environmental and morphologic controls on wave induced dune response abstract the pacific northwest of the united states exhibits complex spatial patterns of storm induced coastal foredune erosion using oceanographic and morphologic data from three field sites encompassing a range of subaqueous and subaerial coastal profile configurations a relationship is found between morphologic characteristics and dune volume changes during storm events producing high water levels the data suggest that dune erosion increases with increasing backshore beach slope and that under particular oceanographic forcing conditions wave driven processes can grow the lower portion of dunes on low sloping dissipative beaches these observations of environmental and morphologic controls on storm induced dune impacts are further explored using xbeach a state of the art numerical model capable of simulating interactions between hydrodynamics and morphology consistent with the field data model simulations indicate that wave driven dune growth may occur on low sloping beaches in cases where the dynamic still water level still water level plus wave setup is lower than the dune toe however these accretional processes are restricted to events where limited incident wave energy impacts the dune cases with steep backshore beach slopes or dynamic still water levels exceeding the dune toe instead typically result in dune erosion additionally the model simulations suggest that morphologic properties of the shelf nearshore and the dune itself influence storm induced dune volume change therefore morphologic features far from the dune face including shelf geometries shaped in part by the regional historical sediment budget may have important implications on the susceptibility of coastal foredunes systems to storm impacts

extensive liquid meltwater storage in firn within the greenland ice sheet surface melt water from the greenland ice sheet can become trapped in firn delaying its journey to the sea radar and ice core observations provide direct evidence of a perennial aquifer in the firn layer in southern greenland that represents a potentially significant contribution to the greenland mass budget

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

accumulation over the greenland ice sheet from historical and recent records water accumulation defined as precipitation minus evaporation was estimated over all of greenland as part of a program to understand changes in ice sheet mass and elevation over 360 historical and recent point accumulation estimates on the greenland ice sheet were evaluated and 276 estimates that were judged to be high quality were used to develop the accumulation map the data set includes 99 points developed as part of four investigations of the past 5 15 years these are judged to have the greatest accuracy using kriging the average accumulation over greenland is estimated to be 30 g cm 2 yr 1 for the interior part of the ice sheet above 1800 m elevation where most of the data were acquired the average accumulation is also estimated to be 30 g cm 2 yr 1 there are still many areas on the ice sheet including northwest southeast and southern greenland where accumulation is highly uncertain exceeding the mean ice sheet uncertainty at a point of 20 25 in these regions further sampling will be required to reduce uncertainty in both regional and ice sheet wide accumulation

punctuated progradation of the seven mile beach holocene barrier system southeastern tasmania abstract prograded barriers are depositional coastal landforms which preserve past shoreline locations and have been studied in order to understand the fundamental drivers of barrier formation this paper reconstructs the holocene history of the seven mile beach prograded barrier in tasmania australia using optically stimulated luminescence osl dating ground penetrating radar gpr light detection and ranging lidar elevation models and sedimentological analyses shoreline progradation of the barrier commenced around 7300 years ago and continued to near present despite a 3000 pause in deposition between 6700 and 3600 years ago indicative of substantial changes in sediment availability gpr imaged subsurface structures contain a record of seaward dipping reflectors preserved as sediment supplied beaches and dunes leading to shoreline progradation in the past 500 years a large transgressive dune has formed built from reworked barrier sands and now dominates the eastern portion of the barrier implying that shoreline progradation has ceased this study reaffirms the notion that relict foredune ridges are strongly aligned with modal wave refraction patterns in planform and emphasises the importance of sediment delivery as a key driver of shoreline progradation through beachface and dune accretion the substantial pause in shoreline progradation on this barrier system as observed on others around the world requires further explanation although changes in sediment delivery have been inferred it may also be appropriate to reopen the debate on holocene sea level change in tasmania

holocene shoreline progradation and coastal evolution at guichen and rivoli bays southern australia prograded barrier systems record shoreline behaviour and palaeoenvironmental information the guichen bay holocene embayment fill succession in south australia has been subject to several prominent

barrier island resilience assessment applying the ecological principles to geomorphological data abstract applying the ecological resilience principles to barrier island geomorphological evolution requires approaches that perceive and interpret resilience far from predefined barrier characteristics and static views accepting that barrier islands like all natural systems are dynamic and adaptively changing in response to external disturbances is fundamental to the formulated approach to this aim geomorphological units and dimensions were used to describe barrier island stability landscape as an actively shifting topography reshaping in response to exogenous events and in relation to intrinsic properties the structure of the subaerial barrier was characterised using the environmental units of beach dune and marsh or bdm where different combinations of bdm structure define distinct barrier stable states under a simplified framework that is applicable over a wide range of barrier structures the methodology is based on reconstructing resilience trajectories of barrier islands through identifying the distinct bdm states and related shifts thresholds crossed and assessing resilience dimensions latitude resistance and precariousness defined as barrier width and height and proximity to mainland respectively that jointly define the shape of the stability domain the approach was applied to the ria formosa barrier island system s portugal using multi decadal geomorphological data and gradually decreasing spatial discretisation passing from individual barrier transects to sectors and to entire barriers the joint evolution of two inland migrating barriers cabanas island and cacela peninsula was used as an exemplar of adaptive capacity in barrier geomorphic change and therefore of resilient response to external pressures resilience pathways showed that the ria formosa barriers have been resilient over the studied timeframe with a tendency for maintaining or increasing bdm structural complexity in general the stability domain tends to shift from low latitude and high resistance forms narrow deep basins of attraction in the west part of the barrier chain to higher latitudes and lower resistance ones wide shallow basins towards the east precariousness peaks near the edges of the system low lagoon width and minimises towards the central part most detached barriers scaling issues regarding smoothing of longshore variability and potential consequences on masking thresholds and critical dimensions are highlighted and discussed along with the key role of the meaning of specified resilience of what in the assessment the methodology is a novel approach easily transferable to different systems and spatiotemporal scales of analysis representing a step forward in interpreting and assessing barrier island resilience

formulating an inverse problem to infer the accumulation rate pattern from deep internal layering in an ice sheet using a monte carlo approach using a monte carlo mc method we determine the accumulation rate profile along a flowband the influx of ice into the upstream end of the flowband and the age of an internal layer the data comprise the depth profile of the internal layer a few velocity measurements at the surface and the average accumulation at one location the data in our example were collected at taylor mouth a flank site off taylor dome antarctica we present three alternative formulations of this inverse problem depending on the formulation used this particular inverse problem can have up to four solutions each corresponding to a different spatial accumulation rate pattern this study demonstrates the ability of a mc method to find several solutions to this inverse problem and how to use a metropolis algorithm to determine the probability distribution of each of these different solutions the only disadvantage of the mc method is that it is computationally more expensive than other inverse methods such as the gradient method

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

integrating millennial and interdecadal shoreline changes morpho sedimentary investigation of two prograded barriers in southeastern australia abstract prograded barriers are distinctive coastal landforms preserving the position of past shorelines as low relief shore parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand prograded barriers have been valued as coastal archives which contain palaeoenvironmental information however integrating the millennial timescale geological history of barriers with observed inter decadal modern beach processes has proved difficult technologies such as airborne lidar ground penetrating radar gpr and optically stimulated luminescence dating osl were utilised at boydtown and wonboyn in southeastern australia and combined with previously reported radiocarbon dates and offshore seismic and sedimentological data to reconstruct the morpho sedimentary history of prograded barrier systems these technologies enabled reconstruction of geological timescale processes integrated with an inter decadal model of ridge formation explaining the gpr imaged subsurface character of the barriers both the boydtown and wonboyn barriers began prograding 7500 8000 years ago when sea level attained at or near present height along this coastline and continued prograding until the present day with an initially slower rate of shoreline advancement sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at wonboyn the towamba river seems to have delivered sediment to twofold bay during flood events after transitioning to a mature estuarine system sometime after 4000 cal yr bp some of this material appears to have been reworked onto the boydtown barrier increasing the rate of progradation in the seaward 50 of the barrier deposited over the past 1500 years the gpr imaged beachfaces are shown to have similar geometry to beach profiles following recent storm events and a model of ridge formation involving cut and fill of the beachface and dune building in the backshore explains the character of the preserved beachface record and the morphology of the ridges this model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill dune building processes and inherited sediment budget conditions

seismic signals in coastal dune systems abstract coastal dune ridge systems throughout the world form initially in response to phases of abundant sand supply and yet researchers rarely consider the importance of seismic related activity to dune formation or destruction new zealand examples of seismic related coastal dune formation and their occasional remobilisation are discussed pulses of sand sized sediment produced by large earthquakes and transported to the coast by geomorphic processes can generate new dune ridges tsunami inundation can modify existing dunes producing features such as relict dune pedestals landward sand sheets hummocky topography and parabolic dunes the case is put forward for the need to consider evidence for catastrophic events in coastal dune systems particularly when working in tectonically active areas of the world recognition of some of the effects of seismic related processes on coastal dunes however does not mean that these are easily identified in the field or even present in the existing landscape it does however mean that they should not be ignored

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

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

retrieving a common accumulation record from greenland ice cores for the past 1800 years 1 in the accumulation zone of the greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations on an annual basis the accumulation rate in different greenland ice cores is highly variable and the degree of correlation between accumulation series from different ice cores is low however when using multiyear averages of the different accumulation records the correlation increases significantly a statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual using this model a common greenland accumulation record for the past 1800 years has been extracted the record shows significant 11 9 years periodicity a sharp transition to very dry conditions is found just before a d 1200 and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the norse population in greenland and may have contributed to their extinction accumulation rates gradually decrease from a distinct maximum in a d 1394 to very dry conditions in the late 17th century and thus reflect the little ice age

relative sea level records preserved in holocene beach ridge strandplains an example from tropical northeastern australia abstract northeastern queensland is a far field site from ice caps formed during the last glacial however the region has experienced glacio hydroisostatically driven coastal elevation change during the holocene that generated a distinctive relative sea level record we tested whether this subtle vertical movement of the coast is recorded in the morphology and stratigraphy of the beach ridge strandplain at cowley beach which comprises a series of 36 prominent and several subdued or truncated beach ridges previous studies have shown that the strandplain records the long term progradation of the coast with the ridges comprising coarse medium sand that was deposited during both fairweather foreshore and berm facies and tropical cyclone events erosional unconformities storm surge deposits over the past approximately 7 ka we utilised a fine scale digital elevation model of the strandplain to examine beach ridge morphology and to compare the elevation pattern with published holocene sea level data for the region the overall elevation pattern of the strandplain surface is consistent with the regional sea level history that includes a highstand at around 6 ka bp generated by isostatic uplift and the elevation of the berm facies matches well robust coral sea level indicator data we also modelled the strandplain topographic patterns that would result under stable and continually rising holocene sea levels the frequencies of elevation classes across the strandplain are normally distributed when the strandplain is deposited during a period of stable sea level and negatively skewed with a continually rising sea level consistent with the expected patterns the results indicate the sensitivity of the elevation of the top of the berm facies preserved in beach ridges to subtle changes in sea level tens of cm over a thousand years our results further underline the utility of beach ridge strandplains a globally distributed coastal landform for building relatively detailed regional records of sea level during the holocene at sites currently lacking this information

improved method to determine radio echo sounding reflector depths from ice core profiles of permittivity and conductivity we present a technique that modifies and extends down hole target methods to provide absolute measures of uncertainty in radar reflector depth of origin we use ice core profiles to model wave propagation and reflection and then cross correlate the model results with radio echo sounding res data to identify the depth of reflector events stacked traces recorded with res near the epica drill site in dronning maud land antarctica provide reference radargrams and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams cross correlations between synthetic and res radargrams identify differences in propagation wave speed they are attributed to uncertainties in pure ice permittivity and are used for calibration removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to res features we find that i density measurements with attenuation or dielectric profiling are too noisy below the firn ice transition to allow clear identification of reflections ii single conductivity peaks less than 0 5 m wide cause the majority of prominent reflections beyond a travel time of about 10 s 900 m depth and iii some closely spaced conductivity peaks within a range of 1 2m cannot be resolved within the res or synthetic data our results provide a depth accuracy to allow synchronization of age depth profiles of ice cores by res modeling of isochronous internal structures and determination of wave speed and of pure ice properties the technique successfully operates with dielectric profiling and electrical conductivity measurements suggesting that it can be applied at other ice cores and drill sites

internal architecture of mixed sand and gravel beach ridges miquelon langlade barrier nw atlantic abstract the internal architecture of a beach ridge system can provide clues into the processes involved in its formation detailed investigation of the mixed sand and gravel beach ridge plain on the miquelon langlade barrier northwest atlantic ocean south of newfoundland provides a better understanding of such sedimentary systems in terms of internal architecture depositional processes and driving mechanisms investigations of this regressive paraglacial barrier included the topographic rtk gps and ground penetrating radar 100 to 500 mhz antennae data collection orthophotographs and optically stimulated luminescence osl dating the miquelon langlade beach ridge plain is composed of two opposing progradational systems reflecting contrasting eastward and westward hydrodynamic exposures four ridge sets each with concave planform shapes define the 500 1400 m wide eastward prograding plain along the sheltered eastern coast two ridge sets with linear and fan shaped planforms define the 200 500 m wide south westward prograding plain along the energetic western coast beach ridge units overlay a basal sedimentary unit that disrupted incoming wave energy and altered the planform morphology of the prograding plain the internal architecture pattern of individual beach ridges are characterized by sigmoidal configurations with seaward dipping beds 2 3 4 7 true dip angles it is proposed that these wave built facies are deposited as beach berms likely by fair weather waves the elevations of these facies are determined by the sea level elevation and the swash height of constructive waves during their formation beach ridges are overlain by either peat resulting from the flooding of topographically low lying areas or by aeolian sand deposits of varying heights and morphologies relict foredunes despite the differences in wave exposure along each coast the sedimentary composition and internal architecture of the two progradational systems are broadly similar bed dip angles of the individual beach ridges differ by only 1 2 steeper along the exposed westward facing coast overall the miquelon langlade beach ridge plain highlights the primary influences of wave exposure inherited topography and proximal sediment sources from erosion of moraines on coastal progradational patterns

vegetation control allows autocyclic formation of multiple dunes on prograding coasts we investigate the formation of multiple dunes using a 15 yr record of dune growth from long beach peninsula washington state usa and a recently published coastal dune model modified to include a feedback between vegetation growth and local dune slope in the presence of shoreline progradation we find that multiple dune ridge formation can be autocyclic arising purely from internal dune dynamics rather than requiring variations in external conditions our results suggest that the ratio of the shoreline progradation rate and the lateral dune growth rate is critical in determining the height number and form of multiple dunes allowing the development of testable predictions our findings are consistent with observations and imply that caution is required when using dune ridges as proxies for past changes in climate sea level land use and tectonic activity because the relationship between external events and the formation of multiple dunes may not be one to one as previously thought

could mars be dark and altered there is a long known dichotomy in the martian albedo with an associated but mostly assumed mineralogical split as well the bright red regions are inferred to be weathered oxidized dust and the dark grey regions unaltered volcanic material a number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re examination of the spectra in light of potential alteration minerals i present an alternate interpretation of the reflectance spectral characteristics of some dark regions on mars that includes dark layer silicates if their presence is confirmed on mars this will have implications for sequestration of current and past volatile inventories clues to the extent and type of geochemical weathering and potential zones where bacterial life forms may have emerged

coastal dunes in westland new zealand provide a record of paleoseismic activity on the alpine fault regional episodes of coastal progradation and dune formation in south westland new zealand have quickly followed all known alpine fault earthquakes since a d 1200 this reflects rapid transport of large postseismic sediment pulses from mountain catchments to the coast and accumulation of this material as a dune ridge this study provides the first demonstration of this link for multiple events over a region the dune sequences also provide evidence of another previously unrecognized regional aggradation event which may be earthquake related and which occurred just 50 yr after a large alpine fault earthquake coastal dunes have great potential for paleoseismic application because the spatial separation of earthquake induced sediment pulses on a prograding coast allows identification of events closely spaced in time coastal dune systems have the potential to improve paleoseismic understanding over the holocene for many plate boundary faults near coastal areas

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

coarse sand beach ridges at cowley beach north eastern australia their formative processes and potential as records of tropical cyclone history storm surges generated by tropical cyclones have been considered a primary process for building coarse sand beach ridges along the north eastern queensland coast australia this interpretation has led to the development of palaeotempestology based on the beach ridges to better identify the sedimentary processes responsible for these ridges a high resolution chronostratigraphic analysis of a series of ridges was carried out at cowley beach queensland a meso tidal beach system with a 3 m tide range optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years the ridge crests sit 3 5 to 5 1 m above australian height datum ca mean sea level a ground penetrating radar profile shows two distinct radar facies both of which are dissected by truncation surfaces hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at 2 5 m australian height datum equivalent to the fair weather swash limit during high tide the lower facies comprises a sequence of seaward dipping reflections beach progradation thus occurs via fair weather wave accretion of sand with erosion by storm waves resulting in a sporadic sedimentary record the ridge deposits above the fair weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide the ridges may also include an aeolian component as cyclonic winds can transport beach sand inland especially during low tide and some layers above 2 5 m australian height datum are finer than aeolian ripples found on the backshore coarse sand ridges at cowley beach are thus products of fair weather swash and cyclone inundation modulated by tides knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges this article is protected by copyright all rights reserved

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar

annual accumulation for greenland updated using ice core data developed during 2000 2006 and analysis of daily coastal meteorological data an updated accumulation map for greenland is presented on the basis of 39 new ice core estimates of accumulation 256 ice sheet estimates from ice cores and snow pits used in previous maps and reanalysis of time series data from 20 coastal weather stations the period 1950 2000 is better represented by the data than are earlier periods ice sheetwide accumulation was estimated based on kriging the average accumulation 95 confidence interval or 2 times standard error over the greenland ice sheet is 30 0 2 4 g cm 2 a 1 with the average accumulation above 2000 m elevation being essentially the same 29 9 2 2 g cm 2 a 1 at higher elevations the new accumulation map maintains the main features shown in previous maps however there are five coastal areas with obvious differences southwest northwest and eastern regions where the accumulation values are 20 50 lower than previously estimated and southeast and northeast regions where the accumulation values are 20 50 higher than previously estimated these differences are almost entirely due to new coastal data the much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long term mass balance in both catchments is closer to steady state than previously estimated however uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland a significant and sustained precipitation measurement program will be needed to resolve this uncertainty copyright 2009 by the american geophysical union