on the factors behind large labrador sea tides during the last glacial cycle and the potential implications for heinrich events 1 labrador sea ls tidal elevations over the last glacial cycle are investigated in a near global numerical model that accurately captures the present day tides from 65 ka to 7 ka the modeled elevations at the debouchement point of the hudson strait ice stream in the ls are exceptionally large comparable to the largest elevations seen anywhere in the present day ocean new numerical simulations performed for this article demonstrate that both local changes in basin geometry e g ice cover over hudson bay and changes outside of the ls led to enhanced ls paleotides new simulations run at higher horizontal resolution and a considered examination of uncertainties including uncertainties in the adopted sea level models strengthen confidence in the robustness of the large ls paleotides the tide model is run with both spatially uniform sea level drops taken from curves of eustatic and red sea sea levels versus time and spatially variable sea level maps taken from two different gravitationally self consistent viscoelastic solid earth sea level models which both account for ice sheet geometry the tides are larger when the spatially variable sea level models are used observations in present day antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves it is postulated here that large ls paleotides played a key role in the formation of heinrich event icebergs that is massive discharges of ice from the ls into the glacial north atlantic ocean the paleotide calculations described here provide a potential explanation for why the ls region more than any other dominated the production of heinrich event icebergs most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing in contrast here the role of tidal mechanical forcing of ice sheets is emphasized

data domain correlation approach for joint hydrogeologic inversion of time lapse hydrogeologic and geophysical data inverse estimations of hydrogeologic properties often are highly uncertain because of the expense of collecting hydrogeologic data and the subsequent lack of information geophysical data potentially can help fill this information gap because geophysical methods can survey large areas remotely and relatively inexpensively however geophysical data are difficult to incorporate into hydrogeologic parameter estimations primarily because of a lack of knowledge concerning the petrophysical relationships between hydrogeologic and geophysical parameters a method can be used that allows time lapse geophysical data to be incorporated directly into a hydrogeologic parameter estimation when a strong correlation exists between changes in geophysical and hydrogeologic properties this approach bypasses the need for an explicit petrophysical transform by formulating the geophysical part of the hydrogeologic inversion in terms of a data domain correlation operator a synthetic electrical resistivity monitoring application is used to estimate the hydraulic conductivity distribution including time lapse resistivity data to supplement sparse hydrologic data appears to improve greatly the resolution of hydraulic conductivity in this case more generally the formulation and results suggest that geophysical monitoring data can be incorporated effectively into a hydrogeologic parameter estimation using a data domain correlation operator assuming a strong correlation exists between changes in hydrogeologic and geophysical properties

a unified approach to orbital solar and lunar forcing based on the earth s latitudinal insolation temperature gradient widespread empirical evidence suggests that extraterrestrial forcing influences the earth s climate but how this could occur remains unclear here we describe a new approach to this problem that unifies orbital solar and lunar forcing based on their common control of the earth s latitudinal insolation gradient lig the lig influences the climate system through differential solar heating between the tropics and the poles that gives rise to the latitudinal temperature gradient ltg which drives the earth s atmospheric and wind driven ocean circulation we use spectral analysis of recent changes in the earth s ltg to support earlier work on orbital timescales davis and brewer 2009 that suggests the climate system may be unusually sensitive to changes in the lig identification of lig forcing of the ltg is possible because the lig varies according to seasonally specific periodicities based on obliquity in summer 41 kyr orbital and 18 6 yr lunar cycle and precession 21 kyr orbital cycle and total solar irradiance 11 yr solar cycle in winter we analyse changes in the northern hemisphere ltg over the last 120 years and find significant 99 peaks in spectral frequencies corresponding to 11 years in winter and 18 6 years in summer consistent with lig forcing the cross seasonal and multi frequency nature of the lig signal and the diffuse effect of the ltg driver on the climate system may account for the complexity of the response to extraterrestrial forcing as seen throughout the climatic record this hypersensitivity of the ltg to the lig appears poorly reproduced in climate models but would be consistent with the controversial theory that the ltg is finely balanced to maximise entropy c 2011 elsevier ltd all rights reserved

pilot scale field validation of the long electrode electrical resistivity tomography method a validation experiment carried out in a scaled field setting was attempted for the long electrode electrical resistivity tomography method in order to demonstrate the performance of the technique in imaging a simple buried target the experiment was an approximately 1 17 scale mock up of a region encompassing a buried nuclear waste tank on the hanford site the target of focus was constructed by manually forming a simulated plume within the vadose zone using a tank waste simulant the long electrode results were compared to results from conventional point electrodes on the surface and buried within the survey domain using a pole pole array both point and long electrode imaging techniques identified the lateral extents of the pre formed plume with reasonable fidelity but the long electrode method was handicapped in reconstructing vertical boundaries the pole dipole and dipole dipole arrays were also tested with the long electrode method and were shown to have the least favourable target properties including the position of the reconstructed plume relativetotheknownplumeandtheintensityoffalsepositivetargets thepoorperformance of the pole dipole and dipole dipole arrays was attributed to an inexhaustive and non optimal coverage of data at key electrodes as well as an increased noise for electrode combinations with high geometric factors however when comparing the model resolution matrix among the different acquisition strategies the pole dipole and dipole dipole arrays using long electrodes were shown to have significantly higher average and maximum values within the matrix than any pole pole array the model resolution describes how well the inversion model resolves the subsurface given the model resolution performance of the pole dipole and dipole dipole arrays it may be worth investing in tools to understand the optimum subset of randomly distributed electrode pairs to produce maximum performance from the inversion model

saline tracer visualized with three dimensional electrical resistivity tomography field scale spatial moment analysis 1 cross well electrical resistivity tomography ert was used to monitor the migration of a saline tracer in a two well pumping injection experiment conducted at the massachusetts military reservation in cape cod massachusetts after injecting 2200 mg l of sodium chloride for 9 hours ert data sets were collected from four wells every 6 hours for 20 days more than 180 000 resistance measurements were collected during the tracer test each ert data set was inverted to produce a sequence of 3 d snapshot maps that track the plume in addition to the ert experiment a pumping test and an infiltration test were conducted to estimate horizontal and vertical hydraulic conductivity values using modified moment analysis of the electrical conductivity tomograms the mass center of mass and spatial variance of the imaged tracer plume were estimated although the tomograms provide valuable insights into field scale tracer migration behavior and aquifer heterogeneity standard tomographic inversion and application of archie s law to convert electrical conductivities to solute concentration results in underestimation of tracer mass such underestimation is attributed to 1 reduced measurement sensitivity to electrical conductivity values with distance from the electrodes and 2 spatial smoothing regularization from tomographic inversion the center of mass estimated from the ert inversions coincided with that given by migration of the tracer plume using 3 d advective dispersion simulation the 3 d plumes seen using ert exhibit greater apparent dispersion than the simulated plumes and greater temporal spreading than observed in field data of concentration breakthrough at the pumping well

detection of spatially limited high porosity layers using crosshole gpr signal analysis and full waveform inversion high permittivity layers related to high porosity layers or impermeable clay lenses can act as low velocity electromagnetic waveguides electromagnetic wave phenomena associated with these features are complicated not well known and not easy to interpret in borehole gpr data recently a novel amplitude analysis approach was developed that is able to detect continuous low velocity waveguides and their boundaries between boreholes by using maximum and minimum positions of the trace energy profiles in measured gpr data by analyzing waveguide models of different thickness dip extent permittivity and conductivity parameters we extend the amplitude analysis to detect spatially limited or terminated waveguides waveguides that show high amplitude elongated wave trains are most probably caused by a change in porosity rather than a change in clay content in a crosshole gpr data set from the boise hydrogeophysical research site two terminated wave guiding structures were detected using the extended amplitude analysis information gained from the amplitude analysis improved the starting model for full waveform inversion which imaged the lateral extent and thickness of terminated waveguides with high resolution synthetic data calculated using the inverted permittivity and conductivity models show similar amplitudes and phases as observed in the measured data which indicates the reliability of the obtained models neutron neutron logging data from three boreholes confirm the changes in porosity and indicate that these layers were high porosity sand units within low porosity poorly sorted sand and gravel units

double celled subtropical gyre in the south atlantic ocean means trends and interannual changes 1 we present here a study of the mean upper layer structure of the south atlantic subtropical gyre sasg and its modes of variability based on archiving validation and interpretation of satellite oceanographic data sea level anomaly data gravity recovery and climate experiment based mean dynamic topography mdt models reynolds sea surface temperatures and two tide gauge time series from permanent service for mean sea level analysis of the mdts shows that the sasg mean structure is represented by a double cell circulation the southern cell being a narrow quasi zonal strip centered around 33 s its southern limb is limited by the recently discovered saint helena current tristan da cunha current sthc tcc and the north subtropical front around 35 s this system is shown to be well separated from the south atlantic current south subtropical front around 42 45 s a method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band passed data sets the altimeter sea level trend analysis suggests that the sasg pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5 10 mm yr occurring in the southern cell flow intensifications in this period 2 3 cm s in the south equatorial current and north brazil undercurrent 3 5 cm s in the benguela current and weakening by 4 5 cm s in the sthc tcc are recorded the altimeter derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges

estimating lithologic and transport properties in three dimensions using seismic and tracer data the kesterson aquifer the identification of aquifer heterogeneities particularly flow paths and barriers has become a critical research topic in hydrology cross well seismic tomography may provide the needed resolution when used in conjunction with hydraulic head and tracer concentration measurements we demonstrate a field application and sensitivity analysis of the split inversion method sim which combines seismic hydraulic and tracer data to estimate the three dimensional zonation of aquifer properties along with the hydraulic properties for these zones for the kesterson aquifer in the san joaquin valley california we first invert seismic travel times measured between six well pairs to obtain seismic slowness 1 seismic velocity cross sections or tomograms we then use conditional simulation to provide three dimensional seismic slowness realizations next the sim is used to split several realizations into three lithologic zones and assign hydraulic properties to the zones to best match six tracer concentration histories

resistivity and induced polarization monitoring of salt transport under natural hydraulic gradients we demonstrate the use of resistivity induced polarization ip monitoring of salt transport under natural hydraulic loads electrical monitoring of saline tracer transport during forced injection has been demonstrated previously detection of tracer transport under natural hydraulic loading is difficult because neither the hydraulic load nor the tracer resistivity can be controlled in one study we identify the electrical response to salt transport in a dynamic beach environment resistivity ip imaging resolved the structure of the saltwater freshwater interface and evidence for tide induced groundwater transport resistivity increases in the near surface and at depth upbeach of the high tide mark accompanied by tidal transgression we attribute this to desaturation and decreasing salinity in the near surface and to decreasing salinity at depth despite tidal transgression monitoring of groundwater levels indicates a phase lag between the tide level and groundwater level supporting the electrical da

observations of overturning in the thermocline the context of ocean mixing abstract the time sequence of events that lead to internal wave breaking and ocean turbulence is investigated data are obtained from depths 100 400 m with a repeat profiling ctd and a coded pulse doppler sonar the instruments were deployed from r p flip during february march 1995 while stationed 30 km west of point arguello california as an aspect of the marine boundary layer experiment although the water depth at the site is 1500 m both rms shear and diapycnal diffusivity as inferred from the average rate and size of overturning events increase with depth below 250 m a deep source of wave energy is implied depth time series of 6 4 m shear s 2 m strain n2 n2 where n is the buoyancy frequency 6 4 m gradient richardson number ri n2 s2 and 2 m effective strain rate the depth derivative of ctd inferred vertical velocity are obtained at 4 minute intervals over a 9 day 100 400 m domain the occurrence of overturns static instabilities of vertical scale 2 m in the observed density

capacitive conductivity logging and electrical stratigraphy in a high resistivity aquifer boise hydrogeophysical research site we tested a prototype capacitive conductivity borehole tool in a shallow unconfined aquifer with coarse unconsolidated sediments and very low conductivity water at the boise hydrogeophysical research site bhrs examining suchahigh resistivitysystemprovidesagoodtestforthecapacitive conductivity tool because the conventional induction conductivity tool known to have limited effectiveness in high resistivity systems did not generate expressive well logs at the bhrs the capacitive conductivity tool demonstrated highly repeatable low noise behavior but poor correlation with the induction tool in the lower conductivity portions of the stratigraphy where the induction tool was relatively unresponsive singular spectrum analysis of capacitive conductivity logs reveals similar vertical length scales ofstructurestoporositylogsatthebhrs also majorstratigraphic units identified with porosity logs are evident in the capacitive conductivity logs however a previously unrecognized subdivision in the upper portion of one of the major stratigraphicunitscanbeidentifiedconsistentlyasarelatively low conductivity body i e an electrostratigraphic unit between the overlying stratigraphic unit and the relatively high conductivity lower portion despite similar porosity and lithology in adjacent units the high repeatability and resolutionandthewidedynamicrangeofthecapacitive conductivity tool are demonstrated here to extend to high resistivity unconsolidatedsedimentaryaquiferenvironments

geochronology and stratigraphy of the ignimbrites from the 21 30 s to 23 30 s portion of the central andes of northern chile the central volcanic zone cvz of the andes which extends from 14 to 28 s is one of the largest provinces of late tertiary to recent ignimbrite volcanism in the world in the 21 30 s to 23 30 s portion of the cvz in northern chile ignimbrite volcanism was initiated at the beginning of the late miocene 10 4 ma ago and continued until the recent the stratigraphy is dominated by the products of five major dacitic ignimbrite eruptions 100 km3 the artola ignimbrite member 9 4 ma the sifon ignimbrite member 8 3 ma the pelon ignimbrite member 5 5 ma the puripicar ignimbrite member 4 2 ma and the atana ignimbrite member 4 1 ma at least three of these represent only portions of larger ignimbrite sheets erupted from centres of sw bolivia two of the ignimbrites the sifon and atana ignimbrites must represent erupted volumes in excess of 1000 km3 each the major units which represent 90 of the total volume of ignimbrite in this area are intercalated with smaller 50 km3 less extensive volcanic units some of which were erupted from source structures within the study area the upper tertiary to recent volcanic stratigraphy has been revised using the large ignimbrites as the major stratigraphic horizons the ignimbrite formations can be divided into two groups on a geographic basis those in the northern and central portions of the study area are known as the san bartolo group while those in the southern portion belong to the silapeti group these two groups appear to be contemporaneous although the silapeti group may represent a period of ignimbrite volcanism which was initiated later about 6 ma ago the ignimbrite formation of sw bolivia and the punense arancaniano formation of nw argentina are equivalent to the san bartolo and silapeti groups based on correlation of the stratigraphy into adjacent areas in sw bolivia and nw argentina the beginning of the late miocene 10 4 ma marks the onset of the most intense phase ignimbrite volcanism in the cvz this phase of volcanism is suggested to be the result of crustal melting in response to crustal thickening during the quechua phase of deformation and subduction approximately 10 000 km3 of ignimbrite erupted over a period of 9 ma in the 21 30 23 30 s portion and led to the development of a major ignimbrite province

40ar 39ar and rbsr analyses from ductile shear zones from the atacama fault zone northern chile the age of deformation abstract the influence of deformation on the k ar and the rb sr isotope system is investigated it is assumed that due to the diffusion processes involved deformation has a similar effect on isotopic equilibrium as has temperature in order to examine the influence of deformation on the k ar and the rb sr isotope systems two shear zones from the atacama fault zone afz situated in the north chilean coastal cordillera have been investigated the afz which was active as a sinistral strike slip fault during the mesozoic has two sets of shear zones one formed under amphibolite sz1 one under greenschist facies conditions sz2 rb sr and 40ar 39ar age determinations were conducted on samples from cross sections of each set in sz1 the hornblendes and bioties from a weakly deformed sample reveal cooling ages of 153 152 and 150 1 ma respectively biotite from the center of the shear zone of sz1 gave an isochron of 143 9 0 3 ma mswd 0 04 which is interpreted as the age of deformation which produced resetting of the mineral system in sz2 hornblendes yielded 40ar 39ar plateau cooling ages of 138 ma biotites from undeformed samples gave rb sr and 40ar 39ar total degassing ages of 130 1 ma whereas biotite from the mylonitic rocks yielded 126 125 ma which dates the time of deformation sr isotope homogenization occurred in the mylonitic rocks and is most likely a result of deformation the formation of sz1 can be correlated to the araucanian nevadan phase the deformation in sz2 is related to the onset of uplift and cooling of the coastal cordilleran magmatic arc

application of time lapse ert imaging to watershed characterization time lapse electrical resistivity tomography ert has many practical applications to the study of subsurface properties and processes when inverting time lapse ert data it is useful to proceed beyond straightforward inversion of data differences andtakeadvantageofthetime lapsenatureofthedata weassess various approaches for inverting and interpreting time lapse ertdataanddeterminethattwoapproachesworkwell thefirst approachismodelsubtractionafterseparateinversionofthedata from two time periods and the second approach is to use the inverted model from a base data set as the reference model or prior information for subsequent time periods we prefer this second approach data inversion methodology should be considered when designing data acquisition i e to utilize the second approach it is important to collect one or more data sets for which the bulk of the subsurface is in a background or relatively unperturbed state athird and commonly used approach to time lapse inversion invertingthedifferencebetweentwodatasets localizes the regions of the model in which change has occurred however varying noise levels between the two data sets can be problematic to further assess the various time lapse inversion approaches weacquiredfielddatafromacatchmentwithinthedry creek experimental watershed near boise idaho u s a we combined the complimentary information from individual static ertinversions time lapseertimages andavailablehydrologicdatainarobustinterpretationschemetoaidinquantifyingseasonalvariationsinsubsurfacemoisturecontent

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

time lapse ert monitoring of an injection withdrawal experiment in a shallow unconfined aquifer toquantifyperformanceof3dtime lapseelectricalresistivity tomography ert a sequential injection withdrawal experiment was designed for monitoring the pump and capture remediation of a conductive solute in an unconfined alluvial aquifer prior information is incorporated into the inversion procedure via regularization with respect to a reference model according to threeprotocols 1independentregularizationinvolvingasingle reference model 2 background regularization involving a referencemodelobtainedviainversionofpreinjectiondata and3 time lapseregularizationinvolvinganevolvingreferencemodel obtained via inversion of data from previous experimental stages emplacementandsequentialwithdrawalofthesoluteisclearly imaged for all protocols time lapse regularization results in greater amounts of model structure while providing significantcomputationalsavings ert estimatedelectricalconductivity is used to predict solute concentration and solute mass in the aquifer at any experimental stage we are able to estimate total solute mass in the aquifer with a maximum accuracy of 60 85 depending on regularization protocol and survey geometry wealsoestimatethewithdrawnsolutemassforeveryexperimentalstagethechangeinmassbetweenexperimentalstages withdrawn mass estimates are more reliable than total mass estimates and do not exhibit systematic underprediction or dependence on regularization protocol withdrawn mass estimates areaccurateforchangesinmassbelow2 4 kgofpotassiumbromide kbr for horizontal and vertical dipole dipole surveys respectively estimating the withdrawn solute mass does not require background subtraction and thus does not require backgrounddata

electrical characterization of non fickian transport in groundwater and hyporheic systems 1 recent work indicates that processes controlling solute mass transfer between mobile and less mobile domains in porous media may be quantified by combining electrical geophysical methods and electrically conductive tracers whereas direct geochemical measurements of solute preferentially sample the mobile domain electrical geophysical methods are sensitive to changes in bulk electrical conductivity bulk ec and therefore sample ec in both the mobile and immobile domains consequently the conductivity difference between direct geochemical samples and remotely sensed electrical geophysical measurements may provide an indication of mass transfer rates and mobile and immobile porosities in situ here we present 1 an overview of a theoretical framework for determining parameters controlling mass transfer with electrical resistivity in situ 2 a review of a case study estimating mass transfer processes in a pilot scale aquifer storage recovery test and 3 an example application of this method for estimating mass transfer in watershed settings between streams and the hyporheic corridor we demonstrate that numerical simulations of electrical resistivity studies of the stream hyporheic boundary can help constrain volumes and rates of mobile immobile mass transfer we conclude with directions for future research applying electrical geophysics to understand field scale transport in aquifer and fluvial systems subject to rate limited mass transfer

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

intensification of the asian monsoon and a chemical weathering event in the late miocene early pliocene implications for late neogene climate change several sedimentary geochemical and isotopic records indicate that the hypothesized intensification of the asian monsoon at about 8 ma triggered a physical and chemical weathering event in the himalayan tibetan plateau records of sediment input and clay composition from the northern indian ocean reveal clear weathering changes in the plateau at this time and ge si ratios of opaline silica as well as biogenic sedimentation rates indicate that increased dissolved element fluxes from this weathering event had an oceanwide effect it is likely that weathering intensity also increased in the andes and amazon basin in this interval as well perhaps the most important impact of this weathering event was to increase the net flux of the biolimiting nutrient phosphorus to the ocean as evidenced by a peak in phosphorus accumulation rates at this time the temporary increase in nutrient inputs to the ocean triggered increased oceanic productivity and organic carbon burial recorded in carbon isotopic records and paleooxygen concentrations the net result of this weathering event may have been an increase in the rate of drawdown of atmospheric co2 through the late miocene early pliocene via direct silicate weathering reactions and increased burial of organic carbon in the ocean this increased rate of atmospheric co2 drawdown may have destabilized the climate system by the late pliocene thus initiating a period of intense cooling and ice buildup leading to the present

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

time lapse seismic imaging using regularized full waveform inversion with a prior model which strategy full waveform inversion is an appealing technique for time lapse imaging especially when prior model information is included into the inversion workflow once the baseline reconstruction is achieved several strategies can be used to assess the physical parameter changes such as parallel difference two separate inversions of baseline and monitor data sets sequential difference inversion of the monitor data set starting from the recovered baseline model and double difference inversion of the difference data starting from the recovered baseline model strategies using syntheticmarmousi data sets we investigate which strategy should be adopted to obtain more robust and more accurate time lapse velocity changes in noise free and noisy environments this synthetic application demonstrates that the double difference strategy provides the more robust time lapse result in addition we propose a target oriented time lapse imaging using regularized full waveform inversion including a prior model and model weighting if the prior information exists on the location of expected variations this scheme applies strong prior model constraints outside of the expected areas of timelapse changes and relatively less prior constraints in the time lapse target zones in application of this process to the marmousi model data set the local resolution analysis performed with spike tests shows that the target oriented inversion prevents the occurrence of artefacts outside the target areas which could contaminate and compromise the reconstruction of the effective time lapse changes especially when using the sequential difference strategy in a strongly noisy case the target oriented prior model weighting ensures the same behaviour for both time lapse strategies the double difference and the sequential difference strategies and leads to a more robust reconstruction of the weak time lapse changes the double difference strategy can deliver more accurate time lapse variation since it can focus to invert the difference data however the double difference strategy requires a preprocessing step on data sets such as time lapse binning to have a similar source receiver location between two surveys while the sequential difference needs less this requirement if we have prior information about the area of changes the target oriented sequential difference strategy can be an alternative and can provide the same robust result as the doubledifference strategy

internal tides and ocean mixing recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features a substantial amount of energy is transferred from the main ocean tides into internal tides in his perspective garrett explains how these internal waves with tidal periods propagate through the density stratified deep ocean and eventually break down into turbulence the resulting mixing affects ocean stratification and ocean circulation it thus influences climate as well as biological production the energy for the internal tides is derived from the rotational energy of the earth moon system changes of the length of the day and the distance to the moon

target oriented joint least squares migration inversion of time lapse seismic data sets two related formulations are proposed for target oriented joint least squares migration inversion of time lapse seismic data sets time lapse seismic images can be degraded when reservoir overburden is complex or when acquisition geometries significantly differ because the migration operator does not compensate for the resulting amplitude and phase distortions under these circumstances time lapse amplitudes are poor indicators of production related changes in reservoir properties to correct for such image degradation time lapse imaging is posed as joint inverse problems that utilize concatenations of target oriented approximations to the linear least squares imaging hessian in both formulations spatial and temporal constraints ensure inversion stability and geologically consistent time lapse images using two numerical time lapse data sets we confirmed that these formulations can attenuate illumination artifacts caused by complex overburden or geometry differences and that they yield better quality images than obtainable with migration

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

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

palaeomagnetism of the cordillera de la costa northern chile evidence for local forearc rotation abstract palaeomagnetic studies of lower jurassic to lower cretaceous volcanic plutonic and sedimentary rocks from the cordillera de la costa of northern chile indicate that there has been no significant latitudinal movement of northern chile since early cretaceous times a palaeomagnetic pole for the cordillera de la costa 63 s 187 e 95 7 7 was derived from combining the results of three studied units the la negra formation jurassic volcanics jurassic lower cretaceous granodioritic plutons and the e1 way formation hauterivian marine carbonates together with the coloso formation lower cretaceous red beds comparison with a cretaceous reference pole for the stable shield area of south america 87 s 235 e 95 2 4 indicates that 24 7 of clockwise rotation has taken place possible mechanisms for the rotation of the andean forearc in this area have been examined in relation to the kinetics of the subducting nazca and over riding south american plates the cordillera de la costa has been subjected to both compressional and extensional tectonics since the lower cretaceous major eastwardly directed thrusting in mid cretaceous and early tertiary times possibly associated with a period of oblique subduction of the nazca plate contributed to the accretion of the cordillera to the main forearc rotation may have occurred during this process in oligo miocene and later tertiary times extensional faulting possibly associated with roll back of the nazca plate led to the reactivation of the atacama fault zone and the formation of oblique extension faults in the cordillera de la costa structural rotation associated with this phase of extension could equally explain the observed palaeomagnetic results

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

inversion of time lapse electrical resistivity imaging data for monitoring infiltration monitoring hydrologic processes in the vadose zone is of great importance in developing management strategies for groundwater resources flow and transport behavior in variably saturated media control the rate at which and path along which fluids or contaminants reach groundwater aquifers electrical resistivity imaging eri is sensitive to changes in the subsurface conductivity structure which is highly dependent on the water saturation distribution in the vadose zone time lapse eri therefore has been widely used for environmental and hydrologic monitoring experiments

late neogene lacustrine record and palaeogeography in the quillagua llamara basin central andean fore arc northern chile abstract the cenozoic quillagua llamara basin northern chile central andes is an asymmetrical intramassif fore arc basin with a relatively wide northern sector separated from a narrower southward extension by a basement threshold the northern sector was characterised by a noticeable oligocene late neogene alluvial fan and lacustrine dominated deposition which resulted in sequences up to 900 m thick whereas the southern sector was often a bypass zone with thinner fluvial and lacustrine sediment accumulation the basin infill includes two third order alluvial lacustrine unconformity bounded units which include other higher frequency 4th to 5th order sequences the evolution of the late miocene pliocene lacustrine episodes in the quillagua llamara basin was not only controlled by the regional variations from arid to hyperarid palaeoclimate conditions due to the combined influence of the pacific high pressure cell the rain shadow effect exerted by the rising andes and the northward flowing cold oceanic currents but also by a the extensional tectonics and evolution and uplift of the fore arc region which defined the location and size of the depocentres b the resulting basement palaeorelief which affected sediment thickness and facies distribution during the late basin infill episodes and c the tectonic modifications of watersheds water divides and drainage networks in the precordillera which caused considerable changes of water income in the lacustrine systems understanding of this regional tectonosedimentary evolution is a necessary first step before analysing of the low to high order lacustrine sequence changes in the region lacustrine water supply was very sensitive to tectonics even gentle tectonic tilting and uplifting in critical water divide zones could result in changes in water balance in the lacustrine basins and trigger variations in the depositional record the very conspicuous lacustrine regime changes recorded in the quillagua llamara basin infill cannot be considered in themselves conclusive proof of an exclusive climatic forcing since they took place close to either major regional drainage changes or to gentle but noticeable tectonic reactivation in the fore arc region

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

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

two and three dimensional electrical resistivity imaging at a heterogeneous remediation site geometrically complex heterogeneities at a decommissioned sour gas plant could not be adequately characterized with drilling and 2d electrical resistivity surveys alone in addition 2d electrical resistivity imaging profiles produced misleading images as a result of out of plane resistivity anomalies and violation of the 2d assumption accurate amplitude and positioning of electrical conductivity anomalies associated with the subsurface geochemical distribution were required to effectively analyze remediation alternatives forward and inverse modeling and field examples demonstrated that 3d resistivity images were needed to properly reconstruct the amplitude and geometry of the complex resistivity anomalies problematic 3d artifacts in 2d images led to poor inversion fits and spurious conductivity values in the images at depths close to the horizontal offset of the off line anomaly three dimensional surveys were conducted with orthogonal sets of wenner and dipole dipole 2d resistivity survey lines the

electrical hydraulic relationships observed for unconsolidated sediments in the presence of a cobble framework mechanistic models now exist to predict hydraulic conductivity k from the spectral induced polarization sip response of granular media we examined the predictions of such a model on unconsolidated coarse fluvial sediments and compared them to those obtained with a modified kozeny carman kc model samples were retrieved from the boise hydrogeophysical research site bhrs located on a gravel bar adjacent to the boise river idaho a sample holder 0 102 m diameter and 0 12 m in length was designed to include the cobble framework in reconstituted samples representing the primary stratigraphic units defined based on porosity variation at this site sip 0 001 1000 hz and k from darcy tests measurements were recorded for twelve samples with sip measurements made as a function of pore fluid conductivity 3 300 ms m grain grain size distribution gsd and total porosity k prediction with the kc model was improved after discounting of the cobble framework and multiplying by the tortuosity resulting from matrix capillaries around the cobbles resulting in estimates within 0 5 orders of magnitude of the measurements k prediction with a mechanistic sip model based on stern layer polarization slp model that requires an estimate of the gsd alsoalso required discounting for the cobble framework to obtain estimates within 0 5 orders of magnitude of the measurements similarly the slp model over predicts the measured imaginary conductivity unless the cobble framework is discounted which then results in estimates of within 0 1 orders of magnitude of the measurements this can be explained by the fact that the cobbles polarize at frequencies well below the minimum measurement frequency 0 001 hz the slp model for k prediction parameterized in terms of the formation factor and imaginary conductivity performed well for the ten samples with a cobble framework without modification as the imaginary conductivity directly senses the matrix grain size characteristics whereas the formation factor captures the porosity reduction and tortuosity resulting from the presence of the cobble framework capillary tortuosity our findings suggest that the estimation of contrasts in hydraulic conductivityk in coarse sediments may be achievable through measurements of electrical properties after appropriate consideration of the cobble fraction

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

cross hole resistivity tomography using different electrode configurations this paper investigates the relative merits and effectiveness of cross hole resistivity tomography using different electrode configurations for four popular electrode arrays pole pole pole bipole bipole pole and bipole bipole by examination of two synthetic models a dipping conductive strip and a dislocated fault it is shown that besides the popular pole pole array some specified three and four electrode configurations such as pole bipole am n bipole pole am b and bipole bipole am bn with their multispacing cross hole profiling and scanning surveys are useful for cross hole resistivity tomography these configurations compared with the pole pole array may reduce or eliminate the effect of remote electrodes systematic error and yield satisfactory images with 20 noise contaminated data it is also shown that the configurations which have either both current electrodes or both potential electrodes in the same borehole i e pole bipole a mn bipole pole ab m and bipole bipole ab mn have a singularity problem in data acquisition namely low readings of the potential or potential difference in cross hole surveying so that the data are easily obscured by background noise and yield images inferior to those from other configurations

potential of electrical resistivity tomography to infer aquifer transport characteristics from tracer studies a synthetic case study 1 with time lapse electrical resistivity tomography ert transport processes in the subsurface can be imaged and monitored the information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ert is generally underdetermined and that ert data acquisition is often limited to two dimensional 2 d image planes to address this problem we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2 d image plane perpendicular to the mean flow direction using time lapse ert the tracer breakthrough patterns in the image plane were interpreted using equivalent transport models an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves equivalent parameters derived from simulated and from ert inverted concentrations showed a good agreement which demonstrates the potential of ert to characterize subsurface transport using first order approximate solutions of stochastic flow and transport equations equivalent model parameters and their spatial variability were interpreted in terms of the local scale dispersion and the spatial variability of the hydraulic conductivity the spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related consequently the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions which can be observed with sufficiently high spatial resolution using ert

tectonic signatures in arid continental basins an example from the upper miocene pleistocene calama basin andean forearc northern chile abstract the calama basin a transtensional basin situated within the andean forearc and its extension to the pampa del tamarugal central depression is filled with 700 m of sediments detailed sedimentary logging and 40ar 39ar dates from interbedded volcanic deposits have established a lithostratigraphic and chronostratigraphic framework for the upper 95 m thick upper miocene pleistocene succession five facies associations fluvio lacustrine diatomite palustrine carbonate massive anhydrite fluvial and alluvial fan have been identified within this part of the basin fill the following events are recognised in the basin evolution 1 deposition of diatomaceous lacustrine sediments in two separate depocentres in the pampa del tamarugal and the central calama basin with alluvial fan accumulation along the basin margins at 8 ma 2 localised deformation within the central calama basin between 7 and 6 ma but continuous sedimentation elsewhere 3 palustrine carbonate deposition across the entire area from 6 to 3 ma except in the pampa del tamarugal where diatomaceous sedimentation continued until 5 ma before being replaced by palustrine carbonate deposition 4 widespread folding after 3 ma and entrenchment as the drainage system cut down to reach a new base level caused by the rio loa breaching the coastal cordillera and reaching the sea localised lacustrine deposition in topographic lows or tectonically created dams also occurred during this period comparison with similar age facies elsewhere in northern chile has shown changes such as these to be localised and diachronous indicating that tectonic controls on accommodation space and drainage patterns are the primary influence on sedimentation in this tectonic setting the lacustrine deposits do not appear to be a reliable recorder of low frequency climatic change this is exemplified by the change from lacustrine to palustrine deposition at 6 5 ma which would appear to record a drying of the climate however a synchronous change from ephemeral alluvial fan deposition to more permanent fluvial deposition at the basin margins indicates increased run off

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

monitoring active fumaroles through time lapse electrical resistivity tomograms an application to the pisciarelli fumarolic field campi flegrei italy abstract volcanoes are usually monitored through observations of many physical and chemical phenomena in the most dangerous cases as the one of the campi flegrei caldera italy great amount of data are collected both in discrete or continuously and regularly stored however how to transform such mass of data in a deeper understanding of the volcano dynamics is still an open question dissimilar information are in fact always hard to compare but just integrating all the available knowledge hazardous events could be prevented in a reliable way fluids as water and gasses mobilized in the subsoil by the heat induced by deep magmatic sources are widely recognized as the first engine of similar occurrences and the volcanic gas emissions represent together with the seismic activity one of the most considered precursors at the same time the electrical geophysical methods are the most applied in order to detect and characterize the fluid patterns in the subsoil so the integration of geoelectrical and geochemical observations should represent one of the most pursued approach in volcanoes monitoring on the contrary standard way to compare such data has been not yet codified the ert tomograms capability to individuate that parts of the subsoil where gasses cumulate is well understood in literature however we look for indications about its proficiency in associating the electrical resistivity changes relative to these zones once compared to the geochemical time series to deep related contributes distinguishing them from the seasonal ones the electrical signature of the fluid patterns reconstructed through a time lapse ert approach could be of relevance to better characterize the volcanic phenomena and their origins in this paper a first test of ert and geochemical time series integration was performed to enhance the understanding of the pisciarelli fumarolic field evolution now the most active area in the whole campi flegrei caldera

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

late miocene earliest pliocene glaciation in southern argentina implications for global ice sheet history abstract in south america at latitude 47 s till was deposited sometime between 7 m y and 4 6 m y ago at a time when the local climate was colder than today s during this same interval glaciers extended to sea level in southeast alaska and widespread cooling of the ocean surface in middle latitudes worldwide marine regression and change in the oxygen isotopic composition of ocean water occurred from the last three events major late miocene expansion of the antarctic ice sheet has been inferred on the assumption that the history of north atlantic ice rafting precludes the existence of northern hemisphere ice sheets until 3 m y ago this is disputed first because precipitation in antarctica would probably have decreased at temperatures below today s second because the antarctic ice sheet cannot expand appreciably until buildup of northern hemisphere ice sheets has lowered sea level third because virtually no late miocene sediments are present at the labrador sea dsdp sites that are critical to the reconstruction of north atlantic ice rafting history and fourth because the scale of late miocene glaciation in alaska is at least permissive for simultaneous buildup of ice at similar latitudes further east if global ice sheet volume at the end of the miocene was greater than it is today by an amount that would have lowered sea level by several tens of meters the excess ice did not accumulate in antarctica but in the northern hemisphere chiefly in north america away from the atlantic coast

imaging and characterization of solute transport during two tracer tests in a shallow aquifer using electrical resistivity tomography and multilevel groundwater samplers 1 the relevance of aquifer heterogeneity for flow and transport is recognized broadly however its characterization is hampered by the inaccessibility of the subsurface time lapse electrical resistivity tomography ert offers the possibility of imaging noninvasively subsurface transport we present results of two tracer tests that were carried out successively in a shallow aquifer at the krauthausen test site germany the breakthroughs of an electrically conductive and a resistive tracer were monitored with ert and local multilevel groundwater samplers mls along two cross sections perpendicular to the mean flow direction sinking of the conductive salt tracer due to density effects was observed with ert we applied a stream tube model to characterize the spatially variable transport ert derived stream tube parameters showed similar patterns for the two tracer experiments reflecting the effect of aquifer heterogeneity on transport mls data did not show similar spatial patterns which indicates that these measurements may be prone to subtle changes of the flow field in the small sampling volume and mixing within screened wells between 50 and 10 of the tracer was recovered in the ert derived breakthrough curves compared with transport simulations in a homogeneous aquifer ert derived time integrated changes in electrical conductivity were locally larger but focused in a smaller area mls data indicated that in this area ert did not underestimate the tracer recovery the relatively low tracer recovery was attributed to undetected tracer breakthrough in regions with low ert sensitivity and in regions where the length of the tracer plume and the electrical conductivity contrast were small

significance of porosity for stratigraphy and textural composition in subsurface coarse fluvial deposits boise hydrogeophysical research site recognition and quantitative characterization of subsurface stratigraphic units in coarse unconsolidated fluvial deposits are difficult because large grain size and the large scale of sedimentary structures make direct interpretation from core difficult or impossible in this paper we use porosity data from well logs and grain size distribution gsd data from core to investigate four pebble and cobble dominated units that have been identified in porosity logs in deposits at a research well field boise hydrogeophysical research site lacking direct observation at an appropriate scale questions about distribution of parameters and textural composition in these units are analyzed with statistical tests the four pebble and cobble dominated porosity stratigraphic units may be grouped into two types 1 units 1 and 3 have low porosity mean 0 17 0 18 and low porosity variance and 2 units 2 and 4 have higher porosity mean 0 23 0 24 and higher porosity variance based on gsd data core samples are subdivided into five lithotypes the five lithotypes occur in different proportions and have different vertical transition probability characteristics in the two types of units 1 units 1 and 3 have only framework gravel dominated lithotypes and have random vertical transition probability between these two lithotypes and 2 units 2 and 4 consist of both framework gravel dominated and sand or matrix dominated lithotypes and have structured vertical transition probability the two framework gravel dominated lithotypes occur in all four stratigraphic units but have distinctly lower porosity in units 1 and 3 i e tighter packing than in units 2 and 4 looser packing considering the repeated stratigraphic occurrence of and the statistical significance of differences between the two types of units both the individual unit distinctions and the two unit groupings appear to be valid it is reasonable to interpret that the observed packing differences associated with units 1 and 3 compared with units 2 and 4 are related to different sedimentary processes that produce different bedforms or grain fabrics perhaps under different bedload transport rates

on sharp spectral lines in the climate record and the millennial peak the existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order thus the appearance of such a spectral peak with a q 20 near 1500 years period in the physical properties of the greenland ice core is intriguing bandwidth less than two cycles in 110 000 years apparently similar phenomena exist in some deep sea cores it is shown however that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately under the nyquist criterion sampled at integer multiples of the common year if this peak is therefore discounted climate variability appears as expected to be a continuum process in the millennial band more generally however aliasing of high frequencies must be a concern in any core analysis

inversion of induced polarization data we present an algorithm for inverting induced polarization ip data acquired in a 3 d environment the algorithm is based upon the linearized equation for the ip response and the inverse problem is solved by minimizing an objective function of the chargeability model subject to data and bound constraints the minimization is carried out using an interior point method in which the bounds are incorporated by using a logarithmic barrier and the solution of the linear equations is accelerated using wavelet transforms inversion of ip data requires knowledge of the background conductivity we study the effect of different approximations to the background conductivity by comparing ip inversions performed using different conductivity models including a uniform half space and conductivities recovered from one pass 3 d inversions composite 2 d inversions limited aim updates and full 3 d nonlinear inversions of the dc resistivity data we demonstrate that when the background conductivity is simple reasonable ip results are obtainable without using the best conductivity estimate derived from full 3 d inversion of the dc resistivity data as a final area of investigation we study the joint use of surface and borehole data to improve the resolution of the recovered chargeability models we demonstrate that the joint inversion of surface and crosshole data produces chargeability models superior to those obtained from inversions of individual data sets

detection of magnetically susceptible dyke swarms in a fresh coastal aquifer groundwater constitutes the main source of freshwater in shalatein on the western coast of the red sea in egypt the fresh aquifer of shalatein is intensively dissected by shallow and deep faults associated with the occurrence of dykes and or dyke swarms in this context synthesis of electrical resistivity ground magnetics and borehole data was implemented to investigate the freshwater aquifer condition locate the intrusive dykes and or dyke swarms and demarcate the potential freshwater zones nine schlumberger ves s with maximum current electrode half spacing ab 2 of 682 m were conducted the subsurface was successfully delineated by general four layers the fresh aquifer of the quaternary and pre quaternary alluvium sediments was effectively demarcated with true resistivities ranged from 30 to 105 m and thickness ranged between 20 and 60 m a ground magnetic survey comprised 35 magnetic profiles each 7 km in length magnetic data interpretation of the vertical derivatives first and second order downward continuation 100 m apparent susceptibility depth of 100 m and wavelength filters butterworth high pass of wavelengths 300 m clearly reflected the deep seated structure the computed depth by the 3d euler deconvolution for geological contacts and faults si 0 ranged from 14 to 545 m whereas for dyke and sill si 1 it ranged from 10 to 1 095 m the western part of the study area is recommended as a potential freshwater zone as it is characterized by depths 100 m to the top of the dykes higher thickness of the fresh aquifer 45 60 m depths to the top of the fresh aquifer ranging from 25 to 40 m and higher resistivities reflecting better freshwater quality 70 105 m

the spectral description of climate change including the 100 ky energy core records both ice and deep sea suggest that the dominant character is that of a red noise process or random walk examination of a few typical records supports the inference that the contribution of the milankovitch frequencies to climate change at most represents only a small fraction of total climate variance most spectral densities are sufficiently flat that rates of change will be dominated by the highest frequencies present in the forcing a broad maximum near 100 ky period can be readily rationalized without invoking an oscillator one need only suppose that there is an approximate threshold beyond which the climate system collapses the quasiperiodicity is then governed by a combination of the collapse threshold the system memory time scale and the intensity of the stochastic forcing changes in the forcing intensity would lead to a shift in the dominant time scale some inferred spectral power laws may be inaccurate owing to undersampling of the records

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

structural evidence of orogen parallel strike slip displacements in the precordillera of northern chile the chilean precordillera situated between the longitudinal valley and the western cordillera of northern chile is made up of several elongate basement ridges following the trend of the andes these ridges which morphologically rise above the mesozoic tertiary cover rocks are developed as anticlinal cores or as pressure ridges bounded by reverse faults and thus show considerable orogennormal shortening several nearly vertical faults cut through the precordillera parallel or at a very low angle to the mountain ranges from the following structures it can be inferred that orogen parallel transcurrent movements took place along the faults a asymmetric en echelon fault arrays b stratigraphic and structural discontinuities across major faults c fabrics in fault rocks and d vertical folds a dextral displacement of the order of tens of km is probable the orogen parallel strikeslip movements as well as the orogen normal shortening are considered as phenomena of magmatic arc tectonics due to the focussing of central andean igneous activity on the precordillera from the late cretaceous until the paroxysm of deformation 45 30 ma deformation along the precordilleran fault system is related with the development of the large porphyry copper ore deposits of that area the structural evolution of the precordillera can be explained by oblique subduction resulting in dextral transpression

time lapse inversion of crosswell radar data the combination of differential radar tomography with conventional tracer and or hydraulic tests facilitates high resolution characterization of subsurface heterogeneity and enables the identification of preferential flow paths in dynamic imaging each tomogram is typically inverted independently under the assumption that data sets are collected quickly relative to changes in the imaged property e g attenuation or velocity however such snapshot tomograms may contain large errors if the imaged property changes significantly during data collection acquisition of less data over a shorter time interval could ameliorate the problem but the resulting decrease in ray density and angular coverage could degrade model resolution to address these problems we propose a new sequential approach for time lapse tomographic inversion the method uses space time parameterization and regularization to combine data collected at multiple times and to account for temporal variation the inverse algorithm minimizes the sum of weighted squared residuals and a measure of solution complexity based on an a priori space time covariance function and a spatiotemporally variable mean we demonstrate our approach using a synthetic 2 d time lapse x z t data set based loosely on a field experiment in which difference attenuation radar tomography was used to monitor the migration of a saline tracer in fractured rock we quantitatively show the benefits of space time inversion by comparing results for snapshot and time lapse inversion schemes inversion over both space and time results in superior estimation error model resolution and data reproduction compared to conventional snapshot inversion finally we suggest strategies to improve time lapse cross hole inversions using ray based inversion constraints and a modified survey design in which different sets of rays are collected in alternating time steps

twentieth century sea level an enigma changes in sea level relative to the moving crust are associated with changes in ocean volume mostly thermal expansion and in ocean mass melting and continental storage t steric t eustatic t recent compilations of global ocean temperatures by levitus and coworkers are in accord with coupled ocean atmosphere modeling of greenhouse warming they yield an increase in 20th century ocean heat content by 2 1023 j compared to 0 1 1023 j of atmospheric storage which corresponds to greenhouse 2000 3 cm the greenhouse related rate is accelerating with a present value greenhouse 2000 6 cm century tide records going back to the 19th century show no measurable acceleration throughout the late 19th and first half of the 20th century we take historic 18 cm century the intergovernmental panel on climate change attributes about 6 cm century to melting and other eustatic processes leaving a residual of 12 cm of 20th century rise to be accounted for the levitus compilation has virtually foreclosed the attribution of the residual rise to ocean warming notwithstanding our ignorance of the abyssal and southern oceans the historic rise started too early has too linear a trend and is too large melting of polar ice sheets at the upper limit of the intergovernmental panel on climate change estimates could close the gap but severe limits are imposed by the observed perturbations in earth rotation among possible resolutions of the enigma are a substantial reduction from traditional estimates including ours of 1 5 2 mm y global sea level rise a substantial increase in the estimates of 20th century ocean heat storage and a substantial change in the interpretation of the astronomic record

major neogene events of the southeastern pacific the chilean and peruvian record abstract according to the biochronostratigraphic model proposed the neogene marine deposits in chile and peru represent two independent transgressive sequences alloformations separated by a major regional hiatus the earlier sequence nseps i would stretch from the top of the early miocene up to the base of the late miocene ca 19 10 m y b p the upper sequence nseps ii would correspond in turn to the late pliocene ca 3 5 1 6 m y b p the regional hiatus separating both sequences would encompass the late miocene and the early pliocene ca 10 3 5 m y b p the planktonic foraminiferal events described suggest an age of terminal early miocene middle miocene and late pliocene respectively the paleoclimatic events recorded are three a warming event lasting from the terminal early miocene to the end of the middle miocene mmwe 18 11 5 m y b p a cooling event of the middle late pliocene lpce 2 5 0 2 m y b p and warming event spanning most of the late pliocene lpwe 3 5 2 2 m y b p restricted to the surface and intermediate sea waters of the middle and low latitudes the last paleoclimatic event not recorded as such so far is both synchronous and mutually exclusive in latitudinal terms with the second one three tectonic regional events are analyzed the quechuan 1 phase 19 1 5 m y b p the quechuan 2 phase 10 1 m y b p and the geographic rhodanian phase 3 5 0 5 m y b p in the studied area there is no late miocene marine sedimentary record to confirm the terminal tortonian or quechuan 3 tectonic phase ca 7 m y b p admitted to occur in the volcanoclastic continental sequences of northern chile and southern peru