stable isotopes of fossil teeth corroborate key general circulation model predictions for the last glacial maximum in north america 1 oxygen isotope data provide a key test of general circulation models gcms for the last glacial maximum lgm in north america which have otherwise proved difficult to validate high 18o pedogenic carbonates in central wyoming have been interpreted to indicate increased summer precipitation sourced from the gulf of mexico here we show that tooth enamel 18o of large mammals which is strongly correlated with local water and precipitation 18o is lower during the lgm in wyoming not higher similar data from texas california florida and arizona indicate higher 18o values than in the holocene which is also predicted by gcms tooth enamel data closely validate some recent models of atmospheric circulation and precipitation 18o including an increase in the proportion of winter precipitation for central north america and summer precipitation in the southern us but suggest aridity can bias pedogenic carbonate 18o values significantly

retardation of 238u and 232th decay chain radionuclides in long island and connecticut aquifers abstract knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the 238u and 232th decay chains groundwaters of varying chemical composition were analyzed from wells in long island new york and connecticut aquifer lithologies are arkose quartz sandstone granite and glacial drift adsorption k1 and desorption k2 coefficients for ra and pb were calculated using 222rn activity as a measure of the supply of other recoil nuclides laboratory tests of the validity of this assumption were made by measuring the flux of 224ra and 222rn from aquifer solids the ratio k 1 k 2 is the distribution coefficient k which is effectively equal to r the retardation factor the average value of k for ra is 6 102 in long island aquifers and 5 104 in connecticut the distribution coefficient for pb is 104 in long island and 105 in connecticut results from this and other studies reveal a strong dependence of retardation on ph o 2 and ionic strength that tends to overwhelm any dependence of retardation on lithology

paleoaltimetry from stable isotope compositions of fossils stable isotope systematics of phosphatic vertebrate and carbonate invertebrate fossils are reviewed emphasizing external vs biological controls on isotope compositions and their variation external controls include elevation and isotopic lapse rates temperature atmospheric circulation patterns aridity and changes to precipitation seasonality e g development of monsoons biological controls include temperature regulation and temperature dependent biological activity water balance behavior and rates of hard part secretion and maturation some key factors include what sources of water an animal samples how those sources respond isotopically to elevation and the isotopic sensitivity of a biologic tissue to environmental changes general research design criteria are enumerated including numbers of fossils and analyses required as well as uncertainties in the interpretability of isotopic shifts isotope zoning from fossil teeth and shells from the indian foreland demonstrate comparable seasonal monsoon signals at 11 ma vs today implying a high and broad plateau at that time mean isotope compositions of fossil teeth from the lee of the cascade range central oregon show a pronounced decrease in 18 o initiating 7 ma signaling topographic rise associated with impingement of basin and range extension on the arc mean compositions and zoning in fossil shells from the northern rocky mountains indicate high elevations and topographic relief in the late cretaceous and early paleogene paleoaltimetry will principally benefit from better estimates of temperature because temperature lapse rates are less variable than isotopic lapse rates and because the combination of temperature and isotopic studies may help distinguish between local isotopic changes and distal ones caused by catchment or rain shadow effects

u sr isotopic speedometer fluid flow and chemical weathering rates in aquifers abstract both chemical weathering rates and fluid flow are difficult to measure in natural systems however these parameters are critical for understanding the hydrochemical evolution of aquifers predicting the fate and transport of contaminants and for water resources water quality considerations 87 sr 86 sr and 234 u 238 u activity ratios are sensitive indicators of water rock interaction and thus provide a means of quantifying both flow and reactivity the 87 sr 86 sr values in ground waters are controlled by the ratio of the dissolution rate to the flow rate similarly the 234 u 238 u ratio of natural ground waters is a balance between the flow rate and the dissolution of solids and recoil loss of 234 u from the solids by coupling these two isotope systems it is possible to constrain both the long term ca 100 s to 1000 s of years flow rate and bulk dissolution rate along the flow path previous estimates of the ratio of the dissolution rate to the infiltration flux from sr isotopes 87 sr 86 sr are combined with a model for 234 u 238 u to constrain the infiltration flux and dissolution rate for a 70 m deep vadose zone core from hanford washington the coupled model for both 234 u 238 u ratios and the 87 sr 86 sr data suggests an infiltration flux of 5 2 mm yr and bulk silicate dissolution rates between 10 15 7 and 10 16 5 mol m 2 s the process of recoil enrichment while primarily responsible for the observed variation in 234 u 238 u of natural systems is difficult to quantify however the rate of this process in natural systems affects the interpretation of most u series data models for quantifying the recoil loss fraction based on geometric predictions surface area constraints and chemical methods are also presented the agreement between the chemical and theoretical methods such as direct measurement of 234 u 238 u of the small grain size fraction and geometric calculations for that size fraction is quite good

sediment deformation and hydrogeology of the nankai trough accretionary prism synthesis of shipboard results of odp leg 131 the main objective of leg 131 was to provide data on the deformational processes and associated hydrogeology of the nankai prism toe drilling succeeded for the first time in the history of ocean drilling in penetrating the complete sedimentary sequence to basaltic basement reaching 1327 mbsf metres below seafloor with good core recovery 55 excellent correlation of the lithology and structure including the frontal thrust and the decollement with seismic reflection images was also determined bedding dips faults and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to nw se shortening as expected from the plate tectonic convergence vector below the decollement no significant deformation features were observed indicating that the decollement is a sharp discontinuity in stress transmission physical properties data show major discontinuities at the decollement notably an increase in porosity below the later this may indicate excess pore pressure in the subducted section and decollement zone a less marked increase in porosity below the frontal thrust may reflect the youthfulness of this feature attempts to make downhole measurements were severely hampered by unstable hole conditions but useful constraints have been placed on the thermal regime and some calibration of laboratory physical properties toin situ conditions has been provided andin situ stress and pore pressure were measured in the uppermost sediments evidence of channelized fluid flows is inconclusive no sharp geochemical signatures or unequivocal geochemical anomalies indicative of channelized fluid flow were found thermal measurements are not significantly different from those predicted by a purely conductive heat flow model a signature of low chloride pore water near the decollement may partly be related to smectite diagenesis but may also be due to episodic fluid flow events we conclude that dewatering probably occurred dominantly through diffuse flow throughout the accreted sediments at this site

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

amount effect recorded in oxygen isotopes of late glacial horse equus and bison bison teeth from the sonoran and chihuahuan deserts southwestern united states stable oxygen isotopes from fossils both vertebrate and invertebrate or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site in general these inferences are made on the centennial to millennial scale serial i e ontogenetic sampling of equus and bison tooth enamel provides climatic data on the scale of months to a few years we present models showing how annual environmental patterns of d 18 o would be replicated in the tooth enamel of equus and bison changes in d 18 o due to shifts in temperature in terrestrial environments d 18 o increases with increased temperature and amount and timing of precipitation increased precipitation may result in a decrease in d 18 o a phenomenon called the amount effect are archived in both equus and bison teeth the input signal is better resolved in bison due to its more rapid enamel growth modeled patterns are compared with actual data from modern sites in the sonoran and chihuahuan deserts of the southwestern united states the isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water known floral and faunal assemblages as well as computer models suggest summer rain for the chihuahuan desert of late glacial time 15 000 10 000 years ago but little summer rain for the sonoran desert at that same time serial data from fossil teeth show a clear pattern interpreted to represent the amount effect that includes increased summer rains in the chihuahuan desert and only minor summer rains in the sonoran desert d 2004 elsevier b v all rights reserved

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

microbial origin for pedogenic micrite associated with a carbonate paleosol champagne france abstract micro rods have been observed in indurated carbonate horizons 30 cm thick that overlie a periglacial chalk formation in contact with the present day soil champagne france they are numerous in the upper part of the hardened layers variations in micro rod morphologies are related to progressive biomineralization of organic matter transforming purely organic rods into calcite mineralized rods undergo diagenesis and their arrangement evolves from a random mesh fabric to recrystallized micritic platelets to microsparite two types of organic micro rods have been observed bacilliform and thread like bacteria mineralogically micro rods are low magnesian calcite crystallographically their length is parallel to the 104 axis and they grow along the 010 plane micro rods can be associated with needle fiber calcite they increase the caco3 content of the primary matrix and infill its microporosity their diagenetic evolution into microsparite contributes to soil layer induration

transport of radionuclides in an unconfined chalk aquifer inferred from u series disequilibria abstract u series disequilibria measured in waters and rocks from a chalk aquifer in france have been used as an analog for long term radionuclide migration drill core samples from a range of depths in the vadose zone and in the saturated zone as well as groundwater samples were analyzed for 238 u 234 u 232 th and 230 th to determine transport mechanisms at the water rock interface and to quantify parameters controlling the migration of radionuclides isotope measurements in rocks were done by tims whereas 234 u 238 u and 230 th 232 th activity ratios in water samples were measured by multi collector icp ms both depletion and enrichment in 234 u relative to 238 u were observed in carbonate rock samples resulting from chemical weathering in the unsaturated zone and calcite precipitation in the zone of water table oscillation respectively the correlation between 230 th 232 th activity ratios and 87 sr 86 sr ratios found in the chalk samples indicates that thorium is mainly contained in a minor silicate phase whose abundance is variable in chalk samples water samples are all characterized by 234 u 238 u 1 resulting from recoil effect of 234 th groundwaters are characterized by a more radiogenic signature in 87 sr 86 sr than the rocks moreover 230 th 232 th activity ratios in the waters are lower than in the rocks and increase with distance from the water divide which suggests that th transport is controlled by colloids formed during water infiltration in the soil a 1 d transport model has been developed in order to constrain the u series nuclide transport considering a transient behavior of radionuclides in the aquifer and a time dependent composition for the solid phase this model permits a prediction of the time scale of equilibration of the system and an estimation of parameters such as weathering rate distribution coefficients and recoil fractions retardation factors of 10 35 and from 1 10 4 to 2 10 5 were predicted for u and th respectively and can be used to predict the migration of radionuclides released as contaminants in the environment at the scale of our watershed 32 km 2 a characteristic migration time from recharge to riverine discharge of 200 600 yr for u and 0 2 3 7 myr for th was obtained

uranium colloidal transport and origin of the 234u 238u fractionation in surface waters new insights from mount cameroon in order to evaluate the spatial variability of the 234u 238u fractionation and its origin in surface waters 234u 238u activity ratios a r and trace element concentrations were measured in 34 streams and springs draining mount cameroon volcano in addition tangential ultrafiltration techniques were applied to 10 of the samples to assess the role of colloids on the transport of the uranium isotopes u concentration variations in the different ultrafiltered fractions indicate that inorganic colloids can significantly influence the transport of this chemical element even in diluted and organic poor waters such influence which may be related to the chemical and physical nature of colloids does induce fractionations between u and sr along with filter size 234u 238u a r variations among the different ultrafiltered fractions of a sample remain small or even negligible only two samples exhibit a significant isotopic difference between colloid associated and solute u colloids of these two samples seem to correspond to a phase which is distinct from the dissolved and particulate loads of the waters at the scale of the volcano the 234u 238u a r in surface waters is large ranging from 1 038 to 1 397 small 234u 238u fractionations between 1 038 and about 1 10 are attributed to surface and meteoric weathering of the bedrock by contrast the highest 234u 238u fractionations up to 1 397 are associated with groundwater contributions thus variations in the 234u 238u a r could correspond to the water source and not to the surface weathering processes consequently 234u 238u disequilibrium may represent a powerful tool for detecting and quantifying the influence of groundwater inputs on the chemical fluxes carried by surface waters

the effects of late quaternary climate and pco2 change on c4 plant abundance in the south central united states the late quaternary was a time of substantial environmental change with the past 70 000 years exhibiting global changes in climate atmospheric composition and terrestrial floral and faunal assemblages we use isotopic data and couple climate and vegetation models to assess the balance between c3 and c4 vegetation in texas during this period the carbon isotope composition of fossil bison mammoth and horse tooth enamel is used as a proxy for c3 versus c4 plant consumption and indicates that c4 plant biomass remained above 55 through most of texas from prior to the last glacial maximum lgm into the holocene these data also reveal that horses did not feed exclusively on herbaceous plants consequently isotopic data from horses are not reliable indicators of the c3 c4 balance in grassland biomes estimates of c4 percentages from coupled climate vegetation models illuminate the relative roles of climate and atmospheric carbon dioxide co2 concentrations in shaping the regional c4 signal c4 percentages estimated using observed modern climate vegetation relationships and late quaternary climate variables simulated by a global climate model are much lower than those indicated by carbon isotope values from fossils when the effect of atmospheric co2 concentration on the competitive balance between c3 and c4 plants is included in the numerical experiment however estimated c4 percentages show better agreement with isotopic estimates from late quaternary mammals and soils this result suggests that low atmospheric co2 levels played a role in the observed persistence of c4 plants throughout the late quaternary

the isotopic ecology of late pleistocene mammals in north america part 1 florida abstract mammoths and mastodons are common in pleistocene deposits yet these proboscideans and many other animals disappeared suddenly 10 000 years ago in this study we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late pleistocene extinction we analyzed specimens from six sites in florida ranging from full glacial 21 000 bp to late glacial 14 750 to 10 000 bp age the oxygen isotope composition of mammalian apatite covaries with meteoric water composition which in turn varies with climate consequently oxygen isotope analysis can be used to assess the potential for time averaging or mixing of specimens from different geographic regions within fossil assemblages the carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests carbon isotope analysis reveals that mastodons ate chiefly c3 plants presumably trees shrubs and herbs whereas mammoths consumed chiefly c4 grass several nutritional hypotheses for late pleistocene extinction entail the assumption that extinct taxa had specialized diets the resource partitioning and focused feeding preferences of florida s proboscideans corroborate this assumption but they do not in themselves prove that nutritional stress was the cause of the late pleistocene extinction

multiple scale hydrothermal circulation in 135 ma oceanic crust of the japan trench outer rise numerical models constrained with heat flow observations anomalous high heat flow is observed within 150 km seaward of the trench axis at the japan trench offshore of sanriku where the old pacific plate 135 ma is subducting individual heat flow values range between 42 and 114 mw m 2 with an average of 70 mw m 2 these values are higher than those expected from the seafloor age based on thermal models of the oceanic plate i e 50 mw m 2 the heat flow exhibits spatial variations at multiple scales regional high average heat flow 100 km and smaller scale heat flow peaks 1 km we found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of 100 km topographic effects combined with hydrothermal circulation may account for the observed smaller scale heat flow variations hydrothermal circulation in high permeability faults may result in heat flow peaks of a subkilometer spatial scale volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well since fractures and faults have been well developed due to bending of the incoming plate

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

234u 238u activity ratios in freshwaters as tracers of hydrological processes the strengbach watershed vosges france abstract 234u 238u and 87sr 86sr isotopic ratios as well as major and trace u ba sr rb element concentrations were analyzed in dissolved loads of the strengbach stream vosges france in order to constrain the sources of u isotopes 234u 238u to river waters the variations of the 234u 238u activity ratios along the stream indicate a clear dependence between the 234u 238u activity ratios of the surface waters and the different types of rocks forming the watershed with near equilibrium values for the waters draining granites and high 234u 238u disequilibria 1 4 for those flowing over carbonates the high 234u 238u disequilibria are related to a supply of 234u enriched groundwaters located within the carbonate rocks the 234u 238u activity ratios of the waters at the outlet of the catchment collecting the sources of the stream on the granitic lithology decrease from 1 02 to 0 96 when the discharge of the stream increases such a tendency requires mixing between a water body enriched in 234u which weathered the granitic bed rock at secular equilibrium and a water with a 234u 238u activity ratio below unity representing a mobilization of u from material that has already been weathered comparison of the geochemical characteristics of waters collected during the year and those collected during a flood event reveals the involvement of two different weathered end members depending on the hydrological conditions during the year the dissolved u transported by the river originates from bed rock and deep horizons of the weathering profile whereas a significant part of u during the flood event is supplied by superficial horizons of soils probably complexed by organic colloids these results outline the potential of 234u 238u activity ratios to investigate hydrological processes and emphasize that their use as tracers of rock weathering should be made cautiously

a submarine canyon as the cause of a mud volcano liuchieuyu island in taiwan abstract in this paper based on 3 5 khz uniboom and conventional seismic data we propose a model for the creation of liuchieuyu island a near shore mud volcano off the southwestern coast of taiwan in support of this model we also discuss the relationship between a nearby submarine canyon kaoping submarine canyon and the mud diapirs and mud volcanoes in the region seismic data suggest that liuchieuyu was originally a mud diapir with a thick continuous accumulation of sediments on its upper surface this sediment load or overburden prevented unconfined growth of the underlying mud diapir while simultaneously acting as a seal that trapped gas and formed a high pressure zone however kaoping paleo canyon eroded these overlying sediments and the overburdening pressure was reduced in consequence the mud diapir rose up to the sea floor to become a mud volcano the uppermost part of which is present day liuchieuyu island the formation of this island in the path of the paleo canyon also diverted the channel of the canyon to its present location

leaching of uranium and thorium from monazite iii leaching of radiogenic daughters abstract the solid state diffusion model of actinide leaching developed in part ii of this series is applied to leaching of radiogenic daughters of the actinide decay chains for an untreated natural monazite the direct leaching component of 228th release is larger than that for 232th because of enhanced solid state mobility for 228th provided by 228ra recoil tracks a significant portion of the 228th which appears in the leachate however is attributed to decay of insoluble 228ra which is continually released from the mineral by matrix dissolution and recoil ejection for a monazite sample that was annealed at 800 c prior to leaching the bulk of the 228th in solution was supplied by decay of 228ra rejected from the mineral matrix during annealing the radiogenic 234u daughter of the 238u decay chain did not exhibit similarly enhanced leaching because the long half life of 234u permitted local radiation damage to be annealed out at ambient temperature prior to 234u decay

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

a new type of intra plate volcanism young alkali basalts discovered from the subducting pacific plate northern japan trench alkali pillow basalts were collected from the toe of the oceanward slope of the northern japan trench these alkali basalts formed as a result of a low degree of partial melting of pacific ocean mantle and rapid rise of the magma no fractionation in shallow magma chambers reconstructing pacific plate motion based on 40ar 39ar age dates of 5 95 0 31 ma for these basalts indicates that they erupted outboard of outer swell or forebulge of the japan trench in the nw pacific we suggest that these alkali basalts represent a new form of intra plate volcanism whereby magmatic activity occurs off the forebulge of the downgoing pacific slab perhaps using conduits related to fracturing of the slab during bending prior to subduction

high pore pressure generation in sediments in front of the barbados ridge complex dsdp data for the barbados ridge complex show the existence of high pore pressures in sediments both oceanward and arcward of oceanic trenches we model the evolution of pore pressure by using a finite element procedure three consecutive stages are recognized 1 in the oceanic basin sedimentation rate is low there is little excess pore pressure 2 approaching the trench but before being incorporated into the accretionary prism sediments are subjected to increasing tectonic compression as well as greater sediment overburden thus high pore pressure can be created an important result is that the lowest effective stress occurs within the sedimentary layer instead of at its base and a decollement may develop along this weakened zone 3 arcward of the trench sediments above the decollement are offscraped while those beneath it are subducted fast sedimentation combined with tectonic compression can create pore pressures so high as to cause porosity to increase with depth this facilitates the formation of mud volcanoes even oceanward of the deformation front

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland pacific northwest of the usa abstract large scale atmospheric circulation patterns determine the quantity and seasonality of precipitation the major source of water in most terrestrial ecosystems oxygen isotope 18o dynamics of the present day hydrologic system in the palouse region of the northwestern u s a indicate a seasonal correlation between the 18o values of precipitation and temperature but no seasonal trends of 18o records in soil water and shallow groundwater their isotope values are close to those of winter precipitation because the palouse receives 75 of its precipitation during winter palouse loess deposits contain late pleistocene pedogenic carbonate having ca 2 to 3 higher 18o values and up to 5 higher carbon isotope 13c values than holocene and modern carbonates the late pleistocene 18o values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter dominated infiltration the 13c values are attributed to a proportional increase of atmospheric co2 in soil co2 due to a decrease in soil respiration rate and 13c discrimination in plants under much drier paleoclimate conditions than today the regional climate difference was likely related to anticyclonic circulation over the pleistocene laurentide and ice sheet

calibration of the clumped isotope geothermometer in soil carbonate in wyoming and nebraska usa implications for paleoelevation and paleoclimate reconstruction abstract recent work has shown that soil carbonates typically form as the soil dries after seasonal rainfall and therefore record seasonal aspects of climate rather than mean annual conditions because soil carbonate formation is closely related to the timing of local rainfall and drying it is necessary to understand the formation seasonality and temperature and soil water o 18 values recorded in modern soil carbonate before accurate estimates of stable isotope based paleoelevation and paleoclimate can be made here we study carbonate clumped isotope 47 and oxygen isotope o 18 compositions of modern soil carbonates and seasonal variations of soil moisture and temperature of nearby climate stations in wyoming and western nebraska usa to understand the seasonality of soil carbonate formation in semi arid to arid temperate montane settings we find that soil carbonate clumped isotope temperatures t 47 are 3 5 c higher than mean summer air temperature and are similar to or higher than average summer soil temperature at depths 40 cm soil moisture dramatically decreases in early summer following the cessation of spring rains and snowmelt and shows only brief increases after major mid late summer rain events soil water o 18 values calculated using carbonate o 18 and t 47 values are similar to the o 18 values of local mean summer precipitation these lines of evidence suggest that soil carbonates in our study area formed during times of soil dewatering in early summer and after major summer storm events in mid late summer and in or near equilibrium with mean summer precipitation o 18 values t 47 values of modern soil carbonates are inversely correlated with elevation with a lapse rate 4 0 c km similar to the modern air and soil temperature lapse rates calculated soil water o 18 values also are inversely correlated with elevation with a lapse rate of 3 7 km sample elevations can be reconstructed using both t 47 values and calculated soil water o 18 values between 900 m and 2600 m in our studied area with an accuracy of 0 5 km or less however o 18 values of precipitation and soil water reflect the complex interaction of climatic environmental and topographic conditions prior to carbonate formation whereas t 47 values may be influenced by site specific conditions we suggest that both soil carbonate t 47 values and calculated soil water o 18 values should be used to corroborate paleoelevation reconstruction and the seasonal nature of soil carbonate formation should be considered when soil carbonate t 47 values and o 18 values are applied for paleoclimate reconstruction

eocene oligocene latitudinal climate gradients in north america inferred from stable isotope ratios in perissodactyl tooth enamel abstract the eocene oligocene transition 34 ma was one of the most pronounced episodes of climate change of the cenozoic in order to investigate this episode of global climate cooling in north america we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl horse and rhino tooth enamel samples from the eocene oligocene rocks of the cypress hills formation southwestern saskatchewan canada we then compared the results with previously published data from the us great plains nebraska south dakota and wyoming average 1 perissodactyl enamel 13 c values vs v pdb in the eocene 8 8 0 3 and oligocene 9 0 0 3 are indistinguishable suggesting no major change in mean annual precipitation in saskatchewan across the transition the 13 c values in saskatchewan indicate the presence of arid ecosystems and are slightly higher than those in the us great plains suggesting drier conditions at higher latitudes with respect to oxygen isotopes average 1 perissodactyl enamel 18 o values vs v smow in the eocene 19 8 2 0 and oligocene 20 1 3 6 are also indistinguishable suggesting no change in the 18 o of meteoric precipitation across the transition in saskatchewan enamel 18 o variability is much larger in the oligocene vs eocene indicating a large increase in temperature seasonality this increase in enamel 18 o variability is much larger than that recorded in the us great plains suggesting that higher latitudes are more sensitive to major episodes of climate change with respect to temperature seasonality finally our data indicate no major change in the oligocene vs eocene latitudinal gradient in local water 18 o in north america which suggests no change in mean annual temperature gradients across the transition this result supports the hypothesis that ascribes the climate change of the transition to a drop in atmospheric p co 2 because climate models show that this mechanism produces uniform cooling at mid latitudes

river incision circulation and wind regime of pleistocene lake bonneville usa abstract pleistocene lake bonneville of the western u s and its associated alluvial systems present a unique opportunity to understand the relationship between prevailing winds of the time lake circulation and river incision the lake underwent a catastrophic flooding event 18 300 yr b p resulting in the incision of streams entering the lake along its eastern border incision patterns of twelve streams and rivers suggest that they were influenced by the prevailing circulation in the lake at the time in order to match patterns of river incisions simulations of lake circulation were performed with a state of the art numerical model for the maximum transgressive bonneville lake elevation simulations were conducted using the forcing of westerly and easterly prevailing winds simulated circulation can be described in terms of simple geostrophic balances in which the currents are generally cyclonic counter clockwise for westerly winds and anti cyclonic clockwise for easterly winds irregularities in lake shorelines and bathymetry cause localized variation of this general pattern comparison of model output with the deflected stream incision patterns suggest that prevailing winds during the pleistocene in the great basin of north america were westerly and that unlike the interior of north america the continental ice sheet did not exert significant influence on the climatological wind patterns of the great basin

mobility of u series nuclides during basalt weathering an example from the deccan traps india abstract u series disequilibria have been measured by tims and mc icp ms in dissolved phases and suspended sediments of the main basaltic rivers from the deccan trap region india for dissolved phases 234u 238u 230th 238u and 226ra 238u range between 1 11 and 1 28 between 0 03 10 2 and 1 35 10 2 and between 0 02 and 0 16 respectively for suspended particles 234u 238u 230th 238u and 226ra 238u range from 0 95 to 1 1 from 1 23 to 1 59 and from 0 1 to 0 47 respectively 230th 238u and 234u 238u systems show direct links with indices of weathering the data also indicate possible redistributions between the solid and aqueous phases and indicate that erosion processes do not presently operate at steady state because present day physical erosion rates are higher than expected 100 400 mm ka versus 40 mm ka for a steady state process for the narmada and the tapti basins models assuming either discrete or continuous particle leaching yield timescales for chemical erosion of 40 90 ka in contrast with basins located in northern latitudes erosion in the deccan basins does not appear to have been significantly disturbed during the last glaciation 234u 238u disequilibria in the dissolved phase of large rivers world wide are also explored and two key factors are highlighted in this study the dissolution of carbonates releasing dissolved u at secular equilibrium and the silicate weathering rate estimated at the scale of the watershed in particular a positive correlation is found between dissolved 234u 238u and basaltic weathering rates for the deccan that could reflect a key role of physical erosion since for silicate monolithological basins chemical erosion rates are primarily controlled by physical erosion rates for basins with mixed lithology dissolved organic matter also plays a key role in the preferential release of 234u from silicate minerals 234u 238u ratios in rivers therefore reflect a mixture between u released by carbonate dissolution and 234u preferentially released from silicate minerals located in high physical erosion and peat areas

high precision u series measurements of more than 500 000 year old fossil corals robust independent age constraints on the absolute timing of climate events based on the u series dating of fossil coral are sparse before the last glacial cycle using multiple collector inductively coupled plasma mass spectrometry with multiple faraday protocols we are able to date 600 ka samples with an uncertainty of better than 15 ka 2 representing a three fold improvement in precision compared with previous techniques using these methods we report u series measurements for a suite of 500 thousand year old ka corals from henderson island an emergent atoll in the south central pacific ocean the fossil corals show extraordinarily little diagenetic alteration for their age and the best preserved sample yields a u series age of 600 15 ka 2 which overlaps with the timing of the warm marine isotope stage mis 15 interglacial the open system model of villemant and feuillet villemant b and feuillet n 2003 dating open systems by the 238u 234u 230th method application to quaternary reef terraces earth and planetary science letters 210 1 2 105 118 and the linear regression or open system isochron is clearly limited for such old samples however the open system model developed by thompson et al thompson w g spiegelman m w goldstein s l and speed r c 2003 an open system model for u series age determinations of fossil corals earth and planetary science letters 210 1 2 365 381 appears to reliably correct for open system effects in roughly half of the corals giving a mis 15 origin for these thus the data provide evidence that the systematic addition of 230th and 234u through recoil is a dominant open system process occurring in the henderson island fossil reef system several coral samples yield significantly older thompson et al open system ages between 650 and 750 ka the uncertainty on these ages typically 30 kyrs is too great for precise assignment but most data overlap with the mis 17 interglacial the reliability of these ages is currently unclear it is shown that separate aliquots of the same coral can yield different thompson model ages therefore there appear to be additional diagenetic mechanisms that create further anomalous excursions in the u series systematics limiting the reliability of the thompson et al open system model

a study of uranium and thorium series isotopes in chalk groundwaters of lincolnshire u k a groundwater investigation is described in which uranium and thorium series radionuclides are applied to the study of the hydrogeologically well documented lincolnshire chalk aquifer system of north lincolnshire england the dominance of eh in controlling the uranium content of groundwaters is discussed and the 230th234u activity ratio used as an indicator of the speciation of uranium in highly reduced waters the 230th234u activity ratio approaches unity suggesting that the uranium in solution is behaving similarly to thorium in the 4 valence state in the oxidised environment the higher uranium content groundwaters exhibit lower 234u238u activity ratios a model of mixing young low 234u238u activity ratio fissure waters with old high 234u238u activity ratio pore waters is discussed but rejected it is considered that preferential dissolution of 234u in the lower rate weathering regimes produces the observed relationship between uranium content and activity ratio a method of in situ rn random release factor determination is suggested however the calculated values for rn are disproportionately high for a fissure flow system this along with evidence of a radium depleted aquifer matrix indicates that radium is being mobilised and transported from the pore water system to the fissure system and subsequently adsorbed by clay minerals lining the chalk fissures

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

high heat flow anomalies on an old oceanic plate observed seaward of the japan trench thirty three new measurements on the seaward slope and outer rise of the japan trench along a parallel of 38 45 n revealed the existence of high heat flow anomalies on the subducting pacific plate where the seafloor age is about 135 m y the most prominent anomaly with the highest value of 114 mw m2 is associated with a small mound on the outer rise which was reported to be a kind of mud volcano on the seaward slope of the trench heat flow is variable high 70 90 mw m2 at some locations and normal for the seafloor age about 50 mw m2 at others the spatial variation of heat flow may be related to development of normal faults and horst graben structures due to bending of the pacific plate before subduction with fluid flow along the fault zones enhancing the vertical heat transfer possible heat sources of the high heat flow anomalies are intra plate volcanism in the last several million years like that discovered recently on the pacific plate east of the japan trench

mud ridge on the crest of the outer swell off japan trench abstract a small mound of sediment was found on the deep ocean floor by a swath mapping survey associated with 3 5 khz subbottom profiling on the outer swell east off the japan trench at a depth of 5220 m it is 130 m high oblately elongated and situated on a ne sw trending normal fault no evidence of active seepage of deep methane rich water such as biological communities and an anomalous sediment color has been found by direct observation of the bottom using a deep towed television system the superficial and surrounding characteristics suggest that this mound is a type of mud volcano and be best called a mud ridge it would be the first diapir discovered in the deep floor oceanward of a trench the origin of this mound may be the injection of fluidized sediment expelled by highly compressed pore water through a normal fault plane associated with an earthquake shock generated by extensional forces caused by downward bending of the oceanic lithosphere near the trench

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

paleoecology of late pleistocene holocene faunas of eastern and central wyoming usa with implications for lgm climate models abstract oxygen and carbon isotope compositions of teeth were measured for a variety of fossil herbivores omnivores and carnivores from natural trap cave ntc and little box elder cave lbec central eastern wyoming usa these sites host some of the best preserved and most abundant late pleistocene to early holocene mammal fossils and provide key information about ecological and climatic change attending the pleistocene holocene transition average pleistocene compositions are consistent with c3 dominated diets but c4 grass consumption increased in bison from the late pleistocene to today a single sangamonian equus tooth also has elevated 13c suggesting that c4 biomass increased during interglacials in general tooth 18o values imply local water 18o values at ntc of 15 to 16 during the last glacial maximum lgm and 14 today consistent with modern regional studies and general circulation models gcm s for the lgm water 18o values at lbec were 12 although herbivore compositions are consistent with theoretical expectations carnivores exhibit lower 13c and higher 18o values relative to herbivores than anticipated these discrepancies could reflect poorly understood carnivore physiologies or diets and emphasize the need for further investigation of isotope systematics in carnivores isotope zoning in several herbivore teeth shows negative correlations between carbon and oxygen isotopes high and low 18o values representing summer and winter seasons occur with low and high 13c values respectively this trend could indicate seasonally changing diets e g consumption of drier foods or conifers during the winter or burning of stored fat during the winter increasing 18o values from the pleistocene to holocene in water dependent taxa are consistent with an increasing proportion of summer moisture derived from the gulf of mexico as predicted by isotope enabled gcm s mean annual precipitation during the late pleistocene is estimated at 350 mm yr similar to modern day c 200 mm yr indicating that dry conditions have prevailed for the last 25 ka in wyoming a revised analytical expression for c4 plant abundance in the western us is proposed that accounts for climate variables and pco2 combination of this expression with the climate predictions of the pmip2 ensemble average gcm explains lgm c4 plant abundances at ntc southern texas and florida changes to c4 plant abundances may provide sensitive tests of gcm accuracies

u isotope ratios as tracers of groundwater inputs into surface waters example of the upper rhine hydrosystem major elements trace elements and sr and u isotopes were analyzed in the dissolved load of water samples collected in the main reservoirs of the rhine graben i e the rhine river its main tributaries and the shallow and deep ground waters in several different aquifers our results confirm that the variations of major elements trace elements especially sr and rb and sr isotope ratios of the water samples are mainly correlated to the lithological variations of the watershed the atmospheric inputs can be considered as a minor cause for the chemical variability of the surface waters in the rhine hydrosystem except for a few chemical elements in the mountain streams human activity in particular the pollution by the exploitation of the alsace potash mines mainly affects the na and cl concentrations of the rhine and the south alluvial groundwaters but remains negligible for the other water samples the specific study of the lauter stream located in the lower triassic sandstones buntsandstein sequences demonstrates the importance of groundwater influences onto the chemical composition of river waters up to 50 of the total dissolved load tds of this stream is supplied by deep waters this contribution significantly modifies the chemical composition of the stream especially the 238u 234u radioactive disequilibrium which in turn can be used as a specific tracer of deep water inputs into surface waters and could be useful to distinguish in the dissolved load of rivers surface weathering fluxes from deeper ones

lacustrine cave carbonates novel archives of paleohydrologic change in the bonneville basin utah usa records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle however these records are often limited by dating precision and temporal resolution here we present data from lacustrine cave carbonates a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the bonneville basin of the northeastern great basin usa these dense carbonates precipitated within caves crevices and other protected spaces flooded by lake bonneville during its highstand in the last glacial period we report on deposits in cathedral and craners caves located 50 km apart at similar elevations approximately 100 m above the modern great salt lake and almost 200 m below lake bonneville s highstand shoreline carbonates from the two caves show similar chronologies mineralogical transitions isotopic compositions and uranium concentrations these findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water importantly the deposits can be precisely dated by u th methods providing the first records of lake bonneville s water balance changes tied to precise u th ages close agreement between paired u th and calibrated 14 c ages in the deposits suggests a minimal o200 a carbon reservoir effect in the lake and allows 14 c dating to be used for age control in portions of the deposits less suitable for u th dating we use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water we also present precisely dated high resolution oxygen and uranium isotope records from the deposits within a first phase of deposition reflecting the lake s transgression between 26 and 18 ka our isotopic data suggest a large influx of freshwater during heinrich stadial 2 a hiatus in deposition beginning at 18 270 3 ka may be the result of freshening related to the lake s overflow calcite deposition resumes at cathedral cave at 16 470 2 ka suggesting that basin overflow had ceased by this time and that the lake s calcite saturation state had increased andd 18 o values increase markedly after 15 9 ka consistent with drying at this time these data imply that the lake s deglacial regression began well before the bolling warming cessation of this second phase of deposition at 14 770 2 ka coincident with the bolling warming may reflect the lake s drop below cathedral cave s elevation a final stage of aragonite deposition between 13 8 and 13 6 ka differs from the underlying facies and may not reflect deposition from lake waters filling the cave

mud volcano field seaward of the barbados accretionary complex a deep towed side scan sonar survey a 30 km2 diapiric field has been identified near 13 50 n up to 12 km seaward of the deformation front of the barbados accretionary complex using a deep towed side scan sonar with a 3 5 khz profiler we identified 31 different diapiric structures based on seismic stratigraphy we show that this field has been active for 200 000 years and that it is a transient feature triggered by the seaward propagation of the high pore fluid pressure associated with the decollement beneath the accretionary complex both basement and decollement in this area are anomalously shallow due to the presence of a n110 basement ridge the height of the diapirs above seafloor does not exceed 40 50 m and can be related to the pressure head of the mud below the decollement two types of structures are identified mud volcanoes and massively emplaced diapirs and ridges on the one hand enigmatic circular very flat mud pies and conical mounds on the other hand the second type of structures has steeper slopes and appears to be associated with very active venting as confirmed by a submersible exploration reported in a companion paper le pichon et al this issue b the venting results in the formation of a stiff carbonate crust and of large subsiding basins around the mud pies continuous active fluid expulsion through these structures indicates that an efficient piping system still connects them to the zone of anomalously high pore pressure below the protodecollement

low δd hydration rinds in yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions hydration of silicic volcanic glass forms perlite a dusky porous form of altered glass characterized by abundant onion skin fractures the timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption during post eruptive cooling or much later at ambient temperatures to learn more about the origin of natural perlite and to fingerprint the hydration waters we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the yellowstone volcanic system perlitic cores are surrounded by a series of conchoidal cracks that separate 30 to 100 m thick slivers likely formed in response to hydration induced stress h2o and d h profiles confirm that most d h exchange happens together with rapid h2o addition but some smoother d h variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration the hydrated rinds 2 3 wt h2o transition rapidly within 30 m or by 1 wt h2o per 10 m to unhydrated glass cores this is consistent with quenched hydration fronts where h2o diffusion coefficients are strongly dependent on h2o concentrations the chemical 18o and d systematics of bulk glass records last equilibrium between 110 and 60 c without chemical exchange but with some 18o exchange similarly the 18o of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at 400 c experimental data the thick hydration rinds in perlites measuring hundreds of microns preserve the original d h values of hydrating water as a recorder of paleoclimate conditions measured d values in perlitic lavas are 150 to 191 or 20 40 lower than glass hydrated by modern yellowstone waters this suggests that yellowstone perlites record the low d signature of glacial ice cooling calculations combined with the observed high water diffusion coefficients noted for 60 150 c suggest that if sufficient hot water or steam is available any rhyolite flow greater than 5 m thick can develop the observed 250 m hydration rinds within the expected timescale of cooling weeks years as the process of hydration involves shattering of 30 to 100 m thick slivers to expose unhydrated rhyolite glass the time required for hydration may be even shorter rapid hydration and formation of relatively thick walled glass shards allow perlites to provide a snapshot view of the meteoric water and thus climate at the time of initial alteration perlites retain their initial hydration d h signal better than thin walled ash which in contrast hydrates over many thousands of years with time averaged precipitation

weathering rates from top to bottom in a carbonate environment abstract this study investigates u series sr isotopes major and trace elements in a chalk aquifer system located in eastern france soil and rock samples were collected along depth profiles down to 45 m in four localities as an attempt to investigate the weathering processes in the soil the unsaturated zone and the saturated zone of the aquifer interstitial water was extracted from soils and rocks by a centrifugation technique u series offer a powerful tool to calculate weathering rates because the relative mobility of the u and th isotopes can be precisely measured and it does not require the determination of a reference state as in other approaches as expected the data show very large mobile element depletion in the soil with large 230 th excess relative to 238 u while the rocks show more limited but not insignificant mobile element depletion the u series data have been used to constrain weathering rates based on a 1 d reactive transport model weathering rates in the near surface are about 10 100 times faster than at depth however when integrated over the depth of the cores including the unsaturated and the saturated zones this underground weathering represents more than 30 of the total weathering flux assuming congruent dissolution of carbonates the 234 u 238 u ratios in interstitial water are consistent with solid samples showing 234 u depletion near the surface and an excess 234 u at depth a leaching experiment performed on chalk shows that the excess 234 u in natural waters percolating through carbonate rocks results both from preferential 234 u leaching and direct recoil in the interstitial water a new approach was used to derive the recoil ejection factor based on bet measurements and the fractal dimension of chalk surface consideration of preferential leaching and recoil allows a more accurate modeling of weathering rates

mammoth tooth enamel growth rates inferred from stable isotope analysis and histology abstract mammoth mammuthus sp teeth are relatively abundant in quaternary deposits from eurasia and north america and their isotopic compositions can be used to reconstruct past seasonal patterns in precipitation diet and migration strategies for collecting and interpreting such data however are strongly dependent on growth rates which can vary among species individuals and within teeth in this study we use histological and isotopic measurements to determine enamel growth rates for a columbian mammoth mammuthus columbi tooth in two directions using histology the growth rate through the enamel thickness et perpendicular to the height of the tooth is estimated at 0 8 to 1 5 mm yr isotopic sampling through the innermost 0 36 mm of the et recovered less than half a period of variation i e half an inferred year of growth which is consistent with the histological estimate for et growth rate a combination of histological and isotopic measurements suggests that the enamel extension rate growth in the height of the tooth is 13 14 mm yr knowledge of enamel growth rates should improve the design and interpretation of future isotopic studies of mammoth teeth the combination of histological and isotopic measurements may also prove useful in determining growth rates for other extinct taxa

comment tooth enamel mineralization in ungulates implications for recovering a primary isotopic time series by b h passey and t e cerling 2002 passey and cerling 2002 presented both direct measurement and a theoretical model that describe rates of tooth enamel mineralization in ungulates hoofed mammals and the retrievability of environmental time series their results are quite important because ungulate teeth are common in the fossil record and readily analyzed for stable isotope compositions which makes them outstanding archives of paleoecological and paleoclimate information e g koch 1998 because tooth enamel grows progressively isotopic zoning in enamel potentially encodes isotopic seasonality however passey and cerling show that enamel mineralization processes must cause records of isotopic seasonality to be damped relative to an environmental signal according to their model damping is strongly dependent on lengths corresponding to rates of enamel maturation lm and lengthwise growth t they measured lm but provided no values for t and in their models instead assumed various ratios of lm t unlike many comments the purpose of this note is not to challenge their results per se but rather to point out that published zoning profiles for several ungulates permit estimation of t this in turn provides broad discrimination of their model results and estimates for the degree of environmental damping likely present in tooth isotopic records

mud diapirism and subcretion in the barbados ridge accretionary complex the role of fluids in accretionary processes mud diapirism has recently been recognized in several modern accretionary wedges it provides an important means of dewatering accretionary wedges and should be regarded as an important process for producing the melanges found in both modern and ancient accretionary terranes mud diapirism affects a large area of the barbados ridge accretionary complex the distribution of the mud diapirs appears to be primarily controlled by the presence of underconsolidated terrigenous submarine fan deposits that are being accreted to the complex the frequency of diapir occurrence decreases northward as the fan becomes thinner mud diapirs are absent from the very eastern most part of the complex formed from sediments accreted at its toe with the exception of a few mud volcanoes on the ocean floor in front of the complex the initiation of diapirism appears to be spatially coincident with the onset of subcretion or underplating of sediment to the base of the complex at a ramp between two levels of decollement it is proposed that the release of mud and pore water from the subcreted sediments is a direct or indirect cause of most of the mud diapirism in the accretionary complex there is a range of diapiric form dependent on the viscosity of the mud from mud volcanoes fed by low viscosity mud to higher viscosity mud ridges the diapirs in the eastern areas of the complex are generally mud volcanoes with narrow conduits feeding a surface mound mud ridges are prominent in the western parts of the complex this is interpreted as reflecting a general westward decrease in the fluid content of the accretionary complex bottom simulating seismic reflectors formed by gas hydrate are commonly developed in the areas of mud volcano occurrences the presence of the hydrate indicates that large volumes of methane are being generated at depth in these regions the generation of methane may be contributing to zones of overpressuring in the wedge methane may also be partly responsible for driving the diapiric material to the surface to form mud volcanoes ridges in the subducting oceanic crust beneath the accretionary complex locally enhance diapirism above their crests and southern flanks faults formed later in the development of the complex are more commonly associated with diapirism than those resulting from accretion at the toe of the wedge these later faults play an important role in controlling the sites of individual mud volcanoes chains of mud volcanoes and mud ridges

mud volcano field seaward of the barbados accretionary complex a submersible survey we describe a 0 55 km2 semicircular mud pie and three adjacent diapiric mounds explored using the submersible nautile near 13 50 n 12 km seaward of the barbados accretionary complex deformation front this diapiric field had been previously explored with an acoustically navigated deep towed side scan sonar thus providing an accurate base map the mud pie is situated at a depth of 4938 m in addition to visual observations water rock sediment and biological sampling we measured temperature gradients and made geochemical analyses of the samples fluid venting associated with chemosynthetic animal communities is widespread on all four structures but is maximal in the central third of the mud pie the chemosynthetic life distribution on the mud pie displays a concentric zonation which we relate to an increase in venting activity toward the center as evidenced by thermal gradients recent mud flows are present in the centralmost part of the mud pie the simplest interpretation of the structure is that it is a mud lake covered by a mechanically resistant carbonate crust we determine that approximately 106 m3 of fluid are advected upward through the crust of the mud lake every year this large amount of fluid implies large scale lateral transport

chemical weathering rates of a soil chronosequence on granitic alluvium iii hydrochemical evolution and contemporary solute fluxes and rates although long term changes in solid state compositions of soil chronosequences have been extensively investigated this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences the most direct linkage between weathering and hydrology over 3 million years of soil development in the merced chronosequence in central california relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans in a highly permeable younger soil 40 kyr old pore water solutes reflect seasonal to decadal scale variations in rainfall and evapotranspiration et this climate signal is strongly damped in less permeable older soils 250 to 600 kyr old where solutes increasingly reflect weathering inputs modified by heterogeneous flow elemental balances in the soils are described in terms of solid state exchange and pore water reservoirs and input output fluxes from precipitation et biomass solute discharge and weathering solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative k weathering flux reflecting aggradation by grassland plants the ratios of solute na to other base cations progressively increase with soil age discharge fluxes of na and si when integrated over geologic time are comparable to solid state mass losses in the soils implying similar past weathering conditions similarities in solute and sorbed ca mg ratios reflect short term equilibrium with the exchange reservoir long term consistency in solute ratios when contrasted against progressive decreases in solid state ca mg requires an additional ca source probably from dry deposition amorphous silica precipitates from thermodynamically saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils the degree of feldspar and secondary gibbsite and kaolinite saturation varies both spatially and temporally due to the seasonality of plant respired co2 and a decrease in organically complexed al in deeper pore waters k feldspar is in equilibrium and plagioclase is about an order of magnitude undersaturated hydrologic heterogeneity produces a range of weathering gradients that are constrained by solute distributions and matrix and macropore flow regimes plagioclase weathering rates based on precipitation corrected na gradients vary between 3 and 7 10 16 mol m 2 s 1 these rates are similar to previously determined solid state rates but are several orders of magnitude slower than for experimental plagioclase dissolution indicating strong inhibitions to natural weathering partly due to near equilibrium weathering reactions

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

in situ radionuclide transport and preferential groundwater flows at ineel idaho decay series disequilibrium studies uranium and thorium decay series disequilibria in groundwater occur as a result of water rock interactions and they provide site specific natural analog information for assessment of in situ long term migration of radionuclides in the far field of a nuclear waste disposal site in this study a mass balance model was used to relate the decay series radionuclide distributions among solution sorbed and solid phases in an aquifer system to processes of water transport sorption desorption dissolution precipitation radioactive ingrowth decay and recoil isotopes of u 238u 234u th 232th 230th 228th 234th ra 226ra 228ra 224ra and rn 222rn were measured in 23 groundwater samples collected from a basaltic aquifer at the idaho national engineering and environmental laboratory ineel idaho the results show that groundwater activities of th and ra isotopes are 2 4 orders lower than those of their u progenitors which average 1 35 0 40 dpm 238u l with 234u 238u ratios of 1 6 3 0 222rn activities range from 20 to 500 dpm l modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water rock interaction at ineel 1 time for sorption is minutes for ra and th time for desorption is days for ra and years for th and time for precipitation is days for th years for ra and centuries for u 2 retardation factors due to sorption average 106 for 232th 104 for 226ra and 103 for 238u 3 dissolution rates of rocks are 70 to 800 mg l y 4 ages of groundwater range from 10 to 100 years contours of groundwater age as well as spatial patterns of radionuclide disequilibria delineate two north south preferential flow pathways and two stagnated locales relatively high rates of dissolution and precipitation and recoil of 222rn occur near the groundwater recharging sites as well as in the major flow pathways decay of the sorbed parent radionuclides e g 226ra and 228ra on micro fracture surfaces constitutes an important source of their daughter 222rn and 228th activities in groundwater

geophysical survey of a mud volcano seaward of the barbados ridge accretionary complex a detailed geophysical investigation that included multibeam bathymetry 3 5 khz channel and single channel seismic profiles 20 heat flow measurements and four piston cores was made of a mud volcano located about 8 km seaward of the toe of the barbados ridge accretionary complex in the northern guiana basin the material erupted from the volcano covers an oval area about 3 9 km with its long axis oriented e w roughly perpendicular to the deformation front a flat topped mound on the western side of the feature is the currently active center acoustic stratigraphy suggests that mud volcanism began at the site about 200 000 ma a piston core taken on the flank of the active mound sampled deposits erupted 20 000 30 000 ma that contain late miocene nannofossils heat flow on the active mound is 4 times that in the surrounding basin one dimensional modeling of this anomaly supports a low level continuing flux of mud and water at rates of 2 5 cm yr the mud volcanism appears to have arisen from the combined action of overpressured water that comes from beneath the accretionary prism and existing overpressures in the oceanic section large east west trending basement escarpments underlie the two known mud volcanoes seaward of the barbados ridge accretionary complex and they probably play an important role in developing vertical pathways for fluid to escape and in determining the location where mud volcanism starts

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

deep tow survey in the kaiko nankai cold seepage areas deep sea biological communities associated with cold venting were located within the eastern portion of the nankai trough using a deep towed tv system five continuous lines approximately 200 km long were observed bivalve communities were found both in the tenryu canyon outlet region and at the outcrop of the frontal thrusts of the accretionary wedge off cape omaezaki the former is a site at which biological communities had been found during the kaiko dives in 1985 however the second site appears to be associated with larger scale venting and was chosen for the 1989 kaiko nankai submersible cruise three small mud volcanoes with diameters of several hundred meters and heights of several tens of meters are found in the seabeam topography map but the present survey showed neither evidence of recent venting nor biological communities

generation of high pore pressures in accretionary prisms inferences from the barbados subduction complex recent geological and geophysical exploration of several accretionary complexes reveals that pore pressures inside them are much higher than the hydrostatic values indirect inferences further suggest that such high pore pressures may be present inside most accretionary complexes in this study the mechanisms for generating excess pore pressures is investigated by focusing on the barbados ridge complex which is an end member of sediment rich accretionary prisms modeling is carried out using a two dimensional finite element procedure with constraints provided by the following data deep sea drilling project results on stratigraphy and lithology seismic results on sediment structure and thickness regional geology on tectonic history and laboratory measurements on mechanical properties of sediments coupling among the equations for fluid flow heat transfer and sediment deformation is made throughout the computation the results of the modeling predict that the principal decollement beneath the barbados ridge complex is a zone of high pore pressure high porosity and reversal in seismic velocity these characteristics may be responsible for the mechanical weakness of the decollement which allows continuous subduction of sediments below it and for its seismic signatures results of the modeling further suggest that tectonic overburden may be the most important mechanism for the generation of high pore pressures inside accretionary prisms the direct effect of tectonic compression is of secondary importance and the effect due to temperature increase with subduction is of little significance thrust faulting near the toe of accretionary prisms can disturb pore pressure patterns and produce localized highs rich sediment supply low permeability high subduction angle and high subduction velocity are all favorable factors in creating high pore pressures inside accretionary prisms

sediment transport time measured with u series isotopes results from odp north atlantic drift site 984 abstract high precision uranium isotope measurements of marine clastic sediments are used to measure the transport and storage time of sediment from source to site of deposition the approach is demonstrated on fine grained late pleistocene deep sea sediments from ocean drilling program site 984a on the bjorn drift in the north atlantic the sediments are siliciclastic with up to 30 carbonate and dated by 18o of benthic foraminifera nd and sr isotopes indicate that provenance has oscillated between a proximal source during the last three interglacial periods volcanic rocks from iceland and a distal continental source during glacial periods an unexpected finding is that the 234u 238u ratios of the silicate portion of the sediment isolated by leaching with hydrochloric acid are significantly less than the secular equilibrium value and show large and systematic variations that are correlated with glacial cycles and sediment provenance the 234u depletions are inferred to be due to recoil loss of 234th and are used to calculate comminution ages of the sediment the time elapsed between the generation of the small 50 m sediment grains in the source areas by comminution of bedrock and the time of deposition on the seafloor transport times the difference between comminution ages and depositional ages vary from less than 10 ky to about 300 to 400 ky for the site 984a sediments long transport times may reflect prior storage in soils on continental shelves or elsewhere on the seafloor transport time may also be a measure of bottom current strength during the most recent interglacial periods the detritus from distal continental sources is diluted with sediment from iceland that is rapidly transported to the site of deposition the comminution age approach could be used to date quaternary non marine sediments soils and atmospheric dust and may be enhanced by concomitant measurement of 226ra 230th 230th 234u and cosmogenic nuclides

moisture source temperatures and precipitation δ18o temperature relationships across the united states 1 understanding and modeling precipitation isotope 18 o and 6d patterns for large regions of the globe requires quantifying processes governing continental scale climatology and hydrology in this study we have evaluated the extent to which inclusion of monthly moisture source temperature and moisture source locations in the rayleigh distillation model aid in reproducing the relationships between monthly time series of precipitation isotope 18 o values and temperature across the contiguous united states the steepest isotope temperature slopes 0 5 0 6 18 o c and greatest 18 o value correlations with temperature r 2 0 5 0 8 derived from 5 continuous years of the data from the united states network for isotopes in precipitation occurred in the high altitudes of the rocky mountains and the upper great lakes region the isotope temperature slopes derived from the site specific time series were consistently lower along the coastal regions of the united states as were the coefficients of determination the low coastal isotope temperature slopes are not easily explained by the simple rayleigh model that uses condensation temperatures as the primary driver of precipitation isotopes however the raleigh model equipped with moisture source temperatures defined by seasonal temperature oscillations and migrating moisture source locations provides a robust replication of the 18 o temperature slopes along coastal regions these findings emphasize the importance of moisture sources conditions when interpreting palaeoclimate proxies i e tree rings ice cores etc and argue that moisture source dynamics should always be included in models that use isotopes as diagnostic tools in testing hydrologic models

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

isotopic evidence for shifts in atmospheric circulation patterns during the late quaternary in mid north america wyoming is now at the eastern margin of westerlies originating in the pacific but in the pleistocene appears to have received moisture from elsewhere possibly the gulf of mexico oxygen isotope ratios of pedogenic carbonate in postglacial terraces correspond to ratios in equilibrium with present meteoric waters which show a strong relation to precipitation seasonality and storm sources in contrast the oxygen isotope ratios of all pre holocene soils are significantly more positive even though the carbon isotope composition of coexisting organic matter suggests that the carbonate formed in temperatures cooler than today the oxygen isotope ratios of paleowaters in mid north america appear to be more useful for identifying past storm sources than for estimating paleotemperatures

234u 238u activity ratios of dissolved uranium in groundwaters from a jurassic limestone aquifer in england abstract uranium contents and234u 238u activity ratios have been determined for groundwaters from the lincolnshire limestone artesian aquifer in eastern england changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone the western part of the aquifer closest to recharge is dominated by oxidising groundwaters which then enter a reducing zone towards the east where there is an abrupt decrease in eh and the chlorinity of the groundwaters begins to increase uranium contents in the oxidising zone range from 0 7 to 3 4 g kg 1 and234u 238u activity ratio of this dissolved uranium is close to unity the equilibrium value the uranium content decreases abruptly when the grounwaaters enter the reducing zone averaging 0 04 g kg 1 east of the oxidation reduction barrier simultaneously with the decrease in uranium content there is an increase in234u 238u activity ratio and this ratio increases to a maximum within 7 km of the oxidation reduction barrier this increase in activity ratio is attributed to enhanced234u solution due to234th recoil from uraniferous fissure surfaces east of the oxidising zone the activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234th recoil from the oolith surfaces however the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium 234th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium bearing surfaces in the process of oolith cementation

the transport of u and th series nuclides in sandy confined aquifers a comprehensive evaluation of the transport of u th ra and rn nuclides of the 238 u and 232 th decay series in an unconfined sandy aquifer long island ny was conducted groundwater data are compared with results of a theoretical transport model of weathering of aquifer grains and interaction with surface coatings to establish relationships between the concentrations of the radionuclide activities in the water and flow line distance the data provide estimates for geochemical parameters including weathering rates and chemical reactivities in both the vadose zone and the aquifer a theoretical treatment of the transport is presented that considers the reaction between the water and a reactive surface layer it is found that a model with chemical exchange between the surface layer and the water for all species is not valid and that the effects of saturation and irreversible precipitation of th is required the water table shows a relatively wide range in u activities the only element in the u th series for which vadose zone input is significant in the aquifer high weathering of u and recoil inputs of 234 u to the water occur in the upper 3 m of the vadose zone while lower weathering and removal of u from the water occur below the deeper aquifer has variable 238 u activities that can be accounted for by input from the vadose zone and is not a result of non conservative behavior the isotopic composition of u is shown to be directly related to the recoil rate relative to the weathering rate the wide range of 238 u in the aquifer waters is a reflection of diverse vadose zone inputs showing that dispersive mixing is not a dominant effect the higher values of 234 u in the aquifer reflect the recoil weathering input ratios from within the aquifer where the weathering rate is lower than the vadose zone both high u activities and high 234 u values cannot be obtained in the vadose zone or within reasonable flow distances in the aquifer radium isotopes are found to be in exchange equilibrium with the surface layer 224 ra 228 ra and 226 ra have comparable activities throughout the aquifer in the vadose zone the dominant input of ra to groundwater is weathering and recoil as found elsewhere the 222 rn in the water is a large fraction 5 of the rn produced in the aquifer rock this cannot be due to ra precipitation onto surface coatings in the aquifer as supported by present weathering with th in exchange equilibrium with the surface layer it is found that th is saturated in the waters under oxidizing conditions so that the weathering input is irreversibly precipitating onto surfaces however it is shown that under somewhat reducing conditions th activities are much higher and the th u ratio in the solution is approximately that of the rock we propose that under oxidizing conditions the source of rn is a surface coating enriched in 232 th and 230 th this th was precipitated in an earlier phase during rapid dissolution of readily weathered phases that contain 10 of the u th inventory of the rock with the associated u carried away in solution therefore the previously precipitated 230 th and 232 th produce daughter nuclides in the surface coating which are the dominant contributors of ra and rn to the ground water in particular rn is provided by very efficient losses by diffusion or recoil from the surface coating this then does not require recent large recoil losses from the parent rock or the presence of nanopores in the rock the first data of both long lived 232 th and short lived 234 th and 228 th in ground water is reported the th isotope activities indicate that desorption kinetics are slow and provide the first estimate based on field data of the th desorption rate from an aquifer surface the mean residence time of th in the surface coating is 3000 y while in the water it is 1 h ra is in partition equilibrium with the aquifer surface layer however the strong fixation of th on surface coatings is very susceptible to changes in oxidation state as is shown by a comparison of two adjacent aquifers this makes it difficult to define with certainty the retentive characteristics in natural systems in general it is shown that the distributions of naturally occurring nuclides can be used to calculate values for transport parameters that are applicable to the transport of anthropogenic nuclides

quantification of chemical weathering rates across an actively eroding hillslope abstract chemical weathering rates for landscapes are difficult to quantify because the timescales over which weathering occurs are often unknown in this study we use timescales defined by prior cosmogenic nuclide analyses and a suite of geochemical measurements to calculate weathering rates in saprolite and soil and to determine how these rates vary across an eroding hillslope we also estimate the relative contributions of solute and erosional mass loss to landscape lowering analyses were conducted on a soil mantled hillslope developed on a granodiorite pluton in southern nsw australia mass loss in solution accounts for 35 to 55 of the total mass loss from the hillslope saprolite close to the soil saprolite boundary is less weathered at the ridge than at distance from the ridge the calculated flux of silica from the saprolite is 5 tons km 2 yr 1 and does not vary with distance from the ridge or overlying soil thickness the assumption of steady state but spatially variable erosion rates with a temporally constant thickness of soil and saprolite allows us to calculate the downslope variation in the rate of solute losses soil silica weathering rates initially increase from 12 tons km 2 yr 1 at the ridge crest to 20 tons km 2 yr 1 on the convex region of the hillslope and then decrease to 13 tons km 2 yr 1 by the time soils have been transported 45 50 m soils closer to the surface are more weathered than deeper soils this geochemical stratification suggests that the soil column does not become thoroughly vertically mixed as soils move down slope dependence of solute loss on transport distance may explain the previously noted discrepancy between the observed soil thickness and that predicted based on curvature variation of solute loss with transport distance may also contribute to the linear dependence of soil thickness on distance from the ridge

the mechanism of 234u238u activity ratio enhancement in karstic limestone groundwater departamento de petrologia e metalogenia universidade estadual paulista campus de rio claro unesp sao paulo

234u 238u 230th 232th systematics in saline groundwaters from central missouri saline groundwaters with 4 7 to 26 total dissolved solids were sampled from springs and artesian wells in mississippian and ordovician carbonates and sandstones in central missouri u th isotopic variations provide a means of evaluating processes of water rock interaction and fluid mixing and estimating the time scales of element transport recently developed mass spectrometric techniques are used to make isotopic measurements on small volume groundwater samples 0 1 4 l with high precision e g 5 for 234 u 238 u activity ratios the groundwaters have a wide range of 238 u concentrations 50 10 12 to 200 10 12 g g 234 u 234 u activity ratios 2 15 16 0 232 th concentrations 0 10 10 12 to 33 10 12 g g and 230 th concentrations 0 91 10 17 to 26 10 17 g g unfiltered and filtered 0 4 m 0 1 m aliquots of a saline sample have the same isotopic composition and concentration of u indicating that 234 u and 238 u occur almost entirely as dissolved species the concentration of 232 th is up to seven times lower in filtered vs unfiltered aliquots indicating that 232 th is predominantly associated with particulates in the groundwaters in contrast most of the 230 th is in solution previous geochemical studies indicate that 1 the saline waters originated as meteoric recharge and evolved through halite dissolution reactions with silicates and saline dilute mixing processes during a long distance flow history and 2 interaction with limestone and dolomite aquifer rocks in central missouri has been limited a consistent relationship between u ca and 234 u 238 u activity ratio is observed in the groundwaters and provides constraints on the u ca ratios and 234 u 238 u activity ratios of end member reservoirs and on the processes of isotopic exchange in this water rock system model calculations that simulate 1 saline dilute groundwater mixing and 2 limited extents of dissolution of carbonate aquifer minerals by the groundwaters can account for the variations in u ca 234 u 238 u and 18 o 16 o in the suite of water samples the model calculations demonstrate that dissolved u isotopic compositions can be a sensitive indicator of water rock interaction which in turn limits the usefulness of 234 u 238 u disequilibria for groundwater age determinations the concentration of dissolved 230 th in the groundwaters is 1 two to three orders of magnitude below 230 th 234 u equilibrium activity levels and 2 significantly in excess of concentrations estimated for the supply of th to solution via desorption and dissolution a model involving the derivation of the excess 230 th from the in situ decay of dissolved 234 u in the groundwaters indicates the operation of an adsorption mechanism on the time scale of 10 10 3 years the results reported here may have broader application to the assessment and management of hazardous chemical species in natural environments