deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

groundwater flow conditions in a low angle fracture zone at finnsjon sweden abstract the performance and results of a series of hydraulic head measurements and differently designed tracer tests are described a combined interpretation of the results is utilized to estimate the natural groundwater flow conditions in a low angle major fracture zone zone 2 investigated at the finnsjon study site central eastern sweden the transport of tracer labelled flushing water used during drilling of a cored borehole was utilized to determine hydraulic connections and estimations of hydraulic parameters the breakthrough of tracer was monitored at a distance of 440 m from the injection point with a mean residence time of 37 days in order to determine transport parameters of the fracture zone a tracer test was performed in conjunction with an interference test the hydraulic fracture conductivity flow porosity equivalent fracture width and dispersivity were calculated for three different tracer routes tracer was also used to detect any bypass around the packers during the interference test a series of groundwater flow determinations are also described which used the point dilution technique in packed off borehole sections carried out under natural gradient conditions the groundwater head measurements indicated that a pressure gradient from high to low exists between the adjacent rocks and zone 2 where zone 2 is located closer to the ground surface the opposite situation prevails the upper highly conductive part of the zone was found to have high natural flow rates whereas in the lower highly conductive part the groundwater flow rates were very low close to the rate of molecular diffusion

hydrochemical investigations at finnsjon sweden abstract ground water collected from within and around a highly conductive low angle fracture zone in crystaline rock has been studied in relation to drilling and sampling methods water quality and hydrogeochemical interpretation air flush percussion drilling was demonstrated to be efficient down to 200 250 m at greater depths large amounts of drilling debris and increasing groundwater contamination from air dissolution become apparent a stepwise drilling sampling procedure using water flush rotary drilling in combination with water analysis carried out on site using a mobile laboratory is recommended for future studies the chemistry of the finnsjon ground waters shows a sharp contact between saline and non saline compositions this contact corresponding to a highly conductive low angle fracture zone zone 2 this zone is therefore a horizon along which ground waters of contrasting age and chemistry come into contact and partially mix this mixing has produced a highly supersaturated water resulting in the precipitation of calcite this is most evident in fractures within the more conductive upper part of zone 2 thus partly forming a seal between the two groundwater environments comparison of the finnsjon saline waters with other saline environments particularly in the fennoscandian shield has shown that the ground waters are dominantly marine in origin but with clear modifications resulting from water rock interaction apparent radiocarbon ages range from 9000 to 15000 years in those waters containing tritum levels below detection limits these ages are considered too young and are thought to have resulted from mainly carbon 14 dilution caused by groundwater mixing during the holocene when large quantities of glacial melt water were available this mixing process is also supported by the oxygen 18 data

fluctuations of the svalbard barents sea ice sheet during the last 150 000 years abstract on spitsbergen western svalbard three major glacial advances have been identified during the weichselian all three reached the continental shelf west of the svalbard archipelago radiocarbon luminescence and amino acid dating of interbedded interstadial and interglacial sediments indicate that these glacial advances have early isotope stage 5d middle stage 4 and late weichselian ages stage 2 an additional more local advance has been dated to isotope stage 5b the late weichselian ice sheet expanded across the entire barents sea however in the south western barents sea the late weichselian till is the only till above eemian sediments indicating that the early and middle weichselian ice advances were restricted to the svalbard archipelago and the northern barents sea a major problem with the onshore sites is the dating of events beyond the range of the radiocarbon method to overcome this the onshore record has been correlated with marine cores from the continental slope and the deep sea west of svalbard where a chronology has been established by oxygen isotope stratigraphy ice rafted detritus ird was used as the main monitor of glaciation the ird record closely mirrors the glaciation history as interpreted from the onshore sections during the late weichselian the largest ird peak occurred during deglaciation a pattern also postulated for the earlier events given this the results from the marine cores indicate that the ages for the first glacial advances during the weichselian were a few thousand years older than interpreted from the onshore stratigraphy

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

deglaciation of the central barents sea abstract the marine based barents sea ice sheet covered the polar continental shelf north of norway and western russia during the last glacial maximum initial ice sheet retreat along the western margin is well established while the retreat pattern in the interior parts of the ice sheet remains poorly known here we present new geological data from the central barents sea the results are based on analysis of several marine geophysical datasets including geomorphological mapping of multibeam swath bathymetry data and analysis of seismic and acoustic stratigraphy the new results provide insights into the configuration and dynamics of the ice sheet during its retreat across the central barents sea in particular they show clear changes in the location of the main ice divides and domes with ice flow becoming gradually more topographically controlled as deglaciation progressed major troughs were characterised by episodic retreat and reoccurring cycles of fast and slow ice flow sometimes leading to stagnation and ice shelf formation meanwhile adjacent bank areas were covered by comparatively slowly retreating ice although evidence of streaming ice is also seen locally

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

microseismicity linked to gas migration and leakage on the western svalbard shelf the continental margin off prins karls forland western svalbard is characterized by widespread natural gas seepage into the water column at and upslope of the gas hydrate stability zone we deployed an ocean bottom seismometer integrated into the masox monitoring arctic seafloor ocean exchange automated seabed observatory at the pinch out of this zone at 389 m water depth to investigate passive seismicity over a continuous 297 day period from 13 october 2010 an automated triggering algorithm was applied to detect over 220 000 short duration events sdes defined as having a duration of less than 1 s the analysis reveals two different types of sdes each with a distinctive characteristic seismic signature we infer that the first type consists of vocal signals generated by moving mammals likely finback whales the second type corresponds to signals with a source within a few hundred meters of the seismometer either due east or west that vary on short tens of days and seasonal time scales based on evidence of prevalent seafloor seepage and subseafloor gas accumulations we hypothesize that the second type of sdes is related to subseafloor fluid migration and gas seepage furthermore we postulate that the observed temporal variations in microseismicity are driven by transient fluid release and due to the dynamics of thermally forced seasonal gas hydrate decomposition our analysis presents a novel technique for monitoring the duration intensity and periodicity of fluid migration and seepage at the seabed and can help elucidate the environmental controls on gas hydrate decomposition and release

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

reconstruction of holocene patterns of change in a high arctic coastal landscape southern sassenfjorden svalbard abstract abrupt shifts in sediment supply relative sea level permafrost regime glacier state snow cover and sea ice conditions associated with holocene climate changes control processes operating on high arctic coasts and make reconstructions of their past evolution a significant research challenge this study attempts to describe the development of the coastal zone in southern sassenfjorden svalbard throughout the holocene focusing on the styles of adjustment to major landscape changes five marine terraces mt1 5 are identified and assessed spatial and chronological analysis suggests that the highest terrace mt5 is pre lgm last glacial maximum and that mt4 3 underwent rapid uplift 151 and 11 4 mm year respectively shortly prior to 11 061 174 cal yr bp and became fully terrestrial by 9100 years ago as indicated by emergence rates during the holocene thermal maximum htm uplift rates for mt2 1 slowed to 5 and 2 mm year respectively with suggested emergence between 7200 and 6800 cal yr bp a final 2 m uplift of the relict alluvial plain probably happened during the medieval warm period 1200 950 cal yr bp most recent coastal development ad 1912 2012 is characterised by episodes of coastal erosion on the cliff and progradation of the noiselva delta interactions between sea ice snow cover permafrost wind and wave regimes are assessed to understand their implications on future coastal development in a warming climate

geological setting and deformation history of a low angle fracture zone at finnsjon sweden abstract in 1984 the swedish nuclear fuel and waste management company skb initiated detailed investigations involving the geological geophysical hydrological and geochemical character of a fracture zone for this purpose a low angle ssw dipping fracture zone in a foliated granodiorite of svecokarelian age approximately 1 8 ga within the sub cambrian peneplain of northeastern uppland central eastern sweden was identified and investigated by extensive drilling the initial formation of this zone which is estimated to have taken place approximately 1 7 ga ago as a result of ductile deformation was followed by shearing during ductile brittle transitional conditions and subsequently by brittle deformation it formed as a thrust in a 20 30 km wnw ese trending strike slip fault zone the fracture zone is approximately 100m wide with an anastomosing shear pattern and is displaced by subvertical faults late reactivation of the zone has occurred preferentially in the upper part which is now open permitting water transport the palaeo flow paths indicated by bedrock alteration and fracture infillings show that the hydraulic flow system in the rock mass has become increasingly restricted during geologic time flow now occurs predominantly along discrete zones which were initiated more than 1 7 ga ago and since then have been repeatedly reactivated the most intense penetrative fracturing associated with hydrothermal activity occurred more than 1 0 ga ago fractures and fracture zones most likely to conduct water i e forming transport pathways between a repository and the biosphere tend to be those with a long and complex tectonic history

stress field evolution of the southernmost andean cordillera from paleostress analysis argentine tierra del fuego this work has been funded by projects ctm2011 30241 c02 02 ctm201460451 c2 2 p and ctm2017 89711 c22 p of the spanish r d national plan and by pict funding from anpcytfoncyt argentina

the russian component of an arctic ice sheet during the last glacial maximum abstract the extent of late weichselian glaciation in arctic russia remains a problem our model of 1995 1998 suggests a continuous and long lived ice sheet centered on the kara sea other reconstructions suggest a smaller and diachronous glaciation the vast majority of dates support the model of restricted glaciation we show that these dates are inconsistent with the geologic record of ice flow across the kara barents divide with second order glacial geology of kola peninsula and with evidence for glacial surges they are also inconsistent with late weichselian climate of the arctic with eurasian continental paleohydrology including meltwater drainage systems cataclysmic megafloods major transgressions of the caspian sea and with the entire paleogeographic context of northern eurasia we believe that due to impeded ventilation of the pleistocene arctic ocean these dates are often too old and that recycling and contamination of the samples would also contribute to the dating errors destructive impacts of late glacial ice sheet surges and megafloods upon the arctic glacial sequences would also aggravate the situation by ignoring the dates until these problems are addressed we find that the field evidence supports continuous glaciation of arctic russia at the lgm and that the resulting ice sheet was part of an arctic ice sheet that included an ice shelf in the arctic ocean and ice sheets in greenland and north america we present 3 d reconstructions of the arctic ice sheet and with an enlarged antarctic ice sheet we show that the ice volume is equivalent to an lgm sea level that was 130 135 m lower than at present the reconstructions depict the arctic ice sheet before and after massive thawing of the bed that allows partial gravitational collapse of the overlying ice with a minimal change in ice volume

from mountain top to the deep sea deglaciation in 4d of the northwestern barents sea ice sheet abstract the timing of the deglaciation of the northern barents sea ice sheet bsis documented in terrestrial and offshore records from the svalbard archipelago is reviewed we present new cosmogenic nuclide cn ages from formerly unexplored inland areas of northern svalbard to investigate the timing of thinning of past local ice domes cn data are compared with radiocarbon ages from marine and terrestrial deposits 10be isotope cn dates on erratic boulders from interior svalbard suggest that glacier surfaces in northern and western svalbard thinned 950 650 m from 26 4 ka and continued over an extended period until 16 ka initial ice retreat from the western outer to the inner shelf began at 20 5 ka and in storfjordrenna southwest of svalbard around 19 18 ka retreat of grounded ice from the northern outer to the inner shelf did not begin before 15 9 ka we therefore suggest increasing summer insolation and aridification due to atmospheric circulation changes and perennial sea ice cover as the main mechanisms for the ice thinning and grounded ice retreat from the outer shelves before and during the heinrich 1 event the frontal position of the grounded ice sheet however did not change during several millennia despite further thinning in interior northern svalbard the inner shelf areas rapidly deglaciated towards the fjord mouths along the western coasts between 15 and 14 ka and became ice free before and during meltwater pulse 1a mwp 1a the collapse of the ice shelves from the inner shelf towards the fjord mouths and inner fjords occurred on a decadal to centennial time scale based on overlapping radiocarbon ages from marine sediment cores in addition to cn data from erratic boulders in lowlands we suggest that additional mechanisms must have caused this rapid collapse together with reduced moisture supply in the accumulation areas we assume that subsurface warm atlantic water masses that reached the western shelf after 17 5 ka may have accelerated debuttressing of the ice shelves in addition to the bolling warming that kicked in around 15 1 ka due to increased insolation and the global sea level rise called mwp 1a conservative calculations estimate the contribution of only the northwestern part of the bsis to sea level rise with 0 0004 cm yr 1 between 26 and 16 ka and 0 02 cm yr 1 in assumed 300 years between 15 and 14 ka

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

reconstructing the retreat dynamics of the bjornoyrenna ice stream based on new 3d seismic data from the central barents sea the stability of contemporary ice sheets is influenced by the discharge from ice streams corridors of fast flowing ice bounded by ice flowing an order of magnitude slower reconstructions of palaeo ice stream dynamics contribute to our understanding of ice stream sensitivity to the ocean climate system and can aid in the numerical modelling and prediction of future changes in contemporary ice sheets here we use 3d seismic data covering 13 000 km2 in the central bjornoyrenna bear island trough barents sea to investigate the record of ice streaming preserved on the seafloor and on a buried palaeo seafloor surface the unusually broad coverage and high resolution of the dataset as well as its location in the central area of the trough enables improved reconstruction of dynamics of the former bjornoyrenna ice stream in terms of number of streaming events their trajectory and their relative age sequence during deglaciation our results reveal major changes in the configuration and flow dynamics of the ice stream with up to 10 flow switching events identified for the first time we also document ice streaming sourced from the eastern barents sea around the time of the lgm this high degree of flow variability is suggested to have resulted from climate driven changes in ice sheet geometry and ice divide migration and variations in topography that influenced calving at the ice stream terminus

deglacial holocene svalbard paleoceanography and evidence of meltwater pulse 1b abstract better understanding of deglacial meltwater pulses mwps is imperative for future predictions of human induced warming and abrupt sea level change because of their potential for catastrophic damage however our knowledge of the second largest meltwater pulse mwp 1b that occurred shortly after the start of the holocene interglacial remains very limited here we studied fossil ostracods as paleoenvironmental indicators of water depth salinity and temperature in two marine sediment cores from storfjorden svalbard margin the arctic ocean to investigate near field i e areas located beneath continental ice sheets at the last glacial maximum evidence of mwp 1b the depositional environment changed from a cold bathyal environment to a warmer bathyal environment at 11 300 yr bp indicating incursion of warm atlantic water into the nordic seas and eventually to a cold neritic environment by 11 000 yr bp because of melting of the svalbard barents sea ice sheet and resultant isostatic rebound this process corresponds to rapid relative sea level fall of 40 80 m of mwp 1b from 11 300 to 11 000 yr bp

postglacial uplift and relative sea level changes in finnmark northern norway abstract the outer coast of finnmark in northern norway is where the former fennoscandian and barents sea ice sheets coalesced this key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines but only a few existing radiocarbon dates constrain their chronology here we present three holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of finnmark located at the islands soroya and rolvsoya and at the nordkinn peninsula we analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments terrestrial plant fragments from these transitions were then radiocarbon dated radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14 600 cal yr bp we find that the gradients of the shorelines are much lower than elsewhere along the norwegian coast because of substantial uplift of the barents sea also the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor after the younger dryas the coast emerged 1 6 1 0 cm per year until about 9500 9000 cal yr bp between 9000 and 7000 cal yr bp relative sea level rose 2 4 m and several of the studied lakes became submerged at the outermost locality rolvsoya relative sea level was stable at the transgression highstand for more than 3000 years between ca 8000 and 5000 cal yr bp deposits in five of the studied lakes were disturbed by the storegga tsunami ca 8200 8100 cal yr bp

overview of the fracture zone project at finnsjon sweden abstract at the finnsjon site central sweden a 100 m wide low angle fracture zone in granodiorite zone 2 has been studied by means of borehole investigations this has included core and geophysical logging as well as hydraulic tests and groundwater sampling zone 2 was developed at 1 7 1 6 ga as a ductile shear zone at a depth of approximately 10 15 km and repeated reactivation has occurred during precambrian time and later today the upper boundary of the zone is defined in nine boreholes at depths ranging from 100 to 295 m pumping tests have demonstrated that the upper part of the zone is highly water conductive with a transmissivity in excess of 10 3 m 2 s 1 from tracer tests the equivalent single fracture hydraulic conductivity was calculated to be 0 03 0 2 ms 1 this extremely high transmissivity and conductivity over such a large areal extent can be speculated to be the result of recent opening of zone 2 during the last inland ice period in situ measurements of the natural groundwater flow show that the flow is high 67 90 m 3 m 2 year 1 at the upper boundary of zone 2 whereas near stagnant conditions occur at the lower boundary and in the relict saline water beneath the zone isotope data suggest a complex origin for the saline water the hydraulic head measurements as well as the groundwater chemistry strongly suggest that the low angle zone 2 acts as a hydraulic barrier preventing ground water from percolating downward through the zone these studies have helped to focus on repository safety assessment problems which hitherto had been oversimplified for the benefit of performance models furthermore the results have shown that these low angle large scale fracture zones are likely to be even more important controls than steep zones when considering bedrock stability rock stress regimes and lateral groundwater flow patterns quantification of such phenomena should provide an invaluable input into the various safety assessment performance codes for model validation and siting criteria for a repository

a gps velocity field for fennoscandia and a consistent comparison to glacial isostatic adjustment models in fennoscandia the process of glacial isostatic adjustment gia drives ongoing crustal deformation crustal velocities from gps observations have proved to be a useful tool in constraining gia models however reference frame uncertainties plate tectonics intraplate deformations as well as other geophysical processes contaminate the results former studies have shown that different international terrestrial reference frames have large discrepancies especially in the vertical component which hamper geophysical interpretation we present new velocity estimates for the fennoscandian and north european gps network our gps velocity field is directly realized in a gia reference frame using this method named the gia frame approach we are able to constrain gia models with minimal influence of errors in the reference frame or biasing signals from plate tectonics the drawbacks are more degrees of freedom that might mask real but unmodeled signals monte carlo tests suggest that our approach is robust at the 97 level in terms of correctly separating different models of ice history but depending on deformation patterns the identified earth model may be slightly biased in up to 39 of cases we compare our results to different one and three dimensional gia models employing different global ice load histories the gia models generally provide good fit to the data but there are still significant discrepancies in some areas we suggest that these differences are mainly related to inaccuracies in the ice models and or lateral inhomogeneities in the earth structure under fennoscandia thus gia models still need to be improved but the gia frame approach provides a base for further improvements

iceland rising solid earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling a broad uplift occurs in iceland in response to the retreat of ice caps which began circa 1890 until now this deformation signal has been measured primarily using gps at points some distance away from the ice caps here for the first time we use satellite radar interferometry interferometric synthetic aperture radar to constrain uplift of the ground all the way up to the edge of the largest ice cap vatnajokull this allows for improved constraints on the earth rheology both the thickness of the uppermost earth layer that responds only in an elastic manner and the viscosity below it the interferometric synthetic aperture radar velocities indicate a maximum displacement rate of 24 4 and 31 4 mm yr at the edge of vatnajokull during 1995 2002 and 2004 2009 respectively the fastest rates occur at outlet glaciers of low elevation where ice retreat is high we compare the observations with glacial isostatic adjustment models that include the deglaciation history of the icelandic ice caps since 1890 and two earth layers using a bayesian approach we derived probability density functions for the average earth model parameters for three satellite tracks based on our assumptions the three best fit models give elastic thicknesses in the range of 15 40 km and viscosities ranging from 4 10 1018 pa s

exploring the ingredients required to successfully model the placement generation and evolution of ice streams in the british irish ice sheet abstract ice stream evolution is a major uncertainty in projections of the future of the greenland and antarctic ice sheets accurate simulation of ice stream evolution requires an understanding of a number of ingredients that control the location and behaviour of ice stream flow here we test the influence of geothermal heat flux grid resolution and bed hydrology on simulated ice streaming the palaeo record provides snapshots of ice stream evolution with a particularly well constrained ice sheet being the british irish ice sheet biis we implement a new basal sliding scheme coupled with thermo mechanics into the bisicles ice sheet model to simulate the evolution of the biis ice streams we find that the simulated location and spacing of ice streams matches well with the empirical reconstructions of ice stream flow in terms of position and direction when simple bed hydrology is included we show that the new basal sliding scheme allows the accurate simulation for the majority of biis ice streams the extensive empirical record of the biis has allowed the testing of model inputs and has helped demonstrate the skill of the ice sheet model in simulating the evolution of the location spacing and migration of ice streams through millennia simulated ice streams also prompt new empirical mapping of features indicative of streaming in the north channel region ice sheet model development has allowed accurate simulation of the palaeo record and allows for improved modelling of future ice stream behaviour

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

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

ice stream retreat dynamics inferred from an assemblage of landforms in the northern barents sea abstract palaeo records of rapid ice stream retreat are important as they can be used to identify the processes involved and inform investigations of present day ice masses here we document a previously unknown retreat stage in northernmost bjornoyrenna bear island trough in the northern barents sea representing the youngest stage in a stepwise retreat of the bjornoyrenna ice stream we present a descriptive landsystem model for retreat of a marine based ice stream which provides new insights into the glacial dynamics of the episodic retreat stages this model captures the landforms produced during a cycle of 1 fast ice stream flow 2 intense calving of large icebergs locked in a dense matrix of smaller icebergs probably from a collapsed ice shelf 3 ice stream stagnation 4 ice stream floating off forming an ice shelf as the grounding line retreats and eventually 5 ice shelf disintegration we hypothesize that the presented ice stream retreat model reflects glacial surging the formation of corrugated furrows in the study area is consistent with interpretation of similar features in pine island bay west antarctica which are interpreted to have been formed during a massive ice shelf break up and associated grounding line retreat two directions of past ice flow are indicated from streamlined glacial landforms in the study area ice flow from north north east is indicated for the last glacial maximum and an early phase of deglaciation whereas a shift to flow from north north west from an ice dome located over hinlopenstretet svalbard is indicated for the latest deglaciation phases of the bjornoyrenna ice stream

hydraulic testing and modelling of a low angle fracture zone at finnsjon sweden abstract the hydraulic characteristics of a gently dipping fracture zone in crystalline rock at the finnsjon test site in sweden are described the information is derived from single hole injection tests of different packer spacings including very detailed tests in 0 11 m sections in a few borehole segments in addition detailed hydraulic interference tests were performed by pumping in different parts of the zone and monitoring pressure changes in multiple section observation boreholes the results of the hydraulic testing show that the fracture zone is composed of two to five thin highly conductive subzones in the boreholes the uppermost subzone is consistently located close to the upper boundary of the major zone and can be correlated over several hundreds of metres there is evidence of both lateral and vertical hydraulic anisotropy along the zone the interference tests show that the fracture zone is delimited by semi permeable boundaries probably constituted by steeply dipping fracture zones the results of the hydraulic testing are used to simulate the pressure responses obtained in the observation boreholes by numerical modelling

the antarctica component of postglacial rebound model ice 6g_c vm5a based on gps positioning exposure age dating of ice thicknesses and relative sea level histories

hydrogeological behaviour of some fault zones in a carbonate aquifer of southern italy an experimentally based model complex flow circulation patterns are likely to be present in fault controlled groundwater flow systems such as carbonate aquifers nevertheless not much information is available for faults in carbonates and their hydrogeological behaviour is often neglected in conceptual and numerical models the understanding of this aspect of subsurface fluid flow has been improved in a carbonate aquifer where hydrogeological investigations at site scale demonstrated the existence of fault zones that act as barriers the hydraulic conductivity of the fault core is as low as that of siliciclastic rocks that represent the regional aquitard of the carbonate aquifer despite the lower permeability the fault zones allow a significant groundwater flowthrough and a good interdependence of piezometric heads upgradient and downgradient of the faults because of this discontinuous heterogeneity the aquifer looks like a basins in series system where seasonal springs can be detected along some fault zones as a function of groundwater level fluctuations

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

a review of postglacial emergence on svalbard franz josef land and novaya zemlya northern eurasia the pattern of postglacial emergence in the barents sea is pivotal to constraining the timing of deglaciation and extent and thickness of the last ice sheet in northern eurasia this review unites records of holocene relative sea level from svalbard franz josef land and novaya zemlya to better understand the geometries of past ice sheet loads emergence data from northern eurasia confine the maximum area of glacier loading to the northwestern barents sea where 100 m of emergence is measured on kongs ya deglacial unloading commenced on western and northern spitsbergen c 13 12 14 c ka ago and by c 10 5 14 ck a on eastern svalbard and more distal sites on franz josef land and novaya zemlya the marine limit phase c 13 12 14 c ka on western and northern spitsbergen is characterized by the construction of spits indicating a dominance of long shore drift over stormgenerated fetch reflecting extensive sea ice coverage of coastal areas at sites in proximity to the ice sheet margin on western and northern spitsbergen there is evidence for a transgressive regressive cycle c 6 4 14 c ka possibly reflecting back migration of displaced mantle material a modern transgression is inferred from the marine erosion of 17th century cultural features and 14 c ages of whalebone and terrestrial peat buried by modern storm gravels that place sea level at its present position by c 2 to 1 ka ago the greatest observed emergence on franz josef land occurs on bell island with a marine limit at 49 m aht formed c 10 14 c ka available emergence data since 9 ka show rising strandlines toward the southwest at b0 3 m km the northern limit of emergence on franz josef land is poorly constrained because relative sea level data is sparse north of 80 30 0 n in contrast to svalbard and franz josef land the marine limit on northern novaya zemlya is only 10 15 m above high tide and formed between 6 5 and 5 0 14 c ka when global sea level was stabilizing all sites show little apparent emergence during the past 2 ka with the youngest raised landforms at identical heights to storm beaches this minimal glacio isostatic signature on novaya zemlya and on vaygach island where deglaciation commenced 10 ka ago indicates ice sheet thicknesses of o1 5 km the spatial variation in emergence for the barents sea indicates that western and northern spitsbergen and novaya zemlya were near the reactive margin of the ice sheet and these areas sustained the briefest ice coverage 2 6 ka and were probably not in isostatic equilibrium in contrast central and eastern svalbard and southern franz josef land were beneath a substantial ice load and probably sustained this load for c 10 14 c ka and achieved isostatic equilibrium isostasy residual from an ice sheet model portrays well the general pattern of uplift and load response at the centre of ice sheets but deviates substantial at the ice sheet margin or areas covered by thin ice like novaya zemlya

late weichselian glaciation of the russian high arctic a numerical ice sheet model was used to reconstruct the late weichselian glaciation of the eurasian high arctic between franz josef land and severnaya zemlya an ice sheet was developed over the entire eurasian high arctic so that ice flow from the central barents and kara seas toward the northern russian arctic could be accounted for an inverse approach to modeling was utilized where ice sheet results were forced to be compatible with geological information indicating ice free conditions over the taymyr peninsula during the late weichselian the model indicates complete glaciation of the barents and kara seas and predicts a maximum sized ice sheet for the late weichselian russian high arctic in this scenario full glacial conditions are characterized by a 1500 m thick ice mass over the barents sea from which ice flowed to the north and west within several bathymetric troughs as large ice streams in contrast to this reconstruction a minimum model of glaciation involves restricted glaciation in the kara sea where the ice thickness is only 300 m in the south and which is free of ice in the north across severnaya zemlya our maximum reconstruction is compatible with geological information that indicates complete glaciation of the barents sea however geological data from severnaya zemlya suggest our minimum model is more relevant further east this in turn implies a strong paleoclimatic gradient to colder and drier conditions eastward across the eurasian arctic during the late weichselian

laterally heterogeneous lithosphere asthenosphere and sub lithospheric properties under laurentia and fennoscandia from glacial isostatic adjustment

glacial isostatic adjustment of scandinavia and northwestern europe and the radial viscosity structure of the earth s mantle summary during the last glacial maximum lgm large ice sheets covered scandinavia the barents sea and the northern british isles subsequent to the lgm the ice sheets disappeared and the solid earth readjusted towards a new isostatic equilibrium the glacial isostatic adjustment process is documented in numerous observations for example palaeoshorelines covering the last deglaciation phase and ongoing crustal deformations monitored by gps stations for example the bifrost project in this study we use palaeoshoreline data from scandinavia the barents sea and northwestern europe nw as well as radial crustal velocities from the bifrost campaign to infer the radial viscosity structure of the earth s mantle underneath scandinavia and nw europe a global inverse procedure based on the neighbourhood algorithm allows us to explore the hypothesis of a low viscosity zone in the upper mantle which has been proposed in the literature our results indicate a low viscosity zone underneath the barents sea with viscosities between 1019 and 1020 pa s in a depth interval of 160 200 km no such low viscosity zone is found underneath scandinavia and no clear indication for such a zone underneath nw europe the thickness of the rheological lithosphere increases from 60 to 70 km underneath nw europe and the barents sea towards values exceeding 120 km underneath scandinavia

late weichselian deglacial history of the svyataya saint anna trough northern kara sea arctic russia abstract marine sediment core and seismic records from the svyataya saint anna trough provide new insight into the distribution of late weichselian glacial coverage ice retreat pattern and post glacial environments in the northern barents and kara seas these records indicate that the saint anna trough was filled with grounded glacier ice which likely reached the shelf edge during the late weichselian maximum several radiocarbon dates suggest early deglaciation of the deep axial part of the trough prior to 13 3 ka two sandy beds in the deglacial section of the cores imply distinct pulses of iceberg calving and or melting which were probably associated with stepwise retreat of the ice margin morainic ridges and glacial sole markings in the western part of the saint anna trough indicate that the northern central barents sea was a site of a large ice mass during deglaciation a smaller ice cap is inferred for the northern kara plateau at later stages ice retreat on the western flank of the trough was directed towards franz josef land and was presumably facilitated by a separation of the barents sea and novaya zemlya ice domes deglaciation of the saint anna trough was completed by ca 10 ka high post glacial sediment fluxes between 10 and 8 ka were probably related to sea floor coastal erosion and or siberian river discharge during the rising sea level

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

high resolution modeling of the advance of the younger dryas ice sheet and its climate in scotland abstract ice sheet modeling tightly constrained by empirical studies provides an effective framework to reconstruct past climatic and environmental conditions scotland was severely affected by the abrupt climate change associated with the younger dryas stade during which an extensive ice sheet formed across the west highlands after a period of ice free conditions here a quasi three dimensional time dependent ice flow mass balance model is developed and applied to scotland at 1 km resolution the flow model is based on the driving stress approximation with an additional longitudinal correction term essential at this scale of operation surface mass balance is driven by temperature and precipitation changes and further mass wastage is achieved through an empirically defined calving term the ice dynamics and mass balance components are coupled through the equation for mass continuity which is integrated through time over a finite difference grid which yields the geometric evolution of the ice sheet initial experiments reveal the model to be relatively insensitive to internal parameters but highly sensitive to mass balance furthermore these experiments indicate that scotland is readily susceptible to glaciation with large glaciers building up on the flanks of ben nevis after a temperature depression of 2 5 c under present day precipitation the younger dryas is modeled using a grip temperature series locally adjusted for amplitude and a systematic series of runs enables the isolation of the climate which best matches mapped ice limits this optimum fit configuration requires an annual temperature cooling of 8 c and the introduction of substantial west east and south north precipitation gradients of 40 and 50 respectively to the present day regime under these conditions a series of substantial independent regional ice centers develop in agreement with trimline studies and after 550 years the modeled ice sheet closely resembles the maximum limits as indicated by field mapping however modeled ice continues to expand beyond 550 yr in conflict with the mapped ice limits which suggest a prolonged period of stability this discrepancy may be explained by the onset of extreme aridity ca 400 yr into the stade associated with a southern migration of the polar front leading to a reduction in atmospheric circulation which effectively starved the ice sheet of its moisture source preventing further expansion introduction of an additional 20 reduction in precipitation to the optimum fit regime after 350 yr brings the modeled ice sheet to equilibrium substantiating this conclusion

subglacial water storage and drainage beneath the fennoscandian and barents sea ice sheets abstract subglacial hydrology modulates how ice sheets flow respond to climate and deliver meltwater sediment and nutrients to proglacial and marine environments here we investigate the development of subglacial lakes and drainage networks beneath the fennoscandian and barents sea ice sheets over the late weichselian utilizing an established coupled climate ice flow model we calculate high resolution spatio temporal changes in subglacial hydraulic potential from ice sheet build up 37 ka bp to complete deglaciation 10 ka bp our analysis predicts up to 3500 potential subglacial lakes the largest of which was 658 km2 and over 70 of which had surface areas

ocean mass from grace and glacial isostatic adjustment 1 we examine geoid rates and ocean mass corrections from two published global glacial isostatic adjustment gia models both of which have been used in previous studies to estimate ocean mass trends from gravity recovery and climate experiment grace satellite gravity data these two models are different implementations of the same ice loading history and use similar mantle viscosity profiles the model results are compared with each other and with geoid rates determined from grace during august 2002 to november 2009 when averaged over the global ocean the two models have rates that differ by nearly 1 mm yr 1 of ocean mass with the first model giving a correction closer to 2 mm yr 1 and the second closer to 1 mm yr 1 by comparing the two models we have discovered that 50 of the difference is caused by a global land ocean mean in the first model while it is appropriate to include this mean when subtracting gia effects from measurements of sea level change measured by tide gauges or satellite altimetry the mean should not be included when subtracting gia effects from ocean mass variations derived from satellite gravity data when this mean is removed the ocean mass corrections from the two models still disagree by 0 4 mm yr 1 we trace the residual difference to the fact that the first model also has large trends over the ocean related to large rates in its predicted degree 2 order 1 geoid coefficients such oceanic trends are not observed by grace nor are they predicted by the second model and they are shown to be inconsistent with the polar wander rates predicted by the first model itself if these two problems are corrected we find that the two model predictions agree at the 3 level on the basis of this analysis we conclude that the ocean mass correction for grace is closer to 1 mm yr 1 than 2 mm yr 1 although significant uncertainties remain

the effect of low permeability fault zones on groundwater flow in a compartmentalized system experimental evidence from a carbonate aquifer southern italy the hydrogeological behaviour of fault zones in carbonate aquifers is often neglected in conceptual and numerical models furthermore no information is available regarding the relationships between piezometric levels when significant compartmentalization occurs due to the occurrence of low flow fault zones the aim of this study was to refine the conceptualization of subsurface flow in faulted carbonate aquifers and to analyse relationships between sub basins within a compartmentalized aquifer system in southern italy the interactions between compartments that straddle low flow faults were investigated over four hydrologic years using a statistical approach to compare i the hydraulic heads within two wells located up and down gradient of tectonic discontinuities as well as ii the rainfall and piezometric levels the results of this study suggest that a set of barriers exists between the wells and therefore the total head loss observed between the wells approximately 80 m should be distributed across several aquitards with one aquitard exhibiting a relatively high permeability or low degree of integrity due to slight differences in permeability transient conditions in aquitards can occur over relatively short periods which is in agreement with the results of the statistical data analysis consequently rather than being caused by pure aquitards aquifer system compartmentalization likely results from slight differences in the permeability between lower permeability fault zones and adjacent higher permeability protoliths copyright 2014 john wiley sons ltd

glacial isostatic adjustment associated with the barents sea ice sheet a modelling inter comparison the 3d geometrical evolution of the barents sea ice sheet bsis particularly during its late glacial retreat phase remains largely ambiguous due to the paucity of direct marine and terrestrial based evidence constraining its horizontal and vertical extent and chronology one way of validating the numerous bsis reconstructions previously proposed is to collate and apply them under a wide range of earth models and to compare prognostic isostatic output through time with known relative sea level rsl data here we compare six contrasting bsis load scenarios via a spherical earth system model and derive a best fit 2 parameter using rsl data from the four main terrestrial regions within the domain svalbard franz josef land novaya zemlya and northern norway poor 2 values allow two load scenarios to be dismissed leaving four that agree well with rsl observations the remaining four scenarios optimally fit the rsl data when combined with earth models that have an upper mantle viscosity of 0 2 2 1021 pa s while there is less sensitivity to the lithosphere thickness ranging from 71 to 120 km and lower mantle viscosity spanning 1 50 1021 pa s gps observations are also compared with predictions of present day uplift across the barents sea key locations where relative sea level and gps data would prove critical in constraining future ice sheet modelling efforts are also identified

numerical reconstructions of the eurasian ice sheet and climate during the late weichselian abstract geological investigations undertaken through the quaternary environments of the eurasian north programme established ice sheet limits for the eurasian arctic at the last glacial maximum lgm sedimentary records of palaeo ice streams and uplift information relating to ice sheet configuration and the pattern of deglaciation ice sheet numerical modelling was used to reconstruct a history of the eurasian ice sheet compatible with these geological datasets the result was a quantitative assessment of the time dependent behaviour of the ice sheet its mass balance and climate and predictions of glaciological products including sediments icebergs and meltwater at the lgm ice cover was continuous from scandinavia to the arctic ocean margin of the barents sea to the north and the kara sea to the east in the west along the continental margin between the norwegian channel and svalbard the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans ice streams may also have been present in bathymetric troughs to the north between svalbard and franz josef land further east however the ice sheet was thinner across the kara sea the ice thickness was predicted to be less than 300 m while on severnaya zemlya the ice cover may have been thinner at the lgm than at present it is likely that the taymyr peninsula was mainly free of ice at the lgm in the south the ice margin was located close to the shoreline of the russian mainland the climate associated with this ice sheet is maritime to the west and in stark contrast desert like in the east atmospheric general circulation modelling has revealed that such a contrast is possible under relatively warm north atlantic conditions because a circulation system develops across the kara sea isolating it from the moisture laden westerlies which are diverted to the south ice sheet decay began through enhanced iceberg calving in the deepest regions of the barents sea which caused a significant ice embayment within the bear island trough by about 12 000 years ago further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas ice decay was complete by about 10 000 years ago

the svalbard barents sea ice sheet historical current and future perspectives abstract the history of research on the late quaternary svalbard barents sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years since the onset of scientific research there in the early 19th century svalbard has been a natural laboratory where ideas and concepts have been tested and played an important but rarely acknowledged role in the break through of the ice age theory in the 1870 s the history of how the scientific perception of the svalbard barents sea ice sheet developed in the mid 20th century also tells a story of how a combination of fairly scattered and often contradictory observational data and through both deductive and inductive reasoning could outline a major ice sheet that had left but few tangible fingerprints since the 1980 s with increased terrestrial stratigraphical data ever more marine geological evidence and better chronological control of glacial events our perception of the svalbard barents sea ice sheet has changed the first reconstructions depicted it as a static concentric single domed ice sheet with ice flowing from an ice divide over the central northern barents sea that expanded and declined in response to large scale late quaternary climate fluctuations and which was more or less in tune with other major northern hemisphere ice sheets we now increasingly perceive it as a very dynamic multidomed ice sheet controlled by climate fluctuations relative sea level change as well as subglacial topography substrate properties and basal temperature in this respect the svalbard barents sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine based ice sheets build up and decay

glaciers on svalbard survived the holocene thermal optimum abstract about 60 of svalbard is covered by glaciers today but many of these glaciers were much reduced in size or gone in the early holocene high resolution modeling of the glacial isostatic rebound reveals that the largest glaciers in nordaustlandet and eastern spitsbergen survived the early holocene warming while the smaller more peripheral glaciers especially in the northwest started to form about 5 500 years ago and reached 3 4 of their current size about 600 years ago relative sea level has been rising during the last few millennia in the north and western parts of spitsbergen while land still emerges in the remaining part of svalbard here we show that this sea level rise in the northwest is caused by the regrowth of glaciers in the mid to late holocene that slowed down and even reversed the post glacial isostatic uplift and caused the crust to subside over large areas of spitsbergen

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago ii extended results for high resolution load models summary in paper i breuer wolf 1995 a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the svalbard archipelago was given the study was based on a simple model of the barents sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin in the present paper the newly developed high resolution load model barents 2 and land uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern barents sea a comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations although values above 110 km are most common for this parameter in contrast to this there are indications of a lateral variation of asthenosphere viscosity whereas values in the range 10 8 1020 pa s are inferred for locations close to the continental margin 1020 102 pa s are suggested further away from the margin a study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model barents 2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected an estimate of the influence of the fennoscandian ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the barents sea ice sheet by about 10 per cent

constraints on the late weichselian ice sheet over the barents sea from observations of raised shorelines abstract direct evidence for late weichselian grounded glacier ice over extensive areas of the barents sea is based largely on indirect observations including elevations of old shorelines on svalbard and arguments of isostatic rebound such isostatic models are discussed here for two cases representing maximum and minimum ice sheet reconstructions in the former model the ice extends over the kara sea whereas in the latter the ice is limited to the barents sea and island archipelagos comparisons of predictions with observations from a number of areas including spitsbergen nordaustlandet edgeoya kong karls land franz josef land novaya zemlya and finnmark support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum this ice sheet is likely to have had the following characteristics conclusions that are independent of assumptions made about the earth s rheological parameters i the maximum thickness of this ice was about 1500 2000 m with the centre of the load occurring to the south and east of kong karls land ii the ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western spitsbergen was about 800 m iii to the north of svalberg and frans josef land the ice sheet extended out to the northern shelf edge iv retreat of the grounded ice across the southern barents sea occurred relatively early such that this region was largely ice free by about 15 000 bp v by 12 000 bp the grounded ice had retreated to the northern archipelagos and was largely gone by 10 000 bp vi the ice sheet may have extended to the kara sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on novaya zemlya models for the palaeobathymetry for the barents sea at the time of the last glacial maximum indicate that large parts of the barents sea were either very shallow or above sea level providing the opportunity for ice growth on the emerged plateaux as well as on the islands but only towards the end of the period of fennoscandian ice sheet build up

past and present day ice mass variation on svalbard revealed by superconducting gravimeter and gps measurements 1 we use superconducting gravimeter sg and global positioning system gps measurements from ny alesund svalbard to infer changes in ice mass loss between september 1999 and september 2010 we find that during this period the gravity rate and vertical crustal velocities are changing with time adding to evidence about varying rates of ice mass loss the gravity rate varies through 10 years of observation 0 23 gal yr in 2000 2002 3 22 gal yr in 2002 2005 and 1 10 gal yr in 2005 2010 the gravity changes agree well with the observed uplift rates measured by gps which are 4 4 11 3 and 7 4 mm yr over the same periods in addition we generate model predictions which account for past and present day ice mass variation we find that the models under predict both the observed uplift rates and gravity changes

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

simulation of vatnajokull ice cap dynamics 1 we apply a coupled model of ice sheet dynamics and subglacial hydrology to investigate the dynamics and future evolution of the vatnajokull ice cap iceland in this paper we describe a new theoretical approach to introducing longitudinal stress coupling in the ice dynamics solution and we analyze our ability to simulate the main features of vatnajokull with and without longitudinal stress effects equilibrium ice cap configurations exist for vatnajokull but under a narrow range of climatic boundary conditions equilibrium reconstructions have an average ice thickness greater than what is observed at vatnajokull consistent with our inability to capture surge dynamics in vatnajokull s outlet glaciers hydrological regulation of basal flow longitudinal stress coupling and a simple parameterization of the subglacial heat flux from vatnajokull s geothermal cauldrons all help to reduce average ice thickness in the equilibrium reconstructions but cases that reproduce the present day ice volume have an ice cap area that is 5 10 less than the actual ice cap present day reconstructions that adopt a realistic climate spin up for the period 1600 1990 provide improved fits to the modern day ice cap geometry this indicates that climatic disequilibrium also plays a significant role in dictating vatnajokull s morphology simulations for the period 1600 2300 illustrate that air temperature is the dominant control on vatnajokull s volume and area longitudinal stress coupling and hydrological coupling both increase vatnajokull s sensitivity to future warming

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

glacial isostatic adjustment in the static gravity field of fennoscandia in the central part of fennoscandia the crust is currently rising because of the delayed response of the viscous mantle to melting of the late pleistocene ice sheet this process called glacial isostatic adjustment gia causes a negative anomaly in the present day static gravity field as isostatic equilibrium has not been reached yet several studies have tried to use this anomaly as a constraint on models of gia but the uncertainty in crustal and upper mantle structures has not been fully taken into account therefore our aim is to revisit this using improved crustal models and compensation techniques we find that in contrast with other studies the effect of crustal anomalies on the gravity field cannot be effectively removed because of uncertainties in the crustal and upper mantle density models our second aim is to estimate the effects on geophysical models which assume isostatic equilibrium after correcting the observed gravity field with numerical models for gia we show that correcting for gia in geophysical modelling can give changes of several kilometer in the thickness of structural layers of modeled lithosphere which is a small but significant correction correcting the gravity field for gia prior to assuming isostatic equilibrium and inferring density anomalies might be relevant in other areas with ongoing postglacial rebound such as north america and the polar regions

elevation changes of the fennoscandian ice sheet interior during the last deglaciation the dynamics of ice sheet interiors during the last deglaciation are poorly constrained hindering evaluation of ice sheet models we provide direct evidence of fennoscandian ice sheet fis interior behaviour during deglaciation through surface exposure dating our results demonstrate early thinning of the fis prior to the younger dryas yd 12 8 11 7 ka interior thinning in central norway was concurrent with retreat along the coastline exposing ice free mountainous tracts potentially as early as 20 15 ka the fis then formed moraines in these ice free tracts during the yd this is contrary to current hypotheses advocating a landscape fully covered by cold inactive ice during this period present empirical and model reconstructions fail to capture rapid interior down wastage increasing uncertainties in ice sheet volume estimates and sea level contributions

the validation and sensitivity of a model of the icelandic ice sheet abstract the derivation and implementation of a three dimensional model used to investigate the last glacial maximum ice sheet across iceland by hubbard et al 2006 a modelling insight into the icelandic last glacial maximum ice sheet quaternary science reviews is described it is applied at 2 km resolution and requires boundary distributions of topography geothermal heat flux surface air temperature and mass balance calculated using a temperature index approach based on reference distributions of annual temperature and precipitation the model enables the variables of ice thickness stress strain and temperature to evolve freely through time and caters for the coupling of thermally triggered basal sliding with non local dynamics through the computation of longitudinal stresses it is driven through perturbations in sea level and annual precipitation and temperature a series of contemporary experiments are initiated to validate the model against the present ice cover across iceland forcing the model from ice free conditions with the 1961 1990 reference climatology yields a good simulation of all the ice masses except for vatnajokull where the model falls well short of its present margins however an experiment forced from ice free conditions for 1000 years with a 2 c cooling perturbation followed by 100 years of reference climatology yields a good simulation of vatnajokull in addition to other ice masses implying that it is a remnant icecap inherited from the little ice age and perpetuated through strong ice elevation mass balance coupling an ensemble of experiments are initiated to investigate the sensitivity of the optimum lgm model isolated in hubbard et al 2006 ice sheet volume and aspect ratio but not area are found to be sensitive to basal boundary conditions in particular to the choice of sliding parameter and the applied geothermal conditions due to strong topographic control in particular the configuration of offshore bathymetry and shelf break ice sheet volume and area is sensitive to the calving parameter and sea level change however an asymmetrical response indicates that the ice sheet is effectively decoupled from further climatic deterioration once it advances to the continental shelf break these experiments imply that there is little latitude in the selection of model parameters which yields an ice sheet compatible with the available evidence and that the optimum lgm experiment represents a sound result by inference at least 63 of the optimum lgm ice sheet was grounded below sea level implying potential instability with the onset of deglaciation

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

dating high arctic holocene relative sea level changes using juvenile articulated marine shells in raised beaches high arctic raised beaches provide evidence for changes in relative sea level rsl sea ice extent storminess and variations in sediment supply in many high arctic areas driftwood and whale bone are usually the preferred targets for radiocarbon dating with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile articulated specimens of astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest radiocarbon dates from articulated valves of a borealis from eight raised beaches from billefjorden svalbard provide a chronology for holocene beach ridge formation and rsl change that compares favourably to the most precise records developed from elsewhere in svalbard using driftwood or whale bone we demonstrate the value of this new approach by comparing our record with previously published rsl data from eastern svalbard to test different models of late weichselian ice load in this region we find support for a major ice dome centred south and east of kong karls land but no evidence for a significant ice dome located over easternmost spitsbergen or southern hinlopen strait as proposed from recent marine geophysical survey the approach is potentially applicable elsewhere in svalbard and the high arctic to address questions of rsl change and beach ridge chronology and hence wider questions regarding palaeoclimate and ice load history

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

massive blow out craters formed by hydrate controlled methane expulsion from the arctic seafloor widespread methane release from thawing arctic gas hydrates is a major concern yet the processes sources and fluxes involved remain unconstrained we present geophysical data documenting a cluster of kilometer wide craters and mounds from the barents sea floor associated with large scale methane expulsion combined with ice sheet gas hydrate modeling our results indicate that during glaciation natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates upon ice sheet retreat methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters we propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets