integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the mekong delta abstract arsenic is contaminating the groundwater of holocene aquifers throughout south and southeast asia to examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of as within soils sediments in the mekong river delta a 50 km2 field site was established near phnom penh cambodia where aqueous as concentrations are dangerously high and where groundwater retrieval for irrigation is minimal dissolved as concentrations vary spatially ranging up to 1300 g l in aquifer groundwater and up to 600 g l in surficial clay pore water groundwaters with high as concentrations are reducing with negligible dissolved o2 and high concentrations of fe ii nh 4 and dissolved organic c within near surface environments these conditions are most pronounced in sediments underlying permanent wetlands often found within oxbow channels near the mekong river there labile c co deposited with as bearing fe hydr oxides under reducing conditions drives the reductive mobilization inclusive of fe and as reduction of as here conditions are described under which as is mobilized from these sediments and near surface as release is linked to aquifer contamination over long time periods 100s to 1000s of years site biogeochemistry is coupled with extensive hydrologic measurements and accordingly a comprehensive interpretation of spatial as release and transport within a calibrated hydraulic flow field is provided of an as contaminated aquifer that is representative of those found throughout south and southeast asia

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

surface complexation modeling of groundwater arsenic mobility results of a forced gradient experiment in a red river flood plain aquifer vietnam abstract three surface complexation models scms developed for respectively ferrihydrite goethite and sorption data for a pleistocene oxidized aquifer sediment from bangladesh were used to explore the effect of multicomponent adsorption processes on as mobility in a reduced holocene floodplain aquifer along the red river vietnam the scms for ferrihydrite and goethite yielded very different results the ferrihydrite scm favors as iii over as v and has carbonate and silica species as the main competitors for surface sites in contrast the goethite scm has a greater affinity for as v over as iii while po43 and fe ii form the predominant surface species the scm for pleistocene aquifer sediment resembles most the goethite scm but shows more si sorption compiled as iii adsorption data for holocene sediment was also well described by the scm determined for pleistocene aquifer sediment suggesting a comparable as iii affinity of holocene and pleistocene aquifer sediments a forced gradient field experiment was conducted in a bank aquifer adjacent to a tributary channel to the red river and the passage in the aquifer of mixed groundwater containing up to 74 channel water was observed the concentrations of as

plume spreading in groundwater by stretching and folding 1 this paper proposes a new approach to the hydraulics of in situ groundwater remediation in situ remediation promotes reactions between an injected treatment solution and the contaminated groundwater but without a hydraulic mechanism to promote spreading the laminar flows characteristic of porous media will keep the two fluids in approximately the same relative configuration as they travel through the aquifer limiting the opportunity for reactions to occur to address this fundamental limitation this paper borrows a key result from the fluid mechanics literature spreading in laminar flows is optimized by chaotic advection previous studies have applied this result to groundwater remediation using the pulsed dipole model but that model depends on reinjection of fluid which presents a number of theoretical and practical limitations accordingly this paper proposes a new conceptual model for plume spreading by chaotic advection using an engineered sequence of extractions and injections of clean water at an array of wells which generates plume spreading by stretching and folding the fluid interface between the injected treatment solution and the contaminated groundwater but does not require reinjection the paper includes an overview of the analytical techniques poincare sections periodic points stable and unstable manifolds heteroclinic points and lyapunov exponents used to demonstrate chaotic advection in the limiting case in which diffusion is negligible numerical simulations show that spreading by stretching and folding is complimentary to spreading resulting from aquifer heterogeneity

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

a multiaxial growth analysis of stable isotopes in the modern shell of saxidomus gigantea implications for sclerochronology studies 1 stable isotope ratios of two modern saxidomus gigantea specimens from namu british columbia are presented to show intraspecimen and interspecimen isotopic variation isotopic profiles 13cshell 18oshell were generated along the axis of maximum growth the profiles show that analogous seasonal variation is recorded in 18oshell however significant variability is recorded in 13cshell we suggest this is caused by differences in metabolic activity between individuals intrashell variability along a growth horizon shows good reproducibility in 13cshell but significant variability in 18oshell especially at the sinistral margin a multiaxial growth analysis generated several profiles from a single valve similar seasonal variations are recorded in 18oshell along all axes 13cshell show significantly less covariation possibly related to internal metabolic activity this study highlights that 18oshell profiles generated from any portion of the shell can be used to evaluate seasonal fluctuations and may be excellent to evaluate types and rates of shell growth

an intractable climate archive sclerochronological and shell oxygen isotope analyses of the pacific geoduck panopea abrupta bivalve mollusk from protection island washington state usa abstract annual growth increment patterns of cardinal teeth ct of panopea abrupta conrad can reportedly provide information about past climate variations however little is known about the intra annual timing and rate of shell growth necessary to interpret such records in addition it remains unclear whether actual temperatures can be reliably inferred from 18o values of geoduck goo e duk shells this study compared high resolution environmental records hourly to monthly resolved temperature bi weekly to monthly 18owater and salinity data with temperatures reconstructed from oxygen isotope values of the outer shell layer t 18oosl and cardinal tooth portions t 18oct of different contemporaneous specimens alive at the same locality results indicate that shell growth mainly occurred between march april and november december with a maximum during may august this finding must be considered when comparing the annual growth increment width chronologies to environmental parameters in addition intra annual 18oshell values require the calculation of weighted averages instead of arithmetic means during ontogeny the duration of the growing season remained nearly unchanged an important finding for paleoclimate studies based on inter annual growth patterns seasonal shell growth was strongly correlated with temperature r 0 93 r2 0 86 p

ionic transport in nano porous clays with consideration of electrostatic effects the mineralogical and chemical properties of clays have been the subject of longstanding study in the research community in fact entire journals are devoted to the topic in the field of hydrology where transport behavior is more routinely considered clays and clay rich rock were largely relegated to a minor role because of their low hydraulic conductivity however this very property explains in part the renewed interest in the behavior of clays and clay rocks in several important subsurface energy related applications including the long term disposal of nuclear wastes in geological repositories and the storage of co2 in subsurface geological formations in these applications and environments the low permeability of the clay rich formations or engineered barriers provides at least part of the safety functions for radionuclide contaminants confinement and subsurface co2 sequestration from a geochemical and mineralogical point of view the high adsorption capacity of clay minerals adds to the effect of low hydraulic conductivities by greatly increasing the retardation of radionuclides and other contaminants making clays ideal where isolation from the biosphere is desired the low permeability of clay rich shales also explains why hydrocarbon resources are not easily exploited from these formations thus requiring in many cases special procedures like hydraulic fracturing in order to extract them clay properties remain also topic of intensive research in the oilfield industry in connection with their swelling behavior which has an adverse impact on drilling operations anderson et al 2010 wilson and wilson 2014 de carvalho balaban et al 2015 while the low permeability and high adsorption capacity of clay minerals are widely acknowledged it is clear nonetheless that there is a need for an improved understanding of how the chemical and mineralogical properties of clay rocks impacts transport through them it is at the pore scale that the chemical properties

reliability of multitaxon multiproxy reconstructions of environmental conditions from accretionary biogenic skeletons abstract evaluation and quantification of climate change require data on subseasonal to daily environmental extremes from those periods before instrumental records were available this study employs a high resolution multitaxon multiproxy approach and analyzes how faithfully accretionary biogenic skeletons record environmental extremes six specimens of two bivalve mollusks chione fluctifraga mytella guyanensi and one barnacle species chthamalus fissus from a single habitat northern gulf of california mexico were collected contemporaneous shell portions from these specimens were analyzed for shell growth rates sclerochronology and stable isotopes 18o 13c and were compared to instrumental records the results of these analyses included some significant observations first shell 18o values overestimate winter temperatures and underestimate summer temperatures second the actual diurnal temperature range is not recorded in the biogenic skeletons third skeletal growth is biased toward a

the shell of the queen scallop aequipecten opercularis l as a promising tool for palaeoenvironmental reconstruction evidence and reasons for equilibrium stable isotope incorporation abstract the queen scallop aequipecten opercularis has been an important part of the marine fauna of the northeast atlantic region since the miocene and is a suitable candidate for palaeoenvironmental studies using stable isotopes modern shells were investigated to determine if carbonate is precipitated in isotopic equilibrium in this species and to confirm that growth continues through the year specimens of a opercularis were cultured under monitored semi natural conditions over an autumn winter period and the analyses of these specimens were supplemented with isotope data from preserved indigenous north sea specimens the results indicated that the cultured specimens grew in relatively low temperatures that oxygen isotopes of shell exterior carbonate were precipitated in isotopic equilibrium and that a large proportion of the ambient temperature range was recorded in shell carbonate the indigenous north sea specimens exhibited a good correspondence to predicted oxygen isotope values for summer the isotopic record related to winter was however somewhat truncated due to growth decelerations in the specimens carbon isotopes of shell exterior carbonate were calculated as being derived primarily from external sources and showed comparatively little influence from metabolically derived carbon this suggests that carbon isotopes were at least close to equilibrium with ambient waters the limited incorporation of metabolic products suggests that a opercularis would be a good monitor of changing carbon isotope ratios in seawater dissolved inorganic carbon the occurrence of equilibrium shell precipitation is explained using a pteriomorph shell calcification model which proposes that transport of ions through the periostracum caused the composition of the extrapallial fluid to be effectively the same as seawater carbonate secretion is therefore not influenced significantly by biological vital effects

dynamic hydrologic and biogeochemical processes drive microbially enhanced iron and sulfur cycling within the intertidal mixing zone of a beach aquifer intertidal aquifers host a reactive zone comprised of fe mineral coated sands where fresh and saline groundwaters mix this zone may significantly influence the export of c n p fe and other metals in submarine groundwater discharge sgd toward determining the roles of microbes in fe and s mineralization and the interplay of microbiology with geochemistry and physical hydrology we conducted a biogeochemical study of pore waters at cape shores delaware here fresh groundwater provides fe ii which precipitates as feiiiooh predominantly through microbial fe ii oxidation candidate division op3 was the dominant microbial group associated with fe ii and fe iii rich regions of the aquifer suggesting that this uncharacterized phylum may be involved in fe ii oxidation saline water brings o2 sulfate and organic c into the intertidal mixing zone microbial reduction of sulfate produces sulfide that is transported to the fe mineralized zone leading to the transformation of feooh to fe ii sulfides microbial populations are structured by the availability of chemical species supplied along groundwater flow paths seasonal changes in the relative supply of fresh and saline groundwater affect solute fluxes and therefore microbial controls on the location and composition of the fe mineralized zone ultimately the composition extent and dynamics of the fe mineralized zone will affect the sequestration affinity and residence time of solutes bound for export to coastal oceans through sgd

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

field study of dispersion in a heterogeneous aquifer 3 geostatistical analysis of hydraulic conductivity observations of the spatial variability of hydraulic conductivity at a tracer test site located at columbus air force base in mississippi are presented direct measurements of hydraulic conductivity of the heterogeneous alluvial aquifer at the site were made using borehole flowmeter logging slug tests and a laboratory permeameter to test undisturbed soil cores indirect methods estimating hydraulic conductivity were also evaluated including soil grain size analyses surface geophysical surveys and mapping of sediment facies the spatial covariance of the 2187 hydraulic conductivity values obtained with the borehole flowmeter method was examined the log hydraulic conductivity variance ln2k and the horizontal and vertical correlation scales h and v of 4 5 12 8 m and 1 6 m respectively were estimated assuming second order stationarity of the conductivity field the covariance parameters are uncertain with bounding values that are 24 76 above or below the estimate covariance parameters estimated with more limited nonflowmeter data were within the same magnitude as those obtained using the extensive flowmeter data suggesting that data from a variety of methods may be used to provide approximate values of the autocovariance parameters nonstationarity of the ln k field was examined by removing three dimensional polynomial trend surfaces and calculating variograms of the residuals significantly lower estimates for ln2k h and v of 2 7 4 8 m and 0 8 m respectively were obtained from the third order log conductivity residuals after trend removal the bounding parameter values differ 15 44 from the estimated values accounting for unsteady flow and the uncertainty in the covariance parameters of the third order log conductivity residuals the calculated longitudinal and horizontal transverse macrodispersivities ranged from 1 5 m to 1 8 m and 0 3 m to 0 6 m respectively

engineered injection and extraction to enhance reaction for improved in situ remediation 1 during in situ remediation a treatment solution is often injected into a contaminated aquifer to degrade the groundwater contaminant since contaminant degradation reactions occur only at locations where the treatment solution and groundwater contaminant overlap mixing of the treatment solution and the contaminated groundwater is necessary for reaction to occur mixing results from molecular diffusion and pore scale dispersion which operate over small length scales thus mixing during in situ remediation can only occur where the separation distance between the treatment solution and contaminated groundwater is small to promote mixing advection can be used to spread the treatment solution into the contaminated groundwater to increase the extent of the region where the two solutions coexist a certain degree of passive spreading is the natural consequence of aquifer heterogeneity which is manifested as macrodispersion an alternative mechanism is active spreading in which unsteady flows lead to stretching and folding of plumes active spreading can be accomplished by engineered injection and extraction eie in which clean water is injected and extracted at wells surrounding a contaminant plume to create unsteady flow fields that stretch and fold the treatment solution and contaminant plumes for a model system in which nested plumes of two reactants undergo scalar transport and instantaneous reaction the simulation results reported here indicate that eie enhances degradation of groundwater contamination in homogeneous and heterogeneous aquifers compared to baseline models without eie furthermore this study shows that the amount of reaction provided by the spreading due to eie is greater than the amount of reaction due to spreading from heterogeneity alone

the ksâr akil lebanon mollusc assemblage zooarchaeological and taphonomic investigations abstract shells of marine molluscs exploited by prehistoric humans constitute archives of palaeoecological and palaeoclimatic data as well as of human behaviour in coastal settings here we present our investigations on the mollusc assemblage from ks r akil lebanon a key site in southwestern asia occupied during the middle and upper palaeolithic the site plays an important role in understanding modern human dispersals into eurasia taxa from intertidal rocky shore subtidal soft bottom and rocky littoral habitats dominate the marine component of the invertebrate assemblage terrestrial snails indicate wooded and open half shaded habitats in the vicinity of the site species composition suggests that these habitats were present throughout the upper palaeolithic humans transported marine molluscs to the rockshelter as food packages for dietary purposes e g patella caerulea patella rustica phorcus turbinatus and shells of other taxa to be used as tools e g glycymeris sp or possibly for ornamental purposes e g nassarius gibbosulus and columbella rustica in the initial upper palaeolithic collection focussed on empty shells as raw material for utilitarian purposes in the subsequent early upper palaeolithic and later periods mollusc gathering was performed in an increasing number of habitats and shifted towards collection for human consumption which was the main reason for the introduction of shells to the site during the epipalaeolithic concurrent size shifts of live collected as well as beached specimens suggests that size changes were linked to environmental change rather than to potential overexploitation of dietary taxa by humans

exploring aberrant bivalve shell ultrastructure and geochemistry as proxies for past sea water acidification throughout much of earth s history marine carbonates have represented one of the most important geological archives of environmental change several pivotal events during the phanerozoic such as mass extinctions or hyperthermal events have recently been associated with ocean acidification nevertheless well defined geological proxies for past ocean acidification events are at best scarce here experimental work explores the response of bivalve shell ultrastructure and isotope geochemistry c 13 o 18 and mg 26 to stressful environments in particular to sea water acidification in this study the common blue mussel mytilus edulis was cultured from early juvenile stages to one year of age at four ph regimes ph nbs 72 to ph 80 shell growth rate and ultrastructure of mainly the calcitic portion of the shells were compared between experimental treatments specimens exposed to low ph environments show patches of disordered calcitic fibre orientation in otherwise well structured shells furthermore the electron backscattered diffraction analyses reveal that under acidified conditions the c axis of the calcite prisms exhibits a bimodal or multi modal distribution pattern similar shell disorder patterns have been reported from mytilids kept under naturally acidified sea water conditions in contrast this study found no evidence that different ph regimes affect shell carbon oxygen or magnesium isotope ratios based on these observations it is proposed that i stressful environments in this case low sea water ph predictably affect bivalve biomineralization patterns and ii these findings bear potential as a novel petrographic proxy for ancient sea water acidification an assessment of the applicability of these data to well preserved fossil shell material from selected time intervals requires additional work

ice marginal dynamics of the last british irish ice sheet in the southern north sea ice limits timing and the influence of the dogger bank the southern north sea is a particularly important area for understanding the behaviour of the british irish ice sheet biis during the last glacial cycle it preserves a record of the maximum extent of the eastern sector of the biis as well as evidence for multiple different ice flow phases and the dynamic re organisation of the biis however to date the known ice sheet history and geochronology of this region is predominantly derived from onshore geological evidence and the offshore imprint and dynamic history of the last ice sheet remain largely unknown using new data collected by the britice chrono project this paper explores the origin and age of the dogger bank re assesses the extent and age of the glaciogenic deposits across the shallow areas of the north sea between the dogger bank and the north norfolk coast and re examines the dynamic behaviour of the biis in the southern north sea between 31 6 and 21 5 ka this paper shows the core of the dogger bank to be composed glaciolacustrine sediment deposited between 31 6 and 25 8 ka following its formation the western end of the dogger lake was overridden with ice reaching 54 n where the ice margin is co incident with the southerly extent of subglacial tills previously mapped as bolders bank fm this initial ice override and retreat northwards back across the dogger lake was complete by 23 1 ka but resulted in widespread compressive glaciotectonism of the lake sediments and the formation of thrust moraine complexes along the northern edge of the bank moraines are on lapped by later phase glaciolacustrine and marine sediments but do not show evidence of subsequent ice override the shallow seafloor to the west and southwest of the dogger bank records several later phases of ice advance and retreat as the north sea lobe flowed between the dogger bank and the yorkshire lincolnshire coasts and reached north norfolk new optically stimulated luminescence osl ages from garrett hill on outwash limit the arrival of the biis on the norfolk coast to 22 8 21 5 ka multiple till sheets and chains of moraines on the seafloor north of norfolk mark dynamic oscillation of the north sea lobe margin as it retreated northwards this pattern of behaviour is broadly synchronous with the terrestrial record of deposition of subglacial glaciofluvial and glaciolacustrine sediments along the yorkshire coast which relate to post dimlington stadial ice marginal oscillations after 21 5 ka with respect to forcing mechanisms it is likely that during the early phases of the last glacial maximum 30 23ka the interaction between the southern margin of the biis and the dogger lake was critical in influencing flow instability and rapid ice advance and retreat however during the latter part of the last glacial maximum 22 21 ka late phase ice advance in the southern north sea became restricted to the western side of the dogger bank which was a substantial topographic feature by this time this topographic confinement in addition to decoupling of the biis and the fennoscandian ice sheet fis further north enabled ice to reach the north norfolk coast overprinting the seabed with late phase tills of the bolders bank fm

adaptive strategies and environmental significance of lingulid brachiopods across the late permian extinction abstract linguliform brachiopods are traditionally considered a conservative group which seems to pass through the late permian extinction without any significant loss and even appear to thrive immediately after the extinction peak in the southern alps lingulids are very common in the post extinction mazzin member early induan of the werfen formation sparse occurrences are also known in the overlying siusi and gastropod oolite members late induan and early olenekian in age respectively the recent discovery of well preserved specimens from a pre extinction bed of the bellerophon formation changhsingian has permitted a detailed comparative analysis mostly based on the interior characters preserved in the lingulid succession from across the extinction beds the following effects on the lingulid populations have been analyzed i change in taxonomic assessment ii adaptive strategies during the surviving and recovery phases and iii environmental proxy connected with the killing mechanisms of the late permian extinction the pre extinction individuals belong to lingularia cf smirnovae biernat and emig a species that is characterized by large sized shells with a short lophophoral cavity the post extinction populations belong to different species and probably even to a different genus the first post extinction population early induan with small sized shells and long lophophoral cavity has been referred to lingularia yini peng and shi it records the most severe effects of the late permian extinction on the marine ecosystems the late induan olenekian lingularia borealis bittner with large sized shells and long lophophoral cavity appears during the first phase of the triassic biotic recovery the main adaptive strategies of lingularia yini in comparison with the permian species include i shell miniaturization ii increasing of the lophophoral cavity surface respiratory surface and iii increasing of shell width length ratio these modifications are interpreted as adaptations towards warming and hypoxia two main killing mechanisms of the marine biota the recovery species lingularia borealis maintains a large lophophoral cavity indicating an adaptation towards predominant low oxygenated bottom marine waters the appearance and the great abundance of lingularia yini in the mazzin member early induan represent a proxy of dysaerobic conditions which determined the appearance of the second phase of the lilliput biota characterized by the definitive disappearance of the rhynchonelliform brachiopods and calcareous algae in the southern alps

late paleocene arctic ocean shallow marine temperatures from mollusc stable isotopes late paleocene high latitude 80 n arctic ocean shallow marine temperatures are estimated from molluscan 18o time series sampling of individual growth increments of two specimens of the bivalve camptochlamys alaskensis provides a high resolution record of shell stable isotope composition the heavy carbon isotopic values of the specimens support a late paleocene age for the youngest marine beds of the prince creek formation exposed near ocean point alaska the oxygen isotopic composition of regional freshwater runoff is estimated from the mean 18o value of two freshwater bivalves collected from approximately coeval fluviatile beds over a 30 34 range of salinity values assumed to represent the tolerance of c alaskensis the mean annual shallow marine temperature recorded by these individuals is between 11 and 22 c these values could represent maximum estimates of the mean annual temperature because of a possible warm month bias imposed on the average 18o value by slowing or cessation of growth in winter months the amplitude of the molluscan 18o time series probably records most of the seasonality in shallow marine temperature the annual temperature range indicated is approximately 6 c suggesting very moderate high latitude marine temperature seasonality during the late paleocene on the basis of analogy with modern chlamys species c alaskensis probably inhabited water depths of 30 50 m the seasonal temperature range derived from 18o is therefore likely to be damped relative to the full range of annual sea surface temperatures high resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude if applied to other regions and time periods the approach used here would contribute substantially to the paleoclimate record of seasonality

a kinetic approach for simulating redox controlled fringe and core biodegradation processes in groundwater model development and application to a landfill site in piedmont italy a three dimensional model for predicting redox controlled multi species reactive transport processes in groundwater systems is presented the model equations were fully integrated within a modflow family reactive transport code rt3d the model can simulate organic compound biodegradation coupled to different terminal electron acceptor processes a computational approach which uses the spatial and temporal distribution of the rates of different redox reactions is proposed to map redox zones the method allows one to quantify and visualize the biological degradation reactions occurring in three distinct patterns involving fringe pseudo core and core processes the capabilities of the numerical model are demonstrated using two hypothetical examples a batch problem and a simplified two dimensional reactive transport problem the model is then applied to an unconfined aquifer underlying a leaking landfill located near the city of turin in piedmont italy at this site high organic load from the landfill leachate activates different biogeochemical processes including aerobic degradation denitrification manganese reduction iron reduction sulfate reduction and methanogenesis the model was able to describe and quantify these complex biogeochemical processes the proposed model offers a rational framework for simulating coupled reactive transport processes occurring beneath a landfill site

the importance and challenge of hyporheic mixing the hyporheic zone is the interface beneath and adjacent to streams and rivers where surface water and groundwater interact the hyporheic zone presents unique conditions for reaction of solutes from both surface water and groundwater including reactions which depend upon mixing of source waters some models assume that hyporheic zones are well mixed and conceptualize the hyporheic zone as a surface water groundwater mixing zone but what are the controls on and effects of hyporheic mixing what specific mechanisms cause the relatively large 1m mixing zones suggested by subsurface solute measurements in this commentary we explore the various processes that might enhance mixing in the hyporheic zone relative to deeper groundwater and pose the question whether the substantial mixing suggested by field studies may be due to the combination of fluctuating boundary conditions and multi scale physical and chemical spatial heterogeneity we encourage investigation of hyporheic mixing using numerical modeling and laboratory experiments to ultimately inform field investigations

the concept of block effective macrodispersivity and a unified approach for grid scale and plume scale dependent transport we present a new approach for modelling macrodispersivity in spatially variable velocity fields such as exist in geologically heterogeneous formations considering a spectral representation of the velocity it is recognized that numerical models usually capture low wavenumber effects while the large wavenumber effects associated with subgrid block variability are suppressed while this suppression is avoidable if the heterogeneity is captured at minute detail that goal is impossible to achieve in all but the most trivial cases representing the effects of the suppressed variability in the models is made possible using the proposed concept of block effective macrodispersivity a tensor is developed which we refer to as the block effective macrodispersivity tensor whose terms are functions of the characteristic length scales of heterogeneity as well as the length scales of the model s homogenized areas or numerical grid blocks closed form expressions are developed for small variability in the log conductivity and unidirectional mean flow and are tested numerically the use of the block effective macrodispersivities allows conditioning of the velocity field on the measurements on the one hand while accounting for the effects of unmodelled heterogeneity on the other in a numerically reasonable set up it is shown that the effects of the grid scale are similar to those of the plume scale in terms of filtering out the effects of portions of the velocity spectrum hence it is easy to expand the concept of the block effective dispersivity to account for the scale of the solute body and the pore scale dispersion

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle