in situ determination of creep properties of sea ice with the pressuremeter a series of pressuremeter creep and relaxation tests was carried out in the spring of 1987 in a sea ice cover at igloolik northwest territories for the purpose of testing some new procedures for in situ determination of creep properties of sea ice compared with a similar field study carried out 9 years earlier the present investigation included some clear improvements not only in the instrumentation and data acquisition system but also in the data interpretation and processing in particular it is shown that consistent values of creep parameters can be obtained only if proper consideration is made of the amount of stress redistribution taking place before and during each new load application key words in situ testing pressuremeter sea ice creep properties stress redistribution

a two phase approach to the simulation of the combined isotope salinity signal of marine ice a modified boundary layer box diffusion model is used to simulate the production of the combined oxygen isotope salinity signal of a body of marine ice the final signal is considered to be the result of fractionation and segregation processes occurring first upon the formation of frazil crystals in suspension and second during their accumulation and consolidation due to the advancement of a freezing front the model results are compared to oxygen isotope and salinity values in a 45 m marine ice core from the nansen ice shelf antarctica parameters more suitable to the modeling of marine ice as opposed to sea ice are introduced and conclusions are drawn on the origin of the impurity characteristics of marine ice including the still unresolved question of its anomalously low salinity

sea ice production over the laptev sea shelf inferred from historical summer to winter hydrographic observations of 1960s 1990s the winter net sea ice production nsip over the laptev sea shelf is inferred from continuous summer to winter historical salinity records of 1960s 1990s while the nsip strongly depends on the assumed salinity of newly formed ice the nsip quasi decadal variability can be linked to the wind driven circulation anomalies in the laptev sea region the increased wind driven advection of ice away from the laptev sea coast when the arctic oscillation ao is positive implies enhanced coastal polynya sea ice production and brine release in the shelf water when the ao is negative the nsip and seasonal salinity amplitude tends to weaken these results are in reasonable agreement with sea ice observations and modeling

in situ measurements of the evolution of young sea ice 1 we present data from in situ measurements of the salinity evolution of young sea ice in the arctic the measurements were carried out with very high vertical and temporal resolution over the course of a few days until the ice had reached a thickness of around 20 cm the measured bulk salinity profiles show that during ice growth sea ice salinity is continuous across the ice ocean interface and that there is no instantaneous loss of salt at the advancing front measured salt fluxes emanating from the ice are as high as 90 g m 2 h 1 during the first few hours of new ice formation and are roughly half as large during later stages of the experiments the bulk salinity within the ice decreases continuously with time from the ocean water salinity to a near steady state value of around 4 parts per thousand ppt these results are interpreted with ideas from mushy layer theory using a rayleigh number to analyze gravity drainage as the driving mechanism for the observed salt loss in our experiments gravity drainage occurs for a critical rayleigh number of around 10 in close agreement with earlier theoretical and experimental studies

tank study of physico chemical controls on gas content and composition during growth of young sea ice during an ice tank experiment samples were taken to study the processes of acquisition and alteration of the gas properties in young first year sea ice during a complete growth warming cooling cycle the goal was to obtain reference levels for total gas content and concentrations of atmospheric gases o2 n2 co2 in the absence of significant biological activity the range of total gas content values obtained 3 5 to 18 ml of gas per kilo of ice was similar to previous measurements or estimates however major differences occurred between the current and quiet basins showing the role of water dynamics at the ice water interface in controlling bubble nucleation processes extremely high co2 concentrations were observed in all the experiments up to 57 in volume parts it is argued that these could have resulted from two unexpected biases in the experimental settings concentrations of bubbles nucleated at the interface are controlled by diffusion both from the ice water interface towards the well mixed reservoir and between the interface water and the bubble itself this double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water towards values close to atmospheric as the ice cover builds up

evolution of the lower saxony basin abstract the lower saxony basin is a 300 km long and 65 km wide late jurassic and early cretaceous trough which parallels the northern margin of the rhenish massif this basin became inverted during the senonian and paleocene the lower saxony basin is the most important oil province of germany past production amounts to 200 10 6 t of oil 1 5 10 9 bbl the lower saxony basin is superimposed on the late carboniferous variscan foredeep basin and the frontal structures of the variscan fold belt during the permian to middle jurassic the area formed part of the northwest european basin differential subsidence of the lower saxony basin was initiated during the late jurassic and persisted till albian time this involved reactivation of permo carboniferous fracture systems by divergent wrenching a major aptian deep seated laccolith is evident in the western part of the lower saxony basin during the senonian and paleocene sinistral convergent wrenching induced uplift of the basin floor and folding of its sedimentary fill the margins of the inverted lower saxony basin are thrust over the adjacent stable platform areas the differential subsidence of the lower saxony basin can be related to a period of major crustal extension in the north sea rift basin inversion coincides with important orogenic events in the alpine system and is thought to have been induced by intra plate compressional stresses

a relationship between heat transfer to sea ice and temperature salinity properties of arctic ocean waters it is demonstrated that the characteristic temperature salinity relationship shown by thermocline waters of the arctic ocean can be reproduced using a simple model based on transfer of heat directly from these waters to sea ice from this we deduce that there is direct sensible heat flux from waters of atlantic origin to the ice cover such interaction could play a major role in determining the physical properties of arctic water masses

modeling the salinity profile of undeformed arctic sea ice the salinity of sea ice affects its physical and ecological properties here a multilayer one dimensional halo thermodynamic sea ice model is used to simulate the vertical salinity profile of undeformed arctic sea ice the model successfully reproduces the desalination pattern observed in first year fy and multi year my ice the model can also be integrated with a prescribed time independent salinity profile substantial differences in the simulated mass balance and ice ocean salt flux arise depending on the salinity after 10 years into the simulation the annual mean ice thickness is 2 85 m with the interactive halodynamic component compared to 2 53 m 2 29 m with a prescribed time independent vertically varying constant salinity profile modelling sea ice salinity is especially important when sea ice is transitioning from a my to fy ice regime thus including a halodynamic component in sea ice models would significantly improve simulations of future climate

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

fission track thermochronology of the ruhla crystalline complex new constraints on the post variscan thermal evolution of the nw saxo bohemian massif abstract to help clarify the relative and absolute timing of post variscan cooling and exhumation processes in the ruhla crystalline complex rcc situated in the nw part of the saxo bohemian massif eight zircon and eleven apatite fission track ages and nine apatite track length measurements have been obtained zircon fission track ages support an existing model of post variscan exhumation of the rcc as three discrete blocks the eastern and western blocks show cooling from peak metamorphic conditions to below 260 30 c by ca 300 ma and exposure by 296 ma the central block shows a later cooling to below 260 30 c by ca 270 ma and exposure at the surface by ca 256 ma apatite fission track data reveal late cretaceous accelerated cooling through the apatite partial annealing zone 120 to 60 c this can be correlated with tectonic inversion at this time the apatite data also indicate that the rocks of the rcc were at temperatures above 110 10 c before ca 85 ma this requires either an anomalously high palaeo geothermal gradient of ca 60 c km 1 during the late cretaceous or that the rcc region was originally covered by up to 1400 m of now eroded jurassic and cretaceous sedimentary rocks we favour a combination of both factors with accelerated erosion of missing overburden during a period of increased heat flow initiated at ca 85 ma

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

rollovers in salt tectonics the inadequacy of the listric fault model abstract rollover anticlines are syn sedimentary extensional structures common in salt tectonics that are classically considered to result from layer bending during hangingwall displacement above a listric normal fault however theoretical considerations and seismic images of natural examples put in question the validity of the listric fault model from which rollover growth is steady state by nature and controlled by the relative displacement of two blocks we used laboratory experiments of gravity driven deformation of brittle ductile models simulating salt tectonics processes to study in which circumstances rollovers are obtained both in time and space it is argued that rollover growth is a nonsteady process that results from a mechanical instability whose critical lifetime can be divided in three characteristic stages birth growth and decay in kinematic terms the development of a synthetic or antithetic rollover requires a three block system an upslope block and a downslope block that move downslope and that separate from each other on top of an extending decollement layer lying above a basement block synthetic and antithetic rollovers developed with upward concave shapes whatever the sense of shear in the salt layer and can pass laterally to each other without transform fault this points out that the concave shape of a rollover base is not an argument in favour of listric faulting the concave shape simply results from the connection between a steeply dipping normal fault and a flat lying or gently dipping decollement

a physically based parameterization of gravity drainage for sea ice modeling we incorporate a physically derived parameterization of gravity drainage in terms of a convective upwelling velocity into a one dimensional thermodynamic sea ice model of the kind currently used in coupled climate models our parameterization uses a local rayleigh number to represent the important feedback between ice salinity porosity permeability and desalination rate it allows us to determine salt fluxes from sea ice and the corresponding evolution of the bulk salinity of the ice in contrast to older established models that prescribe the ice salinity this improves the predictive power of climate models in terms of buoyancy fluxes to the polar oceans and also the thermal properties of sea ice which depend on its salinity we analyze the behavior of existing fixed salinity models elucidate the physics by which changing salinity affects ice growth and compare against our dynamic salinity model both in terms of laboratory experiments and also deep ocean calculations these comparisons explain why the direct effect of ice salinity on growth is relatively small though not always negligible and sometimes different from previous studies and also highlight substantial differences in the qualitative pattern and quantitative magnitude of salt fluxes into the polar oceans our study is particularly relevant to growing first year ice when gravity drainage is the dominant mechanism by which ice desalinates we expect that our dynamic model which respects the underlying physics of brine drainage should be more robust to changes in polar climate and more responsive to rapid changes in oceanic and atmospheric forcing

multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the arctic ocean the conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy imb deployed in the arctic ocean after imb deployment the ice thinned from 1 95 m in late august to 1 46 m by mid october 2008 from then on ice growth until mid june 2009 increased the ice thickness to 3 12 m the ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high frequency variations due to diurnal and synoptic scale atmospheric forcing these signals propagated downward with damped magnitude and temporal lag the competition of oceanic and conductive heat flux dominated the low frequency variations of ice growth however high frequency variations in ice growth were controlled largely by the oceanic heat flux from mid november 2008 to mid june 2009 the average oceanic heat flux along a track from 86 2 n 115 2 w to 84 6 n 33 9 w was 7 1 w m2 this was in agreement with that derived from an imb deployed in 2005 about 1 5 to the north of our buoy we attributed the relatively high oceanic heat flux 10 15 w m2 observed during autumn and early winter to summer warming of the surface ocean upward mixing of warm deep water as observed when our buoy drifted over the shallow region of the lomonosov ridge 85 4 85 9 n 52 2 66 4 w demonstrated the impact of bathymetry on the oceanic heat flux under ice cover and consequently on the basal ice mass balance 2013 american geophysical union all rights reserved

an isotopic method of estimating conductive heat flux through antarctic first year sea ice the deuterium concentration profile in a first year antarctic sea ice cover is used to deduce a growth rate curve applying a previously published model time variations of the conductive heat flux throughout the growth period are then estimated from this growth rate curve results indicate that the isotopic determination of sea ice growth rate can be considered as an alternate method for determining the conductive heat flux through a young sea ice cover however there is need for a further test of the method by measuring in situ temperatures and growth rates during the formation of first year sea ice and by analyzing the isotopic composition of ice samples taken simultaneously along selected profiles during the growth period

late cretaceous intraplate thrusting in central europe effect of africa iberia europe convergence not alpine collision a well established event of intraplate basin inversion and basement thrusting affected central europe in late cretaceous time it is widely accepted to have resulted from the collision of the alpine orogen with europe s margin at that time an early alpine orogen located on the leading edge of the adria microplate still lay far southeast of its present day position and had entered a phase of extension after a first orogenic event characterized by w to nw directed thrusting this configuration is not likely to have induced ssw nne directed thrusting and folding in the future european foreland that was still separated from the alpine wedge by a strip of oceanic lithosphere by contrast the onset of intraplate contraction coincides with an important change in relative motion between the european and african plates at ca 90 ma africa s sse directed sinistral transform motion relative to europe changed to ne directed convergence this agrees well with the timing and kinematics of intraplate thrusting in central europe structures of similar age and kinematics occurring in southern france spain and north africa suggest that the late cretaceous pulse of contraction was caused by pinching west central europe s thin lithosphere between baltica and africa only since the onset of n directed thrusting in the alps in paleocene or eocene time are the kinematics of the alps and their european foreland compatible indicating that mechanical coupling between africa europe and the adria microplate had been achieved

intraformational fluid flow in the thuringian syncline germany evidence from stable isotope data in vein mineralization of upper permian and mesozoic sediments abstract vein mineralization observed in boreholes quarries and outcrops of upper permian and mesozoic sediments in the thuringian syncline germany was investigated for the first time by petrography electron microprobe analysis and stable isotope analysis the objective was a characterization of paleo fluid systems within this basin veins are mostly restricted to nw se trending fault systems and comprise carbonates calcite dolomite minor sulfates gypsum anhydrite celestite barite and rarely sulfides they are variably distributed within the late paleozoic to mesozoic succession calcite vein mineralization occurs in almost all triassic strata though dominating in the lower muschelkalk subgroup mu gypsum anhydrite veins occur in the middle keuper subgroup km middle muschelkalk subgroup mm middle and upper buntsandstein subgroup sm so as well as in the upper permian zechstein sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the upper permian and triassic sediments crystallization from descending meteoric waters was observed especially for calcite veins in the lower muschelkalk but also for gypsum anhydrite veins in the upper buntsandstein mineralization from ascending carbonate ph buffered warm waters was restricted to individual parts of the southern deep reaching main border fault zone of the thuringian syncline mixing and fault crossing fluid movements are subordinate within the thuringian syncline we conclude that no large scale cross formational fluid flow occurred in thuringian syncline over the last millions of years

towards a method for high vertical resolution measurements of the partial pressure of co2 within bulk sea ice fluxes of atmospheric co2 have been reported over sea ice during winter and spring these fluxes are partly driven by the gradient of the co2 concentration between sea ice and the atmosphere we present a new non destructive method to measure the pco2 of bulk sea ice at its in situ temperature this method is based on an equilibration procedure between sea ice and a standard gas of known co2 concentration the concentration is measured by gas chromatography with a precision of 5 tests were performed on artificial standard sea ice and confirmed the reproducibility of the technique in the range of precision of the gas chromatograph to test the accuracy of this method the first profiles of pco2 measured in bulk sea ice are reported and compared with direct in situ measurements of brine pco2 over depth integrated intervals

investigations on physical and textural properties of arctic first year sea ice in the amundsen gulf canada november 2007 june 2008 ipy cfl system study we report sea ice temperature and bulk salinity measurements as well as textural analysis from 33 first year drift and fast ice stations sampled between november 2007 and june 2008 in the southern beaufort sea amundsen gulf canadian arctic during the international polar year circumpolar flaw lead ipy cfl system study we use this significant dataset to investigate the halo thermodynamic evolution of sea ice from growth to melt a strong desalination phase is observed over a small time window in the spring using calculated proxies of sea ice permeability brine volume fraction and of the intensity of brine convection rayleigh number we demonstrate that this phase corresponds to full depth gravity drainage initiated by a restored connectivity of the brine network with warming in the spring most stations had a textural sequence typical of arctic first year ice with granular ice overlying columnar ice unusual textural features were observed sporadically sandwiched granular ice platelet ice and draped platelet ice we suggest that turbulence in leads and double diffusion in strong brine plumes following the refreeze of cracks are plausible mechanisms for the formation of these textures

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

modeling brine and nutrient dynamics in antarctic sea ice the case of dissolved silica sea ice ecosystems are characterized by microalgae living in brine inclusions the growth rate of ice algae depends on light and nutrient supply here the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one dimensional model the model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component characterized by one nutrient namely dissolved silica dsi in the model dsi follows brine motion and is consumed by ice algae depending on physical ice characteristics the brine flow is either advective diffusive or turbulent the vertical profiles of ice salinity and dsi concentration are solutions of advection diffusion equations the model is configured to simulate the typical thermodynamic regimes of first year antarctic pack ice the simulated vertical profiles of salinity and dsi qualitatively reproduce observations analysis of results highlights the role of convection in the lowermost 5 10 cm of ice convection mixes saline nutrient poor brine with comparatively fresh nutrient rich seawater this implies a rejection of salt to the ocean and a flux of dsi to the ice in the presence of growing algae the simulated ocean to ice dsi flux increases by 0 115 compared to an abiotic situation in turn primary production and brine convection act in synergy to form a nutrient pump the other important processes are the flooding of the surface by seawater and the percolation of meltwater the former refills nutrients near the ice surface in spring the latter if present tends to expell nutrients from the ice in summer

impact of heterogeneous permeability distribution on the groundwater flow systems of a small sedimentary basin summary ground water flow systems of shallow sedimentary basins are studied in general by analyzing the fluid dynamics at the real world example of the thuringian basin the impact of the permeability distribution and density differences on the flow velocity pattern the salt concentration and the temperature distribution is quantified by means of transient coupled simulations of fluid flow heat and mass transport processes simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non constant fluid density three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport the relation of permeability between aquiclude and aquifer the variance and the correlation length of the log normal permeability distribution density dependent flow due to temperature or concentration gradients is of minor importance for the distribution of the flow systems but can lead to increased mixing dissolution of salt thermal convection is in general not present the dominant driver of groundwater flow is the topography in combination with the permeability distribution the results obtained for the thuringian basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins

ice formation in subglacial lake vostok central antarctica abstract the investigation of chemical and isotopic properties in the lake ice from the vostok ice core gives clues to the mechanisms involved in ice formation within the lake a small lake water salinity can be reasonably deduced from the chemical data possible implications for the water circulation of lake vostok are developed the characteristics of the isotopic composition of the lake ice indicate that ice formation in lake vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake

a non destructive method for measuring the salinity and solid fraction of growing sea ice in situ we describe an instrument developed to make in situ measurements of salinity and solid fraction profiles in growing sea ice the vertical resolution of the measurements is up to a few millimeters with a temporal resolution of up to fractions of a second the technique is based on impedance measurements between platinum wires around which sea ice grows data obtained using this instrument in laboratory experiments are in good agreement with theoretical predictions in a field test in the arctic the bulk salinity of growing sea ice has been measured in situ throughout the whole depth of the ice layer the data are compared with bulk salinities obtained from ice cores and confirm the general understanding that the bulk salinity in ice core studies is significantly underestimated in the lower parts of the cores the approach can also be used in other glaciological applications and for general studies of two phase two component porous media

strain rate and grain size effects in ice on etudie la resistance de compression de la glace polycristalline en fonction de la taille des grains et de la vitesse de deformation on note l apparition d une inversion dans l effet de la taille des grains lorsque le domaine des vitesses de deformations est etendu a 10 7 s 1

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

thin ice thickness from satellite thermal imagery sea ice thickness is an important parameter in the surface energy exchange and mass balance of the polar oceans remote sensing offers the opportunity to monitor thin ice routinely we combine measurements of surface temperature from an advanced very high resolution radiometer avhrr with a thermodynamic ice growth model to estimate thin ice and its thickness distribution during the cold season in a beaufort sea area of perennial ice we find that thin ice up to a meter thick had a concentration of 18 in december 1990 and 3 in april 1991 thin ice concentrations near the ice edge in the greenland sea range from 20 to 50 these avhrr derived estimates generally compare well with thickness observations from upward looking sonar given the uncertainties in all the model inputs estimated from avhrr such as radiative and turbulent heat flux components and surface albedo we find that ice thickness is estimated with an uncertainty of roughly 50 the uncertainty in the cumulative thickness distribution is about 3 for ice less than 20 cm thick and about 9 for ice around 1 m thick these magnitudes are significantly smaller than the variations in thin ice observed by satellite in different months and regions we conclude that avhrr is capable of resolving the regional and seasonal variations in thin ice to a level of accuracy useful both for establishing a climatology and for testing ice models

salt fingering in subsea permafrost some stability and energy considerations salt fingering appears to be a viable mechanism for salt transport in the thawing layer talik above ice bonded permafrost near the seabed in the arctic shelves baker and osterkamp 1988 these saltwater infusions occur where concentrated brines overlie less concentrated or less dense brines at least two mechanisms exist which cause this condition near the seabed first salts rejected during sea ice growth result in the formation of a concentrated brine layer on the seabed and second salts rejected during sediment freezing near the seabed can result in a concentrated brine layer forming within the deeper and yet unfrozen sediments unstable salt fingering in a vertical tube containing a porous media is known to develop whenever the density gradient exceeds the critical value z 3 390 k gkb2 wooding 1959 this article presents a simple derivation and interpretation of this critical condition in terms of competing time scales a convective time scale represents the time required for formation of a vertical wedge shaped flow due to density differences and a diffusive time scale represents the time required to diffuse the density difference horizontally across the layer the critical density gradient is determined from a ratio of these time scales the stability criterion suggests downward salt fingering whenever the density gradient at prudhoe bay exceeds 6 2 10 5 g cm 4 in thawed subsea permafrost sediments maximum predicted velocity of the saltwater fingering is about 2 m d 1 and this is consistent with the direction and magnitude indicated by measurements of pressure gradients and numerical modeling in the thawing permafrost the energy dissipated by viscous forces in the thawed layer balances the potential energy added by the salt fingers caused by concentrated brines on the seabed

the finne fault zone central germany structural analysis of a partially inverted extensional fault zone by balanced cross sections the finne fault zone located in central germany to the southwest of the harz mountains was studied by means of detailed map analysis investigations of fault displacement and balanced cross sections for the most strongly deformed area in the center of the fault zone ca 50 of total fault zone length the system of the finne fault zone shows a nearly 100 km long straight flexure that symbolizes the morphological and geological northeastern border of the thuringian basin in the central part which should be surveyed here the fault zone corresponds to a distinctive narrow band of highly deformed triassic sedimentary rocks the northwestern and especially the southeastern parts of the research area are developed as several parallel branch faults in the southeastern elongation of the fault zone which is not part of our survey the sedimentary cover is missing here it is possible to gain insight to the fact that the basement is also involved to the kinematics of the fault zone based on our results we propose a subdivision of the fault zone into four sectors from the northwest to the southeast we interpret the structure of these sectors to reflect 1 a compressional flexure 2 an overthrust graben and 3 a partially inverted and folded half graben in the extreme southeast 4 the fault zone is characterized by an anticline with some strike slip movement parallel to the fold axis this segmentation is caused by a thrust fault system whose strike direction deviates slightly from that of the earlier formed graben system the structural configuration can be explained by a two phase deformation in which the contractional strain exceeded the preceding extensional deformation in the investigated area the horizontal shortening attains a maximum of ca 1 km the present study confirms many earlier hypotheses presents new results on the deformation history of the fault zone and attempts to evaluate the deformation in a regional geological context the results of earlier studies were refined and revised using modern methods and a unified structural and kinematic model of the finne fault zone was created

intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central german platform abstract the structural evolution of central europe reflects contrasting tectonic regimes after the variscan orogeny during mesozoic cenozoic time the brittle deformation related to each tectonic regime is localized mainly along major fault zones creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events by contrast fracture patterns in less deformed domains often provide a pristine structural inventory we investigate the brittle deformation of a relatively stable wide area of the central german platform using fault slip data to identify the regional stress fields required to satisfy the data in a non classical approach and in order to avoid local stress variations and misinterpretations the fault slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks direct stress tensor inversion was performed through an iterative refining process and the computed stress tensors were verified using field based observations criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events which begins with a post triassic normal faulting regime with 3 axis trending ne sw the deformation then follows by strike slip and thrust faulting regimes with a change of 1 axis from n s to ne sw supposedly in the late cretaceous two younger events are characterized by cenozoic normal and oblique thrust faulting regimes with nw se trending 3 and 1 axes respectively the fracture patterns of both the cover and basement rocks appear to record the same states of stress

mesozoic intraplate deformation in the southern part of the central european basin results from large scale 3d modelling abstract the central european basin is an intracontinental basin that initially formed due to long lasting thermal subsidence accompanied with several tectonic phases of extension during mesozoic times locally thick evaporites were incorporated in the deformation and led to the formation of detached structures salt pillows and diapirs at the end of the late cretaceous the formation of sub basins and half grabens became interrupted by a short term event of contraction especially along the northern and southern edges of the basin lithospheric shortening resulted in basin inversion and the uplift of large basement blocks hence the present day s structural framework shows a complex pattern of kinematically and chronologically variable structures herein we unravelled these structures for the altmark region in northern saxony anhalt central germany we used regional depth maps reflection seismics and borehole data analysed by use of large scale subsurface mapping and 3d modelling techniques to completely re evaluate the structures in the late palaeozoic to cenozoic sedimentary basin succession our results show a high variability of tectonic structures narrow and distributed in parts reactivated normal fault zones huge inverted basins thin skinned thrust faults detachment folds and large basement thrusts the style of deformation significantly changed during the region s evolution this is indicated by particular structural kinematic thermal and rheological conditions which existed for the individual phases of basin formation and inversion and probably persist until today

linkages between salinity and brine channel distribution in young sea ice a high resolution study of bulk salinity was undertaken on laboratory grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures ice samples at two different stages of development were compared with respect to physical state brine distribution and brine channel structures cold growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels areas of high bulk salinity are found to correspond directly to the positions of the brine channels and these areas are surrounded by ice that shows significant brine depletion it is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases the redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice the distribution of brine in warm ice is shown to be more homogeneous and independent of brine channel structures a number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution

modelling antarctic fast ice growth an existing thermodynamic ice growth model semtner 1976 has been tested for its ability to predict the growth of fast ice in mcmurdo sound antarctica significant discrepancies between observed and predicted ice thicknesses were found to occur primarily due to the presence of sub ice platelets and the formation of a snow ice layer although these ice growth processes are not well enough understood to permit rigorous physical modelling it is shown that fairly simple modifications to the model greatly improve the accuracy of the thickness predictions and serve to highlight the importance of these processes in the antarctic fast ice environment surface flooding and snow ice formation are assumed to occur immediately upon the establishment of a positive hydrostatic water level and a surface temperature in excess of a critical value above which interconnecting channels in the ice matrix permit the flow of water to the surface the presence of the sub ice platelet layer is assumed to increase columnar ice growth at a rate proportional to the volume fraction of ice in the platelet layer a simple technique but one that permits estimates of platelet enhanced growth without detailed knowledge of oceanographic conditions the resulting model predictions are in close agreement with measurements of fast ice growth and decay in mcmurdo sound however data suitable for testing the model over a complete range of conditions and over multi year cycles are not available at the present time

der untere buntsandstein des germanischen beckens das germanische becken das sich von der sudlichen nordsee bis nach polen erstreckte sank vom perm bis einschlieslich trias mehr oder minder kontinuierlich ab die absenkung wurde im unteren buntsandstein durch die ablagerung von klastika kompensiert die vornehmlich aus dem sich hebenden sudlichen vorland herantransportiert wurden im allgemeinen nehmen die korngrosen in richtung becken mitte ab entsprechend der entfernung zum liefergebiet

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

the role of snow on the thermal dependence of microwave backscatter over sea ice our understanding of snow distribution in the polar regions is severely restricted owing to the heterogeneity both in space and time of this solid precipitate processes such as vapor and mass fluxes across the interface are to a large extent controlled by the presence and geophysical state of the snow cover on sea ice numerous studies have shown the importance of snow cover in ecosystem processes and particularly in photosynthetically active radiation extinction researchers are currently exploiting developments in electromagnetic interaction theory in an attempt to measure snow thickness distributions remotely in this paper we investigate the dependence of radar backscatter on snow thickness over smooth first year ice we use data from the seasonal sea ice monitoring and modeling site located in the canadian archipelago results show that the thermodynamics of the snow cover affect wave propagation attenuation and scattering through the control that brine volume exerts on interfacial characteristics of the snow and ice layers the effect is subtle and specific to certain ranges of salinity surface roughness and thickness of sea ice we describe the phenomenon responsible for this effect using a microwave model consistently for both complex effective permittivities and backscatter coefficients coupled to a one dimensional model we validate the physical principles using in situ field data we then discuss the potential of synthetic aperture radar in estimating snow thickness distributions under these specific conditions using both observed and modeled microwave scattering

ice production and brine formation in storfjorden svalbard brines which appear as salty and cold bottom water layers on arctic shelves form by salt rejection during sea ice formation high ice production occurs in latent heat polynyas such as the one that appears in storfjorden under northerly winds using ers 2 synthetic aperture radar imagery we observed the ice cover in storfjorden over the winter 1997 1998 revealing an area of over 6000 km 2 of the open water and thin ice that are characteristic of a polynya changes in the polynya extent correlated well with a simple wind driven polynya size algorithm furthermore using a frazil ice formation algorithm and the hypothesis of ice accumulation at the lee side of the polynya we distinguished between open water thin ice and fast pack ice the average polynya width during the 6 winter months was about 30 km with a maximum of 130 km in march thus storfjorden was composed of 5 6 fast and pack ice and 1 6 polynya open water occupied about half of the polynya the other half was composed of brash ice and thin ice involved in ridging and rafting a total ice volume of 40 km 3 was produced in storfjorden between november 15 1997 and may 15 1998 about 57 of it was formed in the open water area 9 in the thin ice area and 34 in the fast pack ice area this ice production released more than 1 gt gigaton of salt able to increase the salinity of the storfjorden waters by 1 4 practical salinity units psu assuming that brine enriched waters are 0 3 psu more saline than the parent waters the above salt release is able to ventilate storfjorden 4 5 times during the course of the productive season