the present day formation of apatite in mexican continental margin sediments abstract results of pore water and sediment analyses from the western mexican continental margin strongly suggest the present day formation of apatite the interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments apatite is identified within this maximum via x ray diffraction but is elsewhere undetectable in the core radioisotopic thorium uranium and radium data support the conclusion that this deposit is modern the present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value

early marine diagenesis of biogenic aragonite and mg calcite new constraints from high resolution stem and aem analyses of modern platform carbonates prior studies of porewater compositions from modern shallow marine carbonates have established that dissolution and recrystallization of metastable aragonite and mg calcites occur during the earliest stages of sedimentation yet significant microstructural and mineralogical changes in sediment allochems have not been observed in part this is due to the high resolution required to identify diagenetic changes in these finely crystalline materials herein we present ultrastructural and microgeochemical evidence for early marine diagenesis using scanning electron microscopy sem and high resolution scanning transmission analytical electron microscopy stem aem methods to characterize original biogenic materials and sediment boxcores from modern deposits on the floridan bahamas platform we selected the two most common sediment producers a mg calcite foraminifer peneropolid and an aragonitic green algae halimeda for study both are composed of submicron sized crystallites whose excess free energy could provide a thermodynamic driving force for recrystallization stem observations of grain mounts containing dispersed mg calcite and aragonite crystallites from gently disaggregated individual peneropolids and halimeda segments indicate that living specimens contain euhedral prismatic crystals with blunt terminations and smooth faces specimens from the sediment column show abundant evidence for alteration the most dramatic changes involve crystallite dissolution and precipitation of thin overgrowths causing the overall aspect ratio of crystallites to shorten and widen direct measurements of several hundred individual crystallites confirm that crystallite length and width distributions differ significantly between original and altered materials these changes are consistent with crystal growth processes that tend to minimize surface free energy by increasing overall crystal size and by producing more equant shape the precipitated material has a composition and structure which is grossly similar to the host crystallite as determined by aem and electron diffraction analyses aem analyses of hundreds of mg calcite crystallites from living specimens of peneropolid foraminifera indicate a composition of 13 14 mol mgco3 whereas crystallites from altered tests are 1 3 mole lower taken together these data suggest that early diagenesis in shallow marine carbonates is indeed manifested in the solids as well as the sediment pore waters producing significant changes in biogenic mg calcite and aragonite crystallite size and shape this alteration would not produce changes in the mineral assemblage because dissolution is accompanied by precipitation of compositionally similar overgrowths under major element conditions not drastically dissimilar from overlying seawater however crystallite recrystallization likely has implications for incorporation of minor elements which undergo cycling via organic matter decomposition or redox changes e g uranium cadmium manganese rare earth elements

sedimentary pachnolite and fluorite from tampa bay florida deltaic deposits of pachnolite and fluorite occur in tampa bay florida as a result of chemical precipitation from a fluoride rich effluent from a phosphate chemical plant the deposits are crusts up to 8 cm in thickness and cover a total of 5 ha crusts range from discontinuous masses to a solid shield with superimposed distributaries these deposits are the only known deposits where pachnolite and fluorite can be shown to have formed in a marine sedimentary environment journal abstract

system reliability analysis of rock wedge stability considering correlated failure modes using sequential compounding method abstract probabilistic analysis of wedge failure has been used as an effective tool to evaluate inherent uncertainty of the variables in this paper a system reliability analysis of rock wedge stability is presented to perform reliability analysis a cut set system is used for wedge analysis the reliability indices of the individual components and the correlations between the components are determined by the first order reliability method form the sequential compounding method scm is used as an efficient numerical procedure to determine the reliability indices of failure modes and system reliability index considering correlations between failure modes which are calculated by defining equivalent linear safety margin for each failure mode the predicted system reliability indices and corresponding probabilities of failure from the proposed method are compared with those of the monte carlo simulation mcs the results of sensitivity and parametric analyses show that the water pressure parameters are the most effective parameters in rock wedge stability it is also demonstrated that the relative influences of failure modes on the system reliability differ considerably furthermore the probabilistic rock wedge stability curves are presented to evaluate the system probability of failure as a function of safety factor and its coefficient of variation

halide systematics in comparison with nutrient distributions in sites 1033b and 1034b saanich inlet odp leg 169s abstract the entire suite of halogens was measured in the pore fluids of hole 1033b and 1034b from saanich inlet odp leg 169s the fast sedimentation rates and large amount of organic carbon burial coupled with anoxia of the overlying waters promotes an advanced stage of diagenesis within the sediment column chloride interstitial water profiles suggest salinity variations within the waters of saanich inlet concentration profiles for iodide and bromide support the argument that they are produced through the degradation of organic matter although the concentration increases in i and br indicate that these halides are not regenerated in similar proportions to marine organic matter it appears that iodide and bromide are regenerated to similar degrees within the sediment column and in similar proportions to the sediment halide concentrations fluoride porewater values show a complicated pattern most likely caused by secondary reactions involving complexation with mg2 carbonate fluorapatite precipitation carbonate mineral diagenesis and or uptake into alumino silicate minerals

stationary wave reflection as a mechanism for zonalizing the atlantic winter jet at the lgm abstractcurrent estimates of the height of the laurentide ice sheet lis at the last glacial maximum lgm range from around 3000 to 4500 m modeling studies of the lgm using low end estimates of the lis height show a relatively weak and northeastward tilted winter jet in the north atlantic similar to the modern jet while simulations with high end lis elevations show a much more intense and zonally oriented jet here an explanation for this response of the atlantic circulation is sought using a sequence of lgm simulations spanning a broad range of lis elevations it is found that increasing lis height favors planetary wave breaking and nonlinear reflection in the subtropical north atlantic for high lis elevations planetary wave reflection becomes sufficiently prevalent that a poleward directed flux of wave activity appears in the climatology over the midlatitude north atlantic this entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet

a high resolution one layer model of breaking planetary waves in the stratosphere numerical integrations of a one layer hemispheric model of the winter stratosphere have been carried out at very high resolution of the order of a fraction of a degree of latitude the numerical experiments simulate planetary wave breaking and polar vortex erosion under conditions far closer to the real winter stratosphere than those assumed in earlier critical layer models the model has implications for stratospheric photochemistry and the antarctic ozone hole problem

missing molluscs as evidence of large scale early skeletal aragonite dissolution in a silurian sea in the silurian carbonate platform succession of gotland sweden interreef limestone and marl sequences have shallow marine shelly assemblages dominated by brachiopods typical of many paleozoic benthic faunas locally from similar facies where early skeletal silicification occurred associated with bentonites there are rich and diverse assemblages of originally aragonitic molluscs quantitative faunal analysis suggests that massive depletion of skeletal aragonite chiefly molluscs took place and the entire molluscan fauna may generally be underrepresented by at least 100 fold previous workers on the gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization our findings indicate molluscs as the probable source of this diagenetic calcite not aragonite mud as was previously thought the taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original silurian shelf benthos and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect

factors controlling the fluoride content of planktonic foraminifera an evaluation of its paleoceanographic applicability abstract this work is an assessment of the effects of seawater salinity and temperature on the incorporation of fluoride into calcitic shells of planktonic foraminifera and of the subsequent modification of shell chemistry by postdepositional dissolution a strong correlation between the fluoride content of most planktonic species and their calcification depth was observed deeper calcifying foraminifera have lower fluoride content and heavier 18o composition perhaps suggesting a temperature control on the partition coefficient however species deviations from this general trend and the absence of correlation between fluoride and sea surface temperature within an individual species suggest that the coprecipitation of fluoride in foraminiferal calcite is more strongly controlled by biological processes rather than by simple chemical relationships foraminiferal fluoride shows weak or no correlation with sea surface salinity core top planktonic foraminifera from the eastern equatorial atlantic sierra leone rise show a substantial decrease of fluoride and to a lesser extent mg content with increasing water depth 2931 5104 m these decreasing trends with depth are attributed to selective dissolution i e removal of the more dissolution susceptible fraction with a different chemical composition than the residual a process which previously has been suggested to account for variations in the isotopic composition of planktonic foraminifera these findings indicate that foraminiferal fluoride cannot serve as a reliable tracer of oceanic paleo temperature or salinity it is possible however that fluoride may be useful for the study of dissolution in deep sea sediments

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites

climatology of 500 mb cyclones and anticyclones 1950 85 abstract the geographical and monthly frequencies of 500 mb cyclones and anticyclones in the national meteorological center analyses over the western half of the northern hemisphere are investigated for the period 1950 85 these cyclones and anticyclones defined by the appearance of at least one closed approximately 6 dekameter contour around relatively low or high heights in the 500 mb height field are generally observed less than ten percent of the time in any 10 by 10 latitude longitude quadrangle with cyclones being more numerous than anticyclones the 500 mb cyclones are found primarily at middle and high latitudes while anticyclones are observed most frequently over the subtropics cyclone frequency increases over the northern oceanic regions during summer while anticyclone frequency increases throughout the subtropics during summer especially over southwestern north america exceptions to these rules are observed relatively high springtime 500 mb anticyclone frequency is found over the n

a method for seismic stability analysis of jointed rock slopes using barton bandis failure criterion abstract earthquakes are the main cause of slope failure in seismic active regions in this study we present a method for analyzing the seismic stability of a plane jointed rock slope with two blocks in this analysis the barton bandis failure criterion is applied considering the nonlinear characteristics of rock joints based on the limit equilibrium principle we derived the safety factor of a jointed rock slope subjected to the modified pseudo dynamic seismic forces in addition the analytical method developed in this study explains the interaction force between two blocks hence it can effectively analyze the stability of a jointed rock slope and distinguish the failure modes further a parametric study was conducted to investigate the effects of geometric and material properties on the safety factor of a hypothetical slope the results show that the slope stability is significantly influenced by the geometry of the slope and the parameters including the joint roughness coefficient jrc the horizontal seismic acceleration coefficient kh the joint compressive strength jcs and the basic friction angle of the structural plane b moreover the accuracy of the derivation is verified by the universal distinct element code udec 6 0 a parametric sensitivity analysis is used to determine the key parameters affecting slope stability finally a set of seismic stability design charts is produced for preliminary design

northern hemisphere 500 hpa trough merger and fracture a climatology and case study abstract the results of an objective climatology of 500hpa trough merger defined as the amalgamation of two initially separate vorticity maxima and trough fracture defined as the splitting of a single vorticity center into two separate vorticity centers are presented for the northern hemisphere the data source is the gridded national meteorological center nmc now the national centers for environmental prediction analyses available on cd rom on the nmc operational octagonal grid 381 km resolution at 60 n for the period september 1957 to may 1989 a total of 2152 3053 merger fracture events are identified merger and fracture events tend to occur preferentially in the band of middle latitude westerlies merger events exhibit a tendency to avoid major mountainous regions and show a somewhat higher frequency of occurrence downstream of these regions fracture events cluster somewhat over eastern ocean basins the southwestern united states and northwestern africa while also avoiding major mount

storm tracks and barotropic deformation in climate models abstract the relationship between the time mean planetary scale deformation field and the structure of midlatitude storm tracks is studied in wintertime simulations of the national center for atmospheric research ncar community climate model and the national aeronautics and space administration nasa goddard earth observing system model model biases are determined by contrasting model simulations forced by observed ssts with parallel analyses of ncep ncar reanalyses barotropic diagnostics are employed to identify potential dynamical linkages between regional biases in the midlatitude storm tracks and the horizontal deformation field initial observational analyses confirm that synoptic eddies are optimally configured to transfer kinetic energy to the mean flow in the jet exit regions where strong stretching deformation exists in these regions the major axes of the synoptic eddies are aligned along the dilatation axes of the mean flow consequently mean flow advection stretches synoptic eddies a

fluorine mobility during early diagenesis of carbonate sediment an indicator of mineral transformations abstract the abundant occurrence of calcium carbonate minerals in marine sediment their well documented dissolution or precipitation during diagenesis and their high f content suggest that carbonate mineral diagenesis may be an important influence on f behavior in marine sediment to test this hypothesis we have examined the geochemistry of f in shallow carbonate mud bank sediment of florida bay usa the f content of biogenic calcium carbonate in florida bay varies with mineralogy positively correlates with the mg content of calcite and occurs in similar abundance to sr high mg calcite f sr 2 4 mol mol aragonite 0 53 0 79 mol mol low mg calcite 0 22 mol mol models of porewater distributions direct solute flux measurements and reaction rate estimates over the upper 0 16 cm of sediment from bob allen key bank predict net fluxes out of the sediment of 170 mol f m2 d 230 mol sr m2 d and 5 6 mmol ca m2 d the net solute flux ratio of f sr 0 71 mol mol is consistent with dissolution of aragonite or high mg calcite but f ca and sr ca ratios 28 mmol mol and 40 mmol mol respectively are 3 10 that of biogenic carbonate sources selective dissolution of a high f and sr content phase or more likely based on dissolution experiments concurrent dissolution and reprecipitation of phases with different f and sr contents account for this discrepancy the loss of f sr and ca to fluorapatite precipitation as predicted from a stoichiometric model of phosphate release can be added to the transport reaction model predicted net fluxes a resulting more complete mass balance model incorporating both carbonate mineral reactions and fluorapatite formation yields total release estimates of f sr and ca of 770 mol 332 mol and 53 mmol m2 d respectively calcium carbonate minerals apparently undergo transformation whereby 34 mmol high mg calcite m2 d and 19 mmol aragonite m2 d dissolve and 46 mmol low mg calcite m2 d precipitates ignoring other cations besides ca if no fluorapatite formation occurs the required fluxes are that 23 mmol aragonite m2 d dissolves and 3 4 mmol high mg calcite m2 d and 14 mmol low mg calcite m2 d precipitate net loss of caco3 from the deposit by dissolution is 6 7 mmol m2 d 3 of the accumulation flux the magnitude of these fluxes could cause significant mineralogical and chemical changes on rapid time scales in nearshore carbonate sediment fluorine is probably mobile in other carbonate deposits undergoing diagenetic alteration on short and longer time scales and is a powerful additional constraint on the rates and nature of carbonate mineral diagenesis

enriched stable carbon isotopes in the pore waters of carbonate sediments dominated by seagrasses evidence for coupled carbonate dissolution and reprecipitation studies of the 13c of pore water dissolved inorganic carbon 13c dic were carried out in shallow water carbonate sediments of the great bahamas bank gbb to further examine sediment seagrass relationships and to more quantitatively describe the couplings between organic matter remineralization and sediment carbonate diagenesis at all sites studied 13c dic provided evidence for the dissolution of sediment carbonate mediated by metabolic co2 i e co2 produced during sediment organic matter remineralization these observations are also consistent with pore water profiles of alkalinity total dic and ca2 at these sites in bare oolitic sands isotope mass balance further indicates that the sediment organic matter undergoing remineralization is a mixture of water column detritus and seagrass material in sediments with intermediate seagrass densities seagrass derived material appears to be the predominant source of organic matter undergoing remineralization however in sediments with high seagrass densities the pore water 13c dic data cannot be simply explained by dissolution of sediment carbonate mediated by metabolic co2 regardless of the organic matter type rather these results suggest that dissolution of metastable carbonate phases occurs in conjunction with reprecipitation of more stable carbonate phases simple closed system calculations support this suggestion and are broadly consistent with results from more eutrophic florida bay sediments where evidence of this type of carbonate dissolution reprecipitation has also been observed in conjunction with our previous work in the bahamas these observations provide further evidence for the important role that seagrasses play in mediating early diagenetic processes in tropical shallow water carbonate sediments at the same time when these results are compared with results from other terrigenous coastal sediments as well as supralysoclinal carbonate rich deep sea sediments they suggest that carbonate dissolution reprecipitation may be more important than previously thought in general in the early diagenesis of marine sediments

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

on the interpretation of eddy fluxes during a blocking episode abstract using twice daily synoptic charts objectively analyzed at the national meteorological centre horizontal eddy fluxes of temperature and quasi geostrophic potential vorticity are computed for the month of july 1976 when a blocking anticyclone was centered over western europe the local time averaged eddy variance equations are used to provide a dynamical basis for interpreting the spatial pattern of eddy fluxes and their relation to mean gradients it is shown that a rotational non divergent flux can be identified the cross gradient component of which balances the mean flow advection of eddy variance the remaining flux is the dynamically significant one which helps maintain the block and can be understood in terms of a response to sources and sinks of eddy variance

the role of moist processes in the formation and evolution of mesoscale snowbands within the comma head of northeast u s cyclones abstract the role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast u s cyclones is investigated using piecewise potential vorticity pv inversion modeling experiments and potential temperature tendency budgets snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700 hpa low this 700 hpa trough was associated with intense frontogenetical forcing for ascent a variety of pv evolutions among the cases contributed to midlevel trough formation and associated frontogenesis however in each case the induced flow from diabatic pv anomalies accounted for a majority of the midlevel frontogenesis during the band s life cycle highlighting the important role that latent heat release plays in band evolution simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band however changes in the meso

diagenetic f rich ferroan calcite and zircon in the offshore scotian basin eastern canada significance for understanding thermal evolution of the basin in the scotian basin offshore eastern canada an unusual combination of high heat flow in the cretaceous and the abundance of halite has resulted in unusual diagenetic minerals such as sphalerite the newburn h 23 well is the most distal well in the basin with good core samples and has two previously unknown diagenetic mineral occurrences fluorine rich ferroan calcite and diagenetic zircon this study uses sem backscattered electron images and eds analyses emp wds mineral analyses and raman spectroscopy to determine mineral chemistry and textures to investigate the diagenetic and thermal significance of these minerals late diagenetic fe calcite contains 1 2 5 wt fluorine mostly from adsorption but rarely as small fluorite crystals fluoride is also adsorbed on the surfaces of some framework minerals and chlorite fluoride was transported in highly saline formation brines derived from the argo salt formation zircon grains 20 40 m in size have crystal outlines that are straight adjacent to pores partially lobate filling porosity and cross cutting other grains these may be diagenetic some zoned detrital zircon grains show 1 3 m wide diagenetic outgrowths neoformation of diagenetic zircon requires temperatures of 250 c transport of zirconium is favored by ligands in low ph solution principally fluoride and phosphate anions with zirconium mobilized during the alteration of metamict detrital zircon under low grade metamorphic conditions the presence of diagenetic sphalerite and the documented mid cretaceous thermal event in the scotian basin indicate conditions that could have been suitable for the formation of diagenetic zircon in this well suitable geological conditions for such diagenetic formation of zircon will be found in a subsiding rift basin with early evaporites that are affected by a subsequent phase of volcanism due to new rifting or subduction

volcanic glass leaching and the groundwater geochemistry on the semi arid atlantic island of porto santo abstract the groundwater chemistry of the semi arid volcanic island of porto santo part of the madeira archipelago atlantic ocean was investigated generally the groundwater was brackish containing 2 10 mol seawater groundwater with up to 20 mm alkalinity and a na enrichment of up to 30 mm as compared to the na concentration predicted by the seawater na cl ratio was found in the main aquifer also notable are the high concentrations of f up to 0 3 mm b up to 0 55 mm as up to 0 35 m all in excess of who recommendations as well as up to 6 m v geochemical modeling using the phreeqc code was used to explore different scenarios that could explain the genesis of the observed bulk groundwater chemistry first a model for aquifer freshening with the displacement of resident seawater from the aquifer by infiltrating freshwater was tested this scenario leads to the development of nahco3 waters as observed in many coastal aquifers however the measured alkalinity concentration in the groundwater was far higher than the concentration predicted by the freshening model in addition the behavior of modelled ph and pco2 were at variance with their distributions in the field data the second model explored the possible effect of volcanic glass leaching on the groundwater chemistry using insight derived from studies of volcanic glass surface alteration as well as experimental work on water volcanic glass interactions a geochemical model was developed in which the exchange of h for na on the volcanic glass surface is the main mechanism but the exchange of other cations on the volcanic glass surface is also included the uptake of h by the glass surface causes the dissociation of carbonic acid generating bicarbonate this model is consistent with the local geology and the field data it requires however volcanic glass leaching to occur in the unsaturated zone where there is an unlimited supply of co2 the exchange reaction of h for na is confined to the surface layer of volcanic glass as otherwise the process becomes limited by slow solid state diffusion of h into the glass and na out of the glass therefore volcanic ash deposits with their high volcanic glass surface areas and matrix flow are the aquifers where this type of high nahco3 waters can be expected rather than in basalts which predominantly feature fracture flow the trace components f b as and v are believed to originate from hyaloclastites consisting of predominantly 90 of trachy rhyolite volcanic glass although stratigraphically older than the main calcarenite aquifer topographically they are often located at higher altitudes above the phreatic level and located along the main recharge flow path in addition the semi arid climate conditions provide a long groundwater residence time for the reactions as well as limited aquifer flushing

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

influence of the north atlantic oscillation on the canary islands precipitation abstract the aim of this paper is to investigate the relationship between the canary island rainfall and the atlantic large scale circulation characterized by the north atlantic oscillation nao index the canary islands are located in the atlantic subtropical belt under the direct influence of the azores high and the trade winds their steep orography makes the islands very sensitive to small variations in a synoptic situation thus providing an excellent natural observatory for the north atlantic variability associated with changes in pressure patterns a significant relationship between rainfall and the nao is found for five of the seven canary islands in order to characterize the physical mechanisms involved a set of automatic objective techniques for identification and detection of disturbances is applied to the 1000 and 500 hpa geopotential from the ncep ncar reanalysis for the period from 1955 to 1998 this method allows for the identification and detection of four main synoptic systems either

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

carbonate dissolution in nearshore terrigenous muds the role of physical and biological reworking because shallow marine sediments generally underlie waters which are saturated with respect to arago nite and calcite physical chemical dissolution of carbonate in these environments is sometimes discounted the present investigation as well as others before it show such an assumption to be unwarranted in this case study of terrigenous mud deposits from long island sound u s a demonstrates extensive dissolution of molluscan shell debris near the sediment water interface net buildup of carbonate varies significantly between different regions of the sound despite fairly uniform production of shell debris and similar total sedimentation rates aside from this apparent discrepancy between rate of supply and net carbonate sedimentation evidence for carbonate dissolution comes from the pitting of shells elevated ca levels in pore water and calculated undersaturation of pore waters with respect to carbonate minerals models of pore water distributions and carbonate supply imply dissolution ra

the widespread occurrence of coupled carbonate dissolution reprecipitation in surface sediments on the bahamas bank using two complimentary approaches pore water advection diffusion reaction modeling and stable isotope mass balance calculations we show that carbonate dissolution reprecipitation occurs on early diagenetic time scales across a broad range of sediments on the great bahamas bank the input of oxygen into the sediments which strongly controls sediment carbonate dissolution has two major sources belowground input by seagrasses that is seagrass o 2 pumping and permeability driven advective pore water exchange the relative importance of these o 2 delivery mechanisms depends on both seagrass density and on how bottom water flow interacts with the seagrass canopy and leads to this advective exchange dissolution appears to involve the preferential dissolution of high mg calcite and the rates of dissolution increase linearly with increasing seagrass density isotopic evidence of dissolution reprecipitation is consistent with the occurrence of ostwald ripening as the mechanism of reprecipitation in which smaller crystals dissolve and then reprecipitate as larger crystals with little or no change in mineralogy estimates of the aerially integrated dissolution flux on the bahamas bank suggest that carbonate dissolution is an important loss term in the budget of shallow water carbonate sediments and that on bank carbonate dissolution rather than offshore transport may represent an important sink for gross shallow water carbonate production dissolution in carbonate bank and bay sediments may also be a significant alkalinity source to the surface ocean and should be considered in global alkalinity carbonate budget finally coupled dissolution reprecipitation may have a major impact on the stable isotope composition of carbonate sediments that are ultimately preserved in the rock record these processes may therefore need to be considered for example when using carbon isotope records to obtain information on the operation of the global carbon cycle during the phanerozoic

chemical evidence for advection of hydrothermal solutions in the sediments of the galapagos mounds hydrothermal field pore water profiles of ca mg f po4 3 and mn in the galapagos mounds hydrothermal field are believed to reflect in part upwelling of hydrothermal solutions through the sediments concentration depth profiles in a low heat flow area just north of the mounds field display diagenetic changes typical of those found in pore waters underlying highly productive surface waters consistent with the inference of no water flow or very slow downwelling w 5 cm yr of bottom water through these sediments rates of upward advection calculated from mounds field pore water profiles of ca mg and f profiles agree well with each other averaging about 1 cm yr in the pelagic sediments near the mounds and 15 30 cm yr within the hydrothermal mounds themselves the upward advection also modifies the shape of po4 3 and mn profiles advection rates inferred from the pore water data are generally in reasonable agreement with those made from heat flow data the higher ca and lower mg f po4 3 and mn concentrations in mounds field pore waters compared with those of the low heat flow area suggest chemical exchange between the solution and basalt prior to upwelling li k rb sr and so4 concentrations are indistinguishable from bottom water this suggests very high effective water rock ratios during the reactions which produced the upwelling solutions perhaps due to extensive prior alteration of basalt adjacent to the flow path of water through the crust inferred reaction temperatures are between 70 150 c

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

life history of mobile troughs in the upper westerlies abstract increasing evidence indicates that surface cyclogenesis is predominantly a response to the approach of a preexisting trough at upper levels a question then arises about the origin of the upper level predecessor as an initial approach to this question mobile troughs in the major band of westerlies were crudely tracked in daily northern hemispheric 500 mb analysis during nine recent cold seasons these troughs were identified only in the 552 dam height contour between 8 and 15 of them were present on a given day study of a particular cold season showed a median duration of 12 days and a mode of 5 days average zonal phase speed was 13 m s 1 locations or origin and termination of individual troughs were distributed over all longitudes but births greatly exceeded deaths over and east of the rocky mountains in north america and the highlands of central asia trough terminations dominated over the eastern portions of the oceans within the quasi steady planetary waves origins and terminations o

rates of carbonate dissolution in permeable sediments estimated from pore water profiles the role of sea grasses in this study we estimate sediment carbonate dissolution rates for sandy sea grass sediments on the bahamas bank using an inverse pore water advection diffusion reaction model constrained by field observations this model accounts for sea grass o2 input to these sediments and also parameterizes pore water advection through these permeable sediments as a nonlocal exchange process the resulting rates of carbonate dissolution are positively correlated with sea grass density and are comparable with previous rate estimates for florida bay sediments in contrast the advective uptake of o2 by these sediments decreased with increasing sea grass density this suggests that the competing interplay between bottom water flow near seabed pressure gradients and the presence of a sea grass canopy is important in controlling this type of sediment oxygen uptake when the carbonate dissolution rates estimated here are examined in the context of carbonate budgets for shallow water carbonate platforms systems they suggest that carbonate dissolution may be a significant loss term in these budgets sea grass mediated carbonate dissolution may also exert a negative feedback on rising atmospheric co2 although the magnitude of this effect remains to be quantified

interactions between dissolved silica and carbonate minerals an experimental study at 25 50 c abstract replacement of carbonate minerals by silica polymorphs in marine and meteoric environments is a common early diagenetic feature of sedimentary rocks although relatively few experimental investigations have been made of interactions between carbonate minerals and dissolved sio 2 at moderate temperatures available data suggest that silica uptake onto carbonate surfaces can be significant we present results of experiments conducted between 25 and 50 c of the uptake of aqueous sio 2 from artificial seawater mg na cl ca hco 3 i 0 7 and meteoric type cacl 2 na 2 co 3 i m a reasonable upper limit for natural diagenetic waters dissolved silica carbonate mineral interactions were investigated under three experimental conditions 1 in solutions near equilibrium with respect to calcite 2 in calcite seeded precipitation experiments at fixed degrees of calcite supersaturation and 3 during closed system dissolution precipitation of metastable carbonate minerals aragonite and 18 mole mg calcite to low mg calcite lmc in artificial seawater asw maintained near equilibrium with respect to calcite at various p co2 values silica uptake from solution onto calcite surfaces 1 15 mol si gram seed was irreversible and strongly time and ph dependent the rate of uptake was greatest in the first 5 hr and in solutions of lower ph higher p co2 silica uptake was only nominally dependent on solution mg and temperature over the range studied silica uptake was greater in asw than in otherwise comparable experiments conducted in low ionic strength solutions controlled calcite precipitation rates were unaffected by the adsorption of silica during recrystallization of aragonite and mg calcite in low ionic strength solutions silica uptake 1 6 mol g was similar to values frorn near equilibrium experiments for synthetic calcite in asw experimental si adsorption values were comparable to si adsorption values determined for modem metastable sediments 3 4 mol g 1 despite considerable variation in the experimental carbonate equilibrium disequilibrium mineralogy and solution chemistry si uptake at near surface and moderate burial conditions 25 50 c was limited to 15 mol g 1 si even in solutions maintained near opal ct saturation over a period of days to weeks

reactive transport modeling of brine reflux dolomitization anhydrite precipitation and porosity evolution abstract both geothermal convection and brine reflux drive circulation of sea water derived fluids through carbonate platforms during early burial but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood this paper describes high resolution reactive transport model rtm simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin with flow focused in the more permeable shallow carbonates in a baseline simulation involving an elongate 25 km wide grain dominated packstone platform brine reflux resulted in complete dolomitization beneath the 5 km wide brine pool in 335 ky the dolomite body then extends downward at c 22 m 100 ky into an underlying broad area of partial dolomitization this process enhances porosity at shallow depth but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux in contrast geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time 60 dolomite after 1 my with very minor associated anhydrite cementation reflux diagenesis is sensitive to platform geometry with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline fluid flow across thermal gradients enhances reaction rates and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25 and associated anhydrite by 90 the depth and rate of anhydritization is sensitive to the geothermal heat flux whereas platform top temperatures affect dolomitization rate reflux diagenesis is also sensitive to brine density which affects both fluid flow and reaction rates sediment permeability and reactive surface area rsa are key intrinsic controls on diagenesis where the permeability structure permits sufficient fluid flow diagenesis preferentially affects more reactive fine grained sediments however as flow rates decline reactions become focused in the more permeable but less reactive sediments simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments but elsewhere favors grainstones once active reflux ceases brines continue to flow in the subsurface but this latent reflux causes only minor dolomitization due to prior mg2 consumption at shallow depth

impact of basin burial and exhumation on jurassic carbonates diagenesis on both sides of a thick clay barrier paris basin ne france several diagenetic models have been proposed for middle and upper jurassic carbonates of the eastern paris basin the paragenetic sequences are compared in both aquifers to propose a diagenetic model for the middle and late jurassic deposits as a whole petrographic optical and cathodoluminescence microscopy structural fracture orientations and geochemical 18o 13c ree studies were conducted to characterize diagenetic cements with a focus on blocky calcite cements and their connection with fracturation events four generations of blocky calcite cal1 cal4 are identified cal1 and cal2 are widespread in the dominantly grain supported facies of the middle jurassic limestones about 90 of the cementation whereas they are limited in the oxfordian because grain supported facies are restricted to certain stratigraphic levels cal1 and cal2 blocky spars precipitated during burial in a reducing environment from mixed marine meteoric waters and or buffered meteoric waters the meteoric waters probably entered aquifers during the late cimmerian jurassic cretaceous boundary and late aptian early cretaceous unconformities the amount of cal2 cement is thought to be linked to the intensity of burial pressure dissolution which in turn was partly controlled by the clay content of the host rocks cal3 and cal4 are associated with telogenetic fracturing phases the succession of cal3 and cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water rock ratios these meteoric fluids circulated along pyrenean oligocene and alpine fractures and generated both dissolution and subsequent cementation in oxfordian vugs in mud supported facies and in poorly stylolitized grainstones however these cements filled only the residual porosity in middle jurassic limestones in addition to fluorine inputs fracturation also permitted inputs of sulphur possibly due to weathering of triassic or purbeckian evaporites or h2s input during paleogene times

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

organic matter diagenesis in shallow water carbonate sediments muddy carbonate deposits near the dry tortugas florida are characterized by high organic carbon remineralization rates however approximately half of the total sedimentary organic matter potentially supporting remineralization is occluded in caco3 minerals intracrystalline while a portion of nonintracrystalline organic matter appears to cycle rapidly intracrystalline organic matter has an approximately constant concentration with depth suggesting that as long as its protective mineral matrix is intact it is not readily remineralized organic matter in excess of intracrystalline organic matter that is preserved may have a variety of mineral associations e g intercrystalline adsorbed or detrital in surface sediment aspartic acid contributed 22 mole and 50 mole to nonintracrystalline and intracrystalline pools respectively in deeper sediment 1 6 1 7m the composition of hydrolyzable amino acids in both pools was similar aspartic acid 40 mole like amino acids intracrystalline and nonintracrystalline fatty acids have different compositions in surface sediments but are indistinguishable at depth these data suggest that preserved organic matter in the nonintracrystalline pool is stabilized by its interactions with caco3 neutral lipids are present in very low abundances in the intracrystalline pool and are extensively degraded in both the intracrystalline and nonintracrystalline pools suggesting that mineral interactions do not protect these compounds from degradation the presence of chlorophyll a but absence of phytol in the intracrystalline lipid pool demonstrates that chloropigments are present only in the nonintracrystalline pool sedimentary chloropigments decrease with depth at similar rates in dry tortugas sediments as found in alumino silicate sediments from the long island sound suggesting that chloropigment degradation is largely unaffected by mineral interactions overall however inclusion and protection of organic matter by biominerals is a major pathway for organic matter preservation in this low organic carbon biomineral rich regime

tropical plumes and extreme precipitation in subtropical and tropical west africa three cases of extreme precipitation in october january and march april over subtropical north western and tropical west africa have been selected in order to study the moisture transports precipitation generation mechanisms and large scale dynamics involved all cases show strong tropical extratropical interactions and elongated cloud bands extending from the tropics into the subtropics usually referred to as tropical plumes tps investigations are based on observational data and high resolution output from simulations using the university of wisconsin nonhydrostatic modeling system trajectory analyses show that moisture is transported from the tropical easterly mid level flow the monsoonal southerlies and the north easterly trade winds to provide precipitable water and potential instability at mid tropospheric levels the instability is released through ascent related both to weak quasi geostrophic forcing to the east of an upper level trough and to the strong inertially unstable and highly divergent upper level subtropical jet stj accompanying the tp in the january and march cases the passage of a precursor upper level trough over the same location precedes the development and initiates the moisture transport from the deep tropics the associated north westerly cold advection supports the generation of precipitation by triggering convection over the tropical atlantic ocean whose outflow feeds into the stj over africa and by enhancing the vertical mass transport within the intertropical discontinuity over and near west africa in october when the still active african monsoon facilitates the extraction of tropical moisture a wave in the tropical easterlies and strong trade winds from the southern hemisphere are dominant factors low level cyclogenesis and frontogenesis only play roles in the late stages of the developments the elongated mostly positively tilted potential vorticity pv streamers associated with the observed troughs form as a result of an equatorward transport of high pv air downstream of a large ridge over the north atlantic the rapid amplification of the ridge is achieved through a combination of negative horizontal pv advection and diabatic reduction of upper level pv through latent heating within a cloud band that forms in connection with an explosive baroclinic development near the east coast of north america copyright 2005 royal meteorological society

suppression of baroclinic instability in horizontally sheared flows abstract baroclinic instability in the presence of a meridionally sheared barotropic component to the basic flow is studied using a two level model the inclusion of a linear shear results in merldionally confined normal modes with growth rates much reduced compared to the unsheared case similar results hold for more complicated situations such as a baroclinic jet with barotropic shear the results are applied to life cycle calculations in which it is shown that the nonlinear decay phase of a baroclinic disturbance sets up barotropic shears whichtend to suppress further baroclinic developments an example of the southern hemisphere winter mean flow is found to be strongly stabilized by virtue of a strong sheared barotropic part of the zonal flow

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

carbon cycling in coastal sediments 1 a quantitative estimate of the remineralization of organic carbon in the sediments of buzzards bay ma seasonal remineralization rates of organic carbon are calculated in the top 20 30 cm of biologically irrigated organic rich sediments of buzzards bay ma six cores were collected over a period of two years and the pore water concentrations of the following species were measured dissolved inorganic carbon co2 po3 4 h2s alk and ca2 overall these constituents showed large gradients with depth which are larger in summer than in winter remineralization rates in the sediments were estimated by applying a non local exchange vertical molecular diffusion reaction model to the co2 depth profiles the major processes affecting the pore water concentration of co2 described in the model are diffusion irrigation and the oxidation of organic carbon the calculated remineralization rates varied seasonally with the high of 7 5 10 9 mol l sec observed in august 84 and the low 0 6 10 9 in december 1983 the remineralization rates were dependent on the amount of irrigation in the sediments it was possible to calculate remineralization rates between 0 and 20 cm because the amount of irrigation was well characterized at this site we calculated that 69 gc m2 are oxidized annually and 5 33 gc m2 yr are buried it appears that there is a highly reactive portion of organic matter which is oxidized at the sediment water interface examination of the alk and dissolved ca2 profiles indicates that there was significant production of acid which dissolved caco3 in the spring and early summer

time averaged fluxes of lead and fallout radionuclides to sediments in florida bay recent unmixed sediments from mud banks of central florida bay were dated using 210 pb 226 ra and chronologies were verified by comparing sediment lead temporal records with pb ca ratios in annual layers of coral montastrea annularis located on the ocean side of the florida keys dates of sediment lead peaks 1978 2 accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978 smaller lags of 1 2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of 137 cs and pu such lags are consequences of system time averaging sta in which atmospherically delivered particle associated constituents accumulate and mix in a sedimentary reservoir before transferring to permanent sediments and coral sta model calculations using time dependent atmospheric inputs produced optimized profiles in excellent accord with measured sediment 137 cs pu lead and coral lead distributions derived residence times of these particle tracers 16 1 15 7 0 7 19 3 and 16 2 years respectively are comparable despite differences in sampling locations in accumulating media and in element loading histories and geochemical properties for a 16 year weighted mean residence time sta generates the observed 6 year lead peak lag evidently significant levels of nondegradable particle associated contaminants can persist in florida bay for many decades following elimination of external inputs present results in combination with sta model analysis of previously reported radionuclide profiles suggest that decade scale time averaging may occur widely in recent coastal marine sedimentary environments

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

the role of organic acid exudates in liberating phosphorus from seagrass vegetated carbonate sediments sediment bound phosphorus p is a potential nutrient source for p limited seagrasses inhabiting carbonate sediments we explored the role of organic acid oa exudation by seagrasses in liberating mineral p from carbonate sediments organic acids can act to increase available p by dissolving carbonate sediment competing with p for binding sites and complexing dissolution end products and also by fueling microbial processes that change pore water ph we used dialysis tubing placed around individual roots in situ to quantify dissolved species immediately adjacent to roots root zone and compared these to bulk pore water concentrations in vegetated and nonvegetated sediments total oa concentrations were highest in the root zone 29 8 6 1 8 mmol l21 compared to bulk measures of 15 5 6 1 9 and 7 5 6 0 6 mmol l21 in vegetated and nonvegetated sediments respectively phosphate concentrations were also highest in the root zone and were linearly related to oa concentrations r2 5 0 63 organic acid concentrations increased along a seagrass productivity gradient and ratios of oa concentrations to productivity showed a significant response to a gradient in p limitation of seagrasses organic acid concentrations found in and around roots compared to those found in bulk sediment measures indicate that seagrasses are a significant source of oa sampling at small spatial scales mm immediately adjacent to the roots is critical because bulk sediment pore water measures did not capture the observed fluctuations caused by the rapid reaction and consumption of oa in the sediment root zone processes can liberate considerable quantities of p and oa exudates likely contribute significantly to the success of t testudinum in p limited environments

forms and availability of sediment phosphorus in carbonate sand of bermuda seagrass beds primary production by seagrasscs in tropical and subtropical carbonate sediments often appears to be phosphorus p limited and several studies have sought to identify the possible sources of p for long term growth here we quantify concentrations of particulate and dissolved p and fluoride f in carbonate sediments sediment water p exchange and leaf tissue p concentrations in three seagrass beds in bermuda we also present data on the sequential extraction of p and f from the sediments at each site total sediment p tp in the upper 20 cm ranged from 650 to 1 250 mmol p m 2 and was some 500 fold larger than the pool of p dissolved in pore waters loosely adsorbed inorganic p comprised 2 of tpsed while a surface bound inorganic p pool extracted by dithionite buffer constituted 15 20 most of the remaining p and nearly all of the ca and f present in the sediment was recovered when the remaing sediment was dissolved in an acetic acid buffer solution this pool includes calcium fluoroapatite cfa which is considered the primary diagenetic sink for p in carbonate sands dissolved inorganic p and fwere both elevated in the rhizosphere pore waters from the three seagrass beds in combination with our analysis of sediments by sequential extraction this result indicates that the carbonate matrix of the sediment is being dissolved in the rhizosphere with a resulting release of p to the pore water and hence to the seagrass roots we suggest that this is important in the p economy of these subtropical seagrass thalussia testudinum beds and note that the carbonate bound p pool is large enough to sustain seagrass p requirements for decades nonetheless primary production in such seagrass systems can remain p limited if the rate of p release from sediment dissolution is too slow to support maximum seagrass growth rates analysis of seagrass leaf tissues revealed that p availability was highest at the site with the highest anthropogenic influences this site was also characterized by the highest sediment p release indicating that high p availability may also be partly due to higher release of p as sediments are dissolved phosphorus was released from the sediment mainly as dissolved organic p causing a net efflux of dissolved p at all sites in april and at two sites in august

sensitivity of the position and variability of the eddy driven jet to different sst profiles in an aquaplanet general circulation model abstractthe response of the storm track and eddy driven jet to various steady sea surface temperature sst forcings is analyzed using the aquaplanet configuration of the atmospheric general circulation model action de recherche petite echelle grande echelle climat arpege climat the sst profiles are zonally homogeneous and piecewise linear functions of the latitude it allows for modifying the tropical component that controls the intensity of the subtropical jet without changing the midlatitude sst front and vice versa sensitivities to the position width and intensity of the midlatitude sst front as well as to the tropical ssts are investigated the baroclinicity and the storm track eddy activity both intensify for a stronger a wider or a more equatorward sst front the eddy driven jet always lies on the poleward side of the sst front and its relative distance to the front is interpreted in terms of upper tropospheric rossby wave breakings a focus is then made on the eddy driven jet variability t

phosphorus release with carbonate dissolution coupled to sulfide oxidation in florida bay seagrass sediments we hypothesized that caco3 dissolution coupled to sulfide oxidation is an important mechanism by which solid phase inorganic p ip becomes available to seagrass in tropical carbonate sediments to examine this supposition we measured field sulfate reduction rates and simulated the acidity 10 50 mmol h2so4 cm23 sediment generated by subsequent sulfide oxidation from high western and low eastern total p tp sediments in florida bay dissolution experiments were conducted using sediment slurries at field ph pore water ph 6 5 7 5 while caco3 dissolution maximum 1 3 of sediment dry weight was evidenced at all sites by leaching of ca2 into slurries at three of the four sites po 3 4 was primarily recovered in the sediment exchangeable pools and at a lower p ca ratio than observed in source sediments in contrast no po 3 4 was recovered from an eastern bay site with the lowest tp and finest grained sediments suggesting that po 3 4 was either tightly adsorbed or incorporated into the carbonate matrix post acidification the potential for tight po 3 4 resorption by sediment from the low tp site was also supported by the rapid rate of isotopic exchange of 33po 3 4 into the sediment matrix these adsorptive and incorporation processes may explain the low po 3 4 in pore waters in the eastern vs western regions of florida bay even upon dissolution of carbonates carbonate dissolution coupled to sulfide oxidation could potentially provide 1 8 and 23 5 mmol ip m22 d21 at eastern and western bay sites respectively meeting 5 of eastern and 29 of western bay seagrass thalassia testudinum p requirements

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

impact of sea grass density on carbonate dissolution in bahamian sediments carbonate dissolution has been widely observed in shallow water tropical sediments however sediment budgets have generally not been closed with respect to the amount of acid required to produce the observed carbonate dissolution recently it has been suggested that enhanced oxygen transport into sediments through the roots and rhizomes of sea grasses might play a role in resolving this mass balance problem we conducted studies of sea grass carbonate sediment interactions around lee stocking island exuma islands bahamas to further examine this problem our studies showed that alkalinity total dissolved inorganic carbon sco2 and ca 21 increased with depth in the pore waters while ph and calculated carbonate ion concentration decreased with depth these observations are consistent with the occurrence of carbonate dissolution in these sediments the magnitude of pore water alkalinity sco2 and ca 21 changes was also related to sea grass density with the largest gradients seen in the sediments of dense sea grass beds calculations suggested that less than 50 of the o2 needed to drive aerobic respiration and ultimately carbonate dissolution via co2 production could be supplied by transport processes such as diffusion bioturbation and physical pore water advection furthermore the o 2 needed to balance the carbonate dissolution budget could be provided by the transport of 15 of the photosynthetically derived o2 to the sediments through sea grass roots and rhizomes without enhancing the removal of carbonate dissolution end products thus sea grasses play an important role in controlling the rates of carbonate dissolution in shallow water tropical marine sediments

the paleoproterozoic aripuana zn pb ag au cu volcanogenic massive sulfide deposit mato grosso brazil geology geochemistry of alteration carbon and oxygen isotope modeling and implications for genesis aripuana is a paleoproterozoic 1 76 1 75 ga stratiform volcanogenic zn pb ag au cu massive sulfide deposit has an estimated resource of 11 6 million metric tons mt of ore and is located on the south southwest border of the amazon craton brazil aripuana resides in a caldera composed of strongly fractionated felsic metavolcanic rocks transitional between calc alkaline and tholeiitic compositions the entire region was metamorphosed into lower greenschist facies 1 68 1 63 ga and the deposit was subsequently thermally metamorphosed and metasomatized 1 56 1 53 ga the mineralized bodies are lenticular and elongated they are located at the base of a sequence of turbidites which overlie dacitic and rhyolitic ignimbrites the rocks of the footwall are silicified sericitized and chloritized and the hanging wall rocks are carbonate rhythmites and turbidites hydrothermal marbles carbonate breccias and breccia like rocks carbonate talc tremolite chlorite rock talc tremolite and biotite rich rocks and carbonate and fluorite bearing cherts the deposit was formed during at least four submarine exhalative hydrothermal cycles in which siliceous marbles and marls represent the initial phase of each cycle followed by the coprecipitation of pyrite pyrrhotite sphalerite argentiferous galenas chalcopyrite which were disseminated in clay carbonate breccias or formed massive lenses this phase was followed by fluoritic cherts and argillites which were followed by carbonate and fluorite rhythmites and turbidites to close the cycle the variation in total rare earth element ree contents and in the eu and ce anomalies indicates that the original sediments were mixtures of hydrothermal carbonate and smectitic clay and were deposited below a redoxcline isotopic analysis identified 18osmow values between 8 and 13 and 13cpdb values between 7 and 1 modeling isotopic data showed that mineralizing fluids were distinct based on the proportion of magmatic fluid that mixed with the seawater carbonate rocks and sulfide minerals precipitated while hydrothermal activity and volcanism evolved from an exhalative to an exhalative explosive character with temperatures increasing between 100 and 200 c the regional metamorphism of the deposit formed carbonate talc tremolite chlorite rocks tremolite biotite and talc rich rocks it recrystallized the minerals foliated and folded all of the rocks and caused limited decarbonation at the sites where carbonate rocks contained silica and smectite however the original isotopic signatures were maintained the thermal metamorphism erased the metamorphic foliation and the metasomatism generated veinlets of chlorite with sulfides

a simple identification scheme for upper level troughs and its application to winter precipitation variability in northwest africa abstract a simple algorithm for the identification of upper level trough axes is introduced in contrast to the assumption of a basically circular geometry in many comparable routines found in the literature the presented identification scheme is based on the east west gradient in the 500 hpa geopotential height field accounting for the meridionally elongated troughs often found in the subtropics on the basis of the ncep ncar reanalysis data from 1958 to 1998 climatological aspects are discussed for the area 22 5 47 5 n 38 5 w 18 5 e for the period from 1977 to 1998 12 hourly precipitation reports from 37 stations in northwestern africa are used to investigate the influence of the identified troughs on winter precipitation it is demonstrated that more than 90 of the precipitation in this region can be assigned to nearby trough axes a comparison of rainy periods with the climatology reveals a significant enhancement of the occurrence of trough axes in a range of 10 15 longitude close to the re

limestone marl alternations as environmental archives and the role of early diagenesis a critical review limestone marl alternations and other micritic calcareous rhythmites have long appealed to sedimentologists as they appeared to directly reflect high frequency environmental change in particular when orbital forcing gained popularity amongst sedimentologists and paleoclimatologists in 1980s such rhythmites seemed to offer an ideal tool for high resolution chronostratigraphy and environmental reconstruction however in spite of the fact that orbital forcing has become a routine interpretation of calcareous rhythmites and that the processes of formation of calcareous rhythmites are considered well understood research in the past 10 years again has questioned their primary origin and their direct interpretability detailed petrographic paleontological and geochemical data from numerous successions through geological time provided the basis for testing whether or not the regular alternation of limestone beds and marl or shale interlayers represents bimodally fluctuating environmental conditions in a direct way in particular these data supplemented by box model simulations imply that post depositional alteration diagenesis has the potential to not only seriously distort primary environmental signals but also to mimic primary signals this questions the use of micritic calcareous rhythmites for high resolution chronostratigraphy and for environmental interpretations where independent data of diagenetically inert parameters are not available diagenetic changes appear to have a yet widely underestimated influence on the appearance of limestone marl alternations and other calcareous rhythmites the aim of the present review is to summarize new approaches and give an overview of our research results in this field of the past decade this review also aims at pointing to still enigmatic aspects that need to be addressed before the interpretation of micritic calcareous rhythmites can be considered a reliable tool for high resolution chronostratigraphy and paleoenvironmental interpretation

a study of the structure of mid latitude depressions in a numerical model using trajectory techniques i development of ideal baroclinic waves in dry and moist atmospheres trajectory tracing techniques are used to investigate the structure and air flow of developing baroclinic waves simulated by a numerical atmospheric forecast model three stages are described the structure of the linear stage is explained with reference to the normal mode theory of baroclinic instability in the mature stage flow separation zones form which are identified as warm and cold fronts at the occluded stage circulation of cold air round the centre of the depression leads to changes in the structure of the cold front when the initial state is nearly saturated the overall development is speeded up and at the mature stage the rate of deepening of the depression is doubled at the surface in the occluded stage formation of a warm air conveyor belt is observed comparisons are made with previously published integrations by specially constructed models in order to establish a basis for comparison of forecasts from real data which will appear in a future paper

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

a dynamic link between high intensity precipitation events in southwestern north america and europe at the last glacial maximum abstract both hydroclimate proxies and modeling studies alike present compelling evidence for abundant precipitation in southwestern north america and europe at the last glacial maximum lgm however model simulations exhibit an apparent disagreement between changes in precipitation and the orientation of the midlatitude jet streams relative to modern this is surprising as it is well known from modern observations that the jet streams and storm tracks closely follow one another in the time mean the present study shows that a substantial fraction between 35 and 50 of the precipitation along the western seaboards of the northern hemisphere continents at the lgm is due to short lived high intensity events rather than a permanent rearrangement of the circulation moreover these precipitation events are shown to be dynamically linked by a wavenumber 5 stationary wave packet that is trapped in a midlatitude waveguide when the wave energy is concentrated in the eastern north pacific an atmospheric river is excited that makes landfall along the north american west coast days later when the wave packet has reached europe the north atlantic jet stream assumes a zonally oriented state that brings abundant precipitation to the western mediterranean sector understanding the dynamics of this teleconnection pattern is not only key for interpreting proxy data signals in past climates but may also be important for improving predictions of storm track dynamics and water resources availability in the face of climate variability and change

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

a case study of explosive cyclogenesis in the eastern pacific abstract an explosive cyclogenesis that occurred in the eastern pacific on 13 november 1981 is described and discussed on the basis of surface and upper air analyses and satellite imagery during one 12 h period the storm deepened by nearly 40 mb and subsequently attained a central pressure of 950 mb or less peak surface winds were in the 45 50 m s 1 range the limited area fine mesh lfm model 24 h forecast initialized at 0000 gmt on the thirteenth completely failed to predict the storm development the development took place within a strong baroclinic zone as a shallow frontal wave traveled from the relatively stable environment of a long wave ridge to the unstable environment of a long wave trough winds at jet stream level exceeded 90 m s 1 prior to the explosive deepening the lifted index in and ahead of the storm diminished and became negative prior to the rapid intensification measurements revealed that sensible and latent heat fluxes from the ocean contributed significantly to the reduced sta

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

a 15 year climatology of northern hemisphere 500 mb closed cyclone and anticyclone centers abstract a 15 year 1963 77 northern hemisphere 2 5 degree latitude longitude gridded dataset of 500 mb geopotential heights has been used to construct a climatology of 500 mb closed circulation centers these centers defined by at least one closed 30 m contour around a central minimum or maximum geopotential height value were identified objectively between 24 and 82 n from the twice daily analysis grids tracks for all closed circulation centers were computed to establish genesis and lysis distributions and to examine the monthly seasonal and interannual variability characteristics of the closed circulation center distributions for specified regions the occurrence of closed cyclone centers is maximized north of and within the main belt of westerlies extending from northeast asia to the gulf of alaska near 50 n and extending from eastern canada and the extreme northeast united states to southeast of greenland and west of the united kingdom their occurrence is also maximized south of the main be

degradative calcification of a modern siliceous sponge from the great bahama bank the bahamas a guide for interpretation of ancient sponge bearing limestones abstract organic colloids are involved in the early calcification of the modern siliceous sponge spheciospongia vesparium lamarck 1815 from the great bahama bank electron microscopy and in situ fluorescence microspectometry studies indicate that colloids attached within or onto a collagen network promote the precipitation of aragonite crystals in these sponges calcification occurs within those portions of the sponge that are buried in the sediment preferentially in regions of agglutinated sediment particles with sponge connective tissue being subjected to necrosis and significant degradation of the extracellular collagen matrix the dismantling of collagen bundles leads to collagen scaffolds which act as a sorbent and have significant adhesive effects for ions and or organic colloids bacteria and other microorganisms support tissue degradation but neither act as a substrate for aragonite precipitation or are present in significant numbers at calcification sites this process of early calcification may explain the origin of fossil calcified siliceous sponges sponge mummies and tuberoids as well as the occurrence of patchy calcified sponge materials thereby calling into question the commonly accepted idea that pelletoidal texture associated with these fossil sponges indicates that bacteria are directly responsible for the calcification

origin and age of phosphorite from the south central florida platform relation of phosphogenesis to sea level fluctuations and δ13c excursions abstract francolite carbonate fluorapatite from predominantly peloidal phosphorite grains in the miocene hawthorn group from the babcock deep core southwestern florida is highly substituted with an average composition of ca4 61na0 22mg0 14k0 05sr0 02 po4 2 23 co3 0 62 so4 0 12 f 1 04 13c values of 1 0 7 8 pdb of the francolite co3 indicate a substantial contribution of c from an organic source the sulfur isotopic composition of francolite so4 is depleted to slightly enriched relative to miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction the uniformly high sr na mg so4 and co3 contents of the francolite the 18o values of the francolite co3 0 2 4 2 pdb and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation phosphorite from the babcock deep core has sr 87 86 ratios that range from 0 708148 0 708880 and sr derived ages that range from late oligocene 25 6 0 7 ma to early late miocene 9 2 1 4 ma the sr derived ages of relatively fragile calcareous benthic foraminifers are consistently younger than associated hard tightly cemented phosphorite and support textural evidence of extensive reworking the age of the host sediment ranges from early miocene to pliocene and its depositional history is related to sea level fluctuations approximately three quarters of the total phosphorite in the babcock deep core formed during or within 2 my before the major early to mid miocene positive 13cshift as recorded at dsdp site 588 southwest pacific one third of the total phosphorite formed just prior to the carbon shift in the short interval between 21 9 and 20 4 ma these results indicate that reworked phosphorite deposits may provide a proxy of organic carbon cycling on continental shelves that correspond to sealevel fluctuations and to variations in the 13crecord

linkages between extreme precipitation events in the central and eastern united states and rossby wave breaking abstractlinkages between extreme precipitation events epes in the central and eastern united states and synoptic scale rossby wave breaking are investigated using 1979 2015 climatologies of epes

intraseasonal and interdecadal jet shifts in the northern hemisphere the role of warm pool tropical convection and sea ice abstractthis study uses cluster analysis to investigate the interdecadal poleward shift of the subtropical and eddy driven jets and its relationship to intraseasonal teleconnections for this purpose self organizing map som analysis is applied to the ecmwf interim re analysis era interim zonal mean zonal wind the resulting som patterns have time scales of 4 8 5 7 days and undergo notable interdecadal trends in their frequency of occurrence the sum of these trends closely resembles the observed interdecadal trend of the subtropical and eddy driven jets indicating that much of the interdecadal climate forcing is manifested through changes in the frequency of intraseasonal teleconnection patterns two classes of jet cluster patterns are identified the first class of som pattern is preceded by anomalies in convection over the warm pool followed by changes in the poleward wave activity flux the second class of patterns is preceded by sea ice and stratospheric polar vortex anomalies when the arctic se

reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection reactive transport models rtms permit quantitative investigation of diagenesis and its effects on reservoir quality the rtm toughreact is used to investigate diagenesis in an isolated platform driven by geothermal kohout convection of seawater which has been invoked to explain dolomitization during early burial previous short 0 1 m y rtm simulations suggested that convection can drive dolomitization mostly at greater than 50c and anhydritization but complete dolomitization requires greater than 30 60 m y our more extended rtm simulations 30 m y indicate significant nonlinearities in the system consistent with high temperature experiments with parts of the platform completely dolomitized within 10 15 m y as dolomitization proceeds the process becomes predominantly flux controlled with development of a wedge shaped dolomite body which thins from the margin to the interior at considerably shallower depth and cooler temperatures 20 30c than suggested by short simulations dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms sediment permeability and reactive surface area commonly inversely related are key controls dolomitization is limited to the margin of low permeability muddy platforms despite a high reactive surface area dolomitization of more permeable grainy platforms is limited by a lower reactive surface area occurring only in the platform core due to widespread cooling sedimentary layering produces a complex diagenetic stratigraphy dolomitization favoring more reactive beds at shallow depth where permeability is not limiting but switching to more permeable beds at depth bank marginal fracturing limits dolomitization of the platform interior whether the fractures are baffles or conduits for flow

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

diagenetic trends of fluorine concentration in negev phosphorites israel implications for carbonate fluorapatite composition during phosphogenesis an electron probe and chemical study of bulk phosphorite samples and separated constituents from various negev deposits was carried out together with xrd ftir spectroscopy and textural analysis the results allow a better understanding of the distribution of fluorine in these upper cretaceous phosphorite sequences and shed light on variations in the composition of the carbonate fluorapatite cfa phase during phosphogenesis two facies are recognized 1 a pristine microbially generated phosphorite facies 2 a recycled peloidal and biodetrital facies fluorine distribution in the negev phosphorites is facies controlled f p2o5 is much lower in the pristine facies 0 090 0 107 than in the recycled facies 0 107 0 120 in addition f p2o5 varies considerably between the various constituents of the phosphate fraction f poor francolites f p2o5 as low as 0 080 co exist with f rich francolites f p2o5 as high as 0 135 in the same phosphorite bulk sample a lower f p2o5 in francolite is associated with higher cd and zn concentrations in the phosphorite an increase in fe rich smectites in the clay fraction and the presence of structural oh in the francolite the lower f p2o5 ratios in the pristine facies are attributed to high organic deposition rates during the formation of these matted sediments leading to rapid burial of the in situ forming cfa this is possibly coupled with diffusion of f from sea water into bottom sediments being hampered by microbial mat coatings these conditions resulted in o2 depleted porefluids inducing the precipitation of cd rich zn sulphides and the formation of fe rich smectites f enrichment probably takes place when the earlier formed f poor primary cfa is relocated close to the sea floor and bathed with interstitial sea water solutions of higher f concentrations oxidation and removal of the sulphide bound cd and zn apparently occurred together with enrichment in f of the francolite combining chemical data with xrd and ftir results suggests a multistage growth for the negev phosphate constituents in shifting formational sites and porefluids of varying f concentrations this multiphase growth is reflected in the patchy distribution of f in the negev constituents and might explain the inverse correlation between mean co2 f and f p2o5 ratios of the analysed phosphorites in the two facies it also suggests that cfa or an amorphous precursor initially formed with some oh groups in the apatite structure which were subsequently substituted by f ions in recycled francolite through re equilibration with porefluids of higher f concentrations

stability analysis of rock wedge slide subjected to groundwater dynamic evolution abstract heavy rainfall may increase the infiltration rate raising the groundwater table after a short period time variation in the hydrostatic pressure on potential sliding surfaces and trailing edges of fissures in a rock slope may contribute to slope failure the failure mechanisms of rainfall triggered rock wedge slides have been widely studied in the literature however studies on the dynamic evolution of groundwater in rock failure are still limited in this study a typical rock wedge slide that occurred in chengkou county chongqing china is selected as a case study to analyze the stability of rock wedge with double planes and tension crack subjected to groundwater dynamic evolution model tests were designed and performed to reproduce the dynamic evolution of groundwater in the rock slope and analyze its role in wedge failure development and distribution characteristics of water pressure are investigated through monitoring the water pressure distributed along the surfaces of wedge failures from the experimental study it is found that the initial formation process of water pressure along the sliding surface consists of four types of distribution patterns i e triangular distribution type i trapezoidal distribution type ii trapezoidal distribution and type iii trapezoidal distribution based on the model tests and theoretical analysis the order of the calculated safety factors of the chengkou rock wedge slide are triangle type i trapezoid type ii trapezoid type iii trapezoid the existence of inflection points in the trapezoidal distribution mode significantly increases water pressure on both sides of rock wedge which contributes instability the new approach for investigation of the effect of dynamic evolution groundwater on stability of rock wedge slide is developed based on fundamental mechanism and experimental study it can be adopted for stability assessment of similar rock wedge slides in other areas

potential vorticity in the stratosphere derived using data from satellites maps of ertel s potential vorticity q are computed on an isentropic surface in the middle of the stratosphere they are derived using data from stratospheric sounding units on board noaa satellites the reliability of the maps is demonstrated mainly by conservation of q that is shown in successive analyses and by the close agreement obtained using independent data from two satellites the maps are used to follow the movement of material during the course of strong disturbances which occurred in december 1981 they clearly show the breaking of planetary waves in the stratosphere an inherently nonlinear process the effect of wave breaking on the structure of the westerly vortex is considered any mixing of q on isentropic surfaces during wave breaking is shown to be far from complete in the examples studied the behaviour of diagnostics based on zonal averaging such as the eliassen palm flux is accounted for by local changes in the distribution of q the implications of our findings for the study of stratospheric dynamics are discussed

mixing depths and sediment accumulation rates on an arid tropical shelf based on fine fraction 210pb analysis abstract continental shelves in arid tropical settings present particular challenges to 210pb based analysis of sedimentation rates and surface mixing owing to the combination of coarse sediment deep and year round bioturbation and lower atmospheric flux of 210pb the modern continental shelf at the northern terminus of the hyper arid gulf of eilat aqaba goe receives flood runoff of siliciclastics producing a mixed seabed with 20 carbonate that is dominated by larger benthic foraminifera and mollusks focusing analysis on only the fine fraction of deep penetrating cores 70 cm from 15 to 40 m water depths yields reliable 210pb profiles in contrast to analysis of bulk sediment graphical abstract sedimentation rates increase offshore five fold from 0 01 0 04 cm y in 15 m water depth to 0 21 0 27 cm y in 30 40 m depths reflecting offshore redistribution of flood delivered siliciclastic sediments away from the wadi mouth a result also supported by an offshore increase in the inventory of excess 210pb in contrast the thickness of the surface mixed layer sml decreases from 30 cm to 20 cm with proximity to anthropogenic stressors channelized flood runoff historic release of sewage and operation of fish cages which we attribute to the suppression of macrobenthic burrowers the rate of sedimentation on the gulf shelf away from dynamic bypassing in the 15 m shoreface is comparable to other tropical carbonate shelves rich in large benthic foraminifera and is higher than rates documented on the adjacent slope increasing confidence in this approach to 210pb analysis using only the fine fraction analysis of the fine fraction rather than bulk sediment would be a useful adjustment to 210pb methodology in any area with scarce fine grained sediment