integrated electrical resistivity tomography ert and self potential sp techniques for assessing hydrological processes within glacial lake moraine dams moraine dams can be inherently unstable but effective assessment strategies remain poorly identified we integrate electrical resistivity tomography ert with electrical self potential sp and lake level measurements to investigate the structure of and hydrological processes within a moraine dam complex adjacent to miage glacier italy this complex separates two meltwater lakes characterized by an efficient subterranean hydraulic connection our ert data reveal a continuous free surface within the complex whose morphology reflects the topography of the moraine complex akin to unconfined groundwater aquifers sp data were corrected for spatial changes in the thickness of the upper unsaturated layer using principles of electrography the residual streaming potential map is consistent with darcian flow of lake waters through the moraine complex characterized by a negative to positive potential change from 70 mv these electrical signatures are consistent with those generated by water seepage through earth dams in various non glacial settings integrated electrical geophysical methods thus provided an inexpensive and unobtrusive evaluation of the hydrological properties of and processes within the moraine complex since spatio temporal patterns of subsurface water flow critically affect the strengths of moraine sediments such methods promise to be powerful in assessing the long term stability of moraine dammed glacial lakes

impact of water saturation on seismoelectric transfer functions a laboratory study of coseismic phenomenon s u m m a r y seismic waves propagating in a porous medium under favourable conditions generate measurable electromagnetic fields due to electrokinetic effects it has been proposed following experimental and numerical studies that these so called seismoelectromagnetic couplings depend on pore fluid properties the theoretical frame describing these phenomena are based on the original biot s theory assuming that pores are fluid filled we study here the impact of a partially saturated medium on amplitudes of those seismoelectric couplings by comparing experimental data to an effective fluid model we have built a 1 m length scale experiment designed for imbibition and drainage of an homogeneous silica sand the experimental setup includes a seismic source accelerometers electric dipoles and capacitance probes in order to monitor seismic and seismoelectric fields during water saturation apparent velocities and frequency spectra in the kilohertz range are derived from seismic and electrical measurements during experiments in varying saturation conditions amplitudes of seismic and seismoelectric waves and their ratios i e transfer functions are discussed using a spectral analysis performed by continuous wavelet transform the experiments reveal that amplitude ratios of seismic to coseismic electric signals remain rather constant as a function of the water saturation in the s w 0 2 0 9 range consistently with theoretically predicted transfer functions

vertical seismoelectric profiling in a borehole penetrating glaciofluvial sediments 1 seismoelectric signals have been measured as a function of depth in a borehole penetrating glaciofluvial sands silts and glacial till using a broadband surface seismic source and a downhole electrode array transient electric field pulses with amplitudes of 1 to 4 v m accompanied the arrival of seismic p waves at the electrodes but no simultaneous interfacial signals were observed above the noise floor of approximately 0 2 v m the co seismic effect was strongest in a sand and gravel layer where its amplitude is consistent with the predictions of a simplified theoretical model normalization of the amplitude logs by measurements of seismic particle velocity and electrical conductivity enhanced their sensitivity to changes in lithology and porosity the results of this experiment suggest that co seismic seismoelectric effects show potential as a porosity permeability logging tool in the borehole environment

stress strain state monitoring of the geological medium based on the multi instrumental measurements in boreholes experience of research at the petropavlovsk kamchatskii geodynamic testing site kamchatka russia we present the results of the long term study which make it possible to assess the possibilities of two methods used at the petropavlovsk kamchatskii geodynamic site russia for continuous monitoring of the stress strain state of geoenvironment the methods are based on the borehole geoacoustic measurements and electromagnetic measurements with underground electric antennas combined with hydrogeochemical and hydrogeodynamic borehole measurements these methods allow monitoring the changes in the parameters of geological environment and identifying the stages in the changes of its stress strain state as the examples we present the results of the measurements in the time vicinities of the strongest seismic events that occurred during the period of joint borehole geoacoustic and electromagnetic measurements at the petropavlovsk kamchatskii geodynamic site we also analyze the data obtained in the time vicinities of the tohoku mega earthquake march 11 2011 japan mw 9 1 and a close strong zhupanovskoe earthquake january 30 2016 mw 7 2 that occurred at the epicentral distances r 107 km from petropavlovsk kamchatskii it is shown that the discussed methods are promising for medium and short term forecasting of the earthquakes

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

active seismoelectric exploration of glaciers 1 repeatable and strong seismoelectric signals were recorded on glacier de tsanfleuron switzerland using a vertical sounding geometry electromagnetic waves are inferred to be generated by electrokinetic conversion of seismic energy within the snow pack and near the dry wet ice and ice bed interfaces a simple gradient based scheme allows such electrokinetic interface responses eirs to be isolated from noise eirs depend sensitively on the azimuthal orientation of the receiving array of electrical dipoles seismoelectric techniques promise to allow mapping even of thin water bearing strata within or beneath glaciers or frozen ground estimation of hydraulic or fluid properties of such strata as well as monitoring of ice fracturing or basal properties and processes at improved spatial resolution

coseismic electromagnetic field due to the electrokinetic effect in the earth s crust an electromagnetic em field may be generated spontaneously by a seismic wave through a variety of mechanoelectromagnetic transducer mechanisms such as the piezomagnetic effect the piezoelectric effect the electrokinetic effect and the em induction the movement of an electrically conducting crust through a geomagnetic field the coseismic em field contains information about the structure and physical parameters of the crust which complements that which can be obtained by purely seismic or purely em methods the magnitude direction and polarization of this field depend on the origin of the source the type of seismic wave and the geometry of the crust of the possible mechanisms mentioned above the electrokinetic effect produces the largest magnitude of coseismic em field detailed theoretical and computational calculations of the electric and magnetic fields thus induced by a rayleigh wave were obtained several typical models of heterogeneity were considered including horizontally stratified layers and fault like heterogeneities we determined that the polarization and spatial distribution of the electric and magnetic fields arising from the electrokinetic effect are very specific and distinguishable from the fields generated by other sources the expected magnitudes of electric and magnetic fields were large enough to be detected by conventional sensors and specific enough to be separated from the noise the results obtained can be used for the interpretation of electric and magnetic disturbances observed during an earthquake and for prospecting the earth s upper crust from depths of a few meters to a few kilometers

seismoelectric imaging of the vadose zone of a sand aquifer we have acquired a 300 m seismoelectric section over an unconfined aquifer to demonstrate the effectiveness of interfacial signals at imaging interfaces in shallow sedimentary environments the seismoelectric data were acquired by using a 40 kg accelerated weight drop source and a 24 channel seismoelectric recording system composed of grounded dipoles preamplifiers and seismographs in the shot records interfacial signals were remarkably clear they arrived simultaneously at offsets as far as 40 m from the seismic source the most prominent signal was generated at the water table at a depth of approximately 14 m and had peak amplitudes on the order of 1 v m a weaker response was generated at a shallower interface that is interpreted to be a water retentive layer the validity of these two laterally continuous events and of other discontinuous events indicative of vadose zone heterogeneity is corroborated by the presence of reflections exhibiting similar characteristics in a ground penetrating rada

measurement of the seismoelectric response from a shallow boundary field experiments carried out at a site near vancouver canada have shown that a shallow lithologic boundary can be mapped on the basis of its seismoelectric response as seismic waves cross the boundary between organic rich fill and impermeable glacial till they induce electric fields that can be measured at the surface with grounded dipole receivers sledgehammer and blasting cap seismic sources positioned up to 7 m away from the interface have produced clear seismoelectric conversions two types of seismoelectric signals are observed the primary response is distinguished by near simultaneous arrivals at widely separated receivers its arrival time is equal to the time required for a seismic p wave to travel from the shotpoint to the fill till boundary on the surface its maximum amplitude about 1 mv m is measured by dipoles located within a few meters of the shotpoint at greater distances the amplitude of the primary arrival decays rapidly with offset and secondary seismoelectric arrivals become dominant they differ from the primary response in that their arrival times increase with dipole offset and they appear to be generated in the immediate vicinity of each dipole sensor our studies show that the responses cannot be attributed to piezoelectricity or to resistivity modulation in the presence of a uniform telluric current we infer that seismically induced electrokinetic effects or streaming potentials are responsible for the seismoelectric conversion and a simple electrostatic model is proposed to account for the two types of arrivals although our experiments were small in scale the results are significant in that they suggest that the seismoelectric method may be used to map the boundaries of permeable formations

experimental measurements of the streaming potential and seismoelectric conversion in berea sandstone the streaming potential across a porous medium is induced by a fluid flow due to an electric double layer between a solid and a fluid when an acoustic wave propagates through a porous medium the wave pressure generates a relative movement between the solid and the fluid the moving charge in the fluid induces an electric field and seismoelectric conversion in order to investigate the streaming potential and the seismoelectric conversion in the same rock sample we conduct measurements with berea sandstone saturated by nacl solutions with different conductivities we measure the electric voltage streaming potential across a cylindrical sample in nacl solutions with different conductivities and under different pressures to determine the dc coupling coefficients we also measure the seismoelectric signals induced by acoustic waves with a berea sandstone plate at different frequencies and solution conductivities the pressures of the acoustic waves are calibrated with a standard hydrophone bruel 8103 at different frequencies 15 120 khz we calculate the quantitative coupling coefficients of the seismoelectric conversion at dc and at high frequencies with samples saturated by solutions with different conductivities when the berea sandstone sample is saturated by the nacl solution with 0 32 ms m in conductivity for example the dc and seismoelectric coupling coefficients at 15 khz are 0 024 v pa and 0 019 v pa respectively the seismoelectric coupling coefficient is an important and helpful parameter for designing a seismoelectric tool more experimental measurements of seismoelectric coupling coefficients in the frequency range of 100 hz to 15 khz are needed in the future

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

pacific ventilation of the arctic ocean s lower halocline by upwelling and diapycnal mixing over the continental margin 1 pacific winter waters a major source of nutrients and buoyancy to the arctic ocean are thought to ventilate the arctic s lower halocline either by injection isopycnal or penetrative of cold saline shelf waters or by cooling and freshening atlantic waters upwelled onto the shelf although ventilation at salinity s 34 psu has previously been attributed to hypersaline polynya waters temperature salinity nutrient and tracer data suggest instead that much of the western arctic s lower halocline is in fact influenced by a diapycnal mixing of pacific winter waters with s 33 1 psu and denser eastern arctic halocline atlantic waters the mixing taking place possibly over the northern chukchi shelf slope estimates from observational data confirm that sufficient quantities of atlantic water may be upwelled to mix with the inflowing pacific waters with volumes implying the halocline over the chukchi borderland region may be renewed on timescales of order a year

early summer water mass transformation in the eastern chukchi sea abstract pacific water entering the chukchi sea through bering strait can be modified by physical processes such as surface heating and cooling and internal mixing here we document the existence of a previously unobserved water mass in the eastern chukchi sea during the early summer using hydrographic and velocity data from the june july 2010 icescape survey the water mass in question is as salty as pacific winter water pww but is much warmer with temperatures typical of summer waters we label the water mass dense chukchi summer water dcsw which is dense enough to ventilate the upper halocline of the western arctic ocean normally ventilated by the much colder pww satellite sea surface temperature data long term mooring data from bering strait and the beaufort shelfbreak and atmospheric reanalysis fields are used to characterize the spatial and temporal variability of the dcsw and explore potential forcing scenarios that can lead to its formation in 2010 the dcsw did not enter the chukchi sea through bering strait hence it had to be formed locally on the shelf two distinct forcing mechanisms are considered 1 mixing of very warm alaskan coastal water with the cold pww when the two water masses come in contact in the energetic alaskan coastal current and 2 warming of pww when it experiences solar heating within the coastal polynya in the northeastern chukchi sea during the spring melt season finally we explore the conditions under which the springtime polynya has formed over the past three decades as it relates to the formation of dcsw

bayesian inversion of joint sh seismic and seismoelectric data to infer glacier system properties abstract in glacial studies properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system the seismoelectric method could potentially be used to determine key properties of glacial environments here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement considering a one dimensional setting we compute the seismic waves and the electrokinetically induced electric field we then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters namely depth of the glacier bottom porosity permeability shear modulus and saturating water salinity of the glacier basement moreover we study the possibility of inferring these key parameters from a set of very low noise synthetic data adopting a bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above we tackle the resolution of the probabilistic inverse problem with two strategies 1 we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and 2 we use a markov chain monte carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters given the synthetic data set both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation the markov chain monte carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions the inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution in turn the inversion of the electric data alone and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties furthermore the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

comment on evidence for long residence times of rhyolitic magma in the long valley magmatic system the isotopic record in precaldera lavas of glass mountain by a n halliday g a mahood p holden j m metz t j dempster and j p davidson comment and replies on the paper of a n halliday g a mahood p holden j m metz t j dempster and j p davidson 1989 earth planet sci lett 94 274 290

estimating depth of investigation in dc resistivity and ip surveys in this paper the term depth of investigation refers generically to the depth below which surface data are insensitive to the value of the physical property of the earth estimates of this depth for dc resistivity and induced polarization ip surveys are essential when interpreting models obtained from any inversion because structure beneath that depth should not be interpreted geologically we advocate carrying out a limited exploration of model space to generate a few models that have minimum structure and that differ substantially from the final model used for interpretation visual assessment of these models often provides answers about existence of deeper structures differences between the models can be quantified into a depth of investigation doi index that can be displayed with the model used for interpretation an explicit algorithm for evaluating the doi is presented the doi curves are somewhat dependent upon the parameters used to generate the different models but the results are robust

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

seismoelectric and electroseismic responses to a point source in a marine stratified model abstract we investigate the seismoelectric electroseismic wavefields excited by a point source in an air seawater three layered porous medium configuration containing a hydrocarbon layer the results show that if an explosive source for excitation is used receivers at seafloor can record the coseismic electromagnetic fields accompanying the p s fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor employing a vertical electric dipole source shows that with the exception of the interface responses converted from electromagnetic waves at seafloor the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified given that the strength of the explosive source is within excitation capability of industry air guns the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal unless a much larger current is injected into seafloor

multicomponent high resolution seismic reflection profiling multicomponent seismic reflection methods are a new tool for oil and gas exploration and reservoir monitoring miles 1988 but such technologies have not yet been extensively exploited for near surface exploration related to hydrogeological and or geotechnical investigations with the advantage of relatively inexpensive recording systems for near surface applications we show that the use of multicomponent high resolution seismic reflection methods has great potential as a new means of observing and characterizing the physical parameters of the shallow subsurface and in particular of groundwater reservoirs

borehole electrokinetic responses in fracture dominated hydraulically conductive zones electrokinetic borehole logging experiments conducted in fracture dominated devonian metasediments and carboniferous limestone boreholes containing dissolu tion discontinuities indicate a strong relative amplitude correlation between a downhole electrokinetic response and previously obtained hydrogeological data for the respective boreholes voltages in the range 0 2 1 5 volt were recorded per mpa of gauge pressure induced in the borehole fluid a relationship between fracture aperture and the frequency content of the electrical data has also been observed

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

crosshole seismoelectric measurements in borehole models with fractures laboratory experiments are performed in crossborehole models with fractures to investigate seismoelectric conversions in the fractures using an electrode in a borehole we measure the electric field induced by an acoustic wave and we investigate the relationship between the electric signal and the fracture aperture using ultrasonic fracture borehole models the experimental results confirm that a radiating electromagnetic em wave is induced by a guide wave at a fracture between an acoustic source and electric receiver boreholes the position of a vertical or inclined fracture between two boreholes can be determined using the arrival times of the em wave and the formation velocity by placing the acoustic source at a different depth and recording electric signals with real or synthetic arrays of acoustic and electric receivers in the second borehole crosshole seismoelectric measurements might be a technique for investigating fractures between boreholes more directly than traditional acoustic measurements

phytoplankton blooms beneath the sea ice in the chukchi sea in the arctic ocean phytoplankton blooms on continental shelves are often limited by light availability and are therefore thought to be restricted to waters free of sea ice during july 2011 in the chukchi sea a large phytoplankton bloom was observed beneath fully consolidated pack ice and extended from the ice edge to 4100 km into the pack the bloom was composed primarily of diatoms with biomass reaching 1291 mg chlorophyll a m 2 and rates of carbon fixation as high as 3 7 g c m 2 d 1 although the sea ice where the bloom was observed was near 100 concentration and 0 8 1 2 m thick 30 40 of its surface was covered by melt ponds that transmitted 4 fold more light than adjacent areas of bare ice providing sufficient light for phytoplankton to bloom phytoplankton growth rates associated with the under ice bloom averaged 0 9 d 1

dependence of seismoelectric amplitudes on water content summary the expectation behind seismoelectric field measurements is to achieve a combination of the sensitivity of electrical properties to water content and permeability and the high spatial resolution of seismic surveys a better understanding of the physical processes and a reliable quantification of the conversion between seismic energy and electric energy are necessary and need to take into account the effect of water content especially for shallow subsurface investigations we performed a field survey to quantify the seismoelectric signals as the water content changed we measured seismoelectric signals induced by seismic wave propagation by repeating the observations on the same two profiles during several months the electrical resistivity was monitored to take into account the water content variations weshowthatthehorizontalcomponentoftheseismoelectricfield normalizedwithrespectto the horizontal component of the seismic acceleration is inversely proportional to the electrical resistivity 0 42 0 25 assuming that the observed resistivity changes depend only on the water content this result implies that the electrokinetic coefficient should increase with increasing water saturation taking into account the water saturation and combining our results with the archie law for the resistivity in non saturated conditions the normalized seismoelectric field is a power law of the effective saturation with the exponent 0 42 0 25 n where n is archie s saturation exponent

theoretical simulation of the multipole seismoelectric logging while drilling this erratum corrects a type error in the text of guan et al 2013 the continuity condition at the borehole wall of the electric field in the r direction er e o r which was given in the eighth line of the paragraph after eq 20 on p 1242 of guan et al 2013 should be that of the electric current density jr j o r the original results in guan et al 2013 are unchanged because they are calculated by using the correct continuity condition of jr j o r

anatomy of a seismoelectric conversion measurements and conceptual modeling in boreholes penetrating a sandy aquifer 1 conversions of compressional seismic waves to electric fields have been measured in two boreholes drilled in an unconfined sandy aquifer on the gnangara mound near perth australia the seismoelectric conversions at both field sites occurred in the vicinity of the water table at 13 m depth and yielded maximum amplitudes of 1 v m using a sledgehammer source on surface partially cemented layers inferred from geological and geophysical logs straddle the water table and may play a role in generating the conversion and influencing its amplitude distribution the dense vertical sampling used in these borehole experiments reveals spatial and temporal polarity reversals of the interfacial signal which provide new evidence in support of the conceptual model for seismoelectric conversions at interfaces we demonstrate that the growth rate of the source zone and its maximum vertical extent below the water table are encoded in the polarity of the interfacial signal these experiments confirm that vertical seismoelectric profiling can be used to gain further insight into seismoelectric conversions and characteristics of interfaces that makes them amenable to detection

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

evidence of the theoretically predicted seismo magnetic conversion summary seismo electromagnetic phenomena in porous media arise from seismic wave induced fluid motion in the pore space which perturbs the equilibrium of the electric double layer this paper describes with details the original experimental apparatus built within the ultra shielded chamber of the low noise underground laboratory of rustrel france we measured seismo magnetic conversions in moist sand using two induction magnetometers and a pneumatic seismic source to generate the seismic wave propagation we ensured to avoid the magnetometer vibrations which could induce strong disturbances from induction origin interpretation of the data is improved by an analytical description of phase velocities for fast pf and slow ps longitudinal modes transverse mode s as well as the extensional mode due to the cylindrical geometry of the sample the purpose of this paper is to provide elements to measure correctly coseismic seismomagnetic fields and to specify their amplitude the seismic arrivals recorded in the sample showing a 1200 1300 m s 1 velocity have been associated to p and extensional waves the measured seismo magnetic arrivals show a velocity of about 800 m s 1 close to the calculated phase velocity of s waves therefore we show that the seismo magnetic field is associated to the transverse part of the propagation as theoretically predicted by pride 1994 but never measured up to now moreover the combined experimental and analytical approaches lead us to the conclusion that the measured seismo magnetic field is probably about 0 035 nt for a 1 m s 2 seismic source acceleration 0 1 g

seismoelectric wave propagation numerical modelling in partially saturated materials to better understand and interpret seismoelectric measurements acquired over vadose environments both the existing theory and the wave propagation modelling programmes available for saturated materials should be extended to partial saturation conditions we propose here an extension of pride s equations aiming to take into account partially saturated materials in the case of a water air mixture this new set of equations was incorporated into an existing seismoelectric wave propagation modelling code originally designed for stratified saturated media this extension concerns both the mechanical part using a generalization of the biot gassmann theory and the electromagnetic part for which dielectric permittivity and electrical conductivity were expressed against water saturation the dynamic seismoelectric coupling was written as a function of the streaming potential coefficient which depends on saturation using four different relations derived from recent laboratory or theoretical studies in a second part this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half space subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response ir may be best recovered when the shallow layer exhibits low saturation we also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half space our first modelling results suggest that the study of the seismoelectric ir may help to detect a sharp saturation contrast better than a smooth saturation transition in our example a saturation contrast of 50 per cent between a fully saturated sand half space and a partially saturated shallow sand layer yields a stronger ir than a stepwise decrease in saturation

a laboratory seismoelectric measurement for the permafrost model with a frozen unfrozen interface 1 in this study a laboratory seismoelectric measurement for the permafrost model with a frozen unfrozen interface is presented the measurements obtained experimentally confirms that an electric double layer can be formed at the interface due to the electric and mechanical differences of the frozen and unfrozen media and seismoelectric conversion em waves originted from the relative motion of the charges in the electric double layer can be observed at n 10 khz frequency band this suggests a potential application for non destructive detection of the frost depth

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

geophysical applications of electrokinetic conversion in volume 1 of geophysics 1936 r r thompson of humble oil and refining company proposed that the coupling of seismic and electrical energy can be used as an exploration tool subsequent efforts were directed toward using electric field antennas as geophones small scale studies concluded that antennas are not as sensitive as conventional geophones and their response is highly variable depending on the local soil conditions by 1959 martner and sparks of pan american petroleum reported in geophysics a systematic study of seismoelectric coupling using explosives at various depths their results were the first to show that the conversion of seismic to electromagnetic energy at the water table could be detected using surface antennas no studies have systematically explored the full potential of electroseismic methods using the same level of experimental sophistication used in seismic exploration

using borehole electroseismic measurements to detect and characterize fractured permeable zones in 1996 we measured stoneley wave induced electrical fields in an uncased water well drilled in fractured granite and diorite near hamilton massachusetts stoneley waves generated by sledgehammer blows to the surface casing produced a flow of pore fluid in permeable zones intersected by the borehole in turn this flow induced a streaming electrical field even though these electrical signals were very small tens of microvolts we were able to detect them using electrodes placed in the borehole after power line and telluric signals were canceled by remote referencing and notch filtering amplitude analysis of the electrical fields confirmed that they were induced by fluid flow in the fractured formation the normalized amplitudes of these electrical fields correlate with the fracture density log and agree with the theoretical model for this electroseismic phenomenon our biot theory based model predicts that borehole electroseismic measurements can be used to characterize permeable zones according t

field tests of electroseismic hydrocarbon detection geophysicists looking for new exploration tools have studied the coupling between seismic and electromagnetic waves in the near surface since the 1930s our research explores the possibility that electromagnetic to seismic es conversion is useful at greater depths field tests of es conversion over gas sands and carbonate oil reservoirs succeeded in delineating known hydrocarbon accumulations from depths up to 1500 m this is the first observation of electromagnetic to seismic coupling from surface electrodes and geophones electrodes at the earth s surface generate electric fields at the target and digital accelerometers detect the returning seismic wave conversion at depth is confirmed with hydrophones placed in wells the gas sands yielded a linear es response as expected for electrokinetic energy conversion and in qualitative agreement with numerical simulations the carbonate oil reservoirs generate nonlinear conversions a qualitatively new observation and a new probe of rock properties the

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

the effect of possible taylor columns on the summer ice retreat in the chukchi sea the chukchi sea topography consists of a broad flat 50 m deep plain with two prominent shoals herald and hanna which have horizontal dimensions of about 100 km and rise to depths of about 30 m herald shoal in particular is a prominent isolated seamount which because of the warm water flux in summer through bering strait has a warm 0 1 m s 1 flow incident upon it examination of active and passive microwave imagery of the region for 1992 1994 shows that as the general ice cover recedes the ice remains preferentially over herald shoal for 3 4 weeks after the surrounding ice has melted a scale analysis suggests that the cause of the ice persistence is the formation of a taylor column over the shoal which traps cold water and ice above it a similar trapping of ice occurs over hanna shoal and on its eastern slope but the response is complicated by a very different topography and the northward flow down barrow canyon

summertime circulation in the eastern chukchi sea abstract the transport of pacific origin water across the eastern chukchi sea during summer is studied using shipboard hydrographic and acoustic doppler current profiler data from multiple surveys the study identifies two major transport pathways in this region the well known alaskan coastal current acc flows poleward along the alaska coast while a more recently discovered and slower current flows northward through the central channel between herald and hanna shoals the two currents separate past point hope and appear to merge again in barrow canyon via previously unresolved pathways flowing west to east across the chukchi sea the collective flow that transports pacific water from bering strait to barrow canyon is termed the bering to barrow current system bbcs the coastal branch of the bbcs which encompasses the acc is a weakly baroclinic flow with a maximum speed in excess of 80 cm s inside barrow canyon the central channel branch of the bbcs is considerably weaker with a maximum flow speed under 20 cm s a portion of the pacific water that flows towards herald canyon to the west may also contribute to the bbcs the amount but the amount is within the margin of error of our data the difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the bbcs summer water masses occupy most of the southern and central chukchi sea while winter water masses occupy hanna shoal and shelfbreak regions in the northern chukchi sea during summer the total bbcs volume transport in summer is measured at four different locations in the eastern chukchi sea and found to be generally consistent the overall mean transport is 0 86 sv compared to the summer bering strait transport of 1 08 sv this study suggests that the bbcs is the main transport pathway delivering pacific water masses into the western arctic basin