trace element signatures of chilean upwelling sediments at 36 s abstract with this contribution we continue the discussion on trace element te cycling in chilean upwelling sediments from within and below the oxygen minimum zone omz boning et al 2005 marine geology 220 1 21 low authigenic i e non lithogenic contents of te ag cd mo re and se were interpreted to result from the distinct seasonality in productivity induced organic flux bottom water oxygenation as well as dilution by terrigenous matter while all sediments were reducing enough to become depleted in mn highest enrichments in mo cd and re occur in sediments in contact with the omz here for a meaningful discussion total contents of as bi co cr cu ni pb sb tl v u and zn were corrected for the lithogenic background by determining te al ratios from local river samples the latter showed significantly lower te al ratios than average shale crust or andesite which are classically used for background correction hence the precise assessment of the lithogenic te contribution for the calculation of authigenic te contents allows to examine the source sink relationship of individual authigenic te for chilean sediments four te groups may be distinguished i mo re u and sb likely originate from sea water and accumulate via diffusive supply across the swi ii cd cr cu ni and zn require biologically induced pre concentration within biogenic material iii ag as se tl and v show an intermediate behaviour and iv bi and pb are contributed by anthropogenic activity highest enrichments in ni cu u as and v occur in sediments in contact with the omz the distinct depletion in co along with mn indicates the overall reducing but non sulfidic character of the chilean omz the degree of sedimentary sulfate reduction seems to be the most important control on chilean and peruvian near coastal enrichment of cd mo and u

historical evolution and extreme climate events during the last 400years on the rhone prodelta nw mediterranean abstract the rhone river is the most important source of freshwater and sediment to the western mediterranean sea deltaic lobes and littoral prisms compose the sedimentary units that make up the whole rhone subaqueous delta which reaches up to 50 m in thickness individual lobes that accompanied the retreat of the rhone during sea level rise and the subsequent westward then eastward shift of the main outlet display averaged sedimentation rates in excess of 1 cm yr 1 containing both continental and marine material during the industrial period most of the river flow was delivered through the pegoulier and roustan distributary channels which evolved under human influence within the prodeltas associated to these distributaries very expanded sedimentation rates 10 cm yr 1 allow the documentation of historical extreme climate events a 7 71 m long piston core rhs ks57 was retrieved from the distal prodelta 79 m water depth a multi proxy study was carried out using microfossil assemblages ostracods benthic foraminifera and coccoliths in combination with sedimentological and geochemical proxies our results show that 1 four different intervals i iv spanning a time range comprised between 1600 ad and present day have been differentiated from this multi proxy analysis they correspond to a different position of distributary channels each interval correlates with the different phases of channel avulsion induced by climate events or by human activity 2 the signature of extreme floods that can be identified by the punctuated occurrence of freshwater continental ostracods e g candona spp ilyocypris sp correlating with increases in grain size and or organic carbon content they correspond to decadal scale increased runoffs reported in historical archives our study demonstrates the relevance of benthic microfossil studies for reconstructing paleoenvironmental changes in transitional marine continental settings

origin and accumulation of trace elements in sediments of the northwestern mediterranean margin continental margins receive natural and anthropogenic trace elements tes from direct atmospheric deposition of aerosols onto the sea surface and from advection of riverine suspended particles and or resuspended sediments from the continental shelf slope when the margin is incised by submarine canyons as for example in the northwestern mediterranean sea most of these particles are preferentially transferred via these topographic features towards their final repositories in the abyssal plain the gulf of lions gol shelf receives the largest particulate riverine input to the western mediterranean with its associated chemical contaminants originating from the industrialized and urbanized rhone valley sediments samples grabs cores and moored traps collected in the cap de creus cdc canyon and its adjacent areas at the southwestern exit of the gol were analyzed to explore the origin dispersion transfer and accumulation of a suite of tes ag cd co cr cu ni pb zn and v from the gol shelf to the adjacent continental rise distributions of cu cr ni pb zn and v in the surface sediments of the shelf confirm their terrigenous origin in association with clay minerals whereas ag and cd are more associated with organic matter om all these tes are anthropogenically enriched in the rhone prodelta sediments anthropogenic influence remains clearly discernible in the gol shelf surface sediments for ag pb and zn hydrodynamical resuspension and sorting of shelf sediments occur at the head of the cdc canyon during dense shelf water cascading events during these events the material collected in moored sediment traps contains a higher coarse carbonate fraction slightly impoverished in tes compared to the clays of the nepheloid layer and the organically rich particles deposited before and at the end of the cascading period upper and middle canyon sediments are characterized by high sedimentation rates 0 2 cm yr 1 of fine clay material conversely sediments from the lower continental slope and rise exhibit low sedimentation rates 0 06 cm yr 1 and receive carbonaceous planktonic detritus from the water column at the lower continental slope coarse material includes foraminifers and pteropods whereas at the continental rise finer planktonic derived material is more abundant both in the cdc canyon and in its adjacent lower continental slope rise sediments co cu cr ni and v are associated with clay whereas ag cu and pb are preferentially associated with om cadmium cr and zn are also associated with om in canyon sediments carbonaceous plankton appears to be especially efficient for scavenging ag

cadmium diagenesis in laurentian trough sediments the depth distributions of cd mn and fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the laurentian trough the results reveal a surface layer in which the content of solid phase cd first decreases but then increases sharply with depth in contrast mn decreases regularly over the same depth interval in the oxygenated zone of this layer cd probably associated with organic matter is released to the pore water resulting in concentrations that are more than an order of magnitude higher than in the overlying water column some of the dissolved cd is returned to the water column and some migrates downward and is precipitated at depth this part of the cd cycle is virtually complete within the surface layer the base of which corresponds to the base of the zone of mn enrichment in the subsurface layer solid phase cd and mn show little or no concentration change however dissolved cd which reaches often non detectable concentrations 0 05 nm in this layer increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer the presence of dissolved cd complexes revealed by 1 5 to 8 fold increases in electrochemically active cd in pore water following uv treatment as well as inconsistent distributions of dissolved and solid phase cd indicate complexities in diagenesis that merit further investigation

source apportionment of the hydrocarbon background in sediment cores from hecate strait a pristine sea on the west coast of british columbia canada abstract significant reserves of oil and gas have been predicted for hecate strait a pristine semi enclosed sea on the continental shelf adjacent to british columbia on the west coast of canada to establish a baseline for the natural background of hydrocarbons in sediment prior to any further offshore oil and gas development or increase in oil tanker traffic in the hecate strait region three sediment box cores were collected along a west to east transect across southern hecate strait in september 2003 210 pb measurements established that the bottom sections date to 1920 pre 1800 and 1870 respectively which predate any significant industrial development on the coast alkane and polycyclic aromatic hydrocarbon pah concentrations are low in most sediment samples and both the concentrations and fluxes differ little between surface and bottom core sections pah profiles exhibit a dominance of alkyl pahs for each alkyl pah homologous series with varying amounts of parent unsubstituted pahs while alkane chromatograms show no unresolved complex mixture ucm and there is little change in composition between present day and pre 1800 sediments for most parameters principal components analysis pca models and pah and biomarker ratios indicate that composition patterns are consistent with low and varying natural petrogenic and pyrogenic inputs with little or no anthropogenic input the most likely primary source of petrogenic pahs to the sediments is cenozoic lignites from the skonun formation which outcrops on haida gwai and underlies most of hecate strait two subsurface sections deposited in 1990 and 1930 in the core from milbanke sound on the east side of the transect have elevated concentrations for the alkyl phenanthrene anthracenes and dibenzothiophenes with no ucm and most likely also have a source in immature coal this study suggests that the hecate strait environment has low hydrocarbon concentrations with an apparent minor role for oil seeps and a likelihood that most of the petrogenic pah sources are shales or immature coals with limited pah bioavailability if these characteristics are representative of hecate strait sediments overlying the queen charlotte basin it may mean that biota are likely unadapted to the presence of oil and thus would be more sensitive to exposure to oil from an oil spill than those in a more impacted environment

210pb manganese and carbon indicators of focusing processes on the northwestern mediterranean continental margin abstract organic carbon contents 210 pb data and organic and oxidised forms of manganese in sediments are used for reconstructing the shelf and deep sea transport of particulate matter and for evaluating early diagenesis conditions the latter are used as indicators of focusing processes on the northwestern mediterranean continental margin twelve different physiographical sites were sampled between 400 and 2000 m in the pyrenean and golfe du lion canyon axes and on their open slopes in the canyon axes which indent the pyrenean slope 210 pb activities show a regular exponential decrease with sediment depth computed sedimentation rates range from 170 to 198 cm 10 3 yr for an identical regular exponential decrease in the golfe du lion canyon the sedimentation rate is lower 119 cm 10 3 yr on the lower open slopes and deep sea fans rapid deposition turbidites and surficial sliding occurs onto sediments that were deposited regularly at a rate of about 175 cm 10 3 yr a deposit enriched in organic carbon is identified at mid slope between 500 and 1300 m in this area surface sediments of the canyon axes are richer in organic carbon than at the adjacent open slope sites 0 9 against 0 6 dry weight canyon axes are more active than open slopes as channels for organic matter transfer in the axial channel of the pyrenean canyon organic carbon decreases exponentially in the uppermost 12 cm in the golfe du lion canyons only the upper 2 cm of sediment are enriched in organic carbon this is related to lower sedimentation rates in the golfe du lion area as compared to the pyrenean area on the upper and lower open slopes the organic carbon contents decrease rapidly within 1 2 cm of sediment there is no exponential evolution profile and the residence times at the sediment water interface are longer than in the canyons the highest surface mn concentrations are also found in the middle of the continental slope the average is 64 g g 1 for mn associated with the organic phase mn org and 1400 g g 1 for mn ox as for organic carbon contents canyons are areas of high concentrations the lowest values 4 g g 1 for mn org and 495 g g 1 for mn ox are found for the lower open slope 1200 1700 m where there is active surficial remobilisation and gravity mass movements moreover the vertical distribution of mn has allowed us to identify sites located at depths of about 1000 m where the redox discontinuity is located in the first few centimetres and where the mn ox and the mn org profiles display a positive gradient from the deepest layers to the sediment water interface the distribution of the various parameters was caused by three different mechanisms 1 bottom advection of particulate matter transferred from the continental shelf deposits to the slope along the canyon axes 2 scavenging of the dissolved phases of metals and 3 sedimentary focusing of the particles in a favoured area of the continental slope a mid slope depocenter these data contribute to our knowledge of the role of continental margins in the global recycling of carbon and other materials

pyrite in a sulfate poor paleoarchean basin was derived predominantly from elemental sulfur evidence from 3 2 ga sediments in the barberton greenstone belt kaapvaal craton abstract multiple sulfur isotope variability in archean sedimentary rocks provides constraints on the composition of the earth s earliest atmosphere the magnitude and sign of mass independent anomalies reflect not only atmospheric processes but also transformations due to the archean marine sulfur cycle prior to preservation into sedimentary pyrite the processes affecting the archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear here we combine iron fe and multiple sulfur s isotope data in individual pyrite grains with petrographic information and a one dimensional reactive transport model to investigate the sources of fe and s in pyrite formed in a paleoarchean sedimentary basin pyrites were selected from mudstones sandstones and chert obtained from a drill core in the ca 3 2 ga mapepe and mendon formations of the fig tree and onverwacht groups respectively in the barberton greenstone belt kaapvaal craton south africa pyrite textures and 56 fe distinguish early diagenetic pyrite formed with pore water ferrous iron disseminated grains with average 56 fe pyrite 0 from late diagenetic pyrite formed through sulfidation of iron oxide minerals layered and aggregate forms with average 56 fe pyrite 1 mass dependent s isotope variability in pyrite was small 34 s pyrite ranged from 1 1 to 3 3 with a correspondingly minor spread in 33 s pyrite ranging from 0 3 to 2 1 and 36 s pyrite ranging from 3 08 to 0 27 that indicates a lack of post depositional re working with other distinct sulfur sources our combined fe and s isotope data are most readily explained with pyrite sulfide derived from microbial reworking of solid elemental s iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed the lack of a negative 33 s signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis consistent with low sulfate concentrations in the paleoarchean ocean

the provenance of sediments in the gulf of lions western mediterranean sea in this study we undertook a reconnaissance study of sediments provenance in the gulf of lions focusing over the last 16 ka we used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing sediments samples were selected both onshore and offshore from the western eastern and central part of the gulf of lions we analyzed bulk sediments coarse and fine silt and clay fractions elemental and nd isotope compositions appeared to differ from one grain size fraction to another one these are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the nd isotope compositions our results indicate that sediments in the gulf of lions mainly originated from the rhone river watershed although a contribution of saharan dust is seen in one sample influence of pyrenean small rivers is minor in these samples some sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions

input of particulate heavy metals from rivers and associated sedimentary deposits on the gulf of lion continental shelf abstract fluxes of the heavy metals chromium cr cobalt co nickel ni copper cu lead pb cadmium cd and zinc zn delivered by rivers to the gulf of lion nw mediterranean sea were estimated over a three year study of the river rhone and its smaller tributaries most of the particulate metal fluxes 80 90 delivered by these rivers occurred within a very short period of time less than 12 a typical trend for the mediterranean environment where highly contrasting hydrological regimes were observed over the year temporal and spatial variations in the fluxes of these particulate metals were driven by the fluxes in both water discharge and suspended particulate matter load on the shelf these particulate metal fluxes largely arising from the rhone watershed were two to ten times more important than those resulting from atmospheric deposition co cr and ni in the rivers and on the shelf surface sediments were mainly natural and associated with the finest particles cd and phosphorus appeared to be associated with the silt fraction and to be enriched in the prodelta areas pb zn and cu were more closely associated with the organic matter content and also showed enrichment in the organic rich prodeltaic sediments anthropogenic influences diminished offshore except for pb and zn which could be supplied from the atmosphere by man made aerosols although most of the metals tended to be enriched in the prodelta areas these did not constitute a permanent sink due to resuspension processes affecting these shallow depths a resuspension experiment conducted on sediment cores from the rhone prodelta demonstrated that metal deposited on the surface layer especially those associated with the organic matter may be resuspended this should be taken into account for a complete understanding of the biogeochemical cycle of these metals

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

fluxes and budget of on the continental margin of the bay of biscay northeastern atlantic abstract as part of the ecofer experiment ecomarge program jgofs france concentrations of the natural radionuclide 210 pb were measured in particulate matter collected by sediment traps deployed for a 14 month period june 1990 august 1991 on two mooring lines within the cap ferret canyon on the french continental slope of the bay of biscay northeastern atlantic 210 pb concentrations range 63 218 dpm g 1 and fluxes range 0 1 11 2 dpm cm 2 yr 1 displayed typical gradients increasing with depth at both mooring sites also at equivalent trap depths 210 pb activities were systematically higher on the deep slope mooring 3000 m compared to the shallow one 2300 m fluxes of 210 pb generally decreased seaward and exhibited temporal variations but with no marked seasonal trend essentially matching variations in total mass flux various correlations between 210 pb activities and major constituents of trapped particles were examined 210 pb activities were independent of the particle composition indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles the 210 pb budget as determined by the balance of local supply flux and fluxes to sediment traps and sediments implies important lateral inputs to both mooring sites 65 89 of the flux measured by traps a feature typical of continental margin environments on the basis of annual mean 210 pb activity in traps of the two mooring sites two particle sources are hypothesized the first source located in shallow waters of the shelf and upper slope supplies the entire slope region the second source probably composed of resuspended particles from upper slope sediments feeds essentially the upper and intermediate slope region maximum sedimentation rates determined on seven box cores decreased with bottom depth from 0 3 to 0 4 cm yr 1 at the canyon heads down to 0 06 cm yr 1 at 3000 m a good agreement was observed at both mooring sites between 210 pb fluxes registered by the near bottom traps and excess 210 pb inventories within the underlying sediments suggesting that nuclide fluxes measured by traps during this experiment are representative of fluxes on a longer time scale 10 100 yr nevertheless total mass fluxes measured by traps were 3 4 times lower than 210 pb determined sediment accumulation rates a discrepancy that may be more apparent than real given the possible errors in the latter due to bioturbation

natural and anthropogenic trace metals in sediments of the ligurian sea northwestern mediterranean abstract the magnitude and the chronology of anthropogenic impregnation by hg and other trace metals of environmental concern v cr ni cu zn ag cd and pb including its stable isotopes in the sediments are determined at the dyfamed station a site in the ligurian sea northwestern mediterranean chosen for its supposed open sea characteristics the dyfamed site vd is located on the right levee of the var canyon turbidite system at the end of the middle valley in order to trace the influence of the gravity current coming from the canyon on trace metal distribution in the sediment we studied an additional sediment core va from a terrace of the var canyon and material collected in sediment traps at the both sites at 20 m above sea bottom the patterns of hg and other trace element distribution profiles are interpreted using stable pb isotope ratios as proxies for its sources taking into account the sedimentary context turbidites redox conditions and sedimentation rates major element distributions coupled with the stratigraphic examination of the sediment cores point out the high heterogeneity of the deposits at va and major turbiditic events at both sites at the dyfamed site we observed direct anthropogenic influence in the upper sediment layer according to the 210pbxs derived sedimentation rate at the dyfamed site 0 4 mm yr 1 the hg enriched layer of the top core corresponds to the sediment accumulation of the last 50 years which is the period of the highest increase in hg deposition on a global scale with the hypothesis of the absence of significant post depositional redistribution of hg the hg corg ratio changes between the surface and below are used to estimate the anthropogenic contribution to the hg flux accumulated in the sediment the hg enrichment from pre industrial to the present time is calculated to be around 60 consistent with estimations of global hg models however based on the chemical composition of the trapped material collected in sediment traps we calculated that epibenthic mobilization of hg would reach 73 conversely the cd corg ratio decreases in the upper 5 cm which may reflect the recent decrease of atmospheric cd inputs or losses due to diagenetic processes

comparative geochemistry of cadmium rhenium uranium and molybdenum in continental margin sediments the concentrations of authigenic phases of cd re u and mo increase with depth in four 45 cm long sediment box cores collected along the axis of the laurentian trough gulf of st lawrence average authigenic accumulation rates estimated from element inventories are similar to rates in other continental margin environments strong regional variations in sediment accumulation rate and sulfide concentration have little influence on the accumulation rates of cd and re this suggests that slow precipitation kinetics controls the accumulation of cd and re in these sediments the accumulation rate of authigenic u is more variable it may be tied to the kinetics of microbially mediated u reduction and be controlled by the availability of reactive organic matter authigenic mo is distinguished by a sharp subsurface concentration minimum above which mo cycles with manganese mo released to pore water upon reduction of mn oxides diffuses downward and enriches the subsurface sediment mo accumulates most rapidly in the sediment with the highest sulfide content slow conversion of molybdate to thiomolybdate may explain the much slower mo accumulation rate in the less sulfidic sediments a component of authigenic mo accumulates with pyrite in an approximately constant mo fe ratio the accumulation rate of pyrite and associated mo is insensitive to avs abundance pyrite formation may be limited by the reactivity of iron oxide minerals

recent sediment transport and deposition in the nazare canyon portuguese continental margin processes pathways and fluxes of sediment transport and deposition in the nazare submarine canyon portuguese continental margin were investigated by water column profiling of suspended particulate matter recording of near bottom currents and suspended particulate matter fluxes with benthic landers and by analysis of surface sediment cores the results show that fine grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows tidal currents are actively resuspending and transporting sediment in the upper to middle canyon as reflected by high concentration of suspended particles in bottom waters high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale turbidity currents strong enough to transport sand sized material to the lower canyon occur only on centennial or longer timescales

historical levels of heavy metals and artificial radionuclides reconstructed from overbank sediment records in lower rhone river south east france trace metals cu cd cr ni pb zn hg and artificial radionuclides cs 137 am 241 pu 238 and pu239 240 were investigated in overbank sediments located in inter embankment areas of the lower rhone river enrichment factors ef and anthropogenic factors af were calculated to estimate the level of contamination in these sediment storages the results show that in the studied sites co ni and sc display low ef values and are mainly from lithogenic origin for the other studied trace metals a great variability of sedimentary record is observed significant anthropogenic enrichment was highlighted at a particular site that undergoes fluvial inputs occurring in the last 50 years lead is the element with the highest ef values ef 13 followed by cd ef 11 cu ef 5 hg ef 7 and zn ef 2 temporal variations of pb cd and hg show a maximum in the 1960 s and a decreasing trend afterward maximum enrichment of artificial radionuclides were observed in sediment deposit during the period 1960 1990 when maximum liquid releases from nuclear activities occurred these results indicate that despite the high energy conditions and the generally sandy nature of the riverbank sediments significant anthropogenic enrichments were observed in some areas of sediment accumulation in the lower rhone river these enrichments are however relatively low compared to some other rivers in france and europe due to the important suspended sediment discharge in this river in particular during strong floods which dilutes the anthropogenic inputs of contaminant c 2011 elsevier ltd all rights reserved

210pb sedimentation rates from the northwestern mediterranean margin abstract a total of 83 cores were collected in the gulf of lions continental margins and analysed for 210 pb xs excess 210 pb in order to understand sedimentation patterns apparent sedimentation rates asr range from 0 65 cm year 1 in the vicinity of the rhone river mouth to 0 01 cm year 1 in the deep basin except for the prodelta area rates decrease with depth linearly with the water depth on the slope asr do not differ between canyons and open slope except for the western area where the rates are slightly higher in the lacaze duthiers canyon compared to its adjacent open slope in the canyon and open slope areas mass accumulation rates determined from 210 pb xs profiles 0 10 and 0 08 g cm 2 year 1 respectively are in good agreement with particulate fluxes calculated from 5 years of near bottom sediment trap data even when the trap particle fluxes and the apparent accumulation rates are overestimated in response to resuspension and bioturbation effects however differences in sediment trap data between west and east portion of the slope are not observed in the sedimentation rates calculated with 210 pb xs the outer shelf area may have an important role in trapping sediment but it is not sufficiently documented sediment surface mixed layer depths decrease with water depth with a mean value for the whole margin of 8 6 cm 210 pb xs inventories in the sediment are systematically higher than the net 210 pb export flux estimated from the above water column over the margin the ratio between accumulated 210 pb and available 210 pb is about 3 suggesting boundary scavenging effects and advective transport

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

suspended particle movement in and around quinault submarine canyon abstract time and space dependent light transmission temperature salinity and velocity data obtained during two winter experiments in the vicinity of quinault submarine canyon are used to examine processes controlling subtidal cpd fluctuations in suspended particulate concentration in the region in particular local resuspension of particles by waves and currents horizontal advection and vertical advection data include time series from four to eight mooring locations as many as 16 current meters and 10 transmissometers on the shelf over the open slope and in the canyon during each experiment spatial distributions from five ctd transmission surveys and gravity wave information particle concentration in the bottom boundary layer at the shelf edge was dominated by resuspension events the mechanism for resuspension had a large inter annual variation in the first year wave induced resuspension dominated whereas in the second year current induced resuspension dominated the cut off depth for storm related resuspension was generally m subtidal advection across isobaths upwelling downwelling accounted for 20 of the variance in concentration fluctuations at the shelf edge in the bottom boundary layer horizontal advection of material suspended in the bottom nepheloid layer on the shelf resulted in the formation of shelf break depth intermediate nepheloid layers over the canyon in regions where the flow crosses isobaths the existence strength onshore offshore extent and vertical structure of such nepheloid layers at a given time in this asymmetrical canyon appear to be a function of the direction of flow over the outer shelf and over the upper slope in the canyon whether active resuspension is occurring over the shelf and the maximum resuspension depth and magnitude of the active resuspension event the frequency timing and magnitude of previous resuspension events spatial and temporal continuity magnitude and direction of flow over the open slope north and south of the canyon vertical settling and upwelling or downwelling related to the along isobath flow over the upper slope fluctuations in particle concentration below the shelf break depth over the canyon slope were controlled by vertical rather than horizontal advection vertical excursions by the water mass of 100 m occurred both as a result of isopycnal adjustment to the quasi geostrophic along isobath flow and as a result of semidiurnal tidal oscillations when an overhead nepheloid layer was present such water mass excursions produced concentration fluctuations at depths below the maximum depth of storm related local resuspension in open slope regions where strong inls intermediate depth nepheloid layers were absent the portion of concentration variance that could be explained by advective models with constant spatial gradients was almost negligible only one resuspension event was documented in the bottom boundary layer within the deep canyon bottom depth 1000 m suggesting that advection must account for the observed variance in particle concentration however the large scale gradients at these depths are sufficiently weak cf the smaller scale gradients or noise that advective control could only be demonstrated during the second winter experiment when velocities along the canyon axis were relatively large finally the data demonstrate that subtidal concentration fluctuations within 50 m of the canyon floor are correlated to those at the shelf edge this correlation reflects a correlation in the velocity field rather than a transfer of particles as might occur with a turbidity current

mobility of authigenic rhenium silver and selenium during postdepositional oxidation in marine sediments sedimentary records of redox sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions records of re can reveal the intensity of past reducing conditions in sediments at the time of deposition whereas records of ag may record the magnitude of past diatom fluxes to the seafloor confidence in paleoenvironmental reconstruction from records of either metal however requires it to have experienced negligible redistribution since deposition this study examines diagenetic rearrangements of re and ag that occur in response to exposure to bottom water o2 in environments of low sedimentation rate including madeira abyssal plain turbidites and eastern mediterranean basin sapropels authigenic re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments all records are consistent with previous work demonstrating that only a limited reimmobilization of re occurs preferentially in corg rich reducing sediments silver was also mobilized quantitatively by oxidation but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts and these peaks remain immobile in anoxic conditions during long term burial comparison of ag s and se records from various cores suggests that ag is likely to have been immobilized as a selenide a mechanism previously proposed for hg in similar situations mercone et al 1999 coexisting narrow peaks of ag and hg with se offer a means of assessing whether oxidative burndown has ever occurred at the top of corg and sulfide rich sedimentary units although these results suggest that caution must be used when inferring paleoenvironmental information from records of ag and re in cores with low sediment accumulation rates 5 cm ka 1 they should not affect the promise that authigenic ag and re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously

a biomineralization model for the incorporation of trace elements into foraminiferal calcium carbonate measurements of srca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera new data for cdca support previous work in defining a contrast between waters shallower and deeper than 2500 m measured element partition coefficients in foraminiferal calcium carbonate relative to sea water d have been described by means of a one box model in which elements are extracted by rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor such that d 1 f 1 f where f is the proportion of ca remaining after precipitation a modification to the model recognises differences in element speciation the model is consistent with differences between dsr dba and dcd in benthic but not planktonic foraminifera depth variations in d for sr and ba are consistent with the model as are differences in depth variation of dcd in calcitic and aragonitic benthic foraminifera the shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m observations of unusually lower dcd for some deep waters not accompanied by similar dsr or dba may be because of dissolution or a calcification response to a lower carbonate saturation state