the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

rare earth patterns with positive cerium anomaly in alkaline waters from lake van turkey abstract the distribution of rare earth elements has been studied for aerobic alkaline ph 9 6 carbonate rich waters from lake van turkey shale normalized ree ree sn patterns display an almost linear increase from the light to the heavy rees and strong positive ce sn anomalies there exist neither positive nor negative gd sn anomalies the ree sn patterns are consistent with domination of ree speciation in solution by poly carbonato complexes generating enrichment of the heavy rees that is even more pronounced than that seen in seawater this is the first report of positive ce sn anomalies observed in ree sn patterns of aerobic natural waters these anomalies apparently result from stabilization of penta carbonato ce iv complexes in solution leading to enhanced abundances of ce in comparison with its trivalent ree neighbours thus in remarkable contrast to seawater positive ce sn anomalies may be general features of alkaline carbonate rich and aerobic lake waters

oxidative mobilization of cerium and uranium and enhanced release of immobile high field strength elements from igneous rocks in the presence of the biogenic siderophore desferrioxamine b abstract polyvalent trace elements such as the high field strength elements hfse are commonly considered rather immobile during low temperature water rock interaction hence they have become diagnostic tools that are widely applied in geochemical studies we present results of batch leaching experiments focused on the mobilization of certain hfse y zr hf th u and rare earth elements from mafic intermediate and felsic igneous rocks in the presence and absence respectively of the siderophore desferrioxamine b dfob our data show that dfob strongly enhances the mobility of these trace elements during low temperature water rock interaction the presence of dfob produces two distinct features in the rare earths and yttrium rey patterns of leaching solutions regardless of the mineralogical and chemical composition or the texture of the rock type studied bulk rock normalized rey patterns of leaching solutions with dfob show i a very distinct positive ce anomaly and ii depletion of la and other light rey relative to the middle rey with a concave downward pattern between la and sm these features are not observed in experiments with hydrochloric acid acetic acid or deionized water in dfob bearing leaching solutions ce and u are decoupled from and selectively enriched relative to light rey and th respectively due to oxidation to ce iv and u vi oxidation of ce3 and u4 is promoted by the significantly higher stability of the ce iv and u vi dfob complexes as compared to the ce iii and u iv dfob complexes this is similar to the relationship between the ce iv and ce iii pentacarbonate complexes that cause positive ce anomalies in alkaline lakes however while formation of ce iv carbonate complexes is confined to alkaline environments ce iv dfob complexes may produce positive ce anomalies even in mildly acidic and near neutral natural waters siderophore promoted dissolution processes also significantly enhance mobility of other immobile hfse and may not only cause or modify ce anomalies and th u fractionation but also mobilization of and fractionation between zr hf th and redox insensitive rey during weathering pedogenesis diagenesis and incongruent dissolution of particles in seawater and freshwater siderophores may significantly affect the use of hfse as geochemical tools concave downward light rey patterns may be used as a biosignature for water rock interaction in the presence of siderophores enhanced and preferential mobilization of u relative to th in the presence of siderophores may produce th u signals comparable to those indicative of weathering under oxidized conditions which might constrain the use of u concentrations and th u ratios as a paleoredox proxy the enhanced mobilization of zr and especially hf from igneous rocks in the presence of dfob might have implications for the use of the latter as a tracer for the impact of continental weathering on seawater chemistry because siderophore complexes affect the particle reactivity of hf and zr they may prevent effective removal of terrigenous hf and zr during aggregation coagulation of riverine particles in estuaries siderophore promoted solubilization and stabilization might hence be an additional way to transport continental hf and zr to the oceans furthermore siderophore enhanced mobilization may also have implications for the remediation techniques employed to immobilize hfse such as u th and rey at nuclear waste and reprocessing sites and at rey ore processing plants where soils are commonly contaminated with these sometimes radioactive heavy metals

rare earth elements in manganese nodules from the south atlantic ocean as indicators of oceanic bottom water flow abstract the mineralogy and geochemistry of a suite of nine manganese nodules from the south atlantic have been determined the ce la ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the antarctic bottom water as has previously been successfully carried out in the pacific ocean the ce la ratios of the nodules decrease in the sequence lazarev sea weddell sea 10 4 and 9 7 east georgia basin 6 5 and 7 1 argentine basin 5 0 but then increase in the brazil basin 6 2 and angola basin 9 8 and 15 1 a further decrease was observed in the cape basin 7 6 an extremely high ce la ratio of 24 4 had already been determined for nodules sampled north of the nares abyssal plain in the western north atlantic these data reflect the more complicated pattern of bottom water flow in the south atlantic than in the south pacific the penetration of more oxygenated north atlantic deep water into the south atlantic accounts for the higher ce la ratios in the nodules from the angola and brazil basins based on this study the flow path of the antarctic bottom water could only be traced as far north as the argentine basin the unique geochemistry of nodules from the central angola basin high mn fe and ce la ratios high contents of ni cu zn and mo appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules

rare earth elements in conodont apatite seawater or pore water signatures abstract rare earth element ree compositions of lower palaeozoic conodont microfossils from different sites in laurentia are presented and compared to modern pore water ree compositions reported in the literature these data are modelled to account for matrix induced fractionation of rees during uptake by apatite the apatite water partition co efficients k d for adsorption of rees are applied to a range of modern pore water compositions i e pore water n k d the resultant data being similar to palaeozoic conodont apatite compositions similar resemblances to modern pore water ree compositions are shown by palaeofluids derived from conodonts using the inverse relationship in ree adsorption kinetics i e bioapatite k d with rare low concentration samples yielding hree enriched patterns these results clearly show the importance of matrix effects and hence the post mortem physico chemical processes by which elemental uptake occurs in fossil biogenic minerals which are crucial to consider when interpreting geochemical signatures furthermore the similarities between apatite ree compositions of conodonts and those derived from modern pore waters challenge prior hypotheses of seawater ree evolution inferred directly from conodont apatite and question the reliability of conodont apatite as archives of seawater ree chemistry these outcomes likely have broader implications for fossil bioapatites in general given the physico chemical processes occurring within marine sediments and the inherent behaviour of apatite ree systematics

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

mica dominated seismic properties of mid crust beneath west yunnan china and geodynamic implications abstract measurements of crystallographic preferred orientations cpo and calculations of p and s wave velocities v p and v s and anisotropy were conducted on three quartz mica schists and one felsic mylonite which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern tibetan plateau results show that the schists have v p anisotropy av p ranging from 16 4 to 25 5 and maximum v s anisotropy av s max between 21 6 and 37 8 the mylonite has lower av p and av s max but slightly higher foliation anisotropy which are 13 2 18 5 and 3 07 respectively due to the lower content and cpo strength of mica with increasing mica content the deformed rocks tend to form transverse isotropy ti with fast velocities in the foliation plane and slow velocities normal to the foliation however the presence of prismatic minerals e g amphibole and sillimanite forces the overall symmetry to deviate from ti an increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast axis of feldspar aligns parallel to the slow axis of mica and or quartz the effect of quartz on seismic properties of mica bearing rocks is complex depending on its content and prevailing slip system the greatest shear wave splitting and fastest v p both occur for propagation directions within the foliation plane consistent with the fast pms s wave converted from p wave at the moho polarization directions in the west yunnan where mica amphibole bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation the fast pms directions are perpendicular to the approximately e w orienting fast sks s wave traversing the core as p wave directions indicating a decoupling at the moho interface between the crust and mantle beneath the region the seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear waves suffer little splitting

rare earth element composition of precipitation precipitation particles and aerosols we report the rare earth element ree composition of aerosols and precipitation dissolved and particle phases from bermuda lewes delaware and woods hole massachusetts there is large scale fractionation of rees between the continents atmosphere and the oceans the ree compositions of atmospheric samples are highly fractionated relative to 1 each other e g aerosol precipitation pairs 2 the upper crust of the earth and 3 seawater precipitation samples exhibit markedly convex up shale normalized patterns large negative eu anomalies and large and systematic depletions in the heavy ree lu yb er dy aerosols are strongly depleted in the heavy ree which dissolutions experiments show are attributable to the presence of hree enriched refractory minerals we argue that in situ selective dissolution of mineral aerosol particles is responsible for the unusual ree composition of precipitation this has major implications for the interpretation of the biogeochemical cycles of rees in the oceans particularly the partitioning between solution and particle phases residence times and the composition of seawater

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

seawater rare earth element patterns preserved in apatite of pennsylvanian conodonts past workers have used rare earth element patterns recorded in biogenic apatite as proxies for original seawater chemistry to explore the potency of this approach we analyzed pennsylvanian conodonts from limestones gray shales and black shales of the fort scott and pawnee formations desmoinesian and swope and dennis formations missourian in kansas missouri and iowa u s a analysis of individual platform conodonts from seven taxa using laser ablation inductively coupled plasma mass spectrometry la icp ms revealed a consistent enrichment in the middle rare earth elements mree analogous mree enrichment has been observed in authigenic apatite and bulk samples of phosphate rich black shales from the same formations importantly however phosphate depleted shales intimately associated with the p rich intervals are relatively depleted in mree these antithetic patterns argue convincingly for secondary migration from the bulk sediment into the phosphate and the extent of mree enrichment in the conodonts is correlated positively with the total ree content mree enrichment in conodonts does not vary systematically as a function of lithology stratigraphic level conodont genus geographic location or with independent estimates of paleoredox conditions in the bottom waters collectively these results argue for postmortem diagenetic ree uptake resulting in a pronounced and progressive mree enrichment any cerium anomalies if initially present were masked by diagenetic uptake of ree paleoenvironmental interpretations of conodont ree particularly for samples exhibiting mree enrichment should therefore be viewed with caution

mitigation of guided wave contamination in waveform tomography of marine seismic reflection data from southwestern alaska abstractwe have applied 2d frequency domain acoustic waveform tomography to two different sections of a marine seismic reflection line from southwest alaska one section with a deep igneous basement overlain by a thick pile of sediments and the other section with a shallow basement and a thin sedimentary cover we have evaluated the appearance of dispersive guided waves on both sections and we have determined that with appropriate data preconditioning it is possible to invert the data using 2d acoustic waveform tomography where the basement is deep we first reduced the dispersive wave contamination of the seismic field data by trace editing band pass filtering and careful choice of the data window for inversion we then tested different objective functions and inversion scheduling before selecting an approach based on the logarithmic phase which could be followed by joint phase and amplitude inversion where the basement is shallow the starting model itself which was generated by ray based first a

diffusive transfer of oxygen from seamount basaltic crust into overlying sediments an example from the clarion clipperton fracture zone highlights geochemical evidence confirms exchange between sediments and the basaltic crust fluids o2 exchange between the sediment and the basaltic crust produces a fully oxic sediment column transport reaction modeling was performed to quantify the exchange of o2 and nutrients abstract the clarion clipperton fracture zone ccfz in the pacific ocean is characterized by organic carbon starved sediments and meter scale oxygen penetration into the sediment furthermore numerous seamounts occur throughout its deep sea plain which may serve as conduits for low temperature hydrothermal seawater circulation through the oceanic crust recent studies in deep sea environments of the pacific and atlantic oceans have suggested and presented evidence of dissolved constituent exchange between the seawater flowing in the basaltic crust and the pore water of the overlying sediments through high resolution pore water oxygen and nutrient measurements we examined fluxes and geochemical interactions between the seamount basaltic basement and pore waters of the overlying sediments at three sites located on a radial transect from the foot of teddy bare a small seamount in the ccfz at three sites located 1000 700 and 400 m away from the foot of the seamount we found that oxygen concentrations initially decrease with sediment depth but start to increase at depths of 3 and 7 m toward the basaltic basement nitrate view the mathml sourceno3 concentrations mirror the oxygen concentration profiles as they increase with sediment depth but decrease towards the basement these profiles suggest an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments and a downward diffusion of view the mathml sourceno32 from sediment pore water into the basaltic crust at one site we determined that the 87sr 86sr ratios of the bottom water and of the deep sediment near the basaltic crust are similar further supporting diffusive exchange between basaltic crust fluids and sediment pore water transport reaction modeling performed at two of the study sites revealed that 1 the diffusive flux of oxygen from the basaltic basement outpaces the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and 2 the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders of magnitude lower rates than between the upper sediment and the overlying bottom water these results further show that the diffusion of oxygen from the seamount basaltic basement into the overlying pore waters affects the preservation of organic compounds and helps to maintain a completely oxygenated sedimentary column at all 3 sites near the seamount

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

crustal age between the clipperton and clarion fracture zones magnetic anomalies of 52 80 ma age have been mapped in the equatorial pacific in a region where they were previously unrecognized these anomalies now at 7 n are best modeled with crustal rocks of negative inclination apparently because the crust was formed at a spreading ridge that was south of the magnetic equator in late cretaceous early tertiary time magnetic anomalies recorded along a 5900 km trackline that follows a flowline of crustal generation show one long period from 12 to 31 ma of apparent constant half spreading rate over the 0 to 80 ma represented

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

geochemical evolution of the central pacific ocean over the past 56 myr 1 we measured the elemental concentrations of 69 sediment samples collected at ocean drilling program site 1215 and employed a suite of statistical methods and elemental ratios to quantify the lithogenic biogenic and authigenic hydrogenous hydrothermal ahh components we show that the changes in their abundance record 1 northwestward migration of the pacific plate 2 changes in climatic and oceanographic processes associated with the transition from the eocene greenhouse into the oligocene icehouse and 3 changes in pacific spreading rates and plate reorganization the distributions of three separate lithogenic end members depend on the latitudinal positioning of the site underneath the different wind belts locations north of 22 n received material from asia which was transported to the central pacific via the westerlies locations between 20 and 22 n display a silicic volcanic composition and may reflect the boundary between westerlies and northeast trade winds locations south of 20 n are geochemically e g cr ta sc th etc distinct from locations north of 22 n and suggest a north american origin rb sc significantly increases from values of 2 8 g g 1 at 20 22 ma to 5 7 g g 1 in the modern recording the development of the east asian monsoon and formation of asian loess during the early to mid eocene 53 54 ma when site 1215 was located at 11 13 n and was above the carbonate compensation depth export production increased by 40 55 and was 25 greater than the modern value at 9 n the ahh component dominated from late eocene to the late miocene and during the late eocene may have been driven by elevated hydrothermal activity during increased seafloor spreading

calcium phosphate control of rey patterns of siliceous ooze rich deep sea sediments from the central equatorial pacific abstract rare earth elements and yttrium rey are often used as proxies for paleo environmental conditions and for the reconstruction of element sources and transport pathways many geological systems are well described with respect to the behavior of rey but deep sea sediments with their manifold processes impacting the sediment during early diagenesis leave some questions about the origin and development of the shale normalized rey reysn patterns unanswered here we report rey data for sediment solid phase and pore water from the upper 10 m of deep sea sediments from the clarion clipperton zone ccz in the central equatorial pacific the solid phase rey profiles show highest concentrations at depth below 5 8 m the reysn patterns show an enrichment in middle rey mrey lasn gdsn between 0 35 and 0 60 gdsn ybsn between 1 19 and 1 47 and either no or negative cesn and ysn anomalies i e chondritic to sub chondritic y ho ratios between 24 7 and 28 7 based on correlation analyses of bulk sediment element concentrations and sequential extractions we suggest that a ca phosphate phase controls the distribution and the patterns of rey in these silty clay pelagic sediments rich in siliceous ooze the mrey enrichment develops at the sediment water interface and intensifies systematically with depth the negative cesn anomaly intensifies with depth possibly because ce is mostly bound to mn and fe oxyhydr oxides therefore ce concentrations remain relatively constant throughout the sediment core while its trivalent rey neighbors are mostly hosted by the ca phosphate phase that continuously incorporates rey from ambient pore waters the non redox sensitive trivalent rey concentrations increase with depth producing or enhancing a negative cesn anomaly through coupled substitution of rey3 and na for ca2 the solid phase reysn pattern is therefore determined by the pore water reysn pattern and not suitable for paleoceanographic interpretation the similarity of the pore water and solid phase reysn patterns suggests however that only minor fractionation occurs during rey incorporation into the ca phosphate crystal structure

ion probe measurement of rare earth elements in biogenic phosphates abstract the rare earth element ree distributions in individual fish teeth and conodonts have been measured by ion probe concentrations and la yb ratios show little variations except in the enamel which suggests that ree uptake from the sedimented biogenic debris takes place at the water sediment interface as an essentially quantitative process without fractionation late diagenetic disturbances remained of marginal importance hence ree in phosphatic debris might reflect the input from the overlying water column

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

the formation of manganese nodules between the clarion and clipperton fracture zones southeast of hawaii abstract three areas in the equatorial north pacific between the clarion and clipperton fracture zones were investigated regarding depositional and diagenetic processes during manganese nodule formation the areas lie on a nw se trending trace of the pacific plate southeast of hawaii the manganese nodule facies shows low nodule abundance and low grade cu ni co nodules in the northwest but high abundance and high grade nodules in the southeast the abundance size structure and composition of the nodules are determined by the nature of the underlying sediment breaks in sedimentation during the oligocene and miocene play a highly significant role in the formation of manganese nodules this was the time when the growth of most nodules began favoured by an abundance of potential nuclei ample supply of organic matter and of skeletal material was important for the diagenetic growth of nodules rich in cu ni and co a large amount of organic matter stimulated bioturbation and hence lifting by benthic organisms which in turn kept the nodules on top of the sediment even during the post hiatus periods the two areas in the southeast were always located in a zone of high biological productivity and hence much organic matter was supplied to the seafloor as a consequence most of the fields containing a great abundance of nodules rich in cu ni and co are found there due to the northwestward motion of the pacific plate the northwestern area has been located at least since the early miocene outside the region with such favourable conditions nodules of low abundance and poor in cu ni and co are dominant in spite of this distinct differentiation into two major or regional nodule facies areas each area within itself is very complex the development of the minor or local nodule facies is determined mainly by the position of the nodules in relation to the calcite compensation depth the post hiatus sediment thickness the degree of reworking the potential for formation of nuclei during hiatus periods and the rate of supply or decomposition of organic matter these factors are in turn strongly controlled by the morphology of the seafloor and the activity of bottom currents

coupled substitutions involving rees and na and si in apatites in alkaline rocks from the ilimaussaq intrusion south greenland and the petrological implications ansrnlcr apatites from the ilimaussaq augite syenite the sodalite foyaite and a qtartz bearing peralkaline pegmatite have been analyzed using an electron microprobe for the major elements plus na si and selected rare earth elements rees in all three rock types the maximum reeto3 content in the apatite exceeds 16 0 wt0 0 apatite from the augite syenite and primary apatite from the sodalite foyaite are characterizedby a low na content that varies independently of the ree content the composition of these apatites approaches 25 molo o of the end member carreq sio4 3 oh f cl lessingite in response to the substitution ree3 sia ca2 ps ree and na enriched apatites from the quartzbearing peralkaline pegmatite are almost si free and rees and na are positively correlated the composition of these apatites approaches 25 molo o of the hypothetical endmember na5ree5 po4 6 oh f ci 2 in response to the substitution na ree3 2ca2 the compositional trend of late crystalllzing apatite from the sodalite foyaite reflects almost equal contributions of the two substitutions the relationship between these substitutions in a given apatite and its associated mineral assemblage indicates that the na component is only present in considerable amounts when apatite crystallizes in a strongly peralkaline environment

diagenetic uptake of rare earth elements by conodont apatite abstract the rare earth element ree composition of bioapatite has long been used as a proxy for ancient seawater chemistry and paleomarine environmental reconstruction based on the assumption of preservation of a hydrogenous seawater derived ree signal recent work however has begun to question the provenance of rees in conodonts emphasizing the importance of rees released by the lithogenous fraction of the sediment and subsequently adsorbed onto conodont apatite in the burial environment here we investigate patterns of ree and trace element abundance in conodonts and their host sediments from the early to late ordovician huanghuachang and chenjiahe sections of hubei province south china several lines of evidence indicate that rees in the conodont samples were acquired mainly from clay minerals in the host sediment during burial diagenesis 1 rees in conodonts show a strong positive correlation to th and other lithogenic elements 2 conodonts and whole rock samples show general patterns of ree and trace element enrichment that are highly similar to each other and bear no resemblance to seawater elemental concentrations 3 similar patterns are observed in triassic conodonts and whole rock samples and 4 y ho ratios in conodonts are mostly 90 of rees from lithogenous sources conodonts show pronounced middle rare earth element mree enrichment a pattern that is unambiguously of diagenetic origin owing to its association with lower y ho ratios with increasing mree enrichment of conodont samples u concentrations and la n yb n ratios shift from high to low and mn concentrations from low to high these patterns suggest that conodont diagenesis was initiated at shallow burial depths under suboxic conditions i e in the zone of mn iv and fe iii reduction but continued at greater burial depths with most acquisition of secondary rees at later diagenetic stages our findings indicate that 1 conodont apatite frequently does not preserve a recognizable hydrogenous ree signal and 2 the results of many earlier studies in which rees in bioapatite were used as a paleoseawater proxy may need re evaluation

paleoceanographic implications of rare earth element variability within a femn crust from the central pacific ocean abstract results of detailed geochemical analyses of thick fe mn oxide crust accumulations from the central pacific ocean lead to the suggestion that variations in their chemical composition and microstructure reflect the influence of prevailing environmental conditions at the time of formation of the deposit these findings imply that well preserved fe mn crusts represent a geologic record that may extend back to the onset of fe mn oxide precipitation on the subsrtate material current crust growth rate estimates of 1 3 mm m y imply that 6 10 cm thick fe mn oxide accumulations represent a growth record of 20 to a maximum of 100 m y detailed chemical and mineralogical analyses were performed on successive hand picked layers of a 95 mm thick fe mn crust recovered from schumann seamount in the hawaiian archipelago the analyses reveal significant variations in the elemental distribution and abundance of major constituents and rees as a function of depth within the crust the trivalent rees generally exhibit sympathetic concentration changes in pure fe mn oxides but the fractionation observed between the light and heavy rees differs in layers enriched in phosphatic matter the compositional variability and the extent of ree fractionation can be explained in large part by mineralogical control but can also be inferred to reflect differing depositional conditions in the seawater from which the deposits formed variations in the ce anomaly and ree fractionation patterns within the individual layers of the crust are related to their major element composition and mineralogy and to the anomalies observed by other workers these are used to attempt to reconstruct the growth history of the crust

geochemistry of the krivoy rog banded iron formation ukraine and the impact of peak episodes of increased global magmatic activity on the trace element composition of precambrian seawater abstract pure superior type banded iron formation bif samples from the krivoy rog supergroup ukraine are excellent archives of ambient early precambrian seawater they show low concentrations of incompatible elements such as zr hf and th and shale normalized rare earths and yttrium rey sn patterns similar to those of modern seawater i e heavy rey sn enriched patterns with positive la sn gd sn and y sn anomalies lack of ce sn and presence of positive eu sn anomalies indicate rey contributions to anoxic ferruginous seawater from high temperature hydrothermal fluids the depositional age of the krivoy rog bif is ill defined but a late archean to paleoproterozoic age has been suggested based on u pb zircon ages for units stratigraphically above and below the bif we determined sm nd isotopic compositions of pure and impure samples from the krivoy rog bif which yield an errorchron with an apparent age of 2406 350 ma mswd 15 that falls within this broad age range all pure bif samples show chondrite normalized subscript cn rey patterns with strong positive eu cn anomalies that are typical for archean but rather rare and much less pronounced in proterozoic bifs associated schists also show archean rather than post archean style rey distributions the rey geochemistry of both chemical and epiclastic sediments therefore is more consistent with a late archean rather than a post archean depositional age of the krivoy rog supergroup initial nd values of impure bifs and of associated schist reveal variable contributions from ttgs less radiogenic in nd and a more radiogenic component possibly comprised of basement amphibolites or mafic volcanics of the stratigraphically underlying new krivoy rog group the purest krivoy rog bif representing local krivoy rog seawater displays an nd 2 60 ga value of 2 3 this value is less radiogenic than impure krivoy rog bifs or other near contemporaneous neoarchean pure chemical sediments to preserve this specific local isotopic fingerprint in anoxic archean seawater the krivoy rog bif must have been deposited in an isolated sea basin with limited exchange with ferruginous deep waters of the open ocean a compilation of rey data for high purity precambrian bifs reveals that eu cn eu cn ratios of precambrian seawater follow a general global evolution curve that shows specific peaks which reflect times of increased high temperature hydrothermal rey input into seawater following declining eu cn eu cn ratios from the eoarchean to the mesoarchean the ratios suddenly rise at 2 7 ga and reach a maximum at 2 6 ga indicating an increased flux of high temperature hydrothermal rey to neoarchean seawater which supports the hypothesis that times of widespread bif deposition coincided with periods of intense submarine hydrothermal activity probably triggered by major mantle plume events this association is supported by a strong increase of the nd t values of pure seawater archives at 2 7 2 6 ga which reflects an increased flux of mantle nd into seawater these results suggest that eu rey systematics and potentially nd systematics are robust tools to indentify episodes of enhanced mantle plume activity

the impact of sedimentary coatings on the diagenetic nd flux because ocean circulation impacts global heat transport understanding the relationship between deep ocean circulation and climate is important for predicting the ocean s role in climate change a common approach to reconstruct ocean circulation patterns employs the neodymium isotope compositions of authigenic phases recovered from marine sediments in this approach mild chemical extractions of these phases is thought to yield information regarding the end of the bottom waters that are in contact with the underlying sediment package however recent pore fluid studies present evidence for neodymium cycling within the upper portions of the marine sediment package that drives a significant benthic flux of neodymium to the ocean this internal sedimentary cycling has the potential to obfuscate any relationship between the neodymium signature recovered from the authigenic coating and the overlying neodymium signature of the seawater for this manuscript we present sedimentary leach results from three sites on the oregon margin in the northeast pacific ocean our goal is to examine the potential mechanisms controlling the exchange of nd between the sedimentary package and the overlying water column as well as the relationship between the end composition of authigenic sedimentary coatings and that of the pore fluid in our comparison of the neodymium concentrations and isotope compositions from the total sediment sediment leachates and pore fluid we find that the leachable components account for about half of the total solid phase nd therefore representing a significant reservoir of reactive nd within the sediment package based on these and other data we propose that sediment diagenesis determines the end of the pore fluid which in turn controls the end of the bottom water consistent with this notion despite having 1 to 2 orders of magnitude greater nd concentration than the bottom water the pore fluid is still 0 001 of the total nd reservoir in the upper sediment column therefore the pore fluid reservoir is too small to maintain a unique signature and instead must be controlled by the larger reservoir of nd in the reactive coatings in addition to achieve mass balance we find it necessary to invoke a cryptic radiogenic end of 10 trace mineral source of neodymium within the upper sediment column at our sites when present this cryptic trace metal results in more radiogenic pore fluid

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

diagenetic uptake of rare earth elements by bioapatite with an example from lower triassic conodonts of south china abstract the distribution patterns of rare earth elements rees are frequently used as proxies for ancient seawater chemistry or paleomarine environmental conditions however recent work has shown that diagenesis can lead to remobilization and inter elemental fractionation of rees and that these effects often occur in conjunction with redox reactions in sediment porewaters here we review existing literature on the diagenetic fluxes of rees in marine sediments and porewaters in order to systematize existing knowledge on this subject rees undergo significant redistribution among sediment phases during both early and late diagenesis as a consequence of adsorption and desorption processes remobilization of rees commonly leads to inter elemental fractionation variously leading to enrichment or depletion of the light middle or heavy ree fractions further ree remobilization can be facilitated by redox changes e g through reductive dissolution of host phases in suboxic and anoxic porewaters characteristic ree distribution patterns develop through these processes 1 a flat distribution signifying predominantly terrigenous siliciclastic influence 2 a middle ree bulge probably due to adsorption of light and heavy rees to mn and fe oxyhydroxides respectively and 3 heavy ree enrichment indicative of hydrogenous seawater influence note all patterns in this paper are normalized to the ree composition of average upper continental crust or ucc in the second part of this study we undertake an analysis of the ree distributions in conodonts and whole rock samples from west pingdingshan a permian triassic boundary section in south china using ree th and y ho ratios we show that almost all of the conodont samples have a strong diagenetic overprint and that the hydrogenous ree fraction is small and not isolatable furthermore the conodonts contain two diagenetic ree components one characterized by low ree 100 300 ppm high ree th ratios 1000 strong middle ree enrichment and eu eu ratios of 1 5 2 0 and the second by high ree 300 2000 ppm low ree th ratios 20 30 little or no middle ree enrichment and eu eu ratios of 1 0 the first component exhibits a pronounced middle ree bulge that represents an early diagenetic signature associated with suboxic conditions possibly related to adsorption of rees onto fe mn oxyhydroxides in the shallow subsurface environment the second component shows a flat ree distribution that is similar to both our whole rock samples and average ucc indicating derivation from rees released from detrital siliciclastics e g clay minerals probably at a range of burial depths from shallow to deep failure of the conodont samples to yield an isolatable hydrogenous component demonstrates that bioapatite does not always preserve a primary marine ree signature given that bioapatite rees have been widely used for this purpose often on the assumption of minimal or no diagenetic influence our findings are likely to necessitate a re evaluation of the results of many earlier studies in general we counsel caution in inferring a hydrogenous origin for rees in bioapatite owing to frequent diagenetic alteration of ree distributions

siderophore promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater river and ocean water abstract the rare earth elements ree are a group of trace elements that have short marine residence times and that in river lake and marine surface waters are typically associated with organic and inorganic particles explosive volcanic eruptions such as the 2010 eruptions of eyjafjallajokull volcano in iceland produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms to become bioavailable however this iron needs to be solubilized by complexing agents such as siderophores a well studied example of such a chelator is the biogenic siderophore desferrioxamin b dfob based on results from incubation experiments with glacial meltwater rich river waters from southern iceland which are rich in suspended volcanic ash and that had been incubated with and without dfob respectively we here show that siderophores not only enhance the release of iron but also promote the mobilization of ree from these particles in the presence of dfob partial dissolution of volcanic ash and presumably other lithic particles produces a flux of dissolved ree into ambient waters that is characterized by depletion of the light ree over the middle ree and by selective enrichment of cerium due to the formation of dissolved ce iv dfob complexes in siderophore rich environments this siderophore bound ree flux has the potential to modify the concentrations and distribution of the dissolved ree and of the isotopic composition of dissolved nd in glacial meltwaters river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater which are assumed to account for the missing nd flux to seawater thermodynamic data further suggest that siderophore promoted element mobilization could also be important for other polyvalent trace elements such as hf

widespread seawater circulation in 18 22 ma oceanic crust impact on heat flow and sediment geochemistry on the basis of heat flow measurements seismic mapping and sediment pore water analysis we demonstrate widespread and efficient ventilation of the 18 22 ma oceanic crust of the northeast equatorial pacific ocean recharge and discharge appear to be associated with basement outcrops including seamounts and north south trending faults along which sediment cover thins out and volcanic rocks are exposed low temperature hydrothermal circulation through the volcanic crust leads to the reduction of heat flow through overlying sediments with measured heat flow values that are well below those expected from conductive cooling curves for lithosphere of this age typically dissolved pore water oxygen decreases from the sediment surface downward reaching minimum values at mid depth and rising again in the lower part of the cores investigated clearly indicating oxygen rich seawater circulation through the oceanic crust underneath the sediments if the residence time of the circulating fluids in the upper crust is short or the fluid flux is large oxic conditions may be preserved and oxygen can diffuse upwards into the sediments this process leading to widespread oxic conditions in the near basement sediments may cause the oxidation of residual reduced material stored in the deeper sediments resulting in downward fluxes of the reaction products into the basement and from there back into the oceans considering the widespread existence of this type of off axis ventilation the net effect of the resulting return flow of reaction products on biogeochemical cycles and element fluxes e g carbon and nitrogen may be very large

hafnium and neodymium isotopes and rey distribution in the truly dissolved nanoparticulate colloidal and suspended loads of rivers in the amazon basin brazil abstract radiogenic isotopes in river sediments and river waters have been widely used in provenance studies as these samples naturally integrate the geology chemistry of the entire catchment while the hf and nd isotope systems are coupled during igneous processes they are decoupled during supergene processes at the earth s surface which is reflected by the isotope composition of riverine sediments we present the first data for both hf and nd isotope compositions of the dissolved 0 2 m filtrates rich in nanoparticles and colloids npcs and the truly dissolved 1 kda ultrafiltrates load of rivers hafnium and nd isotope compositions and concentrations of the rare earths and yttrium rey and hf were determined for suspended particles 0 2 m as well as for the dissolved and the truly dissolved load of the rio solimoes the amazon s largest tributary draining the andes and of the rio negro an organic npc and particle rich river draining the rainforest of northern amazonia we also analyzed the nd isotope compositions of suspended sediments and 0 2 m filtered water samples from the amazon river and its tributaries rio tapajos rio xingu and rio jari our novel results clearly show that the decoupling of the hf and nd isotope systems is related to incongruent weathering processes on the continent as this decoupling can already be observed in the different hf and nd pools i e in the particulate the npc dominated dissolved and the truly dissolved load of rivers in the rio negro and rio solimoes a strong particle size dependent difference in hf isotope composition is observed values of e hf become more radiogenic as filter poresize decreases which can be related to the density and size dependent distribution of hf rich minerals e g zircons and their absence from the truly dissolved pool in contrast the nd isotope composition of amazonian river waters reflects that of their catchment geology tributaries draining the precambrian brazilian and guyana shields show very unradiogenic e nd values of 19 to 25 in their dissolved load whereas the rio solimoes draining the andes yields a more radiogenic e nd signal of only 7 the dissolved nd isotope composition of the amazon is dominated by its andean tributaries and averages at 8 although nd isotope compositions are thought to not being fractionated by earth surface processes significant differences of 1 3 1 9 e units can be observed between the dissolved and suspended loads in the amazon river and its main tributary the rio solimoes in these rivers the dissolved load is more radiogenic than the suspended sediment which is likely due to incongruent weathering and related mineral sorting in the andean headwaters in contrast the organic rich and mineral poor shield rivers do not show a difference between the truly dissolved dissolved and suspended load as the nd in all these pools is controlled by surface and solution complexation and hence isotopically homogenized by continuous exchange and re equilibration

diffusion of rare earth elements in fish teeth from deep sea sediments the distribution of rare earth elements rees in biogenic phosphate phases in sediments such as the remains of fish teeth has been proposed as an indicator of the depositional environment in the water column recording for example palaeo redox conditions1 and isotope geochemical2 5 and hydrothermal6 7 processes enrichment of these phases in rees takes place only during early diagenesis8 9 for which reason the ree signal has often been assumed to represent the unfractionated record of ree distribution in the water column overlying the sediment surface1 4 5 10 here we report on studies of ree zoning in fish teeth from pacific sediments from which we extract a ree diffusion coefficient of 70 mm2 myr 1 this value suggests that diffusion of rees from sea water into the fish teeth before burial is too slow to produce the enrichments observed instead the ree distributions must derive from the surrounding sediment pore fluids the use of these distributions as palaeoceanographic indicators is therefore called into question

a novel chemical method to quantify fish debris in marine sediments burial of fish bones which consist primarily of hydroxyapatite has been recognized as a mechanism to remove reactive phosphorus from the oceans in this study a new method is presented which differentiates p associated with biogenous apatite pfish from other p fractions the method consisting of a sequential chemical extraction with 2 m nh4cl has been successfully tested on standard materials it enables us for the first time to quantify fish debris in sediment records and to assess their importance for the marine phosphorus cycle the nh4cl extraction has been applied to sediment samples from the arabian sea preservation of fish debris is significantly higher in sediments located above 1 200 m water depth than it is for deeper sediments the distribution of pfish contents in surface sediments is predominantly governed by the extent of fish debris regeneration which is related to differences in water depth and sedimentation rates in addition a good correlation between high sedimentary pfish contents and low oxygen bottom water concentrations suggests that the presence of the intense oxygen minimum zone may account for the enhanced preservation of fish debris in continental slope sediments

the impact of transport processes on rare earth element patterns in marine authigenic and biogenic phosphates abstract rare earth elements rees are commonly used proxies to reconstruct water chemistry and oxygen saturation during the formation of authigenic and biogenic phosphates in marine environments in the modern ocean rees exhibit a distinct pattern with enrichment of heavy rees and strong depletion in cerium ce the wide range of ree enrichment patterns found in ancient marine phosphates lead to the proposition that water chemistry has been very different in the earth s past however both early and late diagenesis are known to affect ree signatures in phosphates altering primary marine signals herein we present a dataset of ree signatures in 38 grain specific la icp ms measurements of isolated phosphate and carbonate grains in three discrete rock samples the phosphates mainly consist of authigenic phosphates and phosphatized microfossils that formed in a microbially mediated micro milieu in addition isolated biogenic and reworked phosphatic grains are also present the phosphates are emplaced in bioclastic grain to packstones deposited on a carbonate ramp setting in the central mediterranean sea during the middle miocene monterey event the results reveal markedly different ree patterns normalized to the post archean australian shale standard in terms of total enrichment and pattern shape analyses of ree diagenesis proxies show that diagenetic alteration affected the samples only to a minor degree grain shape and ree patterns together indicate that authigenic biogenic and reworked phosphates have distinct ree patterns irrespective of the sample our study shows that while ree patterns in phosphates do reflect water chemistry during authigenesis they are often already heavily altered during reworking a process which can occur in geologically negligible timespans ree patterns are therefore more likely to reflect complex enrichment processes after their formation similarities in the ree patterns of reworked and biogenic phosphate further suggest that the frequently observed hat shaped pattern in biogenic phosphates can result from increased middle ree neodymium to holmium scavenging during taphonomic processes prior to final deposition cluster analysis coupled with sedimentological and previously published geochemical data bulk carbon isotope and x ray fluorescence spectrometry allowed the characterization of ree patterns of phosphates in terms of their formation conditions and depositional history such as the distinction of phosphates formed in situ from reworked and transported phosphate grains

quantifying manganese and nitrogen cycle coupling in manganese rich organic carbon starved marine sediments examples from the clarion clipperton fracture zone extensive deep sea sedimentary areas are characterized by low organic carbon contents and thus harbor suboxic sedimentary environments where secondary autotrophic redox cycling becomes important for microbial metabolic processes simulation results for three stations in the eastern equatorial pacific with low organic carbon content 20 m concentrations

rare earth element cycling in the pore waters of the bering sea slope iodp exp 323 abstract we studied the diagenetic behavior of rare earth elements rees in a highly productive passive margin setting of the bering sea slope site u1345 was drilled during the integrated ocean drilling program expedition 323 at a water depth of 1008 m currently in the center of an oxygen minimum zone pore water concentrations of fourteen rees were determined down to 140 meters below the seafloor mbsf the ree concentrations were higher in the pore water than the deep seawater indicating that there was significant liberation from the sediments during diagenesis there was a major peak at 10 mbsf that was more pronounced for the heavy ree hree this peak occurred below the sulfate methane transition zone 6 3 mbsf and coincided with high concentrations of dissolved iron and manganese at 2 mbsf there was a minor peak in ree and mn contents below 40 mbsf the ree concentration profiles remained constant the ce anomaly was insignificant and relatively constant paas normalized ce ce 1 1 0 2 throughout the depth profile showing that the ce depleted in seawater was restored in the pore water hree enrichment was observed over the entire 140 m except for the upper 1 m where a middle ree mree bulge was apparent ree release in shallow depths 2 4 mbsf is attributed to the release of light rees lrees and mrees during the organoclastic reduction of mn oxides in anoxic sediments the high hree concentrations observed at 10 mbsf can be attributed to the reduction of fe and mn minerals tied to anaerobic oxidation of methane or less significantly to ferromagnesian silicate mineral weathering the upward diffusion flux across the sediment water interface was between 3 for tm and 290 for ce pmol m 2 y 1

deep sea mud in the pacific ocean as a potential resource for rare earth elements world demand for rare earth elements and the metal yttrium is rapidly increasing an analysis of more than 2 000 seafloor sediment samples suggests that deep sea mud constitutes a highly promising giant resource for these elements

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

high resolution la icp ms mapping of deep sea polymetallic micronodules and its implications on element mobility abstract enrichments of rey rare earth yttrium and other trace metals co and ni in deep sea ferromanganese fe mn micronodules have received increasing attention in both deep sea research and mineral exploration due to the presence of multiple easily crushed and poorly crystallized phases in micronodules the genesis of micronodules and their adsorption of various trace elements are poorly understood to address this gap we examined the spatial distributions of elements in cross sections of micronodules from the western tropical north pacific ocean using high resolution hr la icp ms raster mapping coupled with laser raman and x ray photoelectron spectroscopy xps the ferromanganese micronodules we studied are dominated by fe and mn oxides with minor carbonate minerals such as siderite rhodochrosite and calcite la icp ms maps show that these micronodules consist of a mn rich core and a fe rich rim the fe enriched rim is enriched in as and surrounds a mg mn cu co and ni concreted core laser raman maps show that the micronodule core contains more birnessite an important scavenger of trace metals in deep sea sediments than the rim the birnessite filled core of these micronodules does not have elevated rey indeed birnessite line channels may feed metal rich fluid containing rey to adjacent minerals including well crystallized bio apatite and zeolite as high ce and y levels are spatially correlated with these minerals the observed element profiles and xps observations showing the coexistence of multiple oxidation states of mn 2 3 and 4 fe 2 and 3 and ce 3 4 demonstrate that the fe mn phases of these micronodules are of a diagenetic origin and that they are sites of redox driven metal enrichment in deep sea sediment

sequential leaching of peru basin surface sediment for the assessment of aged and fresh heavy metal associations and mobility abstract sequential leaching experiments were carried out using the upper 25 cm of oxic to suboxic sediment from the peru basin and ferromanganese nodules in order to assess potential mobility and the associations of heavy metals in the mineral phases the general leaching pattern confirmed that in the nodules as well as in the upper dark brown sediment layer significant proportions of heavy metals like mn co ni zn cu and cd are associated with mno2 and would be released under reducing conditions in the underlying mn poor layers mn oxide hosted metals are minor to distinguish the leaching behaviour of aged and fresh sorbents radiotracers were adsorbed on the solids before leaching the dominant role of the mn oxide phase for scavenging dissolved heavy metals was confirmed for the upper sediment layer and the nodules for sorption equilibration times of 5 h and 7 days respectively the sorption process was rapid freshly sorbed metals were leached mostly in the same fractions as those in aged sorbents and little difference was found for sorption times of 5 h and 7 days in contrast in the mn poor sediment layers a significant amount of adsorbed radiotracers was easily remobilised by simple ion exchange especially cs and cd and an ageing effect shift to less easily leachable fractions was observed after 7 days when surface sediment is resuspended into the bottom water the mn oxide rich surface layer and nodule particles represent a much more effective heavy metal scavenger under oxic conditions compared to other mn poor sediment phases however at the same time the mn rich particles are a stronger potential source of toxic heavy metals in a shift to more reducing conditions