subgrain boundaries in antarctic ice quantified by x ray laue diffraction ice in polar ice sheets undergoes deformation during its flow towards the coast deformation and recrystallization microstructures such as subgrain boundaries can be observed and recorded using high resolution light microscopy of sublimation edged sample surfaces microstructure mapping subgrain boundaries observed by microstructure mapping reveal characteristic shapes and arrangements as these arrangements are related to the basal plane orientation full crystallographic orientation measurements are needed for further characterization and interpretation of the subgrain boundary types x ray laue diffraction measurements validate the sensitivity of different boundary types with sublimation used by microstructure mapping for the classification x ray laue diffraction provides misorientation values of all four crystal axes line scans across a subgrain boundary pre located by microstructure mapping can determine the rotation axis and angle together with the orientation of the subgrain boundary this yields information on the dislocation types tilt and twist boundaries composed of dislocations lying in the basal plane and tilt boundaries composed of nonbasal dislocations were found a statistical analysis shows that nonbasal dislocations play a significant role in the formation of all subgrain boundaries

microstructure and fabric development in ice lessons learned from in situ experiments and implications for understanding rock evolution abstract in this contribution we present a review of the evolution of microstructures and fabric in ice based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz rich rocks advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain boundary migration during the steady state flow of ice to support this review we describe deformation in polycrystalline standard water ice and natural ice samples summarize other experiments involving bulk samples and use in situ plane strain deformation experiments to illustrate the link between microstructure and fabric evolution rheological response and dominant processes most terrestrial ice masses deform at low shear stresses by grain size insensitive creep with a stress exponent n 3 however from experimental observations it is shown that the distribution of plastic activity producing the microstructure and fabric is initially dominated by grain boundary migration during hardening primary creep followed by dynamic recrystallization during transient creep secondary creep involving new grain nucleation with further cycles of grain growth and nucleation resulting in near steady state creep tertiary creep the microstructural transitions and inferred mechanism changes are a function of local and bulk variations in strain energy i e dislocation densities with surface grain boundary energy being secondary except in the case of static annealing as there is a clear correspondence between the rheology of ice and the high temperature deformation dislocation creep regime of polycrystalline quartz we suggest that lessons learnt from ice deformation can be used to interpret polycrystalline quartz deformation different to quartz ice allows experimental investigations at close to natural strain rate and through in situ experiments offers the opportunity to study the dynamic link between microstructural development rheology and the identification of the dominant processes

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

direct observations of seasonal exchange through the bab el mandab strait the exchange flow between the red sea and the gulf of aden indian ocean through the bab el mandab strait was measured continuously for 10 months june 1995 march 1996 adcp and temperature salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the gulf of aden and the high salinity outflow layer from the red sea the timing structure and evolution of the summer season mid depth intrusion of cold low salinity water into the red sea from the gulf of aden is measured for the complete intrusion cycle of 1995 we unexpectedly find the deep outflow still strong in june 1995 with speeds of 0 6 m sec and transport of 0 4 sv 1 sv 106 m sec from july to mid september the deep outflow persists but is attenuated to speeds of 0 2 m sec and transport of 0 05 sv the dominant summer feature the cold low salinity intermediate layer intrusion persists for 3 months occupies 70 of the water column in the strait and carries approximately 1 7 1012 m of cold nutrient rich water into the red sea the winter regime begins in mid september is fully developed by early november and continues to the end of our first observation interval in march 1996 speeds in the lower layer are 0 8 1 0 m sec and 0 4 0 6 m sec in the upper layer at maximum exchange in mid february outflow transport reaches 0 7 sv ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along channel wind forcing and perhaps to coastally trapped waves

relation between neighbouring grains in the upper part of the northgrip ice core implications for rotation recrystallization abstract we propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the northgrip ice core this method shows unexpected correlations between neighbours in the so called normal grain growth regime questioning the classical view on the onset of rotation recrystallization in ice sheets moreover the fractionation rate associated to the rotation recrystallization appears constant through time finally grains with low angle boundaries do not present a special distribution pattern of their c axes this suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain

impeding effect of air bubbles on normal grain growth of ice abstract normal grain growth experiments were performed using polycrystalline ice samples with and without air bubbles the bubble free polycrystalline ice was prepared by a special sample preparation technique that employed a phase change method the ice samples with air bubbles were prepared from a mixture of ice powder and pure distilled water using conventional methods the temperature dependencies of the rate of grain growth were measured in artificial polycrystalline ice samples with and without air bubbles the average grain growth exponent n of the ice with bubbles was much greater than the theoretical value of 2 while that of bubble free ice was close to 2 the activation energy for the grain boundary migration of bubble free ice was 110 120 kj mol 1 whereas that of the ice with bubbles was between 40 and 70 kj mol 1 the observation of the microscopic images of samples and analyses of the evolution of bubble size distribution and location during grain growth revealed that small air bubbles are caught and swept by moving grain boundaries and a coalescence of bubbles occurs this indicates that the slow grain boundary migration of ice with bubbles is controlled by the migration of air bubbles dragged by grain boundary migration

numerical study of the water movement driven by brine rejection from nearshore arctic ice a numerical model of brine induced circulation is used to study circulation in the lagoons and shelf waters of the beaufort sea the model solves the equations of motion continuity and salt transport the salt flux is set as a function of the salinity difference between growing sea ice and seawater and the rate of ice growth several experimental runs show that under ice haline circulation is controlled by salt flux and bottom configuration an idealized model of a shallow arctic lagoon gives currents of 1 cm s 1 for brine induced circulation under landfast ice this agrees very well with observations

evidence of dynamic recrystallization in polar firn 1 microstructural analyses have been performed on polar firn from the european project for ice coring in antarctica drilling site in dronning maud land antarctica the results derived from images of the firn structure in microscopic resolution indicate that dynamic recrystallization is active in firn at all depths and it dominates the evolution of the microstructure when the firn density exceeds a critical value of 730 kg m3 overburden snow load 0 2 mpa at the firn ice transition density 820 kg m3 the microstructure is characterized by many small grains and bulged or irregularly shaped grain boundaries more than half of all grains show subgrain boundaries thus strain induced boundary migration is an essential feature to describe the irregular grain structure in agreement with previous studies significant grain growth has been observed with depth for the largest grains in the samples however our microscopic analysis reveals that the grain growth with depth in fact vanishes if all grains larger than 65 m in diameter are taken into account this result reflects the fact that the growth of the largest grains is counteracted by grain size reduction by shrinking and subdivision of old grains as well as production of new grains consequently previous conclusions that grain growth in polar firn is essentially analogous to normal grain growth in metallic and ceramic sinters and that the stored strain energy is small in comparison with grain boundary energy can no longer be supported additionally our observations show that the incipience of dynamic recrystallization in polar ice sheets is not as sensitive to temperature as supposed so far a discussion of the change of the mean grain size due to the measuring technique is imperative

competition between grain growth and grain size reduction in polar ice static or normal grain growth i e grain boundary migration driven solely by grain boundary energy is considered to be an important process in polar ice many ice core studies report a continual increase in average grain size with depth in the upper hundreds of metres of ice sheets while at deeper levels grain size appears to reach a steady state as a consequence of a balance between grain growth and grain size reduction by dynamic recrystallization the growth factor k in the normal grain growth law is important for any process where grain growth plays a role and it is normally assumed to be a temperature dependent material property here we show using numerical simulations with the program elle that the factor k also incorporates the effect of the microstructure on grain growth for example a change in grain size distribution from normal to log normal in a thin section is found to correspond to an increase in k by a factor of 3 5

a new type of numerical experiment on the spatial and temporal patterns of localization of deformation in a material with a coupling of grain size and rheology abstract the patterns of localization of deformation in recrystallising materials are investigated via a series of two dimensional grain scale numerical simulations these simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes the simulations are able to predict the mechanical microstructural and strain evolution of the polycrystals to moderate strain and allow us to examine the nature of the time dependent feedback between mechanical and microstructural behavior it was found that significant strain localization occurred only when the grain size dependence of the viscosity was non linear and was greatly enhanced by the activity of the grain size modifying processes the intensity and location of the zone of strain localization varied spatially and temporally and displayed two length and time scales with the result that the finite strain state showed a much broader and hence less intense zone of localized deformation than the instantaneous state

multiscale modeling of ice deformation behavior understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change the flow of ice has hitherto received relatively little attention from the structural geological community this paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale and beyond to the scale of polar ice sheets all through these scales various models have been developed to understand describe and predict the processes that operate during deformation of ice with the aim to correctly represent ice rheology and self induced anisotropy most of the modeling tools presented in this paper originate from the material science community and are currently used and further developed for other materials and environments we will show that this community has deeply integrated ice as a very useful model material to develop and validate approaches in conditions of a highly anisotropic behavior this review by no means exhaustive aims at providing an overview of methods at different scales and levels of complexity

a model of crystal size evolution in polar ice masses in the deep ice cores drilled at the grip ngrip and gisp2 sites in greenland and at byrd station and the summit of law dome in antarctica the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth this behaviour has been attributed to the competition between grain boundary migration driven crystal growth and crystal polygonization but the effects of changing crystal dislocation density and non equiaxed crystal shape in this competition are uncertain we study these effects with a simple model it describes how the mean height and width of crystals evolve as they flatten under vertical compression and as crystal growth and polygonization compete the polygonization rate is assumed to be proportional to the mean dislocation density across crystals migration recrystallization which can affect crystal growth via strain induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present is not accounted for when applied to the five ice core sites the model simulates the observed crystal size profiles well down to the bottom of their steady regions although the match for law dome is less satisfactory polygonization rate factors retrieved for the sites range from 10 5 to 10 2 a 1 we conclude that since crystal size and dislocation density evolve in a strongly coupled manner consistent modelling requires multiple differential equations to track both of these variables future ice core analysis should also determine crystal size in all three principal directions

mapping c axis fabrics to study physical processes in ice mapping the spatial distribution of c axis orientations in ice thin sections is not much more difficult than preparing c axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice distributions of angles between c axes of neighboring grains from the byrd station west antarctica ice core suggest that polygonization causes average grain size to stabilize below 400 m depth

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

dynamics of crystal formation in the greenland northgrip ice core the north greenland icecore project northgrip ice core provides palaeoclimatic information back to about 120 kyr bp the size distributions of ice crystals in the upper 880 m of the northgrip ice core which cover a time span of approximately 5300 years have been obtained previously the distributions evolve towards a universal curve indicating a common underlying physical process in the formation of crystals we identify this process as an interplay between fragmentation of the crystals and diffusion of their grain boundaries the process is described by a two parameter differential equation to which we obtain the exact solution the solution is in excellent agreement with the measured distributions

influence of bubbles on grain growth in ice abstract numerical static grain growth simulations of ice with air bubbles as a second phase show a significant drop in grain growth rate compared to bubble free ice the magnitude of this drop in growth rate is dependent on the bubble boundary mobility the volume fraction of air the average bubble size and the bubble size distribution the rate of grain growth decreases at first as the microstructure evolves towards a steady state only then does grain growth follow the expected linear increase of mean grain area with time in experiments this decrease in growth rate could erroneously be interpreted as growth with a deviating growth exponent

sensitivity of red sea circulation to monsoonal variability during the holocene an integrated data and modeling study received 20 october 2009 revised 6 march 2010 accepted 30 june 2010 published 4 november 2010 1 we used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the red sea in response to reduced sea level and modified atmospheric conditions during the holocene with holocene sea level close to the modern level the red sea was sensitive to changes in atmospheric conditions and it only shows a relatively mild response to sea level change changes in the monsoon system influence the exchange flow through the strait of bab el mandab the meridional overturning circulation of the red sea and its hydrography forced by humid conditions the modeled red sea temperature increased by 1 5 c while when arid conditions were imposed the temperature decreased by 2 5 c similar heating and cooling events during the early and late holocene are seen in a sea surface temperature record from the northern red sea derived from the temperature sensitive tex86 molecular biomarker which suggests that humid conditions prevailed during the early holocene and more arid conditions prevailed during the late holocene the gradual decline in red sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength this monsoon trend and the resulting changes in the red sea circulation are supported by the distribution of crenarchaea fossil lipids in red sea sediments from this period monsoon driven changes in the exchange flow through the strait of bab el mandab affected the crenarchaea population structure and therefore their molecular fossil distribution in the sediments of the red sea potentially provides an index for the summer monsoon strength during the holocene

rate controlling processes in the creep of polar ice influence of grain boundary migration associated with recrystallization abstract information on the deformation modes and recrystallization processes in polar ice sheets was obtained thanks to the analysis of the ice structure along two deep ice cores from greenland and antarctica it is shown that the deformation of polar ice at low stresses is produced by intracrystalline slip accommodated by grain boundary migration gbm a deformation model based on an equilibrium between work hardening and recovery processes has been developed the decrease in dislocation density is due to both gbm associated with grain growth and the formation of boundaries by recrystallization the value of the dislocation density along the byrd and grip ice cores obtained thanks to the model is about 1 10 11 m 2 this value is in agreement with data from synchrotron x ray diffraction on samples taken along the core this deformation model can account for the deformation of polar ice at low stresses it is shown that the flow law with a stress exponent lower than 2 can be related to the efficiency of gbm as a recovery process

stratification and mixing in sea straits abstract quantifying the transport through relatively narrow straits connecting basins with differing fluid properties is an important issue in both surface and abyssal flows these flows range from large scale flows in ocean straits connecting the major ocean basins down to small scale regional flows such as in estuaries and lagoons connected to the coastal ocean by relatively narrow straits or channels the exchange rate through these straits is dependent on the topography mixing and stratification and for steady flows the interplay between these three effects can be quantified using the dimensionless parameter gr t a 2 where the grashoff number gr t and the aspect ratio a are evaluated within the strait when gr t a 2 is large the exchange is determined by the well known hydraulic solution as gr t a 2 becomes small the exchange rates progressively decrease below the hydraulic predictions toward values determined by diffusive control and characterized by strong vertical mixing for systems with simple topographic controls we show how the exchange rate in the strait may be linked to the external basin scale forcing characteristics we review recent work on extending this picture to consider the effects of unsteadiness in two forms time dependent forcing in the basin due to seasonal effects and tidal forcing with an associated barotropic forcing in the strait itself

remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern south china sea 1 evidence for baroclinic tide origin of internal solitary waves isws in the northeastern south china sea is presented based on 116 internal wave packets observed in satellite images from 1995 to 2001 these wave packets can be divided into two types a single wave isw packet containing only one isw with without an oscillating tail and a multiple wave isw packet composed of a group of rank ordered isws all of the 22 single wave isw packets occur in the deep water zone it is suggested that the isws instead of being generated by the lee wave mechanism are developed by nonlinear steepening of the baroclinic tides which are produced by the strong tidal currents flowing over a ridge in luzon strait this suggestion is verified by an ers 2 sar image which records such an evolution process from a baroclinic tide to a single isw in its spatial domain

buoyancy driven mean flow in a long channel with a hydraulically constrained exit condition convection plays a major role in a variety of natural hydrodynamic systems those in which convection drives exchange flows through a lateral contraction and or over a sill form a special class with typical examples being the red and mediterranean seas the persian gulf and the fjords that indent many coastlines the present work focuses on the spatial distribution and scaling of the density dierence between the inflowing and outflowing fluid layers using a long water lled channel tted with buoyancy sources at its upper surface experiments were conducted to investigate the influence of the geometry of the strait and the channel as well as the magnitude of the buoyancy flux two dierent scaling laws one by phillips 1966 and one by maxworthy 1994 1997 were compared with the experimental results it has been shown that a scaling law for which g 0 kb 2 3 0 x h 4 3 best describes the distribution of the observed density dierence along the channel where b0 is the buoyancy flux x the distance from the closed end of the channel h its height at the open end sill and k a constant that depends on the details of the channel geometry and flow conditions this result holds for the experimental results and appears to be valid for a number of natural systems as well

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

convectively driven exchange flow in a stratified sill enclosed basin laboratory experiments are used to investigate the processes governing steady convectively driven circulation in a basin that communicates with a large external reservoir over a shallow sill the motion is maintained by a steady loss of buoyancy distributed over the surface of the basin turbulent convection associated with the forcing produces a horizontal buoyancy gradient across the sill and the resulting mean flow consists of a layer directed into the basin near the surface with a dense counter flow below to first order the magnitude of the exchange flow over the sill is determined by the horizontal momentum balance within the basin measurements of the mean and turbulent flow fields are used to show that inertia buoyancy and friction may each contribute significantly to the balance the interior flow produces a horizontal pressure gradient near the surface which must also contribute to the momentum balance the density of the lower layer at the sill reflects the cumulative effect of interior processes such as mixing and these in turn influence the hydraulically controlled exchange flow over the sill the basin dynamics are therefore coupled in a nonlinear fashion with the submaximal sill exchange this coupling is investigated first by showing how interior processes are affected by changes in the magnitude of the forcing and then by observing the associated variation of the flow state at the sill the flow state is defined in terms of its relative proximity to the theoretical maximal exchange limit results show that the exchange flows are submaximal with flow rate approximately 85 of the maximal limit this state appears to change very little in response to increasing forcing for a stratified basin which exhibits a deep stagnant layer under the convectively driven near surface exchange flow the possibility of basin ventilation or erosion of deep fluid exists in the long term this process and its dependence on external parameters is also explored

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

quasi steady exchange flow in the bosphorus current meter moorings and high resolution surveys in the bosphorus reveal important details of the exchange flow during early september 1994 the flow was quasi steady and demonstrated strong mixing particularly in the surface layer after it entered the principal contraction of the strait composite froude numbers in the contraction are lower than expected consistent with recent modeling that shows friction producing significant deviations from predictions of inviscid two layer hydraulic theory

the role of the interface in exchange through the strait of gibraltar five cross strait hydrographic sections repeated several times during the gibraltar experiment in 1985 1986 are used to examine the structure of the interface layer between the inflowing atlantic waters and outflowing mediterranean waters in the strait of gibraltar the interface is 60 100 m thick with a strong vertical salinity gradient identified by fitting individual salinity profiles to a piecewise linear three layer model the interface is deeper thicker fresher and colder on the west end of the strait than in the narrows where there is a minimum in thickness and a maximum in salinity gradient farther east the interface thickens again and continues to get saltier warmer and shallower property variations in all three layers are also cast in terms of the three principal water types involved in the exchange the traditional knudsen model of exchange is extended to three layers assuming that the interface is a transport carrying third layer with uniform vertical shear as much as half of the inflowing or outflowing transport occurs in the interface layer transport converges in both the upper and lower layers implying over the length of the strait vertical exchange between layers that is comparable to about half the horizontal exchange the richness of structure and complexity of interaction between the interface and the upper and lower layers argues against the use of two layer models to characterize exchange through the strait of gibraltar

dynamic recrystallisation of ice aggregates during co axial viscoplastic deformation a numerical approach results of numerical simulations of co axial deformation of pure ice up to high strain combining full field modelling with recrystallisation are presented grain size and lattice preferred orientation analysis and comparisons between simulations at different strain rates show how recrystallisation has a major effect on the microstructure developing larger and equi dimensional grains but a relatively minor effect on the development of a preferred orientation of c axes although c axis distributions do not vary much recrystallisation appears to have a distinct effect on the relative activities of slip systems activating the pyramidal slip system and affecting the distribution of a axes the simulations reveal that the survival probability of individual grains is strongly related to the initial grain size but only weakly dependent on hard or soft orientations with respect to the flow field dynamic recrystallisation reduces initial hardening which is followed by a steady state characteristic of pure shear deformation

when do marginal seas and topographic sills modify the ocean density structure 1 we ask what effect marginal seas at high latitudes have on the abyssal densities and stratification of the oceans although marginal seas are not necessary for the formation of dense abyssal waters topographic sills tend to restrict exchange flows and increase density differences laboratory experiments with a steady state large scale overturning circulation forced by a gradient in surface temperatures or heat fluxes show that a marginal sea and topographic sill influence the abyssal density when the sill depth is less than twice the oceanic thermocline depth the overflow over shallow sills interacts directly with the surrounding thermocline stratification decreasing the abyssal density relative to an ocean with no marginal sea and increasing the density difference between the sea and the ocean experiments show that the effect of the sill depends on the surface boundary conditions and indicate a larger response for conditions approaching a prescribed distribution of temperature rather than of heat flux application of the results to the north atlantic circulation suggests that the greenland scotland ridge is shallow enough to lead to a significant reduction of the density of north atlantic deep water and this is consistent with the conclusions from an analysis of water mass properties the greenland scotland ridge is therefore likely to have a significant effect on the density structure and heat transport in the global oceans

age depth correlation grain growth and dislocation density evolution for three ice cores two previous theoretical analyses of data from the grip vostok and byrd ice cores presenting age depth correlations grain growth and dislocation density evolution are re examined it is found that the age depth correlations are inconsistent with the idealized flow with unchanging history adopted but that good correlations can be obtained by relaxing those restrictions a modified grain growth relation is proposed consistent with the distinct growth profiles of the vostok and other two cores which can be solved simultaneously with the given dislocation density evolution equation these are solved for all three cores with the given parameters and the depth profiles of grain diameter and dislocation density at the present time are determined with the new age depth correlation and with that shown empirically in the papers the varying flow history influences the age depth correlation and hence the depth profiles which is important both for the interpretation of core data and for the determination of constitutive variables at each depth at the present time

polar ice structure and the integrity of ice core paleoclimate records abstract polar ice is a unique archive of the climatic conditions in the past however ice sheets flow and this flow may affect the integrity of paleoclimate records a useful method to analyze the effect of ice flow upon climate records is the combination of microstructure mapping with ice core line scanning microstructure and stratigraphy have been mapped along the entire epica dml ice core with this combined method on the macroscale the stratigraphy seems perfectly preserved down to ca 1700 m depth mis4 below which minor undulations start to develop layers inclined up to 15 and millimeter scale z folds are observed below 2050 m depth notwithstanding the epica dml climate record appears not seriously disturbed down to ca 2400 m depth which marks the climatic transition from the last interglacial mis5e to the mis6 glacial period below this depth the synchronization with the epica dome c record is lost and stratigraphic disturbances appear up to the meter scale on the microscopic scale we observe dynamic recrystallization already in deep firn leading to substantial microstructural changes prior to bubble close off the concentration of visible micro inclusions in the holocene part of the core seems to increase with depth which could possibly indicate post depositional formation of salts in glacial period ice the concentration of visible micro inclusions in certain layers is so high that these strata appear as light scattering bands often called cloudy bands another interesting stratigraphic feature is what we call bubble free bands viz millimeter thick strata deprived of bubbles and rich in clathrate hydrates which are found within the bubble hydrate transition zone 800 1200 m depth and are probably caused by anomalously fast clathration while there is hardly any interaction between visible micro inclusions and grain boundaries down to 2500 m depth in the deeper ice warmer than 10 c many grain boundaries seem to harvest micro inclusions here we discuss these observations and their relevance for the interpretation of climate records

the microstructure of polar ice part ii state of the art an important feature of natural ice in addition to the obvious relevance of glaciers and ice sheets for climate related issues is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point without losing its polycrystalline character this fact together with its strong mechanical anisotropy and other notable properties makes natural ice an interesting model material for studying the high temperature creep and recrystallization of rocks in earth s interior after having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in part i of this work faria et al 2014 here in part ii we present an up todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them in particular we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure also known as the three stage model cf part i these results prove that grain growth in ice sheets is dynamic in the sense that it occurs during deformation and is markedly affected by the stored strain energy as well as by air inclusions and other impurities the strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal which demand large amounts of strain accommodation from the microstructural analyses of ice cores we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice additionally in fine grained high impurity ice layers e g cloudy bands strain may sometimes be accommodated by diffusional flow at low temperatures and stresses or microscopic grain boundary sliding via microshear in anisotropic ice sheared at high temperatures grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets evidence of nucleation of new grains is also observed at various depths provided that the local concentration of strain energy is high enough which is not seldom the case as a substitute for the tripartite paradigm we propose a novel dynamic recrystallization diagram in the three dimensional state space of strain rate temperature and mean grain size which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure dedicated to sepp kipfstuhl on occasion of his 60th birthday

energy of nonlinear internal waves in the south china sea 1 four sets of adcp measurements were taken in the south china sea scs these results were combined with previous satellite observations and internal tide numerical model results analysis suggests that strong internal tides are generated in luzon strait propagate as a narrow tidal beam into the scs are amplified by the shoaling continental slope near tungsha island become nonlinear and evolve into high frequency nonlinear internal waves niw internal waves in the scs have geographically distinct characteristics 1 west of luzon strait the total internal wave energy eiw is 10 that predicted by garrett munk spectra egm levine 2002 there is no sign of niw 2 near tungsha island eiw 13 egm strong nonlinear and high harmonic tides are present repetitive trains of large amplitude niw appear primarily at a semidiurnal periodicity with their amplitudes modulated at a fortnightly tidal cycle the rms vertical velocity of niw shows a clear spring neap tidal cycle and is linearly proportional to the barotropic tidal height in luzon strait with a 1 85 day time lag consistent with the travel time of internal tides from luzon strait to tungsha island 3 at the northern scs shelfbreak eiw 4 egm single depression waves are found but no multiple waves packets are evident 4 on the continental shelf eiw 2 egm both depression and elevation niw exist

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

submaximal exchange between a convectively forced basin and a large reservoir if a sill enclosed basin connected to a large reservoir is suddenly subjected to a de stabilizing surface buoyancy flux it will first mix vertically by turbulent convection before the resulting lateral buoyancy gradient generates a horizontal exchange flow across the sill we present a study which examines the unsteady adjustment of such a basin under continued steady forcing it is shown through theoretical development and laboratory experimentation that two consecutive unsteady regimes characterized by different dynamic balances are traversed as the flow approaches a steady state once established the exchange flow is controlled at the sill crest where it is hydraulically critical in the absence of a lateral contraction the single control at the sill crest allows a range of submaximal exchange states with the flow at the sill being dependent not only on the forcing and geometrical parameters but also on mixing conditions within the basin which are in turn dependent on the sill exchange the sill basin system is therefore strongly coupled although it remains isolated from the external reservoir conditions by a region of internally supercritical flow results from the laboratory experiments are used to demonstrate the link between the forcing and the exchange flow at the sill steady state measurements of the interior mean velocity and buoyancy fields are also compared with previous analytical models

a renewed argument for crystal size control of ice sheet strain rates at present it is generally believed that crystal size has no direct influence on strain rate in the ice sheets and that the fraction of strain rate enhancement there which is not ascribable to c axis fabric is due to impurity content here we challenge this view because it is not consistent with recent results from analyses of deformation at meserve glacier and instead ascribe residual enhancement in the ice sheets to variations in crystal size we resurrect the idea that variations of crystal size can be an important part of the total shear enhancement in the ice sheets though agree with paterson that this effect is generally dominated by variations of crystal fabric we propose that the enhanced shear strain rate of ice age ice in southern greenland as inferred from tilt of the dye 3 borehole can be explained as a result of combined fabric variations and crystal size variations with these two ice properties accounting for roughly 70 and 30 of the average enhancement respectively permitting a grain size dependence of ice viscosity also resolves the quandary concerning closure and tilt of the agassiz ice cap borehole

understanding the red sea response to sea level here we outline a new pragmatic methodology to derive relative sea level estimates from central red sea oxygen isotope records based on a previously published model in this paper the methodology is described in detail and it is shown that sea level change is the dominant factor responsible for the recorded variability in red sea 18o pdb for sea level changes greater than 12 m variables such as temperature or net evaporation are shown to have relatively small effects on the oxygen isotope record the modelled 18o pdb to sea level relationship is given in terms of a fifth order polynomial which may be used to describe relative sea level from central red sea oxygen isotope records we show how established sea level records from fossil reef terraces for the last 20 kyr are successfully simulated from central red sea oxygen isotope records we also examine the spatial variability of 18o pdb in the basin over the last 13 kyr

the coupling between exchange flux through a strait and dynamics in a small convectively driven marginal sea the gulf of aqaba gulf of eilat 1 we investigate the coupling between the dynamics in the gulf of aqaba gulf of eilat northern red sea and the exchange flow through the straits of tiran in response to seasonally varying surface fluxes and northern red sea hydrographic conditions because the gulf is a relatively small basin winter mixing between the surface and intermediate layers occurs over most places in the gulf including in the vicinity of the straits and leads to a maximal exchange flow in the strait during the spring warming in the red sea forces an influx of warm red sea water into the gulf the surface layer is refilled and consequently the exchange flow in the straits changes from a maximal to a submaximal flow regime as a result the dense wintertime water formation in the gulf and the exchange flow through the strait are strongly coupled on seasonal time scales in addition the hydrographic conditions in the northern red sea undergo strong seasonality these characteristics prevent the direct application of current theories for strait marginal sea systems which commonly assume steady conditions in the open ocean side of the strait and or an annual mean surface flux over the marginal sea we explain why the exchange of volume and heat between the gulf of aqaba gulf of eilat and the northern red sea is larger during spring summer despite the net surface buoyancy input into the gulf and why it diminishes during fall winter despite the large buoyancy loss to the atmosphere the applicability of the results to other systems is discussed

dynamic recrystallization and texture development in ice as revealed by the study of deep ice cores in antarctica and greenland the preferred c axis orientation of ice from polar ice sheets develops essentially as a result of intracrystalline slip but dynamic recrystallization appears to alter the kinetics of the development of deformation textures and is at high temperature at the origin of recrystallization textures the purpose of this work is to obtain a better understanding of recrystallization processes that occur in polar ice sheets and to clarify the relationship between dynamic recrystallization and textures the study was based on two deep ice cores from greenland and antarctica the greenland ice core project grip and vostok ice cores the structure along the grip core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and migration recrystallization near the bottom only grain growth and rotation recrystallization appear to occur in the vostok ice core the transition between these recrystallization regimes was studied estimating for interglacial ice the evolution with depth of the dislocation density this calculation has shown the efficiency of grain boundary migration for the absorption of dislocations at vostok the highest value of the dislocation density is found at a depth of about 1000 m and the continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate it is shown that the driving force required to initiate migration recrystallization is not reached in interglacial ice at vostok the observed textures were compared with those predicted by the self consistent approach recrystallization textures are interpreted by assuming that the less stressed grains i e the best oriented for basal slip are favored by the size advantage of subgrains the recrystallization textures are compared with those of other materials

response characteristics of a buoyancy driven sea abstract the authors consider the flow in a semienclosed sea or basin subjected to a destabilizing surface buoyancy flux and separated from a large adjoining reservoir by a sill a series of numerical experiments were conducted to quantify the energetics of the flow within the basin that is the amount of kinetic and potential energy stored within the basin and the rate at which these quantities are transported to and from the reservoir via the exchange flow over the sill the numerical experiments were formulated at laboratory scales and conducted using a boundary fitting clustered grid to resolve the entrainment and mixing processes within the flow and to facilitate quantitative comparison with previous laboratory experiments volume and boundary integrated energetics were computed for both steady and time varying flows in the steady state limit the rate of energy flux through the surface is balanced by dissipation within the basin and advection of potential energy over the sill and into the reser

exchange between a freshwater embayment and a large lake through a long shallow channel we analyze the exchange between a weakly forced lacustrine embayment and a large lake through a long shallow channel exchange in the channel is the result of a multiple and subtle balance in which spatial thermal variations baroclinic forcing oscillations in the water level barotropic forcing bottom friction diffusion wind forcing and the effects of unsteadiness are all important temperature gradients across the channel result from differences in thermal inertia of the embayment and lake at seasonal time scales and differences in the wind driven internal dynamics of the lake and the embayment at diurnal to synoptic time scales these gradients are in general weak and barotropic forcing dominates the channel momentum balance however episodic upwelling in the lake can shift the balance in favor of baroclinic dominance a combination of scaling analysis of observational data and threedimensional simulations are used to demonstrate that bed stress vertical turbulent diffusion wind stress and unsteadiness effect exchange relative to the predictions of internal hydraulic theory the quasisteady inviscid theory that describes the motion resulting from a purely barotropic baroclinic force balance

imaging of firn and bubbly ice in coaxial reflected light a new technique for the characterization of these porous media a new technique for characterizing the structure of firn and bubbly ice is presented this technique based on observation of etched sublimation surfaces in coax ial reflected light enables one to see simultaneously the pore network of the firn or bubbles in the ice and the crystal boundaries at the same time the main stages of image proces sing used to transform the initial photographs into clean binary images are described

microstructure mapping a new method for imaging deformation induced microstructural features of ice on the grain scale this work presents a method of mapping deformation related sublimation patterns formed on the surface of ice specimens at microscopic resolution 3 4 mm pixel 1 the method is based on the systematic sublimation of a microtomed piece of ice prepared either as a thick or a thin section the mapping system consists of an optical microscope a ccd video camera and a computer controlled xy stage about 1500 images are needed to build a high resolution mosaic map of a 4 5 9 cm section mosaics and single images are used to derive a variety of statistical data about air inclusions air bubbles and air clathrate hydrates texture grain size shape and orientation and deformation related features subgrain boundaries slip bands subgrain islands and loops pinned and bulged grain boundaries the most common sublimation patterns are described and their relevance for the deformation of polar ice is briefly discussed

prescriptions for heat flux and entrainment rates in the upper ocean during convection abstract a detailed investigation of the upper ocean during convection reveals the vertical structure of potential temperature to be steady in time and the current shear to vanish in the bulk of the mixed layer these imply that a slab type model may be an adequate representation of the convective ocean boundary layer obl in contrast when convection is not the dominant forcing mechanism the obl is stratified and can support a significant current shear this indicates the inadequacy of slab models for the nonconvective obl two independent estimates of the vertical heat flux profile in the convective obl were made the first estimate results from heat conservation and the steadiness of the vertical structure of potential temperature the second estimate is based on the turbulent kinetic energy tke balance and the vertical profiles of tke dissipation rate the estimates are consistent and suggest that the nondimensional vertical heat flux due to turbulence has a linear depth dependence o

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

the microstructure of polar ice part i highlights from ice core research polar ice sheets play a fundamental role in earth s climate system by interacting actively and passively with the environment active interactions include the creeping flow of ice and its effects on polar geomorphology global sea level ocean and atmospheric circulation and so on passive interactions are mainly established by the formation of climate records within the ice in form of air bubbles dust particles salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls for a half century scientists have been drilling deep ice cores in antarctica and greenland for studying such records which can go back to around a million years experience shows however that the ice sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores destroying the integrity of the oldest records for all these reasons glaciologists have been studying the microstructure of polar ice cores for decades in order to understand the genesis and fate of ice core climate records as well as to learn more about the physical properties of polar ice aiming at better climate record interpretations and ever more precise models of ice sheet dynamics in this part i we review the main difficulties and advances in deep ice core drilling in antarctica and greenland together with the major contributions of deep ice coring to the research on natural ice microstructures in particular we discuss in detail the microstructural findings from camp century byrd dye 3 grip gisp2 northgrip vostok dome c edml and dome fuji besides commenting also on the earlier results of some pioneering ventures like the jungfraujoch expedition and the norwegian british swedish antarctic expedition among others in the companion part ii of this work faria et al 2014 the review proceeds with a survey of the state of the art understanding of natural ice microstructures and some exciting prospects in this field of research

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

what happens to deformed rocks after deformation a refined model for recovery based on numerical simulations deformation in large parts of the middle crust results in strained rocks consisting of grains with variable dislocation densities and microstructures which are characterized by gradual distortion

full field predictions of ice dynamic recrystallisation under simple shear conditions understanding the flow of ice on the microstructural scale is essential for improving our knowledge of large scale ice dynamics and thus our ability to predict future changes of ice sheets polar ice behaves anisotropically during flow which can lead to strain localisation in order to study how dynamic recrystallisation affects to strain localisation in deep levels of polar ice sheets we present a series of numerical simulations of ice polycrystals deformed under simple shear conditions the models explicitly simulate the evolution of microstructures using a full field approach based on the coupling of a viscoplastic deformation code vpfft with dynamic recrystallisation codes the simulations provide new insights into the distribution of stress strain rate and lattice orientation fields with progressive strain up to a shear strain of three our simulations show how the recrystallisation processes have a strong influence on the resulting microstructure grain size and shape while the development of lattice preferred orientations lpo appears to be less affected activation of non basal slip systems is enhanced by recrystallisation and induces a strain hardening behaviour up to the onset of strain localisation and strain weakening behaviour simulations demonstrate that the strong intrinsic anisotropy of ice crystals is transferred to the polycrystalline scale and results in the development of strain localisation bands than can be masked by grain boundary migration therefore the finite strain history is non directly reflected by the final microstructure masked strain localisation can be recognised in ice cores such as the edml from the presence of stepped boundaries microshear and grains with zig zag geometries

subgrain boundaries and related microstructural features in edml antarctica deep ice core subgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization statistical data obtained from the epica dronning maud land edml deep ice core drilled in east antarctica cannot detect a depth region of increased subgrain boundary formation grain boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths the data do not support the classical view of a change of dominating recrystallization regimes with depth three major types of subgrain boundaries reflecting high mechanical anisotropy are specified in combination with crystal orientation analysis

modeling of anisotropic grain growth in minerals the role of surface energy anisotropy during grain growth is investigated using both physical experiments on octachloropropane and numerical experiments using the elle microstructural modelling system in particular the effects of anisotropy on growth rates grain shapes and lattice preferred orientations are analysed anisotropic growth in thin polycrystalline sheets of octachloropropane is found to systematically remove certain c axis orientations from the sample without obviously modifying the grain shapes by comparison with equivalent numerical experiments we can explain these observations with a simple boundary layer model that treats each side of each grain boundary as an independent system the observed growth exponent in the physical experiment of 0 35 is significantly below the theoretical level of 1 and although the numerical experiments have growth rates as low as 0 68 apparently some other factor which suppresses the growth rate in the octachloropropane was also active the anisotropy of surface energies also leads to an increase in the grain size distribution and when it occurs in rocks with a strong pre existing crystallographic preferred orientation may even lead to the development of a shape preferred orientation which is completely unrelated to the shape of the finite strain ellipsoid corresponding author e mail address bons mail uni mainz de accepted for publication in the hans ramberg volume bulletin of the american geological society bons et al anisotropic grain growth 17 januar 2000 page 2

numerical simulation of the flow velocity and temperature of the dongkemadi glacier the flow velocity and ice temperature of a glacier reflect the response of the glacier to climate change however because of the restrictions of observation conditions it is often difficult to acquire the ice velocity and temperature field for the entire glacier profile in this study we use a two dimensional ice flow model and energy balance model to simulate the ice velocity and temperature using field measurements made with ground penetrating radar for the profile of the small dongkemadi glacier and verify the simulated surface velocity with interferometric synthetic aperture radar data the simulation for the flow velocity shows that the velocity depends on the surface and bedrock slopes glacier profile shape and mass supply way and the surface velocity increases with an increase in the surface slope sensitivity analysis shows that the terrain and slope affect the profile velocity simulation results for temperature show that the ice body temperature is highest in the lower ice body at a subglacial position altitude of 5520 m a s l this location not only gathers melt water most easily but also undergoes the strongest effect of geothermal heat flow the distributions of the ice velocity and ice body temperature provide a good reference for research on glacier vulnerability assessment and the response of glaciers to climate change

crystalline texture of the 2083 m ice core at vostok station antarctica crystalline texture and c axis orien tation of the 2083 m ice core at vostok station covering more than 150 kyear reveal the existence of strong anisotropies changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries a smaller growth rate appears to be associated with cold periods a gradual increase in the horizontal elongation of grains was observed between 350 and 680 m but the mean value of the coefficient of the linear dimensional orientation of grains does not cha nge below 700 m the e axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains forming a vertical girdle patt ern this charac teristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longit udi nal tension the rotation of grains was calcu lated with respect to the total strain simulating the form ation of the girdle fabric pattern the fabric enhance ment factor was calculated at various depths it appears that vostok ice hardens gradua lly