controls on mo isotope fractionations in a mn rich anoxic marine sediment gullmar fjord sweden abstract molybdenum isotopes have emerged as an important tool for determining the spatial extent of past ocean redox conditions however our understanding of mo cycling and associated isotopic fractionations in modern and ancient continental margin sediments is limited restricting attempts to fully utilize the potential of mo isotopes this is particularly the case with regard to the relative significance of mo isotope fractionations associated with biogeochemical mn and fe oxide cycling under conditions of low dissolved sulfide to rectify this we have investigated sediments from gullmar fjord sweden which contain high concentrations of mn oxides and exhibit a strong redox zonation between mn and fe reduction a combination of dissolved and particulate mo isotope measurements with porewater and solid phase mn and fe characterization reveals that the main influence on porewater 98 mo compositions is exerted by adsorption and desorption processes during reductive dissolution of both mn and fe oxyhydr oxide minerals in areas enriched in mn oxides distinctively low solid phase 98 mo values are observed 1 0 and 0 4 which occur due to the large mo isotope fractionation associated with mo adsorption to mn oxides however where mn oxide concentrations are lower authigenic 98 mo is largely controlled by fe oxyhydr oxide minerals resulting in more positive 98 mo isotopic compositions 0 5 and 2 our results suggest that for modern anoxic marine sediments where deposition occurs beneath an oxic to suboxic water column 98 mo is dominantly controlled by the relative availability of mn and fe oxides and the production of dissolved sulfide

the 1996 ad delta collapse and large turbidite in lake brienz abstract in spring 1996 ad the occurrence of a large mass transport was detected by a series of events which happened in lake brienz switzerland turbidity increase and oxygen depletion in deep waters release of an old corpse into surface waters and occurrence of a small tsunami like wave this mass transport generated a large turbidite deposit which is studied here by combining high resolution seismic and sedimentary cores this turbidite deposit correlates to a prominent onlapping unit in the seismic record attaining a maximum of 90 cm in thickness it is longitudinally graded and thins out towards the end of the lake basin thickness distribution map shows that the turbidite extends over 8 5 km2 and has a total volume of 2 72 106 m3 which amounts to 8 7 yr of the lake s annual sediment input it consists of normally graded sand to silt sized sediment containing clasts of hemipelagic sediments topped by a thin white clay sized layer the source area the exact dating and the possible trigger of this turbidite deposit as well as its flow mechanism and ecological impact are presented along with environmental data river inflow wind and lake level measurements the combined results indicate that no particular cause i e earthquake explosion flood wind storm lake level change seiche or sediment dredging triggered the 1996 ad large turbidite deposit instead it was due to a delta slope failure most likely caused by normal sediment accumulation

a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

toward direct micron scale xrf elemental maps and quantitative profiles of wet marine sediments 1 here we describe a chemical analysis technique for ca fe k sr ti and s using a recently developed micro xrf analyzer micro xrf with a 100 m resolution and an xrf whole core scanner xrf s with a 5 mm resolution for selected sediment sections from a continental margin sediment core the micro xrf produces highly resolved element maps of individual sections and the calculation of individual continuous element profiles is based on overlap measurements of successive sections by means of discrete subsamples analyzed by icp oes the two xrf data sets are successfully calibrated to provide quantitative profiles of ca fe k sr and ti we discuss the advantages and limitations of both xrf techniques a comparison of the two independent xrf data sets demonstrates the overall high consistency and accuracy of both techniques the resulting element profiles and detailed xrf maps clearly show that the micro xrf is a powerful tool for studying at high resolution the chemical transitions linked to paleoenvironmental changes for example the discrimination between provenance changes and diagenetical effects on the fe profile can be achieved by the combined inspection of the fe ti profile and s maps this highlights the usefulness of the xrf maps for clarification of profile ambiguities and clearly distinguishes the micro xrf from other technical devices producing elemental profiles only

a study of channel changes in a reach of the north nashwaaksis stream new brunswick canada repeated surveys of a short channelized reach of the north nashwaaksis stream near fredericton n b over the period 1971 1981 provide the basis for evaluating the type and magnitude of some physical and botanical changes in the study reach in 1967 a 200 m reach of the stream was shortened by about 10 per cent by cutting a new channel through a pasture the original channel was protected by a dense growth of shrubs along its banks the average width of the top of the channel in the channelized reach widened from 11 m to 17 m in response to a major flood in 1973 rough estimates indicate that as much as 78 per cent of the published suspended sediment load associated with the flood could reasonably have been derived from the banks in this short channelized reach during the 1973 flood a mid channel bar was formed in the portion of the channel which experienced the most widening subsequent to the flood the mid channel bar was first colonized by sedges and then by alders by 1981 the width of the low flow channel in the channelized reach was about the same as that for the unmodified upstream reaches this case study provides useful information for those planning channelization projects on small to intermediate size streams in humid temperate areas

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

computer aided design for channelization the bank protection and grade controls of a river channel must be designed to contain the design flood and extend below the potential riverbed scour because of the convoluted relationships governing the flow and sediment processes mathematical simulation becomes an effective means of evaluating channelbed scour under any flow pattern and design configuration channelization of the santa cruz river has been designed based upon the pattern of river channel responses simulated using a calibrated mathematical model scour and fill of the channel bed invoked by the longitudinal imbalance in sediment load are simulated they are also tied in with the effects of the streamwise variation in spiral motion that induces an uneven bed topography characterized by greater scour near the concave bank variable top and toe elevations for hydraulic structures have been determined and employed to make more efficient use of construction materials while providing effective protection against erosion the study demonstrate

channel bed adjustment along mine affected rivers of northeast tasmania forty million m3 and 1 million m3 of mining waste are estimated to have been supplied respectively to the ringarooma and george rivers between 1875 and 1984 given the volumes involved and the fact that much of the input was less than 5 mm in diameter the size composition of the bed material changed from gravel to sand as the rivers progressively aggraded their beds downstream increases in bed height of over 10 m and 1 m are predicted respectively for the two rivers with change becoming more gradual further downstream with upstream supplies becoming depleted first degradation followed the same pattern as aggradation progressing downstream maximum rates of almost 0 5 m yr 1 were measured degradation has returned the george river to its pre 1875 level but has yet to reach the downstream reaches of the ringarooma where sediment waves continue to pass over a slightly aggrading bed where degradation has been occurring long enough the bed material has again become gravelly through re exposure of the original bed and or lag concentration of coarser fractions within the introduced load such armouring should improve bed stability and slow the rate of degradation however at herrick which is representative of intermediate reaches with only a thin gravel veneer the annual amount of degradation is reasonably well correlated with flow conditions suggesting that high discharges can strip the surface armour and continue to degrade actively incision has not only changed the vertical position of the rivers but also their planimetric and cross sectional geometry in particular non uniform lowering of the bed has narrowed the channel by up to 60 changes which can be predicted quite accurately by chang s quantitative model of channel adjustment at least another 50 years will be needed for degradation to cleanse the ringarooma of mining debris

petrography and high resolution geochemical records of lower jurassic manganese rich deposits from monte mangart julian alps abstract deposits with unusually high mn contents sampled at monte mangart in the julian alps include organic rich marlstone and black shale with interbedded manganoan and siliceous limestone which were deposited during the early toarcian oceanic anoxic event mn enrichment during that period has been related to global sea level change coincident with increasing subsidence rate the formation of fe mn nodules marking a hardground at the base of the monte mangart section seems to be triggered by release of mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed however very high mn contents in carbonate phases above the hardground imply an additional diagenetic source of this element in the lower part of this section the whole stratigraphic sequence ca 30 m displays a transition from mn rich up to 8 8 sediments in the lower part to mn poor less than 1 8 sediments in the middle and upper parts the drastic decrease in mn content s up section is accompanied by a clear decrease in the mean size of pyrite framboids indicating more intense anoxia euxinia in the water column in the presence of mn2 conditions of high alkalinity induced precipitation of mn carbonates during early diagenetic processes negative 13ccarb values coincident with high mn contents indicate involvement of organic matter in the mineralization process the striking similarity of ce ce and mn profiles demonstrates that consistent with redox chemistry of mn and ce under anoxic conditions ce3 and mn2 were mobilized and released into pore water where precipitation of mn carbonates occurred

northeastern pacific oxygen minimum zone variability over the past 70 kyr impact of biological production and oceanic ventilation 1 during the last glacial period the oxygen minimum zone omz within the northeastern pacific ocean strengthened and weakened on a millennial time scale demonstrating a tight linkage with northern high latitude climate although the precise mechanisms responsible remain unknown core md02 2508 retrieved off baja california was analyzed for major and trace elements br ca ti fe mn and sr using a xrf scanner and redox sensitive trace elements cu ni cd as v cr mo and u using the icp ms the trace element content the fe ti ratio and br based organic carbon exhibit higher values during the holocene and during warm dansgaard oeschger events than during the last glacial maximum lgm stadials and heinrich h events a principal component analysis of the element al ratio indicated that the following two main factors controlled the chemical composition of the sediments 1 export production as represented by organic carbon that was lower during cold periods and 2 regional intermediate water oxygenation as represented by u and mo variability that was not supported by a change in export production the latter suggests that intermediate water oxygenation improved during h events but slightly deteriorated during late marine isotope stage mis 3 and mis 2 a local biogeochemical effect forced by atmospheric processes impacted the lgm and h events in the same manner whereas regional intermediate oceanic circulation varied in an opposite manner during the lgm and h events possibly as a result of the global reorganization of intermediate water circulation during the lgm

elemental c n ratios and isotopic δ15norg δ13corg compositions of sedimentary organic matter from a high altitude mountain lake meidsee 2661 m a s l switzerland implications for lateglacial and holocene alpine landscape evolution the deposition of late pleistocene and holocene sediments in the high altitude lake meidsee located at an altitude of 2661 m a s l in the southwestern alps strikingly coincided with global ice sheet and mountain glacier decay in the alpine forelands and the formation of perialpine lakes radiocarbon ages of bottom core sediments point out pre holocene ice retreat below 2700 m a s l at about 16 13 10 and 9 cal kyr bp the meidsee sedimentary record therefore provides information about the high altitude alpine landscape evolution since the late pleistocene holocene deglaciation in the swiss southwestern alps prior to 5 cal kyr bp the c n ratio and the isotopic composition of sedimentary organic matter 15norg 13corg indicate the deposition of algal derived organic matter with limited input of terrestrial organic matter the early holocene and the holocene climatic optimum between 7 0 and 5 5 cal kyr bp were characterized by low erosion decreasing magnetic susceptibility and high c

paleogene record of elemental concentrations in sediments from the arctic ocean obtained by xrf analyses we present a high resolution x ray fluorescence xrf core scanner record for the expanded middle eocene section from integrated ocean drilling program iodp expedition 302 acex drilled on the lomonosov ridge central arctic ocean the division of the middle eocene into two units subunit 1 6 and unit 2 is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment al ti and k strongly correlate throughout the record while the behavior of fe mn and si is more complex utilizing sediment geochemistry calibration to ground truth the xrf data we suggest the middle eocene arctic ocean was predominately euxinic although periodic oxygenation of bottom waters must have occurred during unit 2 49 7 45 4 ma initially the sediments are rich in biogenic silica unit 2 but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1 6 we report changes in the elemental concentrations of these elements and investigate the relationship between fe content and pyrite additionally we explore the potential change in paleoenvironmental conditions across the unit boundary

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

molybdenum isotope fractionation in pelagic euxinia evidence from the modern black and baltic seas here we present stable isotope data for vertical profiles of dissolved molybdenum of the modern euxinic water columns of the black sea and two deeps of the baltic sea dissolved molybdenum in all water samples is depleted in salinity normalized concentration and enriched in the heavy isotope 98mo values up to 2 9 compared to previously published isotope data of sedimentary molybdenum from the same range of water depths furthermore 98mo values of all water samples from the black sea and anoxic deeps of the baltic sea are heavier than open ocean water the observed isotope fractionation between sediments and the anoxic water column of the black sea are in line with the model of thiomolybdates that scavenge to particles under reducing conditions an extrapolation to a theoretical pure mos42 solution indicates a fractionation constant between mos42 and authigenic solid mo of 0 5 0 3 measured waters with all thiomolybdates coexisting in various proportions show larger but non linear fractionation the best explanation for our field observations is mo scavenging by the thiomolybdates dominantly but not exclusively present in the form of mos42 the mo isotopic compositions of samples from the sediments and anoxic water column of the baltic sea are in overall agreement with those of the black sea at intermediate depth and corresponding sulphide concentrations the more dynamic changes of redox conditions in the baltic deeps complicate the black sea derived relationship between thiomolybdates and mo isotopic composition in particular the occasional flushing mixing of the deep waters affects the corresponding water column and sedimentary data 98mo values of the upper oxic waters of both basins are higher than predicted by mixing models based on salinity variations the results can be explained by non conservative behaviour of mo under suboxic to anoxic conditions in the shallow bottom parts of the basin most pronounced on the nw shelf of the black sea

sediment transport modeling review current and future developments the use of computational models for solving sediment transport and fate problems is relatively recent compared with the use of physical models several considerations govern the choice between physical and computational models namely the nature of the problem that needs to be solved the available resources and the overall cost associated with the problem solution in some specific problems a combination of physical and computational models can be used to obtain a better understanding of the processes under investigation de vries 1973 using computational hydrodynamic sediment transport models in general involves the numerical solution of one or more of the governing differential equations of continuity momentum and energy of fluid along with the differential equation for sediment continuity an advantage of computational models is that they can be adapted to different physical domains more easily than physical models which are typically constructed to represent site specific conditions another advantage of computational models is that they are not subject to distortion effects of physical models when a solution can be obtained for the same flow conditions identical reynolds and froude numbers same length scale in the three directions etc as those present in the field with the rapid developments in numerical methods for fluid mechanics computational modeling has become an attractive tool for studying flow sediment transport and associated pollutant fate processes in such different environments as rivers lakes and coastal areas representative processes in these environments include bed aggradation and degradation bank failure local scour around structures formation of river bends fining coarsening and armoring of streambeds transport of point source and nonpoint

modeling of river channel changes a computer based flood and sediment routing model which simulates river channel changes is described together with its application in the case study of a disturbed river simulated results of this study are supported by field observations and measurements this model incorporates the interrelated changes in channel bed profile width and lateral migration in channel bends these changes reflect in part a river s adjustments in power expenditure the interrelation of changes in channel bed profile and width is illustrated by a physical example and explained by the river s tendency to establish equal power expenditure along the channel such power transformation associated with river channel evolution tends to restore the dynamic equilibrium in sediment transport that is equal sediment load along the channel the case study demonstrates that in the case of severely disturbed rivers flood level computation using a fixed bed model may be quite inaccurate and improved accuracy can be provided by an erod

tests of selected sediment transport formulas eleven existing sediment transport formulas were tested against the field data measured at two united states geological survey usgs gauging stations along the sacramento river in california whose bed material sizes are classified as those ranging from fine sand to coarse gravel they include the ackers white einstein brown engelund fredsoe engelund hansen inglis lacey karim meyer peter and mueller rijin schoklitsch toffaleti and yang formulas general flow and sediment input variables required by each transport function as well as dependent variables are summarized and detailed and measured hydraulic and sediment quantities including bed material size distributions are presented the computed sediment discharges are tabulated for comparison and are directly compared against the measured suspended sediment discharges the computed values however are found to deviate significantly from the measured values except for a very few cases the test results clearly demonstrate how difficult a ta

manganese rich brown layers in arctic ocean sediments composition formation mechanisms and diagenetic overprint we present inorganic geochemical analyses of pore waters and sediments of two late quaternary sediment cores from the western arctic ocean southern mendeleev ridge rv polarstern expedition ark xxiii 3 focussing on the composition and origin of distinct brown colored mn rich sediment layers carbonate enrichments occur in association with these layers as peaks in ca al mg al sr al and sr mg suggesting enhanced input of both ice rafted and biogenic carbonate for the first time we show that the mn rich layers layers are also consistently enriched in the scavenged trace metals co cu mo and ni distinct bioturbation patterns specifically well defined brown burrows into the underlying sediments suggest these metal enrichments formed close to the sediment water interface the geochemical signature of these metal and carbonate rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover both rivers and sea ice delivered trace metals to the arctic ocean while enhanced seasonal productivity exported reactive organic matter to the sea floor the coeval deposition of organic matter mn oxyhydr oxides and trace metals triggered intense diagenetic mn cycling at the sediment water interface these processes resulted in the formation of mn and trace metal enrichments and the degradation of labile organic matter with the onset of cooler conditions reduced riverine runoff and or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter resulting in deposition of grayish yellowish metal poor sediments oxygen depletion of arctic bottom waters under these cooler conditions is not supported by our data and did not cause the sedimentary mn distribution while the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes pore water data show that diagenetic mn redistribution is still affecting the organic poor deeper sediments given persistent steady state conditions purely authigenic mn rich brown layers may form while others may be partly or completely dissolved the degree of diagenetic mn redistribution largely depends on the depositional environment the mn and organic matter availability and apparently affected the co mo ratios of mn rich layers thus brown arctic layers are not necessarily synchronous features and should not be correlated across the arctic ocean without additional age control

changes in erosion patterns during the holocene in a currently treeless subalpine catchment inferred from lake sediment geochemistry lake anterne 2063 m a s l nw french alps the role of climate and human activities a high resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine lake anterne 2063 m a s l nw french alps spanning the last 10 ka sedimentation is mainly of minerogenic origin the organic matter quantity toc as well as its quality hydrogen hi and oxygen oi indices both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal bp during this phase the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record between 7850 and 5550 cal bp very low manganese concentrations suggest anoxic conditions in the bottom water of lake anterne these are caused by a relatively high organic matter terrestrial and lacustrine content a low flood frequency and longer summer stratification triggered by warmer conditions from 5550 cal bp a decrease in toc stabilization of hi and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils probably due to a colder and wetter climate then three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the bronze age and by increases in topsoil erosion relative to leptosols hi increases during the late iron age roman period and the medieval periods these periods are also characterized by higher sedimentation rates according to palynological data human impact deforestation and or pasturing activity probably triggered these periods of increased soil erosion

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

bromine counts from xrf scanning as an estimate of the marine organic carbon content of sediment cores 1 xrf sediment core scanning technology is increasingly used to quantify sediment composition the overall good correlation between biophilic halogen bromine br and sedimentary total organic carbon toc potentially allows the fast estimation of down core toc profiles by xrf scanning in order to test this approach we present data from the arabian sea and a mediterranean brine basin comparing xrf core scanning br data with discrete sample toc analyses overall br counts and toc show a clear correlation except when stable carbon isotope and c n data indicate intervals characterized by enhanced input of terrestrial organic matter hence solid phase br is exclusively associated with marine organic matter moc and can be used as a direct estimate of this parameter after a calibration is established high pore water br in the brine core steepens the br toc correlation but after salt correction shows a nearly identical gradient to that of the arabian sea core

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

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

river channel changes adjustments of equilibrium a method for predicting river channel s adjustments of equilibrium is presented and illustrated by examples this method is based upon the quantitative relationships among the variables of water di

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

sulfidity controls molybdenum isotope fractionation into euxinic sediments evidence from the modern black sea molybdenum mo isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry it is therefore fundamental to understand the processes controlling mo partitioning into modern marine environments this study identifies the availability of dissolved sulfide as the dominant control on overall mo removal from the water column in euxinic systems mo isotopic composition of surface sediments from different localities of the black sea demonstrates complete fixation of mo only below 400 m water depth above a critical concentration of 11 mol l 1 aqueous hydrogen sulfide in the bottom water the mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2 3 in contrast significant mo isotope fractionation into less euxinic sediments is evident at shallower depths in the black sea as well as in temporarily euxinic deeps of the baltic sea consistent with the observed lower maximum sulfide concentrations in the respective water columns therefore mo isotope signatures in the modern black sea constrain the processes responsible for global mo removal from the ocean by euxinic sediments furthermore models of past ocean anoxia reconstruction have to consider that the seawater mo isotopic composition is not per se archived in euxinic sediments

kinetic and thermodynamic factors controlling manganese concentrations in oceanic waters abstract data are presented describing the changes in the distribution of dissolved and particulate mn observed over a 16 month period in the periodically anoxic waters of saanich inlet a fjord located on the coast of vancouver island british columbia during the spring and summer when the bottom waters were anoxic a dense cloud of particulate mn was found at mid depths where mn 2 enriched anoxic bottom waters were mixing with oxygenated waters then during the autumn aand winter following an intrusion which reoxygenated the bottom water an intense precipitation of mn was observed throughout the entire water column during this latter period dissolved mn concentrations in the bottom water which exceeded 1000 nmol l under anoxic conditions decreased towards a lower limit of 1 6 nmole l a value comparable to that observed in pacific ocean waters of similar ph and dissolved oxygen content mn in the particulate matter collected just above the oxic anoxic interface was found to have an average oxidation number of 3 05 and on this basis it is proposed that dissolved mn concentrations in oceanic waters are controlled by the precipitation of the metastable oxide mineral manganite mnooh a hypothesis consistent with the fact that dissolved mn values in subsurface pacific ocean waters closely approach the equilibrium solubility of this phase temporal and spatial gradients in the particulate mn distribution were used to calculate the in situ rate of mn precipitation and the results of these calculations then were fitted to theoretical rate equations which suggest that the precipitation of mn is controlled by 2 parallel processes bacterial oxidation and an inorganic autocatalytic oxidation reaction

the sedimentary response to a pioneer geo engineering project tracking the kander river deviation in the sediments of lake thun switzerland human activities such as river corrections and deviations lake level regulations and installations of hydropower plants affect and often strongly modify natural processes in lacustrine systems in 1714 the previously bypassing kander river was deviated into peri alpine lake thun this pioneering geo engineering project the first river correction of such dimensions in switzerland doubled the water and sediment input to the lake in order to evaluate the sedimentary consequences of the kander river deviation the lacustrine sediments were investigated using a combined approach of high resolution 3ae5 khz reflection seismic data and sediment cores maximum length 2ae5 m the significance of this study is increased by the possible hazard represented by ammunition dumped into the lake from 1920 to 1960 and by the recent installation of a gas pipeline on the lake floor in 2007 2008 the first 130 years after the river deviation were dominated by an extremely high sediment input which led to the frequent occurrence of subaquatic mass movements slope failures primarily occur due to rapid sediment accumulation but were occasionally triggered in combination with earthquake induced shocks and lake level fluctuations after 1840 massmovement activity and sedimentation rates decreased due to a reduced sediment input as the kander river adjusted to its new base level and to a smaller degree by further engineering of the kander river bed and gravel withdrawal at the kander delta a further consequence of the kander river deviation is that the shores around lake thun have been more frequently affected by flooding due to the increased water input in the time span from 1850 to 2006 six historically and or instrumentally documented flood events could be correlated to flood turbidites in the sediment cores this study demonstrates the significant usefulness of lacustrine sediments not only in archiving natural hazards and human impact but also in assessing the consequences of future anthropogenic interventions on lacustrine systems

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

geochemical and sedimentological evidence of productivity cycles recorded in toarcian black shales from the belluno basin southern alps northern italy abstract organic carbon rich black shales cyclically alternating with bioturbated limestones and gray marlstones which crop out in the belluno trough southern alps italy are expression of the early toarcian anoxic event in the tethys basin sedimentological and geochemical features such as well developed lamination common very small a negative 13c excursion at the middle part of the studied interval is correlative to maxima in toc v rb and ba rb values identifying within the toarcian anoxic event a stage of more intense bottom water anoxia coupled with high surface fertility

combining sedimentological trace metal mn mo and molecular evidence for reconstructing past water column redox conditions the example of meromictic lake cadagno swiss alps here we present sedimentological trace metal and molecular evidence for tracking bottom water redox state conditions during the past 12 500 years in nowadays sulfidic and meromictic lake cadagno switzerland a 10 5 m long sediment core from the lake covering the holocene period was investigated for concentration variations of the trace metals mn and mo xrf core scanning and icp ms measurements and for the presence of anoxygenic phototrophic sulfur bacteria carotenoid pigment analysis and 16s rdna real time pcr our trace metal analysis documents an oxic intermediate sulfidic redox transition period beginning shortly after the lake formation similar to 12 5 kyr ago the oxic period is characterized by low sedimentary mn and mo concentrations as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria enhanced accumulation preservation of mn up to 5 6 wt in the sediments indicates an intermediate mn enriched oxygenation state with fluctuating redox conditions during a similar to 2300 year long transition interval between similar to 12 1 and 9 8 kyr bp we propose that the high mn concentrations are the result of enhanced mn2 leaching from the sediments during reducing conditions and subsequent rapid precipitation of mn oxyhydr oxide minerals during episodic and short term water column mixing events mainly due to flood induced underflows at 9800 130 cal yr bp a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of mo in the sediments up to 490 ppm accompanied by an abrupt drop in mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column persistently high mo concentrations 80 ppm provide evidence that sulfidic conditions prevailed thereafter until modern times without any lasting hypolimnetic ventilation and reoxygenation hence lake cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over similar to 12 kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment possibly depicting analogous conditions in an ancient ocean our study underscores the value of combining sedimentological geochemical and microbiological approaches to characterize paleo environmental and redox conditions in lacustrine and marine settings

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed