east antarctic ice sheet eais drains display a retreat stratigraphy with distal glacimarine sediments overlying proximal glacimarine sediments and till the distinction between distal and proximal glacimarine sediments is based on degrees of marine influence based on grain size distributions and foraminiferal abundance and diversity glacimarine sediments yielded ams radiocarbon ages that span the past 30 476 cal yr bp indicating that retreat of the eais from the continental shelf occurred prior to the lgm multibeam swath bathymetry data show mega scale glacial lineations in two troughs on the southern continental shelf which indicates the existence of two ice streams draining the west antarctic ice sheet wais more subtle lineations within filchner trough imply more sluggish flow across bedrock and older strata within this trough although there are no radiocarbon ages to absolutely constrain the timing of this grounding event on the southern continental shelf we interpret the lineations as lgm age based on their pristine nature this interpretation is consistent with results from other sectors of the west antarctic continental shelf where compelling evidence for significant wais advance during the lgm exists in the weddell sea this apparent diachronous behavior of the eais and wais is consistent with results from onshore studies

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

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

a simple model to estimate ice ablation under a thick debris layer this paper presents a simple model to estimate ice ablation under a thick supraglacial debris cover the key method employed in the model is to establish a link between the debris heat flux and the debris temperature at a certain depth when the heat transfer in the debris is described by a diffusion process given surface temperature debris thermal properties and relevant boundary conditions the proposed model can estimate mean debris temperature at interfaces of different debris layers using an iterative procedure and then the heat flux for ice ablation the advantage of the proposed model is that it only requires a few parameters to conduct the modeling which is simpler and more applicable than others the case study on koxkar glacier west tien shan china shows in general that the proposed model gives good results for the prediction of debris temperatures except for an apparent phase shift between modeled and observed values we suggest that this error is mainly due to complex phase relations between debris temperature and debris heat flux the modeled ablation rates at three experimental sites also show good results using a direct comparison with observed data and an indirect comparison with a commonly used energy balance model

holocene glacial history of antarctica and the sub antarctic islands abstract a history of holocene glaciation in the antarctic and sub antarctic affords insight into questions concerning present and future ice sheet and mountain glacier behavior and global climate and sea level change existing records permit broad correlation of holocene ice fluctuations within the region in several areas ice extent was less than at present in mid holocene time an important exception to this is the west antarctic ice sheet which has undergone continued recession throughout the holocene probably in response to internal dynamics the first neoglacial ice advances occurred at 5 0 ka although some sites e g western ross sea lack firm evidence for glacial expansion at that time glaciers in all areas underwent renewed growth in the past millennium and most have subsequently undergone recession in the past 50 years ranging from near catastrophic in parts of the antarctic peninsula to minor in the western ross sea region and sections of east antarctica this magnitude difference likely reflects the much greater warming that is taking place in the antarctic peninsula region today as compared to east antarctica

radar detected englacial stratigraphy in the pensacola mountains antarctica implications for recent changes in ice flow and accumulation we used measurements of radar detected stratigraphy surface ice flow velocities and accumulation rates to investigate relationships between local valley glacier and regional ice sheet dynamics in and around the schmidt hills pensacola mountains antarctica ground penetrating radar profiles were collected perpendicular to the long axis of the schmidt hills and the margin of foundation ice stream fis within the valley confines the glacier consists of blue ice and profiles show internal stratigraphy dipping steeply toward the nunataks and truncated at the present day ablation surface below the valley confines the blue ice is overlain by firn data show that upward progressing overlap of actively accumulating firn onto valley glacier ice is slightly less than ice flow out of the valleys over the past 1200 years the apparent slightly negative mass balance 0 25 cm a 1 suggests that ice margin elevations in the schmidt hills may have lowered over this time period even without a change in the surface elevation of fis results suggest that 1 mass balance gradients between local valley glaciers and regional ice sheets should be considered when using local information to estimate regional ice surface elevation changes and 2 interpretation of shallow ice structures imaged with radar can provide information about local ice elevation changes and stability

hydrology of debris covered glaciers in high mountain asia abstract the hydrological characteristics of debris covered glaciers are known to be fundamentally different from those of clean ice glaciers even within the same climatological geological and geomorphological setting understanding how these characteristics influence the timing and magnitude of meltwater discharge is particularly important for regions where downstream communities rely on this resource for sanitation irrigation and hydropower such as high mountain asia the hydrology of debris covered glaciers is complex rugged surface topographies typically route meltwater through compound supraglacial englacial systems involving both channels and ponds as well as pathways that remain unknown low gradient tongues that extend several kilometres retard water conveyance and promote englacial storage englacial conduits are frequently abandoned and reactivated as water supply changes new lines of permeability are exploited and drainage is captured due to high rates of surface and subsurface change seasonal influences such as the monsoon are superimposed on these distinctive characteristics reorganising surface and subsurface drainage rapidly from one season to the next recent advances in understanding have mostly come from studies aimed at quantifying and describing supraglacial processes little is known about the subsurface hydrology particularly the nature or even existence of subglacial drainage in this review we consider in turn the supraglacial englacial subglacial and proglacial hydrological domains of debris covered glaciers in high mountain asia we summarise different lines of evidence to establish the current state of knowledge and in doing so identify major knowledge gaps finally we use this information to suggest six themes for future hydrological research at high mountain asian debris covered glaciers in order to make timely long term predictions of changes in the water they supply

cosmogenic nuclide exposure ages from the pensacola mountains adjacent to the foundation ice stream antarctica we describe glacial geological observations and cosmogenic nuclide exposure ages from the schmidt williams and thomas hills in the pensacola mountains of antarctica adjacent to the foundation ice stream fis our aim is to learn about changes in the thickness and grounding line position of the antarctic ice sheet in the weddell sea embayment between the last glacial maximum lgm and the present glacial geological observations from all three regions indicate that currently ice free areas were covered by ice during one or more past ice sheet expansions and that this ice was typically frozen to its bed and thus non erosive permitting the accumulation of multiple generations of glacial drift cosmogenic nuclide exposure age data from glacially transported erratics are consistent with this interpretation in that we observe both i samples with holocene exposure ages that display a systematic age elevation relationship recording lgm to present deglaciation and ii samples with older and highly scattered apparent exposure ages that were deposited in previous glacial interglacial cycles and have experienced multiple periods of surface exposure and ice cover holocene exposure ages at the thomas and williams hills upstream of the present grounding line of the fis show that the fis was at least 500 m thicker prior to 11 ka and that 500 m of thinning took place between 11 and 4 ka however exposure age data from the schmidt hills downstream of the present grounding line of the fis show no evidence for lgm thickening of the fis and in fact provide some evidence that the fis could have been no more than 200 m thicker than present at the lgm if all these observations are correct they imply that the lgm and early holocene ice surface slope in the vicinity of the present grounding line was steeper than present which is inconsistent with glaciological model predictions of possible lgm ice sheet configurations specifically scenarios in which the lgm grounding line of the fis advanced to the outer continental shelf appear inconsistent with exposure age data from the schmidt hills whereas scenarios in which the fis grounding line did not advance at the lgm appear inconsistent with exposure age data from the williams and thomas hills

backwasting rate on debris covered koxkar glacier tuomuer mountain china a physically based energy balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris covered area the model has been tested against observations between 5 august and 5 september 2008 on 38 ice cliffs in the debris covered area of koxkar glacier tuomuer mountain china we calculated that the energy balance model gave a good estimate of the backwasting rates with errors in the range 1 96 cm d 1 and root mean square errors of 0 99 cm d 1 errors arising from setting of surface albedo and turbulent flux parameterization were limited we found that shortwave radiation is the most important heat source for ice cliff ablation contributing about 76 of the total heat available for ice melt while the sensible heat flux provides nearly 24 of the total heat for ice cliff wastage the latent heat flux and net longwave radiation are comparatively small according to the model calculation the mean backwasting rate of ice cliffs in the debris covered area of koxkar glacier is estimated at 7 64 m a 1 when the winter ablation is neglected with this annual backwasting rate and given a mean slope angle of 46 48 the backwasting of ice cliffs produces about 1 60 10 6 m 3 of meltwater accounting for about 7 3 of the total melt runoff from the debris covered area

bedrock topography and wind erosion sites in east antarctica observations from the 2002 us itase traverse ice stratigraphy from deep penetrating radar data collected during the 2002 us international trans antarctic scientific expedition us itase traverse shows evidence of a significant erosion surface and drift filled basin related to a previously undiscovered 1400 m subglacial mountain between hercules dome 87842 0 s 1088 w and south pole the 3 mhz radar profile crosses three subglacial mountains at approximately 458 to the ice flow direction cross cutting reflectors in the top 500 m of ice stratigraphy are interpreted as angular unconformities resulting from wind erosion as the ice deforms over the mountain tops the unconformities correlate locally with zones of high radarsat reflectivity several nearby sites with similar relatively high radarsat reflectivity adjacent to the traverse indicate that active wind erosion may be taking place at these locations as well based on the local correlation between surface wind scour and subglacial topography we interpret the nearby cluster of bright radarsat reflectivity to indicate the presence of a small range of subglacial mountains the ability to trace isochronal stratigraphy associated with scour sites using shallow and deep radar to nearby dated ice cores presents the possibility of exploiting wind scour zones to access well dated older ice with shallow coring equipment

growth and drainage of supraglacial lakes on debris mantled ngozumpa glacier khumbu himal nepal ablation of debris mantled glaciers in nepal has resulted in the formation of several potentially unstable moraine dammed lakes some of which constitute serious hazards ngozumpa glacier khumbu himal has undergone significant downwasting in recent decades and is believed to lie close to the threshold for moraine dammed lake formation the debris mantled ablation area of the glacier is studded with numerous supraglacial lakes the majority of which occupy closed basins with no perennial connections to the englacial drainage system perched lakes perched lakes can undergo rapid growth by subaerial and water line melting of exposed ice faces and calving subaerial and subaqueous melting beneath thick 1 m debris mantles is comparatively insignificant although lake expansion can contribute substantially to ablation of the glacier perched lakes cannot continue to grow indefinitely but are subject to rapid drainage once a connection is made to englacial conduits the level of one of the lakes on the ngozumpa however is controlled by the altitude of a spillway through the lateral moraine of the glacier this lake underwent only limited growth in the period 1998 2000 but is likely to experience monotonic growth if glacier mass balance continues to be negative

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

importance of longwave emissions from adjacent terrain on patterns of tropical glacier melt and recession tropical glaciers constitute an important source of water for downstream populations however our understanding of glacial melt processes is still limited one observed process that has not yet been quantified for tropical glaciers is the enhanced melt caused by the longwave emission transfer here we use high resolution surface temperatures obtained from the thermal infrared imagery of the cuchillacocha glacier in the cordillera blanca peru in june 2014 to calculate a margin longwave flux this longwave flux reaching the glacier margin from the adjacent exposed rock varies between 81 and 120 w m 2 daily this flux is incorporated into a physically based melt model to assess the net radiation budget at the modeled glacier margin the simulation results show an increase in the energy available for melt by an average of 106 w m 2 during the day when compared with the simulation where the lw margin flux is not accounted for this value represents an increase in ablation of 1 7 m at the glacier margin for the duration of the dry season this study suggests that including the quantification of the glacier margin longwave flux in physically based melt models results in an improved assessment of tropical glacier energy budget and meltwater generation

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

formation and evolution of an extensive blue ice moraine in central transantarctic mountains antarctica mount achernar moraine is a terrestrial sediment archive that preserves a record of ice sheet dynamics and climate over multiple glacial cycles similar records exist in other blue ice moraines els

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

late pleistocene evolution of scott glacier southern transantarctic mountains implications for the antarctic contribution to deglacial sea level abstract glacial deposits preserved adjacent to scott glacier southern transantarctic mountains provide a record of past fluctuations in the thickness of the west antarctic ice sheet geologic mapping of these deposits in conjunction with emerging 10 be surface exposure data indicate that the most recent expansion of scott glacier occurred during the last glacial maximum in response to grounding of ice in the ross sea embayment at that time the ice surface at the confluence of scott glacier and the west antarctic ice sheet lay at 1100 m elevation while this ice surface reconstruction is in accord with other geologic estimates from throughout the ross sea embayment it contrasts with most computer based simulations which tend to overestimate former ice thickness in the southern ross sea together with recently modelled estimates of antarctica s contribution to sea level this finding calls into question an antarctic source for meltwater pulse 1a

marine geological constraints for the grounding line position of the antarctic ice sheet on the southern weddell sea shelf at the last glacial maximum abstract the history of grounded ice sheet extent on the southern weddell sea shelf during the last glacial maximum lgm and the timing of post lgm ice sheet retreat are poorly constrained several glaciological models reconstructed widespread grounding and major thickening of the antarctic ice sheet in the weddell sea sector at the lgm in contrast recently published onshore data and modelling results concluded only very limited lgm thickening of glaciers and ice streams feeding into the modern filchner and ronne ice shelves these studies concluded that during the lgm ice shelves rather than grounded ice covered the filchner and ronne troughs two deep palaeo ice stream troughs eroded into the southern weddell sea shelf here we review previously published and unpublished marine geophysical and geological data from the southern weddell sea shelf the stratigraphy and geometry of reflectors in acoustic sub bottom profiles are similar to those from other west antarctic palaeo ice stream troughs where grounded ice had advanced to the shelf break at the lgm numerous cores from the southern weddell sea shelf recovered sequences with properties typical for subglacially deposited tills or subglacially compacted sediments these data sets give evidence that grounded ice had advanced across the shelf during the past thereby grounding in even the deepest parts of the filchner and ronne troughs radiocarbon dates from glaciomarine sediments overlying the subglacial deposits are limited but indicate that the ice grounding occurred at the lgm and that ice retreat started before 15 1 corrected 14c kyrs before present bp on the outer shelf and before 7 7 corrected 14c kyrs bp on the inner shelf which is broadly synchronous with ice retreat in other antarctic sectors the apparent mismatch between the ice sheet reconstructions from marine and terrestrial data can be attributed to ice streams with very low surface profiles similar to those of ice plains that had advanced through filchner trough and ronne trough at the lgm considering the global sea level low stand of 130 m below present a low surface slope of the expanded lgm ice sheet in the southern weddell sea can reconcile grounding line advance to the shelf break with limited thickening of glaciers and ice streams in the hinterland this scenario implies that ice sheet growth in the weddell sea sector during the lgm and ice sheet drawdown throughout the last deglaciation could only have made minor contributions to the major global sea level fluctuations during these times

thermal regime of a supraglacial lake on the debris covered koxkar glacier southwest tianshan china a supraglacial lake was surveyed on the koxkar glacier in southwest tianshan from july to september 2007 and july to september 2008 and the temperature variation characteristics of the lake debris and debris free ice were analyzed at different depths to determine the thermal regimes in addition the discrepancies of temperature variation characteristics were investigated for different geomorphic units of the ablation zone of the koxkar glacier it was found that daily temperature variation curves for deep water are v shaped because meltwater from the glacier surface at temperatures of around 0 c feeds the lake and mixes with the relatively high temperature surface water during the day as the water temperature rises to approximately 4 c the mixed water sinks and forms a low temperature trough in the deep water of the lake in the middle of the day the vertical lapse rate of the lake water temperature against depth 0 33 c m has a magnitude lower than that of the debris 4 29 c m and that of the debris free ice 0 38 c m in the koxkar glacier s ablation zone the temperature curve for the surface water largely varied between the temperature curves for the debris at depths of 0 2 and 0 5 m the surface thermal condition of the ablation zone is significantly affected by the daily weather and there is a limited influence in debris at a depth of 1 m and in the lake at a depth of 5 m

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

mesoproterozoic lamprophyres in the labrieville massif quebec clues to the origin of alkalic anorthosites mesoproterozoic lamprophyre dikes occur at four localities within the 1010 ma labrieville anorthosite in the grenville province of southern quebec all dikes are thin 20 cm wide oriented n57 w and steeply dipping three are biotite lamprophyres but the fourth is dominated by amphibole laser total fusion 40ar 39ar analyses on amphibole or biotite yield minimum ages for the dikes of 945 5 8 ma 907 0 5 9 ma 892 0 6 2 ma and 889 2 9 8 ma a crystallization age of 1 ga for all dikes is consistent with these data and rb sr isotopic systematics all lamprophyres contain high levels of cr 284 393 ppm ni 101 180 ppm ba 1380 5580 ppm sr 2359 3109 ppm and rare earth elements ree lan 191 288 with average lan lun 26 and no eu anomalies at 1 ga all lamprophyres have a similar initial sr isotopic ratio of 0 7034 similar to bulk earth in contrast e nd values vary considerably from 4 to 10 2 indicating sources with variable long term light ree enrichment negative correlations between 143nd 144nd and la nb and k suggest involvement of at least two source components probably asthenosphere and metasomatized subcontinental lithosphere the lamprophyres are only slightly younger than 1010 ma labrieville massif which is also alkalic and enriched in sr and ba relative to most other anorthosites the lamprophyres provide unequivocal evidence for a sr and ba rich component in the lithospheric mantle that may have contributed to the parental magmas of labrieville and other andesine anorthosites in this part of quebec

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

sequential stagnation of kamb ice stream west antarctica 1 ice penetrating radar data confirm the presence of two relict northern margins of kamb ice stream kis west antarctica in an area called the duckfoot between the two relict margins deep layers are preserved and buried crevasses remain at a constant depth until roughly 1 5 km from the innermost youngest margin suggesting that this outer portion of the ice stream stagnated suddenly 10 years stagnation was likely accomplished through changes in basal conditions i e reduced lubrication beneath this outer portion of the ice stream and resulted in a narrowing of the ice stream trunk by 27 and a reduction in flow speed 200 years prior to complete stagnation flowstripe deformation as a result of duckfoot stagnation provides an estimate of kis paleo velocity of 210 m a after duckfoot stagnation

reconstruction of changes in the weddell sea sector of the antarctic ice sheet since the last glacial maximum the weddell sea sector is one of the main formation sites for antarctic bottom water and an outlet for about one fifth of antarctica s continental ice volume over the last few decades studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice sheet extent and ice sheet thickness since the last glacial maximum lgm at ca 23 19 calibrated kiloyears before present cal ka bp terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the weddell sea ice sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding line advance at the lgm other marine geological and geophysical studies concluded that subglacial bedforms mapped on the weddell sea continental shelf subglacial deposits and sediments over compacted by overriding ice recovered in cores and the few available radiocarbon ages from marine sediments are consistent with major ice sheet advance at the lgm reflecting the geological interpretations different ice sheet models have reconstructed conflicting lgm ice sheet configurations for the weddell sea sector consequently the estimated contributions of ice sheet build up in the weddell sea sector to the lgm sea level low stand of 130 m vary considerably in this paper we summarise and review the geological records of past ice sheet margins and past ice sheet elevations in the weddell sea sector we compile marine and terrestrial chronological data constraining former ice sheet size thereby highlighting different levels of certainty and present two alternative scenarios of the lgm ice sheet configuration including time slice reconstructions for post lgm grounding line retreat moreover we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research the aim of our study is to provide two alternative interpretations of glacial geological datasets on antarctic ice sheet history for the weddell sea sector which can be utilised to test and improve numerical ice sheet models

air temperature distribution and energy balance modelling of a debris covered glacier near surface air temperature is an important determinant of the surface energy balance of glaciers and is often represented by a constant linear temperature gradients tgs in models spatiotemporal variability in 2 m air temperature was measured across the debris covered miage glacier italy over an 89 d period during the 2014 ablation season using a network of 19 stations air temperature was found to be strongly dependent upon elevation for most stations even under varying meteorological conditions and at different times of day and its spatial variability was well explained by a locally derived mean linear tg mg tg of 0 0088 c m 1 however local temperature depressions occurred over areas of very thin or patchy debris cover the mg tg together with other air tgs extrapolated from both on and off glacier sites were applied in a distributed energy balance model compared with piecewise air temperature extrapolation from all on glacier stations modelled ablation using the mg tg increased by 4 using the environmental lapse rate ice melt under thick debris was relatively insensitive to air temperature while the effects of different temperature extrapolation methods were strongest at high elevation sites of thin and patchy debris cover

the glacier inventory of china following recommendations from the international commission on snow and ice for a world glacier inventory an inventory of glaciers in china was carried out by chinese glaciologists from 1978 to 2002 each glacier was measured from aerial photographs and topographical maps and 34 parameters recorded these parameters were then analyzed statistically for the various river systems in china twelve volumes of the glacier inventory of china gic have been published consisting of 22 parts in 21 books the data were subsequently abridged into a concise gic published in chinese 2005 and in english 2008 to make the glacier inventory more accessible and better adapted for assessing glacier response to climate change after the gic was completed new aerial photographs became available and remote sensing techniques became more common to investigate glacier changes since completion of the first gic a second glacier inventory of china was initiated in 2007 this 5 year project supported by the ministry of science and technology will be undertaken mainly using remote sensing techniques

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

late quaternary ice surface fluctuations of hatherton glacier transantarctic mountains abstract former longitudinal profiles of hatherton glacier an outlet through the transantarctic mountains constrain nearby polar plateau elevations and ice shelf grounding in the southwestern ross embayment four gravel drift sheets of late quaternary age beside hatherton glacier are from youngest to oldest hatherton britannia i britannia ii and danum the hatherton drift limit is uniformly 20 to 70 m above the present ice surface the britannia ii drift limit is within 100 m of the present surface of uppermost hatherton glacier but is 450 m above middle hatherton glacier extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present ross ice shelf the britannia i drift limit is parallel to but 50 100 m below britannia ii drift the danum drift limit is parallel to but 50 100 m above the britannia ii profile from correlation with drifts near mcmurdo sound and from local 14 c dates we assign an early holocene age to hatherton drift a late wisconsin age to britannia drifts and an age of marine isotope stage 6 to danum drift by our age model the upper reaches of hatherton glacier and presumably the adjacent polar plateau have not exceeded their current elevations by more than 100 150 m during the last two complete global glacial interglacial cycles whereas the middle and lower reaches of hatherton glacier have thickened considerably during the last two global glaciations late wisconsin and marine isotope stage 6 the effect of ice shelf grounding probably was the major control of these changes of hatherton glacier holocene ice surface lowering probably represents the last pulse of grounding line recession in the southwestern ross embayment

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

evidence for late pleistocene thinning of siple dome west antarctica 1 we use a two dimensional full stress thermomechanical flow band model to investigate late pleistocene and holocene histories of ice thickness and ice flow at siple dome in west antarctica measurements obtained from an ice core and borehole near the ice divide and measurements of radar detected internal stratigraphy are used as targets for modeling models that account for the climate history accumulation rate and temperature alone yield a poor match to observations histories of ice dynamics ice thickness ice divide location and ice flow enhancement also need to be included our favored model includes 350 m of thinning at siple dome between 15 000 and 14 000 years ago onset of divide flow 3000 years ago ongoing divide migration starting 2500 years ago and evolution of ice fabric over the past 30 000 years the timing of thinning is earlier than that inferred from geologic evidence from the margins but is coincident with a 20 m rise in global sea level about 14 500 years ago meltwater pulse 1a this opens the possibility that thinning was a result of increased activity of the ice streams in the late pleistocene forced by meltwater pulse 1a the contribution to meltwater pulse 1a as a result of this thinning was likely small

rapid calculation of terrain parameters for radiation modeling from digital elevation data digital elevation models are widely used to calculate terrain parameters to determine incoming solar and longwave radiation for use in surface climate models interpretation of remote sensing data and parameters in hydrologic models because of the large number of points in an elevation grid fast algorithms are useful to save computation time a description is given of rapid methods for calculating slope and azimuth solar illumination angle horizons and view factors for radiation from sky and terrain calculation time is reduced by fast algorithms and lookup tables

on the influence of debris cover on glacier morphology how high relief structures evolve from smooth surfaces abstract debris covered glaciers receive increasing attention during the current period of sustained negative mass balance and expanding debris cover the debris cover induces various feedback mechanisms that shape the evolution of the glacier geometry and also the glacier surface although the surface morphology of many debris covered glaciers is markedly different from that of debris free glaciers only a few studies have combined different processes to investigate these characteristic glacier surfaces in order to improve our knowledge of glacier evolution on a wider spatial and temporal scale debris covered glacier tongues can consist of parts with a smooth surface as well as surfaces of high local relief with abundant ice cliffs in the lower end in this study we analysed the evolution of the surface features of zmuttgletscher a debris covered glacier in switzerland over a period of 140 years using time series of historic maps high resolution digital elevation models and glacier velocities as well as data on debris cover extent and thickness our results reveal insights into the up glacier expansion of the debris cover over time and the formation of medial moraines in the prolongation of the uppermost areas where debris emerged on the glacier surface moraine ridge prominence increased during periods of negative mass balance and troughs developed in debris free areas between ridges persisting even after a continuous debris cover had developed the changing surface morphology inhibits across glacier meltwater flow both supra and subglacially accordingly we found that large cryo valleys with ice cliffs have formed down glacier of the troughs where meltwater runoff accumulates the meanders of these valleys have enlarged over time especially by ice cliff backwasting at steep slopes and most of the glacier width today is affected by such high relief erosion features we find that about 75 of all ice cliffs are located in this high relief zone the volume lost at these erosion features has increased by a factor of five since the 1980s but is still very small in comparison to the high glacier wide thinning rates

a low power consumption radar system for measuring ice thickness and snow firn accumulation in antarctica in order to measure total ice thickness and surface snow accumulation in antarctica we have designed and built a surveying system comprising two types of radar this system is aimed at having low power consumption low weight volume and low construction cost the system has a pulse compression radar to measure ice thickness and a frequency modulated continuous wave fm cw radar designed to measure hundreds of meters of surface snow firn layers with high resolution the pulse compression radar operates at 155 mhz 20 mhz of bandwidth and the fm cw radar operates from 550 to 900 mhz the system was tested in december 2010 at union glacier 79846 0 s 83824 0 w west antarctica during an oversnow campaign where union and other nearby glaciers schanz schneider and balish were covered through 82 km of track ice thickness of 1540 m and snow firn thickness of 120 m were detected in the area the collected data allowed the subglacial topography internal ice structure isochronous and the snow ice boundary layer to be detected here we describe radar electronics their main features and some of the results obtained during the first test campaign further improvements will focus on the adaptation of the system to be implemented on board airplane platforms

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change the retreat history of the west antarctic ice sheet wais since the last glacial maximum is important for understanding the process of rapid deglaciation constraining models that seek to predict the future trajectory of the ice sheet and for estimating rates of sea level change here we report new glacial geologic data from the southwestern weddell sea embayment that demonstrate that this part of the wais was thinner than previously suggested and that there was progressive thinning of the ice sheet by 230 480 m since ca 15 ka we use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the weddell sea at the last glacial maximum the volume of this ice would have added between 1 4 and 2 0 m to postglacial sea level rise and would not have been sufficient to contribute significantly to meltwater pulse 1a a rapid rise in sea level 14 200 yr ago

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

antarctic blue ice moraines analogue for northern hemisphere ice sheets abstract this paper reviews the distribution character and age of blue ice moraines in antarctica and asks whether there are implications for the study of former pleistocene ice sheets in the northern hemisphere blue ice forms where acceleration of downslope katabatic winds removes snow and causes ice to ablate upward ice flow compensates for the surface ablation and in some places brings rock debris to the surface to form a blue ice moraine blue ice moraines occur where topography focuses katabatic winds notably outlet glaciers cutting through mountains and in the lee of nunataks and escarpments nearer the coast many antarctic blue ice moraines have been accumulating for millions of years the cyclic growth and decay of pleistocene ice sheets and the dominance of surface ablation near the ice sheet margins are clearly different yet there are aspects that apply to pleistocene ice sheets based on antarctic blue ice deposits equivalent deposits associated with former pleistocene ice sheets are likely to 1 lie in topographic sediment traps such as in side valleys or embayments next to outlet glaciers 2 occur in the lee of mountains 3 display a morphology indicating ice flow into the embayment or towards the mountain front 4 include a wide range of lithologies derived from the inland ice sheet yet consist wholly of local debris in places 5 accumulate a thick deposit perhaps over successive glaciations further 6 the location and intensity of moraine formation will change spatially and vertically in response to changes in the relative elevation of the surrounding mountains and its effect on ice flow the extent to which these criteria will help in interpreting the behaviour of pleistocene ice sheets is uncertain but we use examples from the greenland laurentide and eurasian ice sheets to suggest that the concept of enhanced ablation by katabatic winds encouraging surface moraine formation helps resolve several puzzles

de icing progression of ice cored moraines in a humid subpolar climate kotlujokull iceland modes and rates of de icing ice cored moraines under humid subpolar conditions have been determ ined for two dead ice fields of different age representing a mature and a final stage of collapse in the kotlujokull terminus region south iceland the melting processes considered are backwasting defined as the lateral retreat of near vertical ice walls or steep ice cored slopes and downwasting defined as the thinning of the ice core by melting along the top and bottom surfaces in the mature stage of collapse where there is less than 1 m of sediment cover major faces of ice exposed for rapid melting are ordinarily significant and long lived due to intense precipitation in this fully ice cored terrain the predominating processes are backwasting of exposed ice walls and downwasting by bottom melt each contributing to the annual surface lowering of about 0 5 m or 35 the total annual surface lowering melt rate due to all processes averages 1 4 m in those parts of the fully ice cored dead ice field

quantifying volume loss from ice cliffs on debris covered glaciers using high resolution terrestrial and aerial photogrammetry mass losses originating from supraglacial ice cliffs at the lower tongues of debris covered glaciers are a potentially large component of the mass balance but have rarely been quantified in this study we develop a method to estimate ice cliff volume losses based on high resolution topographic data derived from terrestrial and aerial photogrammetry we apply our method to six cliffs monitored in may and october 2013 and 2014 using four different topographic datasets collected over the debris covered lirung glacier of the nepalese himalayas during the monsoon the cliff mean backwasting rate was relatively consistent in 2013 3 8 0 3 cm w e d 1 and more heterogeneous among cliffs in 2014 3 1 0 7 cm w e d 1 and the geometric variations between cliffs are larger their mean backwasting rate is significantly lower in winter october 2013 may 2014 at 1 0 0 3 cm w e d 1 these results are consistent with estimates of cliff ablation from an energy balance model developed in a previous study the ice cliffs lose mass at rates six times higher than estimates of glacier wide melt under debris which seems to confirm that ice cliffs provide a large contribution to total glacier melt

assessing the continuity of the blue ice climate record at patriot hills horseshoe valley west antarctica we use high resolution ground penetrating radar gpr to assess the continuity of the blue ice area bia horizontal climate record at patriot hills horseshoe valley west antarctica the sequence contains three pronounced changes in deuterium isotopic values at 18 cal ka 12 cal ka and 8 cal ka gpr surveys along the climate sequence reveal continuous conformable dipping isochrones separated by two unconformities in the isochrone layers which correlate with the two older deuterium shifts we interpret these incursions as discontinuities in the sequence rather than direct measures of climate change ice sheet models and internal layer continuity index plots suggest that the unconformities represent periods of erosion occurring as the former ice surface was scoured by katabatic winds in front of mountains at the head of horseshoe valley this study demonstrates the importance of high resolution gpr surveys for investigating both paleo flow dynamics and interpreting bia climate records

thickening of the ice stream catchments feeding the filchner ronne ice shelf antarctica 1 earlier ice sheet mass balance estimates disagree with satellite altimeter measured thickening of the catchment area that feeds the filchner ronne ice shelf antarctica in an effort to reconcile these differences we generated a new flux gate mass balance estimate using improved elevation and velocity data our results show a 39 26 gton yr thickening whereas earlier flux gate results indicated minor thinning our results are consistent with altimeter derived estimates of elevation change this suggests that altimeter observed thickening on the east antarctic plateau may be the result of some combination of a 20th century accumulation increase and a continuing response to the 50 accumulation increase that began in the early holocene