the retreat of a tidewater glacier observations and model calculations on hansbreen spitsbergen based on observations and model calculations the retreat over the last two decades of hansbreen a tidewater glacier in southern spitsbergen svalbard is investigated the observations of the calving front position between 1982 and 1998 show an abrupt retreat in 1990 which is suggested to be related to a depression in the glacier bed the observed seasonal variations of the front position are mainly due to variations of the calving rate the observations of hansbreen further indicate that during periods of slow front position changes melting at the water line may play an important role in triggering the process of calving the evolution of hansbreen between 1982 and 1998 is simulated with a numerical model for the dynamics of tidewater glaciers using a flotation criterion for calving in which for each time step the part of the glacier terminus which is below a critical height above buoyancy is removed we are able to reproduce the observed rapid retreat of hansbreen through the depression in the glacier bed from the observations and model calculations we conclude that the rapid retreat is mainly an effect of basal topography in the terminus region and not a direct response to a change in mass balance

how are diagenesis and reservoir quality linked to depositional facies a deltaic succession edgeoya svalbard abstract middle to late triassic strata exposed at edgeoya eastern svalbard represents an uplifted part of the northwestern corner of the barents sea this interval is characterized by a predominantly mud dominated deltaic depositional system where rocks with petroleum reservoir potential are expected both in delta front and channelized sandstone deposits recent drilling campaigns into time equivalent rocks in the barents sea have however been disappointing with porosity and permeability below expectation this study improves the current understanding of reservoir potential within depositional systems of this kind by examining the link between different depositional facies diagenesis and their impact on reservoir quality five depositional facies were mapped and correlated channel floodplain shallow marine prodelta and offshore our study suggests that diagenetic signatures that control the quality of reservoir rocks vary systematically with these depositional facies mechanical compaction was the main cause of porosity destruction in the channel shallow marine and floodplain samples while early carbonate cementation occludes the intergranular volume in the prodelta samples moreover quartz cement reduced the porosity in the shallow marine depositional facies the estimated maximum burial temperature of 124 c indicates burial to several km depths depositional settings within a deltaic to shallow marine system do not exert a strong control on the abundance of chlorite but it does impact whether the chlorite is pore filling or grain coating and porosity preserving efficient chlorite coating have aided in preserving porosities up to 32 in the very well well sorted medium to fine grained sandstones deposited by fluvial dominated channels

contact diagenesis the effect of an intrusion on reservoir quality in the triassic sherwood sandstone group northern ireland abstract intrusion of a dolerite sill into clay bearing arkosic triassic sherwood group sandstones with moderate porosity 22 and high but anisotropic permeability mode 500 md led to the progressive transformation of precursor diagenetic minerals in the host rock locally pore filling mg rich smectite saponite quartz and dolomite existing in the rock following earlier burial diagenesis reacted to produce grain coating flakes of talc at the lowest contact temperatures 130 180 c based on equilibrium reaction path and thermal history calculations at higher temperatures 200 230 c talc reacted with calcite to produce an actinolitic amphibole close to the intrusion at temperatures of 250 c bundles of acicular needles of actinolite protruding into open pores were produced by a second reaction involving saponite hematite and calcite framework feldspar minerals mainly k feldspars played little or no part in the reactions because there were no k al rich minerals produced by contact diagenesis and because the detrital feldspar grains are essentially unaltered thus while equilibrium may have been approached on the intrapore scale 10 m it was not achieved between grains e g detrital feldspars pore water and clays in the pores total porosity has been unaffected by the intrusion and consequent mineral reactions because reactions involved recrystallization of original pore filling minerals despite the contact diagenetic changes in the rock the permeability of the sandstone remained largely unaffected by intrusion

diagenesis and formation water chemistry of triassic reservoir sandstones from southern tunisia the fluvial triassic reservoir subarkoses and arkoses 2409 5 2519 45 m of the el borma oilfield southern tunisia were subjected to cementation by haematite anatase infiltrated clays kaolinite and k feldspar at shallow burial depths from meteoric waters subsequently basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths magnesian siderite minor ferroan magnesite and anhydrite the enrichment of siderite in 12c isotope 13cpdb 14 5 to 9 results from derivation of carbon from the thermal decarboxylation of organic matter during further burial the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred followed by the formation of microcrystalline k feldspar and quartz chlorite and illite prior to the emplacement of oil present day formation waters are na ca cl brines evolved by the evaporation of seawater and water mineral interaction and are in equilibrium with the deep burial 3 1 km minerals these waters are suggested to be derived from the underlying silurian and devonian dolomitic mudstones

effects of initial density on soil instability at high pressures a high pressure triaxial compression and extension testing apparatus was utilized to investigate the effect of initial relative density on soil instability stress paths from a series of undrained tests at confining pressures from 8 to 60 mpa were evaluated to determine the location of the potential instability region experiments were performed on specimens with relative densities of 30 and 60 and compared with previously published results for 90 the results indicate that initial relative density has a small effect on the slope of the instability line with the slope of the line decreasing as initial density is reduced in addition the conditions under which a specimen exhibits unstable behavior were confirmed by performing series of specialized instability tests for tests with undrained conditions imposed inside the region of potential instability instability was observed immediately for tests with undrained conditions imposed outside but relatively close to this region creep effects would cause pore pressures to increase resulting eventually in instability in general it was found that initiation of unstable behavior depends on the relationship between the shape of the yield surface and the effective stress path followed

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

reservoir quality controls on rotliegend fluvio aeolian wells in germany and the netherlands southern permian basin impact of grain coatings and cements abstract reservoir quality in sandstones can be a function of temperature pressure and chemical alterations over time some intrinsic properties of sandstones can additionally impact the evolution of reservoir quality the detrital composition depositional environment and properties controlled thereby dictate some of the diagenetic changes extrinsic processes like external fluids e g from hydrothermal events or dewatering of clay minerals can additionally result in changes of reservoir quality one of these properties are grain coatings on quartz grains which can strongly affect pore cementation by quartz overgrowths to predict and infer the quality of undrilled reservoirs constraints are needed to predict their occurrence we analyse two reservoir settings in the southern permian basin and delineate the impact of depositional systems lithologies detrital and authigenic composition on reservoir quality and with regard to grain coatings results highlight the importance of diagenetic alterations and the source area in regards to burial development in different parts of the southern permian basin samples from the rotliegend bahnsen sandstone member from germany and the slochteren sandstone formation from the netherlands have been petrographically and petrophysically analysed and linked to depositional environments our data shows that the emplacement and presence of grain coating minerals cannot be simply linked to the depositional environment or processes controlled thereby e g grain size and sorting neither on a reservoir nor on a basin scale the dissolution of alumosilicates additionally has no consistent impact on the authigenesis of chloritic grain coatings on the reservoir or basin scale in this study this implies the necessity of sample specific analyses and importance of the assessment of diagenetic alterations when analysing modelling or predicting reservoir quality in similar settings worldwide

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

finite element analysis of the nerlerk underwater berm failures finite element analyses have been carried out to investigate the possible causes of failure during construction of the nerlerk underwater berm a hydraulically placed sand slope designed to form

rapid climate driven changes in outlet glaciers on the pacific coast of east antarctica multidecadal trends in the terminus position of outlet glaciers along the margin of the east antarctic ice sheet reveal three epochal patterns of glacier retreat or advance consistent with a rapid and coherent response to air temperature and sea ice trends it is widely known that glaciers in west antarctica and greenland have been discharging ice into the oceans in response to warming in recent years and that sea levels have risen as a result by contrast we hear little about the much larger east antarctic ice sheet which has been viewed as being less vulnerable to climate change owing to its location in an extremely cold climate chris stokes and colleagues have used satellite imagery to map a large sample of glaciers along the pacific coast of east antarctica and show that in fact they are responding to decadal climate variability in concert with climate glaciers retreated in the 1970s and 1980s advanced in the 1990s and approximately split between advance and retreat since the 2000s the authors conclude that parts of the world s largest ice sheet may be more responsive to external forcing than previously recognized observations of ocean terminating outlet glaciers in greenland and west antarctica1 2 3 4 5 6 indicate that their contribution to sea level is accelerating as a result of increased velocity thinning and retreat7 8 9 10 11 thinning has also been reported along the margin of the much larger east antarctic ice sheet1 but whether glaciers are advancing or retreating there is largely unknown and there has been no attempt to place such changes in the context of localized mass loss7 9 or climatic or oceanic forcing here we present multidecadal trends in the terminus position of 175 ocean terminating outlet glaciers along 5 400 kilometres of the margin of the east antarctic ice sheet and reveal widespread and synchronous changes despite large fluctuations between glaciers linked to their size three epochal patterns emerged 63 per cent of glaciers retreated from 1974 to 1990 72 per cent advanced from 1990 to 2000 and 58 per cent advanced from 2000 to 2010 these trends were most pronounced along the warmer western south pacific coast whereas glaciers along the cooler ross sea coast experienced no significant changes we find that glacier change along the pacific coast is consistent with a rapid and coherent response to air temperature and sea ice trends linked through the dominant mode of atmospheric variability the southern annular mode we conclude that parts of the world s largest ice sheet may be more vulnerable to external forcing than recognized previously

authigenesis of amphibole and its relationship to the diagenetic evolution of lower cretaceous sandstones of the potiguar rift basin northeastern brazil abstract authigenic amphibole occurs in the fan delta front arkoses and lithic sandstones of the neocomian pendencia formation in the potiguar rift basin northeastern brazil as overgrowths fracture healing and replacement of detrital amphibole the amphibole which is closely associated with diagenetic albite chlorite and sphene has precipitated from k na cl brines enriched in ti fe mg at temperatures 100 c these ions were derived from the diagenetic alteration of detrital amphibole and pyroxene chloritization of volcaniclastic sediments at the base of the formation and from brines that ascended along faults from the underlying basement

northern larsen ice shelf antarctica further retreat after collapse changes of larsen ice shelf antarctica and the surrounding glaciers after its collapse in 1995 were investigated using satellite radar imagery with emphasis onchanges in the glaciers which previously nourished the ice shelf north of seal nunataks the large glaciers retreated several kilometres inland of the previousgrounding line the velocity field of drygalski glacier the largest glacier in this area was mapped by means of interferograms derived from pairs of ers syntheticaperture radar images from 1995 and 1999 the main part of the glacier showed significant acceleration of flow over these 4 years with an increase of veocity upto three fold at the terminus similar accelerations were observed by means of interferometry on several other grounded glaciers suggesting that the removal ofice shelves could lead to an effect on eustatic sea level for larsen b the northernmost surviving part of larsen ice shelf the retreat of the ice front to october2000 is documented

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

weathering secondary mineral genesis and soil formation caused by lichens and mosses growing on granitic gneiss in a boreal forest environment abstract lichens and mosses growing on granitic gneiss in a boreal forest environment caused intense chemical weathering of the rock producing exclusively biogenic secondary minerals and soils and accumulating solubilised rock forming elements si and metals but weathering in the absence of these organisms was relatively ineffective apart from primary biotite the only phyllosilicates in the rock were sericite and chlorite formed by hydrothermal metamorphism or abiotic weathering or both but the biogenic soils contained expandable clay minerals and in several cases kaolinite and calcite together with illite and chlorite lichens were especially effective in altering feldspars to clay but mosses generally produced a greater abundance of expandable clay minerals and kaolinite was produced only by certain species of moss specifically the ones whose rock derived element concentrations and mg ca ratios were highest rock derived element concentrations were usually highest in mosses and element enrichment increased with the charge radius ratio of the cation of the element suggesting carrier mediated transport across cell membranes furthermore lichens and mosses produced different assemblages of expandable clay minerals and most mosses but none of the lichens produced authigenic amphiboles and pyroxenes biological weathering is attributable to solubilisation of rock forming elements by chelating agents and h2co3 bioaccumulation of the elements and nucleation of secondary silicates by chelate complexes functioning as templates for epitaxial growth of specific crystal structures the different weathering and soil forming processes of lichens and mosses suggest a mutualistic strategy for maximising the release of inorganic nutrients from rocks and retaining them in bioavailable forms in the soil

evaluation of the in situ state of fraser river sand les glissements de type coulee par liquefaction sont des phenomenes qui arrivent souvent dans le delta de la riviere fraser du cote de sand heads ces ruptures n ont pas trouve d explication et leurs causes restent du domaine de la speculation l etude d un tel glissement ayant eu lieu en 1985 dans la riviere fraser a proximite de sand heads a ete entreprise en utilisant les concepts d etats stationnaires pour qu un glissement par coulee impliquant la liquefaction de depots de sables puisse prendre place le sable doit presenter un ramollissement lors du cisaillement non draine et les contraintes de cisaillement en place doivent etre superieures a la resistance non drainee mobilisable on a effectue des essais de laboratoire sur des echantillons reconstitues de sable de la riviere fraser de facon a etablir les parametres d etat stationnaire les specimens de sol ont ete prepares par compaction humide et pluviation dans l eau des mesures de vitesse de propagation des ondes de cisaillement ont ete utilisees pour evaluer l etat en place des depots de sable recents et non cimentes on a trouve que l etat en place des depots recents au voisinage de sand heads se situait du cote l che de l etat stationnaire ce qui correspond aux instabilites observees sur le site

changes in ice dynamics elevation and mass discharge of dinsmoor bombardier edgeworth glacier system antarctic peninsula abstract the northern antarctic peninsula is one of the fastest changing regions on earth the disintegration of the larsen a ice shelf in 1995 caused tributary glaciers to adjust by speeding up surface lowering and overall increased ice mass discharge in this study we investigate the temporal variation of these changes at the dinsmoor bombardier edgeworth glacier system by analyzing dense time series from various spaceborne and airborne earth observation missions precollapse ice shelf conditions and subsequent adjustments through 2014 were covered our results show a response of the glacier system some months after the breakup reaching maximum surface velocities at the glacier front of up to 8 8 m d in 1999 and a subsequent decrease to 1 5 m d in 2014 using a dense time series of interferometrically derived tandem x digital elevation models and photogrammetric data an exponential function was fitted for the decrease in surface elevation elevation changes in areas below 1000 m a s l amounted to at least 130 15 m between 1995 and 2014 with change rates of 3 15 m a between 2003 and 2008 current change rates 2010 2014 are in the range of 1 7 m a mass imbalances were computed with different scenarios of boundary conditions the most plausible results amount to 40 7 3 9 gt the contribution to sea level rise was estimated to be 18 8 1 8 gt corresponding to a 0 052 0 005 mm sea level equivalent for the period 1995 2014 our analysis and scenario considerations revealed that major uncertainties still exist due to insufficiently accurate ice thickness information the second largest uncertainty in the computations was the glacier surface mass balance which is still poorly known our time series analysis facilitates an improved comparison with grace data and as input to modeling of glacio isostatic uplift in this region the study contributed to a better understanding of how glacier systems adjust to ice shelf disintegration

the retreat of jones ice shelf antarctic peninsula in recent decades several ice shelves along the antarctic peninsula have diminished in size as a result of climate warming using aerial photographic satellite and survey data we document a similar retreat of jones ice shelf which was another small ice shelf on the west coast of the antarctic peninsula this ice shelf was roughly stable between 1947 and 1969 but in the early 1970s it began to retreat and had completely disappeared by early 2003 jones ice shelf has two ice fronts only a few kilometres apart and its retreat provides a unique opportunity to examine how different ice fronts retreat when subjected to similar climate forcing we mapped the retreat of both the east and west ice fronts of jones ice shelf and found that although individual episodes of retreat may be related to particularly warm summers the overall progress of retreat of the two ice fronts has been rather different this suggests that in this case the course of retreat is controlled by the geometry of the embayment and location of pinning points as well as climatic events

a critical state constitutive model for liquefiable sand this paper presents a critical state constitutive model for sands over a wide range of void ratios and consolidation pressures in a triaxial plane a single set of parameters including a unique critical state line reached at large strain is also used in the model and differences in behavior in triaxial compression and extension are modeled by accounting for anisotropy at small and medium ranges of strain the model uses a capped yield surface ys which is characterized by its size and shape following evidence in past literature the stress ratio at the peak point of the capped ys of loose sands is approximated by the stress ratio measured at the peak point of their undrained effective stress path yielding parameters obtained using this stress ratio are also applied in modeling dense sand behavior and drained loading these parameters account for the effects of inherent anisotropy void ratio and confining pressure on yielding stresses and are readily determined from laboratory tests but further r

nature of the antarctic peninsula ice sheet during the pliocene geological evidence and modelling results compared abstract in this paper we examine the nature of the pliocene antarctic peninsula ice sheet by comparing the terrestrial and marine geological records of the antarctic peninsula and surrounding sea floor with estimated net snow accumulation in the region derived from numerical palaeoclimate model experiments pliocene geological data and our new modelling results are consistent and mutually supportive in suggesting that an ice sheet was present even during the warmest episodes of the pliocene the combined results suggest that the ice sheet in the antarctic peninsula is more robust to globally warmer conditions than is generally assumed at least up to the climatic limits examined in our study

late holocene glacial advance and ice shelf growth in barilari bay graham land west antarctic peninsula three marine sediment cores were collected along the length of the fjord axis of barilari bay graham land west antarctic peninsula 65 55 s 64 43 w multi proxy analytical results constrained by high resolution geochronological methods 210 pb radiocarbon 137 cs in concert with historical observations capture a record of holocene paleoenvironmental variability our results suggest early and middle holocene 7022 2815 cal calibrated yr b p retreated glacial positions and seasonally open marine conditions with increased primary productivity climatic cooling increased sea ice coverage and decreased primary productivity during the neoglacial 2815 to cal 730 cal yr b p this climatic cooling culminated with glacial advance to maximum holocene positions and expansion of a fjord wide ice shelf during the little ice age lia ca 730 82 cal yr b p seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming 82 cal yr b p to present our findings agree with previously observed late holocene cooling and glacial advance across the antarctic peninsula suggesting that the lia was a regionally significant event with few disparities in timing and magnitude comparison of the lia antarctic peninsula record to the rest of the southern hemisphere demonstrates close synchronicity in the southeast pacific and southern most atlantic region but less coherence for the southwest pacific and indian oceans comparisons with the northern hemisphere demonstrate that the lia antarctic peninsula record was contemporaneous with pre lia cooling and sea ice expansion in the north atlantic arctic suggesting a global reach for these events

porosity preserving chlorite cements in shallow marine volcaniclastic sandstones evidence from cretaceous sandstones of the sawan gas field pakistan sandstones that have high porosity and permeability at great burial depth and high temperatures are of economic importance because a significant amount of hydrocarbons have been discovered in such reservoirs the sawan gas field with an expected ultimate recovery of more than 1 tcf lies in the middle indus basin the reservoir rocks cretaceous volcaniclastic sandstones of the lower goru formation show very high porosities at a reservoir temperature of 175c and depths of 3000 to 3500 m 9842 to 11 483 ft the sandstones are mostly feldspathic litharenites strongly altered volcanic rock fragments are the most important lithic component the clay fraction consists of fe rich chlorite chamosite and illite diagenetic features such as compaction quartz overgrowths carbonate cements and feldspar dissolution are observed the most distinguishing feature is a double layer of authigenic chlorite lining the pores of the sandstones chlorite additionally occurs as a pore filling cement and as chloritized detrital components all having similar chemical composition the pore lining cement clearly developed in two stages an earlier poorly crystallized and a later better crystallized growth missing rims at grain contacts show that precipitation occurred after an initial stage of compaction but early relative to other diagenetic phases both chlorite rims grew by direct precipitation from pore waters using products derived from volcanic rock fragments in areas with no thin or discontinuous chlorite rims quartz cementation is common well developed chlorite rims inhibited quartz cementation preserved porosities of up to 20 and good permeabilities porosity preserving chlorite cementation in sawan is restricted to sediments of a shallow marine environment

undrained anisotropy and principal stress rotation in saturated sand this paper describes an investigation carried out in a new hollow cylinder apparatus into anisotropy and the effects of principal stress rotation in a medium loose sand tested under undrained conditions principal stresses have been rotated at a constant shear stress during both monotonie and cyclic loading the experimental observations are described and then explained within a framework based on the concept of state boundary surfaces the over riding importance of initial anisotropy in determining the response of the sand to rotations in principal stress directions is demonstrated pore pressures are shown to be generated by rotation of principal stress directions at constant shear stress and their accumulation during cyclic principal stress rotation can lead to failure l article presente une etude de l anisotropie effectuee dans un nouvel appareil creux cylindrique et decrit les effets de la rotation de la contrainte principale dans un sable moyennement l che teste dans des conditions non drainees l

evidence of recent climatic warming on the eastern antarctic peninsula air temperatures at the stations marambio esperanza and matienzo have been analysed to investigate recent climate change on the eastern part of the antarctic peninsula the data are compared with the station orcadas on the south orkney islands the longest record available in antarctica and with faraday on the western coast of the peninsula though the interannual variability is comparatively high and the stations are located in different climatic regimes a pronounced warming trend shows up in all records at marambio a temperature increase of 1 5 c has been observed since the beginning of the record in 1971 this is of similar magnitude as the increase at the station faraday on the west coast with 2 5 c for the longer period since 1945 the steady retreat and collapse of the northern larsen ice shelf coincided with this warming trend of particular importance for the ice shelf mass balance in this region are the summer temperatures which show a statistically significant warming trend at the stations marambio and esperanza the representativity of the summer temperatures of marambio for northern larsen ice shelf is confirmed by intercomparison with the parallel measurements at matienzo which is located on the ice shelf

late 20th century increase in south pole snow accumulation a compilation of the 37 year history of net accumulation at the south pole mosley thompson et al 1995 suggests an increase in net annual accumulation since 1965 this record is sporadic and its quality is compromised by spatially restricted observations and nonsystematic measurement procedures results from a new spatially extensive network of 236 accumulation poles document that the current 5 year 1992 1997 average annual net accumulation at the south pole is 84 5 8 9 mm water equivalent w e this accumulation rate reflects a 30 increase since the 1960s when the best although not optimal records indicate that it was 65 mm w e identification of two prominent beta radioactivity horizons 1954 1955 and 1964 1965 in six firn cores confirms an increase in accumulation since 1965 viewed from a longer perspective of accumulation provided by ice cores and a snow mine study the net accumulation of the 30 year period 1965 1994 is the highest 30 year average of this millennium limited data suggest this recent accumulation increase extends beyond the south pole region and may be characteristic of the high east antarctic plateau enhanced accumulation over the polar ice sheets has been identified as a potential early indicator of warmer sea surface temperatures and may offset a portion of the current rise in global sea level

computing the volume response of the antarctic peninsula ice sheet to warming scenarios to 2200 the contribution to sea level to 2200 from the grounded mainland antarctic peninsula ice sheet apis was calculated using an ice sheet model initialized with a new technique computing ice fluxes based on observed surface velocities altimetry and surface mass balance and computing volume response using a linearized method volume change estimates of the apis resulting from surface mass balance anomalies calculated by the regional model racmo2 forced by a1b and e1 scenarios of the global models echam5 and hadcm3 predicted net negative sea level contributions between 0 5 and 12mm sea level equivalent sle by 2200 increased glacier flow due to ice thickening returned 15 of the increased accumulation to the sea by 2100 and 30 by 2200 the likely change in volume of the apis by 2200 in response to imposed 10 and 20km retreats of the grounding line at individual large outlet glaciers in palmer land southern antarctic peninsula ranged between 0 5 and 3 5mm sle per drainage basin ensemble calculations of apis volume change resulting from imposed grounding line retreat due to ice shelf break up scenarios applied to all 20 of the largest drainage basins in palmer land covering 40 of the total area of apis resulted in net sea level contributions of 7 16mm sle by 2100 and 10 25mm sle by 2200 inclusion of basins in the northern peninsula and realistic simulation of grounding line movement for ap outlet glaciers will improve future projections

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

marine record of holocene climate ocean and cryosphere interactions herbert sound james ross island antarctica abstract the sediment record offshore james ross island northeast antarctic peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the holocene in maritime antarctica an 11 m drill core was collected between herbert sound and croft bay as part of the shaldril nbp 0502 initiative and produced the southernmost sediment record from the eastern side of the ap thirty eight radiocarbon ages are used to construct an age model of centennial scale resolution multi proxy records including magnetic susceptibility pebble content particle size total organic carbon and diatom assemblages were interrogated in the context of nearby holocene age ice core lake and drift records from james ross island differences in the timing and expression of holocene events reflect marine controls on tidewater glaciers such as water mass configurations and sea ice glacial behavior mimics ice core paleotemperatures during the holocene with the exception of distinct ocean warming events herbert sound was fully occupied by grounded ice during the last glacial maximum and experienced rapid lift off followed by a floating ice phase the canopy of floating ice receded by 10 2 4 cal kyr bp presumably in response to early holocene warming herbert sound and croft bay fully deglaciated by 7 2 cal kyr bp when the mid holocene hypsithermal commenced and the sound became open and productive an extreme peak in productivity 6 1 cal kyr bp indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records increase in sea ice cover and ice rafting mark the onset of the neoglacial 2 5 cal kyr bp when pronounced atmospheric cooling is documented in the james ross island ice core our comparison facilitates more holistic understanding of atmosphere ocean cryosphere interactions that may aid predictions of glacial response to future warming and sea level scenarios

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

effect of microstructure on undrained behaviour of sands this paper presents a mathematical modelling of the effects of initial fabric on the mechanical behaviour of sand a stress dilatancy model that incorporates microstructural aspects of sand is hereby obtained while writing energy conservation for an ensemble of particles over a representative elementary volume at micro and macro scales the resulting stress dilatancy model when used within an elastoplastic framework successfully reproduces certain aspects of sand behaviour that are reflective of its microstructure under both drained and undrained conditions the role of microstructure in relation to the characterization of steady quasi steady and phase transformation states is discussed within the framework of the model numerical simulations obtained from the proposed model are generally very con sistent with experimental observations and provide insightful information

2001 2009 elevation and mass losses in the larsen a and b embayments antarctic peninsula we investigate the elevation and mass balance response of tributary glaciers following the loss of the larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively our study uses modis imagery to track ice extent and aster and spot5 digital elevation models dems plus atm and icesat laser altimetry to track elevation changes spanning the period 2001 09 the measured larsen b tributary glaciers hektoria green evans punchbowl jorum and crane lost up to 160 m in elevation during 2001 06 and thinning continued into 2009 elevation changes were small for the more southerly flask and leppard glaciers which are still constrained by a larsen b ice shelf remnant in the northern embayment continued thinning of 3 m a 1 on drygalski glacier 14 years after the larsen a ice shelf disintegrated suggests that mass losses for the exposed larsen b tributaries will continue for years into the future grounded ice volume losses exceed 13 km 3 for crane glacier and 30 km 3 for the hektoria green evans glaciers the combined mean loss rate for 2001 06 is at least 11 2 gt a 1 our values differ significantly from published mass budget based estimates for these embayments but are a reasonable fraction of grace derived rates for the region 40 gt a 1

albitization of detrital plagioclase in triassic reservoir sandstones from the snorre field norwegian north sea abstract detrital plagioclase an12 an28 in triassic reservoir sandstones of the lunde formation in the snorre field offshore norway has been partially to completely albitized during burial diagenesis depths of about 2 500 3 000 m 75 100 c present temperature calcite caco3 99 mole and kaolinite were formed as by products of plagioclase albitization sodium rich detrital plagioclase an2 an11 are usually unalbitized detrital k feldspar is fresh or rarely partly albitized differences in albitization behavior of detrital plagioclase and k feldspar are shown to be related to the chemistry of formation waters reactivity of kaolinite and temperature the diagenetically formed albite pseudomorphs are very pure ab 9 well ordered low albite dark luminescent vacuolized mostly untwinned and comprised of numerous euhedral albite crystals some of the microporosity within the albite pseudomorphs is caused by volume reduction during albitization of the detrital plagioclase the amount of albite formed in the pseudomorphs is related to the molar proportion of albite component in the detrital unstable ca rich plagioclase the microporosity formed during albitization is proportional to the anorthite component which is believed to have dissolved and resulted primarily in the formation of calcite and kaolinite the albitization of detrital plagioclase in the studied sandstones can thus be explained without assuming the consumption of significant amounts of na from pore solutions

a new inventory of mountain glaciers and ice caps for the antarctic periphery although the glaciers in the antarctic periphery make up a large fraction of all mountain glaciers and ice caps on earth a detailed glacier inventory of the region is lacking we compile such an inventory recording areas area altitude distributions terminus characteristics and volume estimates glaciers on the mainland are excluded the inventory is derived from the antarctic digital database and some manual digitization we additionally rely on satellite imagery digital elevation models and a flowshed algorithm to classify ice bodies we find 1133 ice caps and 1619 mountain glaciers covering a total of 132 867 6643 km 2 estimated total volume corresponds to 0 121 0 010 m sea level equivalent of the total glacier area 99 drains either into ice shelves 63 or into the ocean 36 the inventory will provide a database for glacier mass balance assessments modelling and projections and help to reduce the uncertainties in previous studies

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

controls on turbulent mixing on the west antarctic peninsula shelf the ocean to atmosphere heat budget of the west antarctic peninsula is controlled in part by the upward flux of heat from the warm circumpolar deep water cdw layer that resides below 200 m to the antarctic surface water aasw a water mass which varies strongly on a seasonal basis upwelling and mixing of cdw influence the formation of sea ice in the region and affect biological productivity and functioning of the ecosystem through their delivery of nutrients in this study 2 5 year time series of both acoustic doppler current profiler adcp and conductivity temperature depth ctd data are used to quantify both the diapycnal diffusivity and the vertical heat flux q at the interface between cdw and aasw over the period of the study a mean upward heat flux of 1 w m 2 is estimated with the largest heat fluxes occurring shortly after the loss of winter fast ice when the water column is first exposed to wind stress without being strongly stratified by salinity differences in mixing mechanisms between winter and summer seasons are investigated whilst tidally driven mixing at the study site occurs year round but is likely to be relatively weak a strong increase in counterclockwise polarized near inertial energy and shear is observed during the fast ice free season suggesting that the direct impact of storms on the ocean surface is responsible for much of the observed mixing at the site given the rapid reduction in sea ice duration in this region in the last 30 years a shift towards an increasingly wind dominated mixing regime may be taking place

improving ice core interpretation using in situ and reanalysis data 1 back trajectory analysis provided by the british atmospheric data centre using meteorological parameters from the european centre for medium range weather forecasts ecmwf reanalysis era 40 1980 2001 and operational analysis 2002 2006 is used to investigate transport pathways and source regions of climate proxies preserved in a new ice core gomez from the southwestern antarctic peninsula the ecmwf data are compared with automatic weather station data and ice core annual accumulation records to demonstrate that the ecmwf data capture a large proportion of the annual and subseasonal precipitation variability at the site the back trajectories reveal that precipitation preserved in the ice core accumulation record and hence climate proxies contained therein originate from the low pressure systems from the bellingshausen sea transported via circumpolar westerly winds hence precipitation dependent ice core proxies such as isotopic composition will be influenced by both localized sea ice extent and large scale circulation changes such as the southern annular mode sea ice proxies from the ice core are expected to be dominated by sea ice extent in the bellingshausen sea but also influenced by sea ice in the weddell sea with a small proportion of air mass trajectories originating from this region during the summer comparison with other ice core sites reveals a stronger influence of easterly transport at more northerly locations thus explaining the observed differences in snow accumulation records between ice cores and the poor correlation with instrumental records at these sites

ice loss processes in the seal nunataks ice shelf region from satellite altimetry and imagery the seal nunataks ice shelf snis 743 km 2 in 2013 is an unofficial name for a remnant area between the former larsen a and larsen b ice shelves off the northeastern antarctic peninsula analyses using landsat 7 etm and terra aster images from 2001 to 13 and icesat altimetry from 2003 to 09 show it has retreated and thinned following the larsen a 1995 and larsen b 2002 disintegrations despite some regional cooling and more fast ice since 2008 snis continues to lose ice along its margins and may be losing contact with some nunataks detailed analysis of data from four icesat tracks indicates that ice shelf thinning rates range between 1 9 and 2 7 m a 1 and generally increase from west to east an icesat repeat track crossing the adjacent robertson island shows a mean elevation loss of 1 8 m a 1 two tracks crossing the snis s remaining tributary rogosh glacier show sub meter elevation losses comparing shelf remnant and grounded ice thinning rates implies that basal ocean melting augments snis thinning by 1 m a 1 a rate that is consistent with other estimates of ocean driven shelf thinning in the region

origin of low δ18o pre compactional ferroan carbonates in the marine sto formation middle jurassic offshore nw norway siderite delta 18 o pdb 9 3 to 5 7 parts per thousand and fe dolomite ankerite delta 18 o pdb 13 7 to 7 7 parts per thousand occur as texturally early diagenetic pre compactional ce

mesozooplankton in the southern ocean spatial and temporal patterns from discovery investigations mesozooplankton samples taken during the discovery investigations in the southern ocean in the 1930s were analysed from a series of 5 transects along 80w the samples provide a unique level of depth discrete resolution across large spatial scales over most of the productive austral season stratified net hauls were taken between 0 and 1000 m within the period december 1933 to november 1934 within the epipelagic 0 100 m median zooplankton abundance 278 ind m 3 was 22 times greater than at 1000 m a 3 4 fold variability of abundance in the epipelagic contrasted with depths 250 m where variability was 1 fold depth was the strongest factor separating samples anosim r 0 66 p 0 1 with a clear biological distinction between epipelagic and upper and lower mesopelagic horizons results from multidimensional scaling indicated that when plankton abundance was integrated over all depth horizons 3 different groups could be identified these communities were consistent with the spatial extents of antarctic polar frontal zone and sub antarctic water mass regimes such groupings became less distinct when considering only deeper horizons 500 1000 m and excluding seasonal migrants seasonal signals across all data became less distinct with depth rarefaction analysis indicated that diversity increased with depth although depth alone was the most important influence on sample diversity r 2 0 60

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

class a prediction of arctic caisson performance from august 1985 to march 1986 numerical predictions were made of the performance of a mobile arctic caisson subjected to ice forces a constitutive model for soil was calibrated using available laboratory data and the model incorporated within a finite element computer program features of performance predicted included maximum caisson displacement the modes of internal displacement for drained and undrained conditions whether the performance would indeed be drained or undrained and if undrained where high excess pore pressures would be found in april 1986 the caisson was subjected to large ice forces approaching the design limit and the predictions were verified on site to a remarkable degree for this problem physical models predicted an erroneous response dans la periode aout 1985 mars 1986 des predictions numeriques furent effectuees pour le comportement d un caisson arctique mobile soumis aux forces des glaces un modele constitutif pour le sol fut calibre par l emploi des donnees de la

the freshwater system west of the antarctic peninsula spatial and temporal changes climate change west of the antarctic peninsula is the most rapid of anywhere in the southern hemisphere with associated changes in the rates and distributions of freshwater inputs to the ocean here results from the firstcomprehensivesurveyofoxygenisotopesinseawaterinthisregionareusedtoquantifyspatialpatternsof meteoric water glacial discharge and precipitation separately from sea ice melt high levels of meteoric water are found close to the coast due to orographic effects on precipitation and strong glacial discharge concentrations decrease offshore driving significant southward geostrophic flows up to 30 cm s 21 these produce high meteoric water concentrations at the southern end of the sampling grid where collapse of the wilkins ice shelf may also have contributed sea ice melt concentrations are lower than meteoric water and patchier because of the mobile nature of the sea ice itself nonetheless net sea ice production in the northern part of the sampling grid is inferred combined with net sea ice melt in the south this indicates an overall southwardicemotion thesurveyiscontextualizedtemporallyusingadecade longseriesofisotopedatafrom a coastal antarctic peninsula site this shows a temporal decline in meteoric water in the upper ocean contrary to expectations based on increasing precipitation and accelerating deglaciation this is driven by the increasingoccurrenceofdeeperwintermixedlayersandhaspotentialimplications forconcentrations oftrace metals supplied to the euphotic zone by glacial discharge as the regional freshwater system evolves the continuing isotope monitoring described here will elucidate the ongoing impacts on climate and the ecosystem

first survey of antarctic sub ice shelf sediments reveals mid holocene ice shelf retreat the retreat of five small antarctic peninsula ice shelves in the late 20th century has been related to regional possibly anthropogenic climate warming we use the record of ice rafted debris ird in cores to show that the prince gustav channel ice shelf also retreated in mid holocene time early and late holocene age sediments contain ird derived entirely from local ice drainage basins which fed the section of ice shelf covering each site core top and mid holocene 5 2 ka sediments include a wider variety of rock types recording the drift of far traveled icebergs which implies seasonally open water at the sites the period when the prince gustav ice shelf was absent corresponds to regional climate warming deduced from other paleoenvironmental records we infer that the recent decay cannot be viewed as an unequivocal indicator of anthropogenic climate perturbation

coastal change and glaciological maps of antarctica in spite of their importance to global climate and sea level the mass balance of the antarctic ice sheet and the dynamics of the coast of antarctica are largely unknown in 1990 the u s geological survey in cooperation with the scott polar research institute u k began a long term coastal mapping project in antarctica that is based on analysis of landsat images and ancillary sources the project has live objectives 1 to determine coastline changes that have occurred between the mid 1970s and the late 1980s early 1990s 2 to establish an accurate base line series of 24 1 1 000 000 scale maps that define the glaciological characteristics of the coastline 3 to determine velocities of outlet glaciers ice streams and ice shelves 4 to compile a comprehensive inventory of outlet glaciers and ice streams and 5 to compile a 1 5 000 000 scale map of antarctica derived from the 24 maps analysis of images used in producing the first five of the 24 maps has shown that ice fronts iceberg tongues and glacier tongues are the most dynamic and changeable features in the coastal regions of antarctica seaward of the grounding line of outlet glaciers ice streams and ice shelves the floating margin is subject to frequent large calving events and rapid flow although calving does occur along ice walls the magnitude of their change on an annual to decadal basis is generally not discernible on landsat images therefore ice walls can be used as relatively stable reference features for measuring other changes along the coast velocities of outlet glaciers ice streams and ice shelves range from 0 1 to several kilometers per year

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

conditions of riebeckite formation in the iron formation of the dales gorge member hamersley group western australia stability relations in the system na fe mg si c o h at low temperature and pressure at constant temperature riebeckite is stable to lower fo 2 conditions than hematite and higher ph values than magnetite or hematite where riebeckite coexists with carbonates its stability field is enlarged by a decrease of total carbonate at constant ph riebeckite assemblages in the dales gorge member can be divided into two groups carbonate free and carbonate bearing modified journal abstract

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

void ratio redistribution in undrained triaxial extension tests on ottawa sand water pluviated samples of ottawa sand were tested in monotonic undrained triaxial extension tests the specimens exhibited similar limited strain softening behavior and they all experienced ph

constitutive modeling of gassy sand behaviour the behaviour of loose gassy sand was investigated with the use of a constitutive model the constitutive model was modified from an existing model that focused on assessing the liquefaction of loose sands over a wide range of states and loading conditions the modifications involved taking into account the compressibility and solubility of the pore gas and liquids hilf s equation which calculates the pore pressure change in a gassy or unsaturated soil subjected to an applied total stress was incorporated into the model formulation the initial degree of saturation is needed for model prediction and the coefficient of volumetric solubility henry s constant was introduced as a new model parameter the modified model was used to predict the effect of gas on the undrained static behaviour of loose sand the laboratory results of saturated specimens were modeled and the predicted and observed behaviours were found to agree well results from gassy specimens were also predicted and again the model pred

drained and undrained shear behavior of compacted coal wash abstractcoal wash is a granular waste material that is readily available in the vicinity of coal mining operations while its potential use in structural fills has been recognized in the past the effects of particle breakage on the geomechanical performance of the material have not been thoroughly investigated in this paper an experimental study on a selected coal wash is undertaken to characterize the influence of compaction and particle breakage on its corresponding stress strain behavior particular emphasis is given to the role of compaction energy level and associated breakage incurred during compaction on the drained and undrained shearing behavior the incidence of particle breakage for undrained and drained shearing was observed to be different which in turn had a strong influence in the yielding behavior and the critical state furthermore the critical state conditions for coal wash seem to be better described through a three dimensional surface incorporating the effect of breakage

calving of fuerza aerea glacier greenwich island antarctica observed with terrestrial laser scanning and continuous video monitoring a short term series of quantitative observations of calving activity of fuerza aerea glacier greenwich island the south shetland islands antarctica was conducted in order to test new methods of monitoring calving the volume of single calving events was quantified by combining terrestrial laser scanning tls surveys with continuous video recording of the ice front an empirical formula for area volume scaling of the calved ice block was proposed based on the tls measured calved ice volume and the calved ice front area obtained by manual delineation on the images acquired with the video camera this combination of methods proves to be a valuable tool for glacier monitoring providing both high temporal resolution and precise quantitative measurements of the calving volume the size distribution of calving events is best approximated by a power law and within the short period of observations 14 d calving was found to be an intrinsic process not dependent on environmental forcings over the period of 21 january 04 february 2013 the ice flow velocity at the terminus of fuerza aerea glacier was 0 26 0 07 m d 1 and the calving rate was 0 41 0 07 m d 1

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord

multidecadal freshening and lightening in the deep waters of the bransfield strait antarctica the deep waters of the bransfield strait receive considerable amounts of water from the weddell sea continental shelf the restricted connections to the surrounding ocean and relatively easier access makes the bransfield strait an important proxy region for monitoring changes in the dense weddell sea shelf water masses which are an important precursor of antarctic bottom water aabw long term hydrographic data from the period 1960s 2010s showed freshening and lightening of the deep water masses of the bransfield strait which was likely caused by large freshwater inputs originating from the western shelf of the weddell sea the rates of freshening and lightening were 0 0010 0 0005 yr 1 and 0 0016 0 0014 kg m 3 yr 1 for the central basin respectively and 0 0010 0 0006 yr 1 and 0 0029 0 0013 kg m 3 yr 1 for the eastern basin respectively the deep waters showed a high degree of interannual thermohaline variability which appeared to be caused by changes in the proportions of source water mass mixing between the years statistically significant negative correlations between salinity neutral density fields and the southern annular mode sam were observed 0 56 and 0 62 for the central basin respectively and 0 58 and 0 68 for the eastern basin respectively between 1980 and 2014 during sam positive phases communication between the weddell sea and the bransfield strait is reduced which leads to less saline and lighter water masses in the bransfield strait however the opposite trends are observed during sam negative phases

mobility of the high field strength rare earth elements and yttrium during late diagenesis authigenic titanite occurs as a secondary pore filling cement in the permian sandstones of the cock of arran scotland the titanite is apparently not associated with in situ alteration of a specific mineral phase or phases suggesting it crystallized from fluids migrating through these porous and permeable sandstones the titanite contains significant concentrations of zr nb p ce nd gd and y implying that these elements were also carried in solution probably in the form of halogen or carbonate complexes associated with hydrothermal circulation related to the intrusion of the adjacent northern granite

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

the strength and dilatancy of sand the effects of stress path and loading direction in the triaxial test on strength and dilatancy of sand are investigated it is shown that the unique relationship observed between peak friction ang

fracture field for large scale ice dynamics recent observations and modeling studies emphasize the crucial role of fracture mechanics for the stability of ice shelves and thereby the evolution of ice sheets here we introduce a macroscopic fracture density field into a prognostic continuum ice flow model and compute its evolution incorporating the initiation and growth of fractures as well as their advection with two dimensional ice flow to a first approximation fracture growth is assumed to depend on the spreading rate only while fracture initiation is defined in terms of principal stresses the inferred fracture density fields compare well with observed elongate surface structures since crevasses and other deep reaching fracture structures have been shown to influence the overall ice shelf dynamics we propose the fracture density field introduced here be used as a measure for ice softening and decoupling of the ice flow in fracture weakened zones this may yield more accurate and realistic velocity patterns in prognostic simulations additionally the memory of past fracture events links the calving front to the upstream dynamics thus the fracture density field proposed here may be employed in fracture based calving parameterizations the aim of this study is to introduce the field and investigate which of the observed surface structures can be reproduced by the simplest physically motivated fracture source terms

diagenetic albitization of detrital k feldspar in jurassic lower cretaceous and tertiary clastic reservoir rocks from offshore norway i textures and origin abstract the origin of albitized grains in sandstones has been the topic of considerable discussion in recent years some workers believe that the albitization of feldspar can occur in situ during burial diagenesis but others argue that albitization is a feature inherited from source clastic grains our petrological and chemical studies of subsurface samples of the jurassic lower cretaceous and tertiary reservoir sandstones from offshore norway show that detrital grains of potassium feldspar have been albitized during burial diagenesis criteria suggesting that the albitization has occurred during burial diagenesis include 1 euhedral habit of albite crystals with sharp edges and comers and markedly smooth crystal faces 2 generally untwinned albitized grains mostly riddled with minute br wnish inclusions 3 lack of cathodoluminescence in albite 4 homogeneous and pure albite composition 99 ab 5 absence of albitized grains in carbonate cemented zones and 6 increase in the percentage and degree partial to complete of albitized k feldspar with depth under sem albitized grains display two types of fabrics type i albitized grains are composed of numerous tiny albite crystals 1 30 m growing along cleavage planes in parent grains and they have abundant dissolution porosity while type ii albitized grains show blocky albite crystals 5 80 m forming pseudomorphs of detrital k feldspar and they lack any dissolution porosity type i albitized grains are found commonly at shallower depths between 2 2 and 3 km and temperatures varying from 65 to 90 c whereas type ii albitized grains dominate at greater depths 3 5 km and at temperatures 90 c albitization proceeds by a dissolution precipitation mechanism at shallower depth dissolution of the parent k feldspar is more rapid than the precipitation of albite and rates of albite precipitation increase with depth favoring pseudomorphic replacement of k feldspars other factors that influence albitization processes are ana ak permeability reduction and surface dissolution kinetics of the parent grain

late holocene glacier reconstruction reveals retreat behind present limits and two stage little ice age on subantarctic south georgia observational data show that climate in the southern ocean region is rapidly changing however past the instrumental period our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records alpine glaciers present on many southern ocean islands may provide such data because changes in their mass balance extent and erosion rates often mark a response to climate shifts rock flour the fine grained fraction of the glacial erosion process is suspended in meltwater streams and transferred into the sediments of downstream lakes continuously recording glacier variations here we utilize this relationship to present a reconstruction of the late holocene glacier history of subantarctic south georgia using sediments from the glacier fed middle hamberg lake to fingerprint a glacial erosion size signal we used titanium counts validated against changes in sediment density and grain size allowing a continuous reconstruction of glacier variations over the past similar to 1250 years together with local moraine evidence and supporting evidence from other southern hemisphere glaciers on new zealand and in patagonia our findings reveal a series of consecutively diminishing late holocene advances in addition to a glacier maximum before 1250 cal a bp these include a twostage litle ice age with advances around 300 and 120 cal a bp in line with evidence from southern patagonia in addition we present evidence for an unreported retreat behind present limits around 500 cal bp

controls on diagenesis of lower cretaceous reservoir sandstones in the western sable subbasin offshore nova scotia abstract lower cretaceous deltaic sandstones of the scotian basin offshore eastern canada are important gas reservoirs the influence of several factors on diagenesis has been investigated depositional lithofacies sea level changes chemistry of basinal sediments and basinal fluid flux during burial the distribution and chemistry of diagenetic minerals was determined from nine wells located along a dip section of the sable subbasin mineral type and paragenesis were characterized using a combination of optical petrography back scattered electron images and electron microprobe analyses siderite is unusually abundant in marine sediments of the scotian basin and has thus been studied in detail siderite occurs in several generations early and late siderites are similar in chemical composition suggesting buffering by pre existing siderite but rare low mg siderite is related to a greater contribution of meteoric water siderite has locally dissolved to create microporosity and has suppressed quartz overgrowths siderite is most common in those muddy prodeltaic lithofacies where there is the highest availability of detrital ilmenite reactive fe released by breakdown of this ilmenite is responsible for the unusual presence of early siderite in marine sediments with the ca and mg content of the siderite indicating fully marine waters lithofacies have a strong influence on early diagenetic mineral assemblages lithofacies deposited in the transgressive system tract have abundant early fe calcite and siderite early kaolinite occurs principally in proximal fluvial and river mouth lithofacies where meteoric water was most likely available during the deposition contrary to other studies we find little impact of sequence stratigraphy on diagenetic minerals except in the transgressive system tract mesogenetic minerals are related to flux of formation water and maturing hydrocarbon products resulting first in pyrite and siderite and later in ankerite and ferroan calcite the principal controls are interpreted to be high fe 2 and low ca 2 of formation waters and vertical movement of the waters along faults overall the bulk chemical composition of terrigenous sediments and the depositional lithofacies are the most important factors controlling diagenetic minerals in the lower cretaceous of the scotian basin

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

depositional and diagenetic controls on the reservoir quality of lower cretaceous pendencia sandstones potiguar rift basin brazil the quality of the reservoirs of the lower cretaceous pendencia formation of the potiguar basin northeastern brazil is directly controlled by depositional facies related carbonate cementation and compaction the study of the interplay of these processes in the reservoirs offers an opportunity to unravel the diagenetic patterns of clastic sequences in interior rifts and in particular the role of carbonate cementation in poorly understood continental systems the pendencia formation is a thick sequence of fan deltaic fluvial deltaic turbiditic and lacustrine sandstones conglomerates and shales deposited during the rift stage of the basin the sandstones are predominantly arkoses average q49f40l11 with subordinate plutonic and volcaniclastic feldspathic litharenites compaction and cementation had similar importance in the destruction of porosity with a dominance of cementation in the turbidites and of compaction in the fluvial deposits carbonate cementation in pendencia reservoirs increases progressively with depth and is facies controlled eodiagenetic nonferroan calcite i d18opdb 10 7 to 4 0 d13cpdb 17 5 to 8 5 mesodiagenetic rhombohedral ferroan dolomite ankerite d18opdb 9 3 to 3 9 d13cpdb 1 7 to 1 1 and ferroan calcite ii d18opdb 17 2 to 6 8 d13cpdb 13 6 to 2 3 were precipitated at three distinct temperature intervals calculated from the d18o values 21 to 58 c 70 to 79 c and 85 to 150 c respectively according to the d13c values dissolved carbonate for calcite i was derived from oxidation and methanogenic fermentation of organic matter and from methane oxidation ferroan mesogenetic cements were derived from thermal decarboxylation of organic matter the shales were a major source of dissolved begin page 1720 carbonate as indicated by the isotopic similarity between their calcite d13cpdb 0 2 to 1 8 87sr 86sr 0 719 and most cements in the sandstones and by the peripheral cementation along the contacts of interbedded sandstones as a result of this cementation pattern thin turbiditic and deltaic sandstone beds are pervasively cemented the best reservoir quality potential is encountered in the partially cemented fluvial sandstones at moderate depths deltaic and turbiditic sandstones are more pervasively cemented by carbonate derived from the interbedded shales alluvial fan conglomerates and sandstones were flushed by telogenetic meteoric waters close to the borders of the basin and to the proximity to the postrift unconformity however porosity enhancement was very limited due to the precipitation of kaolinite and the intense compaction related to the compositionally immature detrital framework

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis