iceberg calving flux and mass balance of the austfonna ice cap on nordaustlandet svalbard 1 satellite radar interferometry 60 mhz airborne ice penetrating radar data and visible band satellite imagery were used to calculate the velocity structure ice thickness and the changing ice marginal extent of austfonna 8000 km2 and 2500 km3 the largest ice cap in the eurasian arctic ice cap motion is generally less than about 10 m a 1 except where faster flowing curvilinear features with velocities of several tens to over 200 m a 1 are present most drainage basins of austfonna have undergone ice marginal retreat over the past few decades at an average of a few tens of meters per year integrating margin change around the whole ice cap gives a total area loss of about 10 km2 a 1 iceberg flux from the marine margins of austfonna is about 2 5 0 5 km3 a 1 water equivalent about 45 of the total calving flux from the whole svalbard archipelago when mass loss by iceberg production is taken into account the total mass balance of austfonna is negative by between about 2 5 and 4 5 km3 a 1 this iceberg flux represents about 33 5 of total annual mass loss from austfonna with the remainder lost through surface ablation iceberg flux should be included in calculations of the total mass balance of the many large arctic ice caps including those located in the russian and canadian arctic that end in tidewater the neglect of this term has led to underestimates of mass loss from these ice caps and thus to underestimates of the contribution of arctic ice caps to global sea level rise

relating the occurrence of crevasses to surface strain rates the presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met understanding how crevasses form will provide information about the stress and strain rate fields in the ice this study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses a literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded by plotting strain rates converted to stresses using a creep law using axes representing the surface parallel principal stresses failure envelopes were derived by enclosing measurements where surface crevassing was absent the derived failure envelopes were found to conform well to theoretical ones predicted by the coulomb and the maximum octahedral shear stress von mises theories of failure the derived failure envelopes were scaled by the tensile strength which was found to vary from 90 to 320 kpa there was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses the observed variation in tensile strength could result from variations in ice properties e g crystal size impurity content or density or could be related to uncertainty in the constitutive relation creep flow and fracture share a very similar temperature dependence suggesting similar crystal scale processes are responsible for both the observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery the study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large antarctic ice shelves such as the filchner ronne or ross ice shelves

evolution of a surge type glacier in its quiescent phase kongsvegen spitsbergen 1964 95 kongsyegen is a 102 km 2 sub polar polythermal surge type glacier in northwest spitsbergen svalbard it surged just before 1948 and is currently in its quiescent phase measurements of surface geometry since 1966 show a retreat of the front and strong thinning of up to 75 m in the ablation area and a build up of up to 32 m in the accumulation area present day annual velocities along the glacier are low from 1 4 up to 3 6 m a 1 the measured mean net balance for the period 1987 94 and the balance reconstructed back to 1967 show a weak positive balance of about 0 1 m w e the measured actual ice flux is low and the mass transfer down glacier at the ela is only about 3 20 of that required for steady state thus the glacier is building up towards a new surge the total thickening rate on kongsvegen is somewhat higher than in other cases from svalbard but it is small compared with other well studied surge type glaciers in alaska and he pamirs this relatively low rate of change is a function of the low accumulation rate and the relatively cold climate compared to other areas and is common for surge type glaciers in svalbard

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

hydrochemistry as an indicator of subglacial drainage system structure a comparison of alpine and sub polar environments the anion compositions so 2 4 hco 3 and cl of runoff from the haut glacier d arolla switzerland and austre broggerbreen svalbard are compared to assess whether or not variations in water chemistry with discharge are consistent with current understanding of the subglacial drainage structure of warm and polythermal based glaciers these glacial catchments have very different bedrocks and the subglacial drainage structures are also believed to be different yet the range of anion concentrations show considerable overlap for so 2 4 and hco 3 concentrations of cl are higher at austre broggerbreen because of the maritime location of the glacier correcting so 2 4 for the snowpack component reveals that the variation in non snowpack so 2 4 with discharge and with hco 3 is similar to that observed at the haut glacier d arolla hence if we assume that the provenance of the non snowpack so 2 4 is the same in both glacial drainage systems a distributed drainage system also contributes to runoff at austre broggerbreen we have no independent means of testing the assumption at present the lower concentrations of non snowpack so 2 4 at austre broggerbreen may suggest that a smaller proportion of runoff originates from a distributed drainage system than at the haut glacier d arolla

ice bed interface and englacial properties of svalbard ice masses deduced from airborne radio echo sounding data un ensemble de donnees de sondages par echo radio ont ete collectees sur 44 masses de glace au spitsberg et les calottes glaciaires de nordaustlandet svalbard ces donnees ont permis de produire les coefficients de reflexion en puissance pour l interface glace manteau sur une grande etendue de svalbard nord

simulation and parameterization of superimposed ice formation in cold arctic snowpacks meltwater retention is a significant factor controlling the timing and magnitude of runoff meltwater percolates vertically through the snowpack until it reaches an impermeable horizon whereupon a saturated zone is established if the underlying media is below the freezing point accretive ice formation takes place this process has previously been crudely parameterized or modelled numerically such ice is called either superimposed ice on glaciers or basal ice on bare land using theory derived from sea ice formation an analytical solution to basal ice growth is proposed results are compared against growth rates derived from numerical modelling in addition model results are compared to field observations of ice temperatures the analytical solution is further extended to account for the temperature gradient inside the underlying media and the variable thermal properties of the underlying media in the analysis observations and references have predominantly relied on knowledge from glaciers however the process of accretive ice growth is equally important in seasonal snow packs with a cold snow ground interface and on arctic sea ice where the ice snow interface is well below freezing point the simplification of this accretive ice growth problem makes the solution attractive for incorporation in large scale cryospheric models copyright 2007 john wiley sons ltd

submarine landforms and the behavior of a surging ice cap since the last glacial maximum the open marine setting of eastern austfonna svalbard abstract multi beam swath bathymetry data and topographic parametric sonar topas 3 5 khz sub bottom acoustic profiles were acquired from the inlet of hartogbutka an open marine setting offshore of austfonna northeastern nordaustlandet svalbard the largest ice cap in the eurasian arctic using these marine geophysical data the seafloor morphological and sedimentary evidence of former ice extent and dynamics of the three drainage basins basins 3 4 and 5 adjacent to hartogbukta were examined submarine landforms and landform assemblages that provide evidence of past ice dynamics are described and interpreted in the context of previous studies of surge affected submarine environments elsewhere in svalbard a sequence of four distinct ice flow episodes in hartogbukta from the late weichselian deglaciation to the present is identified to explain the morphological evolution of the seafloor a full glacial ice sheet extended over hartogbukta during the late weichselian flowing ese at intervals throughout the holocene the drainage basins adjacent to hartogbukta probably underwent repeated surges most recently basins 3 and 4 probably surged as one cohesive ice mass in the late 1800s and basin 5 most likely underwent a less extensive surge in the 20th century these ice flow events are interpreted in the context of the glaciology and known glacial history of austfonna and the nw barents sea the 200 km long ice cliffs of eastern austfonna provide an unusual and important analog for open marine deposition that would have been much more prevalent under full glacial conditions where ice sheets in many parts of the arctic advanced from fjord systems onto the adjacent continental shelves

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

a mean net accumulation pattern derived from radioactive layers and radar soundings on austfonna nordaustlandet svalbard we present the snow accumulation distribution over austfonna nord austlandet svalbard based on 29 shallow ice cores that were retrieved from this ice cap during 1998 and 1999 mean annual net accumulation is deduced from radioactive layers resulting from the 1954 74 atmospheric nuclear tests maximum in 1963 and the chernobyl accident 1986 the chernobyl layer was located in 19 ice cores in the accumulation area and the nuclear test layer was located in two deeper ice cores in addition the spatial variation of the depth of winter 1998 99 snowpack was mapped using snow probing ground penetrating radar methods and pit studies the altitudinal gradient of the mean annual net mass balance and the altitude of the mean equilibrium line are determined along five transects ending at the top of the ice cap the mean annual net mass balance and the equilibrium line altitudes show a high degree of asymmetry between the western and eastern parts of austfonna in accordance with the distribution of winter accumulation large interannual variations of the accumulation exist however the study of the mean annual net mass balance shows no trend for two different time periods 1963 86 and 1986 to the date of the drillings 1998 99

glacier hydrology in svalbard norwegian high arctic abstract progress in glacier hydrology has focused on temperate glaciers although partly or wholly non temperate glaciers are found in many parts of the world and significant areas of former ice sheets were probably non temperate it has usually been assumed that drainage from non temperate glaciers consists of relatively dilute and invariable supraglacial runoff in this paper the hydrology of glaciers in the high arctic archipelago of svalbard is examined variations in the thermal regimes of glaciers and their implications for drainage are first addressed results from svalbard concerning meltwater discharge and storage and solute and suspended sediment dynamics are then reviewed in general meltwater penetration of non temperate ice is limited and drainage from non temperate glaciers in svalbard has many of the characteristics of sub aerial drainage however it would be erroneous to view this drainage simply as dilute supraglacial runoff as significant material transport occurs in suspension and solution furthermore twentieth century climate change has probably led to changes in the thermal regimes of some svalbard glaciers such that relict drainage structures are sometimes observed while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers at large spatial scales turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non temperate ice

positive mass balance during the late 20th century on austfonna svalbard revealed using satellite radar interferometry determining whether increasing temperature or precipitation will dominate the cryo spheric response to climate change is key to forecasting future sea level rise the volume of ice contained in the ice caps and glaciers of the arctic archipelago of svalbard is small compared with that of the greenland or antarctic ice sheets but is likely to be affected much more rapidly in the short term by climate change this study investigates the mass balance of austfonna svalbard s largest ice cap equilibrium line fluxes for the whole ice cap and for individual drainage basins were estimated by combining surface velocities measured using satellite radar interferometry with ice thicknesses derived from radio echo sounding these fluxes were compared with balance fluxes to reveal that during the 1990s the total mass balance of the accumulation zone was 5 6 2 0 10 8 m 3 a 1 three basins in the quiescent phase of their surge cycles contributed 75 of this accumulation the remaining volume may be attributable either to as yet unidentified surge type glaciers or to increased precipitation this result emphasizes the importance of considering the surge dynamics of glaciers when attempting to draw any conclusions on climate change based on snapshot observations of the cryosphere

the role of zonal winds in the production of a pre reversal enhancement in the vertical ion drift in the low latitude ionosphere 1 the evolution of the pre reversal enhancement in the vertical ion drift in the equatorialfregion is described via an examination of the current systems determined from a coupled ionosphere thermosphere model we find that the pre reversal enhancement is produced by a reversal in thef region zonal wind that results in an additional upward current where the e region pedersen conductivity is declining across the dusk sector the continuity of the total current is maintained through an enhancement in the eastward zonal current and an associated upward drift of the ions

the link between glacier velocity and the drainage of ice dammed lakes comment on a paper by knight and tweed the interesting suggestion by knight and tweed 1991 that a link exists between glacier velocity changes and the filling and draining of a marginal ice dammed lake at solheimajokull southern iceland is examined the main problem lies not with plausibility but with a lack of field data to substantiate the argument some pertinent hydrological glaciological and meteorological data from the area are presented here many of which do not entirely support certain inferences and observations made in their paper it is shown that this very small lake is likely to have limited quantitative significance in the operation of the glacio hydrological or solute and sediment transfer systems in this basin further specific difficulties include the absence of crucial observations on glacier velocity variations and the precise timing and pattern of lake drainage in relation to such velocity changes the lack of evidence for a significant relationship between precipitation receipt and ice velocity here a component of the knight and tweed 1991 proposition and the occurrence of the lake drainage event in a rain free period contrary to the authors suggestion the opportunity is also taken to correct some incidental errors

topography and dynamics of austfonna nordaustlandet svalbard from sar interferometry the ice caps of nordaustlandet svalbard represent one of the largest glaciated areas outside of antarctica and greenland they demonstrate a variety of different flow regimes within a comparatively compact area we report on the first interferometrically derived elevation models and velocity visualisations of austfonna this initial investigation had three purposes to determine whether the coherence and velocity characteristics of the region permitted interferometric survey to determine the accuracy of derived elevations and to assess the possibility of investigating time variant flow of the more dynamic ice bodies using differential interferometry a trio of coherent synthetic aperture radar images from ers 1 s first ice phase was identified the images were combined to separate the topographic and velocity components of the resultant interferograms the topographic phase difference was used to produce a digital elevation model of austfonna its accuracy relative to radio echo sounding derived tie points is 8 m and its resolution 40 m we also present synoptic views of the velocity held of three of austfonna s drainage basins and comment on the extraction of useful velocity information

ground water intrusions in a mine beneath hoganesbreen svalbard assessing the possibility of evacuating water subglacially evacuation of the ground water intruding into a coal mine beneath ho ganesbreen svalbard is difficult and expensive to solve this problem it was proposed thatthe minebeconnectedtotheice bedrock interface pumpinghot waterfromthe mine should establish a flow path along the glacier bed where the ground water would drain gravitationally in this paper we assess the requirements for maintaining such a drainage system in open channel conditions to obtain the bedrock topography we determined the ice thickness by ground penetrating radar and subtracted it from the surface elevation measured by global positioning system a measured temperature profile at the site where themineshouldconnecttotheglacierbed 140mdepth revealedthatthebasal iceisbelow thepressure melting point thelocations of majorsubglacialconduitswereestimatedusing ahydraulic potentialapproach weadoptedamodeloftime dependentdischargethrougha ro thlisberger channel to calculate a set of scenarios using different flow law parameters resultsofthesimulationssuggestthatforthegivenconditions waterflow wouldbepressur ized thereby inhibiting the gravitational drainage of the mine

assessing the paradigm shift deformable glacier beds abstract during the mid 1980s glaciologists recognised that many glaciers and ice masses overlie soft sediments rather than hard bedrock these sediments are typically weaker than glacier ice and may therefore deform this realisation was heralded as a paradigm shift in glaciology since this realisation a wide body of theoretical and field based research has been undertaken to assess the mechanical and hydrological significance of such substrates we review the techniques and results of this work and attempt to assess this paradigm shift in glaciology and in particular its importance for quaternary scientists we suggest areas of research that remain unanswered and identify those in which glacial geology in particular may be able to inform glaciologists

evidence against a late wisconsinan ice shelf in the gulf of maine abstract proposals for the formation of a late wisconsinan ice shelf in the gulf of maine during the retreat of the laurentide ice sheet are considered to be inappropriate an antarctic type ice shelf does not fit the field data that indicate temperate glacial terrestrial and marine climates for the region between 18 ka and 12 ka a temperate ice shelf has no modern analogues and may be physically impossible the preponderance of stratified drift in the gulf of maine region supports temperate climates during late wisconsinan time it also indicates that glacial meltwater rather than ice in either an ice sheet or ice shelf was the primary transport mechanism of glacial sediment and the source for the glaciomarine mud for these reasons we have proposed glacial analogues for the deglaciation of the gulf of maine that consist of temperate or subpolar marine based glaciers characterized by depositional environments dominated by meltwater discharge directly to the sea or the sea by way of subaerial meltwater streams these analogues include alaskan fjord glaciers glaciers on the alaskan continental shelf that discharged meltwater directly into the sea in the not too distant past and austfonna nordaustandet svalbard norway that is presently discharging meltwater in the sea along a grounded ice wall this last example is the best modern day analogue for the depositional environment for most of the glaciomarine mud in the gulf of maine and deglaciation of the gulf

thermal energy conservation in icebergs and tracking by temperature calculations using a two dimensional numerical model which simulates the heat balance and temperature distribution of icebergs show that the temperature in the central region of an iceberg is almost unaffected by the thermal conditions imposed on its boundary hence the original temperature of the iceberg at the time of calving is retained in its core owing to the insulating quality of the ice when correlated with glacioclimatic conditions this temperature conservation may be used to backtrack an iceberg to its parent ice cliff nine different icebergs were manually temperature profiled in the barents sea during late winter 1988 1990 a scenario is considered wherein one of these icebergs under the forces of winds and currents is assumed to set off from franz josef land in late autumn 1987 the numerical heat balance model is used to compute the temperature distribution heat balance and ablation of this iceberg as it drifts through the barents sea the calculations show that the heat balance of the part of the iceberg exposed to air has marginal influence on the ablation and thus on the expected lifetime of the iceberg ablation of the submerged body also occurs during winter when the water temperature is well below the melting point of glacial ice this is caused by freezing point depression leading to an ablation of about 0 5 m per month of the underside and sidewalls of the submerged body for water temperatures above 0 6 c the ablation results in a steep temperature gradient reaching the core temperature 3 m into the ice with a tolerance of 0 4 c the temperature is virtually free of any thermal boundary influence 12 m into the ice the simulated and measured temperature profiles of the iceberg are compared with measurements of the thermal regime of austfonna nordaustlandet and the churlenis ice dome on franz josef land the model calculations indicate that the ice cliffs on svalbard can be excluded as parent ice cliffs for these icebergs and that the core temperature of the bergs appears to be a conservative tracer

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

global equatorial plasma bubble occurrence during the 2015 st patrick s day storm an analysis of the occurrence of equatorial plasma bubbles epbs around the world during the 2015 st patrick s day geomagnetic storm is presented a network of 12 global positioning system receivers spanning from south america to southeast asia was used in addition to colocated vhf receivers at three stations and four nearby ionosondes the suppression of postsunset epbs was observed across most longitudes over 2 days the epb observations were compared to calculations of the linear rayleigh taylor growth rate using coupled thermosphere ionosphere modeling which successfully modeled the transition of favorable epb growth from postsunset to postmidnight hours during the storm the mechanisms behind the growth of postmidnight epbs during this storm were investigated while the latter stages of postmidnight epb growth were found to be dominated by disturbance dynamo effects the initial stages of postmidnight epb growth close to local midnight were found to be controlled by the higher altitudes of the plasma i e the gravity term modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low latitude region which made the plasma more susceptible to rayleigh taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight epbs

calibrating a surface mass balance model for austfonna ice cap svalbard austfonna 8120 km 2 is by far the largest ice mass in the svalbard archipelago there is considerable uncertainty about its current state of balance and its possible response to climate change over the 2004 05 period we collected continuous meteorological data series from the ice cap performed mass balance measurements using a network of stakes distributed across the ice cap and mapped the distribution of snow accumulation using ground penetrating radar along several profile lines these data are used to drive and test a model of the surface mass balance the spatial accumulation pattern was derived from the snow depth profiles using regression techniques and ablation was calculated using a temperature index approach model parameters were calibrated using the available field data parameter calibration was complicated by the fact that different parameter combinations yield equally acceptable matches to the stake data while the resulting calculated net mass balance differs considerably testing model results against multiple criteria is an efficient method to cope with non uniqueness in doing so a range of different data and observations was compared to several different aspects of the model results we find a systematic underestimation of net balance for parameter combinations that predict observed ice ablation which suggests that refreezing processes play an important role to represent these effects in the model a simple pmax approach was included in its formulation used as a diagnostic tool the model suggests that the surface mass balance for the period 29 april 2004 to 23 april 2005 was negative 318 mm w e

facies system of the eastern barents sea since the last glaciation to present abstract twenty two sediment cores raised from the central and eastern parts of the barents sea have been studied to reconstruct the evolution of the facies system since the late weichselian glaciation multiproxy records reveal four lithostratigraphic units which reflect major development stages of paleoenvironments age control is provided by 23 ams 14 c dates for holocene sections of four cores continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase during this phase the barents sea ice sheet detached from the ground resulting in seawater penetration into troughs iceberg calving deposition of ird and fine grained glacier meltwater load in newly formed marine basins the main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor ird redistribution of fine grained suspended matter by bottom currents and brine induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the holocene marine sediments the holocene facies of shelf depressions reflect rather high but variable productivity responding to climate changes and variations of atlantic water inflow into the barents sea

the surface topography of large ice masses from landsat imagery les images de landsat mss de l antarctique et du svalbard ont ete comparees a des mesures altimetriques effectuees a partir d avion

longitudinal and seasonal variation of the equatorial flux tube integrated rayleigh taylor instability growth rate using the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model tiegcm the ionospheric rayleigh taylor instability growth rate is calculated the seasonal and longitudinal variations of the growth rate from the tiegcm appear to match that of the spread f observed by various satellite missions the growth rate is strongly dependent on the angle between the sunset terminator and the geomagnetic field line near the magnetic equator the tiegcm simulations with nonmigrating tides show the zonal wave number 4 structure in the rayleigh taylor instability due to the inclusion of the nonmigrating diurnal eastward zonal wave number 3 and semidiurnal eastward zonal wave number 2 tides

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

postglacial emergence of western franz josef land russian and retreat of the barents sea ice sheet uncertainty remains on the timing and extent of late weichselian glaciers over the qsr barents and kara sea shelves franz josef land russia is a critical area for deciphering the record of glacier fluctuations and postglacial relative sea level change coastal forelands on the archipelago are covered by a well preserved raised beach sequence containing abundant and pristine driftwood whalebone and shell 4c dating of these materials provides site specific emergence records for the archipelago and some of the oldest ages on deglaciation of 10 400 bp three apparent still stands in emergence are inferred from morphology of the raised beach sequence and 4c dating between 9900 and 6200 bp and at ca 5500 bp and 3500 bp the earliest sea level arrest after formation of the marine limit reflects a balance between glacio isostasy and eustasy concomitant with the final phase of global sea level rise the latter two sea level arrests during the middle to late holocene are less pronounced and may indicate increased height of the ocean surface with greater storminess and extended open water conditions raised beaches at 1 2 m a s l and j4c dated at 1000 to 2000 bp give contemporary emergence rates of 1 to 2 mm year the low current rates of emergence on franz josef land are similar to areas in fennoscandinavia that sustained modest late weichselian glacier loads 1500 m within a few 100s of km of the inferred ice sheet margin the pattern of postglacial emergence and strandline tilts indicates that past glacier loads were greater over the adjacent barents sea than franz josef land marine and terrestrial records from franz josef land place retreat of glaciers from coastal areas by 10 400 bp whereas the adjacent franz victoria trough was deglaciated by 13 000 bp retreat of the barents sea ice sheet was probably underway by 13 500 bp coincident with rising global sea level and elevated summer insolation we infer that iceberg calving through the deep troughs bordering the barents sea particularly with rapidly rising sea level ca 12 000 bp was an important process controlling the demise of the barents sea ice sheet copyright 1996 elsevier science ltd

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

eastward electric field enhancement and geomagnetic positive bay in the dayside low latitude ionosphere caused by magnetospheric substorms during sawtooth events 1 substorms cause significant disturbances in the magnetosphere and ionosphere although many substorm induced phenomena have been relatively well understood a serious controversy arises as to how the magnetospheric and ionospheric convection responds to the expansion onset in this paper we present the observations of the low latitude ionospheric electric field and geomagnetic field at substorm onsets during sawtooth events when the interplanetary magnetic field imf remains steady southward so the ionospheric disturbances are attributed solely to the substorm effects in the substorm events we have analyzed the dayside equatorial ionospheric electric field shows an eastward enhancement at the onset and the geomagnetic field northward component at middle and low latitudes shows an increase positive bay on both the dayside and nightside we suggest that the magnetospheric convection is enhanced at substorm onset and that the enhanced magnetospheric convection electric field penetrates to the low latitude ionosphere the penetration electric field driven by substorm onset causes the eastward ionospheric electric field enhancement and geomagnetic positive bay on the dayside and the substorm current wedge causes the geomagnetic positive bay on the nightside our findings are significantly different from the results of most previous studies and provide new insight into the substorm dynamic process

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime