analysis of directional wave fields using x band navigation radar the aim of this work is to present an approach to describe complex sea states including the ones consisting of superpositions of swell and wind sea components using a nautical radar in x band as a remote sensing technique in the present article the inversion method to obtain the spectral representation of the wave fields is described the method is applied to analyse data obtained from simulation techniques as well as from measurements obtained during oceanographic campaigns in the bay of biscay and north sea

trace elements in ilmenite a way to discriminate provenance or age in coastal sands trace elements and ti percentage in ilmenite grains magnetically separated from modern and late pleistocene coastal sands of southeastern virginia and northwestern north carolina were used to distinguish different deposits multivariate analysis of ilmenite composition ti mn mg cr v ni and cu from coastal deposits and potential source rivers enabled the identification of dominant source rivers using the trace element content of one mineral instead of heavy mineral suites eliminated most of the hydraulic sorting selective weathering and intrastratal solution problems that often obscure heavy mineral provenance determinations most ilmenite grains lacked exsolution or twinning which are common to ilmenite however there were no significant optical differences between river and coastal deposits and thus weathering effects were considered to be negligible in provenance determinations based on ilmenite composition owing to the dynamic mixing of beach sands during deposition they contained more homogeneous ilmenite trace element values than did river or bay sands late pleistocene and modern beach deposits were compositionally similar but different from associated bay sands bay sands were more similar to different source river deposits than were beach sands despite a similar primary or distal provenance subtle differences in the mixture of proximal sources were revealed between the ilmenite composition of samples from a modern and a late pleistocene beach deposit besides aiding in provenance determination ilmenite trace element content thus might be used for distinguishing beach deposits of different ages and for subsurface correlation of discontinuous segments from a barrier island chain or other similarly well mixed sand deposit

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

a study on the regulation of the concentrations of some trace metals rb sr zn pb cu v cr ni mn and mo in saanich inlet sediments british columbia canada abstract bulk metal concentrations were measured in the sediments of saanich inlet in an attempt to establish the occurrence of trace metal enrichment in the anoxic central basin ba ni v cr zn pb cu and mo were found to be enriched in the anoxic ooze over the possible contributions from lithogenic sources spatial and seasonal variations in the chemical composition of the settling particulates collected with interceptor traps gave further indications of the mode of incorporation of these metals biogenic ba and cr appeared to be associated with opaline silica although alternative explanations are also possible particularly for ba zinc seemed to be added to the sediment essentially in association with planktonic materials while cu required an additional source directly linked to the anoxic environment similarly ni v and mo were added to the anoxic sediments by reactions occurring at the sediment water interface in the nearshore environment studied here these metals particularly ni and mo were not associated to any significant extent with planktonic materials of all the elements analyzed mo showed the largest enrichment in the anoxic sediments of saanich inlet

insights on geochemical cycling of u re and mo from seasonal sampling in boston harbor massachusetts usa this study examined the removal of u mo and re from seawater by sedimentary processes at a shallow water site with near saturation bottom water o2 levels 240 380 mol o2 l very high organic matter oxidation rates annually averaged rate is 880 mol c cm2 y and shallow oxygen penetration depths 4 mm or less throughout the year under these conditions u mo and re were removed rapidly to asymptotic pore water concentrations of 2 2 3 3 nmol kg u 7 13 nmol kg mo and 11 14 pmol kg re the depth order in which the three metals were removed determined by fitting a diffusion reaction model to measured profiles was re u mo model fits also suggest that the mo profiles clearly showed the presence of a near interface layer in which mo was added to pore waters by remineralization of a solid phase the importance of this solid phase source of pore water mo increased from january to october as the organic matter oxidation rate increased bottom water o2 decreased and the o2 penetration depth decreased experiments with in situ benthic flux chambers generally showed fluxes of u and mo into the sediments however when the overlying water o2 concentration in the chambers was allowed to drop to very low levels mn and fe were released to the overlying water along with the simultaneous release of mo and u these experiments suggest that remineralization of mn and or fe oxides may be a source of mo and perhaps u to pore waters and may complicate the accumulation of u and mo in bioturbated sediments with high organic matter oxidation rates and shallow o2 penetration depths benthic chamber experiments including the nonreactive solute tracer br indicated that sediment irrigation was very important to solute exchange at the study site the enhancement of sediment seawater exchange due to irrigation was determined for the nonreactive tracer br tco2 nh4 u and mo the comparisons between these solutes showed that reactions within and around the burrows were very important for modulating the mo flux but less important for u the effect of these reactions on mo exchange was highly variable enhancing mo and to a lesser extent u uptake at times of relatively modest irrigation but inhibiting exchange when irrigation rates were faster these results reinforce the observation that mo can be released to and removed from pore waters via sedimentary reactions the removal rate of u and mo from seawater by sedimentary reactions was found to agree with the rate of accumulation of authigenic u and mo in the solid phase the fluxes of u and mo determined by in situ benthic flux chamber measurements were the largest that have been measured to date these results confirm that removal of redox sensitive metals from continental margin sediments underlying oxic bottom water is important and suggest that continental margin sediments play a key role in the marine budgets of these metals

mobility of mo u as and sb within modern turbidites modern turbidites uranium molybdenum arsenic antimony we present and discuss porewaters and sediment data of mn fe mo u as and sb within four recent turbidites from the capbreton canyon sw france the deposition of turbidites on continental margins exerts strong influence on the fate of trace metals causing trace metal migration and or immobilization the down core distribution of the elements here depends entirely of ongoing diagenetic processes rather than the diffusion of o2 the persistence of fe mn oxides under anoxic conditions led to anoxic reoxidation of numerous species as nh4 reduced s compounds and trace metals metal oxides thus control the immobilization of mo and as in the solid phase and the remobilization of u and sb to the porewaters although the low sulphide production prevents anoxic authigenesis of mo and as reducing conditions below each horizon rich in mn fe oxides resulted in u and sb accumulation the exact mechanisms of sb immobilization are not known but it is most certainly different from that of as the profile shapes of mn and u were used to estimate the age of the turbidite deposits which cannot be determined by conventional radionuclide methods our interpretations however depend on calculations of diffusion coefficient particularly for u a simple diffusive model applied to mn suggested that the age of the latest deposit noted t1 was 22 months this date is close to the time elapsed between the core sampling and the last known turbiditic event in the capbreton canyon i e martin storm 18 months using the u data set and depending on diffusion coefficients used the estimated ages of the deeper layers were 4 7 yr for t2 and 7 5 14 yr for t3 the reliability and precision of this new approach to date sediments at short timescales is limited by the ignorance of a precise value for u diffusion coefficient reducing uncertainty on u diffusion coefficient will greatly support application of the proposed approach

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

a study on the spectral models for waves in finite water depth spectral models for waves in finite water depths are developed based on an extension of the wallops spectrum huang et al 1981a for the deep water waves it is found that for intermediate water depth stokes wave expansions offer a good approximation in this case the spectral function is controlled by three parameters the significant slope the nondimensional depth kh and the peak frequency n0 for the shallow water waves solitary and cnoidal wave models have to be used the controlling parameters now reduce to two again that is the ursell number ur 2 kh 3 and the peak frequency the resulting spectral models are designed with a specific emphasis on but not limited to the energy containing range of the spectrum they are also not limited to any particular sea state they offer a possible explanation of the variations in the spectral slope observed by previous investigators comparisons with observational results from both laboratory and field show good agreements

remobilization of authigenic uranium in marine sediments by bioturbation uranium behaves as a nearly conservative element in oxygenated seawater but it is precipitated under chemically reducing conditions that occur in sediments underlying low oxygen bottom water or in sediments receiving high fluxes of particulate organic carbon sites characterized by a range of bottom water oxygen bwo and organic carbon flux ocf were studied to better understand the conditions that determine formation and preservation of authigenic u in marine sediments our study areas are located in the mid latitudes of the northeast pacific and the northwest atlantic oceans and all sites receive moderate 0 5 g cm2 kyr to high 2 8 g cm2 kyr ocf to the sediments bwo concentrations vary substantially among the sites ranging from 3 to 270 m a mass balance approach was used to evaluate authigenic u remobilization at each site within each region studied the supply of particulate nonlithogenic u associated with sinking particles was evaluated by means of sediment traps the diffusive flux of u into sediments was calculated from pore water u concentration profiles these combined sources were compared with the burial rate of authigenic u to assess the efficiency of its preservation a large fraction one third to two thirds of the authigenic u precipitated in these sediments via diffusion supply is later regenerated even under very low bwo concentrations 15 m bioturbating organisms periodically mix authigenic u containing sediment upward toward the sediment water interface where more oxidizing conditions lead to the remobilization of authigenic u and its loss to bottom waters

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

tidal forcing of basal seismicity of ice stream c west antarctica observed far inland the seismicity rate beneath the downglacier 85 km of ice stream c west antarctica is modulated by the tide the tide beneath the ross ice shelf modifies the force balance of the ice stream basal environment enough to change the rate of basal microearthquake generation by an order of magnitude this tidal forcing travels up the ice stream as an attenuating wave at approximately 1 6m s 1 and is detectable 85km from the grounding line we successfully model this behavior as an elastic ice stream underlain by a viscous substrate of viscosity and thickness hb and calculate that the substrate has an apparent stiffness hb of o 108 pa s m 1 this finding suggests that the conditions of the till layer at the bed of ice stream c are similar to those of ice stream b and that the reason for the recent stagnation of ice stream c is other than loss of till we further find that the ice stream at the grounding line is more strongly affected by ice shelf processes than by the basal shear stress

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

rhenium geochemical cycling insights from continental margins abstract we measured rhenium re in sediments both pore waters and solid phase from three locations on the mid atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments greater reduction intensity is reflected by shallower oxygen penetration greater ammonium concentrations at depth and shallower first appearances of mn and fe in pore waters this comparison suggests that for the three sites along the mab the reduction intensity from greatest to least is en433 1 oc426 en433 2 all of the pore water profiles show removal of re from pore waters modeled pore water re fluxes follow the trend in reducing conditions en433 1 2 0 0 2 pmol cm 2 y oc426 0 9 0 1 pmol cm 2 y and en433 2 0 60 0 03 pmol cm 2 y respectively solid phase profiles show authigenic re enrichment in sediments from all three locations and the calculated re accumulation rates also mirror the trend in reducing conditions with the values decreasing from en433 1 oc426 en433 2 1 5 0 2 pmol cm 2 y 0 29 0 09 pmol cm 2 y 0 19 0 09 pmol cm 2 y respectively controls on re accumulation are determined from the mab data and from the literature and include 1 the extent of reducing conditions with greater removal of re from pore waters with greater anoxic organic carbon oxidation as determined by the net dissolved ammonium production consistent with the expected removal of pore water re coincident with fe iii and sulfate reduction 2 irrigation which results in net removal of re to sediments augments the diffusive flux of re across the sediment water interface and is more important in shallow coastal sediments rather than locations from deeper water depths mab sites and 3 seasonal remobilization of re from surface sediments due to deepening oxygen penetration depth from 0 2 cm to 1 cm although smaller seasonal changes in oxygen penetration depth e g 0 2 cm to 0 6 cm are less conducive for remobilizing re from sediments there is an empirical relationship with larger re accumulation rates present when the oxygen penetration depth is shallow however there is a stronger correlation between organic carbon oxidation and re accumulation rates this latter relationship is more appropriate since the oxidation of labile organic matter in sediments dictates the sedimentary reducing conditions that are then conducive for re accumulation in the solid phase

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

concentration vertical flux and remineralization of particulate uranium in seawater abstract concentrations and fluxes of particulate u were measured throughout the water column at several locations in the atlantic and pacific oceans with in situ filtration systems and sediment traps the results indicate that dissolved u is fixed to particles in surface seawater organic matter appears to be the carrier phase formation of particulate authigenic u below the surface waters could not be detected authigenic u is remineralized within the bathypelagic layers at the open ocean sites studied in the panama basin an upwelling area with high biological productivity remineralization of authigenic u in the deep water column was not observed the rate of remineralization of authigenic u in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans formation of authigenic u in the water column in areas such as the panama basin is not a significant sink for u on an ocean wide basis

remobilization of barium in continental margin sediments abstract the rate of ba release from california continental margin sediments has been measured using an in situ benthic flux chamber and the range of values 25 50 nmol cm 2 y 1 is larger than any previously published benthic flux estimate for this element the magnitude of the ba flux suggests that a significant fraction of the ba raining from the euphotic zone is recycled at the seafloor ba si regeneration ratios from these margin sediments increase with depth demonstrating that ba is decoupled from si during the earliest stages of diagenesis on the other hand ba regeneration rates and caco3 dissolution rates covary the coupling between these two constituents is supported by the observation that the ba caco3 dissolution flux ratio 1 7 0 4 10 3 is independent of bottomwater depth even in sediments underlying the oxygen minimum zone along the continental margin furthermore this flux ratio is consistent with both the water column ba alkalinity ratio for the world s ocean as well as the ba caco3 ratio in sediment trap solid phases from the equatorial pacific 1 1 2 2 10 3 however the constancy of the ba alkalinity ratio over geologic time remains in question because the mechanism that controls this relationship remains a mystery our flux measurements suggest that diagenesis does not significantly influence the ba ca ratio in the upper 0 5 mm of pacific sediments thereby supporting the idea of using the ba concentration in surface dwelling benthic forams as a proxy for deep water chemical conditions lea and boyle 1989 1990 on the other hand we predict that if a foraminifer lives 0 5 mm or more below this interface then diagenetic effects could influence the ba ca ratio that foram species would record the carrier phase of the particulate ba reactive during early diagenesis does not appear to be organic matter oxyhydroxides or calcium carbonate but rather a mineral phase related to marine barite or perhaps celestite

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

tide induced lateral movement of brunt ice shelf antarctica 1 accurate position data show that brunt ice shelf has an irregular three dimensional motion driven by the ocean tide a 30 day gps record from halley station shows not only the expected vertical tidal displacement but also a significant variation in horizontal velocity the maximum forward velocity occurs about four hours before the maximum tidal height a phase relationship that suggests ocean currents may be responsible however values of ice water friction coefficients needed to make this explanation plausible appear to be too high to be physically reasonable alternative explanations invoke interactions between the ice shelf and a grounded area at the ice front our findings suggest that significant errors might result if these motions are ignored when interpreting double difference satellite sar interferograms where the common assumption is that the horizontal velocity of an ice shelf has no tidal dependence

cause of the chalcophile trace element enrichments marking the holocene to anthropocene transition in northern chesapeake bay sediments abstract in chesapeake bay sediments concentrations of 15 chalcophile trace elements half rarely determined in estuaries display historical profiles having remarkably similar features all element concentrations rose more or less simultaneously in the 1920 1940 interval creating a chemostratigraphic marker of the holocene to anthropocene transition subsequently concentration maxima occurred at 20 year intervals suggesting a link to a documented climate cycle of similar period these elements correlated profiles suggest that sediments approximate binary mixtures of one lithogenic and one multi element anthropogenic component the latter component is characterized by these mass ratios standard error co zn 0 071 0 003 cu zn 0 147 0 007 ag zn 0 0030 0 0002 cd zn 0 0050 0 0004 in zn 0 00031 0 00004 sn zn 0 019 0 002 sb zn 0 0040 0 0002 te zn 0 00059 0 00003 tl zn 0 0016 0 0002 pb zn 0 242 0 013 bi zn 0 00087 0 00005 where comparisons are possible these ratios differ from those of contaminants in the harbor of the region s principal industrial city baltimore but are surprisingly similar to those in sediment contaminants from the susquehanna river the bay s chief tributary thus both the anthropogenic and the lithogenic components in the bay s central channel appear to originate in the river basin many chalcophile element ratios in the anthropogenic component are similar to those in regional aerosols if cumulative aerosol deposition on soils in the river basin is the source of the anthropogenic component then the above ratios could be a regional anthropogenic signature that should be looked for more widely unlike mo the enrichment of these chalcophile elements in the bay s sediments is not controlled by seasonal anoxia mo apparently possesses a unique capacity to record past redox information about estuaries owing to its high seawater concentration

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

sediment geochemical records of eutrophication in the mesohaline chesapeake bay an organic geochemical analysis of sediments in three cores from the mesohaline chesapeake bay was carried out to reconstruct the progression of eutrophication and anoxia hypoxia over the past five centuries evidence of eutrophication was found in the stable isotopic and lipid biomarker signatures of organic matter in sediments of these cores beginning in the late 18th and early 19th centuries and continuing to the present enrichments in the carbon and nitrogen isotopic signature of these sediments likely result from enhanced primary productivity and nitrogen recycling respectively and occur coincidentally with increased fluxes of total organic carbon toc and episodic enrichments relative to toc of algal and bacterially derived lipid biomarker compounds more extreme and enduring changes from the late 19th century to the present are indicated by up to fivefold increases in toc accumulation and 2 to 10 fold enrichments relative to toc in algal and bacterially derived lipid biomarker compounds increased dinoflagellate and other nondiatom algae relative to diatom production is indicated by lipid biomarker compound ratios increases in the ratio of acid volatile sulfur to chromium reducible sulfur in sediment indicate the first occurrence of anoxia hypoxia in 1790 at the deepest site 26 m and in 1915 at a site 15 m deep the history of chesapeake bay productivity is reconstructed using a diagenetic model to estimate the amount of toc and biomarker compounds lost to degradation it is estimated that both toc delivery and algal and bacterial production have increased by 150 or more relative to pre colonial times with a temporal progression similar to anthropogenic alteration of the watershed research has shown that recent increases in net primary production eutrophication in temperate estuaries and coastal ecosystems have occurred e g cooper and brush 1991 1993 barmawidjaja et al 1995 zimmerman and canuel 2000 and are caused in large part by increased loadings of nitrogen nixon 1995 vitousek et al 1997 seasonal anoxia hypoxia is linked to eutrophication because oxygen is consumed during the respiration of organic matter om produced in nutrient enriched waters while rivers deliver the majority of new nutrients to estuarine and coastal environments freshwater inflow can also lead to a strengthening of water column stratification that effectively isolates deeper waters and limits oxygen renewal because the history of anthropogenic alteration of the chesapeake bay cb watershed including the clearance of land for agriculture which may have led to increased freshwater nutrient inflow and the utilization of inorganic nutrients as fertilizers is well 1

modeling tidal currents beneath filchner ronne ice shelf and on the adjacent continental shelf their effect on mixing and transport a depth averaged tidal model has been applied to the southern weddell sea the model domain covers the southern continental shelf including the ocean cavity beneath filchner ronne ice shelf reasonable agreement with the available current meter data has been achieved our results confirm that in areas with shallow water and large topographic gradients tidal oscillations with peak velocities up to 1 m s 1 play a significant role in the vertical mixing and transport of water masses the estimated energy dissipation beneath filchner ronne ice shelf due to surface friction is 25 gw approximately 1 of the world s total tidal dissipation tidally induced lagrangian residual currents converging at the ice front an area of strong mixing draw together water masses from the continental shelf and sub ice shelf cavity the model indicates that lagrangian residual currents have fluxes of up to 250 000 m3 s 1 and speeds of over 5 cm s 1 along the ice front with over 350 000 m3 s 1 being exchanged between the sub ice shelf cavity and adjacent continental shelf these currents are particularly efficient in ventilating the sub ice shelf cavity within 150 km of ronne ice front such strong tidal mixing will significantly modify the properties of water masses that flow through this region particularly to the west of berkner island the model predictions indicate that tidal processes strongly influence the oceanographic conditions in the vicinity of ronne ice front shipborne observations along the ice front support many of the model predictions concerning the effect of tides on the hydrography

reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments abstract sporadic direct observations over a 50 yr period inadequately characterize the history of seasonal hypoxia and anoxia in chesapeake bay a large estuary threatened by eutrophication here we undertake a reconstruction of 20th century oxygen depletion in this estuary using mo concentrations in 210pb dated sediments cu concentrations are used to control for anthropogenic influences cores from the central channel display mild mo enrichments above crustal backgrounds up to 5 g g and strong cu enrichments up to 35 g g temporally cu enrichment mostly anthropogenic began earlier and stabilized in the last two thirds of the 20th century in contrast mo enrichment has grown during the last two thirds of the century molybdenum enrichment is mostly hydrogenic except in a section of the channel that receives additional mo from erosion of early miocene shore deposits two geochemical mechanisms promote mo enrichment manganese refluxing concentrates dissolved moo42 at the sediment water interface and sulfide substitution into moo42 produces thiomolybdates which can be fixed by particles the mo enrichment mechanisms operate primarily during periods when bottom waters are anoxic and thiomolybdate formation can occur near the sediment water interface this implies a temporal coupling between water column anoxia and mo fixation even though fixation occurs only within sediments the mo enrichment profiles suggest that chesapeake bay has experienced growing o2 depletion since the first half of the 20th century but especially after 1960

trace metals in holocene coastal peats and their relation to pyrite formation nw germany abstract three drill cores from the marshlands of nw germany which cover the entire holocene were analyzed at high resolution for bulk composition al fe selected trace metals and stable sulfur isotopes the drill cores contain two lithological types of peat i basal peats overlying pleistocene sands and ii intercalated peats situated between clastic sediments of predominantly marine origin the peat layers are characterized by distinct enrichments in pyrite due to microbial sulfate reduction under almost open system conditions with respect to seawater sulfate as shown by sulfur isotope partitioning the main fe source seems to be the freshwater environment the determination of dissolved and particulate fe of channels and small rivers close to the study area revealed a 50 fold higher fe content of the freshwater environment when compared with north sea water pyrite enrichments are explained by two scenarios i pyrite formation coincides with fen reed peat growth basal and intercalated under the influence of a brackish water zone salinity app 5 15 and ii pyrite was formed after peat growth in the lowest limnic basal peat intervals maximum pyrite accumulation ts 28 occurs in latter peats that contain thin clastic layers as a result of tidal channel activities after peat formation the occurrence of clastic layers may have favoured the inflow of saline groundwater the peat layers are also characterized by enrichments in redox sensitive trace metals as mo re u and cd whereas co cr cu mn ni pb tl and zn reflect the geogenic background leaching experiments have shown that as co cu mo re and tl are predominantly fixed as sulfides and or incorporated into pyrite the remaining trace metals show no distinct trends only cr reveals a strong relation to the lithogenic detritus seawater is the dominating source for as cd mo re and u the remaining trace elements seem to have a freshwater source similar to fe in contrast to the distribution of pyrite highest amounts of redox sensitive trace metals are seen in fen reed peats basal and intercalated that were formed under a direct influence of seawater and brackish water respectively therefore we suggest that saline groundwater entering the basal peats was probably depleted in redox sensitive trace metals e g owing to microbially induced reduction of trace metals and subsequent precipitation as sulfides or fixation by organic matter

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

cycling of trace metals mn fe mo u v cr in deep pore waters of intertidal flat sediments trace metals mn fe mo u cr v were studied in pore waters of an intertidal flat located in the german wadden sea the study system is an example of a permeable tidal flat system where pore water exchange is affected by tidal driven pressure gradients besides diffusion permanently installed in situ samplers were used to extract pore waters down to 5 m depth throughout one year the samplers were either located close to the tidal flat margin or in central parts of the tidal flat despite dynamic sedimentological and hydrological conditions the general trends with depth in deep tidal flat pore waters are remarkably similar to those observed in deep sea environments rates of trace metal cycling must be comparably large in order to maintain the observed pore water profiles trace metals further show similar general trends with depth close to the margin and in central parts of the tidal flat seasonal sampling revealed that v and cr vary concurrent with seasonal changes in dissolved organic carbon doc concentration this effect is most notable close to the tidal flat margin where sulphate doc and nutrients vary with season down to some metres depth seasonal variations of mn fe mo and u are by contrast limited to the upper decimetres of the sediment their seasonal patterns depend on organic matter supply redox stratification and particulate matter deposited on sediment surfaces pore water sampling within one tidal cycle provides evidence for pore water advection in margin sediments during low tide pore water flow towards the creekbank is generated by a hydraulic gradient suggesting that deep pore waters may be seeping out of creekbank sediments owing to the enrichment of specific elements like mn in pore water compared to sea water seeping pore waters may have an impact on the chemistry of the open water column mass balance calculations reveal that the impact of deep pore waters on the mn budget in the open water column is below 4 mn deep pore water discharge of the whole wadden sea is estimated to be about 9 of the total dissolved riverine mn input into the southern north sea

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

the partition of vanadium and molybdenum between manganese oxides and sea water abstract the partition of v and mo between manganese oxides and sea water was investigated in the sea water supply system for aquaria at the marine science museum tokai university where both todorokite and birnessite are precipitated from aerated well sea water the distribution coefficient of v was an order of magnitude higher than that of mo assuming that the distribution coefficients can be applied to marine environments and that manganese oxides are precipitated from sea water the calculated contents of these oxyanionic elements in manganese oxides were comparable to those in marine manganese nodules

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

what regulates rhenium deposition in euxinic basins abstract rhenium is greatly enriched in black shales and euxinic basin sediments relative to its crustal abundance the enrichment process is generally assumed to involve reduction of reo 4 the principal re species in seawater to an insoluble re iv oxide or sulfide in suboxic and anoxic environments the specific biotic or abiotic mechanism of reduction has so far defeated efforts to discover it here an alternative mechanism of fixing re in sediments is examined experimentally thiolation of reo 4 leading to particle reactive thioperrhenates re vii o n s 4 n or to re vii sulfide precipitates or coprecipitates using optical absorption methodology we obtain the first measurements of equilibrium constants for formation of reo 3 s and res 4 as well as a solubility constant for a colloidal re 2 s 7 polymer from these constants we conclude that most euxinic environments contain insufficient sulfide to stabilize thioperrhenates as major species similarly re 2 s 7 polymers are too soluble to form in near neutral ph waters although they might form in acidic mine waters or during supergene hypogene enrichment processes to explain remarkable similarities between mo and re vertical profiles in the black sea we propose that both elements become thiolated at surfaces of a fe mo s colloidal phase and consequently coprecipitate coprecipitation implies that the triggering mechanism for re removal from euxinic basins is neither reduction nor thiolation of reo 4 but instead saturation of sulfidic waters with the fe mo s phase coprecipitation favors removal of mo more than re from the aqueous phase explaining increasing aqueous phase re mo ratios as these elements are depleted from sulfidic waters the raleigh fractionation law describes the process well similar partition coefficients describe the evolution of re mo ratios quantitatively both in sulfidic black sea waters and in sulfidic hingham bay pore waters

century long record of mo isotopic composition in sediments of a seasonally anoxic estuary chesapeake bay abstract a double spike method was used to obtain mo isotope data for sediments and waters of the seasonally anoxic chesapeake bay and its primary tributary the susquehanna river the dissolved mo distribution in the estuary is non conservative reflecting minor mo loss to the sediments although removal of mo to the sediments does not have a large influence on the isotopic composition of the water column the 98mo of dissolved mo in most of the estuary is dominated by seawater six samples with salinity 15 have an average 98mo 2 17 0 12 which agrees well with a 98mo value for the cass 4 seawater standard of 2 23 a single sample of susquehanna river water has a 98mo of 1 02 consistent with recent findings of positive 98mo in rivers worldwide susquehanna river sediments in contrast have 98mo 0 1 the difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin the 98mo values for estuarine sediments are offset from values in the overlying water most samples deposited before 1925 have 98mo less than 0 similar to the susquehanna sediments subsequently there is an increase in the variability of 98mo with values ranging up to 0 8 the transition to increased variability coincides with the onset of authigenic mo deposition which was previously attributed to escalating summertime anoxia authigenic mo concentrations correlate poorly with 98mo in core samples suggesting that independent mechanisms influence the two parameters authigenic mo concentrations may be controlled by shifting pore water h2s levels while 98mo may be primarily affected by annual variations in mn refluxing

hypoxia in the holocene baltic sea comparing modern versus past intervals using sedimentary trace metals abstract anthropogenic nutrient input has caused a rapid expansion of bottom water hypoxia in the baltic sea over the past century two earlier intervals of widespread hypoxia coinciding with the holocene thermal maximum htmhi 8 4 ka before present bp and the medieval climate anomaly mcahi 1200 750 years bp have been identified from baltic sea sediments here we present sediment records from two sites in the baltic sea and compare the trace metal as ba cd cu mo ni pb re sb tl u v zn enrichments during all three hypoxic intervals distinct differences are observed between the intervals and the various elements highlighting the much stronger perturbation of trace metal cycles during the modern hypoxic interval both mo and u show a strong correlation with corg and very high absolute concentrations indicative of frequently euxinic bottom waters during hypoxic intervals during the modern hypoxic interval modernhi comparatively less mo is sequestered relative to corg than in earlier intervals this suggests partial drawdown of the water column mo inventory in the modern water column due to persistent euxinia and only partial replenishment of mo through north sea inflows molybdenum contents in modern sediments are likely also affected by the recent slowdown in input of mo in association with deposition of fe and mn oxides strong enrichments of u in recent sediments confirm that the modernhi is more intense than past intervals these results suggest that u is a more reliable indicator for the intensity of bottom water deoxygenation in the baltic sea than mo sedimentary re enrichment commences under mildly reducing conditions but this element is not further enriched under more reducing conditions enrichments of v are relatively minor for the mcahi and modernhi possibly due to strong reservoir effects on v in the water column indicating that v is unreliable as an indicator for the intensity of bottom water hypoxia in this setting furthermore ba profiles are strongly influenced by post depositional remobilization throughout the holocene the strong relationship between corg and ni tl and particularly cu suggests that these trace metals can be used to reconstruct the corg flux into the sediments profiles of as sb and cd and especially pb and zn are strongly influenced by anthropogenic pollution

instability of bottom water redox conditions during accumulation of quaternary sediment in the japan sea the concentrations of cd cr cu mo ni sb u v and zn were measured in early quaternary sediment 1 32 to 1 08 ma from the oki ridge in the japan sea the elements were partitioned between a detrital fraction composed of terrigenous and volcaniclastic aluminosilicate debris and a marine fraction composed of biogenic and hydrogenous debris derived from seawater the most important factors controlling minor element accumulation rates in the marine fraction were 1 primary productivity in the photic zone which largely controlled the flux of particulate organic matter bound minor elements settling through the water column and onto the seafloor and 2 bottom water redox which determined the suite of elements that accumulated directly from seawater this marine fraction of minor elements on oki ridge recorded six periods of high minor element abundance assuming a constant bulk sediment accumulation rate each period lasted roughly 5 000 to 10 000 years with a 41 000 year cycle accumulation rates of individual elements such as cd mo and u suggest sulfate reducing conditions were established in the bottom water during the 10 000 year periods accumulation rates of cr and v during the intervening periods are indicative of less reducing denitrifying conditions interelement ratios for example cu mo v cr and sb mo further reflect bottom water instability such that bottom water redox actually varied from sulfate reducing to denitrifying during the periods of highest minor element accumulation rates it varied from denitrifying to oxidizing during the intervening periods sediment lithology supports these interpretations of the minor element distributions the sediment is finely laminated for several of the periods represented by cd mo and u maxima and weakly laminated to bioturbated for the intervening periods the geochemistry of this sediment demonstrates the unambiguous signal of mo principally but of several other minor elements as well in recording sulfate reducing conditions in bottom water the forcing function that altered their accumulation that is that altered primary productivity and bottom water redox conditions is problematic currently held opinion suggests that o2 depletion was most strongly developed during glacial advances low sea level during such times is interpreted to have enhanced primary productivity and restricted bottom water advection

processes controlling the regional distribution of210pb 226ra and anthropogenic zinc in estuarine sediments the concentration of226ra in bottom sediments in chesapeake bay is lower than in incoming sediments and decreases systematically in the seaward direction reflecting both a seaward increase in sediment grain size and a displacement of ra from sediments as salinity increases the amount of226ra lost from sediments approximately balances that gained by the water in the seaward 150 km of this estuary where atmospheric deposition is the dominant210pbex source the210pbexorg c ratio is virtually constant in surface samples because the production of carbon is apparently regulated so as to be roughly constant per unit area from independent productivity estimates about 10 of the carbon is found to survive remineralization in the estuary long enough to be incorporated into surface sediments zinc is enriched in surface sediments of the northern two thirds of the bay by a factor of 2 3 over shales theznexorg c ratio decreases systematically southward unlike the210pborg c ratio this reflects a regional decline southward in deposition of anthropogenic zn from the atmosphere a negative210pb anomaly is the most distinctive indicator of sediments deposited by a major flood in 1972 and testifies to the importance of such events in estuarine sedimentation

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

diagenetic separation of cadmium and manganese in suboxic continental margin sediments abstract the vertical distribution of cd differs from that of mn in sediment cores taken from the continental margins of the arctic and atlantic oceans the oxic surface sediment is depleted in cd and enriched in mn whereas the subsurface sediment is enriched in cd and depleted in mn in some cores the distributions of solid phase and dissolved mn are offset the porewater profiles indicate that mn is being precipitated relatively deep in the sediment whereas the solid phase distributions indicate that mn has been precipitated very close to the sediment surface in the recent past at one deep site located near the base of the continental slope 3000 m the offset may be caused by a relatively recent decrease in ocean productivity a corresponding decrease in the organic carbon flux to the sediment and a subsequent migration of the redox boundary deeper into the sediment however at a site where the upper sediment layers have accumulated during the last few decades this explanation cannot account for the offset distributions we propose that a fluctuating input of organic matter to the sediment on seasonal or decadal timescales causes the position of the redox boundary to fluctuate the fluctuating redox boundary pumps dissolved mn upward and concentrates it as mn oxide in a distinct layer at the upper limit of the redox excursion at the same time it pumps cd downward and concentrates it in a distinct layer at the lower limit of the redox excursion the net result of a fluctuating redox boundary is to increase the spatial separation of cd and mn during the early diagenesis of suboxic sediments

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

on the use of laser profilometry for ocean wave studies airborne laser profilometer measurements of wave skewness and spectra are presented the measurements were made during high wind and sea state conditions in the north atlantic the sea states ranged from 4 5 to 8 7 m and varied from swell to wind wave dominated situations skewness values for the five cases ranged from 0 08 to 0 28 and compare favorably with other existing measurements also the phillips and wallops spectral models show excellent agreement with profilometer spectra of developing seas for one case where the seas were fully developed the pierson moskowitz spectrum provides the best representation

formation and solid solution behavior of ca rhodochrosites in marine muds of the baltic deeps authigenic ca rhodochrosites are found in organic rich sediments in the deep anoxic basins of the baltic sea rhodochrosite formation is apparently the result of organic matter degradation the rhodochrosite contains 10 to 40 mol caco3 and 2 to 5 mol mgco3 as determined by microprobe the composition of the carbonates at a given depth varies by about 5 mol mnco3 sem revealed the rhodochrosite to be present as globular aggregates consisting of microcrystallites dissolution features such as cavities within the aggregates are frequently observed and indicate that extensive recrystallization takes place pore waters are greatly supersaturated with respect to both rhodochrosite and calcite rhodochrosite is only found in sediments where pore waters show the highest degree of supersaturation due to ion exchange ca2 diffuses from the underlying freshwater clays this results in increasing aca2 amn2 ratios in the pore waters from the sediment surface downward in response to this the maximum caco3mnco3 ratio also increases with depth the composition of rhodochrosite which forms under these conditions may be determined by both the porewater aca2 amn2 and precipitation kinetics however if their composition is controlled solely by the aca2 amn2 in solution their behavior can be described by a regular solid solution model

uranium geochemistry on the amazon shelf evidence for uranium release from bottom sediments in amazon shelf waters as salinity increases to 36 5 10 3 dissolved uranium activities increase to a maximum of 4 60 dpm 1 1 this value is much higher than the open ocean value 2 50 dpm 1 1 indicating a source of dissolved uranium to shelf waters in addition to that supplied from open ocean and riverine waters uranium activities are much lower for surface sediments in the amazon shelf seabed mean 0 69 09 dpm g 1 than for suspended sediments in the amazon river 1 82 dpm g 1 data suggest that the loss of particulate uranium from riverine sediments and the consequent input of dissolved uranium to shelf waters is probably the result of uranium desorption from the ferric oxyhydroxide coatings on sediment particles and or uranium release by mobilization of the ferric oxyhydroxides the total flux i e riverine flux plus desorbed remobilized particulate flux of dissolved 238u from the amazon shelf about 1 2 1015 dpm yr 1 constitutes about 15 of uranium input to the world ocean commensurate to the amazon river s contribution to world river water discharge approximately 18 measurement of only the riverine flux of dissolved 238u underestimates by a factor of about 5 the flux of dissolved238u from the amazon shelf to the open ocean

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

trace metal diagenesis in sulfidic sediments insights from chesapeake bay abstract sediments were recovered from the mid bay portion of the chesapeake bay when bottom water conditions were sulfidic metal concentrations fe mn ba v ni cu co cd mo u and re were determined in both pore waters and solid phase samples which were determined using total and nitric acid digestion epa 3051a methods v cr and ni were preferentially retained in pore waters even under sulfidic conditions that would normally result in authigenic accumulation likely due to complexation with dissolved organic matter dom mo was efficiently removed from pore waters in the zone in which fes phases and polysufides are available re was not delivered to the sediments through the mn fe shuttle so that its diffusive flux into sediments solely depends on the extent of reducing conditions a non steady state oxygenation event was recorded in the solid phase with coincident solid phase enrichments in fe mn ni cu and co deeper enrichments in u and mo likely reflect remobilization from the relict fe and mn peaks downward diffusion into more reducing conditions and subsequent immobilization the absence of peaks in solid phase re cr and cd was indicative of their lack of association with mn and fe oxides and or resistance of their respective authigenic phases to oxidation on these seasonal to yearly timescales relative changes within the solid phase profiles were captured using the acid digestion method for fe ni and co and acid digestion concentrations were within 90 of the total concentration for mn and cu the presence of excess pore water sulfide may have promoted the removal of trace metals from the detrital fraction resulting in the formation of authigenic sulfides that might become mobile during oxygenation events

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

molybdenum dynamics in sediments of a seasonally hypoxic coastal marine basin abstract molybdenum mo enrichments in marine sediments are a common indicator of the presence of sulphide near the sediment water interface and can thereby record historic bottom water oxygen depletion here we assess the impact of temporal changes in manganese mn cycling and bottom water oxygen on sedimentary mo dynamics in a seasonally hypoxic coastal marine basin lake grevelingen the netherlands high resolution line scans obtained with la icp ms and discrete sample analyses reveal distinct oscillations in mo with depth in the sediment these oscillations and high sediment mo concentrations up to 130 ppm are attributed to deposition of mo bearing mn oxide rich particles from the overlying water the release of molybdate moo 4 2 to the pore water upon reduction of these mn oxides and subsequent sequestration of mo the latter process only occurs in summer when sulphide concentrations near the sediment water interface are elevated gravitational focussing of mn oxides explains the observed increased input of mo with increasing water depth diffusion of moo 4 2 from the overlying water contributes only a small amount to the sediment mo enrichments cable bacteria may indirectly impact sediment mo dynamics by dissolving mn carbonates and thereby enhancing the pool of mn oxides in the system and by contributing to remobilisation of sediment mo during oxic periods a sediment record that spans the past 45 years indicates that sediment mo concentrations have increased over the past decades despite less frequent occurrences of anoxia in the bottom waters based on oxygen measurements from water column monitoring we suggest that the elevated mo in recent sediments reflects both enhanced rates of sulphate reduction and sulphide production in the surface sediment as a result of increased input of organic matter into the basin from the adjacent north sea since 1999 and an associated enhanced mn refluxing in the marine lake in summer

a model for uranium rhenium and molybdenum diagenesis in marine sediments based on results from coastal locations abstract the purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium u rhenium re and molybdenum mo in marine sediments we analyzed these redox sensitive metals rsm in benthic chamber pore water and solid phase samples at a site in buzzards bay massachusetts usa that has high bottom water oxygen concentrations 230 300 mol l and high organic matter oxidation rates 390 mol c cm2 y the oxygen penetration depth varies from 2 to 9 mm below the sediment water interface but pore water sulfide is below detection release of rsm to pore waters during the remineralization of solid phases occurs near the sediment water interface at depths above the zone of authigenic rsm formation this release occurs consistently for mo at both sites but only in the winter for re in buzzards bay and intermittently for u at the buzzards bay site re removal to the solid phase extends to the bottom of the profile while the zone of removal is restricted to 2 9 cm for u and mo authigenic re formation is independent of the anoxic remineralization rate which is consistent with an abiotic removal mechanism the rate of authigenic u formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with u reduction being microbially mediated authigenic mo formation is related to the formation of sulfidic microenvironments the depth and extent of mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation pore water rsm reach constant asymptotic concentrations in sulfidic sediments but only pore water re is constant at depth in buzzards bay the increases in pore water u at the buzzards bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone deep pore water mo concentrations exceed its bottom water concentration due to irrigation induced oxidation and remobilization from the solid phase in sulfidic sediments there is no evidence for higher pore water u or mo concentrations at depth due to the absence of irrigation and or the presence of more stable authigenic rsm phases there are good correlations between benthic fluxes and authigenic accumulation rates for u and mo in sulfidic sediments however results from buzzards bay suggest irrigation ultimately results in the partial loss of u and mo from the solid phase with accumulation rates that are 20 30 of the modeled flux irrigation can augment re possibly u or compromise u mo authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments

redox dynamics in the chesapeake bay the effect on sediment water uranium exchange the effect of seasonal variations in productivity and redox dynamics on the sediment water exchange of uranium was investigated on a twelve cruise time series in the chesapeake bay the deep waters of the bay undergo seasonal anoxia in response to high primary productivity and water column stratification from late spring to early fall dissolved oxygen was used to monitor water column redox conditions and dissolved iron manganese and sulfide were measured to monitor sediment redox conditions dissolved 238u was measured in the water column and sediment porewaters to monitor water column sediment exchange uranium incorporation in bay sediments results from two distinct processes productivity dependent scavenging from the water column and redox dependent cycling of uranium between sediments and bottomwater uranium is removed from surface waters of the bay by scavenging with biodetritus during periods of high primary productivity bottomwater and sediment redox conditions determine whether this particle bound uranium is buried or released to overlying water particulate uranium is released to bottomwaters and porewaters during the degradation of biodetritus and oxidation of authigenic uranium low oxygen in bottomwaters in the summer results in minimal exchange of uranium between the sediments and bottomwater due to the stability of reduced u iv high bottomwater oxygen concentrations associated with bay turnover in the fall results in release of authigenic uranium by oxidation to the soluble vi form enrichment of uranium in fall bottomwater suggests that authigenic uranium is very labile when exposed to oxic environmental conditions this process is enhanced by physical mixing when anoxic sediments are resuspended into the oxic bottomwaters