variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

the dibdibba aquifer system at safwan zubair area southern iraq hydrogeology and environmental situation the objective of this research is to study the environment and hydrogeology of the dibdibba aquifer system in the safwan zubair area southern iraq in relation to the study area s geology and anthropogenic activities ten groundwater samples were collected from safwan zubair geochemical data aquachem and gis arcmap 10 1 were used as tools to identify natural and anthropogenic factors that affect geochemical data we analyzed water samples for major cations and anions polycyclic aromatic hydrocarbons pahs total uranium tu and heavy metals pb ni cr cd v zn as se cu fe mn as well as the metalloid b groundwater composition in the area of study is classified into six types ca mg cl ca mg na cl ca mg cl so4 ca mg na cl so4 ca na mg so4 cl and mg ca cl so4 the groundwater is influenced by natural factors particularly the concentrations of tu and major ions the concentrations of tu and major ions in some water samples exceed limits for drinking water however the average of all examined heavy metals except for fe and b was within the limits for drinking water as well as the concentrations of pahs the potential use of this groundwater for drinking and irrigation is discussed

inverse modelling of elastic thickness by convolution method the eastern alps as a case example an unconventional scheme is used to estimate the flexural rigidity or equivalently the elastic thickness of the lithosphere given the topography and gravity data the flexural rigidity is the parameter that governs the flexural response of the lithosphere in the frame of the thin plate flexure model the scheme is an alternative to the widely used calculation of admittance of topography sea floor or continental topography and gravity bearing some advantages which are explained in the paper the scheme involves the inversion of the gravity data in order to formulate a model of the crust mantle interface cmi undulations in a second step the flexure parameter is then evaluated from the relation between topography and cmi variations instead of calculating the admittance function using a spectral analysis a set of point load response functions are used in order to retrieve the optimal flexure parameter this has two main advantages instabilities of the numerical admittance evaluation at wavenumbers with low spectral energy in the topography are overcome and the analysis can be made over an area which is not necessarily rectangular as required for the spectral analysis the proposed method allows a higher space resolution of elastic thickness than any spectral method for validation the numerical strategy is applied to the situation of a realistic synthetic model where all inputs and outputs are known a priori finally the spatial variations of the elastic thickness are studied in an area across the eastern alps 4 2002 elsevier science b v all rights reserved

a revised relaxation time spectrum for fennoscandia summary the fennoscandian relaxation time spectrum rts first derived by mcconnell 1968 is a classic data set in studies of glacial isostatic adjustment gia we outline a new method for estimating an rts from a set of strandline data which is based on a damped least squares solution for spherical harmonic coefficients associated with the strandline heights in contrast to the hankel transform approach outlined by mcconnell 1968 the method does not require interpolation or extrapolation of the data nor does it use the assumption that peripheral deformations are zero we begin by applying the new approach to a suite of synthetic strandlines these synthetic calculations quantify the effect on the rts estimates of the common assumptions of free decay uplift an axisymmetric fennoscandian deformation field and the uncertainty introduced by limited spatial and temporal sampling of this field recently the accuracy of the sauramo 1958 strandline data upon which the mcconnell 1968 rts was based has been questioned wolf 1996 accordingly we apply our new approach to a set of more robust strandline data published by donner 1964 1969 1980 1995 to compute a revised rts for fennoscandia at high harmonic degrees above 50 our new rts is characterized by weak constraints whereas mcconnell s 1968 rts suggests a significant reduction in relaxation times relative to the values at low degrees this reduction was the basis for mcconnell s 1968 inference of an elastic lithosphere in contrast to this we conclude that the trend is an artefact of the observational data set he adopted at lower degrees mcconnell s 1968 relaxation time estimates lie at the lower end of the range implied by the present analysis to complete our study we apply the techniques of linearized bayesian inference to invert our newly derived rts for mantle viscosity we find that the rts provides an estimate of 5 1020 pa s for the volumetric mean viscosity in a region extending from the base of the lithosphere to about 550 km depth target regions which extend from the transition zone to 1200 km depth are less well constrained however the average viscosity from the base of the lithosphere to 1200 km depth is consistent with the classic haskell 1935 value of 1021 pa s for mantle viscosity finally we demonstrate that viscosity models within the class inferred by mitrovica forte 1997 from joint inversions of postglacial relaxation times associated with gia and mantle convection observables simultaneously fit the revised fennoscandian rts

evaluation of groundwater quality in coastal areas implications for sustainable agriculture seawater intrusion is a problem in the coastal areas of korea most productive agricultural fields are in the western and southern coastal areas of the country where irrigation predominantly relies on groundwater seawater intrusion has affected agricultural productivity to evaluate progressive encroachment of saline water the korean government established a seawater intrusion monitoring well network especially in the western and southern part of the peninsula automatic water levels and ec monitoring and periodic chemical analysis of groundwater help track salinization salinization of fresh groundwater is highly associated with groundwater withdrawal a large proportion of the groundwaters are classified as na cl and ca cl types the na cl types represent effects of seawater intrusion the highest ec level was over 1 6 km inland and high cl values were observed up to 1 2 km inland lower ratios of na cl and so4 cl than seawater values indicate the seawater encroachment a linear relation between na and cl represents simple mixing of the fresh groundwater with the seawater the saline na cl typed groundwaters showed br cl ratios similar to or less than seawater values the ca hco3 type groundwaters had the highest br cl ratios substantial proportions of the groundwaters showed potential for salinity and should be better managed for sustainable agriculture

effects of spatial discretization in ice sheet modelling using the shallow ice approximation this paper assesses a two dimensional vertically integrated ice model for its numerical properties in the calculation of ice sheet evolution on a sloping bed using the shallow ice approxi mation we discuss the influence of initial conditions and individual model parameters on the model s numerical behaviour with emphasis on varying spatial discretizations the modelling results suffer badly from numerical problems they show a strong dependence on gridcell size and we conclude that the widely used gridcell spacing of 20 km is too coarse the numerical errors are small in each single time step but increase non linearly over time and with volume change as a result of feedback of the mass balance with height we propose a new method for the calculation of the surface gradient near the margin which improves the results significantly furthermore we show that we may use dimension analysis as a tool to explain in which situations numerical problems are to be expected

simulations of northern hemisphere ice sheet retreat sensitivity to physical mechanisms involved during the last deglaciation a 3 dimensional thermomechanical ice sheet model is used to simulate the evolution of the geometry of northern hemisphere ice sheets through the last deglaciation the ice sheet model is forced by a time evolving climatology provided by the linear interpolation through time of climate snapshots simulated by the lmd5 3 atmospheric general circulation model agcm at different periods of the last deglaciation 21 15 9 6 and 0 kyr bp the agcm is driven by insolation atmospheric co2 content ice sheet configuration and sea surface temperatures although our approach is able to produce the complete continental ice retreat our simulated deglaciation presents a phase lag with reconstructions based on observational evidences this suggests that physical mechanisms related to climate forcing and or ice sheet internal dynamics are not properly represented the influence of millennial scale forcing feedback mechanisms between ice sheet elevation and surface mass balance and parameterization of the ice flow is also tested through a set of sensitivity experiments the rapid variability has a strong impact on the evolution of the ice volume because of nonlinear effects in temperature mass balance relationships fennoscandia appears to be strongly sensitive to the small scale ice sheet instability both ice sheets are to some extent sensitive to an increased basal sliding

simulated influence of carbon dioxide orbital forcing and ice sheets on the climate of the last glacial maximum a coupled atmosphere ocean sea ice model is used to investigate the climate of the last glacial maximum 21 000 years ago and the relative climate forcing effects of atmosphere co2 the earth s orbital parameters and ice sheet albedo tropical temperatures are found to be 2 2 c less than today s slightly colder than indicated by the climap palaeoclimate reconstruction this result is consistent with a low to medium climate sensitivity to radiative perturbations temperatures are colder still in the northern north atlantic region owing to a weakening and shallowing of the thermohaline circulation a sensitivity analysis suggests that changes in ocean circulation since the last glacial maximum have not contributed directly to the global mean temperature change since that time

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

imaging and quantifying salt tracer transport in a riparian groundwater system by means of 3d ert monitoring abstractdetermining groundwater flow paths of infiltrated river water is necessary for studying biochemical processes in the riparian zone but their characterization is complicated by strong temporal and spatial heterogeneity we investigated to what extent repeat 3d surface electrical resistance tomography ert can be used to monitor transport of a salt tracer plume under close to natural gradient conditions the aim is to estimate groundwater flow velocities and pathways at a site located within a riparian groundwater system adjacent to the perialpine thur river in northeastern switzerland our ert time lapse images provide constraints on the plume s shape flow direction and velocity these images allow the movement of the plume to be followed for 35 m although the hydraulic gradient is only 1 43 the ert time lapse images demonstrate that the plume s center of mass and its front propagate with velocities of 2 10 4 m s and 5 10 4 m s respectively these velocities are compatible with groundwate

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

greenland s contribution to global sea level rise by the end of the 21st century the greenland ice sheet holds enough water to raise the global sea level with 7 m over the last few decades observations manifest a substantial increase of the mass loss of this ice sheet both enhanced melting and increase of the dynamical discharge associated with calving at the outlet glacier fronts are contributing to the mass imbalance using a dynamical and thermodynamical ice sheet model and taking into account speed up of outlet glaciers we estimate greenland s contribution to the 21st century global sea level rise and the uncertainty of this estimate boundary fields of temperature and precipitation extracted from coupled climate model projections used for the ipcc fourth assessment report are applied to the ice sheet model we implement a simple parameterization for increased flow of outlet glaciers which decreases the bias of the modeled present day surface height it also allows for taking into account the observed recent increase in dynamical discharge and it can be used for future projections associated with outlet glacier speed up greenland contributes 0 17 cm to global sea level rise by the end of the 21st century this range includes the uncertainties in climate model projections the uncertainty associated with scenarios of greenhouse gas emissions as well as the uncertainties in future outlet glacier discharge in addition the range takes into account the uncertainty of the ice sheet model and its boundary fields

borehole to surface electrical resistivity monitoring of a salt water injection experiment a field experiment was conducted at the university of california richmond field station to demonstrate the sensitivity of borehole to surface resistivity measurements in groundwater investigations a quantity of saline water was injected into a fresh water aquifer while the resistivity was monitored using a multichannel borehole to surface system two experiments were conducted using pole pole and pole dipole receiver electrode arrays the data from the pole pole experiment were superimposed to simulate a dipole pole array and the data from the pole dipole array were superimposed to simulate a dipole dipole array this superposition of the data was done to enhance the anomaly and facilitate interpretation a numerical modeling study was performed in conjunction with the field experiment in order to interprete the results a three dimensional modeling program was used to simulate the geological setting of the field experiment and the salt water injection this modeling revealed that an asymmetric displacem

potential of the solid earth response for limiting long term west antarctic ice sheet retreat in a warming climate abstract we employ a coupled model for ice sheet dynamics and maxwell viscoelastic solid earth dynamics including a gravitationally consistent description of sea level with this model we study the influence of the solid earth on the future evolution of the west antarctic ice sheet wais starting from steady state conditions close to the present day configuration of the antarctic ice sheet we apply different atmospheric and oceanic forcings and solid earth rheologies in order to analyse the retreat of the wais climate forcing is the primary control on the occurrence of wais collapse for moderate climate forcing and weak solid earth rheologies however we find that the relative sea level rsl fall associated with the viscoelastic solid earth response due to unloading by wais retreat limits the retreat to the amundsen sea embayment on time scales of several millennia whereas stiffer earth structures yield a collapse under these conditions under stronger climate forcing weak earth structures associated with the west antarctic rift system produce a delay of up to 5000 years in comparison to stiffer antarctic average solid earth rheologies furthermore we find that sea level rise from an assumed fast deglaciation of the greenland ice sheet induces wais collapse in the presence of higher asthenosphere viscosities in cases when the climatic forcing is too weak to force wais collapse alone

convective removal of the tibetan plateau mantle lithosphere by 26 ma abstract during the late oligocene early miocene there were several major geological events in and around the tibetan plateau tp first crustal shortening deformation ceased completely within the tp before 25 ma and instead adakitic rocks and potassic ultrapotassic volcanics were emplaced in the lhasa terrane since 26 25 ma several recent paleoelevation reconstructions suggest an oligocene early miocene uplift of 1500 3000 m for the qiangtang qt and songpan ganzi sg terranes although the exact timing is unclear as a possible response to this uplift significant desertification occurred in the vicinity of the tp at 26 22 ma and convergence between india and eurasia slowed considerably at 26 20 ma subsequently e w extension was initiated no later than 18 ma in the lhasa and qt terranes in contrast the tectonic deformation around the tp was dominated by radial expansion of shortening deformation since 25 22 ma the plateau wide near synchroneity of these events calls for an internally consistent model which can be best described as convective removal of the lower mantle lithosphere geophysical and petrochemical evidence further confirms that this extensive removal occurred beneath the qt and sg terranes the present review concludes that other than plate boundary stress the internal stress within the tp lithosphere could have contributed to rapid wholesale uplift and a series of concomitant tectonic events accompanied by major aridification since 26 ma

flexural rigidity of fennoscandia inferred from the postglacial uplift the earth s response to glacial loading unloading offers exceptional promise for the study of the physical properties of the lithosphere in particular tilting of paleoshorelines is very sensitive to the lithosphere rigidity to determine the flexural rigidity the isostatic response to deglaciation in fennoscandia is modeled using an earth model with a layered mantle viscosity overlain by an elastic lithosphere the flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines five different ice thickness models are used for a relatively thin ice 2500 m in central areas the resulting flexural rigidity is more or less uniform over fennoscandia with a value of 1023 n m elastic thickness te 20 km this is regarded as minimum for the flexural rigidity of central fennoscandia the pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity 2 5 1025 n m te 110 km in more central areas of fennoscandia the flexural rigidity at the western coast of norway does not seem to exceed 1023 n m te 50 km the most likely glacier model gives a flexural rigidity of 1023 n m te 20 km at the norwegian coast increasing to above 1024 n m te 50 km in central parts of fennoscandia

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective

hydrochemical and isotopic investigation of groundwater of al batin alluvial fan aquifer southern iraq major ions and important trace elements in addition to 18o and 2h were analysed for 43 groundwater samples sampled from the al batin alluvial fan aquifer south iraq the most dominant ions with respect to molarity were na cl so4 2 ca2 mg2 no3 hco3 with total dissolved solids tds averaging 7855 mg l high concentrations were found for the trace elements u mo v b sr and cr this study suggests a hydraulic connection exists near the fan apex between the uppermost part of the al batin aquifer and the underlying dammam aquifer by means of the abu jir fault system except for the effects of extensive irrigation fertilizer use and poorly maintained sewers the groundwater chemistry is mainly controlled by geological processes such as dissolution of evaporites and the enrichment of dissolved ions as a result of the high evaporation and low recharge rate furthermore it is shown that the kuwaiti fuel oil burning during gulf war in 1991 contributed to the enrichment of v and mo in the studied aquifer the spatial distribution of most ions appears to generally increase from the south west towards the north east in the direction of groundwater flow the stable isotopes show heavier values in groundwater with a gradually increasing trend in the direction of groundwater flow due to the decreasing depth to groundwater and thus increasing of evaporation from both groundwater or irrigation return water additionally the stable isotope signature suggests that rainfall from sources in the arabian gulf and the arabian sea is the major source of recharge for the al batin aquifer except for two samples of groundwater all samples were not suitable for potable use according to the who standards most of the groundwater is suitable for some agricultural purpose and for livestock water supply apart from the high salinity boron represents the most critical element in the groundwater with respect to agricultural purposes

marine and human activity influences on the groundwater quality of southern korinthos area greece in this paper the groundwater quality of the southern part of korinthos region north east peloponnese is discussed the geology is characterized by a thick sequence of neogene marls alternating with sandstones overlain by superficial quaternary deposits the latter consist of a mixture of loose materials such as conglomerates marly sandstones sands and clay to silty sands the area is crossed by a fault system parallel to the coastline and the quaternary sediments have formed extended tyrrhenian marine terraces two aquifers have been identified in the area the first is unconfined and occurs within the quaternary sediments whereas the other is a deep confined aquifer occurring within the underlying neogene marl series analysis of hydrochemical evolution over the past 30 years has indicated significant deterioration of quality owing to seawater intrusion and nitrate pollution the various sources of pollution have rendered to a large extent shallow groundwater unsuitable not only for potable water supply but also for irrigation purposes however this is not the case for the deeper confined aquifer statistical analysis was used to explore the evolution of salinization during the years 1968 and 1998 in view of the alarming conditions caused by the documented groundwater quality deterioration the need for integrated water resources management is stressed to maintain the socio economic growth of the region studied copyright 2003 john wiley sons ltd

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

tests of glacial rebound models for fennoscandinavia based on instrumented sea and lake level records summary evidence for changing sea levels in northwestern europe related to glacial rebound is found in both the geological record of the past millennia and in the instrumental records of the past two centuries the latter records are of two types records of sealevel change primarily from the baltic and the gulfs of finland and bothnia and records of the tilting of some of the larger lakes in both finland and sweden the sealevel records are particularly important because of their long duration and high quality their large number and good spatial distribution and the spatially coherent background noise the two instrumental data types are complementary and provide constraints on the upper mantle rheology and on the distribution of ice during the late glacial stage comparisons of the observed rates of change of the water levels with models for glacial rebound yield earth models with a lithospheric thickness of 80 100 km and an uppermantle viscosity of 4 5 1020 pa s evective parameters that are consistent with those obtained from the analysis of the geological evidence for the same region the mareograph results support ice sheet models in which the late weichselian ice thickness over the eastern and southern parts of fennoscandia is relatively thinner than that for the western region also consistent with the interpretation of the geological evidence for sea level change in addition the instrumental records provide constraints on the eustatic sea level change for about the past 100 years a satisfactory separation of the earth rheology parameters from this rate of change can be achieved by estimating the latter only from those records for which the predicted isostatic evects are small a check on these results is possible by using the lake level records to establish constraints on the earth model parameters and the sea level records to constrain also the eustatic change all approaches lead to an average eustatic sea level rise for the past century of about 1 1 0 2 mm yr 1

terminating the last interglacial the role of ice sheet climate feedbacks in a gcm asynchronously coupled to an ice sheet model climatic deterioration in northeastern canada following the last interglacial resulted in the formation and abrupt expansion of the laurentide ice sheet however the physical mechanisms leading to rapid ice sheet expansion are not well understood here the authors report on experiments using an ice sheet model asynchronously coupled to a gcm to investigate the role of ice sheet climate feedbacks in terminating the last interglacial period in agreement with simpler models the experiments indicate that a specific type of ice albedo feedback the small ice cap instability is the dominant process controlling rapid expansion of the laurentide ice sheet as ice elevations increase in northeastern canada a stationary wave forms and strengthens over the laurentide ice sheet which acts to hinder further expansion of the ice margin and reduce the effect of the small ice cap instability the sensitivity of these feedbacks to ice topography results in a reduction in simulated ice volume when the communication interval between the gcm and ice sheet model is lengthened since this permits larger gains in ice elevation between gcm updates and biases the simulationtowardastrongerstationarywavefeedback theshortestcommunicationinterval 500 yr leadsto a laurentide ice volume of 6 3 10 6 km 3 in 10 kyr which is less than ice volume estimates based on the geological record but is a substantial improvement over previous gcm studies the authors discuss potential improvements to the asynchronous coupling scheme that would more accurately resolve ice sheet climate feedbacks potentially leading to greater simulated ice volume

a case study to assess the potential for saline soil development due to irrigation abstract with the help of a generalized conceptual model for the formation of saline soil we examine whether irrigation proposed for an area near lethbridge alberta will compound an existing salinity problem the geology of the site is characterized by weathered and non weathered tills which overlie cretaceous bedrock locally preglacial sands and gravels occur along the axes of two bedrock valleys beneath the site piezometric data define local groundwater flow from west to east following the regional topographic slope however the depth to the water table is extremely variable and controlled by the preglacial sand and gravel unit the existing problem of soil salinity which is restricted to the western part of the study area is caused by the high water table and large quantities of dissolved mineral mass in the groundwater in the central and eastern part of the area the water table occurs at depths greater than 20m and saline soils have not formed flow modeling along a two dimensional cross section confirms that the water table configuration and hence the distribution of saline soils is controlled by the preglacial deposits indications are that excess recharge due to irrigation will not result in a water table rise unless the quantity involved is considerably larger than the natural rate of recharge thus irrigation will not contributed to a marked increase in the size of the area affected by the saline soil

tectonic zonation of the central himalaya and the crustal evolution of collision and compressional belts abstract the central himalayan segment is divided from south to north into sub parallel structural facies zones the main boundary fault mbf plays the role of an important tectonic element dividing the siwalik molasse along the foothills of the himalaya against the para autochthonous and allochthonous tectonic units of the southern himalaya on the basis of recent researches i suggest that the himalayan region should be divided geologically into two major geologic zones i propose to call the dividing structural line between them the main axial zone maz of the himalaya which is situated in the crystalline complex of the higher himalaya this deep seated structure in the himalaya has played a crucial role in the history of geological development as well as incorporating the root zone of southward pushed thrust sheets the main central thrust mct tectonically separates the carbonate para autochthonous zone of southern himalaya from the metamorphosed crystalline vaikrita complex the vaikrita central crystalline complex in its turn is separated from the huge pile of the sedimentary tethyan complex by the tethyan thrust tt farther north the great himalaya suture ghs called the indus tsangpo suture divides the northern extremity of himalaya from the karakoram erogenic belt the ghs has provided excellent conditions for the study of mantle remains on the oceanic crust with the occurrence of ophiolitic melange which was the result of subduction of a continental type plate and obduction of oceanic material in recent years a large number of data has been recorded especially as a result of sino french and other scientific expeditions in the tibetan region reversed critical wide angle reflection profiles of the crust mantle boundary south of the great himalaya suture ghs or the indus tsango yarlung zangbo suture in tibet reveal a deep 70 km moho extending north of the higher himalaya whilst to the south the moho is 15 km higher thus in the southern region of tibet the crust gets thinner gradually towards the south and reduces to about 38 km in the gangetic plain of india the 300 km of terrain between the ghs and the gangetic plain represent the transitional collision and compressional belt the magnetolluric and explosive seismographic data indicate that the layered structures are developed within the crust transisting to the upper mantle the moho discontinuity exhibits step terraces the low velocity and resistance layer within the crust indicates that the crust is overlapping and superimposed thus the intense compression from south to north caused by the indian plate caused the crust to overlap shorten thicken and become isostatically adjusted to give rise to the tibetan plateau the successive occurrence of nappe shear zones led to progressive superimposing and thickening of the crust it also indicates intra continental subduction and destruction of the lithosphere after plate collision

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

a geoelectrical and hydrogeological study for the assessment of groundwater resources in wadi al bih uae drilling information historical water table levels groundwater salinity records of the existing water wells in wadi al bih area united arab emirates were stored in a geodatabase and used to characterize the geological and hydrogeological settings of this area a 2d earth resistivity imaging survey was conducted for the first time in the northern uae to determine the potential of the quaternary aquifer and its groundwater quality in the areas where there are no monitoring wells the results of the chemical analyses of the collected groundwater samples together with the inversion results of the resistivity data were used to draw a total salinity map and determine the spatial variations in groundwater quality the inversion results of the 2d earth resistivity imaging data indicated that the quaternary aquifer in the study area is in a good connection with the underlying carbonate aquifer it also indicated that the carbonate aquifer is of major regional and vertical extension and it contains the fresh water in this area the data stored in the developed database were used to produce different types of geopotential maps

application of ridge regression in inversion of low latitude magnetic anomalies derived from space measurements abstract anomalies in total field horizontal and vertical components over the indian region derived from magsat measurements have been inverted through the ridge regression method basically to test 1 the application of the method in deriving a stable estimate of crustal magnetisation and 2 the relative amount of information on crustal magnetisation contained in scalar vis a vis vector data results show that the instabilities in magnetisation solution that appear when mayhew s conventional method is applied in low latitudes could be removed through the ridge regression technique it was also noticed that magnetisation distribution estimated through the inversion of the total field b does not relate well with the geological features in the equatorial region inversion of thez anomaly alone gives realistic results for the equatorial region but not over higher latitudes we conclude that a joint inversion ofx andz anomalies provides a magnetisation estimate consistent with known geological features both for equatorial and higher latitudes

modeling the marine extent of northern hemisphere ice sheets during the last glacial cycle mechanisms which determine time dependent changes of the marine ice margin in dynamic ice sheet models are important but poorly understood here we derive an empirical formulation for changes in the marine extent when modeling the northern hemisphere ice sheets over the last glacial cycle in a three dimensional thermo mechanically coupled ice sheet model we assume that the strongest control on changes in marine extent is ice calving and that the variable most crucial to calving is water depth the empirical marine extent relationship is tuned so that the major marine retreat history of the north american and eurasian ice sheets are modeled accurately in time and space we find that this empirical treatment based on water depth is sufficient to reproduce the observations and discuss the implications for the physics of marine margin changes and the dynamics of the northern hemisphere ice sheets since the last glacial maximum

a salt tracer test monitored with surface ert to detect preferential flow and transport paths in fractured karstified limestones in hard rock aquifers fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths one critical issue in hydrogeological research is to identify characterize and monitor such fractured zones at a representative scale a tracer test monitored with surface electrical resistivity tomography ert could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer however multiple challenges exist including the lower resolution of surface ert compared with crosshole ert the finite time that is needed to complete an entire data acquisition and the strong dilution effects we conducted a natural gradient salt tracer test in fractured limestones to account for the high transport velocity we injected the salt tracer continuously for four hours at a depth of 18 m we monitored its propagation with two parallel ert profiles perpendicular to the groundwater flow direction concerning the data acquisition we always focused

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

effect of isostatic rebound on modelled ice volume variations during the last 200 kyr deformation of the lithosphere under an ice load can be approximated using the hypothesis of local damped isostasy this simple formulation has been systematically compared with a three dimensional model of the crust mantle system for simple ice load scenarios with a period in the range 20 100 kyr the comparison enables us to introduce the concepts of effective upper mantle density and effective relaxation time into the isostatic model for the response of the earth to the ice sheets these parameters depend on the earth model considered ice sheet size and the period of the load cycle the local damped isostasy model has been implemented in the louvain la neuve climate model to assess the impact of isostasy on continental ice volume variations for the last 200 kyr results suggest that isostasy acts as a negative feedback for ice volume during the glaciation process and acts as a positive feedback during the deglaciation moreover taking isostasy into account is necessary to simulate variations in northern hemisphere ice volume during isotopic stage 3 lastly the use of effective mantle density and effective relaxation time improves the model performance regarding specmap reconstructions c 2001 elsevier science b v all rights reserved

effect of isostasy on dynamical ice sheet modeling a case study for eurasia 1 isostatic adjustment is an important process when modeling dynamical ice sheet evolution a number of different types of earth model are used to model this process ranging from models with local or elastic lithospheres with a single relaxation time to account for temporal behavior to self gravitating spherically symmetric models of the crust mantle system we performed sensitivity tests to assess the dynamical response of ice sheets to isostatic adjustment the resulting ice sheet geometries depend on the response times of the system including the growth rate of ice sheets versus the relaxation time of the earth differences in lithospheric strength cause large differences in the modeled ice sheets with the largest differences in isostatic adjustment in the vicinity of the ice margins in addition we compared predictions based on an often used flexural model with an elastic plate and a single relaxation time to a spherically symmetric self gravitating viscoelastic approach no flexural model was able to reproduce the viscoelastic response completely due to the fact that the models have an intrinsically different spatial and temporal response when applied to a full transient glacial cycle in eurasia even the best fitting flexural model underestimated the ice volume at the lgm by 30 percent our results indicate that the commonly used value of 3000 years for the relaxation time in flexural models is too short for eurasia by at least 3000 years

a continuous simulation of global ice volume over the past 1 million years with 3 d ice sheet models sea level records show large glacial interglacial changes over the past million years which on these time scales are related to changes of ice volume on land during the pleistocene sea level changes induced by ice volume are largely caused by the waxing and waning of the large ice sheets in the northern hemisphere however the individual contributions of ice in the northern and southern hemisphere are poorly constrained in this study for the first time a fully coupled system of four 3 d ice sheet models is used simulating glaciations on eurasia north america greenland and antarctica the ice sheet models use a combination of the shallow ice and shelf approximations to determine sheet shelf and sliding velocities the framework consists of an inverse forward modelling approach to derive a self consistent record of temperature and ice volume from deep sea benthic 18o data over the past 1 million years a proxy for ice volume and temperature it is shown that for both eustatic sea level and sea water 18o changes the eurasian and north american ice sheets are responsible for the largest part of the variability the combined contribution of the antarctic and greenland ice sheets is about 10 for sea level and about 20 for sea water 18o during glacial maxima however changes in interglacials are mainly caused by melt of the greenland and antarctic ice sheets with an average time lag of 4 kyr between melt and temperature furthermore we have tested the separate response to changes in temperature and sea level for each ice sheet indicating that ice volume can be significantly influenced by changes in eustatic sea level alone hence showing the importance of a simultaneous simulation of all four ice sheets this paper describes the first complete simulation of global ice volume variations over the late pleistocene with the possibility to model changes above and below present day ice volume constrained by observations of benthic 18o proxy data

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

climatology glacial hiccups the climate instability of glacial times probably resulted from abrupt switches in ocean circulation a computer model simulation provides the first glimpse of the dynamics involved

salt water intrusion mapping by geoelectrical imaging surveys the geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore water salinity a new field survey technique that can be used for environmental and geotechnical investigations has been developed this study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt water intrusion boundary in yan state of kedah northwest malaysia the technique was incorporated into these surveys and it has proved to be a robust method for accurately mapping the fresh water saline water boundary the resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the geological survey of malaysia at those sites

contribution of electrical resistivity tomography to the study of detrital aquifers affected by seawater intrusion extrusion effects the river velez delta velez malaga southern spain abstract the coastal aquifer of the plio quaternary delta sediment deposits of the velez river province of malaga spain presents a highly irregular basement morphology and widely varying fill thickness 10 80 m between neighbouring sectors the basin which is tectonically controlled is filled with lutite facies alternating with channel filling rudites this detrital aquifer is affected by seasonal seawater intrusion extrusion processes due to increasing withdrawal of groundwater for human consumption and irrigation during dry periods a study was performed to improve the hydrogeological knowledge of this coastal aquifer system the study examined the morphology of the impervious substratum the facies distribution and the position of the seawater wedge for this purpose an electrical resistivity tomography ert geophysical technique was used and the tomographic data were calibrated using geological observations and borehole studies an analysis was carried out to compare the direct information obtained from the 35 boreholes with the indirect data corresponding to the four electrical tomography profiles in the study over 9660 resistivity data points were processed the ert profiles perfectly corroborated the information derived from the boreholes the profiles made it possible to detect thickness changes lithological changes and the presence of faults moreover from a hydrogeologic standpoint this research technique is capable of detecting the position of the phreatic level and in coastal aquifers such as the one examined in this study the possible horizontal or vertical penetration of seawater intrusion therefore the electrical geophysical prospecting based on ert can be highly useful in areas lacking sufficient geological information and or mechanical borehole data

isostatic response to glacial erosion deposition and ice loading impact on hydrocarbon traps of the southwestern barents sea abstract previous work indicates that a part of hydrocarbon loss from traps in the barents sea is attributed to the pleistocene glacially related spillage due to isostatically driven depth changes and tilting it is however unknown how severe the pleistocene spillage was and how much hydrocarbons were depleted due to other mechanisms including leakage and pre glacial spillage in addition it remains uncertain how much the orientation of the hydrocarbon traps and thus trap capacities and spill directions was affected by glacial sediment redistribution and ice loading the effect of the pleistocene burial history on trap capacity and spillage is addressed by using a combination of the flexural isostasy and secondary migration modelling the impact is modelled in three trap structures in the bjornoyrenna fault complex the results show that the pleistocene burial history led to either increase or decrease the trap capacities in the range of 5 14 the geometrical changes also affected the spill directions of some of the traps apart from the tilt magnitude the most important factor controlling the trap capacity change and spill directions in the analyzed traps was the initial geometric setting of the traps the traps in the western barents sea with present spill points to the west and south experienced trap capacity increase and were not susceptible to spillage during the pleistocene location of the pre glacial spill points determines whether the traps with the present spill points to the east and north experienced capacity increase or reduction structural changes of the traps caused only by the tilting could not have resulted in major loss of oil and gas the tilting together with gas volume expansion might however have been responsible for some part of the hydrocarbon loss during the cenozoic

revised estimates of greenland ice sheet thinning histories based on ice core records abstract ice core records were recently used to infer elevation changes of the greenland ice sheet throughout the holocene the inferred elevation changes show a significantly greater elevation reduction than those output from numerical models bringing into question the accuracy of the model based reconstructions and to some extent the estimated elevation histories a key component of the ice core analysis involved removing the influence of vertical surface motion on the 18 o signal measured from the agassiz and renland ice caps we re visit the original analysis with the intent to determine if the use of more accurate land uplift curves can account for some of the above noted discrepancy to improve on the original analysis we apply a geophysical model of glacial isostatic adjustment calibrated to sea level records from the queen elizabeth islands and greenland to calculate the influence of land height changes on the 18 o signal from the two ice cores this procedure is complicated by the fact that 18 o contained in agassiz ice is influenced by land height changes distant from the ice cap and so selecting a single location at which to compute the land height signal is not possible uncertainty in this selection is further complicated by the possible influence of innuitian ice during the early holocene 12 8 ka bp our results indicate that a more accurate treatment of the uplift correction leads to elevation histories that are in general shifted down relative to the original curves at grip ngrip dye 3 and camp century in addition compared to the original analysis the 1 uncertainty is considerably larger at grip and ngrip these changes reduce the data model discrepancy reported by vinther et al 2009 at grip ngrip dye 3 and camp century a more accurate treatment of isostasy and surface loading also acts to improve the data model fits such that the residuals at all four sites for the period 8 ka bp to present are significantly reduced compared to the original analysis prior to 8 ka bp the possible influence of innuitian ice on the inferred elevation histories prevents a meaningful comparison

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

variations in elastic thickness in the canadian shield we have compared different spectral methods the standard windowed fourier transform the multitaper method mtm and the maximum entropy method mem to determine the coherence between bouguer gravity and topography and estimate the variations of the effective elastic thickness te of the lithosphere these methods differ significantly in spatial resolution 1000 to 2000 km determined by the width of the windows required to resolve the wavelength of transition from low to high coherence the tests with synthetic data show that the standard deviation on elastic thickness estimates is high with the three methods but that the mean value obtained by the maximum entropy is close to the input value while the other methods underestimate the elastic thickness in the canadian shield the effective elastic thickness values vary from c40 km to n100 km over distances less than the width of the moving window there is no clear geographical or geological pattern in these variations as high and low elastic thickness values are found near the edge as well as in the center of the continent and in all provinces regardless of their age correlation between te and the heat flow field is weak the values of te being much higher beneath hudson bay than the williston basin are consistent with models of basin evolution and seismic estimates of mantle temperatures d 2004 elsevier b v all rights reserved

detrital provenance of early mesozoic basins in the jiangnan domain south china paleogeographic and geodynamic implications abstract detrital provenance analysis is an effective way to understand paleogeographic change and geodynamics in this paper we present petrological whole rock geochemical and detrital zircon u pb geochronological analysis of early and middle jurassic terrestrial clastic rocks in the jingdezhen basin and the huangshan basin in the jiangnan domain south china petrology and whole rock geochemistry show that the source rocks are dominated by intermediate to acid component the chemical index of alteration ranges from 69 to 86 suggesting a moderate weathering history for the source rocks the early middle jurassic sediments in the jingdezhen and huangshan basins were mostly sourced from magmatogenic greywackes and felsic magmatic rocks respectively detrital zircons have seven age peaks at 240 ma 430 ma 1390 ma 1880 ma 2500 ma 3200 ma and 788 999 ma a wide peak provenance analysis indicates that the source rocks are in the jiangnan domain the northwest zhejiang basin and the wuyishan domain combining these with previous results and paleocurrent directions we infer that the ne trending wuyishan and xuefengshan domains and the nearly e w jiangnan domain and nanling tectonic belt were orogenic uplifts and watersheds during the late triassic to middle jurassic the early mesozoic geodynamics in the south china block was related to the westward subduction of the paleo pacific plate and the northward continent continent collision following the closure of the paleo tethys ocean

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

seismicity focal mechanisms and their correlation with the geological tectonic history of the tibetan plateau abstract the tibetan plateau appears to have been formed as a result of the welding together of several continental plates of asia these plates have originated during different geological times dating back from the palaeozoic to the tertiary and underwent folding in different orogenic cycles as a result several major faults of continental dimensions trending ene wsw to nw se have developed some examples of these are the siling kunlun altyn tagh kansu and kang ting faults in addition several major lineaments faults trending ne sw to n s were developed seismicity over the tibetan plateau can mostly be explained in terms of activity associated with these faults and transverse lineaments large magnitude m b 7 0 earthquakes have taken place along these faults since historic times strike slip faulting is mostly related to ene wsw to nw se trending faults while normal faulting is related to ne sw trending lineaments and faults the stress system prevailing over the tibetan plateau is quite different from that prevailing along the himalaya front tension is predominant over large parts of tibet at present compared with compression along the himalayas

investigation of seawater intrusion in the dibdibba aquifer using 2d resistivity imaging in the area between al zubair and umm qasr southern iraq electrical resistivity surveying for delineating seawater intrusion was performed in the dibdibba aquifer in the area between the cities of al zubair safwan and al zubair umm qasr in the vicinity of khor al zubair channel basrah governorate southern iraq fourteen 2d resistivity profiles with a total length of 14 km were collected in the study area the resistivity sections were compared with lithological data extracted from 11 boreholes thirty nine groundwater samples were collected within the area and analyzed for chemical constituents internal hydrogeological reports and unpublished studies were also evaluated results reveal the existence of three major resistivity layers ranging from 0 1 to 130 m at various depths and locations the first layer has very low electrical resistivity 0 1 5 m representing a layer saturated with saltwater intruded from khor al zubair channel the second layer shows resistivity in the range of 5 130 m attributed to a transition zone and an unaffected zone saturated with brackish groundwater the last resistivity layer 3 m represents coarse grain sediments saturated with saline groundwater furthermore a hard clay bed jojab appears with a resistivity of 3 7 m in all 2d imaging lines within a depth of 20 28 m electrical conductivity ec measurements from seven wells collected in 2014 and 2016 show a positive ec difference increasing landward with an average increase of 1927 s cm in addition six chemical relationships na cl ca mg hco3 so4 so4 hco3 so4 cl mg ca and cl hco3 co3 are used to detect the source of salinity in groundwater this study proves that extensive use of high resolution 2d imaging sections alongside lithological and hydrogeological data can serve as a useful tool to delineate the boundaries between aquifers identify hydraulic boundaries between groundwater with different salinities and allocate hard clay layers between the upper and lower dibdibba aquifer in general the combination of 2d imaging and hydrochemistry enables conceptualization of the hydrogeological situation in the subsurface and characterization of the salinity source here seawater intrusion in the study area there have been no studies published so far on the characteristics of saltwater intrusion in the study area and this study is considered to be important for monitoring and studying the intrusion and regression of seawater

geochemical calculations and observations on salt water intrusions i a combined geochemical minxing cell model abstract a combined geochemical mixing cell flow model has been developed the geochemical model is based on the computer program eq 3 6 wolery 1982 has been modified to include cation exchange reactions and is incorporated in a one dimensional mixing cell model for stationary one dimensional transport dispersion or diffusion is calculated by mixing the cell contents with neighbouring cells relationships between mixing factors and dispersivity and diffusion coefficients are derived the model is used to simulate concentration changes during salt water intrusions fundamental differences are shown to exist between diffusion of salt water from a stagnant water body and dispersive intrusions during marine transgressions or flooding events with dispersive flow characteristic water compositions develop in space and time as a result of cation exchange with diffusion these steep concentration gradients are smoothed out and mixed compositions occur the concept that characteristic concentrations occur during dispersive flow is used to obtain paleohydrological information in a dutch polder the depth of the fresh salt water interface before polder development is deduced from a simulation of observed exchange reactions in the polder groundwater

mapping groundwater contamination using dc resistivity and vlf geophysical methods a case study geophysical methods can be helpful in mapping areas of contaminated soil and groundwater electrical resistivity and very low frequency electromagnetic induction vlf surveys were carried out at a site of shallow hydrocarbon contamination in utah county utah previously installed monitoring wells facilitated analysis of water chemistry to enhance interpretation of the geophysical data the electrical resistivity and vlf data correlate well and vertical cross sections and contour maps generated from these data helped map the contaminant plume which was delineated as an area of high interpreted resistivities

salinization processes in the unconfined aquifer of bou areg ne morocco a geostatistical geochemical and tomographic study hydrogeological and geochemical data in conjunction with the results of an electrical imaging tomographic survey were examined to determine the main factors and mechanisms controlling the groundwater chemistry and salinity of the unconfined aquifer of bou areg on the mediterranean coast of ne morocco in addition statistical and geochemical interpretation methods were used to identify the distribution of the salinity multivariate statistical analysis cluster and principal component factors revealed the main sources of contamination groups a b and c in the cluster analysis and factors 1 3 factor 1 ce cl k so42 and mg2 factor 2 ca2 hco3 and ph factor 3 no3 represent the signature of seawater intrusion in the coastal zone the influence of marly gypsum outcrops in the upstream zone and anthropogenic sources respectively the ionic delta the ionic ratio the saturation index and stuyfzand s method were applied to evaluate geochemical processes the results obtained indicate on the one hand the phenomenon of salinization in both the coastal and the upstream zones and on the other the dilution of groundwater by recharge cation exchange is shown to modify the concentration of ions in groundwater locally with respect to salinization processes in the coastal zone the results of electrical imaging tomography show that salinity increases both with depth and laterally inland from the coastline due to seawater intrusion

uranium in groundwater of the al batin alluvial fan aquifer south iraq this study focuses on identifying concentrations species spatial distribution and potential sources of uranium u in groundwater in al batin area south of iraq although few studies reported elevated concentration of u in groundwater in some parts of the al batin alluvial fan a comprehensive investigation of u in the groundwater of the entire fan is still missing so far to achieve this goal 43 groundwater samples are collected for major cations and anions trace elements total organic carbon and total inorganic carbon analyses u concentrations range between 0 1 and 98 g l with an arithmetic average of 16 g l the spatial distribution of u in groundwater shows an increase eastward and northeastward with some anomalies uo2 co3 22 uo2 co3 34 and uo2 hpo4 22 are the dominant u species according to phreeqc simulations spearman correlation analysis n 43 p 0 01 shows a positive correlation between u and k hco3 ca mg al si and rare earth elements ree well depth on the other hand had a negative correlation r 0 65 at p 0 01 with u indicating that u is dominant in more shallow groundwater this study assumes a geogenic source of u from the arabian shield in saudi arabia derived by flood plain and trapped in the east and northeast of the study area under reduced conditions of the neighbor marshes the release of uranium into the groundwater can be explained by three hypotheses the first hypothesis is desorption of u sorbed onto ferric minerals e g hematite magnetite and goethite the second hypothesis is desorption of u from clay minerals in mudstone lenses within the aquifer the third hypothesis is the release of u from the carbonate lattice structure due to the replacement with ca the relatively high eh and the elevated concentrations of so42 ca2 and na in groundwater are appropriate conditions to release u load of the supposed sources into groundwater

the crustal evolution and uplift mechanism of the qinghai tibet plateau abstract the qinghai tibet plateau covers part of each of the following four plates the tarim qaidam the qiangtang yangtze the gandise and the indian plates containing four crustal suture zones the northern qilian the east kunlun the karakorum lancang and the yarlung zangbo tsangpo suture zones the tarim qaidam and qiangtang yangtze plates belong to part of the paleo eurasian continent and the gandise and indian plates are component parts of the old gondwana land a typical ancient trench arc basin system and ophiolite belt are developed in both the qilian mountains and the area of the yarlung zangbo river the crust of this particular plateau has an obvious layered structure and comprises three structural layers the upper sialic the middle simatic and the lower mixed crust mantle layers the crustal shortening and thickening since the late eocene has been brought about by deformations of these three structural layers in different ways the uplifting process of the qinghai tibet plateau probably experienced two stages a stage of thickening by compression and a stage of isostatic uplift from the late eocene to pliocene the deformation was mainly of a compressional nature resulting in a large scale crustal shortening and thickening a considerable depression of the upper mantle and formation of a broad and deep plateau mountain root from the early pleistocene to the present time along with the weakening of compression stress relaxation has occurred and with the operation of the mountain root a strong isostatic adjustment has taken place causing the plateau to uplift both rapidly and remarkably

resistivity imaging survey to delineate subsurface seepage of hydrocarbon contaminated water at karbala governorate iraq this research is an attempt to accomplish a 3 d resistivity imaging survey which was carried out near a water well contaminated with hydrocarbon materials in karbala governorate two dimensional resistivity imaging measurements were collected along four parallel profiles using a wenner array with electrode spacing of 1 m the res3dinv program was used to invert the apparent resistivity data the results displayed a resistivity distribution of the subsurface in a three dimensional volume thus both the horizontal and vertical extents of the contaminated zone were displayed this technique revealed a low resistivity zone at depth ranges from 3 to 6 m in the investigation area but the seepage starts at depth ranges between 2 and 3 m and continues down depth may be to the groundwater level this low resistivity zone is the most likely location for a subsurface seepage of contaminated water it is clear that the sufficient measurement points along 2 d lines in a small area can increase the 3 d imaging resolution and nearly real 3 d imaging can be achieved when the size of subsurface anomaly compared with the electrode spacing a of the wenner array is taken into consideration

environmental isotope systematics of the groundwater system of southern kuwait the carbonate dammam formation of eocene age and the unconformably overlying clastic kuwait group of rocks of mio pliocene age are the two aquifers that provide useable groundwater salinity 5000 mg l or less in kuwait these aquifers extend beyond the political limits of the country to saudi arabia and iraq a detailed environmental isotopic 2 1h 18 16o 13 12c 3h 14c characterization of the groundwater system of southern kuwait a regional aquifer extending beyond the political limits of the country to saudi arabia and iraq has been carried out to understand its hydrodynamics so as to evolve a better conceptual flow model of the aquifer system from the study it was observed that the groundwater salinity of the kuwait group aquifer increases generally from south west to north east although locally a few of them show low values groundwater samples from the dammam formation aquifer are characterized by a relatively low mineralization compared with those of kuwait group aquifer the water in the kuwait group aquifer in the south western part of the country is na cl type and in the dammam formation aquifer is na cl to so4 na cl so4 type a wide range of d excess of the groundwater samples was seen kuwait group aquifer 16 0 to 20 6 dammam formation aquifer 22 8 to 19 6 indicating that the groundwater system contains more than one type of water with different origin recharge area and history time evaporation climate in both the aquifers the groundwater samples from south and central parts and along the coast showed negative d excess values with heavier 18o and 2h indicating older recharge and greater degree of evaporation prior to recharge the 18o and 2h of the initial recharge waters respectively are 8 8 and 40 for the kuwait group aquifer and 7 2 and 32 for the dammam formation aquifer the corrected 14c ages tamer s model of groundwater samples of kuwait group aquifer ranged from 5000 to 24 000 a b p and that of dammam formation aquifer ranged from 6000 to 20 000 a b p the intermediate groundwater in the south west and central parts of kuwait group aquifer is recharged during humid period 5000 to 10 000 a b p whereas deeper groundwater in the south is recharged during arid period 9000 16 000 a b p the recharge to the dammam formation aquifer mostly occurred during a cooler humid phase in the past the dammam formation aquifer water is hydraulically well mixed below 350 m depth interconnection between the two aquifers established near the coast and south west border of the country the results of the study were used to refine the existing conceptual groundwater flow model for the aquifer system

mapping of subsurface contamination zone using 3d electrical resistivity imaging in hilla city iraq electrical resistivity imaging eri method is very useful in mapping subsurface contamination zones in this study 3d eri is used to identify the distribution and depth of subsurface soil contamination zone near al furat state company for chemical and pesticides industries in hilla city iraq a 3d pure image of electrical resistivity distribution is obtained from a perpendicular square grid 80 80 m which consists of three parallel and three perpendicular lines the electrical resistivity values range from 1 to 21 o m and the total root mean square rms after four iterations is about 7 the image gives eight different depth slices for the estimated model with a depth interval of about 1 m the maximum depth of investigation is 13 7 m the results mapped the contamination zone where high electrical resistivity values about 21 o m are observed possibly due to accumulation of alkaline waste disposed from the company the eri results show that the subsurface layers up to a depth of 4 99 m are of moderate to high electrical resistivity values the study reveals that 3d eri is an effective tool for subsurface contamination zone mapping in various depths which extends in this study from the near surface to a depth of about 5 m below the ground level

a 3 d coupled ice sheet sea level model applied to antarctica through the last 40 ky abstract we present results from a three dimensional ice sheet shelf model of antarctica coupled to a gravitationally self consistent global sea level model that incorporates maxwell viscoelastic deformation of the solid earth the coupled model captures complex post glacial changes in sea level associated with the gravitational deformational and rotational effects of the evolving surface mass ice plus ocean load over the global ocean including at the grounding lines of marine based ice the simulations are initiated at 40 ka and we focus on ice distributions and sea levels from the last glacial maximum to present our results extend and confirm the key conclusions of earlier work using a simplified 1 d ice sheet model by demonstrating that the sea level coupling has a significant stabilizing influence on marine ice sheet grounding lines the feedback of sea level changes into the ice sheet model acts to slow down the retreat and advance of the grounding line relative to simulations in which the full coupling is not incorporated differences in ice thickness between these simulations can reach 1 km close to the grounding line finally we perform preliminary comparisons of our results to relative sea level rsl histories and gps derived present day uplift rates at sites near the margins of antarctica we find that the coupling improves fits to uplift rates in several regions and that the rsl predictions of the coupled model yield a fit to the observations that is comparable to recent uncoupled simulations in which the underlying earth model was varied to obtain a best fit to the rsl histories

the tethys sea and the alpine himalayan orogenic belt mega elements in a new global tectonic system abstract analysis of meso cainozoic palaeomagnetic data for africa india and eurasia has led to the development of a new mobilistic alpine plate tectonic model characterized by a hierarchical system of plates in relative rotation the new model which discounts seafloor spreading implies that there have been no significant palaeogeographic changes in the overall distribution of continental and oceanic regions the mid oceanic ridges are interpreted as transpressive tectonic features caused by rotation of megaplates containing both continental and oceanic crust the isostatic uplift due to crustal lithospheric thickening giving rise to the general ridge topography as well as to the ridge parallel structural grain the new plate tectonic theory gains strong support from a variety of geophysical geological and palaeoclimatological evidence and several observations that have remained enigmatic or awkward within the context of the orthodox model can be readily accounted for in the new tectonic framework the model maintains the tethys as a relatively narrow epicontinental sea which during its maximum extent stretched latitudinally from the caribbean across the central atlantic to se asia the alpine himalayan orogenic belt developed along the boundary of two megaplates in relative rotation which provided a transpressive tectonic regime the location of the plate boundary to the north of the mediterranean has important implications for discussion of mediterranean microplates for example it now seems that italy has been subjected to 10 15 of clockwise microplate rotation previous conclusions in favour of 30 40 of anticlockwise rotation are regarded as artefacts which arise from incorrectly linking the mediterranean region to the european palaeomagnetic frame instead of to the african one the model suggests further that the indo pakistani plate was closely tied to eurasia this challenges the conventional view that the peninsula was part of an alleged gondwanaland the new pre drift configuration implies that the indo pakistani plate rotated 135 clockwise at around the cretaceous tertiary boundary before redocking with asia in approximately its present relative orientation

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

modelling of last glacial maximum ice sheets using different accumulation parameterizations we use a three dimensional thermomechanical ice sheet model previously tested on the greenland ice sheet to reconstruct last glacial maximum lgm ice sheets we compare the effects on the results of the ice sheet model of three different accumulation parameterization schemes in the first and second schemes lgm precipitation is computed from the present precipitation taking and not taking into account moisture transport in the third scheme lgm precipitation and surface temperatures are computed using outputs of an atmospheric global circulation model agcm treated in anomaly mode results are compared to the last reconstruction of the northern hemisphere ice sheets peltier 1994 computed using global rebound rates in a visco elastic model of the earth s crust the first two accumulation parameterizations do not give satisfactory reconstructions of the lgm ice sheets since they are unable to compute realistic lgm climatic conditions the third method gives very satisfactory results which leads us to conclude that the best way to obtain realistic lgm climatic conditions is to use agcm outputs

rapid early miocene acceleration of uplift in the gangdese belt xizang southern tibet and its bearing on accommodation mechanisms of the india asia collision abstract five samples from a biotite hornblende granodiorite phase of the 42 5 ma quxu pluton gangdese batholith southern tibet have been collected at 250 m vertical intervals biotite from these rocks yields monotonically decreasing40ar 39ar isochron ages with decreasing elevation of 26 8 0 2 23 3 0 5 19 7 0 3 18 4 0 4 and17 8 0 1ma tc 335 c coexisting k feldspars have virtually identical minimum apparent40ar 39ar ages of 17 0 0 4ma tc 285 c these data indicate parts of southern tibet experienced a pulse of uplift in the early miocene with the rate of uplift rising from 0 07 to 4 4 mm year in the interval 20 to 17 ma an apatite fission track age of 9 9 0 9ma from this locality constrains the average uplift rate at this site to about 0 81 mm year between 17 and 9 9 ma and 0 30 mm year from 9 9 ma to present k feldspar from the dagze granite 30 km to the east near lhasa yields a minimum apparent40ar 39ar age of 35 9 0 9ma tc 227 c which indicates an average uplift rate there of 0 21 mm year since then the marked pulse of uplift of the quxu granodiorite and the difference in uplift history between the dagze and quxu plutons suggests southern tibet has experienced discrete pulses of uplift variable in both space and time these data are not consistent with models which require a large proportion of uplift of the tibetan plateau to have occurred in the last 2 ma the data support the suggestion that convergence between india and asia was largely accommodated by tectonic escape during the opening of the south china sea 32 to 17 ma ago and permit distributed shortening as a mechanism for crustal thickening and uplift of this part of the tibetan plateau subsequent to 20 ma

a high resolution model of the 100 ka ice age cycle significant improvements to the representation of climate forcing and mass balance response in a coupled two dimensional global energy balance climate model ebm and vertically integrated ice sheet model ism have led to the prediction of an ice volume chronology for the most recent ice age cycle of the northern hemisphere that is close to that inferred from the geological record most significant is that full glacial termination is delivered by the model without the need for new physical ingredients in addition a relatively close match is achieved between the last glacial maximum lgm model ice topography and that of the recently described ice 4g reconstruction these results suggest that large scale climate system reorganization is not required to explain the main variations of the north american na ice sheets over the last glacial cycle lack of sea ice and marine ice dynamics in the model leaves the situation over the eurasian ea sector much more uncertain the incorporation of a gravitationally self consistent description of the glacial isostatic adjustment process demonstrates that the na and ea bedrock responses can be adequately represented by simpler damped relaxation models with characteristic time scales of 3 5ka and 5 ka respectively these relaxation times agree with those independently inferred on the basis of postglacial relative sea level histories

ice sheet mass balance during the last glacial maximum in the framework of the paleoclimate modelling intercomparison project pmip simulations of the last glacial maximum lgm have been performed more than 10 different atmospheric general circulation models agcms have been used with the same boundary conditions sea surface temperatures prescribed by climap 1981 ice sheet reconstruction provided by peltier 1994 change in insolation and reduced co2 content one of the major questions is to investigate whether the simulations of the lgm are in equilibrium with the prescribed ice sheet reconstruction to answer this question we have used two different approaches first we analyze the results of a sel of lgm simulations performed with different versions of the laboratoire de meteorolo gie dynamique lmd agcm and study the hydrologic and snow budgets over the laurcntide and fennoscandian ice sheets second we use the agcm outputs to force an ice sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by climap 1981 or peltier 1994

the late miocene through present paleoelevation history of southwestern tibet recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre and post mid miocene uplift of the southern tibetan plateau we examined this issue by analysis of well preserved fossil mollusks and plant remains from the zhada basin in southwestern tibet which ranges in age from 9 2 to paleoenvironmental modeling and physical evidence shows that the climate in zhada basin was cold and arid indistinguishable from modern the 13cpm values of well preserved vascular plant material increase from 23 4 to 26 8 permil at the base of the zhada formation to as high as 8 4 permil above 250 to 300 m this shift denotes the expansion of c4 biomass in this high arid watershed at 7 ma and thus corresponds to the c3 c4 transition observed in neogene deposits of the northern indian sub continent

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

the long term strength of europe and its implications for plate forming processes field based geological studies show that continental deformation preferentially occurs in young tectonic provinces rather than in old cratons this partitioning of deformation suggests that the cratons are stronger than surrounding younger phanerozoic provinces however although archaean and phanerozoic lithosphere differ in their thickness and composition their relative strength is a matter of much debate one proxy of strength is the effective elastic thickness of the lithosphere te unfortunately spatial variations in te are not well understood as different methods yield different results the differences are most apparent in cratons where the bouguer coherence method yields large te values 60 km whereas the free air admittance method yields low values or 1 5 gyr old is much larger mean te 60 km than that of younger lithosphere mean te 30 km we propose that this strength difference reflects changes in lithospheric plate structure thickness geothermal gradient and composition that result from mantle temperature and volatile content decrease through earth s history

holocene glacial rebound and sea level change in nw europe summary observations of late pleistocene and holocene sea level change relative to the crust exhibit very considerable variations across nw europe in consequence of the response of the earth s crust to the deglaciation of fennoscandia and of the water added to the oceans from the melting of all late pleistocene ice sheets inversion of sea level observations from a site near the centre of the fennoscandian ice sheet and from three sites located beyond the margin of the ice sheet at the time of maximum glaciation yield a range of plausible models for the earth s response and for the ice models further constraints on this range of models is placed by a comparison of observed sea levels with predicted values at other sites near the former ice sheet margins the resulting mantle parameters are upper mantle viscosity 3 5 x 10 pa s lower mantle viscosity 2 7 x loz1 pa s lithospheric thickness 100150 km these values represent effective parameters that describe the response of the earth to surface loading of short to intermediate wavelengths on a time scale of 104yr the lower mantle viscosity is poorly constrained but the marked increase from upper to lower mantle is a characteristic of all plausible solutions the inversion places a constraint on the total volume of ice in the fennoscandian ice sheet such that the equivalent sea level rise from this contribution is about 13 14 m a less well determined constraint of about 10 m equivalent sea level rise is suggested for the barents kara ice sheet the inversion also indicates that a small amount of melt water from ice sheets far away from europe continued to be added into the oceans during late holocene time so as to raise the equivalent sea level by about 3 m during the past 6000 yr consistent with similar inversions of data from sites in the australian and pacific regions

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

coupling an agcm with an ism to investigate the ice sheets mass balance at the last glacial maximum the aim of this paper is to investigate the consistency between the ice sheets reconstruction at the lgm and the climate simulated by agcm in particular to investigate whether the laurentian and the fennoscandian ice sheets have an equilibrated mass balance we use two complementary approaches first we analyze the changes of snow and water budgets over the ice sheets only using the model results of lgm runs second we use a thermomechanical ice sheet model ritz et al 1997 forced with the agcm simulated climate to perform long term runs at finer spatial resolution analyzing the results obtained with both approaches we show that the ice sheet mass balance computed directly from agcm results may be biaised moreover we show using two versions of the lmd agcm that the ice sheet mass balance computed by the ism is drastically sensitive to the summer surface temperatures simulated by the agcm

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

anticipating the effects of groundwater withdrawal on seawater intrusion and soil settlement in urban coastal areas intensive pumping in urban coastal areas is a common threat to water resource quality due to seawater intrusion in those areas where subsurface water resources are not usually used for human consumption or irrigation intensive pumping is associated with other activities like the lowering of the water table necessary to support underground structures and building foundations this activity also increases the likelihood of soil settlement that affects building stability and the corrosion of concrete structures due to groundwater salinity under these circumstances the awareness of a certain municipality calonge ne spain of the potential effects of groundwater withdrawal upon foundations has led to an integrated approach to anticipate seawater intrusion related to urban development geological mapping and correlation of borehole logs electrical resistivity tomography and hydrochemical data provide comprehensive knowledge of the geology and hydrogeology of the area and act as screening tools necessary to discern the influence of hydrological processes in coastal areas developing strack s analytical solution new comprehensive dimensionless expressions are herein derived to determine the critical pumping rate necessary to prevent seawater intrusion as well as to reproduce the evolution of the wedge toe and the water table stagnation point under different withdrawal rates furthermore the dupuit forchheimer well discharge formula allows the estimation of the effects of the water table lowering due to such critical pumping in the surrounding building foundations field data from the calonge coastal plain illustrate this approach and provide assessment criteria for future urban development and planning copyright 2012 john wiley sons ltd

analysis of the gravity field in the nepalese himalayas tibetan region in the light of plate tectonics abstract the gravity field in the nepalese himalayas tsangpo region has been analysed along a profile starting from near giridih 24 10 n 86 20 e and continuing over the indian peninsular shield to near tingri 28 50 n 87 e close to the tsangpo suture the profile passes through the ganga basin lower higher and tethys himalayas and finishes near the indus tsangpo suture explosion seismology data obtained by hirn et al in the himalaya tibetan region of nepal has been used to restrict moho depth along the profile the model presented suggests that the density contrast between the crustal root beneath the high himalaya tibet region and the moho is of the order of 0 32 g cm 3 the upper mantle should have a density of about 3 32 g cm 3 the upper crust in the high himalayas region appears to have higher than normal density as compared to the crust south of the indus tsangpo suture the model does not support continental underthrusting of the indian plate underneath tibet in the manner envisaged by powell and conaghan the concept of lithospheric flexure underneath mountain ranges as proposed by karner and watts although generally valid does not explain the behaviour of the moho underlying the high himalayas in nepal and the tibetan plateau when examined in detail

net retreat of antarctic glacier grounding lines grounding lines are a key indicator of ice sheet instability because changes in their position reflect imbalance with the surrounding ocean and affect the flow of inland ice although the grounding lines of several antarctic glaciers have retreated rapidly due to ocean driven melting records are too scarce to assess the scale of the imbalance here we combine satellite altimeter observations of ice elevation change and measurements of ice geometry to track grounding line movement around the entire continent tripling the coverage of previous surveys between 2010 and 2016 22 3 and 10 of surveyed grounding lines in west antarctica east antarctica and at the antarctic peninsula retreated at rates faster than 25 m yr 1 the typical pace since the last glacial maximum and the continent has lost 1 463 km2 791 km2 of grounded ice area although by far the fastest rates of retreat occurred in the amundsen sea sector we show that the pine island glacier grounding line has stabilized probably as a consequence of abated ocean forcing on average antarctica s fast flowing ice streams retreat by 110 metres per metre of ice thinning grounding lines in parts of west antarctica east antarctica and the antarctic peninsula retreated faster than typical post glacial pace according to satellite observations and ice geometry measurements

monitoring of tidal influences on the saline interface using resistivity traversing and cross borehole resistivity tomography summary tidal influences on the saline interface of a shallow unconfined aquifer have been investigated by using both dc resistivity traversing and cross borehole resistivity tomography crt variations in bulk resistivity structure obtained through resistivity traversing provide a clear general picture of the structure of the saline interface and its mixing zone on all three resistivity traverses there are also indications that a small degree of mixing of saline and fresh water is occurring ahead of the main saline boundary for one of the traverses much more detail of variations in resistivity structure is provided by crt utilising three 10 m long electrode strings installed at 10 m separation crt images of the saline mixing zone do not reveal any significant difference between low and high tide for tidal ranges of about 2 m but for a tidal range of approximately twice this clearly show effects due to both increased wave run up and tidal head correlation of the bulk resistivity with fluid resistivity values measured in parallel bores suggests that although there is no apparent widening of the mixing zone during the tidal cycle significant variations in salinity do occur which can be envisaged in terms of the horizontal movement of near vertical salinity contours