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

pore fluid advection and reaction in sediments of the eastern flank juan de fuca ridge 48 n abstract pore water data collected during ocean drilling program odp leg 168 provide an opportunity to study advection and reaction in hemipelagic sediments in an off axis hydrothermal setting we have modelled the pore water so42 profiles to obtain estimates of vertical advective darcy velocities strong downwelling at rates of 0 3 0 9 mm a 1 occurs at a site 4 km from the boundary between sediment free and sediment covered ridge downwelling velocities weaken away from the boundary twenty kilometres to the east strong upwelling at 2 mm a 1 is indicated at two sites 1030 and 1031 drilled above a basement high further eastwards where sediment thicknesses are in excess of 200 m vertical advective pore fluid flow through the sediment column is weak confining flow to the basement aquifer extension of the so42 model to pore fluid alkalinity mg2 and ca2 profiles enables the effects of reactions within the sediment column to be examined sulfate reduction leads to the production of alkalinity but the alk so42 ratios are less than the theoretical ratio of 2 at all the sites studied the discrepancy is largely explained by the precipitation of calcium carbonate and by the diagenetic reactivity of magnesium in the pore fluids alkalinity results are consistent with both sources and sinks for mg2 within the sediment column dependent on the direction of pore fluid advection

estimation of actual evapotranspiration from an alluvial aquifer of the kouris catchment cyprus using continuous streamflow records the kouris catchment is located in the south of the troodos massif in cyprus the hydrology is driven by a mediterranean climate a mountainous topography and a complex distribution of hydrogeological properties resulting from complex geology to quantify the regional water balance further a simple method using continuous streamflow records in the river limnatis kouris catchment was applied to calculate the actual evapotranspiration rate in the dry seasons it was found that daily cycles of streamflow recorded by automatic pressure logger were caused by direct evaporation from the groundwater table and by transpiration of riparian forest the daily amounts of missing streamflow were calculated for the period 30 october 4 november 2001 and were extrapolated to the entire dry season and to the whole kouris catchment the actual evapotranspiration rate from the alluvial aquifer of the region is 2 4 0 5 mm3 for april september 2001 the validity of the assumptions and the uncertainties in the estimates used in the method are discussed copyright 2005 john wiley sons ltd

a physical model of the bidirectional reflectance of vegetation canopies 2 inversion and validation a physically based analytical model of the bidirectional reflectance of porous media was derived in a companion paper verstraete et al this issue this model is validated against laboratory and ground based measurements taken over two vegetation covers both in the visible and near infrared spectral regions an inversion procedure based on a nonlinear optimization technique is used to infer the intrinsic optical properties of the leaves as well as information on the morphology of the canopies that is on the geometrical arrangements of these scatterers in space the model is then used to generate theoretical bidirectional reflectances using the values of the relevant parameters retrieved from the inversion procedure and these values compare favorably with the actual observations over the entire range of illumination and observation angles the values of the parameters retrieved from the inversion procedure are discussed validated against actual independent measurements and interpreted in terms of the physical and morphological properties of the vegetation covers

oxygen isotope constraints on surface ocean temperatures published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time the possible impacts of bioturbation and of the redistribution of 18o16o ratios within the sea putting aside the oxygen isotope results are consistent with the climap project conclusion that tropical ocean temperatures remained within 2 c of their present value

calcium isotope evidence for suppression of carbonate dissolution in carbonate bearing organic rich sediments pore fluid calcium isotope calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep sea sediments containing abundant clay and organic material this type of study of deep sea sediment diagenesis provides unique information about the ultra slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo environmental information in carbonate fossils for this study calcium isotope ratios 44 40ca of pore fluid calcium from ocean drilling program odp sites 984 north atlantic and 1082 off the coast of west africa were measured to augment available pore fluid measurements of calcium and strontium concentration both study sites have high sedimentation rates and support quantitative sulfate reduction methanogenesis and anaerobic methane oxidation the pattern of change of 44 40ca of pore fluid calcium versus depth at sites 984 and 1082 differs markedly from that of previously studied deep sea sites like 590b and 807 which are composed of nearly pure carbonate sediment in the 984 and 1082 pore fluids 44 40ca remains elevated near seawater values deep in the sediments rather than shifting rapidly toward the 44 40ca of carbonate solids this observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate rich sites the data are fit using a numerical model as well as more approximate analytical models to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material our models give mutually consistent results and indicate that calcite dissolution rates at sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate rich sites and the rate correlates with the abundance of clay our calculated rates are conservative for these sites the actual rates could be significantly slower because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included the results provide direct geochemical evidence for the anecdotal observation that the best preserved carbonate fossils are often found in clay or organic rich sedimentary horizons the results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals slowing dissolution dramatically even in relation to the already slow rates typical of carbonate rich sediments

gravitational trapping of carbon dioxide in deep sea sediments permeability buoyancy and geomechanical analysis 1 liquid carbon dioxide injected in deep sea sediments at km depths and near freezing temperatures is denser than surrounding pore water and will be trapped by gravitational forces storage capacity for co2 in such formations below the ocean floor is shown to vary with seafloor depth geothermal gradient porosity and pore water salinity the formation permeability or the successful engineering of such permeability through hydraulic fracturing will determine the capacity for gravitational trapping in deep sea geological formations we conclude that most ocean sediments at appropriate depth will lack the required permeability and that conventional hydraulic fracturing would only be possible in carefully selected sites

introduction to calcium isotope geochemistry past lessons and future directions abstract calcium ca isotopes have been utilized as geochemical tools since the 1970s increasing in popularity and scope since the mid to late 1990s research conducted over the past thirty years has revealed a range of applications for ca isotopes that are highlighted in this introduction and special issue as well as a series of interesting and fundamental problems that have yet to be resolved for such a chemically simple system in comparison to redox active elements for instance the level of complexity is both surprising and intellectually attractive while the advent of multiple collector inductively coupled plasma mass spectrometers made metals such as fe mg and zn considerably more accessible analytically the precision and ease of ca isotopic analysis did not radically improve in a comparable manner for a variety of reasons one of which may be perceived analytical difficulty the application of ca isotopes to geological questions remains in the shadows to some extent in the geosciences in this introduction we identify i areas that we think are most fertile for the application of ca isotopes as tools and ii outstanding questions and future directions that can move the field towards increased utility and broader acceptance by the geosciences community

controls on calcium isotope fractionation in sedimentary porewaters abstract the calcium isotopic composition of porewaters and authigenic carbonates in the anoxic sediments of a convergent continental margin drilled during ocean drilling program odp provides first insight into the different processes that control ca geochemistry in clastic marine organic rich sedimentary environments in 4 sites drilled during leg 204 at hydrate ridge cascadia margin offshore oregon usa sulfate is consumed during anaerobic oxidation of methane and of organic matter via sulfate reduction within the upper meters of the sedimentary section these reactions promote the precipitation of authigenic carbonates through the generation of bicarbonate which is reflected in a pronounced decrease in calcium concentration although ca isotope fractionation is observed during carbonate precipitation ca concentration in the pore fluids from odp leg 204 is decoupled from ca isotopy which seems to be mainly controlled by the release of light ca isotopes that completely overprint the carbonate formation effect different processes such as the release of organically bound ca ion exchange and ion pair formation may be responsible for the released light ca deeper within the sedimentary section additional processes such as ash alteration influence the ca isotopic composition of the porewater two sites drilled into the deeper core of the accretionary prism reveal the nature of fluids which have reacted with the oceanic basement these deep fluids are characterized by relatively high ca concentrations and low 44 40ca ratios

a paleoceanographic model for the late campanian early maastrichtian sedimentation in the polish carpathian flysch basin based on nannofossils abstract the study is a qualitative and semi quantitative analysis of calcareous nannofossils in marlstone and calcareous mudstone beds in a 4 6 m thick section of the kropivnik fucoid marls late campanian early maastrichtian in the skole nappe of the polish outer carpathians this turbiditic succession is conspicuous by its short term alternation of marlstone rich and siliciclastic rich packages ca 1 m thick a model for paleoceanographic control on sedimentation is proposed on the basis of nannofossil assemblages in the studied section the nannofossils form assemblages of mixed synsedimentary taxa derived from diverse marine environments differing in trophy water temperature and distance from land the mixing occurred due to submarine resedimentation processes the nannofossils indicate that the siliciclastic rich packages were deposited during periods of lowered water temperature decreased calcareous nannoplankton production and oligotrophic to mesotrophic water conditions which corresponded to the sea level fall and lowstand anti estuarine circulation and downwelling due to arising shelf break front are inferred as the factors responsible for oligotrophy in contrast in the marlstone rich packages the calcareous nannofossils indicate sedimentation during periods of significantly increased calcareous nannoplankton production which corresponded to the sea level rise and highstand the increased nannoplankton production is attributed to estuarine circulation and upwelling the changes in sea level and water circulation conform to the climate changes postulated independently for the late campanian early maastrichtian

evaluation of topographic effects in remotely sensed data abstract remotely sensed data are generally analyzed assuming flat terrain as the spectral signature of the ground depends upon the orientation of the surface slope the topography has to be considered for efficient radiometric corrections in mountainous regions in this paper we present a modelization of the atmospheric downward radiance at the ground level which gives us the relative contributions of the direct solar beam and of the diffused radiation for different atmospheric turbidities and different solar incidence angles lastly we estimate the influence of the topography on these contributions to show up which effects can be neglected

numerical models for diagenesis and the neogene sr isotopic evolution of seawater from dsdp site 590b abstract a numerical model for the diagenetic exchange of sr between carbonates and their pore fluids during sedimentation and compaction has been developed the model has been applied to data from dsdp site 590b in order to assess the accuracy with which the sr isotope record in the carbonate sediment reflects that of seawater the most important process affecting the sr in the solid carbonate is exchange with the pore fluid due to solution reprecipitation but the concentration or isotopic composition of sr in the solid itself gives little or no information as to the magnitude of this exchange the key to determining the rate of exchange is the pore fluid where the variations of sr2 and87sr 86sr with depth are very sensitive indicators the logical structure of applying the model to data from dsdp 590b is to find by successive iteration an ocean history i e the initial87sr 86sr and sr concentration of each increment of carbonate deposited and a rate of sr exchange between pore water and solid carbonate such that the model matches the present sr concentration and87sr 86sr of both pore water and solid carbonate once all the data are matched the model provides an estimate of the rate of sr exchange due to solution reprecipitation and the evolution of87sr 86sr in seawater over the past 20 million years for dsdp 590b we find that solution reprecipitation decreases rapidly with depth from a near surface value of about 10 per million years to about 1 per million years below 200 m this rate of exchange of sr results in the carbonates of dsdp 590b preserving an accurate record of the sr isotopic evolution of the ocean over the past 5 million years but for ages greater than 5 million years the87sr 86sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited the maximum difference is of order 5 10 5

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

fluid flow in deep sea carbonates estimates based on porewater sr abstract fluid flow of up to 200 m myr is documented in thick about 500 m deep sea carbonate sections by numerical modeling of the porewater sr 2 and 87 sr 86 sr profiles at dsdp sites 572 573 and 574 these sites were selected as likely candidates for significant fluid flow in the sedimentary part of the section because it had already been shown that they are underlain by rapidly flowing fresh seawater in the basaltic basement the nature of the exercise is to fit the porewater sr properties at these sites by finding a common rate of sr exchange as a function of sediment age and a local rate of vertical fluid flow the flow rates determined in this way are 20 m myr upwards at site 574 20 m myr downwards at site 573 and 200 m myr downwards at site 572 because of uncertainties of about a factor of 2 in the assumption of a common rate of sr exchange at all sites and trade offs between the sr exchange and fluid flow in determining the shape of sr 2 and 87 sr 86 sr profiles at a given site the precision of the method is of the order of 10 m myr thus at least at site 572 the sr properties of the interstitial waters provide a convincing measure of vertical fluid flow through a thick carbonate section

models for the coupled sr sulfate budget in deep sea carbonates a numerical model for the sr and sulfate budgets during deposition of deep sea carbonate sediments was developed and used to fit porewater sr2 and so42 data from dsdp sites 593 590 574 573 572 516 and 289 the sr and sulfate budgets are coupled whenever the porewaters become saturated with respect to celestite srso4 models for the porewater sr and sulfate at sites 593 590 516 and 289 suggest that porewater sr concentrations are controlled by the precipitation of celestite and predict maximum celestite concentrations of the order of 0 02 wt for sediments at sites 593 590 and 289 and trace amounts of celestite at site 516 the actual amount of celestite predicted by the model is not well constrained because it depends on the as yet poorly known value of the equilibrium distribution coefficient for sr between calcite and porewaters the fact that celestite has been found in sediments from sites 590 and 593 is used to derive an upper bound for the sr distribution coefficient that suggests that all laboratory determined values for the sr distribution coefficient between calcite and porewater are too large the occurrence of celestite at sites 593 590 516 and 289 does not significantly change earlier estimates of the rates of solution reprecipitation of calcite and its consequences in terms of shifting the sr content or sr isotopic composition of the bulk sediment from what the sediment incorporated when originally deposited the sulfate data at sites 593 and 590 are best fit by invoking a flow of porewater within the sediments of the order of 75 m ma the sr and sulfate concentrations in porewaters from sites 572 573 and 574 never reach celestite saturation and thus the two budgets are decoupled both the sr and the sulfate data require that all three sites have abundant unaltered seawater flowing in the underlying basement and can only be modeled if seawater concentrations of sr and sulfate are imposed as boundary conditions at both the sediment water interface and the bottom of the section model sulfate profiles for sites 572 573 and 574 confirm prior estimates of the rate of porewater flow at these sites that were made using sr data

strontium and its isotopic composition in interstitial waters of marine carbonate sediments abstract the concentrations and isotopic compositions of strontium in interstitial waters from several dsdp sites where sediments consist chiefly of carbonate oozes and chalks are used as indicators of carbonate diagenesis by reference to a recently produced curve showing detailed variations in the87sr 86sr ratio of seawater with time carbonate sediments of the walvis ridge show increases in interstitial sr2 concentrations in the upper carbonate ooze sections with the highest concentrations near the ooze chalk boundary where maximum rates of carbonate recrystallization occur below this in situ production of sr2 diminishes and there is a diffusive flux of sr to an underlying sink presumably volcanogenic sediments or basalts leading to sr isotopic disequilibrium between carbonates and interstitial waters in some other sites however there is no apparent sr sink at depth and isotopic equilibrium is retained overall diffusive smoothing of profiles exerts an important control on the87sr 86sr ratios although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of mg2 loss and reflect a combination of a flux of sr2 from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter

anaerobic methane oxidation and the formation of dolomite abstract we examine the link between organic matter degradation anaerobic methane oxidation amo and sulfate depletion and explore how these processes potentially influence dolomitization we determined rates and depths of amo and dolomite formation for a variety of organic rich sites along the west african margin using data from ocean drilling program odp leg 175 rates of amo are calculated from the diffusive fluxes of ch4 and so4 and rates of dolomite formation are calculated from the diffusive flux of mg we find that the rates of dolomite formation are relatively constant regardless of the depth at which it is forming indicating that the diffusive fluxes of mg and ca are not limiting based upon the calculated log iap values log ksp values for dolomite were found to narrowly range between 16 1 and 16 4 dolomite formation is controlled in part by competition between amo and methanogenesis which controls the speciation of dissolved co2 amo increases the concentration of co32 through sulfate reduction favoring dolomite formation while methanogenesis increases the pco2 of the pore waters inhibiting dolomite formation by regulating the pco2 and alkalinity methanogenesis and amo can regulate the formation of dolomite in organic rich marine sediments in addition to providing a mechanistic link between amo and dolomite formation our findings provide a method by which the stability constant of dolomite can be calculated in modern sediments and allow prediction of regions and depth domains in which dolomite may be forming

ca isotopes in carbonate sediment and pore fluid from odp site 807a the ca2 aq calcite equilibrium fractionation factor and calcite recrystallization rates in pleistocene sediments abstract the calcium isotopic compositions 44ca of 30 high purity nannofossil ooze and chalk and 7 pore fluid samples from odp site 807a ontong java plateau are used in conjunction with numerical models to determine the equilibrium calcium isotope fractionation factor s f between calcite and dissolved ca2 and the rates of post depositional recrystallization in deep sea carbonate ooze the value of s f at equilibrium in the marine sedimentary section is 1 0000 0 0001 which is significantly different from the value 0 9987 0 0002 found in laboratory experiments of calcite precipitation and in the formation of biogenic calcite in the surface ocean we hypothesize that this fractionation factor is relevant to calcite precipitation in any system at equilibrium and that this equilibrium fractionation factor has implications for the mechanisms responsible for ca isotope fractionation during calcite precipitation we describe a steady state model that offers a unified framework for explaining ca isotope fractionation across the observed precipitation rate range of 14 orders of magnitude the model attributes ca isotope fractionation to the relative balance between the attachment and detachment fluxes at the calcite crystal surface this model represents our hypothesis for the mechanism responsible for isotope fractionation during calcite precipitation the ca isotope data provide evidence that the bulk rate of calcite recrystallization in freshly deposited carbonate ooze is 30 40 myr and decreases with age to about 2 myr in 2 3 million year old sediment the recrystallization rates determined from ca isotopes for pleistocene sediments are higher than those previously inferred from pore fluid sr concentration and are consistent with rates derived for late pleistocene siliciclastic sediments using uranium isotopes combining our results for the equilibrium fractionation factor and recrystallization rates we evaluate the effect of diagenesis on the ca isotopic composition of marine carbonates at site 807a since calcite precipitation rates in the sedimentary column are many orders of magnitude slower than laboratory experiments and the pore fluids are only slightly oversaturated with respect to calcite the isotopic composition of diagenetic calcite is likely to reflect equilibrium precipitation accordingly diagenesis produces a maximum shift in 44ca of 0 15 for site 807a sediments but will have a larger impact where sedimentation rates are low seawater circulates through the sediment pile or there are prolonged depositional hiatuses

variations in the marine ca cycle over the past 20 million years a 20 million year marine ca isotope record is constructed based on measurements of 36 nannofossil ooze samples from dsdp site 590 the ca isotopic composition d 44 ca relative to our bbulk earthq average of carbonate ooze samples varies between 0 2 and 0 9 and the inferred d 44 ca of seawater calcium varies between 1 1 and 0 4 modern seawater value is 0 95 on our scale fluctuations in the seawater ca isotope ratio occur in 2 to 4 million year intervals and indicate that the supply and removal of ca from the oceans are seldom in balance the ca isotope record is used to reconstruct past weathering fluxes and marine calcium concentrations the inferred marine concentration of ca fluctuates by about f20 on 2 4 million year time scales and by about f50 over the 20 million year record these variations are presumably superimposed on the previously inferred 100 million year variations the seawater ca concentration was about 0 5 times present at 20 ma and generally increased until 6 ma 1 7 times present local maxima in seawater calcium concentrations occur at 6 4 and 4 ma preceding periods of enhanced marine productivity and high mass accumulation rates at site 590 while the calculated calcium concentrations are sensitive to the assumed d 44 ca value for the weathering flux the 2 4 million year features of the derived

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

δ44ca evolution in a carbonate aquifer and its bearing on the equilibrium isotope fractionation factor for calcite abstract to improve understanding of ca isotope transport during water rock interaction on the continents we measured dissolved 44 ca values along a 236 km flow path in the madison aquifer south dakota where fluids have chemically evolved according to dolomite and anhydrite dissolution calcite precipitation and ca for na ion exchange over a timescale spanning 15 kyr we used a reactive transport model employing rate data constrained from major ion mass balances to evaluate the extent to which calcite precipitation and ion exchange fractionate ca isotopes elevated 44 ca values during the initial and final stages of water transport possibly result from calcite precipitation under supersaturated conditions and ca for na ion exchange respectively however for the bulk of the flow path 44 ca values evolve by mixing between anhydrite and dolomite dissolution with no fractionation during calcite precipitation under saturated conditions we attribute the absence of ca isotope fractionation to the long timescale of water rock interaction and slow rate of calcite precipitation which have enabled fluids to chemically and isotopically equilibrate with calcite we therefore conclude that the equilibrium ca isotope fractionation factor between calcite and water cal w is very close to zero to the extent that the madison aquifer typifies other groundwater systems where calcite slowly precipitates from solutions at or near chemical equilibrium this study suggests that groundwater contributions to 44 ca variability on the continents can be modeled according to simple mixing theory without invoking isotope discrimination

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

the rate and consequences of sr diagenesis in deep sea carbonates we have used a diffusion advection reaction model for sr exchange during deep sea carbonate diagenesis to determine the rate and consequences of sr exchange between porewaters and bulk carbonate at six dsdp sites 590b 575 593 516 305 and 289 where the required sr concentration and isotopic composition data for the interstitial waters are available from the literature the model can reproduce both the sr2 and 87sr 86sr profiles in the porewaters at each of the sites by adjusting the rate of sr exchange due to solution reprecipitation as a function of sediment age we find that the rate of solution reprecipitation at all of the sites is highest for the youngest sediment 1 10 m y and decreases by about an order of magnitude over the first 10 m y of sediment age the effect of this exchange on the properties of the bulk carbonate is to reduce the sr content by 5 25 depending primarily on the sedimentation rate and shift the 87sr 86sr by as much as 0 00004 from the value the sediment had when first deposited isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate 87sr 86sr for stratigraphic correlation the average sr loss in the carbonate sections studied is about 15 from which we conclude that the sr flux from carbonate sediments to the overlying ocean is of the order of 15 of the riverine sr flux we also show that the isotopic composition of the diagenetic sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall sr budget that determines the sr isotopic composition of seawater the range of sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in sr content seen in pelagic carbonates as a function of age about 70 over the first 100 m y we conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself

diagenesis and sr isotopic evolution of seawater using data from dsdp 590b and 575 new sr isotopic and concentration analyses of bulk carbonate and porewaters from a carbonate rich miocene section sampled at dsdp site 575 are reported and used along with our earlier data from a section of similar age at dsdp site 590b in a numerical model to determine for each site the rate of sr exchange during diagenesis and the degree to which this amount of exchange has shifted the87sr86sr of the bulk carbonate from the ratio each increment of sediment had when first deposited despite the fact that the two sites have very different water depth 4536 m at 575 vs 1299 m at 590b different sedimentation rate 10 m my at 575 vs 40 m my at 590b and significantly different porewater sr2 gradients we find that the rate of sr exchange as a function of sediment age is almost indistinguishable between the two sites the rate of sr exchange determined at the two sites is such that the resulting shift in bulk carbonate87sr86sr due to diagenesis is small compared to the total range of87sr86sr values measured but large compared to the analytical uncertainty of the individual isotopic ratio measurements by taking this shift into account we reconstruct the original87sr86sr of each increment of carbonate sampled which when plotted as a function of age becomes our best estimate of the sr isotopic evolution of seawater because sr is very well mixed in the ocean at any given time there is a single worldwide value of seawater87sr86sr therefore if we are quantitatively accounting for the effect sr exchange we should find the same seawater evolution curve regardless of what dsdp site is used when we compare the observed bulk carbonate87sr86sr vs age at the two sites they are seen to differ by amounts that are sometimes large compared to the analytical uncertainties of the measurements however when these data are corrected for the post depositional sr isotopic shifts predicted by our diagenetic model we find almost perfect agreement this agreement suggests that we have made a realistic determination of the rate of sr exchange and its consequences in terms of shifting the87sr86sr of the bulk carbonate and more importantly that sr isotopes can be used to correlate marine sediments with an accuracy comparable to the very small analytical uncertainties of modern isotopic measurements

topographic effects on bidirectional and hemispherical reflectances calculated with a geometric optical canopy model the effects of topography on both the bidirectional reflectance distribution function brdf and the hemispherical reflectance surface albedo of a forested scene are investigated with the li strahler geometric optical model the li strahler geometric optical model treats a vegetation canopy as an assemblage of partially illuminated tree crowns of spheroidal shape and through geometric optics and boolean set theory models the proportion of sunlit or shadowed canopy and background as functions of view angle illumination angle and crown geometry the model has been modified to accommodate a sloping surface in its computation of bidirectional and hemispherical reflectance when the brdf of a flat vegetated surface is compared to the brdf of a sloping surface that is similarly vegetated the interaction of the illumination angle and the slope distort the shape of the brdf a hemispherical integration of this distorted brdf provides an albedo for the sloping surface

constraining magnesium cycling in marine sediments using magnesium isotopes abstract magnesium concentrations in deep sea sediment pore fluids typically decrease down core due to net precipitation of dolomite or clay minerals in the sediments or underlying crust to better characterize and differentiate these processes we have measured magnesium isotopes in pore fluids and sediment samples from ocean drilling program sites 1082 1086 1012 984 1219 and 925 that span a range of oceanographic settings at all sites magnesium concentrations decrease with depth at sites where diagenetic reactions are dominated by the respiration of organic carbon pore fluid 26mg values increase with depth by as much as 2 because carbonates preferentially incorporate 24mg low 26mg the increase in pore fluid 26mg values at these sites is consistent with the removal of magnesium in mg carbonate dolomite in contrast at sites where the respiration of organic carbon is not important and or weatherable minerals are abundant pore fluid 26mg values decrease with depth by up to 2 the decline in pore fluid 26mg at these sites is consistent with a magnesium sink that is isotopically enriched relative to the pore fluid the identity of this enriched magnesium sink is likely clay minerals using a simple 1d diffusion advection reaction model of pore fluid magnesium we estimate rates of net magnesium uptake removal and associated net magnesium isotope fractionation factors for sources and sinks at all sites independent estimates of magnesium isotope fractionation during dolomite precipitation from measured 26mg values of dolomite samples from sites 1082 and 1012 are very similar to modeled net fractionation factors at these sites suggesting that local exchange of magnesium between sediment and pore fluid at these sites can be neglected our results indicate that the magnesium incorporated in dolomite is 2 0 2 7 depleted in 26mg relative to the precipitating fluid assuming local exchange of magnesium is minor at the rest of the studied sites our results suggest that magnesium incorporated into clay minerals is enriched in 26mg by 0 to 1 25 relative to the precipitating fluid this work demonstrates the utility of magnesium isotopes as a tracer for magnesium sources sinks in low temperature aqueous systems

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

calcium isotope fractionation in selected modern and ancient marine carbonates the calcium isotope composition 44 42ca was analyzed in modern cretaceous and carboniferous marine skeletal carbonates as well as in bioclasts non skeletal components and diagenetic cements of cretaceous and carboniferous limestones in order to gain insight in ca2 aq caco3 isotope fractionation mechanisms in marine carbonates splits of samples were analyzed for sr mg fe and mn concentrations and for their oxygen and carbon isotopic composition biological carbonates generally have lower 44 42ca values than inorganic marine cements and there appears to be no fractionation between seawater and marine inorganic calcite a kinetic isotope effect related to precipitation rate is considered to control the overall discrimination against 44ca in biological carbonates when compared to inorganic precipitates this is supported by a well defined correlation of the 44 42ca values with sr concentrations in cretaceous limestones that contain biological carbonates at various stages of marine diagenetic alteration no significant temperature dependence of ca isotope fractionation was found in shells of cretaceous rudist bivalves that have recorded large seasonal temperature variations as derived from 18o values and mg concentrations the reconstruction of secular variations in the 44 42ca value of seawater from well preserved skeletal calcite is compromised by a broad range of variation found in both modern and cretaceous biological carbonates independent of chemical composition or mineralogy despite these variations that may be due to still unidentified biological fractionation mechanisms the 44 42ca values of cretaceous skeletal calcite suggest that the 44 42ca value of cretaceous seawater was 0 3 0 4 lower than that of the modern ocean

effects of ocean acidification on the marine calcium isotope record at the paleocene eocene thermal maximum highlights 44ca was measured in bulk carbonate and barite at two sites over the petm diagenetic effects on 44ca are observed associated with ocean acidification multiple sites and proxy archives necessary to reconstruct the past accurately abstract carbonates are used extensively to reconstruct paleoclimate and paleoceanographic conditions over geologic time scales however these archives are susceptible to diagenetic alteration via dissolution recrystallization and secondary precipitation particularly during ocean acidification events when intense dissolution can occur despite the possible effects of diagenesis on proxy fidelity the impacts of diagenesis on the calcium isotopic composition 44ca of carbonates are unclear to shed light on this issue bulk carbonate 44ca was measured at high resolution in two pacific deep sea sediment cores odp sites 1212 and 1221 with considerably different dissolution histories over the paleocene eocene thermal maximum petm 55 ma 55 ma the 44ca of marine barite was also measured at the deeper site 1221 which experienced severe carbonate dissolution during the petm large variations 0 8 0 8 in bulk carbonate 44ca occur in the deeper of the two sites at depths corresponding to the peak carbon isotope excursion which correlate with a large drop in carbonate weight percent such an effect is not observed in either the 1221 barite record or the bulk carbonate record at the shallower site 1212 which is also less affected by dissolution we contend that ocean chemical changes associated with abrupt and massive carbon release into the ocean atmosphere system and subsequent ocean acidification at the petm affected the bulk carbonate 44ca record via diagenesis in the sedimentary column such effects are considerable and need to be taken into account when interpreting ca isotope data and potentially other geochemical proxies over extreme climatic events that drive sediment dissolution

topographic effects in avhrr ndvi data an investigation is made of the errors induced in the normalized difference vegetation index ndvi by topographic variation the advanced radiometric ray tracer ararat is used to simulate avhrr imagery for various viewing and illumination conditions at 1 1 km and 50 m resolution topographic error is calculated as the difference between the variable terrain simulation and a flat plane simulation correlation between this error and various topographic factors such as shadowing and adjacement hill illumination are examined the importance of sky occlusion as a topographic factor is highlighted while topographic errors of 13 5 are found in the 50 m resolution simulations these errors are reduced markedly in the 1 1 km dataset to approximately 3

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment