solid electrical conductivity ecm from four agassiz ice cores ellesmere island nwt canada high resolution signal and noise over the last millennium and low resolution over the holocene the solid dc electrical conductivity ecm electrical conductivity method of polar ice cores has become an important tool in identifying and quantifying volcanic acid layers and this paper addresses the question of how much signal and noise there is in single ecm series a number of high resolution 10 samples year ice core ecm records from the agassiz ice cap are correlated over the last 900 years corre lations decrease with distance apart due to local drift and melt layer noise but correlations are probably reduced also by differences in methodology and core storage it is found that only peak sizes in the uppermost two percentiles retain their ranking and recognizability from core to core with continuous sampling however the smaller peaks can be cross identified between cores even though they lose their size rank averaging or stacking several ecm records reduces the noise five year averages of ecm for the holocene are presented for the agassiz cores and their correlations interpreted as functions of distance apart and differences in method the large scale melting in the early holocene 8ka to 10ka almost completely de acidifies the ice in all the agas siz cores

collapse mechanism of the overlying strata above a salt cavern by solution mining with double well convection in solution mining of salt formations unreasonable salt cavities formed may lead to surface collapse hazards in this paper a mathematical model was proposed to analyze the collapse mechanism of the overlying strata above a salt cavern induced by solution mining with double well convection in the proposed model the collapses of the overlying strata were supposed to occur layer by layer and a thin plate with four edges clamped was introduced to calculate the critical collapse span of each layer the limit breaking distance of the thin plate can be solved by setting the corresponding surrounding condition according to the solution the limit breaking distance is related to the dimensions the mechanical properties of the rock the buried depth and the force status for the convenience of calculation a span criterion was introduced to distinguish the limit breaking distance to keep the immediate roof more stable the span criterion should be larger as a case study the collapse incidents at dongxing salt mine were analyzed by the proposed model and the collapses were verified to be inevitable under its mining and geological conditions discussions were finally carried out to study the influences of the thickness of the immediate roof tension strength poisson ratio and buried depth on the collapses above all the collapses will occur more easily with the decrease of the thickness tension strength and poisson ratio of each stratum especially the collapse depth will not increase linearly with the buried depth because of the bulking effect of the overlying strata

effect of wind scouring on climatic records from ice core oxygen isotope profiles removal of winter snow by wind explains why the annual mean oxygen isotope ratio at an ice divide is 2 5 less negative than it is 1 2 km downslope cores from two sites on an ice cap ellesmere island canada show past variations in the difference depending on where the ice originated relative to the scoured zone some ice core climatic records may need correction for scouring

a record of holocene summer climate from a canadian high arctic ice core melt layers in ice cores are formed by melting on the snow pack surface which produces water that percolates down and refreezes in the colder snow layers below melt layers are distinguished by their bubble texture because more ice forms in the snow pack in warm summers than in cool summers the changing concentration with depth of melt layers in snow pits1 2 and ice cores3 5 is an indicator of past summer climate here we report on studies of melt layers in two canadian high arctic surface to bedrock ice cores although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40 of the total climatic signal recorded in the melt layers we interpret their varying concentrations in terms of changing summer temperatures over the past 10 000 years the warmest summers occurred 8 10 kyr ago and the coldest only 150 years ago the summers over the past 100 years have been the warmest for more than 1 000 years but are still not as warm as those of the early holocene the melt layer record is in broad agreement with geological records of glacier retreat during the holocene6 8 indicating that these data also contain information of regional significance

modeling aquifer system compaction and predicting land subsidence in central taiwan abstract changhua is a county in central taiwan that will house several major economic development projects extracting groundwater has caused large scale land subsidence in changhua with the largest cumulative subsidence being 210 cm over 1992 2010 a multi sensor monitoring system consisting of continuous gps stations a leveling network multi layer compaction monitoring wells and groundwater wells is deployed to monitor land subsidence and its mechanism in changhua data from the monitoring well cgsg in dacheng township of changhua show a cumulative compaction of 110 6 cm over 1997 2010 occurring mainly at two aquifers and one aquitard a novel combination of gps and monitoring well data was used to determine the stress strain relations the stratum compaction turns from plasticity to elastoplasticity after a long term compaction at the second aquifer below the surface four hydrogeological parameters of the three sediment layers in dacheng vertical hydraulic conductivity elastic skeletal specific storage inelastic skeletal specific storage and the initial maximum preconsolidation stress in the one dimensional compaction model compac are estimated using the genetic algorithm with the parameters compac predicts compactions to an accuracy consistent with in situ measurements and the mean absolute percentage errors of prediction are below 10 the result provides a key reference for water management in central taiwan

early holocene climate oscillations recorded in three greenland ice cores a new ice core chronology for the greenland dye 3 grip and ngrip ice cores has been constructed making it possible to compare the 18 o and accumulation signals recorded in the three cores on an almost annual scale throughout the holocene we here introduce the new time scale and investigate 18 o and accumulation anoma lies that are common to the three cores in the early holocene 7 9 11 7 ka before present three time periods with significant and synchronous anomalies in the 18 o and accumulation signals stand out the well known 8 2 ka event an event of shorter duration but of almost similar amplitude around 9 3 ka before present and the preboreal oscillation during the first centuries of the holocene for each of these sections we present a 18 o anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the greenland ice cap

synchronizing ice cores from the renland and agassiz ice caps to the greenland ice core chronology 1 four ice cores from the agassiz ice cap in the canadian high arctic and one ice core from the renland ice cap in eastern greenland have been synchronized to the greenland ice core chronology 2005 gicc05 which is based on annual layer counts in the dye 3 grip and ngrip ice cores volcanic reference horizons seen in electrical conductivity measurements ecm have been used to carry out the synchronization throughout the holocene the agassiz ice cores have been matched to the ngrip ice core ecm signal while the renland core has been matched to the grip ice core ecm signal thus tying the cores to gicc05 furthermore it has been possible to synchronize the renland ice core to ngrip gicc05 in the glacial period back to 60 000 years b2k years before a d 2000 on the basis of a matching of transitions between stadials and interstadials this work brings the total number of ice core records that have been rigorously tied to the gicc05 timescale up to nine renland annual layer thicknesses are increasing with depth during the period from 7 to 8 5 ka b2k a highly unusual observation only matched by a similar thickness increase in the glacial section of the renland core some 60 ka ago annual layer thicknesses in the agassiz ice cores point to a well developed raymond bump in the agassiz ice cap

holocene warming in western continental eurasia driven by glacial retreat and greenhouse forcing the global temperature evolution during the holocene is poorly known whereas proxy data suggest that warm conditions prevailed in the early to mid holocene with subsequent cooling model reconstructions show long term warming associated with ice sheet retreat and rising greenhouse gas concentrations one reason for this contradiction could be the under representation of indicators for winter climate in current global proxy reconstructions here we present records of carbon and oxygen isotopes from two u th dated stalagmites from kinderlinskaya cave in the southern ural mountains that document warming during the winter season from 11 700 years ago to the present our data are in line with the global holocene temperature evolution reconstructed from transient model simulations we interpret eurasian winter warming during the holocene as a response to the retreat of northern hemisphere ice sheets until about 7 000 years ago and to rising atmospheric greenhouse gas concentrations and winter insolation thereafter we attribute negative 18o anomalies 11 000 and 8 200 years ago to enhanced meltwater forcing of north atlantic ocean circulation and a rapid decline of 13c during the early holocene with stabilization after about 10 000 years ago to afforestation at our study site we conclude that winter climate dynamics dominated holocene temperature evolution in the continental interior of eurasia in contrast to regions more proximal to the ocean models and proxy data diverge on the global temperature evolution of the holocene perhaps due to representation of the seasons isotopic analyses of stalagmites from the ural mountains suggest that winter climate dominated in the eurasian interior

prediction of cavern configurations from subsidence data an analytical method has been developed to predict the location depth and size of caverns created at the interface between salt and overlying formations a governing hyperbolic equation is used in a statistical analysis of the ground survey data to determine the cavern location maximum subsidence maximum surface slope and surface curvature under the sub critical and critical conditions the regression produces a set of subsidence components and a representative profile of the surface subsidence under sub critical and critical conditions finite difference analyses using flac code correlate the subsidence components with the cavern size and depth under a variety of strengths and deformation moduli of the overburden empirical equations correlate the subsidence components with the cavern configurations and overburden properties for the super critical condition a discrete element method using udec code is used to demonstrate the uncertainties of the ground movement and sinkhole development resulting from the complexity of the post failure deformation and joint movements in the overburden

a new method of surface subsidence prediction for natural gas storage cavern in bedded rock salts the surface subsidence above underground natural gas caverns in salt formations is mainly induced by the volume shrinkage of the cavern in this paper a new method based on the mogi model to predict the subsidence above bedded rock salts gas storage cavern is proposed firstly the equivalent elastic boundary deformation of the cavern volume decrease is assumed to be the first order approximation of the real subsidence induced by creep shrinkage secondly the cavern shape is simplified to be a spherical one with the same depth and volume subjected to the pressure change of hydrostatic pressure in the sphere and then solving for the subsidence above the storage is analyzed as the boundary displacement problem of the spherical cavern subjected to pressure change of hydrostatic pressure in the sphere in semi infinite space based on the equivalent elastic model the mogi model which has been developed for subsidence prediction in volcano seismology is introduced to solve the boundary displacement problem then the expressions for subsidence and for horizontal displacement are obtained the advantage of the new method is that the ground displacements can be calculated directly from the cavern volume shrinkage thus the calculation has much been simplified the validity of the method is verified by comparing to numerical simulation results which show that the mogi model has high validity for subsidence prediction for the gas cavern in salt formations in the end some constructive discussions on the application and improvement of the mogi model are presented for its further applications

an integrated approach for the prediction of subsidence for coal mining basins abstract in this study land subsidence caused by underground mining activities was investigated by means of a new subsidence prediction approach isp tech which takes into account the most important parameters contributing subsidence development such as coal production methods depth mining sequence and other geomechanical characteristics of underground rock strata etc isp tech can be applied to operating mines to keep land subsidence under control as well as virgin coal sites to predict surface subsidence prior to mining activities in the method geological information gathered from the geographic information system gis and the mining information system mis are utilised to obtain geological cross sections which are used in finite element models for mesh building then a number of two dimensional finite element modelling analyses are carried out to determine land subsidence occurring due to mining operations finally land subsidence predicted from modelling studies is compared to the gps and or differential interferometry synthetic aperture radar din sar measurements if incompatibility of the results is detected finite element meshes should be optimised and then reanalysed to obtain more compatible results in the study two different case studies were given as examples of the application of isp tech results of the case studies showed that isp tech can successfully be applied to complex mine subsidence problems the proposed approach gives more accurate results than those obtained from other classical subsidence prediction methods

environmental changes in northern iceland since the younger dryas inferred from periglacial slope deposits the slopes in northern iceland show the widespread occurrence of solifluction features indicative of an active periglacial environment due to annual mean temperatures around 3 c at sea level and s

sea ice ice rafting and ocean climate across denmark strait during rapid deglaciation 16 12 cal ka bp of the iceland and east greenland shelves

abrupt holocene climate transitions in the northern north atlantic region recorded by synchronized lacustrine records in iceland abstract two high sediment accumulation rate icelandic lakes the glacial lake hvitarvatn and the non glacial lake haukadalsvatn contain numerous tephra layers of known age which together with high resolution paleomagnetic secular variations allow synchronization with a well dated marine core from the shelf north of iceland a composite standardized climate record from the two lakes provides a single time series that efficiently integrates multi proxy data that reflect the evolution of summer temperatures through the holocene the first order trends in biogenic silica bsi 13c and c n rise relatively abruptly following deglaciation reaching maximum values shortly after 8 ka following a complex minimum between 8 7 and 8 0 ka the holocene thermal maximum htm in the lakes is marked by all proxies with a sharp transition out of the 8 ka cold event into peak summer warmth by 7 9 ka and continuing warm with some fluctuations until 5 5 ka decreasing summer insolation after the htm is reflected by incremental cooling initially 5 5 ka with subsequent cold perturbations recorded by all proxies 4 3 to 4 0 ka and 3 1 to 2 8 ka the strongest disturbance occurred after 2 ka with initial summer cooling occurring between 1 4 and 1 0 ka followed by a more severe drop in summer temperatures after 0 7 ka culminating between 0 5 and 0 2 ka following each late holocene cold departure bsi re equilibrated at a lower value independent of the sediment accumulation rate some of the abrupt shifts may be related to icelandic volcanism influencing catchment stability but the lack of a full recovery to pre existing values after the perturbation suggests increased periglacial activity decreased vegetation cover and glacier growth in the highlands of iceland the similarity in timing direction and magnitude of our multi proxy records from glacial and non glacial lakes and from the adjacent marine shelf suggests that our composite record reflects large scale shifts in ocean atmosphere circulation throughout the northern north atlantic

denmark strait during the late glacial maximum and marine isotope stage 3 sediment sources and transport processes abstract the sediment records from north and south of denmark strait cores ps2644 and md99 2323 and on the kangerlussuaq trough mouth fan ktmf md99 2260 are evaluated for the period 12 to 60 cal ka bp with the goal of evaluating 1 the relative roles of the greenland and iceland ice sheets in sediment composition 2 the processes of sediment supply and 3 the relationship if any between the atmospheric derived ice core records and glacial marine sediment history these questions were addressed using counts of coarse 2 mm ice rafted debris ird magnetic susceptibility grain size spectra and sediment mineral composition a significant difference in these variables occurred between ms3 and mis2 with the latter showing small to modest abrupt changes in felsic and mafic minerals and in ird compared to larger and less variable changes during mis2 the dominant bedrock source archived in the cores is the cenozoic basaltic outcrops from east greenland and iceland 60 but there are frequent pulses of felsic rich sediments 17 36 which coincided with greenland stadials there is also a persistent detrital carbonate input the largest shift in most sediment proxies occurred 28 30 cal ka bp reflecting the sustained expansion of the ice sheets the grain size spectra on the snorri drift md99 2323 reflected complex depositional histories involving the supply of poorly sorted glacially derived sediment sand silt and clay and reworking by bottom currents

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

deformation in the vicinity of ice divides calculs numeriques aux elements finis de la variation de la vitesse horizontale avec la profondeur au voisinage d une difference de la glace symetrique isotherme et ou glissement sur un lit plat

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

in situ la icp ms trace elemental analyses of magnetite the mesozoic tengtie skarn fe deposit in the nanling range south china abstract the nanling range in south china hosts numerous world class w sn deposits and some fe deposits the mesozoic tengtie fe skarn deposit in the southern nanling range is contemporaneous with the regional sn mineralization the deposit is composed of numerous ore bodies along the contacts between the late paleozoic or mesozoic carbonate rocks and the yanshanian lianyang granitic complex interaction of the magma with hosting dolomitic limestone and limestone formed calcic ca rich and magnesian mg rich skarns respectively the tengtie deposit has a paragenetic sequence of the prograde stage of anhydrous skarn minerals followed by the retrograde stage of hydrous skarn minerals and the final sulfide stage magnetite in the prograde and retrograde skarn stages is associated with diopside garnet chlorite epidote and phlogopite whereas magnetite of the final stage is associated with chalcopyrite and pyrite massive magnetite ores crosscut by quartz and calcite veins are present mainly in the retrograde skarn stage laser ablation icp ms was used to determine trace elements of magnetite from different stages some magnetite grains have unusually high ca na k and si possibly due to the presence of silicate mineral inclusions magnetite of the prograde stage has the highest co contents but that of the sulfide stage is extremely poor in co which partitions in sulfides magnetite of magnesian skarns contains more mg mn and al than that of calcic skarns attributed to the interaction of the magma with compositionally different host rocks magnetite from calcic and magnesian skarns contains 6 185 ppm sn and 61 1246 ppm sn respectively the high sn contents are not due to the presence of cassiterite inclusions which are not identified in magnetite instead we believe that sn resides in the magnetite structure regionally intensive mesozoic sn mineralization in south china indicates that concurrent magmatic hydrothermal fluids may be rich in sn and contribute to the formation of high sn magnetite our study demonstrates that trace elements of magnetite can be a sensitive indicator for the skarn stages and wall rock compositions and as such trace elemental chemistry of magnetite can be a potentially powerful fingerprint for sediment provenance and regional mineralization

penny ice cap cores baffin island canada and the wisconsinan foxe dome connection two states of hudson bay ice cover ice cores from penny ice cap baffin island canada provide continuous holocene records of oxygen isotopic composition 18 o proxy for temperature and atmospheric impurities a time scale was established with the use of altered seasonal variations some volcanic horizons and the age for the end of the wisconsin ice age determined from the grip and gisp2 ice cores there is pre holocene ice near the bed the change in 18 o since the last glacial maximum lgm is at least 12 5 per mil compared with an expected value of 7 per mil suggesting that lgm ice originated at the much higher elevations of the then existing foxe dome and foxe ridge of the laurentide ice sheet the lgm 18 o values suggest thick ice frozen to the bed of hudson bay

synchronization of the ngrip grip and gisp2 ice cores across mis 2 and palaeoclimatic implications abstract we here present a synchronization of the ngrip grip and gisp2 ice cores based mainly on volcanic events over the period 14 9 32 45 ka b2k before ad 2000 corresponding to marine isotope stage 2 mis 2 and the end of mis 3 the matching provides a basis for applying the recent ngrip based greenland ice core chronology 2005 gicc05 time scale to the grip and gisp2 ice cores thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores based on the matching a period of anomalous high accumulation rates in the gisp2 ice core is detected within the period 16 5 18 3 ka b2k the 18 o and ca 2 profiles of the three cores are presented on the common gicc05 time scale and generally show excellent agreement across the stadial interstadial transitions and across the two characteristic dust events in greenland stadial 3 however large differences between the 18 o and ca 2 profiles of the three cores are seen in the same period as the 7 9 increase in the gisp2 accumulation rate we conclude that changes of the atmospheric circulation are likely to have occurred in this period altering the spatial gradients in greenland and resulting in larger variations between the records

spatial analysis of land subsidence induced by groundwater withdrawal abstract a comprehensive study of the factors influencing magnitude and distribution of ground settlements observed during the second half of the twentieth century in the area of bologna italy is presented to derive a unified framework useful for interpreting the observed phenomena and for predicting future scenarios information collected over a surface of more than two hundred square kilometres includes previous geological studies hydro geological geotechnical and topographical investigations carried out with various purposes the geological features of the whole region have been initially reviewed to figure out the local geological and hydro geological setup then the stratigraphic sequence has been obtained by integrating the results of an extensive campaign carried out over the whole region for water exploitation the mechanical characterization of the soil has been based on geotechnical tests performed in the area for the construction of new transportation infrastructures groundwater levels periodically recorded on a distributed net of wells have been interpreted with a two dimensional seepage model capable of back calculating the modification of the groundwater regime induced by water withdrawal the spatial and temporal distributions of settlements have been derived by combining sequential topographical monitoring campaigns covering a period of about sixty years with satellite records to simultaneously analyse all information and provide an interpretation of the observed phenomena all data have been collected in a geographical information system interpolating the measured data with a geostatistical method in such a way the role of the different factors has been captured finding a logical correlation between land subsidence subsoil composition and groundwater withdrawal and a strategy has been traced which can be exported to the analysis of other similar situations

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

detrital cave sediments record late quaternary hydrologic and climatic variability in northwestern florida usa abstract detrital sediment in florida s usa submerged cave systems may preserve records of regional climate and hydrologic variability however the basic sedimentology mineralogy stratigraphic variability and emplacement history of the successions in florida s submerged caves remains poorly understood here we present stratigraphic mineralogical and elemental data on sediment cores from two phreatic cave systems in northwestern florida usa on the dougherty karst plain hole in the wall cave hitw and twin cave water flowing through these caves is subsurface flow in the apalachicola river drainage basin and the caves are located just downstream from jackson blue 1st magnitude spring 2 8 m3 s 1 discharge sedimentation in these caves is dominated by three primary sedimentary styles i ferromanganese deposits dominate the basal recovered stratigraphy which pass upsection into ii poorly sorted carbonate sediment and finally into iii fine grained organic matter gyttja deposits resolving the emplacement history of the lower stratigraphic units was hampered by a lack of suitable material for radiocarbon dating but the upper organic rich deposits have a punctuated depositional history beginning in the earliest holocene for example gyttja primarily accumulated in hitw and twin caves from 5500 to 3500 cal yr bp which coincides with regional evidence for water table rise of the upper floridian aquifer associated with relative sea level rise in the gulf of mexico and evidence for invigorated drainage through the apalachicola river drainage basin gyttja sediments were also deposited in one of the caves during the bolling allerod climate oscillation biologically these results indicate that some floridian aquatic cave stygobitic ecosystems presently receive minimal organic matter supply in comparison to prehistoric intervals the pre holocene poorly sorted carbonate sediment contains abundant invertebrate fossils and likely documents a period of enhanced limestone dissolution and cave formation speleogenesis during lower paleo water levels further work is still required to a determine whether precipitation of the ferromanganese deposits is inorganically or biologically mediated b temporally constrain the emplacement history of the primary sedimentary styles and c determine the full geographic extent of these sedimentary signals however these preliminary observations suggest that sedimentation in the inland underwater caves of northwestern florida is related to quaternary scale hydrographic variability in the apalachicola river drainage basin in response to broader ocean and atmospheric forcing

wisconsin and holocene δ18o variations barnes ice cap canada new 18o measurements on ice samples from barnes ice cap show a relatively large shift from about 23 in the blue ice that makes up the bulk of the ice cap to 38 in a basal layer of clean white ice this strongly suggests that the latter is of pleistocene age thus confirming an earlier interpretation based on less comprehensive data the shift between the pleistocene and holocene ice is attributed in part to the change in climate at the end of the pleistocene and in part to a decrease in elevation of the accumulation area of 700 m beneath the clean white ice there is a layer of dirty white ice with less negative 18o values this ice is believed to have been deposited during a climatically warm period in early to middle wisconsin time in addition however the less negative 18o values in it are in part attributed to fractionation at a time in the past when the basal ice was at the melting point and some of the water produced by pressure melting was lost through a permeable bed

dating synthesis and interpretation of palaeoclimatic records of the last glacial cycle and model data integration advances by the intimate integration of ice core marine and terrestrial records cost action es0907 since 2010 the intimate integration of ice core marine and terrestrial records network has been operating as a cost action designated es0907 this paper outlines the accomplishments of the intimate cost action in the context of how the intimate ideas have evolved during the network s twenty year life span and highlights a number of challenges that can guide further work in the second part of the paper the contributions that comprise this intimate special issue are introduced

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

salt cavern gas storage in an ultra deep formation in hubei china abstract the target formation of jianghan salt district qianjiang city hubei province china for underground gas storage ugs construction has a depth of more than 1800 m the cavern will be the deepest salt cavern ugs in asia a 3d geomechanical model of the proposed salt cavern ugs is built based on the geologic characteristics and mechanical parameters of the target formation a new indexes system composed of displacement volume shrinkage plastic zone dilatancy safety factor and equivalent strain is proposed to quantitatively evaluate the safety of jianghan salt cavern ugs the thresholds of each indicator are proposed based on the characteristics of rock salt in china by using the proposed indexes system the cavern shape dimensions operating parameters and pillar width are optimized calculating results show that the optimized cavern has a slender cylindrical shape with a domed roof and an inverted cone bottom its diameter ranges from 80 to 90 m its height is about 210 m and its free volume accessible to gas is about 50 65 104 m3 the maximum operating gas pressure is about 34 mpa and the minimum gas pressure is no less than 17 mpa the width of the pillar between adjacent caverns is about 2 5 3 times the cavern diameter the gas storage capacity of a single cavern is about 1 1 109 m3 and the working gas is about 0 7 109 m3 which is about three times that of a single cavern in jintan salt cavern ugs jiangsu province china the results indicate that jianghan salt cavern ugs has a good feasibility for large scale gas storage

stratigraphic correlations between the european project for ice coring in antarctica epica dome c and vostok ice cores showing the relative variations of snow accumulation over the past 45 kyr 1 high resolution chemistry analysis and electrical measurements performed on two ice core records european project for ice coring in antarctica epica dome c and vostok spanning the last 45 kyr allow stratigraphic correlations by matching volcanic events several common events were identified along the two ice cores on the basis of acidity and sulphate spikes in snow layers timescales were matched through comparison with isotope d profiles and using the antarctic cold reversal acr minimum a 10be peak and a dust spike as temporal checkpoints ratios of relative snow accumulation at the two sites during the holocene in the glacial interglacial transition and in the last part of the glacial period were reconstructed by finding the best fit between dome c and vostok depths recording the same events after accounting for thinning of the layers as they are buried within the glacier the dome c vostok accumulation ratio expected to be roughly constant from the conventional accumulation temperature isotope approach is 1 12 for the glacial period but increases to as much as 1 44 for a large part of the holocene glaciological effects mainly related to the geographic origin of the vostok ice along the ridge b vostok axis can account for only a minor fraction of this change instead we argue that accumulation variability between the cores stems from differential changes in atmospheric circulation during these respective climatic periods at the two sites regional changes in atmospheric circulation are proposed with a negative anomaly in dome c a positive accumulation anomaly in vostok or a combination of both during glacial climate our approach may help to improve ice core dating by 1 revealing anomalies in accumulation rate estimation based on the classical thermodynamic method and 2 supporting the necessity to take into account contributions due to changes in atmospheric circulation processes

retrieving a common accumulation record from greenland ice cores for the past 1800 years 1 in the accumulation zone of the greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations on an annual basis the accumulation rate in different greenland ice cores is highly variable and the degree of correlation between accumulation series from different ice cores is low however when using multiyear averages of the different accumulation records the correlation increases significantly a statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual using this model a common greenland accumulation record for the past 1800 years has been extracted the record shows significant 11 9 years periodicity a sharp transition to very dry conditions is found just before a d 1200 and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the norse population in greenland and may have contributed to their extinction accumulation rates gradually decrease from a distinct maximum in a d 1394 to very dry conditions in the late 17th century and thus reflect the little ice age

time dependent subsidence prediction model and influence factor analysis for underground gas storages in bedded salt formations abstract taking into account the impurity and creep of rock salt a new model is proposed to predict the time dependent subsidence of the surface above underground gas storage caverns in bedded salt formations in this model the shape of the storage cavern is assumed to be a sphere formulae are developed for the volume and volume reduction of the cavern over time during both the construction and the operating periods a probability integral method is adopted to determine the shape of the subsidence regions and corresponding formulae are derived for the time dependent surface subsidence radial tilt and radial curvature flac3d was used to verify the proposed prediction model using the proposed model parametric analyses are carried out to study the influences of draw angle volume adjusting coefficient brine withdrawal rate internal pressure cavern depth material properties of the rock salt cavern diameter and operating time on the surface subsidence the results show that the subsidence increases with an increase of the draw angle volume adjusting coefficient brine withdrawal rate cavern diameter material properties of the rock salt and time but decreases with an increase of internal pressure subsidence increases first and then decreases with increasing cavern depth draw angle volume adjusting coefficient cavern depth cavern diameter material properties of the rock salt time and internal pressure have a large influence on the subsidence but there is little influence from the brine withdrawal rate and salt impurity

numerical modelling of shallow abandoned mine working subsidence affecting transport infrastructure abstract this work presents details of a shallow mining subsidence event that occurred in the summer of 2001 causing the formation of crown holes at the surface which affected the east coast main railway line in the uk this subsidence event caused significant disruption and the remediation effort required the construction of a 1 8 km long diversion built on a piled reinforced concrete raft details of the ground investigation are summarised along with a large parametric numerical modelling study undertaken in flac 3d into the potential causes of the instability including the role of variations of the level of the groundwater table the influence of the structure of the rock mass and also the potential geometry of the abandoned workings ultimately the modelling allowed constraints to be placed on the likely excavation width of the workings at the site along with bedding spacing and strength of the overlying rock mass the modelling also suggests that the increase in the ground water table may also have been a factor in the occurrence of instability on the site

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the greenland ice core chronology 2005 15 42 ka part 1 constructing the time scale the greenland ice core chronology 2005 gicc05 is extended back to 42 ka b2k before 2000 ad i e to the end of greenland stadial 11 the chronology is based on independent multi parameter counting of annual layers using comprehensive high resolution measurements available from the north greenland ice core project ngrip these are measurements of visual stratigraphy conductivity of the solid ice electrolytical melt water conductivity and the concentration of na c a 2 s o 4 n o 3 n h 4 a n uncertainty estimate of the time scale is obtained from identification of uncertain annual layers which are counted as 0 570 5 years the sum of the uncertain annual layers the so called maximum counting error of the presented chronology ranges from 4 in the warm interstadial periods to 7 in the cold stadials the annual accumulation rates of the stadials and interstadials are on average one third and half of the present day values respectively and the onset of the greenland interstadials 2 3 and 8 based on 20 year averaged d 18 o

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

pairwise comparisons to reconstruct mean temperature in the arctic atlantic region over the last 2 000 years existing multi proxy climate reconstruction methods assume the suitably transformed proxy time series are linearly related to the target climate variable which is likely a simplifying assumption for many proxy records furthermore with a single exception these methods face problems with varying temporal resolutions of the proxy data here we introduce a new reconstruction method that uses the ordering of all pairs of proxy observations within each record to arrive at a consensus time series that best agrees with all proxy records the resulting unitless composite time series is subsequently calibrated to the instrumental record to provide an estimate of past climate by considering only pairwise comparisons this method which we call paico facilitates the inclusion of records with differing temporal resolutions and relaxes the assumption of linearity to the more general assumption of a monotonically increasing relationship between each proxy series and the target climate variable we apply paico to a newly assembled collection of high quality proxy data to reconstruct the mean temperature of the northernmost atlantic region which we call arctic atlantic over the last 2 000 years the arctic atlantic is a dynamically important region known to feature substantial temperature variability over recent millennia and paico allows for a more thorough investigation of the arctic atlantic regional climate as we include a diverse array of terrestrial and marine proxies with annual to multidecadal temporal resolutions comparisons of the paico reconstruction to recent reconstructions covering larger areas indicate greater climatic variability in the arctic atlantic than for the arctic as a whole the arctic atlantic reconstruction features temperatures during the roman warm period and medieval climate anomaly that are comparable or even warmer than those of the twentieth century and coldest temperatures in the middle of the nineteenth century just prior to the onset of the recent warming trend

new modeling of the vostok ice flow line and implication for the glaciological chronology of the vostok ice core 1 we have used new spaceborne elevation and airborne ice thickness data to constrain a 2d1 2 model of snow accumulation and ice flow along the ridge b vostok station ice flow line east antarctica we show that new evaluations of the ice flow line geometry from the surface elevation ice thickness from low frequency radar data and basal melting and sliding change significantly the chronology of the vostok ice core this new vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the dome fuji glaciological timescale at the same time the new model shows significantly older ages than the previous gt4 timescale for the last glacial part being thus in better agreement with the grip and gisp2 chronologies

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

evidence for the asynchronous retreat of large outlet glaciers in southeast greenland at the end of the last glaciation recent rapid changes in the marine terminating sectors of the greenland ice sheet gris have prompted concerns about the future stability of the ice sheet long term records of ice sheet behaviour provide valuable context to assess the magnitude of current change and may help resolve the mechanisms driving deglaciation we report 23 new 10be exposure ages which constrain the deglacial history of two large fjord systems in southeast se greenland we compare our chronologies with existing data from the centre of the sector to examine the timing and style of deglaciation at a regional scale glacial erratic 10be exposure ages demonstrate that kangerdlugssuaq fjord deglaciated at 11 8 ka at the end of the younger dryas yd 12 8 11 6 ka retreat at kangerdlugssuaq fjord coincided with known incursion of the warm irminger current ic onto the continental shelf this is inferred to have initiated retreat comparison with recently published results from sermilik fjord and new 10be ages from bernstorffs fjord indicates deglaciation occurred 1 ka later in the south of the se region sermilik fjord 10 9 ka and bernstorffs fjord 10 4 ka deglaciated later retreat likely occurred in response to dramatic climatic amelioration at the termination of the yd stadial we suggest that the disparate timing of deglaciation across the se region may be primarily explained by the varying influence of the warm ic glaciers in southern se greenland were isolated from warm atlantic waters during the yd by complex shelf bathymetry in all fjord settings ice retreat was rapid and persistent consistent with the absence of geomorphological evidence for stillstand or readvance events ice retreat was accompanied by rapid thinning and likely continued to well within present day ice sheet margins glacial erratic 10be age determinations and geomorphological observations show no evidence for holocene readvance events prior to the little ice age lia

speleothems as sensitive recorders of volcanic eruptions the bronze age minoan eruption recorded in a stalagmite from turkey mounting evidence exists that variations in sulphur content in stalagmites are closely linked to changes in volcanic or anthropogenic atmospheric sulphur the strong dependency of sulphur on soil ph and ecosystem storage however can result in a delay of several years to decades in the registration of volcanic eruptions and anthropogenic emissions by stalagmites here we present synchrotron radiation based trace element analysis performed on a precisely dated section of a stalagmite from sofular cave in northern turkey as this section covers the time interval of the intensively studied minoan volcanic eruption between 1600 and 1650 bc we can test whether this vigorous eruption can be traced in a stalagmite of all measured trace elements only bromine shows a clear short lived peak at 1621 251621 25 bc whereas sulphur and molybdenum show peaks later at 1617 251617 25 and 1589 251589 25 respectively we suggest that all trace element peaks are related to the minoan eruption whereas the observed phasing of bromine molybdenum and sulphur is related to differences in their retention rates in the soil above sofular cave for the first time we can show that bromine appears to be an ideal volcanic tracer in stalagmites as it is a prominent volatile component in volcanic eruptions can be easily leached in soils and rapidly transferred from the atmosphere through the soil and bedrock into the cave and stalagmite respectively highly resolved oxygen and carbon isotope profiles indicate that the minoan eruption had no detectable climatic and environmental impact in northern turkey

atmospheric circulation variability associated with shallow core seasonal isotopic extremes near summit greenland seasonal back diffused 18o time series reconstructed for nine shallow firn cores from the greenland summit for 1959 1987 are evaluated in terms of 1 their spatial and temporal variability and 2 their association to the atmospheric circulation rotated principal component analysis evaluates spatial and temporal patterns of organization in the back diffused 18o ice core time series mean sea level pressure and 500 hpa height fields are obtained for winter and summer seasons that fall in the isotopically warmest and coldest thirds of the seasonal data the winter back diffused 18o data indicate that some degree of longitudinal separation takes place between isotopic records from western and eastern greenland in agreement with coastal station climatic data temporal variability is linked with statistical significance to the variability of the atmospheric circulation over the denmark strait as well as over the norwegian and barents seas the north atlantic oscillation nao and the mean icelandic low in the denmark strait affect isotopic variability over the cores west of the ice divide just as they have been shown to prominently affect west coast air temperature records isotopic variability at some ice cores east of the divide is influenced by pressure variability over the norwegian and barents seas although statistical significance is lower the nao appears insignificant in summer isotopic variability as the circulation in that season is very much localized and dominated by either ridging warm cases or troughs cold cases over eastern greenland and the arctic ocean results suggest that long term winter 18o variability can potentially be linked to climate variation over europe especially from the mediterranean basin northward to about 55 n and as far east as central siberia

geomechanical investigation of roof failure of china s first gas storage salt cavern abstract jk a cavern is the first operating cavern of jintan underground gas storage which is also the first operating salt cavern gas storage in china in 2015 the sonar survey carried out under working conditions indicated that a massive roof collapse of the jk a cavern had taken place to prevent similar accidents from happening again finding the causes and the collapse time of jk a cavern would be valuable by using the target salt formation information rock properties and monitored gas pressure a 3d geomechanical model of jk a cavern has been built the responses of the rock mass around jk a cavern under leaching sealing tests debrining and gas injection delivery have been investigated a safety evaluation system consisting of cavern volume shrinkage dilatancy safety factor displacement vertical stress and equivalent strain is proposed to find the likely collapse time and the reason for the jk a cavern roof collapse results show that there are two main causes for the cavern roof failure 1 a large span flat roof detrimental for bearing loads once local damage takes place massive collapse may be triggered by the self weight of the loosened rock 2 the decrease speed of the internal gas pressure is too fast the loads applied to the cavern roof cannot be transferred in a timely fashion which causes a stress concentration zone to form and local damage develops the roof collapse of jk a cavern took place 1 3 years after its gas injection delivery started numerical analysis results show that dilatancy safety factor and vertical stress have high accuracy and sensitivity in the prediction of the cavern roof collapse there is a high potential for a roof collapse of jk a cavern to happen again we propose that the gas pressure and pressure decrease rate are to be controlled strictly in the later operating period to prevent any collapses in the future