scattering of vhf radio waves from within the top 700 m of the antarctic ice sheet and its relation to the depositional environment a case study along the syowa mizuho dome fuji traverse

self organization in the thermomechanical flow of ice sheets this paper uses a three dimensional thermomechanical ice sheet model to investigate the initiation and evolution of ice streams within ice sheets ice streams are distinguished within general ice sheet flow by their relatively fast of the order of kilometers per year velocity and are thought to be crucial in determining the response of ice sheets to climatic change we show that streaming can arise solely as a consequence of internal feedback between ice sheet flow and temperature inhomogeneities in topography and or geology are not therefore necessary conditions for ice stream development this spatial patterning replaces the large scale surging reported from previous modeling work in one horizontal dimension we suggest that surging is restricted to situations where ice flow is channelized e g valley glaciers and that it is replaced by streaming where horizontal ice flow is unconstrained ice sheets the ice streams in some of our experiments show switching behavior reminiscent of that known from the siple coast ice streams west antarctica the cause appears to be the competition for ice discharge and drainage basin area between adjacent ice streams this may lead to the gradual reduction of a stream s discharge below the threshold necessary to generate enough frictional heat to maintain warm viscous ice at the ice stream bed in this case the stream will stagnate abruptly which then prompts localized ice thickening and the initiation of a new stream in a different location

re evaluation of paleo accumulation parameterization over northern hemisphere ice sheets during the ice age examined with a high resolution agcm and a 3 d ice sheet model

the impact of parametric uncertainty and topographic error in ice sheet modelling ice sheet models isms developed to simulate the behaviour of continental scale ice sheets under past present or future climate scenarios are subject to a number of uncertainties from various sources these sources include the conceptualization of the ism and the degree of abstraction and parameterizations of processes such as ice dynamics and mass balance the assumption of spatially or temporally constant parameters such as degree day factor atmospheric lapse rate or geothermal heat flux is one example additionally uncertainties in ism input data such as topography or precipitation propagate to the model results in order to assess and compare the impact of uncertainties from model parameters and climate on the glimmer ice sheet model a parametric uncertainty analysis pua was conducted parameter variation was deduced from a suite of sensitivity tests and accuracy information was deduced from input data and the literature recorded variation of modelled ice extent across the pua runs was 65 for equilibrium ice sheets additionally the susceptibility of ism results to modelled uncertainty in input topography was assessed resulting variations in modelled ice extent in the range of 0 8 6 6 are comparable to that of ism parameters such as flow enhancement basal traction and geothermal heat flux

bacterial fossil record in whale falls petrographic evidence of microbial sulfate reduction abstract whale fossils from a variety of geologic ages and depositional environments were thin sectioned and analyzed for evidence of microbial activity comprising a combination of microborings authigenic pyrite botryoidal cements and micropeloids borings are dense in some samples with an average diameter of 8 02 m framboidal pyrite crystals with an average diameter of 61 84 m in diameter occur within the pore spaces of the bone in borings and at the bone sediment interface the pyrite crystals are densely packed at the edges of the bone and scattered more randomly throughout the pore spaces aragonitic botryoidal cements line pore spaces in samples from deep bathyal settings potential bacterial peloids occur within pore spaces with an average size of 77 45 m or diffuse to comprise clotted micrite since bacterial body fossils are extremely rare in the fossil record recognition of past microbial ecosystems must be based on multiple lines of supporting evidence of the independent signatures studied the bacterial peloids and botryoids provide the most convincing evidence of a sulfophilic stage these fossil biosignatures suggest that a sulfophilic stage is preserved at least as far back as the eocene

origin of saline groundwaters in the carnmenellis granite cornwall england natural processes and reaction during hot dry rock reservoir circulation saline groundwaters up to 19 100 mg 1 1 total mineralisation issue in tin mines in the carnmenellis granite in cornwall u k at depths up to 800 m their stable isotope composition rules out seawater as a contributor to salinity circulation experiments carried out during hot dry rock hdr reservoir development in the same granite also produce return fluids with enhanced salinities acid hydrolysis of plagioclase and biotite are proposed as the main sources of salinity in the groundwater experimental studies carried out on biotites from a borehole used for hdr evaluation demonstrate the reactivity of the biotite and confirm the hypotheses of the field studies mg li k and silica levels in reacted solutions reflect the stoichiometric composition of the biotite chloride na and ca in solution on the other hand are enriched between 1 and 3 orders of magnitude over that of biotite reflecting the strongly incongruent nature of the reaction quartz and chalcedony saturation of the groundwaters encourages silica or silicate deposition rather than dissolution of rock forming quartz this argues against fluid inclusions as the source of salinity and suggests that new inclusions might be formed the proposed model for the genesis of saline water therefore links together or explains several processes groundwater movement convective heat transport the chemistry of the water water rock interaction secondary mineral including kaolinite formation and fluid inclusion formation and stability

experimental interaction of hydrothermal na cl solution with fracture surfaces of geothermal reservoir sandstone of the upper rhine graben abstract the upper rhine graben urg is a tertiary rift structure in central europe offering favorable conditions for geothermal energy utilization relatively high heat flow combines with sufficiently high permeability of the hydrothermal reservoirs one of the target stratigraphic levels is the lower triassic sandstone formation buntsandstein where hot water resources at temperatures up to 250 c can be utilized extensional neotectonics and hydraulic stimulation form new fracture surfaces in the reservoir rocks enhanced geothermal system egs the exposed fresh rock fracture surface reacts with the highly saline reservoir brines na cl up to 200 g l 1 with consequences for the permeability of the reservoir in order to better understand the dynamic evolution of fault systems caused by fluid rock interaction we conducted batch type experiments in a stirred autoclave system and reacted arkosic sandstone with synthetic 2 molal na cl solution at temperatures of 200 c and 260 c after 45 55 days reaction time altered rock samples were compared with the starting material and the geochemical mineralogical processes were deduced with the help of xrd sem methods and emp measurements fluid compositions were examined by icp ms icp oes and ic the arkosic sandstones show a surprisingly high reactivity during the experiments quartz grain surfaces show deep dissolution features and all reaction fluids were saturated with respects to quartz illite and kaolinite from the primary sandstone cementation completely dissolved from the sample surface perfectly euhedral crystals of metastable analcime formed during the experiment as separate crystals on quartz as groups or clusters and as surface covering mats the overall net transfer process dissolves quartz illite kaolinite k feldspar and precipitates analcime chlorite albite the process is accompanied by a total volume increase of the solids of 20 30 vol k feldspar dissolution is hampered by albitization rims shielding k feldspar and efficiently preventing an equilibration of the na k exchange with the fluid the experiments show changes on the rock surface leading to an increase of the aperture of a single fracture during the early phases of reaction and later to a decrease as the fluid rock reaction progresses alteration of the fracture surface also generates loose fragments and altered minerals this fine material may efficiently reduce the fracture aperture at narrow points along the fracture

taphonomy and paleoenvironmental conditions of deposition of fossil whales in the diatomaceous sediments of the miocene pliocene pisco formation southern peru a new fossil lagerstatte the pisco formation in peru contains abundant fossil cetaceans in middle miocene to lower pliocene sandstone siltstone and tuffaceous and diatomaceous mudstone fossil whales are especially abundant in the uppermost diatomaceous units most specimens are well articulated or partially disarticulated but associated degree of preservation is exceptionally high and uniform among articulated and disarticulated specimens and on the lower and upper surfaces of the bones some specimens have baleen preserved in anatomical position bones show no evidence of bioerosion by macro or micro invertebrates except for a very limited amount of microbial borings diatomaceous layers seem to lack bioturbation however bioturbation did occur in a few tuffaceous silty and sandy layers of the lower part of the formation shark teeth are found associated with many of the specimens however despite abundance of whale skeletons shark tooth marks are extremely rare several lines of evidence indicate that sediments and whales were deposited in a shallow to deep shelf environment an embayment and not in a beach environment the thick diatomaceous successions record conditions of strong ocean upwelling indicated by the abundant occurrence of the diatom species thalassionema nitzschioides the exceptional preservation of diatom frustules suggests that they reached the seafloor very rapidly and were not successively reworked the hundreds of whale specimens found their excellent preservation and their high degree of articulation make the pisco formation fossil whales the best representative assemblage of fossil mysticeti known so far the abundance of whale skeletons and other vertebrates in the diatomaceous beds their excellent preservation including evidence that soft tissue baleen was still present at burial and the degree of articulation point to frequent mortalities followed by rapid sedimentation that prevented decay of the skeletons and colonization by invertebrates sedimentation rates appear much higher than rates inferred from some other modern and ancient settings where whale skeletons have been found

modeling the evolution of antarctic ice sheet over the last 420 000 years implications for altitude changes in the vostok region a new thermomechanical three dimensional model designed to simulate the evolution of the antarctic ice sheet over long time periods is presented this model incorporates the various types of ice flow found in antarctica relatively slow inland ice flow that is essentially due to ice deformation fast ice flow in the regions with ice streams and ice shelf flow by coupling these three types of flow it is possible to predict grounding line migration simulations covering four glacial interglacial cycles have been conducted by forcing this model with a temperature record from vostok and a sea level record from marine cores our findings indicate that grounding line migration induced by sea level changes is the primary factor governing the evolution of the antarctic ice volume on the other hand the altitude of the ice sheet surface at vostok is driven by accumulation rate variations the amplitude of the altitude change does not exceed 150 m and is very similar for all the sites located on the antarctic plateau

the dynamics of central main ethiopian rift waters evidence from δd δ18o and 87sr 86sr ratios abstract water samples from cold and geothermal boreholes hot springs lakes and rivers were analyzed for d 18o and 87sr 86sr compositions in order to investigate lake water groundwater mixing processes water rock interactions and to evaluate groundwater flow paths in the central main ethiopian rift mer of the ziway shala basin different ranges of isotopic values were recorded for different water types hot springs show 18o 3 36 to 3 69 and d 15 85 to 24 23 deep aluto langano geothermal wells show 18o 4 65 to 1 24 and d 12 39 to 9 31 groundwater wells show 18o 3 99 to 5 14 and d 19 69 to 32 27 whereas the lakes show 18o and d in the range 3 98 to 7 92 and 26 19 to 45 71 respectively the intersection of the local meteoric water line lmwl d 7 18o 11 2 r2 0 94 n 42 and the local evaporation line lel d 5 63 18o 8 n 14 r2 0 82 was used to estimate the average isotopic composition of recharge water into the basin d 5 15 and 18o 2 34 these values are depleted if compared with the modern day average precipitation presumably indicating paleo groundwater components recharged during previous humid climatic phases the measured stable isotope values indicate that the geothermal wells some of the hot springs and groundwater wells mainly consist of meteoric water the sr isotopic signatures in all waters are within the range of the sr isotopic composition of the rift basalts and rhyolites the variability of sr isotopic data also pinpoints complex water rock interaction and mixing processes in groundwater and surface water the 87sr 86sr ratio ranges from 0 70445 to 0 70756 in the hot springs from 0 70426 to 0 70537 in two deep geothermal wells and from 0 70673 to 0 70721 in the rift lakes ziway langano shala and awasa the radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments there is a change in mer water composition between the recharge infiltration zone surrounding highlands and the discharge areas from depleted d 18o and less radiogenic sr isotope compositions to enriched d 18o and more radiogenic sr isotope compositions isotope analyses are therefore useful in providing further understanding of the hydrologeological processes occurring within a productive aquifer and the surface water system

results from the eismint model intercomparison the effects of thermomechanical coupling this paper discusses results from the second phase of the european ice sheet modelling initiative eismint it reports the intercompartison of ten operational ice sheet models and uses a series of experiments to examine the implications of thermomechanical coupling for model behaviour a schematic circular ice sheet is used in the work which investigates both steady states and the response to stepped changes in climate the major finding is that radial symmetry implied in the experimental design can under certain circumstances break down with the formation of distinct regularly spaced spokes of cold ice which extended from the interior of the ice sheet outward to the surrounding zone of basal melt these features also manifest themselves in the thickness and velocity distributions predicted by the models they appear to be a common feature to all of the models which took part in the intercomparison and may stem from interactions between ice temperature flow and surface form the exact nature of these features varies between models and their existence appears to be controlled by the overall thermal regimne of the ice sheet a second result is that there is considerable agreement between the models in their predictions of global scale response to imposed climate change

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

rock fluid interactions in a temperature gradient biotite granodiorite h2o abstract a biotite granodiorite was reacted in a controlled temperature gradient with distilled water for 60 days at 1 3 kbar p tot p h 2 o polished rock prisms were placed in the gradient at 72 119 161 209 270 and 310 c scanning electron microscope and microprobe analyses show the appearance of several secondary phases ca montmorillonite at 72 c and 119 c zeolite either stillbite or heulandite at 161 c and another zeolite thomsonite at higher temperatures solution analyses show a constant composition after about 2 weeks of reaction the phase assemblages observed in this experiment are connected by reaction relationships the reactions show the transition from clay to zeolite i stilbite or heulandite to zeolite ii thomsonite with increasing temperature and decreasing chemical potential of silica additional relations can be used to predict mineral assemblages not directly observed in this experiment but which may occur at different pressures and temperatures as well as at different chemical potentials of water and silica

fluid rock interactions in the rhine graben a thermodynamic model of the hydrothermal alteration observed in deep drilling abstract deep drilling at soultz sous forets france on the western flanks of the rhine graben has penetrated hercynian granite underlying mesozoic sediments veins are present throughout the drilled granite and there are flows of warm water localized in fractures within the granite detailed mineralogical study of core material from the research drillhole eps 1 has been carried out in order to assess the alteration history of the soultz granite part of the crystalline basement of the rhine graben the results of the study have been used in conjunction with analyses of present day fluids from deep drilling in the rhine graben reported in the literature to model thermodynamically the alteration process and in particular to evaluate if it is likely to be continuing today reaction path calculations show that if deep basinal brines such as are known from sediments of the central rhine graben react with hercynian granite they will form different alteration assemblages depending on both the path that the fluid follows e g descending through sediments or through granite and the extent of preexisting alteration of the granite the calculations suggest that fluid now sampled from granite in eps 1 achieved its peak temperature c 200 c while within permo triassic sandstone the modeling also indicates that present day fluids from the rhine graben system are capable of producing the vein quartz and possibly also the baryte veins seen in the eps 1 core much of the alteration present in the granite in the vicinity of veins and fractures may have been produced by a flow regime similar to that prevailing today

parameterization of the annual surface temperature and mass balance of antarctica this study entails the parameterization by means of a linear multiple regression analysis of the annual surface temperature and mass balance of antarctica the analysis was performed for the entire ice cap as well as for three separate regions ice shelves elevation less than 200 m the interior elevation above 1500 m and the escarpment region in between it was found that temperature can be parameterized very well in terms of elevation and latitude the latitudinal gradient on the ice shelves can be explained by the super adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves the surface mass balance can be parameterized reliably only in the interior where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere and a significant correlation with the shape of the dome the convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer this results in precipitation as radiative cooling in the inversion exceeds adiabatic warming an estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior based on regression results and a physical analysis of the precipitation processes in this region a temperature sensitivity analysis was performed for the current mass balance distribution for a 1 k rise in surface temperature the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea level lowering of 0 2 mm a 1 this is about 30 less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere

saline groundwaters in the hercynian granites chardon mine france geochemical evidence for the salinity origin abstract in this study the chemical evolution of high cl chardon mine groundwaters is modelled as a mixing between an oxidising recharge and an old marine component on which the water rock interaction is superimposed chemical and isotopic similarities with saline carnmenellis mine groundwaters are emphasised and a general comparison with other brines is discussed the cation content of deep granitic groundwaters is indicative of the water rock interaction in the case of chardon and carnmenellis groundwaters the high na cl ratio can still be related to the contribution of a brine of sedimentary origin to the water salinity the differences in the hydrochemistry related to their geological context only appears at the trace metals level on the contrary brines in plutonic rocks which exhibit a low na cl ratio represent groundwaters having a residence time in the host rock long enough to equilibrate with secondary aluminosilicates in that case the brine origin is difficult to assess if only based on the water cation content

rock water interactions in hot dry rock geothermal systems field investigations of in situ geochemical behavior abstract two hot dry rock hdr geothermal energy reservoirs have been created by hydraulic fracturing of precambrian granitic rock between two wells on the west flank of the valles caldera in the jemez mountains of northern new mexico heat is extracted by injecting water into one well flowing it through the fractured region and recovering the heated water from the second well the produced fluid is cooled on the surface and reinjected into the system the first reservoir was formed by fracturing the injection well at a depth of 2 75 km where the initial rock temperature was 185 c a heat extraction experiment conducted in this reservoir was run from january 27 to april 13 1978 a second larger reservoir was created after cementing the fracture to wellbore connections at 2 75 km in the injection well and refracturing 180 m deeper this second reservoir was tested from october 23 to november 16 1979 during each of these experiments samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead the production wellhead and at the make up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal recirculating operating conditions certain of the dissolved species appear to be derived by displacement of an indigenous pore fluid while others appear to be derived by dissolving minerals known to be present in the reservoir rock in this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat extraction experiments in particular the implications of the silica and na k ca geothermometers and the pore fluid displacement theory are examined for insight about the long term effects of fluid geochemistry on heat extraction from hdr reservoirs

miocene whale fall community from hokkaido northern japan whale bones have been found in two large concretions in the uppermost part of the lower middle miocene chikubetsu formation northwestern hokkaido japan the bone surfaces are coated in pyrite and some of the most exterior bone portions and associated bone chips are extensively bored by an unknown organism possibly microbial closely associated with the whale bones is a fossil mollusc assemblage including the mytilid adipicola chikubetsuensis amano solemya sp vesicomya sp and calyptogena sp and the gastropod provanna sp these molluscs represent a chemosynthetic community dependent on the decaying whale bone lipids for nutrition and the mytilids vesicomyids and solemyids almost certainly had symbiotic chemoautotrophic bacteria since the oligocene small mussels such as adipicola or idas and vesicomyid bivalves have been common elements of whale fall communities in the pacific provanna similarly since at least the miocene however there are some important differences between modern and fossil whale fall communities not least that there appear to be no shared species

clavate borings in a miocene cetacean skeleton from tarragona ne spain and the fossil record of marine bone bioerosion abstract clavate borings found in the tympanic bulla of a miocene cetacean from el camp de tarragona basin constitute the first evidence of the ichnogenus gastrochaenolites in bones of an autochthonous cetacean carcass previous records of similar trace fossils on marine bones were described from transported or reworked remains based on their morphology and ichnotaxonomy the borings are assigned to the activity of pholadid bivalves which would have colonized the skeletal carcass on the sea floor after removal of covering soft tissues sedimentological and paleontological data indicate a low energy depositional setting with low sedimentation rate which would have provided the temporal window for bivalve colonization this new finding contributes to widen our knowledge of bioerosion in marine vertebrate skeletons

a paleogene deep sea methane seep community from honshu japan an isolated limestone deposit occurs within late eocene to early oligocene submarine fan deposits of the tanamigawa formation in the outskirts of kushimoto town in southern honshu japan the petrography the very negative carbon isotope signature of early diagenetic cements and the abundance of chemosymbiotic bivalves namely thyasirids vesicomyids and bathymodiolins clearly identify this carbonate block as the first paleogene methane seep deposit in honshu from a biogeographical point of view distinctive features of paleogene seep faunas in japan are the apparently endemic vesicomyid hubertschenckia ezoensis and the scarcity of lucinid bivalves whereas the bivalves conchocele bisecta and bathymodiolus spp and the gastropod cryptonatica were widespread in north pacific seep communities of this age although cenozoic seep communities generally consists of members of the same families that inhabit seeps today marked differences in the genus level composition of the major chemosymbiotic bivalve families such as vesicomyidae and lucinidae and the subfamily bathymodiolinae are noted when paleogene seep communities in japan are compared to those of early neogene age on the one hand and to paleogene seep communities elsewhere on the other

feedbacks between deformation hydrothermal reaction and permeability evolution in the crust experimental insights abstract in this paper we present experiments that explore the interaction between crustal deformation hydrothermal reaction and permeability evolution we postulate that deformation should result in changes to mineral surface area which will either favour or inhibit water rock reactions involving the formation of secondary minerals mineral precipitation can greatly affect hydrologic properties such as permeability so it is therefore crucial that the controlling parameters are well constrained experiments were conducted using a paterson gas apparatus capable of independently controlling confining pressure p c pore pressure p p and axial load most experiments were conducted at p c 100 mpa and p p 50 mpa with temperatures of 200 600 c using a fine grained granitic rock in the experiments permeability evolution was measured under different stress regimes ranging from the isostatic to the shear failure case we find that permeability decreases with time by a well defined exponential function with a rate constant r representing the duration of the transient in permeability the rate constant is lowest when the specimen is in the compactional regime where mineral surface areas are minimized conversely the permeability reaction rate constant changes at the greatest rate when the specimen is stressed into the dilatant regime or undergoes shear failure these stress states result in the generation of fresh reactive mineral surface areas leading to enhanced reaction and a rapid associated change in permeability results from this study suggest that in natural systems a negative feedback effect might be operative in which enhanced mineral precipitation moderates permeability generated during episodes of deformation this feedback is likely to be important in dynamic environments such as fault zones or injection sites intended as emerging hydrothermal energy sources

a thermomechanical model of ice flow in west antarctica this study uses a three dimensional thermo mechanical model to investigate the internal flow dynamics of the west antarctic ice sheet wais the model allows ice thickness flow and temperature to interact freely its domain is prescribed as that of the present day grounded wais realistic present day climatic and topographical boundary conditions are employed the analysis of a series of experiments pays particular attention to the location and dynamics of concentrations of ice flow ice streams underlying topographic troughs are crucial in determining the strength and location of these concentrations of flow the flow pattern generated by subglacial troughs is made more distinct by the inclusion of ice flow temperature coupling the inclusion of sliding leads to the generation of limit cycles in the ice flow they are concentrated around the present day ice streams b and c of the siple coast and have a period of 5 to 10 ky there appears to be competition between several preferred ice flow pathways in this area the two end members of the flow regime are a strong ice stream c with a weakened ice stream a b complex and strong ice streams a and b with a dormant ice stream c ice streams appear to require ice discharges above a certain threshold in order to maintain frictional heat generation and fast flow individual ice streams can therefore interact through changes in catchment area size a reduction in catchment area reduces the volume of ice entering a stream and can cause stagnation as the amount of frictional heating falls

application of a continuum mechanical model for the flow of anisotropic polar ice to the edml core antarctica we present an application of the newly developed caffe model continuum mechanical anisotropic flow model based on an anisotropic flow enhancement factor to the epica ice core at kohnen station dronning maud land antarctica referred to as the edml core a one dimensional flow model for the site is devised which includes the anisotropic flow law and the fabric evolution equation of the caffe model three different solution methods are employed 1 computing the ice flow based on the flow law of the caffe model and the measured fabrics 2 solving the caffe fabric evolution equation under the simplifying assumption of transverse isotropy and 3 solving the unrestricted caffe fabric evolution equation method 1 demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity the anisotropic enhancement factor produced with method 2 agrees reasonably well with that of method 1 even though the measured fabric shows a girdle structure which breaks the transverse isotropy in large parts of the ice core for method 3 we find that the measured fabric is reproduced well by the model down to 2100 m depth systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model

consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses accurate computation of ice stream location and dynamics is a key aspiration for theoretical glaciology ice sheet models with thermo viscous coupling have been shown to exhibit stream like instabilities using shallow ice approximation mechanics but the location and width of these streams depends on the numerical implementation and are not unique we present results from thermo viscously coupled ice sheet models incorporating membrane stresses spontaneous generation of fast flowing linear features still occurs under certain parameter regimes with computed stream widths between 20 km to 100 km comparable with observations these features are maintained as the grid size is decreased the thermo viscous feedback mechanism that generates ice streams under the shallow ice approximation still operates now selecting a unique stream size computations of thermo viscous ice flows should include membrane stresses when the bed is approximately flat e g parts of antarctica and former ice sheets of the northern hemisphere previous calculations of spontaneous ice stream generation using the shallow ice approximation should be reassessed citation hindmarsh r c a 2009 consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses geophys res lett 36 l06502 doi 10 1029 2008gl036877

paleoecology of whale fall habitats from deep water oligocene rocks olympic peninsula washington state fossil mollusks associated with eight oligocene whales from the makah and pysht formations on the northwestern part of the olympic peninsula washington suggest that whale carcass sulfide production supported small numbers of some chemosymbiotic invertebrates as early as 30 million years ago thyasirid and modiolid bivalves usually dominate these very localized molluscan assemblages lucinid and nuculanid bivalves scaphandrid naticid and buccinid gastropods are rarely present brachiopods were found once these fossils include tentatively the first fossil record for the bivalve genus idasola and the first record of the bivalve thyasira peruviana olsson outside of probable cold seep deposits in south america strata surrounding the fossil whales contain low diversity megafaunas that include rare deep water gastropods and bivalves large isopods and localized cold seep communities the whale fall assemblages differ significantly because of the presence of idasola sp and thyasira peruviana and the absence of vesicomyid bivalves vertebrate carcasses have probably not contributed significantly to the dispersal of cold seep and hydrothermal vent invertebrates seep vent communities were well established much earlier than the evolution of cetaceans and seep vent invertebrates have not been found with carcasses of other large vertebrates

an improved numerical scheme to compute horizontal gradients at the ice sheet margin its effect on the simulated ice thickness and temperature in three dimensional numerical ice sheet models that use finite difference schemes the position of ice margins is poorly represented with a regular quadratic grid as a result in a centered difference scheme the surface gradient term and the flux divergence term computed for the gridpoints next to the ice margin may be inaccurate in this paper an improved scheme is presented that computes the horizontal gradients at the ice sheet margin using an asymmetric upstream second order difference scheme in order to avoid using information from the zero thickness gridpoints the model is applied to an idealized synthetic geometry to obtain a steady state ice sheet topography the improved model shows a realistically smooth thickness distribution near the margin thermomechanical coupling is found to enhance the error near the margin the error in simulated thicknesses with the centered difference method was significantly reduced with the new upstream scheme

subglacial erosion and englacial sediment transport modelled for north american ice sheets abstract reconstructions of north american glacial history have either been based on interpretation of the geologic record or on numerical models of continental ice dynamics because such models make no explicit reference to the geological products of glaciation the full potential of a combined approach has not been realized we present the results of a process based model of sediment production entrainment transport and deposition that represents a first step toward uniting these two lines of investigation in this model basal ice processes are dependent on ice sheet geometry hydrology and dynamics a three dimensional thermomechanical ice sheet model yields the ice geometry flow and thermal conditions that are used by a model of subglacial hydrology together these drive the basal process model comparisons of simulation results with mapped debris distributions of the hudson bay paleozoic carbonates and of the distinctive dubawnt group are used to test the validity of the transport model dispersion of debris radially out of hudson bay is greatly overestimated by the model and dispersion toward the bay equally underestimated this is because the modelled ice sheet has a single dome over hudson bay at glacial maxima including last glacial maximum rather than a saddle separating ice domes over quebec labrador and keewatin estimated rates of glacial erosion for the cordilleran and laurentide ice sheets are compared against those predicted by the model the model underestimates these rates because it underestimates the vigour of the quarrying process

dynamics and mass balance of the ice sheet ice shelf regime at nivlisen antarctica as derived from a coupled three dimensional numerical flow model

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

exotic stable isotope compositions of saline waters and brines from the crystalline basement the overwhelming majority of groundwaters reported in literature show isotopic compositions that place them on or right of the meteoric water line mwl in a 2h vs 18o diagram a closer look to the steadily increasing data from the deeper crystalline basement reveals nevertheless that points left of the mwl are not so unusual as has been suggested during the last decades their supposed rareness seems to be due to a bias of sampling the concerned fluids develop only at greater depths and in low permeability environments which makes access to them so difficult paradoxically exotic stable isotope compositions may be the rule in a restricted depth zone in all crystalline basements with slow groundwater movements but not too high temperatures the present study takes stable isotope data on saline fluids from the deep french granitic basement as a starting point in order to situate the french data from the vienne region in a more general context a literature review has been undertaken assembling more than 1300 stable isotope analyses of waters and brines in crystalline rocks from stable cratons and mountain belts world wide the french fluids show some particular features with respect to the majority of other studies as their major ion composition close to seawater or a significant isotopic shift at relatively low salinities detailed knowledge on the hydrological and chemical history of the site allowed to develop a conceptual model of isotopic evolution by interaction of fracture fluids with fracture minerals this model considers interactions of the last fluids flushing the system marine water unaltered evaporated or diluted with previously precipitated mineral phases and the neoformation of the last generation of fracture minerals the model has been tested quantitatively for several combinations of dissolution precipitation reactions involving formation of carbonates clay minerals and fe hydroxides most of the modelled scenarios would leave the residual liquid phase depleted in 18o and either enriched or depleted in 2h and produce waters with isotopic signatures corresponding to the observed 2h vs 18o correlation it is therefore suggested that the general phenomenon of an isotopic shift in deep fissured silicate rocks which seems to be rather independent of lithology may result from a combination of different reaction mechanisms implying not solely the rock matrix but also the different generations of fracture minerals

polar firn densification and grain growth a 50 m firn core from dome c east antarctica was found to consist of coarse firn which comprised 90 to 95 of the core and fine firn coarse firn was characterized by large crystals with a vertical shape orientation near the surface connected to nearest neighbors by relatively large necks in a structure different from closest packing fine firn was of higher density and consisted of smaller more spherical crystals connected by relatively narrow necks in a more nearly closest packed configuration higher surface free energy in fine firn causes crystals and necks to grow more rapidly than in coarse firn however we find that coarse firn densifies more rapidly with time contrary to the predictions of unconfined sintering models load driven densification due to a power law creep mechanism is found to account for the larger coarse firn densification rate however if the exponent in the power law exceeds one then densification rates are predicted to increase with depth due to increasing load contrary to observed behavior we speculate that different mechanisms may control the densification process in fine and coarse firn

a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes 1 a new three dimensional thermomechanically coupled ice sheet model is developed contrary to the majority of three dimensional ice sheet models shallow ice approximation higher order stress gradients longitudinal and transverse are accounted for in the force balance equations the horizontal velocity field is determined from the force balance equations in their derivative form elliptical equation using the method presented by pattyn 2000 2002a the model is solved on a regular grid in the horizontal and an irregular grid in the vertical and is numerically stable basic experiments include the european ice sheet modeling initiative eismint benchmarks for largescale ice sheet models and a comparison with the saito blatter ice sheet model including higher order stress gradients saito et al 2003 detailed calculations of ice flow over three dimensional bedrock perturbations showed the validity of the higher order solution the model is capable of simulating the evolution of an ice stream within the ice sheet and shows important aspects of observed ice stream features such as the surface flattening and the importance of side drag the simulation of the ice flow over a subglacial lake results in a flattening of the surface a local velocity increase over the lake and a deviation of the ice flow from the main flow direction features which are also observed at lake vostok antarctica index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3230 mathematical geophysics numerical solutions keywords higher order ice sheet model thermomechanical ice stream subglacial lake citation pattyn f a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes j geophys res 108 b8 2382 doi 10 1029 2002jb002329 2003

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

the dynamic response of the greenland and antarctic ice sheets to multiple century climatic warming new calculations were performed to investigate the combined response of the greenland and antarctic ice sheets to a range of climatic warming scenarios over the next millennium use was made of fully dynamic 3d thermomechanic ice sheet models which were coupled to a two dimensional climate model the experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent co2 increases of two four and eight times the present 1990 a d value by the year 2130 a d and a stabilization after that the calculations brought to light that during the next century short term effect the background evolution trend would dominate the response of the antarctic ice sheet but would be negligible for the greenland ice sheet on that timescale the greenland and antarctic ice sheets would roughly balance one another for the middle scenario similar to the ipcc96 is92a scenario with respective contributions to the worldwide sea level stand on the order of about 610 cm on the longer term however both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the greenland ice sheet sensitivity experiments highlighted the role of ice dynamics and the height massbalance feedback on the results it was found that ice dynamics cannot be neglected for the greenland ice sheet not even on a century timescale but becomes only important for antarctica on the longer term the latter is related to an increased outflow of ice into the ice shelves and to the grounding line retreat of the west antarctic ice sheet which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century21 of which 60 cm would originate from the greenland ice sheet alone

ice sheet model sensitivities to environmental forcing and their use in projecting future sea level the searise project ten ice sheet models are used to study sensitivity of the greenland and antarctic ice sheets to prescribed changes of surface mass balance sub ice shelf melting and basal sliding results exhibit a large range in projected contributions to sea level change in most cases the ice volume above flotation lost is linearly dependent on the strength of the forcing combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments suggesting that nonlinear feedbacks are modest our models indicate that greenland is more sensitive than antarctica to likely atmospheric changes in temperature and precipitation while antarctica is more sensitive to increased ice shelf basal melting an experiment approximating the intergovernmental panel on climate change s rcp8 5 scenario produces additional first century contributions to sea level of 22 3 and 8 1 cm from greenland and antarctica respectively with a range among models of 62 and 14 cm respectively by 200 years projections increase to 53 2 and 26 7 cm respectively with ranges of 79 and 43 cm linear interpolation of the sensitivity results closely approximates these projections revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice sheet response to complicated forcings over 200 years can be linearized

a three dimensional ice sheet flow solution an accurate three dimensional reduced model shallow ice approximation flow with velocity depending on all three spatial coordinates is constructed for the commonly adopted isotropic viscous law with temperature dependent rate factor the solution is for steady flow with a prescribed temperature distribution but can be extended to flow with a coupled energy balance and to unsteady flow the accuracy hinges on the reduction to a two point ordinary differential equation problem for the surface profile on an unknown span for which established accurate numerical methods are available this is achieved by setting one horizontal velocity component in elliptic cylindrical coordinates to zero but the other two components depend on all three spatial variables while not of direct physical interest such an exact solution is valuable as a test solution for the large scale numerical codes commonly used in ice sheet modelling which have not yet been subjected to such a comparison

european ice sheet modelling initiative eismint model intercomparison experiments with first order mechanics 1 the european ice sheet modelling initiative eismint intercomparison experiments with thermomechanical coupling are repeated with an ice sheet model that applies the first order approximation for computing the flow field the experiments impose radially symmetric boundary conditions most of the previous results have shown the loss of implied radial symmetry i e the formation of distinct regularly spaced spokes of cold ice in the simulated basal temperatures a similar result is also observed in the presented first order model results the computed velocity components scatter widely along the marginal grid points this indicates that the spokes may be triggered by the poor representation of the margin with a regular grid where the steep gradients in the surface enhance the numerical errors additionally the generally applied second order discretization scheme tends to decouple even and odd numbered grid points thus leading to wavy solutions with a wavelength of two grid cells these patterns strongly suggest that the loss in radial symmetry is a numerical artifact

stress gradient damping of thermoviscous ice flow instabilities 1 calculations of thermomechanically coupled ice sheet evolution using the shallow ice approximation exhibit the development of fingering instabilities in velocity temperature and thickness which have been argued to resemble and therefore explain ice stream formation however workers have had difficulty in obtaining comparable results it has been suggested that this is due to ill posing of the evolution problem when the shallow ice approximation is used the influence of additional mechanical terms are examined using both the full system and the hybrid lubrication membrane stress approximation the three dimensional equivalent of the longitudinal stress approximation linearization techniques are used to formulate an analytical problem and a numerical eigenvalue problem the analysis shows that the shallow ice approximation gives highly erroneous stability maps for the combination of shorter transverse wavelengths and longer along flow wavelengths i e ice stream dimensions while the lubrication membrane stress approximation and full systems give different but consistent results which remove the ill posing calculations in two horizontal dimensions of thermoviscous coupling using the shallow ice approximation which comprise a large proportion of ice sheet modeling results need reexamination

geochemical results of a single well hydraulic injection test in an experimental hot dry rock geothermal reservoir soultz sous foreˆts alsace france abstract as part of the investigation of the hot dry rock hdr potential of the soultz test site 25 300 m 3 of fresh water were injected into borehole gpki in granite between depths 2850 and 3400 m the returned fluids were chemically monitored during the 57 h of production that followed the 21 h of shut in time and there is evidence of mixing and water rock interactions although the chemical composition of the two sampled indigenous fluids 1817 m and 3485 m depth which circulate at various levels in the granite is very similar participation of both fluids in mixing with injected water has been revealed from the slight chemical differences this test also suggests evidence for the presence of a third fluid the large volume of injected water induced greater cooling of the reservoir than in previous tests and a temperature effect on water rock interactions has been demonstrated there is release of mg and of sio 2 and f to a lesser extent whereas so 4 release is greater because it is partly related to anhydrite dissolution mixing of the injected water with the highly saline indigenous fluid conceals part of the water rock interactions because there is no evidence of the release of major elements k na however trace elements are useful for determining some dissolution reactions for example relatively high concentrations of f and relatively low 87 sr 86 sr ratios the presence of the brine also induces some chemical reactions as it increases calcite and anhydrite solubility lithium and b in the indigenous fluid are taken up during the test and adsorption reactions on solid surfaces are proposed as an explanation for this depletion chemical monitoring during this single well hydraulic test has proved relevant for determining which parts of the processes dissolution and precipitation are liable to modify the physical properties of the reservoir during fluid circulation for energy extraction particularly in the vicinity of the injection borehole

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

results from the ice sheet model intercomparison project heinrich event intercomparison ismip heino results from the heinrich event intercomparison heino topic of the ice sheet model intercomparison project ismip are presented ismip heino was designed to explore internal large scale ice sheet instabilities in different contemporary ice sheet models these instabilities are of interest because they are a possible cause of heinrich events a simplified geometry experiment reproduces the main characteristics of the laurentide ice sheet including the sedimented region over hudson bay and hudson strait the model experiments include a standard run plus seven variations nine dynamic thermodynamic ice sheet models were investigated one of these models contains a combination of the shallow shelf ssa and shallow ice approximation sia while the remaining eight models are of sia type only seven models including the sia ssa model exhibit oscillatory surges with a period of 1000 years for a broad range of parameters while two models remain in a permanent state of streaming for most parameter settings in a number of models the oscillations disappear for high surface temperatures strong snowfall and small sediment sliding parameters in turn low surface temperatures and low snowfall are favourable for the ice surge cycles we conclude that further improvement of ice sheet models is crucial for adequate robust simulations of cyclic large scale instabilities

the isotopic and chemical composition of co2 rich thermal waters in the mont dore region massif central france chemical and isotope compositions of fluid samples collected between 1974 and 1986 from 52 springs or shallow boreholes located in the mont dore region massif central france were examined some springs and wells were sampled several times during this period the fluids emerge from quaternary volcanic rocks or paleozoic granite at temperatures between 4 and 62 c and the origin of the h2o is meteoric the waters can be classified into three groups bicarbonate fluids mixed bicarbonate chloride fluids with a mineralization up to 8 g l and acid sulfate fluids only two fluids contain sufficient cl to be considered as mature waters previous work has demonstrated that they all contain partly mantle derived co2 gas and that the co2 rich gas phase and bicarbonate chloride waters are separated at substantial depth mineralized fluids circulate at depth and undergo several processes such as cooling or dilution with recent freshwater during their ascent to the surface therefore the co2 rich gas phase can be partly dissolved in the freshwater or in deep fluids after their dilution this process leads to the dissolution of surrounding rocks such dissolution is discussed on the basis of major element concentrations na k ca mg as well as the sr 87 86 isotope ratio dissolution of s bearing minerals has also been demonstrated the presence of the co2 rich gas phase also leads to isotope exchange between co2 and h2o some mineralized fluids are less affected by these processes than others in which case they display the chemical and isotopic characteristics of the original deep fluids it was shown that the applicability of geothermometer calculations for these waters is hampered by several processes that modify the chemical composition however some geothermometers can be used for estimating the temperature of the deep fluids using the chemical composition of the less modified fluids they indicate that fluids emerging from volcanic rocks in the dordogne valley reach temperatures of around 100 130 c at depth while the temperature of the fluid that issues from the granite at saint nectaire is 160 175 c at depth

steady thermomechanical flow along two dimensional flow lines in large grounded ice sheets a thermomechanical flow model has been developed in order to perform simultaneous calculations of the surface elevation and the distribution of stresses velocities and temperatures along two dimensional flow lines on large grounded ice sheets in order to solve the complex system of full thermomechanical coupled equations the following approximations have been made a coordinate scaling giving a lead order reduced model and an iteration procedure which decouples the energy balance equation from the rest of the equations glen s flow law is used as the constitutive relationship between stresses and deformation in the model and it is found that the longitudinal deviatoric stresses have a significant role in the lead order equations at the ice divide the solution shows that the velocity stress and temperature distributions change rapidly here the basal temperature increases creating a hot spot the surface strain rates increase 50 and the horizontal velocity profile is concave near the base with an inflection point away from the ice divide basal temperature increases and in the example presented here the basal temperature reaches the pressure melting point after 2 3 of the lateral extent and basal sliding begins to influence the flow in the ablation region it is seen that the heat produced by internal deformation is of the same order of magnitude as the geothermal heat flux from the bedrock

saline ground waters and brines in the canadian shield geochemical and isotopic evidence for a residual evaporite brine component abstract saline ca na cl type groundwaters and brines sampled in deep mines over an extensive area of the canadian precambrian shield have elevated br cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines remnants of the great marine incursions of the paleozoic era boron concentrations in these waters are generally low i e 11 b 10 b ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values 4 19 approaching that of present day seawater 4 20 moreover the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the br cl relationship that most of the chloride in shield brines is of marine origin rather than a product of water rock interactions if this is correct crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides

a miocene chemosynthetic community from the ogaya formation in joetsu evidence for depth related ecologic control among fossil seep communities in the japan sea back arc basin abstract two large carbonate bodies within deep water sediments of the uppermost middle miocene ogaya formation at kita kuroiwa niigata prefecture central japan are identified as an ancient hydrocarbon seep site based on petrographic features such as acicular and sparry calcite cements and clotted micrite with 13c values as low as 38 0 vs vpbd and a low diversity fauna of vesicomyid and mytilid bivalves and provannid gastropods compared to well studied coeval seep communities from the japan sea back arc basin species diversity is particularly low at the kita kuroiwa site while the percentage of seep obligate taxa taxa that are restricted to this type of environment is very high largely due to the absence of predatory gastropods such as naticids and buccinids modern seep communities show a decrease in species diversity and an increase in seep obligate taxa with depth due to the lower abundance and diversity of background colonists entering cold seep habitats likewise depth is here considered as the most likely cause for the observed differences in community structure because the kita kuroiwa seep site was located in considerably deeper water 1000 2000 m than the comparable coeval seep sites in the japan sea back arc basin

balance velocities and measured properties of the antarctic ice sheet from a new compilation of gridded data for modelling this paper presents a new compilation of gridded data sets for three dimensional modeling of the antarctic ice sheet these are for surface elevation icethickness bedrock elevation and accumulation rate as interpolated on a 281 x 281 mesh with 20 km spacing and encompass all of the ice sheet and thesurrounding continental shelf data sources include the bamber digital elevation model from ers 1 radar altimeter data a redigitization of available ice thicknessdata the giovinetto accumulation data recent ice thickness data from british and german expeditions as well as accumulation data from german and norwegianexpeditions in particular new data were incorporated for the filchner ronne schelfeis and for dronning maud land arising from the epica pre site survey special attention was devoted to carefully match the various data sources both among themselves as across the grounding line and below the ice shelves toenable ice sheet expansion and retreat in dynamic situations as an application the balance flow is calculated over the entire ice sheet using a two dimensionalfinite difference scheme and compared with a previous assessment this brought to light the existence of ice streaming features extending well inland of the icesheet a detailed zoom over dronning maud land exhibits the general flow characteristics of interest for locating a future deep drilling site as a by product anupdated value of 26 4 x 106 km3 was obtained for the total volume of the ice sheet and ice shelves or equivalent to 61 1 m of global sea level rise after removalof the ice sheet and subsequent oceanic invasion and isostatic rebound the total accumulation over the grounded ice sheet including the antarctic peninsula is1924 gta 1 or between 5 and 20 higher than earlier estimates including all of the ice shelves the value is 2344 gta 1

modelled response of the volume and thickness of the antarctic ice sheet to the advance of the grounded area numerical experiments are performed for the antarctic ice sheet to study the sensitivity of the ice volume to variations in the area of grounded ice and to changes in the climate during the most recent deglaciation the effect of the variations in the grounded area is found to be the major source of changes in the ice volume while the effect of climate change was minor the maximum possible contribution of the ice volume change to sea level rise during the deglaciation is estimated to be 36 m which covers most values estimated in previous studies the effect of the advance of the ice sheet margin over those regions not connected to the major ice shelves contributes one third of the total ice volume change which is comparable to the effect of the grounding of the filchner ronne ice shelf and the contribution of the ross and amery ice shelves together

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project i antarctica atmospheric oceanic and subglacial forcing scenarios from the sea level response to ice sheet evolution searise project are applied to six three dimensional thermomechanical ice sheet models to assess antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies results indicate i growth with warming except within low latitude basins where inland thickening is outpaced by marginal thinning ii mass loss with enhanced sliding with basins dominated by high driving stresses affected more than basins with low surface slope streaming ice and iii mass loss with enhanced ice shelf melting with changes in west antarctica dominating the signal due to its marine setting and extensive ice shelves cf minimal impact in the terre adelie george v oates and victoria land region of east antarctica ice loss due to dynamic changes associated with enhanced sliding and or sub shelf melting exceeds the gain due to increased precipitation furthermore differences in results between and within basins as well as the controlling impact of sub shelf melting on ice dynamics highlight the need for improved understanding of basal conditions grounding zone processes ocean ice interactions and the numerical representation of all three key points sensitivity study of antarctica to atmospheric oceanic and subglacial forcings different sectors of antarctica are vulnerable to the forcings atmospheric forcing lead to a growth but dynamic forcing lead to a mass loss 2013 american geophysical union all rights reserved

the eismint benchmarks for testing ice sheet models we present a series of benchmark experiments designed for testing and comparing numerical ice sheet models following the outcome of two eismintworkshops organized to intercompare large scale ice sheet models currently in operation model benchmark experiments are described for ice sheets underfixed and moving margin conditions these address both steady state and time dependent behavior under schematic boundary conditions and with prescribedphysics a comparison was made of each model s prediction of basic geophysical variables such as ice thickness velocity and temperature consensusachieved in the model intercomparison provides reference solutions against which the accuracy and consistency of ice sheet modeling codes can be assessed

modelling landscape evolution under ice sheets we use an ice sheet model glimmer with an erosion component to examine the evolution of landscapes under ice sheets over long time scales in hypothetical situations glimmer is a fully coupled thermomechanical 3 dimensional ice sheet model with a sliding component the model thus has the ability to predict ice thickness the distribution of areas at pressure melting point and basal velocities the erosion rate is assumed to be a simple linear function of the basal velocity and therefore erosion only occurs where the bed is not frozen and basal sliding is possible in addition sliding velocities are assumed to be related to basal water production thus giving a mechanism for smooth temporal and spatial transitions between eroding and non eroding portions of the bed the eroding glacial landscape system is modelled for long term persistent glaciation assuming a variety of initial landscapes results indicate that without the inclusion of basal water production in the calculation of sliding velocities any thermal feedbacks are exaggerated because of steep horizontal basal temperature gradients additionally bed morphology exerts a greater influence under low basal slip conditions because ice cannot respond readily to thermal instabilities we suggest that erosion and valley overdeepening may aid stabilisation of the thermal regime of an ice sheet and that it is possible to generate glacial signals in previously fluvial systems after only 100 kyr of glaciation at conservative erosion rates

water rock interactions during experiments within the geothermal hot dry rock borehole gpk1 soultz sous foreˆts alsace france abstract hydraulic injection backflow tests were carried out in borehole gpk1 at a site designed for geothermal hot dry rock experiments located in the rhine graben near soultz sous fore ts france the injected fresh water was in contact with granite at 137 c for a few hours through the monitoring of the chemical composition of the production fluids it was noticed that substantial mixing with the indigenous brine from the granite and chemical exchanges between the granite and the fluids release of co 2 so 4 f ba and sio 2 took place the mineralogical origin of these components is discussed it appears that at least calcite biotite sulphide minerals and feldspar were dissolved from the rock for most of the components the dissolution kinetics are very fast during the first steps of the interaction and then slow down after a few minutes sulphate concentration data indicate that the fluid entered into different fractures the chemical compositions of both the indigenous brine and the injected fresh water are relevant to determine the behaviour of the minerals

exact solutions to the thermomechanically coupled shallow ice approximation effective tools for verification we describe exact solutions to the thermomechanically coupled shallow ice approximation in three spatial dimensions although artificially constructed these solutions are very useful for testing numerical methods in fact they allow us to verify a finite difference scheme that is to show that the results of our numerical scheme converge to the correct continuum values as the grid is refined in three dimensions comparison of numerical results with exact solutions has helped us to precisely quantify and understand some of the numerical errors we are making our verified numerical scheme shows the basal temperature spokes which arose in the eismint european ice sheet modelling initiative ii intercomparison payne and others 2000 a careful analysis describes these warm spokes as numerical errors which occur when the derivative of the strain heating term with respect to the temperature is large on the other hand the appearance of basal temperature spokes in a verified numerical scheme strongly suggests that they are a feature of the eismint ii experiment f continuum problem in fact they are clear evidence of an unstable equilibrium point of the continuum problem this paper is a sequel to bueler and others 2005 which addresses exact solutions and verification in the isothermal case

a new miocene whale fall community from japan abstract whale bones with associated molluscs have been found in a carbonate concretion in the late middle miocene nupinai formation of eastern hokkaido japan the concretion contains volcaniclastic grains pyrite and authigenic carbonate and quartz cements pyrite also coats and occurs within bone fragments which are corroded and partially bored the whale bone associated molluscs are the bivalves vesicomya kawadai aoki vesicomya sp calyptogena chitanii kanehara conchocele bisecta conrad and adipicola sp and the gastropod provanna sp these species represent a whale fall community in the sulphophilic ecological stage the nupinai formation community shares genera and species with contemporary whale fall and cold seep assemblages which suggests there was a regional pool of molluscs that could utilize both seeps and whale falls in the nw pacific during the miocene it is possible that during this time sedimentation rate had a control on species composition at contemporary whale fall sites

water rock interaction processes in the triassic sandstone and the granitic basement of the rhine graben geochemical investigation of a geothermal reservoir saline fluids have been collected in the rhine graben over the last two decades both from the triassic sandstone aquifer and the granitic basement down to a depth of 3500m their salinities and location are compared in order to distinguish the respective influences of temperature and host rock mineralogy in the water rock interaction processes the comparison shows that sulphates in the sedimentary formations were dissolved by the fluids which also led to br enrichment mica dissolution has strongly increased the rb and cs contents which then provide an indication of the degree of water rock interaction the sr isotopic ratios are used to compare the fluids with the granite minerals two relationships are revealed for the fluids in the sandstone and the granite one related to widespread mica dissolution which could have affected both the buntsandstein and the granite and the other to subsequent plagioclase dissolution which is observed only in the granite computations showed that 12 5g of mica and 1 658 of plagioclase per liter of fluid have been dissolved the nature of these two relationships suggests two different evolutions for the fluids and the individualization of the two reservoirs during the graben s history the cation concentrations are mainly controlled by temperature and are independent of the type of host rock equilibrium with the rock mainly caused ca and k concentration variations which has induced clear ca k and ca 18o k 18o correlations geothermometric computations indicate that with increasing depth the cations the silica and the 18o so4 geothermometers evolve towards a value close to 230 c this demonstrates the existence of a hot reservoir in the granite of the graben at a depth estimated at 4 5 5 km

fossil evidence for micro and macrofaunal utilization of large nekton falls examples from early cenozoic deep water sediments in washington state usa abstract whale and fish carcasses and wood in the deep sea host diverse and specialized faunas related to the hydrothermal vent and hydrocarbon seep biota fossil examples of such food falls were found in the eocene to oligocene crescent humptulips lincoln creek and pysht formations in western washington state usa they are used to document paleoecologic and taphonomic features of such sites paleontological evidence for ecologic processes occurring at ancient whale falls include shark teeth indicating the presence of scavengers bored bone surfaces showing microbial bone degradation and bivalves belonging to chemosymbiotic groups the latter indicator shows that sulfide was released from the anaerobic decay of carrion and or bone lipids it appears that the type of taxa and the low number of specimens mark a chemotrophic opportunist stage that lasted only a few years furthermore detritus in the marrow spaces of cancellous bones indicate that the bones were hollow for a significant length of time before burial perhaps 1000 years or more these spaces are now mostly filled with clotted micrite and other cement phases the 13c values of which are in the same range as those of the concretionary matrix enclosing the bones indicating cement formation within the sediments a piece of wood from the pysht formation shows evidence for two generations of wood boring bivalves such that some boreholes have calcitic linings characteristic for teredinids and some are lined with a crust of decomposed wood characteristic for xylophagains several investigated fossil wood falls show that wood boring bivalves were active on the seafloor fecal pellets composed of woody detritus are abundant in the concretionary matrix surrounding the wood the excellent preservation of these fecal pellets indicates that these concretions with wood and associated mollusks represent undisturbed in situ wood fall communities in sum undisturbed deep water sediments can preserve evidence of life and ecologic processes at short lived nekton falls however the data also indicate a long time interval between the macrofaunal utilization of the substrates and the cementation and fossilization of these associations thus using mineral deposits such as clotted micrite and pyrite as evidence for microbial activity during the macrofaunal utilization of the substrates is doubtful

simulations of the greenland ice sheet 100 years into the future with the full stokes model elmer ice it is likely that climate change will have a significant impact on the mass balance of the greenland ice sheet contributing to future sea level rise here we present the implementation of the full stokes model elmer ice for the greenland ice sheet which includes a mesh refinement technique in order to resolve fast flowing ice streams and outlet glaciers we discuss simulations 100 years into the future forced by scenarios defined by the searise sea level response to ice sheet evolution community effort for comparison the same experiments are also run with the shallow ice model sicopolis simulation code for polythermal ice sheets we find that elmer ice is 43 more sensitive exhibits a larger loss of ice sheet volume relative to the control run than sicopolis for the ice dynamic scenario doubled basal sliding but 61 less sensitive for the direct global warming scenario based on the a1 b moderate emission scenario for greenhouse gases the scenario with combined a1b global warming and doubled basal sliding forcing produces a greenland contribution to sea level rise of 15cm for elmer ice and 12cm for sicopolis over the next 100 years