mixing between fresh and salt waters at aquifer regional scale and identification of transverse dispersivity summary in aquifers in which freshwater flows above saltwater a mixing layer develops between the two water bodies in a typical regional aquifer this mixing layer is thin compared to the length scale of the aquifer its modeling by available numerical codes is impractical due to the needed fine discretization here an approximate model of the mixing layer in steady state 3d flow is developed based on the boundary layer approach at first mixing is neglected and a sharp interface solution is derived subsequently the flow and mixing equations are rewritten in a curvilinear coordinates system attached to the sharp interface solution in line with the boundary layer approximation only transverse dispersion is considered a simplified solution for the mixing layer is obtained by assuming similarity and using von karman integral method the approach is demonstrated for yarkon taninim basin israel a karstic aquifer extending over 6000 km 2 the main aim of the research was to identify the regional scale transverse dispersivity for the aquifer the determined value was t 0 04 m this is an important finding as it is the first time the parameter is evaluated for an aquifer at regional scale

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

constant concentration boundary condition lessons from the hydrocoin variable density groundwater benchmark problem in a solute transport model if a constant concentration boundary condition is applied at a node in an active flow field a solute flux can occur by both advective and dispersive processes the potential for advective release is demonstrated by reexamining the hydrologic code intercomparison hydrocoin project case 5 problem which represents a salt dome overlain by a shallow groundwater system the resulting flow field includes significant salinity and fluid density variations several independent teams simulated this problem using finite difference or finite element numerical models we applied a method of characteristics model mocdense the previous numerical implementations by hydrocoin teams of a constant concentration boundary to represent salt release by lateral dispersion only as stipulated in the original problem definition was flawed because this boundary condition allows the release of salt into the flow field by both dispersion and advection when the constant concentration boundary is modified to allow salt release by dispersion only significantly less salt is released into the flow field the calculated brine distribution for case 5 depends very little on which numerical model is used as long as the selected model is solving the proper equations instead the accuracy of the solution depends strongly on the proper conceptualization of the problem including the detailed design of the constant concentration boundary condition the importance and sensitivity to the manner of specification of this boundary does not appear to have been recognized previously in the analysis of this problem

a correction factor to account for mixing in ghyben herzberg and critical pumping rate approximations of seawater intrusion in coastal aquifers 1 the classic ghyben herzberg estimate of the depth of the freshwater saltwater interface together with the dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems on the basis of these assumptions strack 1976 developed a single potential theory to calculate critical pumping rates in a coastal pumping scenario the sharp interface assumption and in particular this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers the sharp interface assumption neglects mixing and implicitly assumes that salt water remains static consequently this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply we investigate the error introduced by adopting the sharp interface approximation and we include the effects of dispersion on the formulation of strack 1976 to this end we perform numerical three dimensional variable density flow simulations we find that strack s equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor 1 t b 1 6 where t is transverse dispersivity and b is aquifer thickness we find that this factor can be used not only to estimate the critical pumping rate but also to correct the ghyben herzberg estimate of the interface depth its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

a hemispheric circulation asymmetry during late tertiar recent data obtained within the deep sea drilling project legs 28 29 35 36 in the southern oceans revealed that the formation of antarctic sea ice started 38 m y b p ago at the begin of the oligocene the antarctic ice cap reached nearly its present volume during the middle miocene 14 12 m y b p and a volume greater than the present during the messinian 6 5 m y b p apart from local mountain glaciations the first large scale glaciation of the northern continents was developed about 3 m y b p followed by the formation of the arctic sea ice which has probably survived more than 20 fully developed interglacials certainly during the last 0 7 m y this evolution indicates a period of about 10 m y during which east antarctica was highly glaciated while the arctic ocean was essentially ice free this asymmetric pattern is compared with the present asymmetry unipolar versus bipolar glaciation the annually averaged position of the meteorological equator had then displaced from about lat 6 n to day to about 10 n some estimates of the heat budget terms in polar latitudes at a glaciated continent and at an ice covered ocean are given a preliminary review of paleoclimatic data reveals significant shifts of the position of the climatic belts at both hemispheres these shifts coincide rather well with an extrapolation of the actual seasonal variations which confirm a simple equation for the latitude of the subtropical anticyclonic belts as the boundary between ferrel and hadley regimes finally the role of equatorial upwelling as correlated with an asymmetric circulation pattern for the water balance is outlined these asymmetries may become of major importance if an expected rise of co2 level above an estimated threshold should restore an ice free arctic ocean

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

transient dupuit interface flow with partially penetrating features a comprehensive potential is presented for dupuit interface flow in coastal aquifers where both the fresh water and salt water are moving the resulting potential flow problem may be solved for incompressible confined aquifers using analytic functions the vertical velocity of the interface may then be computed analytically and the change of the position of the interface may be simulated by numerical integration through time starting with a known or estimated initial position the upconing of the interface below a partially penetrating ditch or well may be studied if dupuit solutions for such features are available a new dupuit solution is derived for a ditch that penetrates the aquifer partially from above a dupuit solution for a partially penetrating well may be obtained following a similar derivation the new dupuit solution is combined with the interface solution to simulate the upconing of an initially horizontal interface below a series of partially penetrating ditches the interface converges to the known steady state position

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

marine cobalt resources ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts ocean ridges and other raised areas of the ocean the cobaltrich crusts may be the slowest growing of any earth material accumulating one molecular layer every 1 to 3 months attention has been drawn to crusts as potential resources because they contain cobalt manganese and platinum three of the four priority strategic metals for the united states moreover unlike abyssal nodules whose recovery is complicated by their dominant location in international waters some of the most cobalt rich crusts occur within the exclusive economic zone of the united states and other nations environmental impact statements for crust exploitation are under current development by the department of the interior

flux and grain size variation of eolian dust as a proxy tool for the paleo position of the intertropical convergence zone in the northeast pacific abstract a 328 cm long piston core kodos 02 01 02 collected from the northeast equatorial pacific at 16 12 n 125 59 w was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo position of the intertropical convergence zone itcz the eolian mass fluxes of the lower interval below 250 cm 15 5 7 6 ma are very uniform at 5 1 mg cm2 103 yr while those of the upper interval above 250 cm from 7 6 ma are over 2 times higher than the lower interval at 12 1 mg cm2 103 yr the median grain size of the eolian dusts in the lower interval increases from 8 4 to 8 0 downward while that of the upper interval varies in a narrow range from 8 8 to 8 6 the determined values compare well in magnitude to those of central pacific sediments for the upper interval and equatorial and southeast pacific sediments for the lower interval this result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the itcz and subsequently of the northeast trade winds for a later period when the upper sediments were deposited this interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to central south america for the lower interval and to asia for the upper interval this study suggests that the distinct differences in eolian mass flux and grain size observed across the itcz can be used to trace the paleo latitude of the itcz

convection in groundwater below an evaporating salt lake 2 evolution of fingers or plumes the downward convection of salt fingers or plumes developed from the unstable boundary layer of an evaporating dry salt lake is examined using a numerical model and hele shaw cell experiments in the convecting layer the early small waves evolve into fingerlike or plumelike formations the number of fingers or plumes decreasing with time owing to differential growth and or coalescence comparison of intermediate formational stages of this pattern with the pattern generated by a two dimensional numerical simulation shows good qualitative agreement however there is a significant mismatch of the growth rates at long times in the computer simulation the plume length develops approximately twice as rapidly as it does in the experimental case a simple numerical experiment independent of the salt lake boundary conditions is compared to previously published laboratory scale measures of plume development in hele shaw cells which confirms the retardation of hele shaw plumes by a factor of approximately 50 this departure is attributed to the differences in dimensionality between the hele shaw flow domain and the model domain the data indicated that leading plumes develop isolated behavior at long times and may not be adequately represented in hele shaw analog models and numerical simulation provides a more accurate simulation of field scale behavior

correlation of co concentration and growth rate a method for age determination of ferromanganese crusts abstract based on the analysis and comparison of metal content and growth rate determination by the 10be method an empirical law has been developed to calculate the growth rate evaluating after 520 chemical analyses we have shown that the flux of co into ferromanganese seamount crusts has been constant over the entire growth period of all crusts investigated the amount of co supplied per unit of time and seabottom area is nearly constant in the oceanic water column the layered texture of ferromanganese crusts reflects the change of phases and hydrogenetically precipitated amounts as well as their different growth rates the most important indicator revealing the growth rate is the co enrichment of each crust layer the higher the growth rate the lower the co concentration therefore it is possible to recalculate the age and growth rate of each ferromanganese crust layer by g mm ma 1 1 28 co 0 24 based on the intense phosphorite impregnation of the lower part of the ferromanganese crust which has grown within the time period 18 12 ma so called older crust two additional effects have to be taken into account a the intense phosphorite impregnation causing dilution and b the chemical dissolution of the ferromanganese crusts caused by the phosphate rich pore water both reduce the co concentration and the relating co contents co x and co x have thus to be compensated a co x co x m mn co x mn co b b co x co x 1 0 05 p 1 where co x double corrected co concentration of the layer x of the older crust generation co x corrected co concentration of the layer x of the older crust generation concerning the phosphate dilution co x m measured co concentration of the layer x of the older crust generation mn co x mn co ratio measured of the layer x of the older crust generation mn co b mn co ratio measured of the boundary layer between younger and older crust generation and p difference between the apatite fraction of the older crust of the layer x and the average value of the younger crust generation this simple cobalt calculation model makes it possible to recalculate the growth rate and age of each simple layer of ferromanganese crusts

interelement relationships in ferromanganese crusts from the central pacific ocean their implications for crust genesis the fine scale chemical variations in ferromanganese fe mn crusts from the central pacific ocean were investigated using a variety of techniques in order to elucidate their genesis thirty seven major minor and trace elements were determined by icp oes and icp ms in sub samples collected at approximately 2 mm intervals throughout the crust sequences an inverse relationship is observed between the logarithm of the elemental distribution coefficients log cmncsw and the mean residence time tr of elements in seawater these associations provide evidence supporting the strong link between seawater and fe mn crust chemistry results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elements displaying associations with several groups these statistical associations are interpreted to represent hydrogenetic mn ni co cu ce zn biogenic ba zn cu pt fe detrital al si fe and carbonate fluorapatite ca p ree groups a comparison between elemental associations in fine scale data from individual crust sequences and bulk compositional data from samples collected in separate locations reveals very similar elemental associations the similar elemental associations in bulk samples and in fine scale subsamples from individual crusts are consistent with the notions that hydrogenetic crusts exhibit no significant post depositional remobilization of elements and that elemental distributions within crusts reflect the chemistry of oceanic water during the period in which they accreted chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts our results show that there is internal consistency between the chemical evolution previously proposed seamount paleotracks and nanofossil biostratigraphy dating results

age determinations and growth rates of pacific ferromanganese deposits using strontium isotopes abstract 87 sr 86 sr ratios trace element and ree compositions and textural characteristics were determined for three hydrogenetic fe mn crusts one hydrothermal deposit and two mixed hydrothermalhydrogenetic crusts from the pacific the sr isotope data are compared to the sr seawater curve for the cenozoic to determine the ages and growth rates of the crusts the 87 sr 86 sr in the crusts does not increase monotonically with depth as expected if the sr were solely derived from seawater and perfectly preserved since deposition this indicates post depositional exchange of sr or heterogeneous sources for the sr originally contained in the crusts textures of hydrogenetic crusts generally correlate with sr isotopic variations the highest porosity intervals commonly exhibit the highest 87 sr 86 sr ratios indicating exchange with younger seawater intervals with the lowest porosity commonly have lower 87 sr 86 sr and may preserve the original sr isotopic ratios minimum ages of crust growth inception were calculated from dense low porosity intervals growth of the hydrogenetic crusts began at or after 23 ma although their substrates are cretaceous estimated average growth rates of the three hydrogenetic crusts vary between 0 9 and 2 7 mm ma consistent with published rates determined by other techniques within the marshall islands crust growth rates for individual layers varied greatly between 1 0 and 5 4 mm ma for one crust very low 87 sr 86 sr ratios occurred in detrital rich intervals hydrothermal fe mn oxide from the active lau basin back arc spreading axis valu fa ridge has an 87 sr 86 sr ratio with a predominantly seawater signature 87 sr 86 sr 0 709196 indicating a maximum age of 0 9 ma one crust from an off axis seamount west of gorda ridge may have begun precipitating hydrogenetically at 0 5 ma 0 709211 and had increasing hydrothermal or volcanic input in the top half of the crust indicated by a significantly lower 87 sr 86 sr ratio 0 709052

a dupuit formulation for modeling seawater intrusion in regional aquifer systems 1 a new formulation is presented for the modeling of seawater intrusion in coastal multiaquifer systems the formulation is intended for the simulation of three dimensional regional seawater intrusion starting from a specified salinity distribution the dupuit approximation is adopted and diffusion and dispersion are not taken into account the formulation is based on a vertical discretization of the groundwater into zones of either constant density stratified flow or continuously varying density piecewise linear in the vertical direction the zones are separated from each other by curved surfaces representing interfaces for stratified flow and isosurfaces of the density for variable density flow during a simulation both the change of the elevations of the surfaces and the change in head are computed through consistent application of continuity of flow a simple tip and toe tracking algorithm is applied to simulate the horizontal movement of the surfaces the resulting differential equations are equivalent in form to the differential equation for single density flow the density effects are incorporated through the addition of pseudosource terms this makes it easy to implement the formulation in existing numerical groundwater codes the main advantage of the formulation is the tremendous reduction of the number of cells needed for a simulation because every aquifer may be represented by a single layer of cells the accuracy of the formulation is demonstrated through comparison with existing exact solutions and a numerical solution

modeling of seawater intrusion in a coastal aquifer of karaburun peninsula western turkey seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater this study presents the development of a conceptual and numerical model for the coastal aquifer of karareis region karaburun peninsula in the western part of turkey the study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers the seawat model is used in this study to solve the density dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months the model was calibrated using the average values of a 1 year dataset and further verified by the average values of another year five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years the result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area as a result of the numerical model seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under increased pumping scenario while a slight change in water level and tds concentrations was observed in climate change scenario results also revealed that a reduction in the pumping rate from karareis wells will be necessary to protect fresh groundwater from contamination by seawater

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

effects of phosphatization on the geochemical and mineralogical composition of marine ferromanganese crusts most hydrogenetic ferromanganese crusts in the central pacific consist of two growth generations a phosphatized older growth generation that is impregnated with carbonate fluorapatite cfa and a younger non phosphatized growth generation geochemical and mineralogical investigations of non phosphatized and phosphatized crust layers revealed significant differences that are not simply dilution effects by cfa certain elements are depleted in old crusts compared to young crusts in the order si fe al ti co mn pb others like ni zn cu y and rees rare earth elements are mostly enriched suboxic conditions in the phosphate rich water of the oxygen minimum zone that infiltrated the crusts caused a partial redissolution of crust phases resulting in mobilization of associated elements a partial recrystallization of more stable phases and a secondary input of nutrient type elements the frequent occurrence of todorokite in phosphatized crust layers indicates that mn mobilized from the vernadite crust phase was partially recrystallized as todorokite which is more stable under suboxic conditions incorporating ni cu and zn into the crystal lattice but rejecting co other metals like pb y and rees probably form stable phosphate phases in phosphatized crusts our investigations emphasize that under the influence of phosphatization diagenetic remobilization and reorganization in fe mn crusts took place in contrast to non phosphatized crusts the older phosphatized crust generation no longer represents a complete primary crust precipitate therefore young non phosphatized and old phosphatized crust generations should be considered as two different sample types with respect to geochemical composition mineralogy and evolution we also suggest that most methods for age determination like the 87sr86sr isotopic dating method or co chronometry cannot be used for phosphatized crusts without caution

understanding and modelling spatial drain aquifer interactions in a low lying coastal aquifer the thurne catchment norfolk uk seawater intrusion into fresh groundwater formations generally results inadvertently from human activities such as over abstraction from coastal aquifers this article describes the data analysis to quantify drain aquifer interactions in a low lying pump drained coastal aquifer which is subject to saline intrusion due to widespread land drainage and the resulting development and application of a numerical groundwater model to understand the spatial groundwater system behaviour including groundwater salinity fluxes without measured flow data in this pump drained catchment a novel groundwater head dependent approach to hydrograph separation is described time variant and time invariant modflow analyses are utilised to examine the flow processes a new approach to calculate drain coefficients which represent the extensive network of drainage ditches in the regional model using field information is described the sum of the drainage coefficients are close to the values independently estimated from the head dependent hydrograph separation results show that 1 the groundwater flows into the drainage systems are well reproduced using the new drain coefficients 2 particle tracking of fresh and saline water can explain observed spatial salinity distribution within drainage networks and 3 the modelled flow of seawater across the coast is approximately 25 greater than that discharged by the pumps demonstrating the need for drainage management to be aware of the slow response of groundwater systems to past drainage system changes the article demonstrates that numerical groundwater modelling can produce the improved understanding needed to inform management decisions in such complex environments copyright 2010 john wiley sons ltd

three dimensional streamlines in dupuit forchheimer models an approximate method is presented for determining streamlines in three dimensions using two dimensional dupuit forchheimer models the latter models of horizontal flow which may comprise several aquifers are based on the assumption that the resistance to flow in the vertical direction is neglected this assumption does not preclude the occurrence of flow in the vertical direction vertical components of flow are determined in an approximate fashion by requiring continuity of flow the problem of leakage from a shallow pond above an unconfined aquifer is discussed as an example of determining streamlines in three dimensions the errors induced by the approximation are determined for a few idealized flow problems that can be solved exactly

the geometric relationship between hot spots and seamounts implications for pacific hot spots abstract hot spots and the seamounts produced by them provide both geometric and temporal evidence for changes in absolute plate motion the main limitation in using hot spot produced seamounts in plate tectonic reconstructions arises from the multiple sources of error and ambiguity that plague radiometric age estimates in particular unless the hot spot has maintained a steady and voluminous flux rate over long periods of time the exact location of a hot spot which represents the zero age origin along the hot spot trail is poorly known here we discuss a unique geometric relationship between a hot spot and the seamounts produced by it that we recently have discovered i e hot spot produced seamounts have seafloor crustal flow lines that intersect at the hot spot location furthermore we obtain images of cumulative volcano amplitudes cva by convolving seamount shapes with their flow lines hot spots correspond to clear local maxima in this image and the amplitudes are proportional to cumulative hot spot flux this technique dubbed hot spotting allows us to determine hot spot locations based only on a set of seamount locations no age information is required we use the hot spotting technique to examine the pacific plate hot spots in general and the bowie and cobb hot spots in the gulf of alaska in particular we find that the hawaii louisville caroline cobb and bowie hot spots have clear representations in the cva images rurutu and or rarotonga are close to a large cva high while the other french polynesian hot spots in general exhibit a much more subdued and blurred expression we also conclude that the cobb hot spot plume may have been entrained by the juan de fuca ridge about 2 ma ago or alternatively is in a waning phase and cannot penetrate juan de fuca plate lithosphere the bowie hot spot appears to have encountered the ridge more recently

reconciling the intertropical convergence zone himalayan tibetan tectonics and the onset of the asian monsoon system abstract numerous climate proxies from across central south and east asia have yielded different ages for the start or intensification of a monsoon climate system common estimates include the early part of the early miocene 23 20 ma and the late miocene 11 8 ma in the early miocene the average position of the intertropical convergence zone itcz was likely to be the 2000 km closer to the himalaya than at present based on published data for the palaeolatitude of the central pacific itcz such that himalayan climate was marked by high precipitation but not necessarily seasonality here we propose that increased seasonality in the late miocene in the himalaya and neighbouring regions was a response to an increase in the distance between the itcz and the himalaya tibet such that the itcz was only brought northwards during the northern hemisphere summer each year this is essentially the pattern of the modern south asian monsoon system these climatic changes coincide with a switch from north south extensional shear on the northern side of the high himalaya thrusting on the main central thrust and rapid metamorphic exhumation to thrusts further south in the himalaya main boundary thrust and a reduction in high himalayan exhumation rates we speculate that the tectonic changes were at least in part a response to a reduction in precipitation over the high himalaya the himalayan thrust belt re organised to maintain a critical taper appropriate to a drier orogen the reduction in metamorphic exhumation after the early miocene would also have led to a reduction in the flux of metamorphic co2 to the atmosphere thereby promoting the global shift to a cooler climate in the mid miocene

stream functions and equivalent freshwater heads for modeling regional flow of variable density groundwater 1 review of theory and verification steady state flow of variable density groundwater is simulated using equivalent freshwater heads and stream functions on the basis of the work by de josselin de jong 1960 1969 fluids with different fluid densities are replaced by one hypothetical fluid and singularities are introduced along interfaces where the actual fluids change densities the basic flow equation describing variable density flow written in terms of equivalent freshwater head is used to derive the corresponding stream function equation and associated boundary conditions neumann boundary conditions for the stream function equation can be determined from gradients of equivalent freshwater heads along the boundary stream functions provide a direct representation of the groundwater flow pattern and flow rates where fluid densities vary in space in comparison equivalent freshwater heads and fluid densities describe the two driving forces hydraulic gradient and buoyancy force but head gradients do not necessarily describe the flow direction of variable density groundwater in isotropic media comparison of the finite element formulations indicates that potential errors in the centroid consistent velocity calculation based on the stream function solution can be expected to be smaller than those in the velocity calculation based on the head solution for cross sectional flow models because discretization in the vertical direction is typically finer than in the horizontal direction

vertical average for modeling seawater intrusion 1 seawater intrusion in coastal aquifers is a 3 d phenomenon however 3 d regional aquifer models are often limited by insufficient geological and hydrological data the large horizontal to vertical scales ratio and by numerical constraints we present an effective formulation for modeling seawater intrusion that relies on a dimensional reduction of the original density dependent flow and transport problem we carry out a vertical integration of the 3 d problem and arrive at a coupled set of 2 d equations for the mean flux and salt concentration which are essentially identical to those of 2 d groundwater flow however two new terms emerge from the integration 1 darcy s law needs not only the buoyancy term reflecting aquifer bottom slope but also another one reflecting variability of aquifer thickness and 2 transport requires a new term reflecting vertical variations of groundwater flux which are essential for density dependent flow and we approximate by means of a fickian dispersion term the proposed equations are verified by direct steady state numerical simulations of confined aquifers the results show that the effective formulation correctly reflects the effective dynamics in the 3 d system

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

sr and nd isotopic variations in ferromanganese crusts from the central pacific implications for age and source provenance abstract isotopic analyses of two hydrogenetic ferromanganese fe mn crusts from volcanic edifices in the central pacific ocean reveal systematic variations in 87 sr 86 sr and 143 nd 144 nd with both ratios decreasing as a function of depth into the fe mn crusts leaching experiments suggest that sr in the crusts is contained in at least two discrete sites a loosely bound sr dominated by modern marine sr is removed by leaching with a 10 percent acetic acid solution the 87 sr 86 sr ratio of the residue is significantly less than the 87 sr 86 sr ratio of the unleached material the sr isotope ratios of leached samples are compared with the temporal variation in seawater to provide ages for layers within the fe mn crusts these data suggest that the oldest crust layers began to accrete in the early to middle miocene correlated to the 87 sr 86 sr variations 143 nd 144 nd ratios suggest that the nd isotope composition of central pacific ocean seawater also changed systematically over this time interval or that the fe mn crusts simply incorporated nd from various parts of an isotopieally heterogeneous ocean as the crusts were carried along with the oceanic plate in contrast to the layered ferromanganese crust the phosphatized volcaniclastic substrates have sr and nd isotope compositions that are consistent with their volcanic origin

cenozoic history of phosphogenesis recorded in the ferromanganese crusts of central and western pacific seamounts implications for deepwater circulation and phosphorus budgets abstract ages of seamount phosphatization episodes have been revised for 14 mid plate seamounts in the western and central pacific using the most up to date marine sr isotope curve and 87 sr 86 sr data from the literature the new ages provide a composite geologic history of phosphatization consistent with cenozoic climate history phosphatization on mid pacific seamounts took place only between 36 and 12 ma and it peaked at the eocene oligocene e o transition 34 ma the unprecedented appearance of prominent amounts of phosphorites at the e o transition and frequent recurrences of it afterwards suggests that a new mechanism came into play at that time namely the intensification of the advective flow of bottom water which accelerated the phosphorus cycle in contrast the absence of phosphorites younger than 12 ma suggests another fundamental change in process associated with the shift to a dry and cold climate that probably resulted in a decrease in the riverine input of labile phosphorus the drastic decrease in the frequency of hiatuses in ocean floor depositional records also indicates weakened bottom currents as a possible explanation for the absence of seamount phosphorite since 12 ma a phosphorus flux is a critical variable in modeling the response of the earth system to climate forcing in the geologic past thus the changes in phosphorus flux across the e o boundary and around 12 ma justify further study

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

electron microscopy study on the formation of ferromanganese crusts western pacific magellan seamounts abstract variations in mineralogy and chemical composition layer structures redox states of fe and mn and microbial diversity are closely linked to the biogeochemical process when a ferromanganese crust layer forms a sample collected from the magellan seamount osm11 in the western pacific was characterized in five well defined layers top to bottom l1 5 fe vernadite occurs in all layers compared to detritus quartz feldspar goethite and hematite in l1 and l3 and carbonate fluorapatite cfa in l4 5 the relatively high concentrations of ca and p in l4 5 and fe co and si in l1 and l3 correspond to the mineralogical variations in the crust layer disappearance of elongated voids along the convex growth line is likely due to void filling precipitation of cfa in l4 5 resulting in the void reduction 31 6 to 6 0 the oxidation states of fe in fe vernadite measured by electron energy loss spectroscopy eels ranges from 36 to 63 of fe3 fetot and a layer where cfa appeared l4 contains a more reductive form of fe fe3 fetot 36 48 presence of fe coxc and mn oxidizing gene cuma particularly displaying a strong pcr band of coxc in l2 3 indicates a dominant oxidizing condition direct evidence of microbial activity in fe and mn oxide precipitation with various redox conditions was identified in the focused ion beam sectioned microfossil particularly a spectrum image displaying a more reducing form of fe around the voids previously occupied by microorganisms strongly supports that microorganisms play an important role in the redox reaction in the growth of a crust

on the maas problem of seawater intrusion combated by infiltration summary the problem of maas maas k 2007 influence of climate change on a ghijben herzberg lens j hydrol 347 223 228 for infiltration inflow into a porous flat roofed fresh water lens floating on the interface of an ascending darcian saline water flow is shown to be in exact match with the polubarinova kochina polubarinova kochina p ya 1977 theory of ground water movement nauka moscow in russian problem for flow in a lens capped by a cambered phreatic surface with a uniform accretion the maas complex potential in the domain of a heavy saline water seeping beneath the lens corresponds to one of an ideal fluid flow past an elliptical cylinder that makes possible conversion of this potential into ascending descending seepage flows with floating but stagnant dnapl lnapl volumes similar matching is possible for the velocity potential of an axisymmetric flow past an ellipsoid and hydrostatic pressure of a stagnant napl body stored in a semi ellipsoidal pond

mineralogical and geochemical compositions of the eolian dust from the northeast equatorial pacific and their implications on paleolocation of the intertropical convergence zone 1 eolian components of a 328 cm long piston core collected from the northeast equatorial pacific at 16 12 n and 125 59 w were investigated for mineral and geochemical compositions in order to constrain the sources of dust and determine the latitudinal position of the intertropical convergence zone itcz recorded in the core the eolian components below 250 cm are characterized by smectite and phillipsite rich mineral composition depleted rare earth elements rees and high eu sm ratios indicative of volcanic rich composition these characteristics are found in equatorial and south pacific surface sediments of which eolian particles are supplied from central and south america in contrast eolian components above 250 cm are characterized by quartz and illite rich mineralogy and more shale like ree and trace element compositions which are common in surface sediments of the central pacific north of the itcz where eolian particles are sourced from the asia and north america the observed changes are attributed to the shifting of its eolian sources from the central and south america to the china and north america across the hemispheric dust barrier of the itcz this result suggests that smectite illite transition a phenomenon that smectite amount increases over illite at a depth can be used as a tracking tool for the paleolocation of the itcz in the northeast and central pacific backtrack path construction of pacific plate indicates paleolocation of the itcz north of 12 n 2 prior to late miocene

seasonal migration of itcz precipitation across the equator why can t gcms simulate it 1 the secondary meridional circulation induced by convective momentum transport cmt within the ascending branch of the hadley circulation is a missing dynamical mechanism that can cause common failure of general circulation models gcms in simulating seasonal migration of the intertropical convergence zone itcz precipitation maximum across the equator this failure is manifested by the model bias that the precipitation peak remains north of the equator during november march the cmt induced secondary circulation characterized by strong downward motion along the equatorial belt and upward motion south and north of the belt tends to modify the meridional distribution of precipitation with the strongest impacts during boreal winter and spring a 20 year gcm simulation with the cmt parameterization successfully reproduces the observed seasonal migration of the itcz precipitation across the equator with the peaks near 8 n during boreal summer and near 8 s during boreal winter

cenozoic mass accumulation rates in the equatorial pacific based on high resolution mineralogy of ocean drilling program leg 199 1 we use continuous mineralogy logs derived from multisensor track physical properties data and reflectance spectroscopy to calculate high resolution carbonate opal and terrigenous mass accumulation rates mar for the eight sites cored during ocean drilling program leg 199 in the equatorial pacific the largest change in equatorial pacific sedimentation patterns of the last 55 myr occurs at the greenhouse icehouse transition shortly after the eocene oligocene boundary calcite compensation depth deepened dramatically the equatorial zone of opal accumulation narrowed and the intertropical convergence zone shifted to the equator during the paleogene the opal equatorial accumulation bulge extended to about 12 n whereas the neogene bulge extended only to about 7 n very low eocene carbonate mar was followed by much higher oligocene and early miocene mar with the carbonate equatorial bulge extending to 4 n terrigenous mars indicate the paleoposition of the intertropical convergence zone and a pliocene pleistocene increase in asian dust flux

an anthropogenic origin of the sirente crater abruzzi italy in this paper we review the recent hypothesis based mostly on geomorphological features that a 130 m wide sag pond surrounded by a saddle shaped rim from the sirente plain abruzzi italy is the first discovered meteoritic crater of italy sub circular depressions hosting ponds with geomorphological features and size very similar to those exhibited by the main sirente sag are exposed in other neighboring intermountain karstic plains from abruzzi we have sampled present day soils from these sag ponds and from the sirente sags both the main crater and some smaller ones recently interpreted as a crater field and various abruzzi paleosols from excavated trenches with an age range encompassing the estimated age of the sirente crater for all samples we measured the magnetic susceptibility and determined the ni and cr contents of selected specimens the results show that the magnetic susceptibility values and the geochemical composition are similar for all samples from sirente and other abruzzi sags and are both significantly different from the values reported for soils contaminated by meteoritic dust no solid evidence pointing at an impact origin exists besides the circular shape and rim of the main sag the available observations and data suggest that the sirente crater together with analogous large sags in the abruzzi intermountain plains have to be attributed to the historical phenomenon of transumanza seasonal migration of sheep and shepherds a custom that for centuries characterized the basic social economical system of the abruzzi region such sags were excavated to provide water for millions of sheep which spent summers in the abruzzi karstic high pasture lands on carbonatic massifs deprived of natural superficial fresh water conversely the distribution of the smaller sags from the sirente plain correlates with the local pattern of the calcareous bedrock and together with the characteristics of their internal structure are best interpreted as natural dolines in fact reported radiocarbon ages for the formation of the main sag pond and of the smaller sags differ significantly by more than two millennia thus excluding that they were all contemporaneously formed by a meteoritic impact

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

element supply to surface manganese nodules along the aitutaki jarvis transect south pacific supply of metals to manganese nodules in the south equatorial pacific is heavily dependent on variations in biological productivity in the northern part of the aitutaki jarvis transect under high biological productivity in the surface waters there is a high flux of mn ni cu and zn to the nodules diagenetically cycled through the interstitial waters of the uppermost sediments together in the nodules with the formation of 10a manganite to the south of the high productivity zone these elements decrease in the nodules at the expense of fe co and pb of hydrogenetic provenance and mno2 is more abundant however nodule compositions also reflect the position of the deposits relative to the carbonate compensation depth ccd which deepens northwards throughout the region with mn ni cu and zn being enriched in 10a manganite bearing nodules from near the ccd under high productivity waters and fe co and pb being more abundant in x ray amorphous or mno2 bearing nodules away from the ccd and or in the south of the transect under low productivity waters

a multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems model development and application a quasi three dimensional finite difference model that simulates freshwater and saltwater flow separated by a sharp interface has been developed to study layered coastal aquifer systems the model allows for regional simulation of coastal groundwater conditions including the effects of saltwater dynamics on the freshwater system vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer leakage through confining layers is calculated by darcy s law accounting for density differences across the layer the locations of the interface tip and toe within grid blocks are tracked by linearly extrapolating the position of the interface the model has been verified using available analytical solutions and experimental results application of the model to the soquel aptos basin santa cruz county california illustrates the use of the quasi three dimensional sharp interface approach for the examination of freshwater saltwater dynamics in regional systems simulation suggests that the interface today is still responding to long term pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions

formation of ferromanganese crusts on northwest intertropical pacific seamounts electron photomicrography and microprobe chemistry abstract seven ferromanganese crusts from the northwest intertropical pacific seamounts were analyzed for photomicroscopic growth structures microprobe chemistry and ages based on co chronometer growth rate the crusts on the marshall islands seamounts are thick and are divided into phosphatized lower older and nonphosphatized upper younger growth generations the older crust consists of compact laminations and columns impregnated with carbonate fluoapatite cfa whereas the younger crust is characterized by porous botryoids and columns of mno2 and fe oxyhydroxide the crusts on the federated states of micronesia fsm and palau islands seamounts are thin and are often incorporated with inorganic opal a in the uppermost part comprising the younger generation some crusts show scours and fractures although the growth of crusts has been often interrupted by mass failure of slope sediments the crusts on the marshall islands seamounts are estimated to have grown at rate of about 3 mm ma since the middle eocene and to have been phosphatized in the late oligocene during the host seamounts were located beneath the equatorial zone of high productivity prolonged infiltration of the oxygen minimum zone omz water into shallower water older crusts redistributed crust composition by precipitating cfa enriching subsequent amounts of mn and ni and removing some co the younger crust has formed at slower rate about 2 mm ma under the stronger influence of bottom water circulation in the north of the equatorial zone concentrating abundant co in the uppermost part of some crusts siliceous skeletons transform with burial to inorganic opal a and si rich fe oxyhydroxide suggesting that biosilica diagenesis can enhance crust growth

cenozoic accumulation history of a pacific ferromanganese crust to investigate the growth rates and absolute time stratigraphy of marine hydrogenetic ferromanganese encrustations we performed 10be profiling and co chronometry of crustal layers as well as 87sr86sr and 18o analysis of phosphatised limestone francolite within a 9 5 cm thick ferromanganese crust from schumann seamount in the hawaiian archipelago together with microfossil stratigraphy our results indicate that some seamount crusts greatly exceed the commonly accepted miocene maximum age in this case probably approaching the cretaceous age of the seamount in addition to the unconformity at the crust substrate boundary at least eight major disconformities are indicated in the schumann seamount crust which probably represent depositional hiatuses or episodes of crust erosion three of the six upper disconformities can be placed at the plio pleistocene middle miocene and paleocene eocene based on 10be microfossil and co chronometer evidence 87sr86sr and 18o values of purified francolite from an inclusion rich layer between the depths of 44 and 49 mm suggest apparent ages that approach those of eocene late paleocene microfossils reported in overlying layers whereas francolite vein infillings in the lower part of the crust and in the basaltic substrate yield values that if interpreted as ages of phosphatization suggest a minimum oligocene age paleotracking suggests the phosphogenesis observed here and on other central pacific seamounts could not have resulted from upwelling enhanced productivity associated with equatorial divergence if the oligocene and middle miocene isotopic ages reported here and elsewhere are correct however a maximum late paleocene age for the phosphogenesis consistent with the stratigraphy would place these seamounts within 10 n of the equator paleotracking also suggests northeast tradewind transport of aluminosilicates in the cenozoic in agreement with other evidence for the antiquity of this ferromanganese crust

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

an evaluation of strontium isotopic dating of ferromanganese oxides in a marine hydrogenous ferromanganese crust abstract in order to assess the utility of dating marine hydrogenous ferromanganese crusts with strontium isotopes we conducted a series of leaching experiments on samples selected from several stratigraphic layers of a well preserved 9 5 cm thick crust from the pacific ocean initially using a method similar to that of previous studies acetic acid leached residues of twelve subsamples were leached with hcl and the leachates analyzed for their isotopic composition the results did not make stratigraphic sense so we carried out two sequences of more detailed leaches on subsamples from four layers representing the chemical and textural spectrum observed in the crust in one sequence mineral specific leaches were selected for optimal extraction of strontium associated with the respective manganese and iron oxide phases the main compositional endmembers within ferromanganese crusts strontium isotopic ratios for these leaches were compared with those from the other sequence involving acetic acid plus hcl leaches on the same material residues remaining at the end of each leaching sequence were also analyzed it is evident from the results that hcl extracts strontium associated with both phosphatic material and aluminosilicate detritus present within the ferromanganese layers 87 sr 86 sr ratios obtained on the manganese oxides indicate that the strontium within the oxides exchanges with seawater strontium throughout the history of the deposit regardless of the porosity of the layer assuming that this crust is representative of other marine hydrogenous crusts strontium isotopes appear to be of little value for the direct dating of ferromanganese oxide deposits

southward shift of the intertropical convergence zone in the western pacific during the late tertiary evidence from ferromanganese crusts on seamounts west of the marshall islands 1 hydrogenetic ferromanganese crusts were dredged from four seamounts in the western pacific osm7 osm2 lomilik and lemkein aligned in a nw se direction parallel to pacific plate movement the crusts consist of four well defined layers with distinct textural and geochemical properties the topmost layer 1 is relatively enriched in mn co ni and mo compared to the underlying layer 2 which is relatively enriched in al ti k and rb and cu zn and excess ba textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux such conditions are met in the equatorial pacific i e between the intertropical convergence zone itcz and equatorial high productivity zone layer 2 likely formed when each seamount was beneath the equatorial pacific along its back track path on the other hand layer 1 probably started to grow after seamounts moved northwest from the itcz this interpretation is consistent with the thickness of layer 1 across the four crusts which increases to the northwest ages of the layer 1 layer 2 boundary in each crust a potential proxy for northern margin of the itcz also increase to the northwest at 17 11 8 and 5 ma for osm7 osm2 lomilik and lemkein respectively assuming pacific plate motion of 0 3 myr the seamounts were located at 12 n 11 n 9 n and 8 n at the time of boundary formation this result suggests that the north edge of the itcz has shifted south since the middle miocene in the western pacific which agrees with information from the eastern pacific

regional scale impact of tidal forcing on groundwater flow in unconfined coastal aquifers summary this paper considers the impact of tidal forcing on regional groundwater flow in an unconfined coastal aquifer numerical models are used to quantify this impact for a wide range of hydrogeological conditions both a shallow and a deep aquifer are investigated with regard to three dimensionless parameter groups that determine the groundwater flow to a large extent analytical expressions are presented that allow for a quick estimate of the regional scale effect of tidal forcing under the same conditions as used in the numerical models quantitatively the results in this paper are complementary to previous studies by taking into account variable density groundwater flow dispersive salt transport and a seepage face in the intertidal area qualitatively the results are in line with previous investigations the time averaged hydraulic head at the high tide mark increases upon a decrease of each of the three considered dimensionless parameter groups r including the ratio of the hydraulic conductivity and the precipitation excess a the slope of the intertidal area and al the ratio of the width of the fresh water lens and the tidal amplitude the relative change of the location and the hydraulic head of the groundwater divide which together characterize regional groundwater flow increase as a and al decrease but decrease as r decreases the difference between the analytical solutions and numerical results is small therefore the presented analytical solutions can be used to estimate the bias that is introduced in a numerical model if tidal forcing is neglected the results should be used with caution in case of significant wave forcing as this was not considered

using 234u 238u to assess diffusion rates of isotope tracers in ferromanganese crusts abstract ferromanganese crusts record seawater isotope history for several elements useful for paleoceanography interpreting crust isotope profiles however requires an assessment of the rate of diffusion of each element within the crust we address this issue using u and th isotope profiles coupled with concentration measurements of some trace elements whose isotopes are often measured in crusts a depth profile of 230thxs 234u for a north atlantic crust alv539 yields a growth rate of 3 05 mm myr consistent with an existing 10be 9be record but the growth rate implied by a 234u 238u profile in the same crust is 6 times faster due to diffusion of u in the crust the difference between the observed 234u 238u profile and that expected from 230thxs 234u enables the effective diffusivity of u to be calculated as 1 2 10 6 cm2 year recalculated literature data indicate that other crusts have diffusivities which range down to 4 7 10 8 cm2 yr this variation is to be expected given the range of porosity observed for ferromanganese crusts concentration measurements of various elements in the surface layer of the crust provide relative distribution coefficients for each element between seawater and crust these distribution coefficients enable the effective diffusivity of each element to be calculated by comparison with the diffusivity of u such diffusivities are assessed for crust alv539 and give a first indication of the expected preservation of isotope signals in ferromanganese crusts li os and sr have diffusivities of 2 10 4 3 10 5 and 2 10 5 cm2 year respectively and diffusion is expected to be sufficiently fast that crusts will not accurately preserve past seawater compositions th nd pb and be have diffusivities less than 10 9 cm2 year and are highly immobile in crusts a reassuring result for th and be crust chronologies and for nd and pb isotope tracing of past water masses using crusts hf has a diffusivity of 3 10 8 in alv539 fast enough to perturb but not destroy its isotope history for studies of hf in this and other crusts diffusion should therefore be considered measuring u isotope profiles provides a potential way of assessing such diffusion for hf or for other elements with relatively low distribution coefficients into ferromanganese crusts

chemical transport to the seafloor of the equatorial pacific ocean across a latitudinal transect at 135 w tracking sedimentary major trace and rare earth element fluxes at the equator and the intertropical convergence zone we have analyzed the major trace and rare earth element composition of surface sediments collected from a transect across the equator at 135 w longitude in the pacific ocean comparing the behavior of this suite of elements to the caco3 opal and corg fluxes which record sharp maxima at the equator previously documented at the same sampling stations enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial pacific seafloor the 1 1 high biogenic source at the equator associated with equatorial divergence of surface water and upwelling of nutrient rich water and 2 2 high aluminosilicate flux at 4 n associated with increased terrigenous input from elevated rainfall at the intertropical convergence zone itcz of the tradewinds are the two most important fluxes with which elemental transport is affiliated the biogenic flux at the equator transports ca and sr structurally bound to carbonate tests and mn primarily as an adsorbed component trace elements such as cr as pb and the rees are also influenced by the biogenic flux at the equator although this affiliation is not regionally dominant normative calculations suggest that extremely large fluxes of ba and p at the equator are carried by only small proportions of barite and apatite phases the high terrigenous flux at the itcz has a profound effect on chemical transport to the seafloor with elemental fluxes increasing tremendously and in parallel with ti normative calculations however indicate that these fluxes are far in excess of what can be supplied by lattice bound terrigenous phases the accumulation of ba is greater than is affiliated with biogenic transport at the equator while the p flux at the itcz is only 10 less than at the equator this challenges the common view that ba and p are essentially exclusively associated with biogenic fluxes many other elements including mn pb as and rees also record greater accumulation beneath the itcz than at the equator thus adsorptive scavenging by terrigenous paniculate matter or phases intimately associated with them appears to be an extremely important process regulating elemental transport to the equatorial pacific seafloor these findings emphasize the role of vertical transport to the sediment and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes

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