climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

evidence for long term instability in the storegga slide region off western norway abstract shallow seismic surveys around the storegga slide off western norway have allowed greater understanding of the development of this part of the european margin the northern flank of the scarp is formed of seismically well layered hemipelagic and distal glaciomarine deposits in which a variety of luid escape structures probably due to gas are locally abundant there is evidence of slides that substantially pre date the earliest slide previously recognized surveying on the north sea fan to the southwest of the storegga slide shows the markedly different nature of the autochthonous sediments on the southern flank of the storegga slide there is a predominance of glacigenic debris flows in the upper part of the sequence lesser maximum slopes and an apparent absence of interstitial gas and or hydrates this contrast has had considerable effect on slope stability and has influenced the position of the southwestern storegga slide boundary the north sea fan succession includes at least three major buried slides termed the vigra more and tampen slides all of which substantially pre date the storegga event and probably pre date predominantly glacigenic margin sedimentation post late weichselian slope failure is locally significant the region has a long but as yet chronologically poorly defined history of instability in which seismic triggering is considered to have been important

reduction of saltwater intrusion by modifying hydraulic conductivity we present an approach for reducing saltwater intrusion in coastal aquifers by artificially reducing the hydraulic conductivity in the upper part of selected areas by using a precipitate we apply a previously presented analytical approach to develop formulas useful for the design of artificial barriers equations for the location of the tip of the saltwater wedge are presented and verified through a sand tank experiment the analysis is capable of computing discharges exactly but requires the dupuit forchheimer approximation to compute points of the interface between flowing fresh and stationary saltwater we consider a vertical coastline and boundaries in the fresh water zone of either given discharge or given head we demonstrate in the paper that reduction of the hydraulic conductivity in the upper part of a coastal aquifer will result in a decrease of saltwater intrusion and present analytic expressions that can be used for design purposes the previously presented analytical approach can be applied to design systems to reduce salt water intrusion caused by pumping inland from the zone that contains salt groundwater this article is protected by copyright all rights reserved

how does layered heterogeneity affect the ability of subsurface dams to clean up coastal aquifers contaminated with seawater intrusion abstract the main purpose of this work was to examine how aquifer layering impacts the ability of subsurface dams to retain seawater intrusion swi and to clean up contaminated coastal aquifers using both experimental and numerical techniques four different layering configurations were investigated including a homogeneous case case h and three different layered cases where a low permeability layer was set at the top of the aquifer case lh at the middle part of the aquifer as interlayer case hlh and at the lower part of the aquifer case hl the subsurface dam was able to retain the saltwater wedge associated with a drop of the hydraulic gradient from 0 0158 down to 0 0095 in all the cases thereby achieving up to 78 reduction in the saltwater toe length in cases lh and hlh the start of the saltwater spillage was delayed compared to the homogeneous case and the time taken for the freshwater zone to be fully contaminated post spillage was twice and three times longer respectively by contrast the existence of a low k layer at the bottom of the aquifer case hl considerably weakened the ability of dams to retain the intrusion allowing for quicker saltwater spillage past the wall the natural cleanup of swi contaminated coastal aquifers was for the first time evidenced in heterogeneous settings depending on the stratification pattern the presence of stratified layers however prolonged the cleanup time to various degrees compared to the homogeneous scenario particularly in case hl where the cleanup time was nearly 50 longer

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

post lgm sedimentation on the outer shelf upper slope of the northernmost part of the sao paulo bight southeastern brazil abstract sedimentary and isotope data as well as 14 c ams dating on 15 box cores were used to identify the main post last glacial maximum lgm processes in the outer shelf and upper slope of the northernmost part of the sao paulo bight southeastern brazil results show slight but significant variations in calcium carbonate total sulphur and nitrogen contents as well as carbon and oxygen isotope ratios sedimentation rates varying from 5 to 184 mm kyr 1 are controlled by the shelf and upper slope morphology the brazil current meander dynamics and the coastal water offshore motion

free surface flow toward a well and interface upconing in stratified aquifers of random conductivity aquifers are known to display spatial variability of their properties to account for the seemingly erratic variation and the uncertainty affecting the permeability the common approach is to regard it as random and to characterize it statistically the present note studies the steady axisymmetric water table flow toward a well and interface upconing due to freshwater pumping the hydraulic conductivity is modeled as a stationary random function of the vertical coordinate and the dupuit assumption is adopted it is found that the impact of heterogeneity upon the mean equivalent conductivity and the mean profiles is small the standard deviation of these variables may be appreciable depending on the hydraulic conductivity variance on the ratio between the well head and the conductivity integral scale and on the drawdown

sea level rise impact on fresh groundwater lenses in two layer small islands the fresh groundwater lenses fgls of small islands can be highly vulnerable to climate change impacts including sea level rise slr many real cases of atoll or sandy islands involve two layer hydrogeological conceptualizations in this paper the influential factors that affect fgls in two layer small islands subject to slr are investigated an analytical solution describing fgls in circular islands composed of two geological layers is developed for the simplified case of steady state and sharp interface conditions an application of the developed model is demonstrated to estimate the fgl thickness of some real world islands by comparison with existing fgl thickness data furthermore numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases sensitivity analyses are used to assess the importance of land surface inundation caused by slr relative to other parameters i e thickness of aquifer layers hydraulic conductivity recharge rate and land surface slope that influence the fgl dimensionless parameters are used to generalize the findings the results demonstrate that land surface inundation has a considerable impact on a fgl influenced by slr as expected although the fgl volume is more sensitive to recharge aquifer thickness and hydraulic conductivity than slr impacts considering typical parameter ranges the methodology presented in this study provides water resource managers with a rapid assessment tool for evaluating the likely impacts of slr and accompanying lsi on fgls

a formulation for vertically integrated groundwater flow in a stratified coastal aquifer we present the comprehensive discharge potential for steady three dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline the gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer i e the specific discharge vector as a function of three dimensional space integrated over the saturated portion of the aquifer the boundary values of the comprehensive potential along the coast can be computed precisely given the geometry of the aquifer the hydraulic conductivities of the strata the elevations of the horizontal planes that separate the strata and the elevation of the impermeable base of the aquifer relative to sea level boundary conditions of the comprehensive potential may either be given in terms of its gradient or computed from given heads along the boundaries the governing equation of the comprehensive potential is the poisson equation in areas of infiltration and the laplace equation elsewhere the computation of interface elevations piezometric heads and the vertical distribution of flow requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads we adopt the dupuit forchheimer approximation for this purpose and make use of the ghyben herzberg equation we present several applications of the approach and find that the stratification may have a significant effect on the boundary value of the comprehensive potential and thus on the flow rates in the aquifer this article is protected by copyright all rights reserved

vertically integrated flow in stratified aquifers abstract we present a set of continuous discharge potentials that can be used to determine the vertically integrated flow in stratified aquifers the method applies to cases where the boundaries are vertical and either the hydraulic head is given or the boundary is a seepage face or the integrated discharge is given the approach is valid for cases of given recharge through the upper and or lower boundaries of the aquifer the method is valid for any values of hydraulic conductivity there are no limitations of the contrast for the method to be valid the flows in the strata may be either confined or unconfined and locally perched conditions may exist but the effect of capillarity is not included the hydraulic head is determined by applying the dupuit forchheimer approximation the main advantage of the approach is that very complex conditions in stratified aquifer systems including locally perched conditions and extremely complex flow systems can be treated in a relatively straight forward approach by considering only the vertically integrated flow rates the approach is particularly useful for assessing groundwater sustainability as a model to be constructed prior to developing a fully three dimensional numerical model

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

impact of layered heterogeneity on transient saltwater upconing in coastal aquifers abstract this research investigated the effect of layered heterogeneity on transient saltwater upconing in a laboratory scale coastal aquifer the experiments were conducted in a 2d laboratory flow tank and the response of the saltwater wedge to pumping was analysed in a heterogeneous aquifer system where a low permeability layer was constructed in the middle of the aquifer the seawat code was used for validation and to perform additional simulations to explore the sensitivity of the critical pumping rate and the critical time to the main parameters characterising the low permeability layer which included its permeability thickness and position the experimental results showed that the presence of layered heterogeneity noticeably altered the shape and the intrusion length of the upconing wedge without inducing a change in the abstraction rate triggering saltwater upconing mechanism compared to the homogeneous case the numerical results of the layered aquifer provided excellent agreement with the experimental data for both the transient toe length and the shape of the steady state saltwater wedges the sensitivity analysis revealed that the critical pumping rate and the critical time was found to decrease considerably with decreasing hydraulic conductivity and thickness of the middle layer which evidences the higher vulnerability of such layered aquifer systems to the saltwater upconing in comparison to idealised homogeneous systems the results nonetheless showed that varying the position of the interlayer induced very little change on the critical pumping rate but the critical time would tend to decrease as the low permeability layer was moved deeper away from the pumping well particularly for smaller middle layer thickness

a simplified equation of approximate interface profile in stratified coastal aquifers abstract in this study we provide a simplified equation with a new concise set of parameters defining the approximate interface profile in stratified coastal aquifers we derive the solution directly by applying the dupuit forchheimer approximation at the outset and mathematically prove its sameness for the uniform flow in a vertical plane with the interface profile computed using the comprehensive discharge potential theory by strack and ausk 2015 we present a surprising result that interface elevation in the case with a seepage and outflow face at the coastal boundary turns out to be same as in which water table and interface coincides with the coastline the interface profile is a function of the transmissivity field centroid elevation and the total transmissivity of the freshwater flow domain above the interface we found that the boundary potential at the coast in the discharge potential theory solution represents the first moment of the transmissivity we also analyzed the differences in the interface profiles in aquifers with different hydraulic conductivity contrasts for two sets of boundary conditions constant head and constant flux for a given flux boundary interface profiles in aquifer configurations with different conductivity contrasts converge in the upper part of the aquifer and diverge at the aquifer bottom leading to different toe positions conversely for a given head boundary interface profiles in aquifer configurations with different conductivity contrasts significantly differ in the upper part of the aquifer while converge at the aquifer bottom resulting in the same toe position we provide explicit solutions for the toe position and freshwater discharge in unconfined aquifers an extension to our previous work for confined aquifers insights from the newly identified parameters can also potentially help in reducing the uncertainty in the estimation of the real world swi extent and optimize the requirement of the extent of the hydraulic conductivity field characterization

regional groundwater modeling of the yucca mountain site using analytic elements abstract two of the complicating factors in modeling the regional groundwater flow at yucca mountain are the large distance to hydrogeologic boundaries and the large thickness of the aquifer the hydrogeologic boundaries are up to 500 km away from yucca mountain and the aquifer is up to 5000 m thick the distant hydrogeologic boundaries may be taken into account explicitly by application of the analytic element method which is applied to a model of this size for the first time in this study the analytic element method makes it possible to include distant hydrogeologic boundaries and at the same time allows for local detail without the excessive computational effort that would be required with the finite difference method regional flow in the aquifer is modeled with a single layer based on a theoretical argument and supported by the model results the match between simulated and measured heads is similar to that of previous finite difference models of parts of the region these previous studies consist of multiple layers and include inferred boundary conditions head or flux specified along most of the boundary of the domain

circulation changes in the faeroe shetland channel correlating with cold events during the last glacial period 58 10 ka a core from the margin of the faeroe shetland channel covering the last glacial period 58 10 ka reveals a very detailed record of oscillations in benthic and planktic foraminifera oxygen isotopes and ice rafted detritus the oscillations correlate almost exactly with the dansgaard oeschger cycles in the greenland ice cores including similar subdivision of the cycles into warmer interstadial and colder stadial sections the remarkably close agreement between the benthic faunas and their 18 o data and the record of the ice cores provides new empirical evidence for a close relationship between the deep ocean circulation and the abrupt climatic changes of the last glacial period

exact versus dupuit interface flow in anisotropic coastal aquifers the dupuit solution for interface flow toward the coast in a confined aquifer is compared to a new exact solution which is obtained with the hodograph method and conformal mapping the position of the toe of the interface is a function of two dimensionless parameters the ratio of the hydraulic gradient upstream of the interface where flow is one dimensional over the dimensionless density difference and the ratio of the horizontal hydraulic conductivity over the vertical hydraulic conductivity the dupuit interface which neglects resistance to vertical flow is a very accurate approximation of the exact interface for isotropic aquifers the difference in the position of the toe between the exact and dupuit solutions increases when the vertical anisotropy increases for highly anistropic aquifers it is proposed to add an effective resistance layer along the bottom of the sea in dupuit models the resistance of the layer is chosen such that the head in the dupuit model is equal to the head in the exact solution upstream of the interface where flow is one dimensional