fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

novel 3d centimetre to nano scale quantification of an organic rich mudstone the carboniferous bowland shale northern england x ray computed tomography and serial block face scanning electron microscopy imaging techniques were used to produce 3d images with a resolution spanning three orders of magnitude from 7 7 m to 7 nm for one typical bowland shale sample from northern england identified as the largest potential shale gas reservoir in the uk these images were used to quantitatively assess the size geometry and connectivity of pores and organic matter the data revealed four types of porosity intra organic pores organic interface pores intra and inter mineral pores pore sizes are bimodal with peaks at 0 2 m and 0 04 m corresponding to pores located at organic mineral interfaces and within organic matter respectively these pore size distributions were validated by nitrogen adsorption data the multi scale imaging of the four pore types shows that there is no connected visible porosity at these scales with equivalent diameter of 20 nm or larger in this sample however organic matter and clay minerals are connected and so the meso porosity 20 nm within these phases provides possible diffusion transport pathways for gas this work confirms multi scale 3d imaging as a powerful quantification method for shale reservoir characterisation allowing the representative volumes of pores organic and mineral phases to be defined to model shale systems the absence of connected porosity at scales greater than 20 nm indicates the likely importance of the organic matter network and associated smaller scale pores in controlling hydrocarbon transport the application of these techniques to shale gas plays more widely should lead to a greater understanding of properties in the low permeability systems

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

seismic monitoring of pressure depletion evaluated for a united kingdom continental shelf gas reservoir the possibility of using 4d seismic data for monitoring pressure depletion in the low porosity tight gas bearing rotliegende sandstones of the uk southern gas basin is investigated the focus here is on whether fractures in the upper part of the reservoir known to enhance productivity can also enhance the time lapse seismic response the study uses laboratory data to evaluate core plug stress sensitivity published data for the stress behaviour of the fractures followed by petro elastic and 4d seismic modelling of both the fractured and unfractured formation the magnitude of the resultant 4d signatures suggests that production induced changes in the unfractured sands are unlikely to be observed except perhaps with highly repeatable time lapse surveys on the other hand the presence of fractures could render production effects visible in dedicated 4d acquisition or prestack parallel processed data if present however the signature will be sporadic as fractures in the area are known to exist in clusters the 4d signature may be enhanced further by certain classes of vertical geological variability and also areas of high reservoir pressure the strongest evidence of depletion is expected to be time shifts seen at the base of the rotliegende reservoir

the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

hydro biogeochemical coupling beneath a large polythermal arctic glacier implications for subice sheet biogeochemistry 1 we analyze the interannual chemical and isotopic composition of runoff from a large high arctic valley glacier over a 5 year period during which drainage evolved from a long residence time drainage system feeding an artesian subglacial upwelling sgu at the glacier terminus to a shorter residence time drainage system feeding an ice marginal channel imc increased icemelt inputs to the sgu are thought to have triggered this evolution this sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time the biogeochemistry of the sgu is consistent with prolonged contact between meltwaters and subglacial sediments in which silicate dissolution is enhanced anoxic processes e g sulphate reduction prevail and microbially generated co2 and sulphide oxidation drive mineral dissolution solute in the imc was mainly derived from moraine pore waters which are added to the channel via extraglacial streams these pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate silicate dissolution we present the first evidence that microbially mediated processes may contribute a substantial proportion 80 in this case of the total glacial solute flux which includes coupling between microbial co2 generation and silicate carbonate dissolution the latter suggests the presence of biofilms in subglacial ice marginal sediments where local perturbation of the geochemical environment by release of protons organic acids and ligands stimulates mineral dissolution these data enable inferences to be made regarding biogeochemical processes in longer residence time glacial systems with implications for the future exploration of antarctic subglacial lakes and other wet based ice sheet environments

an estimation method for effective stress changes in a reservoir from 4d seismics data advances in seismics acquisition and processing and the widespread use of 4d seismics have made available reliable production induced subsurface deformation data in the form of overburden time shifts inversion of these data is now beginning to be used as an aid to the monitoring of a reservoir s effective stress past solutions to this inversion problem have relied upon analytic calculations for an unrealistically simplified subsurface which can lead to uncertainties to enhance the accuracy of this approach a method based on transfer functions is proposed in which the function itself is calibrated using numerically generated overburden strain deformation calculated for a small select group of reference sources this technique proves to be a good compromise between the faster but more accurate history match of the overburden strain using a geomechanical simulator and the slower less accurate analytic method synthetic tests using a coupled geomechanical and fluid flow simulator for the south arne field confirm the efficacy of the method application to measured time shifts from observed 4d seismics indicates compartmentalization in the tor reservoir more heterogeneity than is currently considered in the simulation model and moderate connectivity with the overlying ekofisk formation

sensitivity of time lapse seismic data to pore pressure changes is quantification possible time lapse seismic data have contributed to increased reservoir knowledge and improved hydrocarbon recovery mainly by monitoring changes in fluid saturation seismic signatures of pore pressure changes have been less commonly reported although some observations such as large depletion magnus field and secondary effects such as associated gas out of solution shiehallion field and geomechanical effects in the reservoir and overburden ekofisk valhall and hthp fields have been made quantification of the pore pressure changes from seismic data has rarely been performed to date

characterization of dissolved organic matter dom from glacial environments using total fluorescence spectroscopy and parallel factor analysis aquatic dissolved organic matter dom is a major reservoir of reduced organic carbon and has a significant influence on heterotrophic biological productivity and water quality in marine and freshwater environments although the forms and transformations of dom in temperate aquatic and soil environments have been studied extensively this is not the case for glacial environments in this study fluorescent excitation emission matrices eems parallel factor analysis parafac and cluster analysis were used to characterize the fluorescing components of dom in ice and water samples from supraglacial englacial subglacial and proglacial environments of seven glaciers in the canadian arctic norway and antarctica at least five significant fluorescent dom fractions were identified which accounted for 98 2 of the variance in the dataset these included four protein like components and one humic like component the predominantly proteinaceous character of dom from these glaciers is very different from the more humic character of dom described previously from lacustrine fluvial estuarine and marine environments dom from the sampled glaciers is broadly similar in character despite their geographically distinct locations different thermal regimes and inter and intra site differences in potential organic matter sources glacier ice samples had a relatively low ratio of humic like protein like fluorescence while meltwater samples had a higher ratio

a classification for the pressure sensitivity properties of a sandstone rock frame a three parameter formula is proposed to describe the sensitivity of the bulk modulus or shear rigidity for a sandstone rock frame under applied isotropic loading the theoretical basis for this relation is the use of excess compliance as a pseudo function to describe all internal weaknesses in the rock regardless of their origin the law is fitted to 179 sets of laboratory measurements on unsaturated reservoir core and outcrop sandstones that have low to moderate porosity and a range of clay fractions and cementation a stress index defined to quantitatively rank the reservoir sands indicates that laboratory derived pressure sensitivity is highest 10 per mpa maximum for the clean moderate porosity paleocene sands from the forties formation and west of shetlands whereas the lower porosity cemented and more consolidated permian sands rank as least pressure sensitive 1 per mpa maximum higher porosity sands are stress sensitive because of the overall rock frame compressibility all of t

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

exploring the effect of meso scale shale beds on a reservoir s overall stress sensitivity to seismic waves abstract intra reservoir sub seismic shale beds with a thickness range from 1 10 m are present in most clastic reservoirs they are often studied to investigate their effect on fluid flow and reservoir performance here it is found that shales with such thicknesses can also strongly affect the effective elastic wave behaviour of the composite reservoir particularly when observed with frequent time lapse surveys more specifically for reservoirs experiencing pressure depletion the effective impedance of the reservoir interval is usually expected to harden however our results indicate that shales can reduce this hardening effect or perhaps unexpectedly soften the overall impedance the overall in situ stress sensitivity of the reservoir is reduced below that predicted from taking laboratory core plug measurements of sand stress sensitivity alone these predictions are based on a combination of geomechanical and pressure diffusion phenomena that are in turn controlled by the shale thickness permeability and the mechanical properties as sub seismic shale layers of approximately 1 m thickness take less than three months to pressure equilibrate whilst thicker shale layers of 10 m can take over 20 years in the context of repeated seismic surveying our predictions require accurate knowledge of the shale properties and statistics and hence a good description of the sedimentology based on our default property values it appears that reduced or anomalous stress sensitivity is likely to be more important for 4d projects with frequent acquisitions of 3 12 months but is of less concern when seismic is repeated on conventional time periods of every 5 10 years the critical set of parameters required to carry out accurate calibration of these predictions is not yet fully available from published literature

basal ice microbiology at the margin of the greenland ice sheet basal ice at the margin of the greenland ice sheet was studied with respect to its physical characteristics and microbiological community the basal ice contained high concentrations of dissolved ferrous fe and must therefore be anoxic oxygen consumption experiments indicate that 50 of the oxidation was due to biological activity while the rest could be attributed to chemical processes most likely weathering reactions with ferrous fe at least six different fe containing mineral sources were detected in basal ice together with potential bioavailable fe nanoparticles an active denitrifier population was identified due to formation of 30 n dinitrogen gas after amendment of anoxic sediment slurries with 15 n no3 sulfate reduction could not be detected the solid ice facies contained an abundant 10 8 cells cm 3 and complex microbial community that harbored representatives of at least eight major phyla within the domain bacteria the clone library was dominated by members of the subdivision of proteobacteria of which the largest proportion was affiliated to the genus rhodoferax that comprises facultative aerobic iron reducers the second most abundant phylum was bacteroidetes the solid ice facies had many physical similarities with the overlying debris rich banded ice facies indicating that they formed by similar subglacial processes and harbor similar microbial communities this study extends our knowledge of life in subglacial environments such as beneath ice sheets genbank accession numbers hm439882 hm439950 hq144215 hq144221

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

reponse aux commentaires de lattanzi et al au sujet des articles sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie

the cryoconite ecosystem on the greenland ice sheet this paper presents an assessment of biological activity associated with ice surface debris cryoconite at the ice sheet scale estimates of the mass distribution of cryoconite over the greenland ice sheet gis and the biological activity associated with it are presented and then coupled with a surface mass balance model to estimate total carbon fluxes due to respiration and photosynthesis we find an average loading of 66 g m 2 at kangerlussuaq southwest greenland which compares well with recent estimates from kronprins christians land 17 440 g m 2 boggild and others 2010 in northeast greenland we also report a significant microbial biomass in cryoconite at both these places 10 3 10 4 cells mg 1 and carbon fluxes of the order of 1 3 m mcg 1 d 1 for both respiration and photosynthesis the modelling indicates that total respiration and photosynthesis fluxes are likely to be 10 1 10 2 gg c a 1 and thus far from trivial however estimation of the net ecosystem impact across the entire ice sheet on atmospheric co2 concentrations is problematic because photosynthesis rates were almost certainly low during our field campaign therefore like its water balance the carbon balance of the gis is now known to be important but its accurate quantification will remain elusive until more data are forthcoming

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

an introduction to reservoir geomechanics production of hydrocarbons leads to changes in reservoir pore pressure resulting in changes in the stress acting on the reservoir and surrounding rocks a decrease in pore pressure due to depletion leads to an increase in stress carried by the load bearing rock frame of the reservoir and may be accompanied by microscale deformation mechanisms such as cement breakage at grain contacts grain sliding and rotation hertzian cracking at point contacts plastic deformation of clay and mica grains and opening and closing of microcracks schutjens et al 2004 the increasing stress acting on the rock framework may also lead to compaction of the reservoir and may result in problems such as surface subsidence casing deformation reactivation of faults or bedding parallel slip evidence for stress changes in and around reservoirs undergoing depletion is provided by seismic events resulting from production segall 1989 grasso 1992 and by time shifts observed using time lapse seismic hatchell et al 200

analysis of time lapse travel time and amplitude changes to assess reservoir compartmentalization fluid depletion within a compacting reservoir can lead to significant stress and strain changes and potentially severe geomechanical issues both inside and outside the reservoir we extend previous research of time lapse seismic interpretation by incorporating synthetic near offset and full offset common midpoint reflection data using anisotropic ray tracing to investigate uncertainties in time lapse seismic observations the time lapse seismic simulations use dynamic elasticity models built from hydro geomechanical simulation output and a stress dependent rock physics model the reservoir model is a conceptual two fault graben reservoir where we allow the fault fluid flow transmissibility to vary from high to low to simulate non compartmentalized and compartmentalized reservoirs respectively the results indicate time lapse seismic amplitude changes and travel time shifts can be used to qualitatively identify reservoir compartmentalization due to the high repeatability and good quality of the time lapse synthetic dataset the estimated travel time shifts and amplitude changes for near offset data match the true model subsurface changes with minimal errors a 1d velocity strain relation was used to estimate the vertical velocity change for the reservoir bottom interface by applying zero offset time shifts from both the near offset and full offset measurements for near offset data the estimated p wave velocity changes were within 10 of the true value however for full offset data time lapse attributes are quantitatively reliable using standard time lapse seismic methods when an updated velocity model is used rather than the baseline model

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

subglacial sediment dispersal and till composition dispersal of subglacial sediment down ice from its bedrock source assumes the form of a negative exponential decay curve dispersal decay curves can be quantified by their decay constants half distances half lives and total transport distances mapped dispersal decay curves associated with pleistocene ice sheets in north america and europe identify several scales of dispersal ranging from local kilometers to continental 100 s to 1000 s km scales till composition reflects the various scales of dispersal local scales short transport distances result in tills that reflect underlying bedrock whereas continental scales long transport distances result in tills derived largely from sources far up ice a number of parameters proposed as influencing subglacial sediment dispersal and transport distances do not explain the range of scales observed although they may explain minor variations kilometers in transport distances topography and basal ice velocity sliding velocity are interpreted as

organic carbon export from the greenland ice sheet abstract glacial meltwater exports a unique type of organic carbon to marine systems distinct from non glacially derived riverine export potentially capable of stimulating downstream marine primary productivity here we describe for the first time the bulk level dissolved organic carbon doc and particulate organic carbon poc isotopic composition of glacial meltwater draining the greenland ice sheet gris these data in conjunction with an earlier study that investigated the molecular level composition of gris dissolved organic matter collectively describe the concentration radiocarbon content and lability of organic carbon in subglacial discharge from a land terminating outlet glacier during a melt season by scaling up our measurements across the ice sheet we estimate that the annual doc flux from the gris 0 08 tg y is equivalent to that from a small arctic river discharge q 3 y and that the annual poc flux from the gris 0 9 tg y may be comparable to that of a large arctic river q 200 km 3 y the doc flux is derived primarily from beneath the glacier subglacial 75 in the early season and from surface ice melt up to 100 transmitting through the subglacial environment at the peak of the meltseason the poc flux is primarily derived from the subglacial environment throughout the meltseason the early season low flow glacier discharge contains higher doc concentrations 0 5 4 1 mg l 1 and exports more enriched carbon 14 c doc 250 compared to the peak season high flow discharge when the concentrations are lower 0 1 0 6 mg l 1 and the 14 c is more depleted 14 c doc 400 conversely the poc export 1 4 13 2 mg l 1 14 c poc 250 shows no temporal variation in either concentration or radiocarbon content throughout the meltseason dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system confirming the influence of subglacial hydrology on the composition of the bulk carbon pools based on this work we conclude that 1 different mechanisms control the doc and poc flux from glacial systems 2 chemically distinct doc pools are accessed by seasonally evolving hydrological flow paths and 3 the gris can deliver labile carbon which may also be 14 c depleted to downstream proglacial and marine environments

asymmetry in the time lapse seismic response to injection and depletion large changes in seismic reflection amplitude have been observed around injectors and result from the decrease in elastic wave velocity due to the increase in pore pressure in the reservoir in contrast the velocity change resulting from the decrease in pore pressure in depleting reservoirs is observed to be smaller in magnitude elastic wave velocities in sandstones vary with stress due to the presence of stress sensitive grain boundaries within the rock grain boundary stiffness increases non linearly with increasing compressive stress due to increased contact between opposing faces of the boundary this results in a change in velocity due to a decrease in pore pressure that is smaller than the change in velocity caused by an increase in pore pressure in agreement with time lapse seismic observations the decrease in porosity resulting from depletion is not fully recovered upon re pressurization and this leads to an additional steepening of the velocity vs effective stress curve for injection relative to depletion this difference is enhanced by any breakage of cement or weakening of grain contacts that may occur during depletion and by the reopening or formation of fractures or joints and dilation of grain boundaries that may occur during injection

recent large increases in freshwater fluxes from greenland into the north atlantic 1 freshwater fw fluxes from river runoff and precipitation minus evaporation for the pan arctic seas are relatively well documented and prescribed in ocean gcms fluxes from greenland on the other hand are generally ignored altogether despite their potential impacts on ocean circulation and marine biology here we present a reconstruction of the spatially distributed fw flux from greenland for 1958 2010 we find a modest increase into the arctic ocean during this period fluxes into the irminger basin however have increased by fifty percent 6 3 0 5 km3 yr 2 in less than twenty years this greatly exceeds previous estimates for the ice sheet as a whole the rate of increase since 1992 is 16 9 1 8 km3 yr 2 the cumulative fw anomaly since 1995 is 3200 358 km3 which is about a third of the magnitude of the great salinity anomaly gsa of the 1970s if this trend continues into the future the anomaly will exceed that of the gsa by about 2025

inverting for reservoir pressure change using time lapse time strain application to genesis field gulf of mexico there are increasing numbers of published examples from around the world in which significant 4d time shifts have been observed in the overburden above producing reservoirs

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

effects of increase glacier discharge on phytoplankton bloom dynamics and pelagic geochemistry in a high arctic fjord arctic fjords experience extremely pronounced seasonal variability and spatial heterogeneity associated with changes in ice cover glacial retreat and the intrusion of continental shelf s adjacent water masses global warming intensifies natural environmental variability on these important systems yet the regional and global effects of these processes are still poorly understood in the present study we examine seasonal and spatial variability in kongsfjorden on the western coast of spitsbergen svalbard we report hydrological biological and biogeochemical data collected during spring summer and fall 2012 our results show a strong phytoplankton bloom with the highest chlorophyll a chla levels ever reported in this area peaking 15 5 g l during late may and completely dominated by large diatoms at the inner fjord that may sustain both pelagic and benthic production under weakly stratified conditions at the glacier front a progressively stronger stratification of the water column during summer and fall was shaped by the intrusion of warm atlantic water t 3 c and sal 34 65 into the fjord at around 100 m depth and by turbid freshwater plumes t 1 c and sal 34 65 at the surface due to glacier meltwater input biopolymeric carbon fractions and isotopic signatures of the particulate organic material pom revealed very fresh and labile material produced during the spring bloom 13c enriched with values up to 22 7 at the highest chl a peak and high in carbohydrates and proteins content up to 167 and 148 g l respectively and a clear and strong continental signature of the pom present during late summer and fall 13c depleted with values averaging 26 5 and high in lipid content up to 92 g l when freshwater melting is accentuated our data evidence the importance of combining both physical i e water mass dominance and geochemical i e characteristics of material released by glacier runoff data in order to understand the timing intensity and characteristics of the phytoplankton bloom in kongsfjorden a continuously changing system due to sustained warming in a scenario where glacial retreat is predicted to increase the impacts of meltwater discharge and associated delivery of organic and inorganic material to the surrounding waters special attention is required in order to predict the consequences for arctic fjords and adjacent shelf ecosystems

comments on the paper of r dechomets sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie

an insightful parametrization for the flatlander s interpretation of time lapsed seismic data an approximation is developed that allows mapped 4d seismic amplitudes and time shifts to be related directly to the weighted linear sum of pore pressure and saturation changes the weights in this relation are identified as key groups of parameters from a petroelastic model and include the reservoir porosity this dependence on groups of parameters explains the inherent non uniqueness of this problem experienced by previous researchers the proposed relation is of use in 4d seismic data feasibility studies and inversion and interpretation of the 4d seismic response in terms of pore pressure and water saturation changes a further result is drawn from analysis of data from the north sea and west africa which reveals that the relative interplay between the effects of pore pressure and saturation changes on the seismic data can be simplified to the control of a single spatially variant parameter cs cp combining these results with those from published literature we find that cs cp 8 appears to be a generality across a range of clastic reservoirs with a similar mean porosity using this cs cp value an in situ seismic scale constraint for the rock stress sensitivity component of the petroelastic model is constructed considering this component carries the largest uncertainty

shale permeability and its significance in hydrocarbon exploration a complex dynamic series of chemical physical and geologic processes influence the creation sediment infilling and fluid quality history of sedimentary basins deposits of sands and muds for example through progressive burial and compaction become exposed to increased temperatures and pressures this exposure precipitates a series of interrelated diagenetic and mechanical processes that in turn alter the physical and chemical properties of the sediments and their pore fluids hydrocarbon generation from kerogens organic material is one important consequence of sediment diagenesis such processes also control the capacity of a particular sediment to transport and store fluids which in some cases results in hydrocarbon bearing reservoirs

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

source and biolability of ancient dissolved organic matter in glacier and lake ecosystems on the tibetan plateau the tibetan plateau is the world s largest and highest plateau and holds the largest mass of ice on earth outside the icesheets of greenland and antarctica as well as abundant lakes this study examined the molecular and isotopic signatures of dissolved organic matter dom along with its biolability in glacier ice glacier fed streams and alpine lakes on the tibetan plateau the aim was to assess the sources of dom and the potential of dom to provide a carbon subsidy to downstream ecosystems tibetan glaciers and glacier streams exhibited low dissolved organic carbon doc concentrations 17 7 27 9 lm and ancient doc radiocarbon ages 749 2350 ybp the optical properties stable carbon isotope ratios d 13 cdoc and the molecular composition fourier transform ion cyclotron resonance mass spectrometry of tibetan glacier dom are consistent with data from other glacier systems around the world the geochemical signatures and the ancient apparent ages of tibetan glacier dom suggest a significant fraction is derived from the atmospheric deposition of pre aged possibly fossil fuel derived organics within the tibetan alpine lakes doc was also ancient 525 675 ybp due to either inputs of pre aged organics from glacier runoff direct deposition or due to the aging of organics in situ i e a radiocarbon reservoir effect the glacier ice and glacier stream sites exhibited high biolability of doc and so provide a carbon subsidy to downstream environments that will change as glaciers on the tibetan plateau recede

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

trickle or treat the dynamics of nutrient export from polar glaciers cold based polar glacier watersheds contain well defined supraglacial ice marginal and proglacial elements that differ in their degree of hydrologic connectivity sources of water e g snow ice and or sediment pore water meltwater residence times allochthonous and autochthonous nutrient and sediment loads we investigated 11 distinct hydrological units along the supraglacial ice marginal and proglacial flow paths that drain joyce glacier in the mcmurdo dry valleys of antarctica we found that these units play unique and important roles as sources and or sinks for dissolved inorganic nitrogen and dissolved inorganic phosphorus and for specific fractions of dissolved organic matter dom as waters are routed from the glacier into nutrient poor downstream ecosystems changes in nutrient export from the glacial system as a whole were observed as the routing and residence times of meltwater changed throughout the melt season the concentrations of major ions in the proglacial stream were inversely proportional to discharge such that there was a relatively constant trickle of these solutes into downstream ecosystems in contrast no3 concentrations generally increased with discharge resulting in delivery of episodic pulses of dissolved inorganic nitrogen rich water treats into those same ecosystems during high discharge events dom concentrations or fluorescence did not correlate with discharge rate but high variability in dom concentrations or fluorescence suggests that dom may be exported downstream as episodic treats but with spatial and or temporal patterns that remain poorly understood the strong nutrient specific responses to changes in hydrology suggest that polar glacier drainage systems may export meltwater with nutrient compositions that vary within and between melt seasons and watersheds because nutrient dynamics identified in this study differ between glacier watersheds with broadly similar hydrology climate and geology we emphasize the need to develop conceptual models of nutrient export that thoroughly integrate the biogeochemical and

the iron isotopic composition of subglacial streams draining the greenland ice sheet abstract in this study we present the first measurements of iron fe stable isotopic composition 56 fe of subglacial streams draining the greenland ice sheet gis we measure the 56 fe values 56 fe 56 fe 54 fe sample 56 fe 54 fe standard 1 10 3 of both dissolved and suspended sediment fe in subglacial outflows from five distinct land terminating glaciers suspended sediments have 56 fe values that lie within the crustal array 56 fe 0 in contrast the 56 fe values of dissolved fe in subglacial outflows are consistently less than 0 reaching a minimum of 2 1 in the outflow from the russell glacier the 56 fe values of dissolved fe vary geographically and on daily time scales major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream fe chemistry and that the extent of chemical weathering influences the 56 fe of dissolved fe the largest difference in 56 fe between dissolved and suspended load is 2 1 and occurs in the subglacial system from the russell glacier southwest gis major element chemistry indicates this outflow to be the least chemically weathered while more mature subglacial systems i e that exhibit greater extents of subglacial weathering have dissolved loads with 56 fe that are indistinguishable from suspended sediments 56 fe suspended dissolved 0 ultimately the dissolved fe generated in some subglacial systems from the gis is a previously unrecognized source of isotopically light fe into the hydrosphere the data illustrate that the dissolved fe supplied by subglacial weathering can have variable 56 fe values depending on the degree of chemical weathering thus fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode finally based on our regional fe concentration measurements from each glacial outflow we estimate a flux weighted continental scale dissolved iron export of 2 1 gg fe yr 1 to the coastal ocean which is within the range of previous estimates

a sulfur isotope study on pyrite deposits of southern tuscany italy the s isotope composition 34scdt of 213 samples of sulfides sulfates and native sulfur from the pyrite mineralizations of southern tuscany and associated country rocks were determined the sulfur isotopic composition of pyrite is quite homogeneous and similar for all studied ore bodies with an average 34s value near 9 5 pyrite disseminated within the filladi di boccheggiano formation and thought to be authigenic shows a much larger range of 34s values 13 1 to 14 5 the isotopic compositions of other sulfides associated with pyrite in the deposits show that isotopic equilibrium among sulfides was approached on a regional scale but seldom fully attained isotopic data suggest that sedimentary marine sulfate was the ultimate source of sulfur in ores

the 4d seismic signature of oil water contact movement due to natural production in a stacked turbidite reservoir combined time lapse reservoir simulation and seismic modelling has been performed on both 1d and 3d models of a channelized turbidite reservoir the models have been built using core log laboratory and seismic data from the nelson field central north sea as a template oil and water movement in the main channels channel margins and interchannel regions is investigated with a particular focus being the effect of poor net to gross the analysis confirms that saturation effects dominate the response whilst stress sensitivity effects play a minor role the trough peak signature in the seismic difference volumes formed by the sweep of the water can be continued and mapped slightly further than the channel margins this characteristic 4d signature remains roughly intact despite the complicated depositional architecture and accurately delineates the area of moved fluid but it needs additional calibration to combat the detrimental influence of the low net to gross signal strength is largely dependent on reservoir quality but is also compromised by the net to gross fluid distribution and more critically by the exact timing of the seismic survey for example a region of bypassed oil zone remains undetected as it forms early during the production this work demonstrates that to understand fully the 4d signature at a quantitative level requires adequate knowledge of the fluid properties but also more critically the geology

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

induced stresses due to fluid extraction from axisymmetric reservoirs earthquakes can be induced by fluid extraction as well as by fluid injection segall 1989 proposed that poroelastic stresses are responsible for inducing earthquakes associated with fluid extraction here i present methods for computing poroelastic stress changes due to fluid extraction for general axisymmetric reservoir geometries the results ofgeertsma 1973 for a thin disk reservoir with uniform pressure drop are recovered as a special case predicted surface subsidence agrees very well with measured leveling changes over the deep lacq gas field in southwestern france the induced stresses are finite if the reservoir pressure changes are continuous computed stress changes are on the order of several bars suggesting that the preexisting stress states in regions of extraction induced seismicity are very close to frictional instability prior to production

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

chemical weathering across the western foreland of the greenland ice sheet abstract proglacial streams deliver melt water and chemical weathering products including nutrients and radiogenic isotopes from continental ice sheets to the ocean weathering products are also delivered to the ocean in non glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides if weathering reactions differ in non glacial and proglacial stream catchments the streams could deliver different types and magnitudes of solutes to the ocean depending on relative discharge volumes unlike proglacial streams however little is known of non glacial stream solute compositions or discharge here we show specific discharges are similar from a proglacial stream draining the greenland ice sheet gris with several streams disconnected from the ice sheet we also evaluate weathering reactions across a 170 km transect in western greenland that contains one proglacial stream draining the gris and two coastal ice distal and three inland ice proximal areas with non glacial streams non glacial streams exhibit solute compositions and offsets between dissolved and bedload sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in stream weathering that consumes co2 about 5 times less co2 is consumed per liter in the proglacial than inland non glacial streams however arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total co2 weathering than proglacial stream one coastal area consumes less co2 per liter than the proglacial stream and another coastal area exhibits net co2 production these results indicate estimates for glacial foreland solute fluxes and co2 weathering consumption and production should include estimates from both non glacial and proglacial streams understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and co2 fluxes associated with continued ice sheet retreat

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie l etude detaillee du gisement de niccioleta revele les reactions metasomatiques ayant transforme l anhydrite en grenatite la dolomie en pyroxenite et les micaschistes en epidotite et celles qui ont entraine la reduction du sulfate en pyrite les solutions ferriferes ont lessive na k co2 et partiellement ca mg et s l inertie de al et ti et les deplacements de ca si s et sr precisent les modalites des transformations dont on a evalue les bilans pour un volume restant constant le comportement de s est complexe lessive lors de la grenatisation il est apporte lors de la cristallisation de la pyrite sans que le bilan global soit equilibre l origine de ce s est discutee en liaison avec le contexte evaporitique et un systeme geothermique regional tertiaire en l absence de preuve d eventuelles preconcentrations sulfurees syn sedimentaires le gisement parait resulter d une metasomatose de l anhydrite dans un systeme geothermique semblable a celui de larderello mais a alimentation marine

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie physico chimie de la mtallogense nature et origine des fluides hydrothermaux systme gothermal

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

deepwater turbidite system analysis west africa sedimentary model and implications for reservoir model construction the complex sedimentary architecture of various offshore turbidite systems within the tertiary formations of gulf of guinea offshore west africa can be explained by using 3d seismic interpretation to define sedimentary and stratigraphically units which then become input for reservoir models and simulations the geologic model is composed of sedimentary units of different scales whose width thickness and lateral continuity composition facies partitions and lateral vertical succession are determined from analysis of 3d seismic and well data

transformation of organic matter in a barents sea sediment profile coupled geochemical and microbiological processes process based mechanistic investigations of organic matter transformation and diagenesis directly beneath the sedimentwater interface swi in arctic continental shelves are vital as these regions

the ice age methane budget 1 accounting for the natural 40 reduction in methane during the last glacial maximum lgm represents one of the most challenging problems posed by polar ice core studies inverse modelling constrained by observations suggest it is driven by a decline in wetland sources but this is not supported by forward modelling using a comprehensive earth system model we show that closure of the methane budget requires reduced emissions and an amplified sink caused by reduction in emissions of volatile organic compounds vocs from lgm forests our study emphasizes a key role for the terrestrial biosphere in the methane budget during the quaternary

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the larderello travale geothermal field different authigenic mineral assemblages and mineral compositions have been found in different areas of the larderello travale geothermal field in the peripheral areas the most abundant authigenic minerals are quartz calcite chlorite and sulfides they formed in a temperature range of 150 sup 0 to 250 sup 0 c and with a p sub co2 range of 0 1 to 1 0 atm in a hotter part of the field at depths between 200 and 1 300 m where the main productive fractures are located the most important authigenic minerals are quartz chlorite calcite k feldspar and k bearing mica with which wairakite hematite anhydrite and barite are sometimes associated deposition of all these minerals occurs in a temperature range of 200 sup 0 to 300 sup 0 c under p sub co2 of about 1 atm and relatively high p sub o2 in fluids sometimes characterized by silica oversaturation below the 1 300 m depth in the hottest part of the field k feldspar chlorite epidote sulfides with minor sphene prehnite clinopyroxene and clinoamphibole are present these minerals form in a temperature range of 250 sup 0 to 350 sup 0 c under a p sub co2 of less than 1 atm and a p sub o2 ranging from 10 sup 40 to 10 sup 33 atm and reasonablymore reflect the physicochemical parameters of the geothermal fluid before exploitation evidence of an earlier hydrothermal stage characterized by higher temperatures can be seen in the occurrence of relic wollastonite and andradite less

carbon dating reveals a seasonal progression in the source of particulate organic carbon exported from the greenland ice sheet surface melt from the greenland ice sheet gris collects particulate organic carbon poc as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate we hypothesized that older poc is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer to test this poc samples were collected from a meltwater river exiting the gris over an ablation season and 14c dated resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area we found that poc ages increased from 5000 to 9000 years b p until peak discharge and catchment size afterward significant fluctuations in poc age were observed interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion these observations suggest a seasonal progression in the source of poc exported from the gris and provide evidence for a seasonally evolving subglacial drainage system

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd