validation of the ice 3g model of wurm wisconsin deglaciation using a global data base of relative sea level histories a global data base consisting of radiocarbon controlled relative sea level rsl histories from 392 different geographic locations has been compiled for use in analyses of the glacial isostatic adjustment process these data may be employed to constrain both the spatiotemporal characteristics of the last deglaciation event of the current ice age and the rheological structure of the planetary interior in a previous paper in this series tushingham and peltier 1991 we employed the rsl data in this set from sites that were once ice covered to refine the apriori model of deglaciation that had been delivered by past research in the area of pleistocene geomorphology peltier and andrews 1976 wu and peltier 1983 to produce a new global model of this event that we have called ice 3g in the present paper following a description of the full data base and of the methods used to compile it we employ data from the sites that were not ice covered 200 time series to verify the plausibility of this refined model of deglaciation and to test the extent to which the totality of the observations constrain the radial viscoelastic structure of the planet the analysis of solutions to the forward problem presented here reinforce previous inferences of a preference for a thick lithosphere by rsl data from sites along the u s east coast and a preference by data from most near field sites for an increase in viscosity across the 670 km discontinuity in the mantle by a factor of approximately 2 when the viscosity of the upper mantle is fixed to the value of 1021 pa s originally deduced by haskel 1935 on the basis of his analysis of the data from fennoscandia

greenland glacial history and local geodynamic consequences summary space time reconstructions of the continental ice sheets that existed at last glacial maximum lgm have previously been produced using two entirely independent methodologies one based upon the use of theoretical models of ice sheet accumulation and flow and one based upon the geophysical inversion of relative sea level rsl histories from previously ice covered regions the analyses described in this paper demonstrate the significant advantages that derive from the simultaneous application of both methods to the particular case of greenland we thereby show that the ice 4g reconstruction of the glaciation history of this region from lgm to present which was based upon the geophysical inversion of rsl data alone was reasonably accurate in the peripheral regions where rsl data were available but inaccurate in the interior of the ice sheet which was unconstrained by such information we test the new model of greenland glacial history determined by the simultaneous application of the constraints that derive from ice sheet modelling and the geophysical inversion of rsl data by employing recently published geodetic inferences of mass balance over the entire interior region of the ice sheet and of gps measurements of vertical crustal motion these observations which were not employed to constrain the ice sheet reconstruction provide significant support for the new glacial history for greenland that our analyses have led us to infer

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

ice age ice sheet rheology constraints from the last glacial maximum form of the laurentide ice sheet state ot the art thermomechanical models of the modern greenland ice and the ancient laurenticle ice sheet that covered canada at the last glacial maximum lgm are not able to explain simultaneously the observed forms of these cryospheric structures when the same anisotropy enhanced version of the conventional glen flow law is employed to describe their rheology the lgm laurenticle ice sheet predicted to develop in response to orbital climate forcing is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface geomorphological and solid earth geophysical constraints we show that if the glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress strain rate relation then the aspect ratios of both the modern greenland ice sheet and the laurenticle ice sheet that existed at the lgm are simultaneously explained with little or no retuning of the flow law

reasons for the low sedimentation and slow progradation in the pearl river delta southern china during the middle holocene abstract holocene sea level rise monsoonal discharge and human activity have been the main drivers for the evolutionary history of asian deltas in theory when sea level ceased to rise in around 7000 cal a bp deltas should have started to prograde seawards however previous studies revealed that the progradation of modern deltas was initially very slow and more importantly sediment accumulation within central deltaic basins was exceptionally low between 7000 and 4000 cal a bp in order to investigate the main reasons for such slow progradation and low sedimentation during the middle holocene this study reconstructed the sedimentary history of the head area of the pearl river delta the results show marine transgression from 9500 to 7500 cal a bp followed by marine regression starting from 7500 to 4000 cal a bp in response to sea level change during the latter period sedimentation was concentrated in the head area the amount of sediment entering the central basin was significantly reduced this limited amount of sediment was spread thinly across the wide deltaic basin a portion of it could have been transported out into the south china sea by the strong tidal currents resulting in an exceptionally low sedimentation in the central basin however in locations adjacent to former present islands locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal a bp by about 4000 cal a bp the deltaic shoreline advanced into the central basin this period saw an increase of human activity that caused soil erosion and sediment supply leading to a marked increase in sedimentation rate active land reclamations also helped the acceleration of shoreline advance this sedimentary evolution model in the pearl river delta mirrors those of other deltas in the monsoonal asia

extraction of a lithospheric cooling signal from oceanwide geoid data abstract the geoid an equipotential surface of earth s gravity field reflects the distribution of mass within the planet and hence a variety of geodynamic processes because these data are dominated by sublithospheric processes notably mantle convection they have not played a major role in the ongoing debate concerning models of the thermal evolution of oceanic lithosphere application of spatial filtering to the age derivative of the geoid however extracts an age dependent signal which reflects lithospheric thermal evolution the data are much better fit by a thin about 100 km thick thermal plate than by a cooling halfspace and so provide a valuable constraint complementary to and consistent with the variations in oceanic depth and heat flow with age

modelled ice sheet margins of three greenland ice sheet models compared with a geological record from ice marginal deposits in central west greenland ice sheet modelling is an essential tool for estimating the effect of climate change on the greenland ice sheet the large spatial and long term temporal scale ofice sheet models limits the amount of data which can be used to test model results the geological record is useful because it provides test material on the timescales typical for the memory of ice sheets millennia this paper compares modelled ice marginal positions with a geological scenario of ice marginpositions since the last glacial maximum to the present in west greenland morphological evidence of ice margin positions is provided by moraines moraine systems are dated by 14c dated marine shells and terrestrial peat we compared three greenland ice sheet models there are distinct differences inmodelled ice margin positions between the models and between model results and the geological record disagreement between models and the geologicalrecord in the near coastal area are explained by the insufficient treatment of marginal processes in a tidewater environment a smaller than present ice sheetaround the warm period in the holocene holocene climatic optimum only pops up when an unsmooth forcing is used this underlines the importance ofshort term variations in climatic variables in determining ice margin positions in the past but also in the future

surficial glaciology of jakobshavns isbrae west greenland part i surface morphology jakobshavns isbrae is a large fast moving ice stream outlet glacier in west greenland which ends at a floating calving front it drains about 6 5 of the area of the greenland ice sheet studies of its surface morphology are described in this paper the surface is relatively steep 0 01 0 03 and the thickness is large up to 2600 m along the center line clarke and echelmeyer 1989 indicating very high driving stresses 200 300 kpa the ice stream is about 6 km wide and 85 90 km long all of which is in an area of surface melting the base of the ice stream and of much of the drainage area is below sea level marginal crevasse zones have a width on the order of the width of the ice stream itself unique surficial features are ice blisters and lakes the latter have a sequence of ogive like features on their floating ice cover which can be used to determine velocity there is a pinning point near the terminus which may act as a stabilizing influence possibly playing a role in halting at least temporarily a recent retreat of the terminus ice thickness estimates at the terminus lead to a flux which is less than previously assumed by others e g bindschadler 1984 pelto and others 1989 when estimating jakobshavns isbrae s drainage basin to be nearly in balance the driving stresses on jakobshavns isbrae are an order of magnitude higher than those of the ice streams of west antarctica its crevasse patterns are much less localized its relatively unconfined terminus is more comparable to that of relatively unbuttressed ice streams such as pine island and thwaites glaciers than it is to other west antarctic ice streams which terminate in large confined ice shelves

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

basal temperature conditions of the greenland ice sheet during the glacial cycles a high resolution three dimensional thermomechanical ice sheet model which includes isostasy the possibility of ice sheet expansion on the continentalshelf and refined climatic parameterisations was used to investigate the basal thermal regime of the greenland ice sheet the thermodynamic calculations takeinto account the usual terms of heat flow within the ice a thermal active bedrock layer in transient situations and all of the effects associated with changes inice thickness and flow pattern basal temperature conditions are documented with respect to glacial interglacial shifts in climatic boundary conditions both insteady state as during simulations over the last two glacial cycles using the grip d180 record it is found that the basal temperature field shows a largesensitivity in steady state experiments but that during a glacial cycle basal temperature variations are strongly damped in particular in central areas acomparison has been made with measured data from deep ice cores and implications are discussed

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

experimental study of cone penetration in silica sand using digital image correlation the problem of cone penetration particularly deep penetration remains one of the most challenging in geotechnical engineering it involves large displacements rotations and deformation of soil elements in the path of the cone as well as complex response of the soil including crushing and the development of large mean stresses to the displacements imposed by the penetration process as a result rigorous theoretical solutions are not available for this problem and experimental simulations of penetration provide insights that would not otherwise be available this paper presents the results of a series of cone penetration tests performed in a half circular chamber in sand samples prepared with three silica sands with different crushability cone resistance was measured and digital images of the cone penetrating into the sand samples were acquired simultaneously during the entire penetration process the digital image correlation dic technique was then used to process these images to obtain the soil

large deformation finite element simulation of displacement pile installation experiments in sand abstractdisplacement piles are driven to support a wide range of structures predicting their axial limiting capacities and load displacement behavior is critical to many such engineering applicati

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

unblocking of the nares strait by greenland and ellesmere ice sheet retreat 10 000 years ago the extent of glaciation at the northern margin of the canadian greenland high latitude arctic region over the past 30 000 years is uncertain geological arguments have been made for greenland and ellesmere island ice sheets that coalesced to block the nares strait1 and for restricted ice sheets on the two islands2 leaving the strait open as it is today3 distinguishing between these two possibilities would provide significant constraints on present understanding of the past circulation between the arctic and atlantic oceans4 5 on estimates of past ice volume6 and on the response of the greenland ice sheet to climate change7 radiocarbon analyses provide dates for the deglaciation of the islands coasts but do not yield information on whether ice filled the strait here we present measurements of cosmogenic 36cl that has accumulated in situ in erratics and glacially polished bedrock on islands within the nares strait these data allow us to determine the time for which the rocks have been recently exposed to the atmosphere and thus the age of the final deglaciation of the strait we show that greenland and ellesmere ice sheets retreated from the nares strait about 10 000 years ago the strait was filled with ice during the last glaciation blocking this connection between the arctic and atlantic oceans and supporting the model of extensive and long lasting ice on land and sea in this region8 9 10 11

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

effects of particle breakage and stress reversal on the behaviour of sand around displacement piles the stresses acting in the soil mass adjacent to the tips and shafts of displacement piles during installation and loading in medium dense sand have been simulated in triaxial stress path tests on

numerical investigation of bearing capacity due to spudcan penetration in sand overlying clay numerical studies were carried out to investigate the bearing capacity of spudcan foundations of offshore jack up rigs in sand overlying normally consolidated clay by using the coupled eulerian lag

methodology for use of isotopic climate forcings in ice sheet models in ice sheet models an internally consistent calculation of climatic temperature forcing from ice core isotopic records requires that corrections be made for an ice core site s elevation changes such corrections can be important for two reasons first elevation change at an ice divide can be large compared to elevation change at the migrating ice margin resulting in erroneous estimates of marginal melt rate second the of precipitation at an ice divide responds less to regional climatic temperature changes than to local temperature changes of the same magnitude that are caused by elevation changes significant elevation change corrections may also be necessary for inferring the relationships used to calculate climatic temperature from a simple methodology incorporating both of these elevational effects is presented here further i recommend that the to temperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and time series rather than from spatial correlations and justify this recommendation based on current understanding of the atmospheric isotopic distillation system

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

time step limits for stable solutions of the ice sheet equation various spatial discretizations for the ice sheet are compared for accuracy against analytical solutions in one and two dimensions the computational efficiency of various iterated and non iterated marching schemes is compared the stability properties of different marching schemes with and without iterations on the non linear equations are compared newton raphson techniques permit the largest time steps a new technique which is based on the fact that the dynamics of unstable iterated maps contain information about where the unstable root lies is shown to improve substantially the performance of picard iteration at a negligible computational cost

mantle viscosity from the simultaneous inversion of multiple data sets pertaining to postglacial rebound we employ the formalism of bayesian inference to invert three distinct data sets related to the phenomenon of glacial isostatic adjustment these data consist respectively of the wavenumber spectrum of relaxation times for fennoscandian rebound inferred by mcconnell 1968 the characteristic relaxation times for a large collection of distinct 14c dated relative sea level curves from both canada and fennoscandia and two data related to the rotational response of the earth to the glaciation deglaciation cycle of the late pleistocene ice age our analyses show that the spherically symmetric viscosity structure objectively inferred on the basis of these data from the once glaciated regions of the northern hemisphere allows a fully satisfactory reconciliation of both us east coast relative sea level observations as well as providing a close fit to the requirements of aspherical geoid anomalies

finite element analysis of progressive failure of carsington embankment progressive failure occurs when brittle soils are loaded non uniformly the average shear stress at collapse is less than peak strength the effect cannot be examined by conventional limit equilibrium stability analysis the carsington embankment slipped in 1984 just before it reached full height the slide was 30 m deep and 500 m long and instrumentation had been installed and read up to the moment of collapse the strengths of the soils involved were carefully established as was the exact geometry of the slip limit equilibrium analysis showed that at collapse the average shear stress mobilized was less than peak strength with a safety factor based on peak strength of 1 2 since the soils involved were brittle progressive failure was a probable cause of the discrepancy finite element analyses were performed in which strain softening soil properties were assumed some of these analyses are reported here the pre failure displacements the collapse height and collapse mechanism were recovered by t

assessing the punch through hazard of a spudcan on sand overlying clay a complete analytical method to describe the full load penetration resistance profile of a mobile jack up spudcan footing penetrating a sand over clay stratigraphy is described it is based on both large deformation finite element analyses and geotechnical centrifuge experiments the coupled eulerian lagrangian cel approach is used to accommodate the large deformations of a spudcan footing penetrating sand overlying clay modified mohr coulomb and tresca models describe the sand and clay behaviour with modifications accounting for the effects of strain softening on the response of the soil the cel results are shown to match centrifuge tests well allowing the numerical study to be extended parametrically and with confidence to cover the range of layer geometries sand relative densities and footing shapes that are of practical interest to offshore jack ups the results are used to a assess the performance of an existing model to predict the peak resistance in the sand layer extending its range of

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

a high resolution model of the 100 ka ice age cycle significant improvements to the representation of climate forcing and mass balance response in a coupled two dimensional global energy balance climate model ebm and vertically integrated ice sheet model ism have led to the prediction of an ice volume chronology for the most recent ice age cycle of the northern hemisphere that is close to that inferred from the geological record most significant is that full glacial termination is delivered by the model without the need for new physical ingredients in addition a relatively close match is achieved between the last glacial maximum lgm model ice topography and that of the recently described ice 4g reconstruction these results suggest that large scale climate system reorganization is not required to explain the main variations of the north american na ice sheets over the last glacial cycle lack of sea ice and marine ice dynamics in the model leaves the situation over the eurasian ea sector much more uncertain the incorporation of a gravitationally self consistent description of the glacial isostatic adjustment process demonstrates that the na and ea bedrock responses can be adequately represented by simpler damped relaxation models with characteristic time scales of 3 5ka and 5 ka respectively these relaxation times agree with those independently inferred on the basis of postglacial relative sea level histories

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

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

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet