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

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

diagenetic mobility of trace elements in sediments covered by a flash flood deposit mn fe and as the vertical distribution and concentrations of fe mn and as were measured in porewaters and sediments recovered with box cores taken each year since the 1996 flood along the main axis of the saguenay fjord and in the baie des ha ha time series analyses reveal that mn remobilization was not significantly affected by the accumulation of the flood deposit authigenic mn oxi hydroxides present at the original sediment water interface and in the flood material were progressively reduced and much of the mn ii diffused to the current interface where it was oxidized and precipitated first order rate constants for the reduction and precipitation of the authigenic mn oxi hydroxides were estimated by fitting the time series data to a diagenetic model on the basis of these rate constants and given that the maximum reactive solid mn remains concentrated in the thin oxic layer near the sediment water interface an upper limit to the biodiffusion coefficient db was also evaluated in contrast to mn fe associated with the authigenic oxi hydroxides at the original interface was mostly trapped as acid volatile sulfides i e avs under the so4 reducing conditions established rapidly after the flood most of the as associated with the authigenic oxi hydroxides at the original buried interface also appears to be trapped with the authigenic sulfides thus limiting its diffusion through the flood deposit

processes controlling arsenic enrichment along the eastern arabian sea surficial sediments the processes enriching redox sensitive arsenic as was investigated in 111 surficial sediments 27 3679 m water depth overlain by varying levels of dissolved oxygen along the eastern arabian sea under oxygenated conditions diagenetic enrichment of as was noticed at deeper water depths 1200 m while lattice held as dominant at few station from shallow depths 150 m in sediments impinged by oxygen minimum zone omz 150 1200 m as is released from organic matter during sub oxic diagenesis as seems to precipitate as as iron sulfide mineral under intense omz based on a positive correlation between as and s and cd in northeastern part of the study area while as may diffuse to water column under less intense omz evidenced by lack of correlation between as and s and cd in southeastern part several processes can enrich as a careful approach is recommended for its usage in understanding anthropogenic sources transport and paleodepositional environment along eastern arabian sea

biogeochemical redox cycling of arsenic in mine impacted lake sediments and co existing pore waters near giant mine yellowknife bay canada abstract lacustrine sediments submerged tailings and their pore waters have been collected at several sites in yellowknife bay great slave lake canada in order to investigate the biogeochemical controls on the remobilization of as from mining impacted materials under different depositional conditions radiometric dating confirms that a mid core enrichment of pb zn cu and sb corresponds to the opening of a large au mine 60 a ago this was evident even in a relatively remote site arsenic was enriched at mid core coincident with mining activity but clearly exhibited post depositional mobility migrating upwards towards the sediment water interface swi as well as down core deep water 15 m yellowknife bay sediments that contain buried mine waste are suboxic relatively organic rich and abundant in microbes with as in pore waters and sediments reaching 585 g l and 1310 mg kg respectively late summer pore waters show equal proportions of as iii and as v 16 415 g l whereas late winter pore waters are dominated by as iii 284 947 g l this can be explained by as iii desorption mechanisms associated with the conversion of fes to fes 2 and the reduction of as v to as iii through the oxidation of dissolved sulfide both microbially mediated processes processes affecting as cycling involve the attenuating efficiency of the oxic zone at the swi sediment redox heterogeneity and the reductive dissolution of fe hydr oxides by labile organic matter temporarily and spatially variable

arsenic speciation in soil porewaters from the ashanti mine ghana abstract at the ashanti au mine in southwest ghana arsenopyrite constitutes an important part of the hypogene ore assemblage often hosting significant concentrations of au the oxidation of arsenopyrite either through lateritic weathering or during mineral processing releases as into the environment the speciation of as in soil porewaters both from uncontaminated soils and those overlain by mine waste has been assessed in aerobic soils overlying weathered au as mineralization in the bedrock as was present in concentrations of 189 1025 ppm in soil and porewater concentrations ranged from 86 2 to 557 g l 1 arsenic in these waters was found to be largely present as arsenate approximately 78 95 of the total as with arsenite monomethylarsonic acid mmaa and dimethylarsinic acid dmaa also present where arsenite concentrations are greater than arsenate no organoarsenical species were observed in the uncontaminated soils overlying unmineralized bedrock background as concentrations were in the range of 12 5 20 2 ppm and porewater concentrations ranged from 11 2 to 20 g l 1 in these porewaters arsenate was the dominant species no organoarsenical species were observed in these waters suggesting that there is a possible threshold level of total as concentration required above which methylation of as by soil microorganisms takes place in the acidic soils contaminated by mine tailings arsenite was the major species present up to 45 of total as in the aerobic soils and 79 of total as in the anaerobic soils although the soils were underlain by the unmineralized bedrock soil as concentration ranged from 40 5 to 1290 ppm and as concentration in extracted porewaters from anaerobic soils ranged from 70 2 to 110 g l 1 and in aerobic soil from 70 8 to 599 g l 1 in the aerobic soils mmaa dmaa and arsenate were also present but only arsenate was found along with arsenite in the anaerobic soil porewaters

arsenic distributions in porewaters and sediments of puget sound lake washington the washington coast and saanich inlet b c solid phase as mn al and excess 210pb and dissolved total as as 3 as 5 mn 2 fe 2 po 34 nh 4 and h2s profiles in 12 cores from puget sound lake washington the washington coast and saanich inlet b c are presented typically strong correlations between solid phase as and mn concentration maxima in surficial sediments are a result of intense as scavenging in the overlying waters by mn or ferich phases or solid phase as dissolution at depth followed by upward diffusion and co precipitation with mn or fe oxides at or near the sediment water interface atypically anthropogenic inputs cause high sedimentary as concentrations without accompanying high mn levels sedimentary as fluxes are an order of magnitude greater in puget sound and lake washington than off the washington coast and in saanich inlet porewater total as concentration profiles exhibit sub surface maxima with magnitudes 10 60 times greater than in overlying bottom waters porewater maxima in marine environments are proportional to associated solid phase as concentrations these maxima consistently occur within 1 0 cm of the bottom of the 210pb derived surface mixed layer suggesting solid phase as release to porewater in response to a redox gradient across this mixing boundary dissolved as behavior beneath these maxima indicates as removal to solid phases in marine but not lacustrine porewaters porewater as 3as 5 ratios are 1 0 for washington coastal environments and usually between 1 0 4 0 for puget sound and lake washington as 5 is below the detection limit in porewaters of saanich inlet when the overlying bottom water is anoxic but as 3as 5 ratios as low as 2 8 exist in near surface porewater under oxic bottom water conditions

trace metal solubility in an anoxic fjord abstract intermittent anoxia in the saanich inlet water column provides an easily accessible marine o2 h2s interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron thiosulfate and sulfite are below detection limits 1 m and 0 1 m respectively and thus not important in metal complexation elemental sulfur concentrations are high at the oxic anoxic interface and throughout the anoxic zone indicating the potential for metal complexation by polysulfides a thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron copper and cadmium the extension of this scheme to other transition and class b metals in other marine environments with redox fronts is suggested

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

mobility of arsenic in groundwater in the obuasi gold mining area of ghana some implications for human health arsenic in drinking water from streams shallow wells and boreholes in the obuasi gold mining area of ghana range between 0 5 probably as a result of methylation and reduction reactions mediated by bacteria and algae concentrations of as in groundwaters reach up to 64 gl 1 being highest in deeper 40 70 m and more reducing 220 250 mv waters the as is thought to build up as a result of the longer residence times undergone by groundwaters in the deeper parts of the aquifer the proportion of as present as as iii is also higher in the deeper groundwaters deep mine exploration boreholes 70 100 m have relatively low as contents of 5 17 gl 1 possibly due to as sorption onto precipitating ferric oxyhydroxides or to localized low as concentrations of sulphide minerals median concentrations of inorganic urinary as from sample populations in two villages one a rural streamwater drinking community and the other a suburb of obuasi using groundwater for potable supply were 42 gl 1 and 18 gl 1 respectively the value for the community drinking groundwater is typical of background concentrations of urinary as the slightly higher value for the streamwater drinking community probably reflects different provenance of foodstuffs and higher as concentrations of water sources local to the village the low value obtained for the inhabitants of the obuasi suburb living close to and abstracting groundwater from the area of major mining activity suggests that groundwater can form a useful potable supply of good inorganic quality provided that deep long residence time sources are avoided

diagenesis of ferriferous phases in the northampton ironstone in the cowthick quarry near corby england berthierine siderite and pyrite are the major ferriferous phases in the northampton ironstone nis mineralogical and chemical data suggest a formation of these phases in a diagenetic marine environment changing from post oxic to sulphidic conditions berthierine was formed first when the fe 2 activity in the diagenetic system increased later this phase was partially replaced by siderite and or pyrite a second stage of the diagenetic development in the nis with increasing co 2 partial pressure p co 2 is documented by siderite the isotopic composition 18 o mean value 1 7 pdb 13 c mean value 8 6 pdb points to siderite precipitation from a marine porewater environment with a microbial co 2 source the shift from post oxic to sulphidic conditions is indicated by the occurrence of pyrite and can be considered as a final stage the diagenetic processes in the marine environment and the formation of the ferriferous phases were stopped by the influx of brackish or fresh water when the midland shelf turned estuarine

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

geochemistry of surficial and ice rafted sediments from the laptev sea siberia the laptev sea as a part of the world s widest continental shelves surrounding the arctic ocean is a key area for understanding the land ocean interaction in high latitude regions with a yearly freshwater input of 511 km3 the lena river one of the eight major world rivers has an influencing control over the environment of this arctic marginal sea which is ice covered during most of the year in this paper the first measurements are presented of the major and trace element distribution within the 20 m grain size fraction of surficial sediments and of particulate matter in new and young ice from the laptev sea siberian arctic the concentration and distribution of major and trace elements have been determined in 51 surficial sediment samples covering the whole laptev sea shelf south of the 50 m isobath thirty one samples of particulate matter in newly formed ice were taken during the freeze up period in 1995 median concentration levels of heavy metals in surficial sediments ni 46 g g 1 cu 26 g g 1 zn 111 g g 1 and pb 21 g g 1 are within the concentration range of marine unpolluted sediments also the sediment laden ice showed no indication of anthropogenic perturbation of the trace metal inventory spatial distribution patterns of heavy metals are mainly determined by variation of mineral composition and different fluvial sediment sources in the eastern and western laptev sea the laptev sea shelf is cut by five north south trending submarine valleys enrichment of manganese in the oxic surficial sediment layer within these valleys and the occurrence of small ferromanganese nodules are caused by a high input of dissolved and particulate mn from the lena river and a strong diagenetic cycling of mn on the laptev sea shelf evidence is given that the content of as in surficial sediments is also strongly affected by diagenetic cycling this causes surficial sediment as concentrations of more than 100 g g 1 enrichment of mn and as was mainly observed in the submarine valleys distant from the major river mouth the sediment dilution due to higher sedimentation rates near the river outlets and a strong sediment re working by ice gouging in the shallow areas are the principle causes for the absence of diagenetic accumulation in this region during the formation of new ice scavenging of riverine suspended matter and resuspension of sediments followed by an incorporation of particles into the ice are important processes for the river shelf ocean transport of particulate trace elements it could be shown that particle loaded ice posseses the same geochemical signatures as the suspended matter and surficial seafloor sediments in the area of ice origin this has also strong implications for the contaminant transport on the arctic shelves and allows to use the geochemical signature of sea ice for the reconstruction of ice drift pattern within the arctic ocean

natural enrichment of arsenic in loch lomond sediments abstract concentrations of arsenic in surface or near surface sediment in 12 of 13 cores from the three major basins of loch lomond are substantially enhanced up to 675 mg kg compared with background values of 15 50 mg kg sedimentary as profiles are attributed to post depositional enrichment processes since there are no recent significant sources of environmental as contamination anthropogenic or natural in the loch lomond area the enrichments can be interpreted in terms of post depositional diagenetic remobilization processes in sediment reducing zones followed by upward migration of as through interstitial waters and oxidation adsorption precipitation reactions in near surface oxidizing layers confirmation of the diagenetic adsorption hypothesis is provided directly by the analysis of as species 1 5 81 g l in pore water and indirectly via comparison with sedimentary phosphorus

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

210pb derived sediment accumulation and mixing rates for the greater puget sound region abstract recent sediment accumulation rates of 46 1200 mg cm2 yr are calculated from excess 210pb activity profiles in 44 sediment cores from 27 sites in the greater puget sound region rates calculated for nine stations in the deeper waters of central puget sound average 480 mg cm2 yr and are greatest between seattle and tacoma near the southern end of this region the standard error of this mean is 113 mg cm 2 yr magnitudes and geographic trends of 210pb derived accumulation rates agree with limited data on sediment inputs and transport paths their accuracy is further supported by several independent approaches including comparison with particle fluxes collected in year long series of sediment trap deployments at two sites accumulation rates are calculated assuming no mixing beneath surface mixed layers of 2 22 cm sediment mixing coefficients in these surface layers average at least 43 cm2 yr four times greater than those reported in open washington coast sediments the difference is attributed to the greater benthic biomass in puget sound sediments particle residence times in surface mixed layers vary from 1 5 to 68 years and introduce corresponding uncertainties in ages of horizons beneath the mixed layers for most of this region these residence times will cause a 20 30 year time lag in achieving an equivalent response of surface sediment chemical concentrations to changes in concentrations in freshly depositing particles for constituents whose stability and phase associations resemble those of 210pb these time lags limit the ability of sediment chemistry monitoring programs to recognize recent changes in composition and fluxes of chemicals to sediments recent fluxes calculated from the product of surface sediment chemical concentration and accumulation rates will be inaccurate for chemicals if their input concentrations have changed in the last 20 30 years

arsenic enrichment in lakes near the smelters at sudbury ontario roughly 200 tonnes of arsenic are produced annually with the base metal ores at sudbury about 125 tonnes of which are released to the ambient environment via the atmosphere the dispersion of this highly toxic element in lakes around the smelters is described the total as concentrations in unfiltered lake waters vary from 0 2 to 0 6 ug 1 1 the suspended particulates in the water column with as contents of 2 6 ug g 1 play a major role in the flux of arsenic to the lake sediments the present day rates of as accumulation in the sediments are found to be 1 5 6 4 mg m 2 yr 1 these rates exceed those of precolonial times by factors of 5 47 the changes in the rates of as flux to the sediments are shown to parallel the history of cu and ni production in the district

enhanced geochemical gradients in a marine shallow water hydrothermal system unusual arsenic speciation in horizontal and vertical pore water profiles the shallow marine hydrothermal vents near ambitle island in eastern papua new guinea discharge hot slightly acidic as rich chemically reduced fluid into cool slightly alkaline oxygenated seawater gradients in temperature ph and total as as t among others are established as the two aqueous phases mix the hydrothermal fluid contained 900lg l as t almost exclusively present as the reduced as iii while local seawater measured between 1 2 and 2 4lg l as with approximately equal levels of as iii and as v of particular interest in this study was as speciation and abundance in pore waters as a function of sediment depth and as a function of distance from the area of focused venting with increasing distance as t concentration in the pore water decreased rapidly but remained elevated up to 300 m from the area of focused venting when compared to a non hydrothermal control site as a function of depth to 100 cm as t concentration in the pore water profiles was elevated and generally increased with depth surprisingly aqueous as v far exceeded aqueous as iii at almost all distances and depths investigated while at the control site the as iii concentration exceeded that of as v in the tutum bay hydrothermal system chemical disequilibria among as species provide potential metabolic energy for arsenite oxidizing microorganisms where hydrothermal fluid mixes with seawater near the vent orifice and for arsenate reducing microorganisms with increasing distance and depth from the hydrothermal point source 2007 elsevier ltd all rights reserved

effects of salinity and an ions on arsenic behavior in sediment of bosten lake northwest china bosten lake the largest inland lake in china has been contaminated with arsenic as due to anthropogenic activities salinity of the lake water has been increasing due to the extremely dry climate and salt drainage from the farmland effects of the increasing salinity on the geochemical behavior of arsenic in sediment are still unclear in this study vertical variation of geochemical fractions of as in sediment and arsenic concentration in porewater along the salinity gradient of bosten lake was studied effects of salinity and ions and anions in porewater on arsenic concentration were also examined arsenic content in the five tessier fractions followed the decreasing order of residual exchangeable fe and mn oxides organic carbonate the ecological risk of arsenic in the sediment was at low or medium levels indicated by the low percentage of exchangeable and carbonate bound fractions contrary to the decreasing electrical conductivity of porewater with depth arsenic concentration in porewater showed an increasing trend with depth arsenic concentration in porewater increased from around zero at the surface layer of sediment to over 600 g l 1 in deeper layers of some sites arsenic concentration inversely correlated with electrical conductivity in porewater arsenic concentration generally decreased with increasing concentrations of so4 2 ca2 mg2 and na but showed no clear relation with concentrations of k and cl this study implies that increase of salinity may decrease the release of arsenic from sediment and its ecological risk

formation of south facing bald mudstone slopes in southwestern taiwan abstract in the southwestern part of taiwan most foothills are covered by mudstones the mudstone formed during miocene to pliocene and pleistocene is a young and weak sedimentary rock when subjected to water slaking of the mudstone can easily take place and in dry seasons severe shrinkage can occur thus erosion of mudstone slopes is easily induced by rainfalls heavily eroded natural mudstone slopes in southwestern taiwan frequently become bald i e not covered by any plants or bushes and are very susceptible to geologic damages such as mudflow and slope failure one interesting observation of the mudstone slopes in southwestern taiwan is that most of the bald slopes are south facing the causes of this directional variation are thoroughly examined in this paper it is concluded that solar radiation rather than the direction of typhoons is the main reason for forming bald slopes in the south facing direction

from cadomian subduction to early palaeozoic rifting the evolution of saxo thuringia at the margin of gondwana in the light of single zircon geochronology and basin development central european variscides germany

interelement relationship in abyssal pacific ferromanganese nodules and associated pelagic sediments abstract by r mode factor analysis and enrichment factor calculations most of the elements in abyssal ferromanganese nodules and associated pelagic sediments excluding common authigenic minerals like apatite barite opal and carbonates are found to be preferentially concentrated in one of the following three major phases aluminosilicates e g al si sc ga cr be na k rb and cs fe oxides e g fe p s v se te as b sn u hg pb ti ge y zr nb pd in rare earths hf th pa pu am ru and bi and mn oxides e g mn tl ag cd mg ca ba ra co ni cu zn mo sb and probably w the specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties e g the ph of zero point of charge and dieletric constant of these three phases

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

the fate of geothermal arsenic in the madison and missouri rivers montana and wyoming geothermal as from yellowstone national park causes high as concentrations 10 370 g l in the madison and missouri rivers in montana and wyoming arsenic transport is largely conservative in the upper basin as demonstrated by the near equivalence of dissolved and total recoverable as concentrations the constancy of as loads and consistent ratios of concentrations of as to conservative geothermal tracers diurnal cycling of as between aqueous and solid phases in response to ph induced changes in sorption equilibria causes small variations of about 10 20 in dissolved as concentrations hcl extractable as concentrations in river and lake sediment in the upper basin are variable depending on position relative to the as rich headwaters and geochemical and physical processes associated with lakes in the lower missouri river large quantities of suspended sediment from tributaries provide sufficient sorption sites for substantial conversion of as from the aqueous phase to the solid phase

chalcophile elements and ir in continental cretaceous tertiary boundary clays from the western interior of the usa abstract this study presents data for ir and the chalcophile elements as sb and zn in seventeen samples from continental k t boundary layers in the western interior of the usa the results show that in contrast to previously studied marine boundary clays the continental boundary layers show no correlation between ir and any of the chalcophile elements compared with average shale the continental boundary layers are significantly to strongly enriched in ir as and sb but show ordinary zn concentrations the ir enrichments can be attributed to fallout of extraterrestrial matter whereas as and sb enrichments can be readily explained by the close spatial association of the boundary layers with coal and the abundance in the layers of jarosite goethite and other weathering products of pyrite if compared to jarosite rich coal associated background samples the boundary layers show much higher ir concentrations but similar or possibly slightly enhanced concentrations of as sb and zn the correlation between chalcophile elements and ir in marine boundary clays and the absence of such a correlation in continental boundary clays concurs with the idea that a major fraction of the ir in extremely ir rich 30 460 ppb ir marine boundary clays has precipitated from seawater that was enriched in ir being derived from a vaporized asteroid

mixing and cycling of uranium thorium and 210pb in puget sound sediments abstract activity profiles of excess 234 th excess 210 pb 232 th 230 th 234 u and 238 u and 228 232 th ratios determined in eight box cores of sediment from six sites in central puget sound provide new insights into the dynamic nature of solid phase mixing in surface sediments the exchange of 228 ra and other soluble species across the sediment water interface and the cycling of u th and 210 pb in this coastal zone comparison of excess 234 th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central puget sound water column surface sediment horizons with excess 234 th have no excess 228 th which might be used to ascertain sediment accumulation rates over the past decade instead deficiencies of 228 th due to loss of soluble 228 ra from pore water to the overlying water persist to 20 30 cm revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of puget sound solid phase u isotope concentrations tend to increase by up to a factor of two with depth in sediments as a result of dissolved u being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing 232 th and 230 th activities and 230 232 th ratios are constant with depth in sediments indicating constant detrital phase compositions and essentially no authigenic 230 th steady state 210 pb depositional activities in and fluxes to puget sound sediments average only about onehalf those for sediments of the open washington coast north of the columbia river mouth primarily because of a much lower supply of dissolved 210 pb in sea waters adverting into puget sound excess 234 th profiles in sediments reveal much more detail about the depth dependency dynamic nature and recent history of solid phase mixing processes than excess 210 pb profiles at least six of eight 234 th profiles show that mixing within the 210 pb defined surface mixed layer is depth dependent in three profiles 234 th derived mixing rates are fastest several centimeters below the sediment water interface indicating greater macro benthic activity at these depths depth dependent mixing coefficients derived from the best fit of a four layer advection diffusion decay model to the 234 th data are consistent with 210 pb profiles determined for the same sediments strongly suggesting that 234 th and 210 pb are mixed equivalently and in a multilayered manner

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

a geochemical application of the itrax scanner to a sediment core containing eastern mediterranean sapropel units the itrax micro x ray fluoresence xrf core scanner has been applied in a sediment geochemistry investigation the core sections selected contain examples of the organic rich sedimentary units sapropels that form periodically in the eastern mediterranean basin sapropels are visually obvious from their dark coloration but the itrax x radiograph also reveals physical property changes that result mainly from the high pore water content of sapropels a consideration of wavelength dispersive xrf data from discrete samples of the most recent sapropel s1 was made along with the set of elements reported by the itrax instrument s energy dispersive xrf system over core sections containing s1 this allowed selection of a suite of eight inter element ratios or element integrals through which characteristic features of sapropel development and geochemistry were revealed while recognizing that the measured xrf element integrals from the itrax do not have an exact constant relationship with element concentration over changing sediment types this combination of ratios provides significant information for geochemical interpretation these include evidence for i the presence of high corg contents in the visual sapropel from ba ti and br cl ratios ii a thinning of the original sapropel thickness by post depositional oxidation from mn ti and cu ti ratios iii pyrite authigenesis in the residual visual sapropel from fe ti and s cl ratios and the as integral and iv aragonite formation in and around the sapropel from the sr ca ratio these same ratios were then used to interpret itrax data from a deeper section of the same core containing the older sapropel s3 where the same characteristics including the relict post depositional oxidative thinning of the original unit could be identified with only minor differences of detail directions of supply of fe as and cu into the sapropels could be inferred from profile shapes

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

arsenic iron and organic matter in sediments and groundwater in the pannonian basin hungary in the central part of the pannonian basin factors controlling the distribution of as in sediments and groundwater of the upper 500 m were studied in core samples the amounts of as fe and mn extractable with hydroxylamine hydrochloride nh2oh hcl in 25 acetic acid the proportion of the 0 063 mm size fraction and the sediment organic c corg contents were measured in the groundwaters concentrations of as humic substances and selected major chemical components were determined in most core samples extractable fe as feooh and corg are correlated but some samples have excess fe or organic matter in cases where either excess fe or excess organic matter is found the amount of as is also elevated the spatial distribution of as in the groundwater and the lack of a consistent correlation of as with a single component indicate that there is no single factor controlling the concentration of dissolved as over the entire study area the only consistent feature is enrichment of as relative to fe in the groundwater compared to the sediments this suggests that the dissolution of fe minerals which primarily adsorb as is not congruent in reducing conditions fe iii oxyhydroxides together with adsorbed as dissolve and siderite with little or no as precipitates when sub regions are separated and studied individually it can be shown that hydrogeological features of the sediments the proportions of fe minerals and sedimentary organic matter and the concentration of dissolved humic materials all influence the accumulation and mobilization of as the significance of the different mobilizing processes however and the mean concentration of as is different in the recharge through flow and discharge areas

the composition of suspended matter from ganges brahmaputra sediment dispersal system during low sediment transport season abstract suspended matter supplied from the ganges brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load november december 1997 the absolute amount of suspended matter ranges between 500 mg l near the river mouth and chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source compositional changes are based on grain size partitioning quartz and heavy minerals are precipitating sooner leaving the suspended matter from the outer shelf depleted in quartz ree zr hf nb ta w u th y and ca the other part of the compositional changes is based on the reaction of suspended matter with seawater manganese hydroxide is producing coatings on suspended matter grains and adsorbing elements out of the seawater as a consequence enrichment of mn zn ni cr co li cs as sb pb tl and cd can be observed in the suspended matter from the outer shelf arsenic is accumulating on the inner shelf by a factor of 2 chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals more than 90 of the total arsenic is bound to nearly insoluble phases of the suspended matter e g crystalline iron oxides residual minerals for comparison with suspended matter adjacent surface sediments were sampled and analysed in this sediment the dominating phase is the one which settled down during the times of high suspended load with more quartz and heavy minerals and consequent chemical composition the enrichment of manganese oxide and adsorbed transition metals gets lost because of anaerobic conditions in the bottom near seawater they dissolve from the sediment and get recycled in seawater arsenic is found in nearly insoluble parts of the sediment as it is the case in the suspended matter