authigenic vivianite in potomac river sediments control by ferric oxy hydroxides abstract sand size particles of vivianite fe3 po4 2 8h2o have been identified by x ray diffraction and scanning electron microscopy in surficial sediments of the tidal potomac river near a major sewage treatment plant vivianitc particles are concentrated in a surface layer of coarse sand dredge spoil which overlies much finer sediment similar to that found in adjacent areas although saturation indices indicate that the pore waters of virtually all the sediments in the study area are supersaturated with respect to vivianite it is found only in association with dredge spoil pore water profiles of fe p and eh as well as the size and morphology of individual grains indicate that the vivianite is authigenic and was not introduced with he dredge spoil it is suggested that the major control on the occurrence of the mineral is the presence or absence of amorphous ferric oxy hydroxides which apparently react with pore water phosphorus to form stable ferric hydroxy phosphates preferentially to the formation of vivianite

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

vivianite formation and its role in phosphorus retention in lake orn denmark abstract vivianite fe 3 po 4 2 8h 2 o may precipitate in anoxic lake sediments affecting the porewater orthophosphate concentration and thereby the trophic status of lakes we have investigated changes in lake diagenesis of fe and p 1969 2009 with particular attention focused on vivianite formation with sediment depth 0 20 cm in an iron silica carbon rich lake sediment ornso denmark porewaters were supersaturated for vivianite by two to five orders of magnitude upper 10 cm with porewater phosphate concentrations ranging between 0 69 and 10 mol l 1 in winter and summer concentrations ranging between 9 8 and 40 mol l 1 significant formation of vivianite was confirmed by x ray diffraction while scanning electron microscopy and electron dispersive x ray spectroscopy indicated an increase in vivianite crystal size with depth 20 to 70 m across variations in elemental composition of vivianite crystals in relation to at p and fe were especially seen going from 9 5 cm to 24 5 cm the total sediment fe pool was very large 3000 mol g 1 and total p increased from 200 mol g 1 to 400 mol g 1 descending down the sediment profile differential extraction experiments of p release at ph 3 estimated that vivianite amounts to between 3 and 5 of the total fe pool the total p burial fluxes estimate that 38 mol cm 2 yr 1 or 26 of sedimentary p in the lower sediments is sequestered as vivianite there are seasonal variations in the porewater composition with lower fe orthophosphate and higher sulfate concentrations during winter 5 c than during summer 15 c this suggests that temperature modulates the rate of organic matter degradation which in turns affects the rate of fe iii phase reduction release of phosphate and thereby the porewater fe 2 and orthophosphate concentrations and hence vivianite formation this work highlights the role vivianite can play for p retention in a si fe c rich lake sediment

zone of metal driven anaerobic oxidation of methane is an important sink for phosphorus in the taixinan basin south china sea abstract phosphorus p is an important nutrient and has an important impact on global primary productivity presently the dynamics of the p cycle in low sulfate anoxic settings are largely unknown in this study the adsorption desorption behavior of fe bound p organic p loosely bund p detrital apatite p and refractory p was described in the sulfate and methane transition zone smtz at site 973 4 in the cold seep area of the taixinan basin south china sea results showed that the fe bound p and organic p were influenced by sulfate driven anaerobic oxidation of methane sd aom and metal driven anaerobic oxidation of methane md aom and subsequently the fe bound p and organic p were released as hpo42 into the pore water meanwhile significant increases were detected in authigenic carbonate fluorapatite pcfa and vivianite within the md aom zone which indicate that this zone is an important p sink area the md aom plays an important role in the formation of pcfa and vivianite because md aom provide the necessary hpo42 and fe2 for the formation of these minerals our findings have major implications for understanding the p cycle in low sulfate anoxic settings and are important for understanding the influence of md aom on the phosphate cycle

development of a modified sedex phosphorus speciation method for ancient rocks and modern iron rich sediments abstract we report the development of a modified method for evaluating different reservoirs of sedimentary phosphorus p in ancient marine sedimentary rocks and in modern fe rich sediments utilising the existing sedex scheme for p partitioning in modern sediments we initially demonstrate limitations in the application of the original scheme to sediments and rocks containing crystalline hematite and magnetite we tested additional extractions for these crystalline fe phases using both synthetic minerals and modern and ancient sediments the addition of 6 h oxalate and 6 h citrate dithionate acetate extractions considerably enhanced the total recovery of synthetic magnetite and hematite to 88 7 1 1 and 76 9 3 8 respectively in addition application of the 6 h oxalate extraction to synthetic p containing magnetite recovered 93 9 1 7 of the fe present and 88 2 12 8 of the co precipitated p based upon these results we developed a modified sedex extraction scheme the modified scheme was applied to modern fe rich sediments from golfo dulce costa rica which resulted in 16 higher fe bound p recovery application of the scheme to a variety of ancient marine rocks increased the recovery of fe bound p by up to 22 we also highlight the potential for authigenic carbonate fluorapatite to convert to more crystalline apatite in ancient rocks during deep burial and metamorphism we suggest that in such systems minimum and maximum estimates of the total reactive p pool may be calculated with and without the inclusion of crystalline p it is noted that the application of the revised method may have important implications for understanding the cycling of p in ancient marine environments

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

local and field scale stochastic advective vertical solute transport in horizontally heterogeneous unsaturated soils description of field scale solute transport in unsaturated soils is essential for assessing the degree of contamination estimating fluxes past a control plane and for designing remedial measures the flow field is usually described by numerical solution of the richards equation followed by numerical solution of the advection dispersion equation to describe contaminant movement these numerical solutions are highly complex and do not provide the insights that are possible from simpler analytical representations in this study analytical solutions at the local scale are developed to describe purely advective vertical transport of a conservative solute along the principle characteristic of the flow field local scale model development is simplified by using a sharp front approximation for water movement these local solutions are then upscaled to field scale solute transport by adopting a lognormally distributed horizontal hydraulic conductivity field to represent the natural heterogeneity observed in field soils analytical expressions are developed for the mean behavior of solute transport at the field scale comparisons with experimental observations find that trends of field scale solute behavior are reasonably reproduced by the model the accuracy of the proposed solution improves with increasing spatial variability in the hydraulic conductivity as revealed by further comparisons with numerical results of the richards equation based field scale solute movement in some cases the sharp front approximation may lead to anomalous field scale behavior depending on the role of pre and postponded conditions in the field and this limitation is discussed the proposed method shows promise for describing field scale solute movement in loamy sand and sandy loam soils

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

geochemical characteristics of iron in sediments from the sea of marmara abstract two 1000 cm long sediment cores were recovered from the sea of marmara one with the occurrence of gas hydrates in the western high and the other without hydrates in the cinarcik basin differences in mineralogical and chemical compositions have been identified between the two sediment cores based on the results of the mineralogical and geochemical analyses the main sources of the sediments are quite similar for both investigated areas but the authigenic components are different particularly iron sulfides and carbonates authigenic fe ii carbonate are much higher in core mrs cs 05 in the western high while crystalline fe iii phases are more abundant in core mrs cs 16 in the cinarcik basin notably the enrichments of greigite fe3s4 a metastable ferromagnetic iron sulfide mineral and intermediate polysulfide as well as iron carbonates are identified at 400 cmbsf with the maximum iron content in core mrs cs 05 these indicate the presence of a more reducing and acidic environment in the western high mainly due to higher organic matter content and seepage of heavy hydrocarbons in the sediments

distribution of iron in the western indian ocean and the eastern tropical south pacific an inter basin comparison abstract the western indian ocean wio and eastern tropical south pacific etsp are distinctly different regimes yet they share several important features these include a strong upwelling system a large oxygen minimum zone omz with active denitrification a spreading center with extensive hydrothermal activity and a vast oligotrophic upper water column here we show that the distribution and geochemistry of iron shows remarkable similarities as well in particular both basins exhibit large sub surface plumes of iron derived from sediments underlying the oxygen minimum zones and from hydrothermal sources moreover the behavior of fe especially its redox cycling is remarkably similar in the arabian sea and peruvian oxygen minimum zone reflecting similar processes associated with the nitrogen cycle in each region the large fe plumes under each omz are well below the oxygen free depth yet they are probably dependent on internal redox cycling and scavenging of fe within the overlying omzs globally both the arabian sea and peru margin sediments are hot spots of carbon oxidation which probably contributes to their importance as fe sources the fate of hydrothermally derived fe in the wio and etsp is particularly interesting to compare because their source terms are very different even though their oxidation rates once they have entered the water column should be directly comparable in the etsp hydrothermal inputs from along a section of the ultra fast spreading southern east pacific rise sepr are integrated into a single coherent plume that is exported west across the ocean interior for 4000 km in contrast hydrothermal inputs to the wio derive from multiple sources including outflow from the red sea via the gulf of aden the indonesian throughflow and from multiple vent sources along the carlsbad ridge central indian ridge and sw indian ridge which are slow medium and ultra slow spreading respectively as a result hydrothermally sourced fe distributions are more complex in the wio with several overlapping plumes and distinctly different distributions of two other hydrothermally derived metals aluminum and manganese here we argue that comparative studies of these basins with a future emphasis on benthic water column interactions will advance knowledge about fe biogeochemistry and how distributions in the wio in particular are likely to change in the future

vivianite is a key sink for phosphorus in sediments of the landsort deep an intermittently anoxic deep basin in the baltic sea phosphorus p is an essential nutrient for marine organisms its burial in hypoxic and anoxic marine basins is still incompletely understood recent studies suggest that p can be sequestered in sediments of such basins as reduced iron fe p but the exact phase and the underlying mechanisms that lead to its formation are unknown in this study we investigated sediments from the deepest basin in the baltic sea the landsort deep site m0063 that were retrieved during the integrated ocean drilling project iodp baltic sea paleoenvironment expedition 347 the record comprises the whole brackish marine littorina sea stage including past intervals of extensive hypoxia in the baltic sea that occurred during the holocene thermal maximum htmhi and the medieval climate anomaly mca1hi and mca2hi various redox proxies e g the presence of laminations and high mo contents suggest almost permanent bottom water hypoxia during the littorina sea stage in the landsort deep the bottom waters were likely even seasonally anoxic or sulfidic during the mca1hi and mca2hi and permanently sulfidic during the htmhi with the use of micro analysis of sieved minerals sem eds xrd and synchrotron based xas we show that mn and mg rich vivianite crystals are present at various depths in the littorina sea sediments we also have indications for vivianite in the mca1hi mca2hi and htmhi deposits the formation of vivianite thus likely explains the high fe bound p fraction throughout the whole littorina sea stage shuttling of fe and mn from the shelves into the basin and high inputs of p in settling organic matter are likely key drivers for vivianite formation our study shows that vivianite can likely form in near surface sediments under a broad range of bottom water redox conditions varying from hypoxic and anoxic to sulfidic

iron dependent anaerobic oxidation of methane in coastal surface sediments potential controls and impact anaerobic oxidation of methane aom is an important process of methane ch4 removal in sediments various studies suggest that aom coupled to iron oxide fe oh 3 reduction fe aom may complement sulfate driven aom in ch4 rich sediments here we apply a transient reaction transport model to depth profiles of key porewater and sediment constituents for a site in the bothnian sea where fe aom has been suggested to occur at the site increased eutrophication has led to an upward shift of the sulfate methane transition zone submerging fe oh 3 in a zone with high ch4 concentrations fe aom is thought to lead to a strong accumulation of dissolved iron fe2 in the porewater results of a sensitivity analysis identify three potential controls on the occurrence of fe aom in coastal surface sediments 1 bottom water sulfate inline image concentrations 2 fe oh 3 availability and 3 organic matter om loading in situ ch4 production is particularly sensitive to the om loading and inline image bottom water concentration with higher inline image concentrations significantly inhibiting methanogenesis and decreasing the potential rates of fe aom we find that only environments with a low salinity and a relatively high fe oh 3 loading allow for fe aom to occur in surface sediments this suggests that fe aom in surface sediments is restricted to areas with relatively high rates of sediment deposition such as estuaries and other nearshore systems by enhancing porewater fe2 concentrations in surface sediments and the flux of fe2 from sediments to the overlying water fe aom may contribute to the lateral transfer of iron iron shuttling from the coastal zone to deep basins

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the baltic sea microanalysis of epoxy resin embedded sediments is used to demonstrate the presence of authigenic iron fe ii phosphates and manganese mn calcium ca carbonate phosphates in the deep euxinic basins of the baltic sea these minerals constitute major burial phases of phosphorus p in this area elevating the total p burial rate above that expected for a euxinic depositional environment particle shuttles of fe and mn oxides into the deep euxinic basins act as drivers for p bearing mineral authigenesis while fe ii phosphates are formed continuously in the upper sediments following the sulfidization of fe oxyhydroxides and release of associated p mn ca carbonate phosphates are formed intermittently following inflow events of oxygenated north sea water into the deep basins the mechanism of fe ii phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments by occurring within rather than below the sulfate methane transition zone the spatial distribution of both authigenic phases in baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales the results highlight the potential importance of authigenic p bearing minerals other than carbonate fluorapatite for total p burial in euxinic basins

the manganese and iron shuttle in a modern euxinic basin and implications for molybdenum cycling at euxinic ocean margins a meaningful application of mo as a paleo redox proxy requires an understanding of mo cycling in modern reducing environments stagnant euxinic basins such as the black sea are generally regarded as model systems for understanding euxinic systems during early earth history however drawing direct parallels between the black sea and open marine euxinic margins is somewhat complicated by differences in the seawater residence time between these two environments we report sediment and pore water mo u mn and fe data for a euxinic basin with a short seawater residence time the weakly restricted gotland deep in the baltic sea here prolonged periods of euxinia alternate with brief inflow events during which well oxygenated saline water penetrates into the basin during these inflow events dissolved mn and fe that has accumulated within the euxinic deep water can be oxidized and precipitated co variations of mo and u within the sediment suggest that these inflow and oxygenation events may favor mo accumulation in the sediment through adsorption to freshly oxidized mn and fe solid phases once mo is sequestered within the deeper euxinic water and sediments mo retention can be further facilitated by conversion to thiomolybdate species and interactions with organic matter and metal sulfides by comparing our data with those from previous studies where a mn and fe shuttle for mo has been demonstrated we identify two prerequisites for the occurrence of this mechanism first there must be a water column oxic anoxic redox boundary this provides a solubility contrast for mn and fe second the residence time of seawater in the system has to be short weeks to a few years the latter criterion can be met through regular inflow in weakly restricted basins or upwelling in oxygen minimum zones at open marine continental margins based on prior work we suggest that similar conditions to those currently represented by the gotland deep may have prevailed at euxinic ocean margins during the proterozoic a boundary between euxinic and oxic water masses overlying the continental shelf may have resulted in accelerated mo transport through the water column with mn and fe oxyhydr oxides we propose that this mechanism along with mo isotope fractionation during adsorption could contribute to the light mo isotope composition observed in open marine euxinic sediment facies of the proterozoic

solute transport through a heterogeneous coupled vadose saturated zone system with temporally random rainfall the transport of nonreactive solutes through a coupled two dimensional randomly heterogeneous vadose saturated zone system subject to temporally random rainfall is predicted by monte carlo simulation and compared with previously published analytic results for three different rainfall patterns the relative contributions of the uncertain inputs i e rainfall and saturated conductivity to the prediction uncertainty of solute transport are quantified in terms of the statistical moments of the pore water velocity the plume spatial moments and solute flux breakthrough curves at downstream control planes results show that the mean and variance of the saturated zone pore water velocity were approximately equivalent for the cases of uniform and random rainfall and were well predicted by the analytical relationships developed by rubin and bellin 1994 as a result the mean plume displacement estimated by the trajectory of the mean plume center of mass was found to be nearly identical for these cases in the temporally random rainfall case the saturated zone mean plume experienced more spread in the direction of mean flow at early times however the asymptotic rates of spatial spreading of the mean solute plumes were found to be approximately equivalent for the uniform and random rainfall cases and well predicted by the approximate expressions for longitudinal macrodispersivity in nonuniform flow proposed by destouni and graham 1995 random rainfall and random soil properties increased prediction uncertainty of the solute plume behavior in the vadose zone by an order of magnitude when compared with the uniform rain and random soil case this effect was reduced considerably when the solute entered the saturated zone where random rainfall produced only slightly larger prediction uncertainty than the uniform rainfall case the analytic model developed by destouni and graham 1995 accurately predicted the temporal breakthrough of the mean solute plume at saturated zone control planes for all cases if transport through the unsaturated zone accounted for the effects of temporally random rainfall using the methodology developed by foussereau et al 2000a 2000b results of this work indicate that for the humid climates studied here uncertain rainfall patterns dominate transport prediction uncertainty in the shallow unsaturated zone while uncertain solute breakthrough to the saturated zone and uncertain hydraulic conductivity dominate prediction uncertainty in the saturated zone

large eddy simulation of stable atmospheric boundary layers with a revised stochastic subgrid model simulations of stable atmospheric boundary layers have been conducted at various stabilities with a revised stochastic backscatter model based on mason and thomson s theoretical and numerical results compared to the previous results of mason and derbyshire there is more turbulence and a deeper boundary layer as was expected from the tendency of the parametrization change to increase the surface stress scatterplots of various local non dimensional quantities against the gradient richardson number are presented which indicate a high degree of collapse to a single local scaling curve agreement of the non dimensional gradients with the surface layer observations is greatly improved by the inclusion of backscatter

geochemical evidence for iron mediated anaerobic oxidation of methane anaerobic oxidation of methane aom by sulfate has been recognized as a critical process to maintain this greenhouse gas stability by limiting methane flux to the atmosphere we show geochemical evidence for aom in deep lake sediments and demonstrate that aom is likely driven by iron fe reduction pore water profiles from lake kinneret sea of galilee israel show that this sink for methane is located below the 20 cm depth in the sediment which is well below the depths at which nitrate and sulfate are completely exhausted as well as below the zone of methanogenesis iron dependant aom was verified by fe iii amended mesocosm studies using intact sediment cores and native iron oxides were detectable throughout the sediments because anaerobic fe iii respiration is thermodynamically more favorable than both sulfate dependent methanotrophy and methanogenesis its occurrence below the zone of methane production supports the idea that reduction of sedimentary iron oxides is kinetically or biologically limited similar conditions are likely to prevail in other incompletely pyritized aquatic sediments indicating that aom with fe iii is an important global sink for methane

wind driven internal waves and langmuir circulations in a numerical ocean model of the southern baltic sea 1 a one dimensional numerical ocean model of the southern baltic sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations the turbulence model is a k e model that includes extra source terms piw and plc of turbulent kinetic energy tke due to unresolved breaking internal waves and langmuir circulations respectively as tides are negligible in the baltic sea topographic generation of internal wave energy iwe is neglected instead the energy for deepwater mixing in the baltic sea is provided by the wind at each level the source term piw is assumed to be related to a vertically integrated pool of iwe e0 and the buoyancy frequency n at the same level according to piw z e0n z this results in vertical profiles of e the dissipation rate of tke and kh the eddy diffusivity according to e n and kh n 2 below the main pycnocline earlier observations are inconclusive as to the proper value of and here a range of values of is tested in hundreds of 10 year simulations of the southern baltic sea it is concluded that 1 0 0 3 and that a mean energy flux density to the internal wave field of about 0 9 0 3 10 3 w m 2 is needed to explain the observed salinity field in addition a simple wind dependent formulation of the energy flux to the internal wave field is tested which has some success in describing the short and long term variability of the deepwater turbulence the model suggests that 16 of the energy supplied to the surface layer by the wind is used for deepwater mixing finally it is also shown that langmuir circulations are important to include when modeling the oceanic boundary layer a simple parameterization of langmuir circulations is tuned against large eddy simulation data and verified for the baltic sea

sulfur and iron diagenesis in temperate unsteady sediments of the east china sea inner shelf and a comparison with tropical mobile mud belts mmbs redox cycling of iron fe and sulfur s exerts profound influences on fates of numerous elements in coastal marine sediments in this study s and fe cycling and its geochemical expressions in the east china sea ecs inner shelf a representative of temperate mobile mud belts mmbs were characterized and compared with tropical counterparts the amazon shelf and the gulf of papua fe and s speciation consistently points to the dominance of authigenic nonsulfidized fe ii phases i e poorly crystalline clays pccs and carbonates and the prevalence of fe redox cycling in the suboxic or weakly sulfidic regimes of the ecs mmbs high contents of authigenic magnetite may be a common diagenetic expression in all mmbs compared to the tropical mmbs three main differences of diagenetic expressions in the ecs mmbs are i light 34spyrite in the ecs mmb vs characteristically heavy 34spyrite in the amazon shelf mmbs ii lower total reactive fe fetr total diagenetic fe ii and ratio of fetr to total fe in the ecs mmbs iii fe ii carbonates and pccs are equally important sinks for nonsulfidized fe ii in the ecs mmbs whereas pccs are the predominant sink in the tropical counterparts these differences are ascribable to factors including low degradability of organic matter small diffusion scales less intense chemical weathering in the drainage basin and or weaker reverse weathering in the ecs mmbs despite the differences above fe and s diagenetic expressions that characterize the prevalence of fe redox cycling in the unsteady suboxic regimes are shared by the ecs and tropical mmbs

internal wave mixing in the baltic sea near inertial waves in the absence of tides 1 the dynamics of near inertial motions and their relation to mixing is investigated here with an extensive data set including turbulence and high resolution velocity observations from two cruises conducted in 2008 summer and 2010 winter in the bornholm basin of the baltic sea in the absence of tides it is found that the basin scale energetics are governed by inertial oscillations and low mode near inertial wave motions that are generated near the lateral slopes of the basin these motions are shown to be associated with persistent narrow shear bands strongly correlated with bands of enhanced dissipation rates that are the major source of mixing inside the permanent halocline of the basin in spite of different stratification near inertial wave structure and atmospheric forcing during summer and winter conditions respectively the observed dissipation rates were found to scale with local shear and stratification in a nearly identical way this scaling was different from the gregg henyey type models used for the open ocean but largely consistent with the mackinnon gregg scaling developed for the continental shelf

sedimentary phosphorus dynamics and the evolution of bottom water hypoxia a coupled benthic pelagic model of a coastal system the present study examines oxygen and phosphorus dynamics at a seasonally hypoxic site in the arkona basin of the baltic sea a coupled benthic pelagic reactive transport model is used to describe the evolution of bottomwater solute concentrations as well as pore water and sediment profiles aerobic respiration dominates remineralization with iron reduction denitrification and sulphate reduction playing secondary roles while other pathways are negligible sediments represent a significant oxygen sink chiefly due to the aerobic degradation of organic matter as well as nitrification and iron oxyhydroxide precipitation most phosphorus deposited in sediments is in organic matter yet cycling is dominated by iron bound phosphorus due to rapid dissimilatory iron reduction coupled with aerobic iron oxyhydroxide formation sustained hypoxia results in an initial decrease in sediment phosphorus content due to dissolution of phosphorus bearing iron oxyhydroxides resulting in a pulse of phosphate to overlying waters although an organic rich layer is formed under low oxygen conditions enhanced remineralization of organic phosphorus relative to organic carbon tempers sedimentary phosphorus accumulation upon reoxygenation of bottom waters after a decade of sustained hypoxia oxygen concentrations do not immediately achieve values observed prior to hypoxia because the organic rich layer creates a higher benthic oxygen demand artificial reoxygenation of bottom waters leads to a substantial increase in the ironbound phosphorus pool the total phosphorus content of the sediment however is unaffected a relapse into hypoxia would consequently produce a large pulse of phosphate to the overlying waters potentially exacerbating the situation

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

rapid high amplitude variability in baltic sea hypoxia during the holocene hypoxia oxygen concentrations of 2 ml l and so called dead zones are a growing concern in coastal marine environments the baltic sea is a shelf sea that is highly sensitive to hypoxia and may serve as a laboratory for studying the interplay between natural and anthropogenic forcing of redox conditions in the global coastal zone past occurrences of hypoxia in the baltic sea have been shown by previous studies but high resolution quantitative reconstructions of past hypoxia intensity are lacking here we present bulk sediment geochemical records from the deep basins of the baltic sea that show multicentennial oscillations during intervals of past hypoxia suggesting rapid alternations between hypoxic and relatively oxic conditions while the onset of past hypoxic events was likely forced by climatic variability these events intensified and terminated rapidly due to feedbacks in the phosphorus p cycle the modern intensity of hypoxia is similar to several past events suggesting that hypoxia in the baltic sea has a maximum potential intensity however using ultrahigh resolution laser ablation inductively coupled plasma mass spectrometry scanning of sediment blocks we show that modern hypoxia intensified more rapidly than any past event this confirms the role of anthropogenic nutrient loading in driving this system into its current hypoxic state

a quantitative reconstruction of organic matter and nutrient diagenesis in mediterranean sea sediments over the holocene abstract a multicomponent diagenetic model was developed and applied to reconstruct the conditions under which the most recent sapropel s1 was deposited in the eastern mediterranean sea simulations demonstrate that bottom waters must have been anoxic and sulphidic during the formation of s1 and that organic matter deposition was approximately three times higher than at present nevertheless most present day sediment and pore water profiles with the exception of pyrite iron oxyhydroxides iron bound phosphorus and phosphate can be reproduced under a wide range of redox conditions during formation of s1 by varying the depositional flux of organic carbon as a result paleoredox indicators e g c org s ratio c org p org ratio trace metals are needed when assessing the contribution of oxygen depletion and enhanced primary production to the formation of organic rich layers in the geological record furthermore simulations show that the organic carbon concentration in sediments is a direct proxy for export production under anoxic bottom waters the model is also used to examine the post depositional alteration of the organic rich layer focussing on nitrogen phosphorus and organic carbon dynamics after sapropel formation remineralisation is dominated by aerobic respiration at a rate that is inversely proportional to the time since bottom waters became oxic once again a sensitivity analysis was undertaken to identify the most pertinent parameters in regulating the oxidation of sapropels demonstrating that variations in sedimentation rate depositional flux of organic carbon during sapropel formation bottom water oxygen concentration and porosity have the largest impact simulations reveal that sedimentary nutrient cycling was markedly different during the formation of s1 as well as after reoxygenation of bottom waters accumulation of organic nitrogen in sediments doubled during sapropel deposition representing a significant nitrogen sink following reventilation of deep waters n 2 production by denitrification was almost 12 times greater than present day values phosphorus cycling also exhibits a strong redox sensitivity the benthic efflux of phosphate was up to 3 5 times higher during the formation of s1 than at present due to elevated depositional fluxes of organic matter coupled with enhanced remineralisation of organic phosphorus reoxygenation of bottom waters leads to a large phosphate pulse to the water column that declines rapidly with time due to rapid oxidation of organic material the oxidation of pyrite at the redox front forms iron oxyhydroxides that bind phosphorus and thus attenuate the benthic phosphate efflux these results underscore the contrasting effects of oxygen depletion on sedimentary nitrogen and phosphorus cycling the simulations also confirm that the current conceptual paradigm of sapropel formation and oxidation is valid and quantitatively coherent

early diagenetic processes fluxes and reaction rates in sediments of the south atlantic abstract porewaters recovered from sediment cores gravity corers box corers and multicorers from various subrogions of the south atlantic amazon river mouth equatorial upwelling congo river mouth benguela coastal upwelling area and angola basin were investigated geochemically objectives included determination of eh ph oxygen nitrate sulfate alkalinity phosphate ammonium fluoride sulfide cal mg sr fe mn and si in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes porewater profiles from the eastern upwelling areas of the south atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation whereas organic matter degradation by sulfate reduction is restricted to the near surface sediments further a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m far below the zone of bioturbation or bioirrigation because other sedimentological reasons seem to fail as explanations an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed porewater profiles from the sediments of the amazon fan area are mainly influenced by reactions with fe iii phases the remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments in contrast to the upwelling sediments the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5 3 m probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals a comparison of organic matter degradation rates from the different areas of the south atlantic show the expected relationship to primary productivity oxygen is the dominating oxidant whereas organic matter degradation by nitrate mn iv and probably also fe iii reduction is several orders of magnitude lower sulfate reduction is quantitatively of similar importance as oxygen respiration in the organic rich sediments but may also include methane oxidation reoxidation of ammonium and mn2 by oxygen or nitrate do not alter significantly the estimation of organic matter degradation in the oxic zone but may contribute to the nitrate reduction in suboxic layers

modeling the pathways and ages of inflowing salt and freshwater in the baltic sea abstract a three dimensional eddy permitting ocean circulation model with implemented bottom boundary layer model and flux corrected transport scheme is used to calculate the pathways and ages of various water masses in the baltic sea the agreement between simulated and observed temperature and salinity profiles of the period 1980 2004 is satisfactory especially the renewal of the deep water in the baltic proper by gravity driven dense bottom flows is better simulated than in previous versions of the model based upon these model results details of the mean circulation are analyzed for instance it is found that after the major baltic inflow in january 2003 saline water passing the slupsk furrow flows directly towards northeast along the eastern slope of the hoburg channel however after the baroclinic summer inflow in august september 2002 the deep water flow spreads along the southwestern slope of the gdansk basin further the model results show that the patterns of mean vertical advective fluxes across the halocline that close the large scale vertical circulation are rather patchy mainly within distinct areas are particles of the saline inflow water advected vertically from the deep water into the surface layer to analyze the time scales of the circulation mean ages of various water masses are calculated it is found that at the sea surface of the bornholm basin gotland basin bothnian sea and bothnian bay the mean ages associated to inflowing water from kattegat amount to 26 30 28 34 34 38 and 38 42 years respectively largest mean sea surface ages of more than 30 years associated to the freshwater of the rivers are found in the central gotland basin and belt sea at the bottom the mean ages are largest in the western gotland basin and amount to more than 36 years in the baltic proper vertical gradients of ages associated to the freshwater inflow are smaller than in the case of inflowing saltwater from kattegat indicating an efficient recirculation of freshwater in the baltic sea

factors controlling long term phosphorus efflux from lake sediments exploratory reactive transport modeling abstract we perform for the first time a global sensitivity analysis on a generic diagenetic reaction transport model rtm to elucidate the effects of environmental thermodynamic and kinetic factors on the magnitudes of phosphorus release fluxes from aquatic sediments under a range of conditions typically found in lake sediments our model includes the processes that describe redox sensitive phosphorus releases the so called classical model and processes by which phosphorus mobilization is affected by porewater sulfate on decadal and longer time scales sediment phosphorus effluxes are primarily determined by sedimentation flux of reactive organic matter sedimentation flux of iron oxyhydroxides concentrations of dissolved oxygen and sulfate at the sediment water interface and the rate at which phosphate is immobilized in reduced sediment we show that the effects of these factors on phosphorus effluxes are interdependent and discuss the mechanisms of such interactions the dominant pathways by which dissolved sulfate increases phosphorus efflux in iron rich hypoxic sediments are discussed in detail in contrast to short term phosphorus releases such as described by the classical model long term phosphorus retention is controlled by phosphorus removal to deep reduced sediment rather than processes at the sediment water interface hence the results of short term laboratory or in situ studies such as sediment incubations experiments cannot be unequivocally extended to long time scales our results provide explanations to the reports that lake restoration measures such as restricting phosphorus inputs to a lake or oxygenating the lake s hypolimneon or both in the long term often fail to decrease sediment phosphorus effluxes the re deposition of sediment substances after their release into the water column the feedback often overlooked in sediment rtms can critically affect the magnitude and dynamics of phosphorus efflux from sediments depending on sediment history the same set of external boundary conditions can generate diagenetic regimes with either high or low phosphorus effluxes bistability

stochastic analysis of simulated vadose zone solute transport in a vertical cross section of heterogeneous soil during nonsteady water flow the problem of transport of a conservative nonreactive solute in a vertical cross section of a hypothetical partially saturated scale heterogeneous soil under transient water flow was analyzed here it was assumed that locally the water flow and the solute transport can be described by the richards equation and by the one component convection dispersion equation respectively the simulated water content and the solute concentration distributions in the vertical cross section of the soil at different elapsed times were quantified in terms of space averages and two point autocorrelation functions the time evolution of the solute plume was quantified in terms of its first two normalized spatial moments from which the time dependence of the longitudinal and the transverse components of the solute velocity vector and the spatial covariance tensor were estimated the results of this study which are relevant to solute transport at the local or the plume scale demonstrated the considerable variability in the solute concentration in space and time due to the complex heterogeneity of the soil hydraulic properties in both the vertical and the horizontal directions consequently the movement of the solute plume was characterized by a compression expansion phenomenon attributed to the decrease in the effective solute velocity through the zones of relatively fine textured soil material it was concluded that existing stochastic vadose zone transport models may be applicable to shallow depths but may fail to describe the actual spread of a solute plume when the transport takes place at relatively large depths mainly because of the neglect of the significant vertical heterogeneity in the soil hydraulic properties

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern hikurangi margin abstract we present geochemical data collected from volcanic ash bearing sediments on the upper slope of the northern hikurangi margin during the rv sonne so247 expedition in 2016 gravity coring and seafloor drilling with the marum mebo200 allowed for collection of sediments down to 105 meters below seafloor mbsf release of dissolved sr2 with isotopic composition enriched in 86sr 87sr 86sr minimum 0 708461 at 83 5 mbsf is indicative of ash alteration this reaction releases other cations in the 30 70 mbsf depth interval as reflected by maxima in pore water ca2 and ba2 concentrations in addition we posit that fe iii in volcanogenic glass serves as an electron acceptor for methane oxidation a reaction that releases fe2 measured in the pore fluids to a maximum concentration of 184 m several lines of evidence support our proposed coupling of ash alteration with fe mediated anaerobic oxidation of methane fe aom beneath the sulfate methane transition smt which lies at 7 mbsf at this site in the 30 70 mbsf interval we observe a concurrent increase in fe2 and a depletion of ch4 with a well defined decrease in 13 c ch4 values indicative of microbial fractionation of carbon the negative excursions in 13 c values of both dic and ch4 are similar to that observed by sulfate driven aom at low so 4 2 concentrations and can only be explained by the microbially mediated carbon isotope equilibration between ch4 and dic mass balance considerations reveal that the iron cycled through the coupled ash alteration and aom reactions is consumed as authigenic fe bearing minerals this iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals as estimated from sequential extraction analyses using a numerical modeling approach we estimate the rate of fe aom to be on the order of 0 4 mol cm 2 yr 1 which accounts for 12 of total ch4 removal in the sediments although not without uncertainties the results presented reveal that fe aom in ash bearing sediments is significantly lower than the sulfate driven ch4 consumption which at this site is 3 0 mol cm 2 yr 1 we highlight that fe iii in ash can potentially serve as an electron acceptor for methane oxidation in sulfate depleted settings this is relevant to our understanding of c fe cycling in the methanic zone that typically underlies the smt and could be important in supporting the deep biosphere

shelf to basin iron shuttling enhances vivianite formation in deep baltic sea sediments coastal hypoxia is a growing and persistent problem largely attributable to enhanced terrestrial nutrient i e nitrogen and phosphorus loading recent studies suggest phosphorus removal through

temporal moment analysis for stochastic advective vertical solute transport in heterogeneous unsaturated soils summary temporal moment analysis of solute transport in unsaturated soils subjected to rainfall events is typically achieved by the numerical solution of the flow field from the richards equation followed by a numerical solution of the advection dispersion equation before computing moments these numerical solutions are computationally very intensive and may not provide the insights that are possible from simpler analytical representations in this study temporal moments of solute transport for unsteady unsaturated flows under rainfall conditions at the soil surface are presented for the first time a local scale model for water movement is derived from a sharp front approximation and is combined with a model for transport of solute particles along the main characteristics of the flow field expressions for travel times from the local scale model are first presented for pre and post ponding conditions these local solutions are upscaled to field scale solute transport by adopting a log normally distributed spatial hydraulic conductivity field semi analytical expressions are developed for temporal moments of travel times these expressions are compared to 1 d monte carlo simulation results and to 3 d numerical results for model corroboration the model is used to investigate the behavior of macroscopic eulerian effective velocities and dispersion at the field scale expressions for asymptotic effective properties show that effective velocity achieves a constant value while effective dispersion increases linearly with depth the roles of pre ponding and post ponding conditions in determining field scale dispersion are described

a model for iron deposition to euxinic black sea sediments sulfur isotope and c s fe elemental data from the lower devonian siegenian emsian hunsruck slate of germany allow the conditions that led to the pyritization of soft bodied fossils to be determined the slates preserving pyritized soft tissues generally contain low concentrations of organic matter 0 3 0 4 percent c and pyrite sulfur 0 0 2 percent s respectively but are unusually rich in total and hcl extractable iron concentrations of iron are significantly lower in samples of the hunsruck slate from areas where fossils lack pyritized soft tissues the fossil pyrite is very enriched in s 34 compared to fine grained disseminated pyrite in the adjacent slates delta fossil sediment 10 to 50 permil suggesting that pyritization of the fossils persisted into later stages of authigenic mineralization pyrite formation in the sediments was limited by the low concentrations of metabolisable organic matter leaving residual sulfate and iron available for continued fossil pyritization in organic rich microenvironments a diffusion with precipitation model indicates that a critical control on the initial preservation of readily metabolisable soft tissue in this way is the presence of high concentrations of sediment iron capable of being solubilized during shallow burial diagenesis in association with low concentrations of metabolisable organic matter in the matrix pore waters rich in dissolved iron allow the sulfide generated by the decay of readily metabolisable soft tissue to be trapped efficiently within the carcass

authigenesis of vivianite as influenced by methane induced sulfidization in cold seep sediments off southwestern taiwan abstract authigenesis of iron rich phosphate nodules occurs in iron rich cold seep sediments md052911 core at yung an ridge offshore southwestern taiwan raman ftir and quantitative x ray energy dispersive spectroscopic analyses indicate that the phosphate mineral is vivianite or baricite and shows fe mg molar ratios spanning from ca 0 6 to 4 0 and a general down core trend of increasing fe mg ratios the formation of vivianite is limited to a depth interval of 13 17 mbsf meters below seafloor and is most prominent at 16 mbsf in association with high dissolved iron concentrations and depleted dissolved sulfide below a peak sulfidization zone enriched in mackinawite and greigite alternate growths of vivianite and iron monosulfides and compositional zoning with mg enriched towards the peripheries of individual nodules occur in the transition from the zone of vivianite mineralization to the sulfidization zone the crystallization of vivianite below the sulfidization front could have been favored by scavenging of downward diffusive dissolved sulfide from pore waters in the sulfidization zone alternate growths and overlapping of the zones of iron monosulfides and vivianite can be attributed to fluctuations of the sulfidization front and methane flux the discovery of vivianite in the yung an ridge sediments implies that authigenic vivianite can be an important sink for phosphorus burial in cold seep sediments that have high reactive iron contents and high sedimentation rates

stochastic analysis of transport in a combined heterogeneous vadose zone groundwater flow system 1 first order analysis was used to investigate the effect of a few characteristics of the vadose zone and the solute source at the soil surface on the expected breakthrough curves btcs of tracer solutes in a combined unsaturated saturated spatially heterogeneous formation with a three dimensional statistically anisotropic structure the analysis is based on a stochastic continuum representation of the stationary and nonstationary eulerian velocity vectors in the unsaturated and saturated domains respectively and a general lagrangian description of the solute mass flux in steady state flow results of the present analysis suggest that the length scales and the flow characteristics of the spatially heterogeneous unsaturated zone that affect the travel time probability density function between the soil surface and the water table also affect the expected solute btc at a control plane located downstream in the groundwater the flow in the unsaturated zone might enhance the early arrival time and the spreading of the expected solute btc in the groundwater especially when the vertical extent of the unsaturated zone is relatively large when the unsaturated zone consists of relatively dry coarse textured stratified soil material and when the horizontal extent of the solute source in the direction of the mean groundwater flow is relatively large the effect of the characteristics of the vadose zone and the solute source at the soil surface on the expected solute btc in the groundwater decreases as the distance to the control plane increases and as the process of the solute breakthrough is more advanced the relatively good agreement between the results of the presentfirst order stochasticanalysiswiththeresultsofdetailed numericalanalysesofflow and transport in a three dimensional heterogeneous combined vadose zone groundwater flow domain suggests that the first order stochastic analyses may be sufficiently reliable to showappropriatetrendswhichmightoccurinrealisticcombinedvadosezone groundwater flow systems citation russo d and a fiori 2009 stochastic analysis of transport in a combined heterogeneous vadose zone groundwater flow system water resour res 45 w03426 doi 10 1029 2008wr007157

optimized sequential extraction for carbonates quantification and δ13c analysis of calcite dolomite and siderite siderite is present in diverse types of rocks and sediments but its quantification is cumbersome when present in relatively low contents a new analytical method for the sequential separation of different carbonate phases is presented the separation quantification and characterization of the carbonates is based on different kinetic reactions during acid digestion in combination with monitoring the solution composition and the concomitant release of co2 trapping the released gasses permits the isotopic characterization 13c of the different phases based on published rate laws an idealized model was built to identify ph and temperature conditions for optimal separation of the various carbonates by taking the size distribution of carbonate particles into consideration results from the theoretical survey were implemented in an extraction scheme which was optimized and evaluated by tests on pure mineral phases and their mixtures further tests on a diverse array of sediment and rock samples validated the specificity and reproducibility of the method

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

iron oxide reduction in methane rich deep baltic sea sediments abstract methane is a powerful greenhouse gas and its emission from marine sediments to the atmosphere is largely controlled by anaerobic oxidation of methane aom traditionally sulfate is considered to be the most important electron acceptor for aom in marine sediments recent evidence suggests however that aom may also be coupled to the reduction of iron fe oxides in the baltic sea the post glacial transition from the ancylus freshwater phase to the littorina brackish marine phase a l transition around 9 7 kyr bp before present resulted in the accumulation of organic rich brackish marine sediments overlying organic poor limnic deposits rich in fe oxides methane produced in the organic rich layer diffuses into the lake sediments thus allowing for the possible coupling between fe oxide reduction and methane oxidation here we combine detailed geochemical analyses of the sediment and pore water retrieved from three sites that were drilled during the iodp baltic sea paleoenvironment expedition 347 with multicomponent diagenetic modeling to study the possible role of fe mediated aom as a mechanism for the apparent fe oxide reduction in the methane bearing lake deposits below the a l transition our results reveal a complex interplay between production oxidation and transport of methane showing that besides organoclastic fe reduction oxidation of downward migrating methane with fe oxides may also explain the elevated concentrations of dissolved ferrous fe in deep baltic sea sediments our findings imply that the transition of a lake toward a marine system could lead to reactivation of deeply buried mostly crystalline fe oxides in organic poor lake deposits through reactions with downward diffusing methane from the overlying organic rich marine sediments based on the geochemical profiles and numerical modeling we propose that a potential coupling between fe oxide reduction and methane oxidation likely affects deep fe cycling and related biogeochemical processes such as burial of phosphorus in systems subject to changes in organic matter loading or bottom water salinity

diagenetic alteration of magnetic signals by anaerobic oxidation of methane related to a change in sedimentation rate geochemical and rock magnetic investigations of sediments from three sites on the continental margin off argentina and uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane aom the western argentine basin represents a suitable sedimentary environment to study nonsteady state processes because it is characterized by highly dynamic depositional conditions mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals as a typical feature of these deposits distinct minima in magnetic susceptibility are observed pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate methane transition smt where hs is generated by the process of aom the released hs reacts with the abundant iron oxyhydr oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate sr which occurred during the pleistocene holocene transition we assume that the strong decrease in mean sr encountered during this glacial interglacial transition induced a fixation of the smt at a specific depth the stagnation has obviously enhanced diagenetic dissolution of iron oxyhydr oxides within a distinct sediment interval this assumption was further substantiated by numerical modeling in which the mean sr was decreased from 100 cm kyr 1 during glacial times to 5 cm kyr 1 in the holocene and the methane flux from below was fixed to a constant value to obtain the observed geochemical and magnetic patterns the smt must remain at a fixed position for 9000 yrs this calculated value closely correlates to the timing of the pleistocene holocene transition the results of the model show additionally that a constant high mean sr would cause a concave up profile of pore water sulfate under steady state conditions copyright 2005 elsevier ltd

iron phosphate in the ediacaran doushantuo formation of south china a previously undocumented marine phosphate sink abstract ediacaran phosphorites capture the dynamics of the ultimate biolimiting nutrient phosphorus during perhaps the most critical transition of earth s climatic and ecological history concomitant with the neoproterozoic oxygenation event was the deposition of the first extensive phosphorites across marine shelves typically interpreted as a basinward shift in the locus of phosphogenesis facilitated by deep ocean oxygenation petrographic and spectroscopic analyses of proximal phosphorites from the ediacaran doushantuo formation near the yangtze gorges area of south china reveal the presence of interlaminated pristine muddy and granular phosphorites that were cemented by early diagenetic iron phosphate an additional previously undocumented seafloor p sink transmitted and reflected light microscopy cathodoluminescence microscopy and back scattered electron scanning electron microscopy were used to reconstruct the paragenesis of phosphorites at the wanjiagou section near zhangcunping hubei province and demonstrate that pristine phosphorite precipitated authigenically as francolite via microbially mediated phosphogenesis as evidenced by preserved microbial laminations along with filamentous and coccoidal microfossils subsequent tidal reworking of pristine hardgrounds and phosphatic mudstones produced minimally coated intraclasts and peloidal phosphatic grains that were cemented by iron phosphate soon after deposition but before compaction raman spectroscopy bulk sample and micro x ray diffractometry indicate the iron phosphate cement is composed of phosphosiderite strengite fe 3po4 2h2o the presence of phosphosiderite can be attributed to either syndepositional oxidation of phosphorites or thermal stabilization of vivianite fe2 3 po4 2 8h2o in both cases the occurrence of phosphosiderite represents the first direct evidence for iron phosphate minerals as a p sink during the ediacaran and suggests phosphogenesis may have partially proceeded in ferruginous porewaters in contrast to the redox independent process of francolite precipitation integration of petrographic and geochemical techniques such as those employed in this study offers the ability to corroborate p speciation analyses and provides an independent determination of p phase partitioning ultimately this approach is paramount in testing hypotheses that suggest ferrous iron phosphate minerals played a regulatory role in global proterozoic oxygenation

geochemistry and mineralogy of rare earth elements in high phosphorus ooidal ironstones a case study of the kamysh burun deposit azov black sea iron province abstract this study is aimed at characterizing the distribution and speciation of the rare earth elements and yttrium ree y in ooidal ironstones from the kamysh burun deposit kerch peninsula with implications for the depositional environments and contributions of different ree y carriers to the ore budget the lower pliocene ooidal ironstone sequence of the so called kerch ores up to 15 m thick occupies an area of 28 km2 the ore sequence lies between miocene lower pliocene shell limestones and upper pliocene pleistocene sandy and clayey sediments and consists of horizontal ooidal ironstone beds composed mainly of goethite and x ray amorphous fe3 oxy hydroxides intercalated with siderite and or rhodochrosite beds iron is a main component in ooidal ironstones 50 03 66 19 wt fe2o3 and 1 61 wt feo as well as in fresh carbonate ores 34 wt feo and 14 70 wt fe2o3 the kerch ores contain up to 4 59 wt p2o5 and show significant positive correlation between p and fe r 0 75 the bulk ore samples and their coarse 1 10 mm fractions are goethite dominated and have similar phase major and trace element and ree compositions the fine la nd ca pr sm the ree content in fresh carbonate ores is below that in paas xav 103 ppm but approaches the latter in oxidized crusts xav 178 ppm the kerch ironstones also contain ree poor early diagenetic fe2 phosphate vivianite ree xav 0 93 ppm and ca fe2 phosphate anapaite ree xav 6 95 ppm with typical seawater ree y distributions the ooidal ironstones show mree enriched patterns with distinct negative y anomalies which reveals fe3 oxy hydroxides as chief carriers of adsorbed ree mainly mree the kerch ironstones accumulated ree progressively due to hysteretic dissolution and precipitation of fe3 oxy hydroxides in oscillating redox conditions the diagenetic source of ree stored in ooidal goethite ironstones was inferred from the paas normalized values cen cen vs nd and cen cen vs yn hon discrimination diagrams in general the ree y budget of the kerch ooidal ironstones mainly formed during early diagenesis and scavenging from pore water with a minor contribution of siliciclastic inputs in the absence of hydrothermalism

chemical variability in mineralized veins observed by chemcam on the lower slopes of mount sharp in gale crater mars chemcam has observed a wide range of diagenetic features along the curiosity rover traverse including pervasive ca sulfate veins observations by multiple instruments on curiosity indicate that these veins are hydrated formed during diagenetic fluid event s in this study we delve into the chemical variability in these ca sulfate bearing veins and have identified two subsets in the murray formation with enrichments in fe and fe mg these chemical trends do not reflect a sampling mixture with the surrounding host rock but likely indicates the presence of authigenic phases formed during the emplacement of these veins based on passive reflectance spectral analysis and correlation with other elements fe 3 oxides and or sulfates are proposed to account for the fe rich observations in the vicinity of the naukluft plateau whereas the fe mg trend is also observed in adjacent dark toned features with elevated mn and p near the old soaker outcrop the specific localization of these observations in the gale stratigraphy implies changing ph and redox conditions in the groundwater at the time of formation of these veins from oxidizing and likely more acidic near the naukluft plateau to more reducing conditions in the upper part of the murray formation

stochastic backscatter for cloud resolving models part i implementation and testing in a dry convective boundary layer abstract in simulations of deep convection with cloud resolving models the turbulence is often rather poorly resolved and the influence of the subfilter scale parameterization used in such circumstances is probably greater than in better resolved simulations therefore a study to investigate the influence of stochastic backscatter was performed and presented in two papers this first paper focuses on a description of the stochastic backscatter model and its effect on a neutral and a dry convective boundary layer the second paper then deals with two cases of deep convection the dry convective boundary layer is typical of the subcloud layer in deep convection and this study allows for influences on this layer to be investigated separately as a simple case of convection it also allows for general effects to be identified the implementation of stochastic backscatter was improved to ensure an appropriate scale of backscatter that is independent of any mesh refinements and always spatially isotropic it ca

the baltic sea tracer release experiment 2 mixing processes 1 deep water mixing processes in the largest basin of the baltic sea gotland basin are investigated here with the help of long term moored instrumentation and turbulence microstructure measurements budgets for heat and salinity reveal a strong temporal variability in the deep water mixing coefficients that is shown to be coupled to the wind forcing down to time scales of individual wind events consistent with the results from a simultaneously conducted tracer release experiment near boundary turbulence was identified as the key processes for basin scale mixing turbulent bottom boundary layers were found to be thick and stable in the flat deep part of the basin where highest dissipation rates were observed and comparatively thin less energetic and highly variable on the slopes due to a permanent tendency for boundary layer restratification in the absence of internal tides strongly damped basin scale topographic waves with periods of a few days a deep rim current and to a smaller extent near inertial waves were identified as the main energy sources for boundary mixing these results are likely to be relevant also for other medium sized stratified basins

the effect of vertical soil heterogeneity on field scale solute flux vertical heterogeneity is incorporated in a stochastic transport model in which the soil is viewed as consisting of an ensemble of essentially vertical independent stream tubes the saturated hydraulic conductivity in each stream tube is defined as the vertical average of the corresponding point random process the statistics of the vertically averaged hydraulic conductivity and the resulting statistics of solute travel time are depth dependent the evolution of the field scale breakthrough curve with depth is analyzed in terms of the first two moments of solute travel time to an arbitrary depth below the soil surface the arrival time of the solute center of mass quantified by the expected travel time grows linearly with depth also for vertically heterogeneous soil the temporal solute spreading around its center quantified by the travel time variance may exhibit a compression expansion that is qualitatively analogous to the solute plume behavior in the studies of butters and jury 1989 russo 1991 and ellsworth and jury 1991 the relative solute spreading quantified by the travel time coefficient of variation decreases with increasing depth

phosphorus recycling and burial in baltic sea sediments with contrasting redox conditions in this study redox dependent phosphorus p recycling and burial at 6 sites in the baltic sea is investigated using a combination of porewater and sediment analyses and sediment age dating pb 21

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

phosphorus burial in sediments of the sulfidic deep black sea key roles for adsorption by calcium carbonate and apatite authigenesis abstract sedimentary burial of the essential nutrient phosphorus p under anoxic and sulfidic conditions is incompletely understood here we use chemical and micro scale spectroscopic methods to characterize sedimentary p burial along a water column redox transect six stations 78 2107 m water depth in the black sea from the shelf with its oxygenated waters to the anoxic and sulfidic deep basin organic p is an important p pool under all redox regimes accounting for up to 60 of p burial we find a general down core increase in the relative importance of organic p especially on the shelf where p bound to iron fe and manganese mn oxyhydr oxides is abundant in the uppermost sediment but rapidly declines in concentration with sediment depth our chemical and spectroscopic data indicate that the carbonate rich sediments unit i 3000 years 0 30 cm depth of the sulfidic deep black sea contain three major p pools calcium phosphate apatite organic p and p that is strongly associated with caco3 and possibly clay surfaces apatite concentrations increase from 5 to 25 of total p in the uppermost centimeters of the deep basin sediments highlighting the importance of apatite formation for long term p burial iron ii associated p ludlamite was detected with x ray absorption spectroscopy but was shown to be a minor p pool 5 indicating that lateral fe p transport from the shelf shuttling likely occurs but does not impact the p burial budget of the deep black sea the caco3 p pool was relatively constant throughout the unit i sediment interval and accounted for up to 55 of total p our results highlight that carbonate bound p can be an important sink for p in caco3 rich sediments of anoxic sulfidic basins and should also be considered as a potential p sink and p source in case of caco3 dissolution when reconstructing past ocean p dynamics from geological records

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

diagenetic changes of magnetic and geochemical signals by anaerobic methane oxidation in sediments of the zambezi deep sea fan sw indian ocean abstract the zambezi deep sea fan the largest of its kind along the east african continental margin is poorly studied to date despite its potential to record marine and terrestrial climate signals in the southwest indian ocean therefore gravity core geob 9309 1 retrieved from 1219 m water depth was investigated for various geophysical magnetic susceptibility porosity colour reflectance and geochemical pore water and sediment geochemistry fe and p speciation properties onboard and onshore data documented a sulphate methane transition smt zone at 450 530 cm sediment depth where the simultaneous consumption of pore water sulphate and methane liberates hydrogen sulphide and bi carbonate into the pore space this leads to characteristic changes in the sediment and pore water chemistry as the reduction of primary fe oxyhydr oxides the precipitation of fe sulphides and the mobilization of fe oxyhydr oxide bound p these chemical processes also lead to a marked decrease in magnetic susceptibility below the smt we find a reduction of porosity possibly due to pore space cementation by authigenic minerals formation of the observed geochemical magnetic and mineralogical patterns requires a fixation of the smt at this distinct sediment depth for a considerable time which we calculated to be 10 000 years assuming steady state conditions following a period of rapid upward migration towards this interval we postulate that the worldwide sea level rise at the last glacial interglacial transition 10 000 years b p most probably caused the fixation of the smt at its present position through drastically reduced sediment delivery to the deep sea fan in addition we report an internal redistribution of p occurring around the smt closely linked to the de coupling of sedimentary fe and p and leaving a characteristic pattern in the solid p record by phosphate re adsorption onto fe oxyhydr oxides above and formation of authigenic p minerals e g vivianite below the smt deep sea fan deposits may potentially act as long term sinks for p

effective hydraulic conductivities of transient unsaturated flow in stratified soils the effective hydraulic conductivities of transient unsaturated flow in stratified soils are evaluated using a three dimensional stochastic approach because of the disparity of the correlation scales in a stratified soil the general stochastic equations are simplified and this allows analytical evaluation and derivation of generic expressions for the effective hydraulic conductivities simple asymptotic expressions valid at particular ranges of the soil property and the mean flow characteristics are also derived several examples illustrating the results using data from two real soils are also presented it was found that the effective hydraulic conductivities show significant hysteresis and are anisotropic with a degree of anisotropy depending on the mean flow conditions wetting or drying such hysteresis and anisotropy are produced by the spatial variability of the hydraulic soil properties rather than hysteresis or anisotropy of the local parameters a physical interpretation of the results is given along with a qualitative comparison with field observations the ramifications of this study need to be further investigated and be considered in field applications such as waste disposal control

dynamics of rotating shallow gravity currents passing through a channel part i observation of transverse structure abstract a detailed dataset describing a quasi stationary bottom gravity current approximately 10 m thick and 10 km wide passing through a channel like constriction in the western baltic sea is presented the data include full depth synoptic and highly resolved transects of stratification and turbulence parameters as well as detailed velocity transects across the gravity current at different down channel locations the velocity data reveal a persistent transverse circulation creating a characteristic wedge shaped density structure in the interface a strong asymmetry was also found in the interior of the gravity current where the evolution of a dynamically significant transverse density gradient to the right of the down channel flow was observed spectral analysis of the near bottom velocities showed a surprisingly strong contribution to the bottom stress from low frequency motions with periods up to 30 min that are possibly related to internal wave effects cross channel transects of shear microst

the impact of ocean deoxygenation on iron release from continental margin sediments in the oceans high nitrate low chlorophyll regions such as the peru humboldt current system and the adjacent eastern equatorial pacific1 primary productivity is limited by the micronutrient iron within the peruvian upwelling area bioavailable iron is released from the reducing continental margin sediments2 the magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones3 4 here we show that measurements of molybdenum uranium and iron concentrations can be used as a proxy for sedimentary iron release and use this proxy to assess iron release from the sea floor beneath the peru upwelling system during the past 140 000 years we observe a coupling between levels of denitrification as indicated by nitrogen isotopes trace metal proxies for oxygenation and sedimentary iron concentrations specifically periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column we attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides we argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present we therefore suggest that future deoxygenation in the peru upwelling area would be unlikely to result in increased iron availability whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply

phosphorus cycling in marine sediments advances and challenges abstract phosphorus p is a critical macronutrient for all living cells as it provides the phosphate ester backbone of nucleic acids plays a crucial role in the transmission of chemical energy by the atp molecule and is also a structural constituent in many cell components while p cycling in the marine water column has been the subject of many studies and reviews many aspects of the sedimentary p cycling remain poorly understood this is mainly due to low p concentrations in sediments and analytical difficulties associated with isolating distinct p forms from sediment samples the aim of this review is to highlight the advances made in our understanding of p cycling in marine sediments as a result of improved instrumentation and novel approaches some of these techniques range from sediment sequential extractions sedex to spectroscopic techniques 31p nmr and innovative isotope tracer experiments stable oxygen ratios in phosphate radioactive p isotopes while our understanding of p cycling has considerably improved numerous aspects of sedimentary p cycling including the fate of organic p in sediments as a function of redox conditions organic matter content and burial depth as well as turnover rates of different sedimentary p compounds remain poorly constrained the techniques presented in this review along with yet to be utilized innovative approaches used in soil and lacustrine sediment p research will play an important role in addressing these important questions and in furthering our understanding of this critical component of the p global biogeochemical cycle

the influence of temporal hydrological randomness on seawater intrusion in coastal aquifers we investigate general effects of temporal hydrological randomness on seawater intrusion in coastal aquifers using a 2d conceptualization and model parameterization of three coastal aquifer zones on the mediterranean sea these three aquifer cases represent quite different examples of hydrogeological conditions and temporal hydrological and groundwater management variability and statistics a general result for all aquifer cases is that the effects of temporal randomness on expected salinity in pumped groundwater are greater for spatially homogeneous than for spatially heterogeneous aquifer representations we quantify also prediction uncertainty around expected groundwater salinity in terms of the salinity standard deviation and coefficient of variation cv in the different aquifer cases in general the salinity cv appears to depend much more on the aquifer depth than on the input temporal fluctuation statistics of each aquifer case aquifer depth may thus be a main indicator for resulting prediction uncertainty in salinity of pumped groundwater due to temporal hydrological randomness

stochastic analysis of transient flow in unsaturated heterogeneous soils a stochastic unsaturated water flow model is developed for heterogeneous soils subject to a transient flow regime equations are developed for a fully three dimensional soil profile and results are presented for an example one dimensional problem the model predicts the mean and covariance of the soil water content darcy s flux and pore water velocity as a function of the boundary flux and saturated hydraulic conductivity statistics the statistics of the pore water velocity can be used to predict solute transport in soils as shown by foussereau et al this issue approximate flow related moment equations are solved analytically in the laplace domain then the analytical results are numerically inverted using a modified fast fourier transform algorithm the model predictions are compared to results obtained from monte carlo simulations for two different boundary flux patterns characteristic of humid climates and two different soil types a fine sand and a sandy loam comparing the approximate solutions of the statistical moments to the outputs of the monte carlo simulations shows 1 the dominance of the boundary flux variability over that of the saturated conductivity on the overall prediction uncertainty particularly at shallow depths and 2 the good performance of the stochastic unsaturated flow model particularly for fine textured soils subject to boundary fluxes with coefficients of variation up to 1 5 as the boundary flux coefficient of variation increases and the soil becomes coarser the model performance deteriorates because the flow system becomes significantly more nonlinear

equivalent vadose zone steady state flow an assessment of its capability to predict transport in a realistic combined vadose zone groundwater flow system 1 the applicability of an equivalent steady state vadose zone flow model to a realistic transient three dimensional heterogeneous combined vadose zone groundwater flow system was tested here two cases pertinent to semiarid regions and the presence or absence of an irrigated crop were analyzed and are presented in detail using the hydraulic properties from the bet dagan trench in addition the case of a more humid region characterized by additional summer precipitation and soils of different textures was analyzed and is discussed briefly results of the analyses suggested that when the water table is located at sufficiently large distance from the soil surface the vadose zone can be divided conceptually into two distinct zones a highly transient near surface zone and a deeper quasi steady state zone under these conditions an equivalent steady state influx obtained by averaging the cumulative flux of the net applied water over the relevant time period may provide a relatively good approximation of the cumulative water flux that crossed the water table as for solute transport in all cases examined the trajectories of the centroid of the solute plume and the mean and the standard deviation of the solute breakthrough curves at a given horizontal control plane cp expressed as functions of the cumulative flux crossing the pertinent horizontal cp associated with the transient flows were in relatively good agreement with their counterparts associated with the equivalent steady state flows particularly under noncropped conditions and when the soil texture is coarser the main finding of this study is that for the case in which the water table is located at sufficiently large distance from the soil surface equivalent steady state vadose zone flow may reconstruct the true solute btc or the solute travel time pdf at a horizontal cp located in the vicinity of the water table depth the latter finding applies to heterogeneous soils of different textures and to different atmospheric forcing conditions at the soil surface and in the presence or absence of vegetation and despite the fact that features of the transport unique to vadose zone transient flow induced by the temporal fluctuations in the water table depth cannot be reproduced by the equivalent steady state vadose zone flow

first order and numerical analyses of flow and transport in heterogeneous bimodal variably saturated formations 1 addressed here are bimodal heterogeneous variably saturated formations viewed as mixtures of two populations background soil and embedded soil of differing spatial structures two distinct cases are considered in the first case the texture of the embedded soil is finer than that of the background soil in the second case the reverse is true first order lagrangian stochastic analysis of vadose zone transport was used to investigate the combined effect of the texture of the embedded soil and the mean pressure head on solute spread and breakthrough in these formations the main results of the first order analysis suggest that features of solute transport associated with the two different formations exhibit a crossover behavior and that the mean pressure head associated with the crossover may be estimated from the asymptotic macrodispersivities associated with the two formations the applicability of the results of the first order analysis to more realistic conditions was tested with a series of detailed numerical simulations of the flow and transport in three dimensional heterogeneous bimodal variably saturated formations relatively simple steady state flow and more complicated transient nonmonotone flow originating from periodic influx and water uptake by plant roots were considered for the steady state flows results of the simulations were in qualitative agreement with the results of the first order analysis for the more realistic flow regime the results of the simulations suggested that the difference between the responses of the two different bimodal formations might decrease substantially similar to the situation in steady state flow associated with mean pressure head at which a crossover occurs

phosphorus diagenesis in deep sea sediments sensitivity to water column conditions and global scale implications abstract the geological record bears evidence of various periods of wide scale oceanic anoxia that are associated with perturbations of the marine carbon and phosphorus p cycles in this study we examine the impact of changes in bottom water oxygen and organic matter om input on burial of p in deep sea sediments using a reactive transport model results show that the burial of key reactive p phases namely authigenic calcium associated p minerals ca p organic p org p and iron bound p fe p responds non linearly to both water column forcings namely water column oxygenation and om loading high organic matter om flux with either very low or high oxygen 180 m favor the formation of authigenic ca p while low oxygen and intermediate to high om fluxes promote org p burial iron bound p is only preserved in the sediment when oxygen levels are high and om fluxes low the conditions for maximum p recycling or minimum p burial are low bottom water oxygen concentrations and low om fluxes to the sediment water interface hypoxic oligotrophic deep sea settings the bivariate dependence of p burial on oxygen and om flux was implemented in an existing box model of the global marine p oxygen and organic carbon cycles replacing simple empirical redox functions for p burial the response of the original and new box model to decreased ocean mixing was then assessed in the context of a long term response in the new model org p instead of authigenic ca p is the dominant burial phase of p in deep sea environments during periods of oceanic anoxia nevertheless reduced ocean mixing leads to a similar response in total p burial and as a consequence to a similar increase in deep water anoxia and decrease in open ocean productivity whether an empirical or mechanistic description of phosphorus diagenesis is considered

millennial scale decline in coho salmon abundance since the middle holocene in a coastal oregon watershed usa the population size of anadromous salmon in the pacific northwest is strongly influenced by decadal variation in watershed and oceanographic conditions and therefore should also be influenced by larger magnitude millennial scale variations in these conditions we studied 15 n of bulk organic matter in lake sediment from woahink lake oregon as a proxy of marine derived nutrients mdn from spawning coho salmon we compared this site to a control lake with a natural barrier to salmon migration from 7 5 to 5 4 ka a dune was emplaced breached and emplaced again forming woahink lake in a former estuary 15 n decreased steadily since 5 4 ka at woahink but not at the control lake 15 n reached a minimum just prior to anthropogenic nutrient loading which caused an increase in 15 n thus precluding a comparison with the historical decline in salmon abundance a mixing model of lake water nitrate developed to explore alternate scenarios for the observed range of 15 n could not explain these results without invoking mdn input from at least several hundred salmon annually our results show a previously unreported pattern of a millennial scale decline in salmon that has plausible linkages to parallel changes in ocean circulation and productivity

effects of progressive oxygen depletion on sediment diagenesis and fluxes a model for the lower st lawrence river estuary we applied a diagenetic model to examine the effects of a decadal timescale progressive decrease in bottomwater oxygen concentration on sediment geochemistry and fluxes across the sediment water interface the model was calibrated using geochemical data acquired over the last 30 yr in the lower st lawrence river estuary canada where the bottom water oxygen concentration has been decreasing at an average rate of 1 mmol l21 yr21 over the past 70 yr benthic fluxes calculated from the model are comparable to fluxes derived from shipboard sediment incubations by propagating the model forward in time and allowing the oxygen concentration to decrease further at 1 mmol l21 yr21 we predict changes in the distributions and fluxes of iron manganese phosphorus nitrogen and sulfur as the oxygen concentration decreases the concentrations and distributions of reactive phases in the sediment change at an accelerating pace fluxes of reduced substances out of the sediment increase reactive iron and manganese oxide phases become depleted and the sediment becomes progressively enriched in iron sulfides a notable exception is the efflux of phosphate which remains invariant at the study site these changes are likely to become measurable within the next 20 yr model results are sensitive to the effects of decreasing oxygen concentrations on the benthos the response of which we represent by two different approximations of the bioturbation and bioirrigation formulations a gradual decrease and a thresholdtype decrease the principal obstacle to reliable predictions of how sediments will respond is the lack of knowledge about the response of bioturbation and bioirrigation to decreasing oxygen in bottom waters

pyrite oxidation during sample storage determines phosphorus fractionation in carbonate poor anoxic sediments abstract we investigated the phosphorus p and iron fe fractionation in four cores with anoxic sediments deposited during the mid cretaceous oceanic anoxic event 2 94 ma and the paleocene eocene thermal maximum 55 ma that were exposed to oxygen after core recovery surprisingly p associated with iron oxyhydroxides fe bound p was a major p phase in these laminated sediments deposited under euxinic conditions a significant fraction of total fe was present as poorly crystalline ferric fe this fraction increased with increasing storage time of the investigated cores in carbonate poor samples fe bound p accounted for up to 99 of total p and its abundance correlated with pyrite contents in samples with higher caco3 contents 5 wt in the investigated samples p was mostly present in authigenic ca p minerals irrespective of pyrite contents we conclude that the p fractionation in anoxic carbonate poor sediments is strongly affected by pyrite oxidation that occurs when these sediments are exposed to oxygen pyrite oxidation produces sulfuric acid and iron oxyhydroxides the abundance of poorly crystalline fe oxyhydroxides provides further evidence that these were indeed formed through recent post recovery oxidation rather than in situ tens of millions of years ago the acid dissolves apatite and the released phosphate is subsequently bound in the freshly formed iron oxyhydroxides pyrite oxidation thus leads to a conversion of authigenic ca p to fe bound p in more calcareous samples caco3 can act as an effective buffer against acidic dissolution of ca p minerals the results indicate that shielding of sediments from atmospheric oxygen is vital to preserve the in situ p fractionation and to enable a valid reconstruction of marine phosphorus cycling based on sediment records

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

vivianite is a major sink for phosphorus in methanogenic coastal surface sediments abstract studies of authigenic phosphorus p minerals in marine sediments typically focus on authigenic carbonate fluorapatite which is considered to be the major sink for p in marine sediments and can easily be semi quantitatively extracted with the sedex sequential extraction method the role of other potentially important authigenic p phases such as the reduced iron fe phosphate mineral vivianite fe ii 3 po4 8h2o has so far largely been ignored in marine systems this is in part likely due to the fact that the sedex method does not distinguish between vivianite and p associated with fe oxides here we show that vivianite can be quantified in marine sediments by combining the sedex method with microscopic and spectroscopic techniques such as micro x ray fluorescence xrf elemental mapping of resin embedded sediments as well as scanning electron microscope energy dispersive spectroscopy sem eds and powder x ray diffraction xrd we further demonstrate that resin embedding of vertically intact sediment sub cores enables the use of synchrotron based microanalysis x ray absorption near edge structure xanes spectroscopy to differentiate between different p burial phases in aquatic sediments our results reveal that vivianite represents a major burial sink for p below a shallow sulfate methane transition zone in bothnian sea sediments accounting for 40 50 of total p burial we further show that anaerobic oxidation of methane aom drives a sink switching from fe oxide bound p to vivianite by driving the release of both phosphate aom with sulfate and fe oxides and ferrous fe aom with fe oxides to the pore water allowing supersaturation with respect to vivianite to be reached the vivianite in the sediment contains significant amounts of manganese 4 8 wt similar to vivianite obtained from freshwater sediments our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments we suggest that vivianite may act as an important burial sink for p in brackish coastal environments worldwide

stochastic analysis of unsaturated flow in heterogeneous soils 3 observations and applications results of stochastic theory for flow in heterogeneous soils are analyzed by comparisons with laboratory experiments and field observations and through applications examples the two key theoretical results are 1 the variability of capillary pressure or moisture content increases when mean capillary pressure increases and 2 the anisotropy ratio horizontal vertical of effective mean unsaturated hydraulic conductivity increases when mean capillary pressure increases or mean moisture content decreases comparisons with the field data on moisture content and capillary pressure variability show trends similar to those predicted by the theory calculations of hydraulic conductivity anisotropy based on two actual soils show that the variations in soil texture produce large changes in anisotropy as the mean capillary pressure changes several previously reported field observations and laboratory experiments support the theoretical finding of a capillary pressure dependent hydraulic anisotropy for unsaturated flow the importance of this anisotropy effect in applications involving groundwater recharge irrigation surface runoff generation and waste isolation is discussed

a model for the vertial circulation of the baltic deep water abstract the time dependent vertical circulation of the baltic proper is modeled using a horizontally integrated model of high vertical resolution a seasonal pycnocline model computes the properties of the mixed layer below this an advection vertical diffusion model computes the evolution of the salinity and temperature fields a simple model for an entraining dense bottom current which carries the intruding seawater and drives the vertical advection in the basin is developed and used in the derivation of entrainment velocity we it is shown that e we u where u is the speed of the bottom current may be expressed in the well known empirical constants m0 and cd the hypsographic features of the baltic are accounted for in the model the model is forced using realistic meteorological and hydrological time series the inflow of dense seawater to the baltic with large fluctuations in flow rate and salinity is realistically described and constitutes the upstream boundary condition for the bottom current

the occurrence identification and environmental relevance of vivianite in waterlogged soils and aquatic sediments abstract in this article we review the nature occurrence and environmental relevance of the authigenic ferrous iron phosphate mineral vivianite fe 3 po 4 2 8h 2 o in waterlogged soils and aquatic sediments we critically discuss existing work from freshwater and marine systems laboratory studies and microbial batch culture experiments aiming to deduce common characteristics of the mineral s occurrence and the processes governing its formation vivianite regularly occurs in close association with organic remains in iron rich sediments simultaneously it is a biogenic mineral product of metal reducing bacteria these findings suggest that vivianite nucleation in natural systems is directed by the activity of such bacteria and crystal growth is particularly favoured within protected microzones taking into account recent findings from coastal marine sediments where vivianite authigenesis has been shown to be coupled to the anaerobic oxidation of methane small scale microbially mediated reactions appear to be crucial for the formation of vivianite small scale heterogeneity within the sediment matrix may also explain why saturation calculations based upon bulk pore water constitutions often fail to accurately predict the occurrence of the mineral vivianite is not restricted to a specific trophic state of a system the mineral forms in oligotrophic as well as in eutrophic waters however depending on the iron inventory the production supply and degradation of organic matter determine the relative contribution of iron sulphide formation to the iron pool and the concentration of inorganic phosphate and fe 2 in pore waters thus vivianite authigenesis is also governed by bulk chemical conditions such as the rate of sulphide formation relative to that of fe 2 production this situation allows stimulation of vivianite formation by iron supplementation aimed at restoring eutrophic lakes recent results from coastal marine sediments suggest that vivianite authigenesis is of significance for p burial in the marine realm vivianite authigenesis is likely important at the global scale but has so far largely been ignored

establishment of euxinic conditions in the holocene black sea the paleoenvironmental evolution of the black sea is closely linked to the ingression of mediterranean seawater over the bosporus sill after the last glacial maximum we have reconstructed the temporal and spatial development of the black sea suboxic chemocline which divides oxic surface water from anoxic sulfi dic euxinic deep water by combining high resolution geochemical records of bulk parameters carbonate total organic carbon sulfur trace metals cu mo v and an isotopic proxy 56 fe from seven sediment cores in the black sea we generated a single composite geochemical core log that serves as a reference archive for the entire basin our proxy records refl ect the changing depositional and redox conditions of the black sea and permit us to estimate the infl ow budget of mediterranean seawater throughout the holocene our data indicate a gradual rise of the chemocline until ca 5 3 ka when suboxic waters fl ooded the shelf for the fi rst time trace metal and isotopic inventories document one major descent of the chemocline since the onset of brackish marine conditions before the present stable situation was established

phosphorus dynamics around the sulphate methane transition in continental margin sediments authigenic apatite and fe ii phosphates abstract the formation of authigenic phosphate minerals in marine sediments is an important process for the burial and long term storage of the bio essential nutrient phosphorus p in this context we report the composition of pore waters bulk sediments and the speciation of p in four sediment cores recovered on the continental margins off the amazon rio de la plata and zambezi rivers here pronounced sulphate methane transitions smts occur between 4 5 and 6 5 m sediment depth where sulphate is consumed by the anaerobic oxidation of methane and free hydrogen sulphide builds up in the pore waters this leads to the reductive dissolution of primary fe oxyhydr oxides feox by hydrogen sulphide and the subsequent liberation of feox adsorbed phosphate into pore waters at the smt the released phosphate builds up to significant concentrations making it available for the precipitation of authigenic minerals within and below the smt using a sequential p extraction we find consistently high contributions of carbonate fluorapatite cfa to the total p pool within the smt where it likely precipitates due to high local phosphate concentrations high alkalinity and abundant dissolved ca in the pore waters phreeqc calculations confirm these results with highest saturation states with respect to authigenic apatite calculated at all smts cfa authigenesis however is insufficient to completely consume pore water phosphate leading to diffusive loss of phosphate from the smt while the upward decrease in phosphate above the smt is relatively gentle the significantly steeper phosphate gradient into underlying sediments suggests the formation of another authigenic mineral phase sequential p extraction and phreeqc results clearly show that the dominant authigenic phase below the smt is not cfa instead geochemical conditions below the sulphidic zone at all four sites are favourable for the precipitation of fe ii phosphate minerals e g vivianite these conditions are summarized as the absence of sulphate and free hydrogen sulphide but the presence of fe 2 and phosphate in pore waters and low calcium carbonate contents in the sediment while we did not directly detect or quantify fe ii phosphate minerals fe bound p clearly increases in the sediments below the sulphidic zones at all studied sites and this is where highest pore water saturation states with respect to vivianite are calculated with phreeqc in addition geochemical inverse models performed in phreeqc show that vivianite formation is an important geochemical process controlling the observed patterns of dissolved p and fe ph and redox potential of the pore waters analysed below the smt we therefore argue that fe ii phosphate minerals are formed in these ocean margin sediments on a large scale and pore water and sediment data indicate that this fe bound p largely originates from feox adsorbed phosphate liberated within the sulphidic smt this study suggests that under specific but not unusual depositional conditions smts are hotspots for biogeochemical p cycling in marginal marine sediments worldwide with cfa precipitating within the smt and fe ii phosphates forming below it it also adds to the growing evidence that fe ii phosphates may contribute significantly to the long term burial of reactive p phases in fe rich methanic marine sediments and thus act as a previously underestimated sedimentary p sink

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity

why the phosphorus retention of lakes does not necessarily depend on the oxygen supply to their sediment surface in order to improve the trophic state of lake sempach a eutrophied lake in central switzerland its external phosphorus p load has been decreased and its hypolimnion has been artificially oxygenated to lower the lake internal p recycling based on more than 15 yr of experience we conclude that the reduction of the external p load resulted in a corresponding decrease of the lake s p concentration however contrary to initial expectations increased hypolimnetic dissolved oxygen concentrations neither 1 reduced the p release from sediments during summer nor 2 resulted in an increased permanent p retention these observations warrant a reevaluation of the well accepted management strategy of decreasing the lake internal p cycling by maintaining an aerobic hypolimnion and sediment surface we hypothesize that oxygenation only results in an increased permanent benthic p burial if because of the depressed sulfide production more ferrous phosphate e g vivianite and less fes is deposited in the anoxic sediment hence it is not the oxic sediment surface that directly affects the permanent redox dependent sediment p retention but the molar ratio of the available reactive fe ii s 2 po 4 in the anoxic sediment this ratio is driven by the settling rate and the nature of organic matter and particulate iron as well as the supply of oxygen nitrate and sulfate to the sediment