paired dissolved and particulate phase cu isotope distributions in the south atlantic abstract copper cu is both an essential micronutrient and toxic to photosynthesizing microorganisms at low concentrations its dissolved vertical distribution in the oceans is unusual being neither a nutrient type nor scavenged type element this distribution is attributed to biological uptake in the surface ocean with remineralisation at depth combined with strong organic complexation by dissolved ligands scavenging onto particles and benthic sedimentary input we present coupled dissolved and particulate phase cu isotope data along the uk geotraces south atlantic section alongside higher resolution dissolved and particulate phase cu concentration measurements our dissolved phase isotope data contribute to an emerging picture of homogeneous deep ocean 65cu at about 0 65 relative to nist srm 976 we identify two pools of cu in the particulate phase a refractory lithogenic pool at about 0 and a labile pool accessed via a weak acidic leach at about 0 4 these two pools are comparable to those previously observed in sediments we observe deviations towards lighter 65cu values in the dissolved phase associated with local enrichments in particulate cu concentrations along the continental slopes and in the surface ocean copper isotopes are thus a sensitive indicator of localised particle associated benthic or estuarine cu inputs the measurement of cu isotopes in seawater is analytically challenging and we call for an intercalibration exercise to better evaluate the potential impacts of uv irradiation storage time and different analytical procedures

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

copper isotope fractionation in sedimentary copper mineralization timna valley israel abstract copper isotopes 65 cu 63 cu are potentially powerful new geochemical proxies for oxidation reduction processes and metallic cycling this research presents a cu isotope study of mineralization in historically mined stratiform sediment hosted copper ssc ore deposits of the precambrian and cambrian rocks of the timna valley southern israel these deposits provide a natural laboratory for studying isotopic fractionations between cu sulphides and cu ii minerals copper carbonates hydroxides and silicates formed during sequential cycles of low temperature alteration of igneous copper porphyries marine sedimentary diagenesis and epigenetic mobilization in sandstones isotopic measurements were made using mc icp ms after ion chromatographic separation of the copper from matrix elements in accord with abiogenic experimental studies showing that there should be a negative isotopic fractionation between reduced and oxidized copper minerals 65 cu values of cu sulphides are significantly lower 3 4 to 1 2 than coexisting cu ii carbonates and hydroxides 1 2 to 0 5 cu ii silicates which should only show a very small isotopic fractionation relative to parent cu ii solutions give average 65 cu values of 0 09 0 24 consistent with the fact that the primary source of sedimentary copper was the precambrian igneous rocks isotopic zoning profiles in cu sulphides of the cambrian dolomites suggest they were formed through the interaction of small disconnected cu solution reservoirs with h 2 s formed by bacterial reduction of sulphate containing pore waters mass balance modeling based on the measured cu isotope compositions and experimental fractionation factors shows that the main copper reservoir is the cambrian sandstone shale sequence and that the cu sulphide reservoirs are relatively small thus most of the copper transport occurred in relatively oxidized conditions the calculated reservoir sizes are in agreement with field observations and confirm that copper isotopes are able to trace both the oxidation reduction cycles and mass transfer during sedimentary copper mineralization

zn sr isotope records of the ediacaran doushantuo formation in south china diagenesis assessment and implications abstract recent studies show that zinc isotopes could provide valuable clues to environmental change and biogeochemical cycle of the past oceans this study reports a modified procedure for leaching the carbonate fractions in sedimentary rocks a thorough evaluation of diagenetic effects and systematic variations of zn and sr isotope ratios in lower part of the ediacaran stratigraphic unit deposited in the aftermath of the marinoan glaciation in south china the influence of post depositional diagenesis on zn isotope compositions of the studied samples is assessed by comparing 66zn to other geochemical indexes 87sr 86sr 13c 18o and mn sr ratios in the five studied cap carbonate sections member i of the doushantuo formation dolostones from four sections have 66zn values positively correlated with 18o values and negatively correlated with 87sr 86sr ratios 0 7081 0 7204 these correlations suggest that these cap dolostone samples have been modified by post depositional diagenesis the light 66zn value 0 02 suggests that initial zn isotope ratios of cap dolostones could have been reset by hydrothermal fluids with relatively high zn concentration and low 66zn values by contrast carbonates from member ii of the doushantuo formation above cap dolostones are relatively pristine based on their low 87sr 86sr ratios 0 7079 0 7086 being indistinct from the proposed early ediacaran seawater 87sr 86sr values chemical and isotopic variations in these samples are interpreted to reflect primary signals that record paleo environmental changes of the early ediacaran ocean a rapid increase of 66zn from 0 3 to 1 1 occurs in the middle part of member ii accompanying by relatively invariant 87sr 86sr ratios that imply insignificant changes in input from continental weathering considering the limited change in atmospheric oxygen during this period the rapid 66zn raise indicates an increase in buried organic matters which is consistent with the coupled positive shift of 13ccarb as well as the fossil records found in the same strata these results provide insights into zn cycling in the post marinoan oceans and facilitate the application of zn isotopes in carbonates as a proxy for the fate of marine organic matter

a new purification method for ni and cu stable isotopes in seawater provides evidence for widespread ni isotope fractionation by phytoplankton in the north pacific abstract nickel and copper are cofactors in key phytoplankton enzymes and the stable isotope composition of ni and cu 60ni and 65cu in seawater have the potential to identify major processes that influence their biogeochemistry however accurate analysis of 60ni and 65cu is challenging because of the difficulties in separating these metals from interfering elements in the seawater matrix here we report a fast and simple method for purification of ni and cu from seawater samples that is able to completely remove interfering elements mn ti cr and fe this method was verified by analyzing four reference materials that contain significant levels of interfering elements powdered plankton natural soils and two marine sediments using this technique we generated a dataset of 49 seawater 60ni and 65cu measurements from the upper water column of the north pacific ocean which show preferential uptake of light ni isotopes by phytoplankton bio sw 0 9997 1 but no net fractionation of cu isotopes this new method simplifies treatment of seawater samples for ni and cu isotope analysis enabling high throughput investigations of 60ni and 65cu throughout the global ocean

three dimensional modeling of negatively buoyant flow in diverging channels diverging channels also known as diffusers represent common natural and industrial outlets to lakes reservoirs and rivers if the outflow in a diffuser has a larger density than the ambient water the inflow may plunge and form a density underflow in this paper a three dimensional numerical study was conducted to gain insight into the mechanism of negatively buoyant flows in diffusers with a sloping bottom of particular interest is the formation of separated flows such as wall jet and free jet flows various cases of plunging and the associated density current in a diffuser with different divergence angles and inflow densimetric froude numbers are considered the model successfully simulates the formation of attached flow wall jets and free jets in a negatively buoyant environment the onset evolution and stabilization of a stall and the subsequent development of a wall jet in a negatively buoyant flow are investigated in detail computed results also show favorable agreement with some published experimental data on density current generated by the plunging of cold water in ambient warm water in a diverging channel

the estuarine geochemical reactivity of zn isotopes and its relevance for the biomonitoring of anthropogenic zn and cd contaminations from metallurgical activities example of the gironde fluvial estuarine system france abstract zinc stable isotopes measurements by mc icp ms validated by laboratory intercalibrations were performed on wild oysters suspended particles and filtered river estuarine water samples to provide new constraints for the use of zn isotopes as environmental tracers the samples selected were representative of the long range 400 km transport of metal zn cd etc contamination from former zn refining activities at decazeville i e 66 zn 1 and its phasing out recorded during 30 years in wild oysters from the gironde estuary mouth rno rocch sample bank the study also addresses additional anthropogenic sources urban and viticulture and focuses on geochemical reactivity of zn in the turbidity gradient and the maximum turbidity zone mtz of the fluvial gironde estuary in this area dissolved zn showed a strong removal onto suspended particulate matter spm and progressive enrichment in heavy isotopes with increasing spm concentrations varying from 66 zn 0 02 at 2 mg l to 0 90 at 1310 mg l these signatures were attributed to kinetically driven adsorption due to strongly increasing sorption sites in the turbidity gradient and mtz of the estuary oysters from the estuary mouth contaminated sediments from the lot river and spm entering the estuary showed parallel historical evolutions 1979 2010 for zn cd ratios but not for 66 zn values oysters had signatures varying from 66 zn 1 43 in 1983 to 1 18 in 2010 and were offset by 66 zn 0 6 0 7 compared to past 1988 and present spm from the salinity gradient isotopic signatures in river borne particles entering the gironde estuary under contrasting freshwater discharge regimes during 2003 2011 showed similar values 66 zn 0 35 0 03 1sd n 15 i e they were neither related to former metal refining activities at least for the past decade nor clearly affected by other anthropogenic sources therefore the zn isotopic signatures in gironde oysters reflect the geochemical reactivity of zn in the estuary rather than signatures of past metallurgical contaminations in the watershed as recorded in contaminated river sediments the study also shows that the isotopic composition of zn is strongly fractionated by its geochemical reactivity in the gironde estuary representative of meso macrotidal estuarine systems

cu isotope variations between conduit and sheet style ni cu pge sulfide mineralization in the midcontinent rift system north america abstract disseminated ni cu pge sulfide mineralization in sheet like intrusions of the duluth complex are characterized by elevated bulk rock cu ni ratios typically in the range of 3 to 8 in order to evaluate whether the addition of crustal cu to parental magmas may have contributed to the high cu ni ratios cu isotope ratios were measured from sulfide minerals in the disseminated mineralization found within the sheet style partridge river and south kawishiwi intrusions of the duluth complex as well as sulfide mineralization in geometrically distinct conduit style deposits in the eagle intrusion and tamarack igneous complex these intrusions were emplaced during early stages of rift evolution 1110 1105 ma from picritic parental magmas with associated mineralization characterized by lower cu ni ratios in addition cu isotope ratios were determined from sulfidic and carbonaceous sedimentary country rocks to the intrusions 65cu values of disseminated sulfide mineralization in intrusions of the duluth complex range from 0 85 to 0 45 whereas values from the eagle intrusion and the tamarack igneous complex range from 0 69 to 1 84 65cu values of the sedimentary rocks range from 0 33 to 1 18 with two samples showing higher values of 2 65 and 3 12 the 65cu values of the duluth complex mineralization is consistent with the assimilation of significant amounts of sedimentary cu only if the 65cu value of the parental mantle derived magma was lower than 0 25 a value less than that proposed for the mantle based on analyses of terrestrial mafic igneous rocks the distinct difference in 65cu values between the sheet style and conduit style mineralization suggests that either mantle sources of the parental magmas in the rift differed or that cu isotope fractionation accompanied magmatic processes i e variable degrees of melting and sulfide retention sulfide liquid fractionation that were responsible for the relative enrichment of cu in the sheet style intrusions of the duluth complex

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

copper and zinc isotope systematics of altered oceanic crust at iodp site 1256 in the eastern equatorial pacific this paper presents the first combined cu and zn isotopic study of altered oceanic crust aoc at iodp hole 1256d that penetrates a volcanic section a lava dyke transition zone a sheeted dyke complex and a plutonic complex in the volcanic section all but one rocks have cu and zn isotopic compositions similar to fresh mid ocean ridge basalt morb reflecting restricted seawater circulation and low oxygen fugacity rocks in the transition zone have morb like 65cu and 66zn indicating the dominant influence of basalt derived cu and zn during alteration rocks in the dyke complex have more variable 65cu 0 50 0 90 and 66zn 0 19 0 55 and those in the plutonic complex have 65cu of 0 43 to 0 20 and 66zn of 0 21 to 0 41 the rocks with heavier 66zn and heavier or lighter 65cu relative to morb are characterized by cu zn depletions low li yb 1 0 and low 18o 5 suggesting that hydrothermal extraction during high temperature alteration of oceanic crust can result in significant cu and zn isotope fractionation such large cu and zn isotopic variations are the results of redox transformation of cu as well as cu and zn isotope fractionation between altered basaltic rocks and dissolved cu and zn species in hydrothermal fluids e g cucl3 1 zn hs 42 this work is the first to define the distribution of cu and zn isotopes in an intact oceanic crust with concentration weighted averages of 65cu 0 05 0 03 and 66zn 0 27 0 01 the potential implications of these new observations are discussed

evidence for basaltic volcanism on the moon within the past 100 million years the majority of basaltic volcanism on the moon occurred more than 3 billion years ago small mounded formations on the lunar nearside may be products of basaltic eruptions less than 100 million years ago suggesting a long decline of magmatic activity

the influence of flow inertia buoyancy wind and flow unsteadiness on mixing at the asymmetrical confluence of two large rivers summary the rates and patterns of mixing of two large rivers with large density differences at a strongly asymmetrical confluence in northern spain are analyzed we assess the factors controlling the site where the denser river plunges and the mixing rates between the rivers in particular we focus on the interaction between inertial and buoyancy forces the effect of wind forcing and the unsteady nature of the hydraulic forcing the steady state location of the plunge line is shown to be controlled by an inertia buoyancy balance which accounts for the relative magnitude of the buoyancy forcing associated with density differences between the confluent rivers and the magnitudes of both the main stream and the side flow tributary inertia the plunge line moves to upstream locations as the inertia of the tributary increases for low tributary inertia and or the density contrast between the rivers increases this has important consequences for river mixing since mixing rates increase as the plunging occurs at the confluence the high mixing rates in this case occur as a result of a large mixing interface surface area and high diffusivities as the plunging area moves upstream or downstream of the confluence vertical diffusivities or the area of contact available for mixing decrease and constrain mixing rates wind forcing depending on its velocity and direction affects mixing rates through 1 altering the buoyancy inertia equilibrium and so changing the location of the plunge line 2 altering the pattern of secondary circulation within the confluence and or 3 increasing shear at the confluence flow unsteadiness can lead to changes in the location of the plunge line through time and thus can strongly modify mixing rates at the confluence the downstream movement of the plunge line is advection dominated while its upstream movement seems to respond to a baroclinic response of the confluence

mercurian impact craters implications for polar ground ice abstract recent radar observations of mercury have detected strong depolarized echoes from the north and south polar regions which have been interpreted by some as ice deposits in the floors of permanently shadowed impact craters we have used the experience from mars where subsurface ice lowers the depth to diameter ratio d d of impact craters to test for subsurface ice deposits on mercury this analysis determines the d d ratios for 170 impact craters in the borealis north polar tolstoj equatorial kuiper equatorial and bach south polar quadrangles of the planet possible effects from sun angle and terrain were eliminated to test whether d d differences could be detected at mariner 10 resolutions 1 km pixel we perform a similar analysis using mariner 9 images of mars which have similar resolutions we demonstrate that d d differences due to terrain softening can be detected between craters in the martian polar regions and the equatorial regions at the mariner 9 resolutions although our initial results indicate that the south polar bach quadrangle has a statistically lower d d than the north polar borealis or two equatorial tolstoj and kuiper quadrangles further investigation reveals that this finding is most likely the result of the filtering which was applied to the images of the bach quadrangle by jpl thus no unequivocal evidence exists that the possible ice deposits in craters at mercury s north and south poles are the exposed portions of more extensive subsurface ice caps combined with the temporal constraint imposed by the fact that the proposed ice deposits are found only in usgs class 4 craters this suggests a large rapidly emplaced exogenic source of water to mercury during the mansurian period we suggest that the source was multiple impacts from a fragmented comet or a comet shower

on the mixing of rivers with a difference in density the case of the negro solimoes confluence brazil abstract confluences are common components of all riverine systems and characterized by converging streamlines and potential mixing of separate flows the fluid dynamics of confluences possess a highly complex structure with several common types of flow features observed an investigation was carried out in both low and relatively high flow conditions at the confluence of the negro and solimoes rivers brazil which ranks among the largest river junctions on earth during this field research acoustic doppler velocity profiling adcp and water quality sampling were applied to investigate hydrodynamics sediment transport and mixing characteristics at this confluence it was found that the location and the width of the mixing interface were closely related to changes of the discharge ratio between the tributaries due to both seasonal and annual variations second a timescales analysis was applied to comparatively identify the contribution to mixing at the negro solimoes confluence of four processes difference in 1 velocity and 2 density between the rivers 3 bed friction including form drag and 4 change in channel width the analysis demonstrated that adjustments of confluence hydrodynamics and morphodynamics can modify the relative importance of each contribution immediately downstream of the junction the effects of differences in velocity and density were comparable while farther downstream the latter was predominant and the role of bed friction was significant at the end this study suggests that mixing at the negro solimoes confluence can be explained as a combination of the four hydrologic and morphologic processes

modern and paleofluid pathways revealed by cu isotope compositions in surface waters and ores of the pebble porphyry cu au mo deposit alaska copper isotope ratios measured in minerals and shallow groundwater and surface waters provide insight into high temperature mineralization and active weathering processes at the pebble porphyry cu au mo deposit alaska the west zone of the deposit contains hypogene mineralization with a supergene overprint and a thin oxide leached capping whereas the contiguous east zone contains only hypogene mineralization sulfide rich rock powders and mineral separates have 65cu values that range from 0 78 to 2 28 hypogene west 0 02 to 1 55 hypogene east 3 49 to 1 88 oxide west and 5 04 to 1 27 supergene west the results from hypogene samples show that there is a systematic increase in 65cu values from deeper to shallower portions of the deposit furthermore the 65cu values correlate with silicate alteration assemblages mostly positive values correspond to quartz illite pyrite sericite and quartz pyrophyllite alteration zones which formed at relatively lower temperatures whereas negative values characterize the higher temperature potassic and sodic potassic domains this empirical evidence could indicate that fractionation of cu isotopes during hypogene alteration is controlled by ph and or temperature variations shallow surface waters proximal to the deposit and which likely interacted with underlying concealed mineralization have heavy 65cu values which contrast with lighter values in waters distal from the deposit patterns measured in the copper isotope ratios of both solids and surface waters demonstrate the potential use of copper isotope distribution as a vectoring tool in mineral exploration and aid in understanding the sources of copper in the surface and near surface environments

small craters population as a useful geological investigative tool apollo 17 region as a case study abstract small craters below a few decametres in diameter are ubiquitous on the lunar surface and numbered in billions thanks to the expanding availability of global high resolution imagery their size frequency distribution has increasingly been employed as an investigative tool to derive relative or even absolute age estimations of resurfacing events within small regions of geological interest based on a combined survey of tens of thousands of craters this work investigates the 7 50 meter crater distributions across a wide range of lunar terrains centred around the apollo 17 exploration region data analysis using a wide array of approaches reveals distribution patterns consistent with a complex geochronological scenario confirming crater tycho as the source of the main secondary surge which was followed by seismic led modification of the small crater population within the taurus littrow valley and a possible more recent arrival of small secondaries from the fabbroni impact some 70 km to the south this study also confirms that applying standard absolute model ages fits to small craters size frequency distributions to estimate resurfacing ages will only work for surfaces no older than a few tens of ma using an application of monte carlo simulations of crater degradation based on diffusion equations we matched the cumulative sfd of each area to derive size dependent diffusivity rates the results produce equilibrium age estimates that vary among the proposed geological units and crater sizes between 10 and 100 m in diameter this work concludes that the distribution of small craters does not appear to be stochastic in terms of relative size representation and their use for mapping surface variations in terms of physical properties represents a new tool in the remote sensing investigation of planetary surfaces

molecular controls on cu and zn isotopic fractionation in fe mn crusts abstract the isotopic systems of the transition metals are increasingly being developed as oceanic tracers due to their tendency to be fractionated by biological and or redox related processes however for many of these promising isotope systems the molecular level controls on their isotopic fractionations are only just beginning to be explored here we investigate the relative roles of abiotic and biotic fractionation processes in controlling modern seawater cu and zn isotopic compositions scavenging to fe mn oxides represents the principal output for cu and zn to sediments deposited under normal marine oxic conditions using fe mn crusts as an analogue for these dispersed phases we investigate the phase association and crystal chemistry of cu and zn in such sediments we present the results of an exafs study that demonstrate unequivocally that cu and zn are predominantly associated with the birnessite mno2 phase in fe mn crusts as previously predicted from sequential leaching experiments e g koschinsky and hein 2003 the crystal chemistry of cu and zn in the crusts implies a reduction in coordination number in the sorbed phase relative to the free metal ion in seawater thus theory would predict equilibrium fractionations that enrich the heavy isotope in the sorbed phase e g schauble 2004 in natural samples fe mn crusts and nodules are indeed isotopically heavy in zn isotopes at 1 compared to deep seawater at 0 5 consistent with the predicted direction of equilibrium isotopic fractionation based on our observations of the coordination environment of sorbed zn further 50 of inorganic zn is chloro complexed the other 50 is present as the free zn2 ion and complexation by cl is also predicted to favour equilibrium partitioning of light zn isotopes into the dissolved phase the heavy zn isotopic composition of fe mn crusts and nodules relative to seawater can therefore be explained by an inorganic fractionation during uptake however cu in fe mn crusts is isotopically light at 0 3 to 0 5 compared to the dissolved phase in seawater at 0 9 we suggest that this is because dissolved cu in the oceans is overwhelmingly complexed to strong organic ligands which are better competitors for the heavy isotope

numerical simulation of three dimensional time averaged flow structure at river channel confluences current confluence research emphasizes three broad controls on flow structure generation 1 planform curvature 2 topographic steering and 3 anisotropic turbulence associated with flow separation and shear layer dynamics the relative importance of these processes in explaining observed flow structures is controversial a situation that may be related to the fact that different investigators have examined different confluence configurations this paper uses a three dimensional numerical model with a fully elliptic solution a free surface treatment and a turbulence model based on a renormalized group rng to help to provide a physically based explanation of the controls upon flow structure generation for both a laboratory rectangular and a field confluence the confluence of the kaskaskia river and copper slough and to identify the particular conditions under which particular flow structures are observed results suggest that an analogy with back to back meanders is possible for symmetrical configurations but that there will be progressive divergence from this state as confluence asymmetry increases in asymmetric situations a dual cell structure may be limited to the immediate vicinity of the junction because of the effects of streamline curvature and topographic steering these differences can be explained by consideration of the dynamic pressure field which may be specific to each confluence configuration as such this study partially reconciles differing views over what controls time averaged flow structures in river channel confluences although further research into the interaction of these processes with instantaneous velocity fluctuations is required

causes of rapid mixing at a junction of two large rivers rio parana and rio paraguay argentina 1 airborne and satellite observations show that when large rivers join they can take hundreds of kilometers to mix completely but on occasion may mix very rapidly application of established semitheoretical analyses shows that long mixing lengths should be expected the first measurements of mixing processes at a large river junction rio parana and rio paraguay argentina combined width 2 8 km are presented at two occasions first when they mix in 400 km and second when mixing is complete in only 8 km downstream of the junction for the case of slower mixing at a point surveys showed that mixing driven by turbulent shear associated with a near vertical shear layer was restricted to close to the junction to 0 272 multiples of the postconfluence width downstream transect surveys showed penetration of more turbid water from the rio paraguay underneath the rio parana but this was insufficient to promote more rapid mixing there was no clear channel scale circulation present and slow mixing was compounded by reverse topographic forcing on the mainstream rio parana side of the river this kept more turbid water on the rio paraguay side of the river close to the bed in the case of rapid mixing we found clear channel scale circulation the momentum ratio between the combining flows reinforced the effects of the discordance in bed height between the tributaries at the confluence and allowed penetration of more turbid rio paraguay water further across the channel width deeper within the flow the importance of the interaction between momentum ratio and bed morphology at channel junctions makes mixing rates at the confluence dependent upon basin scale hydrological response which is more likely to differ between large confluent rivers than small rivers as a result of the different climatic topographic zones that they may capture

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

chromium fluxes and speciation in ultramafic catchments and global rivers abstract the role of ultramafic rock weathering in global chromium cr budgets and how these may be linked to changes in earth s climate over geological time was investigated by compiling dissolved cr speciation and fluxes in i 73 of the worlds large rivers representing 35 of global river discharge to oceans and in ii an ultramafic catchment putah creek watershed in the california coast range mountains usa weathering of ultramafic rocks creates ideal conditions for cr release and redox cycling alkaline river water draining ultramafic catchments is naturally enriched in cr up to 582 nmol l chromium concentrations increase with the extent of rock water interaction as indicated by correlations with mg and hco3 concentrations and ph whereas cr cycling depends on the availability of electron donors and acceptors e g fe ii organics mn iii iv oxides thus dissolved cr is exported from ultramafic watersheds as both the soluble hexavalent cr vi species mgcro4 cro42 and also as trivalent cr iii species croh co3 22 cr oh 3 the latter cr iii species were previously thought to have low solubility ultramafic catchments have higher area normalized cr and major ion fluxes for a given runoff when compared to global rivers and may thus have a disproportional impact on global cr budgets long term carbon cycling and moderation of the earth s climate over million year timescales riverine export fluxes of cr are linearly correlated with fluxes of ca mg and alkalinity in both ultramafic catchments and global rivers this suggests that silicate weathering is a key control on cr fluxes and that major element weathering fluxes may be a useful proxy for estimating cr and other trace element fluxes globally present day riverine dissolved cr fluxes to oceans are spatially variable and estimated to be 1 7 109 mol yr three times higher than previously reported however when geochemical reactions in estuaries are considered riverine cr fluxes may be lower throughout earth history cr weathering fluxes also may have varied with changes in the global distribution of ultramafic rocks cr concentrations in continental rocks or climactic conditions e g atmospheric co2 levels or runoff such variation should be considered when interpreting both modern and past cr seawater isotopic compositions and residence times

total dissolved zinc in the upper water column of the subarctic north east pacific abstract total dissolved zn concentrations are reported for winter and summer along the e w line p transect and for summer along s n line z transect extending from ocean station papa osp 50 n 145 w to the respective shelf waters surface water 10 m concentrations ranged from 0 04 nm in the open ocean to 0 9 nm at the canadian shelf station a clear gradient is evident with dissolved zn concentrations decreasing with increasing distance from shore along the e w transect in both summer and winter no consistent trend was observed along the s n transect low concentrations of zn 0 05 0 07 nm were observed in near surface water at osp in winter the vertical distribution of dissolved zn is oceanographically consistent showing a silicon like vertical profile concentrations of silicic acid and dissolved zn at depth are higher than those at equivalent depths in the atlantic as expected from deep water circulation patterns and build up in concentration of these elements dissolved zn si ratios in the upper 200 m indicate a trend of decreasing with distance from shore which infers a decoupling between dissolved zn and silicic acid in the upper ocean we hypothesise that the silicon like profile of dissolved zn is a result of recycling from relatively biologically resistant organic particulate phases that leads to profiles very similar to those of dissolved silicon other than at two stations where there is very high primary production there is no apparent horizontal relationship between total dissolved zn and chlorophyll a or production

anthropogenic sources and biogeochemical reactivity of particulate and dissolved cu isotopes in the turbidity gradient of the garonne river france abstract high precision mc icp ms cu isotope measurements were performed on suspended particulate matter spm and filtered water sampled along the turbidity gradient of the fluvial gironde estuary garonne branch following a summer lasting period of low freshwater discharge high cu concentrations up to 200 g g in particulate organic carbon poc rich up to 14 particles upstream from the maximum turbidity zone mtz coincide with the most negative 65 cu values down to 0 39 this suggests the preferential uptake of light cu isotopes by phytoplankton or anthropogenic contamination from cuso 4 fungicides related to intensive wine farming in the area 65 cu 0 37 for vineyard soils suspended particulate matter samples in the mtz exhibit lower cu concentrations 35 g g and heavier isotopic compositions 65 cu 0 20 in average as recorded by other samples from the gironde watershed along the fluvial estuary dissolved cu is mostly enriched in heavy isotopes up to 65 cu 0 21 but negative signatures down to 65 cu 0 66 occur near the city of bordeaux release of dissolved cu was attributed to the mineralization of organic matter with a total addition of 600 ng l in the fluvial estuary continuously decreasing amounts of dissolved cu added with distance suggest that the observed cu release evolved towards completion in the mtz and contributed to negative values for dissolved cu isotopes as modeled by a rayleigh process urban wastewater effluents probably also contribute to both i the dissolved cu addition 10 20 in the mtz and ii negative cu isotope signatures further work is necessary to assess the respective roles of anthropogenic sources and biogeochemical fractionation processes accordingly the present study provides new insights into the potential of cu isotopes for fingerprinting sources and mechanisms involved in the biogeochemical cycle of cu in temperate aquatic environments impacted by anthropogenic activities

influence of wind and lake morphometry on the interaction between two rivers entering a stratified lake the interaction of two rivers flowing into coeur d alene lake united states was investigated with a field experiment and three dimensional numerical simulations the focus was on the influence of basin morphology wind speed and wind direction on the fate and transport of the inflowing water data from the field campaign showed that intrusions from the two rivers propagated into the lake at different depths with the trace element polluted coeur d alene river flowing into the lake above the trace element poor and nutrient rich st joe river inflow the inflows initially intruded horizontally into the lake at their level of neutral buoyancy and later mixed vertically model results revealed that as the intrusions entered the main lake basin a forced horizontal mode two basin scale internal wave interacted with the intrusions to frequently siphon them into the lake proper and where rapid vertical mixing followed the results serve to show how detailed transport and mixing patterns in a lake can have im

the zn abundance and isotopic composition of diatom frustules a proxy for zn availability in ocean surface seawater we have developed cleaning methods for extracting diatomopal from bulk marine sediment samples for measurement of both zinc zn abundance and isotope composition this cleaning technique was then applied to a set of holocene core top samples from the southern ocean the measured 66zn reported relative to the jmclyon standard and zn si ratios from the southern ocean diatomopal samples range from 0 7 to 1 5 and from 14 to 0 9 mol mol respectively the zn abundance and isotope composition data show a clear correlation with opal burial rates and other oceanographic parameters in common with previous work we interpret the systematic changes in the zn si ratio to be linked to the variability in the concentrations of bioavailable zn in the ambient surface seawater where the diatom opal is formed this variability is likely to be primarily controlled by the degree to which zn is taken up into phytoplankton biomass the observed systematic pattern in the 66zn compositions of the diatomopal core top samples is similarly likely to reflect changes in the 66zn composition of the ambient zn in the surface waters above the core top sites which is progressively driven towards isotopically heavier values by preferential incorporation of the lighter isotopes into phytoplankton organic material thus the systematic relationship between zn isotopes and abundance observed in the core top diatomopal samples suggests a potential tool for investigating the biogeochemical cycling of zn in the past surface ocean for down core diatomopal material in this respect it may be possible to test hypotheses that attribute variations in atmospheric co2 on glacial interglacial timescales to the degree to which trace metals limited primary productivity in hnlc zones

the sculptured hills of the taurus highlands implications for the relative age of serenitatis basin chronologies and the cratering history of the moon 1 new images from the lunar reconnaissance orbiter camera show the distribution and geological relations of the sculptured hills a geological unit widespread in the highlands between the serenitatis and crisium basins the sculptured hills shows knobby undulating radially textured and plains like morphologies and in many places is indistinguishable from the similarly knobby alpes formation a facies of ejecta from the imbrium basin the new lroc image data show that the sculptured hills in the taurus highlands is imbrium ejecta and not directly related to the formation of the serenitatis basin this occurrence and the geological relations of this unit suggests that the apollo 17 impact melts may not be not samples of the serenitatis basin forming impact leaving their provenance undetermined and origin unexplained if the apollo 17 melt rocks are serenitatis impact melt up to half of the basin and large crater population of the moon was created within a 30 ma interval around 3 8 ga in a global impact cataclysm either interpretation significantly changes our view of the impact process and history of the earth moon system

the copper isotope geochemistry of rivers and the oceans abstract we present the first extensive dataset for copper cu isotopes in rivers as well as preliminary data for estuaries and seawater rivers exhibit a range in dissolved 65 cu relative to nist srm 976 of 0 02 to 1 45 per mil the discharge weighted average dissolved 65 cu and cu concentration for the studied rivers representing around 25 of the global riverine water discharge are 0 68 and 18 8 nmol kg 1 respectively isotopic data for the dissolved phase in two small estuaries in se england exhibit relatively minor variation through the salinity gradient 0 42 to 0 94 and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths analyses of the particulate phase in the estuaries reveal a complementary light pool 0 24 to 1 02 the isotopic composition of the total cu inventory is however close to that of the crustal source these data along with published constraints suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by cu bound to strong organic complexes open ocean seawater samples generally exhibit even heavier dissolved cu isotopic compositions than the riverine input 65 cu 0 9 to 1 5 the heavy isotopic composition of seawater is inferred to originate from intra oceanic processes the small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom perhaps reflecting the relative importance of scavenging and thus the sequestration of light cu to particulate material at different depths

copper and iron isotope fractionation during weathering and pedogenesis insights from saprolite profiles abstract iron and copper isotopes are useful tools to track redox transformation and biogeochemical cycling in natural environment to study the relationships of stable fe and cu isotopic variations with redox regime and biological processes during weathering and pedogenesis we carried out fe and cu isotope analyses for two sets of basalt weathering profiles south carolina usa and hainan island china which formed under different climatic conditions subtropical vs tropical unaltered parent rocks from both profiles have uniform 56 fe and 65 cu values close to the average of global basalts in the south carolina profile 56 fe values of saprolites vary from 0 01 to 0 92 in the lower reduced part and positively correlate with fe 3 fe r 2 0 90 whereas 65 cu values are almost constant by contrast 56 fe values are less variable and negatively correlate with fe 3 fe r 2 0 88 in the upper oxidized part where large 4 85 65 cu variation is observed with most samples enriched in heavy isotopes in the hainan profile formed by extreme weathering under oxidized condition 56 fe values vary little 0 05 0 14 whereas 65 cu values successively decrease from 0 32 to 0 12 with depth below 3 m and increase from 0 17 to 0 02 with depth above 3 m throughout the whole profile 65 cu positively correlate with cu concentration and negatively correlate with the content of total organic carbon toc overall the contrasting fe isotopic patterns under different redox conditions suggest redox states play the key controls on fe mobility and isotope fractionation the negative correlation between 56 fe and fe 3 fe in the oxidized part of the south carolina profile may reflect addition of isotopically light fe this is demonstrated by leaching experiments which show that fe mineral pools extracted by 0 5 n hcl representing poorly crystalline fe hydr oxides are enriched in light fe isotopes the systematic cu isotopic variation in the hainan profile reflects desorption and downward transport of isotopically heavy cu leaving the organically bound cu enriched in light isotope as supported by the negative correlation of 65 cu with toc r 2 0 88 the contrasting mostly positive vs negative cu isotopic signatures in the upper parts of these two profiles can be attributed to the different climatic conditions e g high rainfall at a tropical climate in hainan favors desorption and the development of organism whereas relatively dry climate in south carolina favors cu re precipitation from soil solutions and adsorption onto fe hydr oxides our results highlight the potential applications of fe and cu isotopes as great tracers of redox condition ancient climate and biological cycling during chemical weathering and pedogenic translocation

temporal variations in dissolved and suspended iron and manganese in the kalix river northern sweden abstract particulate and dissolved fe and mn were measured once a week from may to september 1982 in the kalix river north sweden during winter baseflow the dissolved fe concentration was 450 g l 1 early snow melt discharge increased the concentration slightly but during springflood maximum the concentration decreased to a minimum value of 60 g l 1 in mid july particulate matter in the kalix river is dominated by fe which ranges between 14 and 38 of the ashed suspended load 70 80 of the total fe load being retained by 0 45 m filters approximately 10 of particulate fe can be accounted for by a detrital phase the particulate fe al ratio showed a mean value of 6 5 which is more than ten times the ratio in mean world river particulate fe showed a peak during early snowmelt and decreased during maximum discharge similar to dissolved fe dissolved mn concentrations ranged from 1 1 to 53 4 m l 1 with a mean value of 11 2 12 4 g l 1 whereas particulate mn ranged from 3 1 ti 18 2 g l 1 with a mean concentration of 10 6 4 9 g l 1 during may and june most mn was transported in the dissolved phase whereas in july and august the particulate fraction dominated there was a drastic increase in non detrital particulate mn with a concomitant decrease in the dissolved fraction in early july with peak values in mid july and early august the decrease in dissolved mn and increase of particulate mn is probably the consequence of two processes namely addition of non detrital particulate mn to the river possibly from lakes and transformation of dissolved mn to a particulate phase within the river a combination of increased ph temperature and particulate mn triggered the precipitation of dissolved mn although the significance of each factor can not be evaluated from this study

coastal fresh water discharge in the northeast pacific very high annual rates of precipitation in the coastal mountains that border the northeast pacific ocean produce large fresh water discharges 23000 m3 s 1 this discharge has been ignored previously since it does not enter the ocean in the form of large rivers but instead the water enters by way of numerous small rivers and streams thus it acts as a line source instead of a point source this coastal discharge contributes at least 40 of the fresh water that enters the northeast pacific from the atmosphere the discharge is comparable to the mean annual discharge of the mississippi river system the fresh water creates a cross shelf density gradient that drives an alongshore baroclinic jet the width of this jet is less than 25 km with speeds in excess of 100 cm s 1 it extends along the coast from southeast alaska to at least kodiak island apparently the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year

controls on trace metal authigenic enrichment in reducing sediments insights from modern oxygen deficient settings any effort to reconstruct earth history using variations in authigenic enrichments of redox sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry further unravelling the multiple controls on sedimentary enrichments requires a multi element approach of the range of metals studied most is known about the behavior of fe mn and mo in this study we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined cd cu zn and ni in three oxygen poor settings the black sea the cariaco basin venezuela and the peru margin these three settings span a range of biogeochemical environments allowing us to isolate the different controls on sedimentary enrichment our approach relying on the covariation of elemental enrichment factors ef defined for element x as efx x al sample x al lithogenic has previously been applied to mo and u to elucidate paleoenvironmental information on for example benthic redox conditions the particulate shuttle and the evolution of water mass chemistry we find two key controls on trace metal enrichment first the concentration of an element in the lithogenic background sediment used in calculating efx controls the magnitude of potential enrichment maximum enrichment factors of 376 and 800 are calculated for mo 1 ppm in detrital sediments and cd 0 3 ppm respectively compared to values not greater than 17 in any setting for the other five metals 45 ppm to 4 5 wt in detrital sediments second there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment we further identify four important processes for delivery of trace metals to the sediment these are 1 cellular uptake especially important for zn and cd 2 interaction co precipitation with sulfide mo cu and cd 3 passive scavenging via the traditional particulate shuttle mo ni and cu and 4 an association with the benthic fe redox shuttle mn ni finally we summarize the oceanic mass balance of cd and mo and place the first constraints on the contribution of reducing sediments to the oceanic mass balance of cu zn and ni we show that reducing sediments are the ultimate repository for up to half the total output flux of these elements from the oceanic dissolved pool

copper isotope fractionation during excretion from a phototrophic biofilm abstract the metal excretion and metal sorption are two important microbial processes in the regulation of intracellular metal concentration however the contribution of freshwater phototrophic biofilm to metal efflux in the environment and its related isotopic fractionation remain poorly known in this study cu efflux from a mature phototrophic biofilm and related cu isotopic fractionation between the biofilm and aqueous solution were studied over 4 days in closed batch and open drip flow reactors br and dfr respectively the impact of a 48 h drying event on cu efflux from the biofilm and its isotopic signature was quantified in the br cu excretion from the biofilm depended on cu concentration in the biomass and did not show a latent phase for the wet biofilm in dfr the cu efflux rate decreased over time whereas in br cu efflux exhibited fluctuations with a net re sorption phase during short term early excretion over the first 4 h br and 24 h dfr the enrichment of solution in heavy isotopes with a 65cu sol biofilm of 0 7 0 2 could be explained by a combination of i desorption via competition between h and cu2 for surface sites and ii release of isotopically heavy cu ii organic complexes in addition there was a retention of isotopically light cu i within the cells which is consistent with the biofilm ability to reduce cu with further exposure of the wet biofilm to the solution a progressive decrease of 65cu sol biofilm down to 0 and 0 36 respectively in br and dfr after 96 h could be explained by an active efflux of cu i and by a passive diffusion of cu2 both of these processes favoring light isotopes the re hydrated and wet biofilms showed distinctly different behavior during excretion in terms of magnitude of the flux and direction of the fractionation for long term exposure indeed the efflux from the re hydrated biofilm was ten times higher than the one from the wet biofilm and the re hydrated biofilm did not exhibit a decrease of 65cu sol biofilm after 24 h of reaction this could be related to partial devitalization of the biofilm during drying producing a release of isotopically heavy cu and decreasing the intensity of cu i active efflux of light isotopes taken together the cu isotopic signature in natural aquatic environments containing phototrophic biofilms varies up to 1 on a daily scale

fractionation of cu and mo isotopes caused by vapor liquid partitioning evidence from the dahutang w cu mo ore field the study presents 65cu and 97mo isotope values from cogenetic chalcopyrite and molybdenite found in veins and breccias of the dahutang w cu mo ore field in china the samples span a 3 4 km range both isotopes show a significant degree of fractionation cu isotope values in the chalcopyrite range from 0 31 to 1 48 and mo isotope values in the molybdenite range from 0 03 to 1 06 for the cogenetic sulfide veined samples a negative slope relationship exists between 65cu and 97mo values which suggest a similar fluid history rayleigh distillation models the vein samples change in isotope values the breccia samples do not fall on the trend thus indicating a different source mineralization event measured fluid inclusion and d and 18o data from cogenetic quartz indicate changes in temperature and mixing of fluids do not appear to cause the isotopic shifts measure related equilibrium processes associated with the partitioning of metal between the vapor fluid in the hydrothermal system could be the probable cause for the relationship seen between the two isotope systems

fractionation of fe and cu isotopes in acid mine tailings modification and application of a sequential extraction method abstract sulfidic mine tailings have a high potential for contamination of the environment by triggering acid mine drainage hence it is crucial to understand metal mobilization processes and to develop monitoring tools metal isotope fingerprinting as a potential monitoring tool for metal sulfide oxidation processes was in the focus of this study by using stable isotope signatures of cu and fe for fe a six step sequential extraction method was applied in order to separate potential fe bearing minerals water soluble exchangeable fraction fe iii oxyhydr oxides fe oxides sulfides and organic compounds and residual silicates for cu this method was modified into a four step extraction method water soluble exchangeable fraction oxalate fraction bound to fe oxides and sulfides residual to verify accuracy and precision of the sequential extraction method for metal isotope analysis isotope fractionation during the extraction procedure was investigated employing minerals for which the mineral composition and the isotopic composition was known the developed procedure is suitable to separate target minerals with only a small loss in the elemental budget no significant isotope fractionation was observed during the extraction procedure application of this method on two sites of porphyry copper mine tailings in the atacama desert in chile chanaral bay revealed several implications about the mobilization of fe and cu in an environmental setting iron contents and fe isotope compositions are homogeneous with depth 0 61 cm 56fe 0 2 0 3 for the bulk and the fe hyr oxide fraction and only the deepest samples at 60 cm exhibited lower 56fe values 0 which are likely related to the occurrence of an alluvium at this depth the fe silicate fraction shows higher 56fe values 0 6 0 9 most likely because of preferential leaching of the light fe isotopes this consequently indicates a more pronounced fe isotope fractionation with depth as is expected from longer weathering the fe sulfide fraction is isotopically lighter compared to the fe hydr oxide fraction because during sulfide oxidation the heavy fe isotopes prefer the oxidized forms and oxidative precipitation results in an enriched fe isotopic signature for fe hydr oxides the cu isotope compositions of all bulk samples and individual fractions except the cu sulfides of one site ch1 exhibited a decrease of the 65cu values from the depth towards the surface which is potentially related to cu mobilization during capillary water rise in the arid climate a correlation of 65cu with ph indicates preferential adsorption of 65cu on fe oxy hydroxides at site ch1 which is evident by a change of 65cu from 0 5 to 0 7 in the water soluble fraction at another site ch12 where ph at depths was potentially not high enough for the formation of fe minerals that could adsorb cu only minor cu isotope fractionation was observed in the water soluble fraction the cu sulfide fraction at site ch1 exhibits higher 65cu values with an increase from the bottom 0 42 to the surface 0 92 which might be related to preferential leaching of the light isotopes e g by microorganisms

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

tracing low temperature aqueous metal migration in mineralized watersheds with cu isotope fractionation abstract copper isotope signatures in waters emanating from mineralized watersheds provide evidence for the source aqueous copper in solution low temperature aqueous oxidation of cu sulfide minerals produces significant copper isotopic fractionation between solutions and residues abiotic experimental data of fractionation defined as liquid solid 65culiquid 65cusolid are on the order of 1 3 and are unique for copper rich sulfide minerals data presented here from ores and waters within defined boundaries of porphyry copper massive sulfide skarn and epithermal ore deposits mimic abiotic experiments thus the oxidation of sulfide minerals appears to cause the signatures in the waters although significant biological temperature and ph variations exist in the fluids regardless of the deposit type water type concentration of cu in solution or location the data provide a means to trace sources of metals in solutions this relationship allows for tracking sources and degree of metal migration in low temperature aqueous systems and has direct application to exploration geology and environmental geochemistry

on the distribution of copper nickel and cadmium in the surface waters of the north atlantic and north pacific ocean concentrations of copper nickel and cadmium have been determined for about 250 surface water samples nonupwelling open ocean concentrations of these metals are cu 0 5 1 4 nmol kg ni 1 2 nmol kg and cd less than 10 pmol kg in the equatorial pacific upwelling zone concentrations of ni 3 nmol kg and cd 80 pmol kg are higher than in the open ocean but cu 0 9 nmol kg is not significantly enriched metal concentrations are higher in cool nutrient rich eastern boundary currents cu 1 5 nmol kg ni 3 5 nmol kg and cd 30 50 pmol kg copper is distinctly higher in the coastal waters of the gulf of panama 3 4 nmol kg and also higher in the shelf waters north of the gulf stream 2 5 nmol kg these copper enrichments may be caused by copper remobilized from mildly reducing shelf sediments and maintained by a coastal nutrient trap in the open ocean events of high cu water 1 5 3 5 nmol kg are seen on scales up to 60 km presumably these are due to the advection of coastal water into the oceanic interior the lowest copper concentrations in the north pacific central gyre 0 5 nmol kg bruland 1980 are lower than in the sargasso sea 1 3 nmol kg while for nickel the lowest concentrations are 2 nmol kg in both the north pacific and the north atlantic nickel and cadmium while generally correlated with the nutrients in surface waters show distinct regional changes in their element nutrient correlations the residual concentrations of trace metals in the surface waters of the ocean can be explained if biological discrimination against trace metals relative to phosphorus increases as productivity decreases

mixing and circulation at the confluence of two rivers entering a meandering reservoir 1 a field data set collected under different conditions is analyzed to characterize the spatial arrangement of two large inflows ebro and segre with distinct physical chemical characteristics as they join at the upstream end of ribarroja reservoir in northern spain given the short average residence time of water in the reservoir the spatial arrangement of the rivers at their confluence and their mixing rates are likely the drivers of the stratification patterns observed near the dam in winter inflows have similar densities 0 o 10 5 and their spatial distribution is largely determined by inertial forces and in particular by the discharge ratio downstream of the confluence both rivers flow side by side and largely unmixed over long distances in summer with 0 of o 10 3 the flow fields at the confluence are largely controlled by buoyancy forces atmospheric forcing during strong wind events and centrifugal forces caused by the meandering shape of the reservoir induce significant tilting of the isotherms leading to localized high mixing rates mixing in general though is weak at this time of the year in fall and early winter density differences are largely controlled by conductivity differences between the incoming flows the warmer ebro water with larger thermal inertia flows beneath the colder segre water the spatial arrangement of the inflows is largely controlled by the discharge ratio and mixing between sources is strong likely as a result of mixed water being denser than either of the incoming flows

the chromium isotopic composition of seawater and marine carbonates article history chromium isotopes are fractionated during redox reactions and have the potential to provide a record of changes in the oxygenation levels of the oceans in the geological past however cr is a trace metal in seawater and its low concentrations make isotopic measurements challenging here we report the first determinations of 53 cr for seawater from open ocean argentine basin and coastal southampton water settings using a double spike technique the total chromium concentration in seawater from southampton water is 1 85 nm whereas the cr content of argentine basin samples is 5 8 6 6 nm the 53cr value of seawater from the argentine basin is 0 491 0 556 in intermediate and deep waters and varies between 0 412 and 0 664 in surface waters 150 m the 53

lithium isotopes as a probe of weathering processes orinoco river abstract lithium isotopes have the potential to be effective tracers of weathering processes due to their large relative mass difference and therefore fractionation in this study an attempt is made to fill a major gap in the knowledge of li isotope fractionation during continental weathering and of the mechanisms involved finally the relationship between the suspended and dissolved material is made on a basin wide scale the orinoco basin provides a clear contrast in reaction limited and transport limited weathering regimes that has already been documented by a comprehensive study on its fluvial geochemistry edmond et al geochim cosmochim acta 60 1996 2949 2976 edmond et al geochim cosmochim acta 59 1995 3301 3325 conspicuous in our new results is the difference in 6li of the dissolved load between the andean 30 to 22 and shield 22 to 7 tributaries while the 6li of the suspended load is similar between the two to a first approximation during superficial weathering in high relief tectonically active terrains the dissolved load is high in li and isotopically heavy more negative 6li whereas in stable shield regions the concentrations are low and isotopically light in proportion to the increasing degree of weathering

planetary cratering 2 studies of saturation equilibrium a realistic computer model has been developed to display images of imaginary cratered surfaces taking into account empirically measured input size distributions of primary and secondary craters ejecta blanket morphology including feathering with distance obliteration due to ejecta from outside the imaged area lighting effects etc the model allows us to track surface evolution of morphology as new craters are added using the model as well as lunar photos we have studied the approach to saturation equilibrium defined as a condition when no further proportionate increase in crater density occurs as input cratering increases we find that an identifiable saturation equilibrium occurs close to a level previously identified for this state hartmann 1984 typically fluctuating around a crater density from 0 4 to 2 times that level this result is fairly robust vis a vis the range of model parameters we have chosen flooding basin ejecta blankets and other obliterative effects can introduce structure and oscillations within this range even after saturation equilibrium is achieved these findings may constrain or revise certain earlier interpretations of satellite and planet surface evolution and impactor populations which were predicated on the assumed absence of saturation equilibrium in our fourth experimental run we found that suppression of sandblasting by subresolution impacts allows the smallest secondaries to rise above the saturation equilibrium line a result that might be relevant to a similar situation on gaspra and perhaps some other asteroids

zinc and copper behaviour at the soil river interface new insights by zn and cu isotopes in the organic rich rio negro basin abstract the complex behaviour of zn and cu at the soil river interface was investigated in soil and riverine water samples from the rio negro basin a secondary tributary of the rio amazonas using their stable isotope compositions this acidic and organic river drains two types of intensely weathered terrains podzols in its upstream part and lateritic soils downstream bulk soil particles suspended particulate matter spm as well as colloidal fractions were sampled across the whole basin during low and high water stages in the basin zn and cu are mostly exported from lateritic soils and transported by organic colloids where significant losses are observed in the downstream part of the river the use of 66zn and 65cu measurements reveals distinct stories for these two metals in suspended sediments and colloids in the colloids the constant 66zncoll across the basin is induced by the same weak association mode between zn and organic ligands regardless of the origin of the water by contrast in spm the speciation of zn and thus 66znspm differ according to the type of drained soils zn is associated with organic complexes in particles exported with water draining podzol whereas zn2 is incorporated in the structure of the remaining kaolinite clays in lateritic output the stronger reactivity of cu than zn with organic ligands induces its complete complexation copper is controlled by refractory particulate organic matter pom and by reactive colloidal organic matter the latter being enriched in 65cu due to stronger binding interactions than in pom while the cu content remains constant in the upstream part of the rio negro downstream the decrease of spm and colloidal cu fluxes is associated with a constant 65cuspm and with an increase of 65cucoll at the rio negro outlet geochemical mass balance modelling based on spm cu and zn fluxes in spm and their associated isotopic signatures confirms distinct host phases for zn and cu and identifies the most probable places where losses of these two metals occur in colloids the observed cu isotope fractionation from 0 24 to 0 45 superimposed on the significant cucoll loss is assumed to result from a new isotopic equilibrium in a low velocity and high productivity zone cu rich colloids enriched in 63cu aggregate and settle down whereas the remaining heavy cu is partially complexed on strong organic ligands secreted by phytoplankton forming new cu colloids

fe isotope variations in the modern and ancient earth and other planetary bodies iron the fourth most abundant element in the earth s crust has four naturally occurring stable isotopes 54fe 5 84 56fe 91 76 57fe 2 12 and 58fe 0 28 and the natural mass dependent isotope variations of fe in the rock record span a range of 4 per mil in 56fe 54fe ratios fig 1 the field of fe isotope geochemistry is relatively new but has received considerable attention because it may allow us to gain a better understanding of how fe is cycled in different environments iron typically occurs as either reduced ferrous fe in oxygen poor environments or as oxidized ferric iron in oxygen rich environments notably only the reduced species is soluble in oxygenated aqueous solutions unless the ph is low in the archean and early proterozoic the earth may have been relatively oxygen poor e g kasting et al 1979 grandstaff 1980 holland 1994 suggesting that there may have been significant quantities of fe 0 9 millimolar dissolved in the oceans as fe ii aq e g ewers 1983 sumner 1997 the extensive iron formations of archean to early proterozoic age may have been deposited from such fe ii rich oceans e g beukes and klein 1992 in the modern oxic oceans however fe contents are exceedingly low 1 nanomolar in the open oceans e g martin and gordon 1988 bruland et al 1991 martin 1992 johnson et al 1997 and it is now recognized that marine productivity is fe limited in parts of the open oceans e g martin and fitzwater 1988 martin et al 1989 1994 the differences in the behavior of fe with redox state and the significant isotope fractionations 1 or more in 56fe 54fe that are associated with redox conditions suggests that fe isotope studies will be extremely useful for tracing

fractionation of cu fe and zn isotopes during the oxidative weathering of sulfide rich rocks abstract we measured the fe cu and zn isotopic compositions of the fluids generated during leaching experiments with pyrite chalcopyrite and sphalerite rich rocks and with a sphalerite mineral separate our study demonstrates that the oxidative weathering of sulfide rich rocks can produce substantial variations in fe 1 75 to 1 0 56 fe solution pyrite rock and cu 0 0 to 2 0 65 cu solution chalcopyrite rock isotopes and small variations in zn isotopes 0 0 to 0 2 66 zn solution sphalerite in the fluid phase relative to the rock for the fe and cu systems we suggest that isotopic fractionation is caused by electron exchange driven e g fe ii fe iii and cu i cu ii redox reactions at the surfaces of the sulfide minerals that occur during air and aqueous chemical reactions under acidic conditions these reactions tend to enrich the fluid phase in the heavier fe and cu isotopes however under circumneutral ph conditions the fe isotopic composition in solution was controlled by the precipitation of fe iii oxide phases which enriched the solution in the lighter fe isotopes this investigation provides a preliminary framework for interpreting the impact of sulfide oxidation reactions on the distributions of stable fe cu and zn isotopes in natural waters

the columbia river plume study subtidal variability in the velocity and salinity fields a comprehensive study of the strongly wind driven midlatitude buoyant plume from the columbia river located on the u s west coast demonstrates that the plume has two basic structures during the fall winter season namely a thin 5 15 m strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker 10 40 m weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress the plume and its velocity field respond nearly instantaneously to changes in wind speed or direction and the wind fluctuations have timescales of 2 10 days frictional wind driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds respectively farther downstream currents turn to parallel rather than cross salinity contours consistent with a geostrophic balance in particular during periods when the plume is separated from the coast currents tend to flow around the mound of fresher water at distances exceeding about 20 km from the river mouth the along shelf depth averaged flow over the inner to midshelf is linear and depth averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone in this region along shelf geostrophic buoyancy driven currents at 5 m calculated from surface density and along shelf geostrophic wind driven currents computed from a depth averaged linear model are comparable in magnitude 10 25 cm s 1

gravity current dynamics and entrainment a process study based on observations in the arkona basin abstract a 19 h time series of dissipation stratification and horizontal velocities has been obtained for a dense gravity current flowing into the arkona basin in the western baltic sea the observations are compared with one dimensional quasi steady theory in which the gravity component in the flow direction is balanced by bottom friction while that in the cross flow direction is balanced by the coriolis force the observations deviate from the theory in that the bottom shear stress is more than 2 times as large as that required to balance the gravity several reasons for this discrepancy are discussed a 1d turbulence model is also compared with the observations profiles of velocity stratification and dissipation rates generally show similar variations with depth as the observations although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed subsequently the model is used to investigate the variation of t

distribution of bioactive trace metals fe co ni cu zn and cd in the sulu sea and its adjacent seas abstract here we present the first vertical distribution of dissolved d and acid dissolvable ad bioactive trace metals fe co ni cu zn and cd in the sulu sea and the south china sea together with those observed previously by the same method in the western north pacific at a depth of 50 75 m concentration minima of some trace metals were observed in the sulu sea d zn cu and fe and the south china sea d zn which coincided with the chl a maximum indicating scavenging of these metals including biological uptake above 150 m in the south china sea elevated concentrations of d co and cu were observed which could result from fluvial coastal waters and or shelf sedimentary sources in the surface mixed layer in the sulu sea d fe concentrations were high 2 nm presumably due to the flowing of waters across the philippine archipelago except for fe concentrations of d and ad species at each corresponding depth were not significantly different concentrations of ad fe 6 8 17 nm below 500 m in the sulu sea were much higher than those of d fe 0 2 1 7 nm indicating that particulate fe is abundant in the basin probably coming from nearby sedimentary sources the vertical distributions of d ni cu zn and cd in the south china sea were nutrient like and deviated slightly from those in the western north pacific this is caused by a rapid flushing of waters from the philippine sea coupled with vertical mixing within the south china sea the distribution of these metals in the sulu sea was more uniform below 500 m the average concentrations of d ni cu zn and cd in the deep water of the sulu sea were 6 1 1 5 3 3 and 0 5 nm significantly lower than those of the western north pacific 9 6 2 8 10 1 and 1 0 nm respectively we also found lower d cd po4 ni po4 and zn si oh 4 ratios in the sulu sea than those of the pacific the depletion of these concentrations and the d cd po4 and ni po4 ratios in the sulu sea is probably because the deep water of the basin is rapidly exchanged with shallow waters but isolated from nutrient rich deep waters derived from the north pacific due to the surrounding topographic barriers including the islands and the shallow sills while subsurface waters were flowing along density surfaces sigma t values of 26 from the south china sea to the sulu sea the concentrations of macronutrients d ni cu zn and cd increased due to the regeneration from biogenic particles the increases in the concentrations of bioactive elements relative to that of po4 were n p si ni cu zn cd 15 1 40 2 4 10 3 0 6 10 3 2 7 10 3 0 03 10 3 in a molar unit

formation of the density currents in the zone of confluence of two rivers summary the peculiarities of the formation of density currents in the zone of confluence of two rivers with strongly different hydrochemical regimes are studied numerically and experimentally the three dimensional numerical simulation shows that the water of the river of higher mineralization and density flows under the water of the river of lower mineralization and density and vice versa and besides such overlapping of the water streams is observed both upstream and downstream of the confluence of two rivers the results of numerical simulation are supported by the data of expedition observations and in situ measurements a similar phenomenon namely a flow of two overlapped oppositely directed water streams was previously discovered in the mouth zone of the rivers flowing in the sea our study reveals the existence of a new type of the hydrological systems in which such a phenomenon occurs

clementine uvvis multispectral data and the apollo 17 landing site what can we tell and how well multispectral data obtained by the clementine mission are correlated to compositional and petrographic information for individual sample stations at the apollo 17 landing site the soils contain a variety of fe2 bearing phases in different proportions including low and high ca pyroxene olivine ilmenite and glass in the mare soils ilmenite carries a substantial proportion of the fe2 and in all soils glasses particularly agglutinates carry nearly as much or more fe2 as the silicates using an empirical calibration concentrations of feo and tio2 estimated from the ultraviolet visible uvvis data correlate well with measured compositions of surface soils yielding correlation coefficients of 0 94 and 0 95 respectively the ferrous absorption however is weak in the mostly submature to mature apollo 17 soils thus spectral curvature is useful only for investigating the mafic silicate mineralogy around fresh craters and deposits the effects of local topography cause significant variations in feo and tio2 derived from clementine uvvis data but do not impair first order geologic interpretations parameters derived from the uvvis data allow quantification of the composition and nature of the soils and by inference underlying rock formations and are consistent with the known geologic character of the landing site the highland regions along this part of the serenitatis rim are relatively feo rich partly as a result of abundant mafic impact melt breccia and partly from the addition of basaltic material in the form of impact debris and pyroclastic deposits at high elevations massif soils are rich in a mafic melt breccia component although slopes and areas mixed by small craters reveal a mixture of melt breccia and older highland material of anorthositic norite composition soils developed on hummocky deposits that postdate the massifs such as the sculptured hills have a similar range of compositions as the massifs elevated plains northeast of the sculptured hills are more mafic than the known impact melt breccias suggesting that they may also contain an older volcanic component sources of low ti basalt or very low ti basalt though not present in the immediate vicinity of the landing site occur east and northeast of taurus littrow valley and are readily identified using the uvvis data

the oceanic mass balance of copper and zinc isotopes investigated by analysis of their inputs and outputs to ferromanganese oxide sediments abstract the oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time many of them have isotope systems that are fractionated by key biological and chemical processes so that significant information about such processes may be gleaned from them however for many of these nascent isotopic systems we currently know too little of their modern oceanic mass balance making the application of such systems to the past speculative at best here we investigate the biogeochemical cycling of copper cu and zinc zn isotopes in the ocean we present estimates for the isotopic composition of cu and zn inputs to the oceans based on new data presented here and published data the bulk isotopic composition of dissolved cu and zn in the oceans 65cu 0 9 66zn 0 5 is in both cases heavier than their respective inputs at around 65cu 0 6 and 66zn 0 3 respectively implying a marine process that fractionates them and a resulting isotopically light sedimentary output for the better known molybdenum isotope system this is achieved by sorption to fe mn oxides and this light isotopic composition is recorded in fe mn crusts hence we present isotopic data for cu and zn in three fe mn crusts from the major ocean basins which yield 65cu 0 44 0 23 mean and 2sd and 66zn 1 04 0 21 thus for cu isotopes output to particulate fe mn oxides can explain the heavy isotopic composition of the oceans while for zn it cannot the heavy zn in fe mn crusts and in all other authigenic marine sediments measured so far implies that a missing light sink is still to be located these observations are some of the first to place constraints on the modern oceanic mass balance of cu and zn isotopes

isotopic disequilibrium of cu in marine ferromanganese crusts evidence from ab initio predictions of cu isotope fractionation on sorption to birnessite abstract in the oceans cu is strongly scavenged by ferromanganese fe mn crusts the isotopic fractionation of cu between seawater and crusts provides insight into the mechanisms of trace metal cycling in the oceans dissolved cu in seawater is isotopically heavy 0 66 0 19 relative to cu in crusts 0 31 0 24 the primary mineral phase sorbing divalent trace metals in fe mn crusts is birnessite recent laboratory measurements show that isotopically light cu is preferentially sorbed on birnessite with a fractionation factor of 0 45 0 18 here we use first principles quantum mechanical calculations to predict the isotopic fractionation between aqueous cu2 complexes and cu as a surface complex on birnessite we find that isotopic fractionation between the cu h2o 5 complex and sorbed cu should be 0 49 at 25 c in close agreement with experiments confirming that these experimental results reflects equilibrium fractionation we then predict the isotopic fractionation between dissolved inorganic cu in seawater and birnessite given the thermodynamic speciation of dissolved cu at ph 8 we find dissolved inorganic cu should be 0 94 at 5 c heavier than cu sorbed to birnessite this value is substantially greater than the observed fractionation between seawater and fe mn crusts sw fmc 0 35 moreover it is well established that dissolved cu in seawater is strongly complexed by organic ligands based on model cu complexes and published experimental data we estimate that fractionation of cu by organic ligands should increase the equilibrium fractionation between seawater and fe mn crusts by 0 2 to 1 5 to yield sw fmc 1 1 to 2 4 we conclude that cu in marine fe mn crusts in not in isotopic equilibrium with dissolved cu in seawater and consider the possible explanations of this surprising finding

mixing dynamics at the confluence of two large rivers undergoing weak density variations simulations of tracer experiments conducted with a three dimensional primitive equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers ebro and segre with distinct physical and chemical properties at their confluence upstream of a meandering reservoir ribarroja reservoir mixing rates downstream of the confluence are subject to hourly scale oscillations driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence even though density contrasts are low at most o 10 1 kg m 3 difference among sources and almost negligible from a dynamic point of view compared with inertial forces they are important for mixing mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40 larger than those occurring under neutrally buoyant conditions the buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing distortion of the mixing layer for strong density contrasts though when the contact area between the streams becomes nearly horizontal larger density differences between streams will lead to weaker mixing rates as a result of the stabilizing effect of vertical density gradients

iron isotope systematics in estuaries the case of north river massachusetts usa abstract recent studies have suggested that rivers may present an isotopically light fe source to the oceans since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing it is important to investigate potential fractionation of fe isotopes during this process in this study we investigate the influence of the flocculation of fe rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles the samples were collected along a salinity gradient from the fresh water to the ocean in the north river estuary ma usa estuarine samples were filtered at 0 22 m and the iron isotope composition of the two fractions dissolved and particles were analyzed using high resolution mc icp ms after chemical purification dissolved iron results show positive 56 fe values with an average of 0 43 0 04 relative to the irmm 14 standard and do not display any relationships with salinity or with percentage of colloid flocculation the iron isotopic composition of the particles suspended in fresh water is characterized by more negative 56 fe values than for dissolved fe and correlate with the percentage of fe flocculation particulate 56 fe values vary from 0 09 at no flocculation to 0 1 at the flocculation maximum which reflect mixing effects between river borne particles lithogenic particles derived from coastal seawaters and newly precipitated colloids since the process of flocculation produces minimal fe isotope fractionation in the dissolved fe pool we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values however this study also suggests that 56 fe composition of rivers can also be characterized by more positive 56 fe values up to 0 3 relative to the crust than previously reported in order to improve our current understanding of the oceanic iron isotope cycling further work is now required to determine the processes controlling the fractionation of fe isotopes during continental run off

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

rates and patterns of thermal mixing at a small stream confluence under variable incoming flow conditions confluences are important locations for river mixing within drainage networks yet few studies have examined in detail the dynamics of mixing within confluences this study examines the influence of momentum flux ratio the scale of the flow cross sectional area and the density differences between incoming flows on thermal mixing at a small stream confluence results reveal that rates and patterns of thermal mixing depend on event specific combinations of the three factors the mixing interface at this confluence is generally distorted towards the mouth of the lateral tributary by strong helical motion associated with curvature of flow from the lateral tributary as it aligns with the downstream channel as the momentum flux from the lateral tributary increases mixing is enhanced because helical motion from the curving tributary flow expands over the width of the downstream channel the cross sectional area of the flow is negatively correlated with mixing rates suggesting that the amount of mixing over a fixed distance downstream of the confluence is inversely related to the scale of the flow density differences are not strongly related to rates of mixing results confirm that mixing rates within the region of confluent flow interaction can be highly variable among flow events with different incoming flow conditions but that in general length scales of mixing are short and rates of mixing are high at this small confluence compared with those typically documented at large river confluences copyright 2015 john wiley sons ltd

time averaged flow structure in the central region of a stream confluence previous process oriented field studies of stream confluences have focused mainly on fluvial dynamics at or immediately downstream of the location where the confluent flows enter the downstream channel this study examines in detail the spatial evolution of the time averaged downstream velocity cross stream velocity and temperature fields between the junction apex where the flows initially meet and the entrance to the downstream channel a well defined vertically oriented mixing interface exists within this portion of the confluence suggesting that lateral mixing of the incoming flows is limited the downstream velocity field near the junction apex is characterized by two high velocity cores separated by an intervening region of low velocity or recirculating fluid in the downstream direction the high velocity cores move inwards towards the mixing interface and high velocity fluid progressively extends downwards into a zone of scour resulting in an increase in flow velocity in the centre of the confluence the cross stream velocity field is dominated by flow convergence but also includes a component associated with a consistent pattern of secondary circulation this pattern is characterized by two surface convergent helical cells one on each side of the mixing interface the helical cells appear to be the mechanism by which high momentum fluid near the surface is advected downwards into the zone of scour for transport ineffective flows the dimensions and intensities of the cells are controlled by the momentum ratio of the confluent streams and by the extant bed morphology within the confluence although the flow structure of formative events was not measured directly in this study documented patterns of erosion and deposition within the central region of the confluence suggest that these events are dynamically similar to the measured flows except for the fact that formative flows are not constrained by but can reshape the bed morphology the results of this investigation are consistent with and augment previous findings on time averaged flow structure in the downstream portion of the confluence 1998 john wiley sons ltd

effect of bed morphology on flow mixing length at river confluences mixing processes at river confluences have an important bearing on problems such as pollutant dispersal and the management of river systems but remain poorly understood previous studies1 11 have indicated that flow mixing downstream of a confluence is a slow process typically completed at distances greater than 100 times the channel width bed morphology is now emerging as a critical factor flume experiments have shown that the width to depth ratios12 and height discordance13 14 between the confluent channels should influence mixing rates12 14 but the magnitude of these effects in real rivers is not known here we report measure ments from three river confluences of moderate size which show that bed discordance can markedly increase mixing rates for the rivers studied mixing is complete at distances five to ten times shorter than those reported previously

the behaviour of cu and zn isotopes during soil development controls on the dissolved load of rivers abstract the stable isotopes of copper cu and zinc zn are finding increasing applications in surface earth geochemistry an important early observation is that aqueous pools of cu rivers and oceans are isotopically heavier than rocks of the continental crust for zn the global average 66 zn for rivers is identical to estimates of the upper continental crust but the oceans are slightly heavier here we study cu and zn abundances and isotopes in soils to assess how processes in the weathering environment control isotopic values of rivers and ultimately the oceans we investigated a range of soils developed on granitoid scotland and basaltic hawaiian islands rock substrates representing soil development times from 0 1 to 400 kyr mean annual temperatures of 6 16 c and mean annual precipitation map of 1060 5050 mm soils developed on the island of maui over 400 kyr and under high rainfall show the clearest chemical weathering signatures here in oxic soils cu and zn are both depleted by 50 90 with preferential loss of heavy cu 65 cu up to 1 2 lower than parent material and small shifts in 66 zn we attribute this to equilibrium fractionation between aqueous organic species that are removed from the soil versus sorption to residual fe oxyhydroxides in soils that are 0 1 150 kyr old in scotland and hawaii this same pattern is overprinted by biological cycling and the addition of mineral aerosol cu and zn with heavier isotope compositions in reducing soils on maui developed under the highest rainfall cu and zn are almost completely stripped from the soil leaving a very small residual pool with 65 cu and 66 zn values that range from those for the oxic soils back to and beyond parent material this removal of the light sorbed cu seen in oxic soils is attributed to the dissolution of fe oxides under anaerobic conditions perhaps microbially mediated leaving a very small residual isotopically heavier pool overall these data suggest that processes in soils create significant variability in cu isotopes with the heavy isotope exported from oxic soils in contrast small isotope fractionations of zn are generated in the soil environment these observations are consistent with those made previously for cu and zn isotopes in rivers but the maximum amount of cu and zn stored by world soils equates to only 30 130 years of the dissolved riverine flux soils cannot be the ultimate repository of the residual cu and zn required balancing the riverine flux and this must ultimately reside in the erosive products of soil formation in continental and ocean margin sediments

modeling intrajunction dispersion at a well mixed tidal river junction abstractthe relative importance of small scale intrajunction flow features such as shear layers separation zones and secondary flows on dispersion in a well mixed tidal river junction is explored a fully nonlinear nonhydrostatic and unstructured three dimensional 3d model is used to resolve supertidal dispersion via scalar transport at a well mixed tidal river junction mass transport simulated in the junction is compared against predictions using a simple node channel model to quantify the effects of small scale 3d intrajunction flow features on mixing and dispersion the effects of three dimensionality are demonstrated by quantifying the difference between two dimensional 2d and 3d model results an intermediate 3d model that does not resolve the secondary circulation or the recirculating flow at the junction is also compared to the 3d model to quantify the relative sensitivity of mixing on intrajunction flow features resolution of complex flow features simulated by the full 3d model is not

two dimensional mass transport in estuaries on a tidally averaged basis the two dimensional estuarine circulation is characterized by a horizontal seaward velocity in the upper layer and a landward velocity in the lower layer with a compensating vertical velocity to maintain hydraulic continuity a relatively simple method of analysis is developed for this type of circulation from the hydrodynamic equations of momentum continuity and state it is based on the condition that the salinity distributions in both the longitudinal and vertical directions are known or may be assigned in addition to an analytical solution for the horizontal and vertical velocities the analysis generates the values of vertical eddy viscosity which characterizes the vertical exchange of momentum an important process of circulation in partially mixed estuaries successful applications of the analysis to a number of estuaries throughout the country prove that the present method is efficient and simple to use the present method of analysis offers a definite advantage as

from biological to lithological control of the b geochemical cycle in a forest watershed strengbach vosges abstract there is a fast growing interest in understanding the coupling between mineralogical and biological processes responsible for the migration of elements through continental ecosystems this issue has fundamental impacts at the soil plant scale because it can explain the tight links between soil and plant development and at the watershed scale because it gives a direct access to the water quality in the present study we performed an extended investigation of the bio geochemical cycle of boron which is an element known to be suitable for investigating water rock interactions and vegetation cycling new b data are provided along the hydro bio geochemical continuum in a forest ecosystem strengbach basin vosges france from rainwaters down to the outlet of the basin including systematic analyses of throughfalls soil solutions springs and brooks scattered in the watershed at the watershed scale we evidence a relationship between the b isotopic composition of river waters and the weathering regime outlining a predominant control of the parent rock mineralogy on the b geochemical behavior at the soil plant scale it appears that the b geochemical cycle is controlled by the vegetation cycling which is characterized by an uncommon easy to distinguish b isotopic composition 11b ranging from about 30 to 45 each year the amount of b being involved in the vegetation cycle is about four times greater than that of b being exported out of the watershed at 10 cm depth in soil where the plant roots are expected to be the most active we observe a marked seasonal oscillation of the b isotopic values which is interpreted as resulting from the vegetation activity a mass balance calculation based on the assumption that that 10b is preferentially accumulated in the biomass tends to indicate that the soil plant system does not behave at steady state with respect to b because of the very distinct b isotopic signature of vegetation and minerals in soil box modeling allows to quantify the part of the b fluxes involved in the vegetation cycling and the mineral reactions respectively this calculation reveals a clear correlation between the amount of b derived from soil weathering and the amount of b absorbed by plant roots this result clearly supports the idea that a coupling exists between mineral weathering and plant activity for the study of which b isotopes appear particularly suitable

modeling and understanding turbulent mixing in a macrotidal salt wedge estuary 1 a high resolution three dimensional numerical simulation is performed with the parallel unstructured grid suntans model to study the spatiotemporal dynamics of turbulent mixing in a shallow macrotidal salt wedge estuary that experiences periodic mixing and strong stratification unresolved vertical mixing is parameterized with the k kl closure scheme with the canuto a stability functions based on a careful comparison of multiple two equation closure schemes and stability functions via the generic length scale approach the predictions of velocity salinity richardson number and reynolds stress are in good agreement with field observations and the top and bottom salinity predictions achieve skill scores of 0 86 and 0 91 respectively the model shows that the salt wedge starts to strengthen upstream at the beginning of weak ebb and gradually expands downstream during the weak tide mixing is most active along a density interface during the weak ebb while it is most active in a bottom mixed layer during weak flood consistent with the findings inferred from the observations stratification decays during the strong ebb in a mixing event along the horizontal extent of the salt wedge while it is also being advected offshore local mixing is shown to account for roughly half of the decay rate of the stratification in this process numerical experiments are performed to investigate the response of stratification and mixing to changes in the magnitude of the buoyancy high sensitivity is shown under intermediate levels of stratification that occur in the real system which becomes considerably weaker under more extreme conditions

numerical investigation of plunging density current when a buoyant inflow of higher density enters a reservoir it sinks below the ambient water and forms an underflow downstream of the plunge point the flow becomes progressively diluted due to the fluid entrainment the entrainment rate is strongly dependent on the richardson number and reaches a constant value well downstream of the plunge point this study is concerned with the analysis of the plunging phenomenon and the determination of the entrainment a k e model including buoyancy effects both in a sloping and a diverging channel is used to reproduce the main flow characteristics a relation between the depth at the plunge point in a channel of constant width and in a diverging channel is established and theoretical results for the calculation of the dense layer thickness are provided the latter indicates that the spreading rate of the dense layer in a diverging channel is a function of both the entrainment rate and the channel width the predictions of the plunge line location are in agreemen

reactive trace metals in the stratified central north pacific abstract vertical concentration profiles of the dissolved and suspended particulate phases were determined for a suite of reactive trace metals al fe mn zn and cd during summertime at a station in the center of the north pacific gyre during summer the euphotic zone becomes stratified forming a shallow 0 25 m oligotrophic mixed layer overlying a subsurface 25 140 m strongly stratified region the physical biological and chemical structure within the euphotic zone during this period enhanced the effect of atmospheric inputs of al fe and mn on mixed layer concentrations for example the concentration of dissolved fe in the surface mixed layer was eighteen times that observed at a depth of 100 m the observed aeolian signature of these metals matched that predicted from estimates of atmospheric input during the period between the onset of stratification and sampling the distributions of suspended particulate al fe and mn all exhibited minima in the euphotic zone and increased with depth into the main thermocline particulate al and fe were then uniform with depth below 1000 m before increasing in the near bottom nepheloid layer average particulate phase concentrations in intermediate and deep waters of the central north pacific were 1 0 0 31 and 0 055 nmol kg 1 for al fe and mn respectively the distribution of particulate cd exhibited a maximum within the subsurface euphotic zone particulate zinc also exhibited a surface maximum albeit a smaller one concentrations of particulate zn and cd in intermediate and deep waters were 17 and 0 2 pmol kg 1 substantial interbasin differences in particulate trace metals occur concentrations of suspended particulate al fe and mn were three to four times lower in the central north pacific than recently reported for the central north atlantic gyre consistent with differences in atmospheric input to these two regions concentrations of suspended particulate cd and zn were enriched in the north pacific relative to the north atlantic an observation consistent with their assimilation by plankton reactive trace metals exhibit a range of biogeochemical behaviors that can be characterized by two endmembers nutrient type and scavenged type nutrient type metals best exemplified by zn and cd are primarily removed from surface waters by biogenic particles and then remineralized at depth internal biogeochemical cycles together with physical mixing and circulation patterns control the distributions of nutrient type metals scavenged type metals best exemplified by al continue to be removed onto particles in intermediate and deep waters as well as at the surface external inputs such as the deposition of aeolian dust control the concentrations and distributions of scavenged type metals other metals such as fe exhibit a mixture of the characteristic behaviors of these two endmembers

cadmium isotope fractionation in seawater a signature of biological activity investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element here we present the results of cd isotope and concentration analyses for 22 seawater samples from the atlantic southern pacific and arctic oceans the results reveal for the first time large and well resolved cd isotope fractionations in the marine environment the majority of the seawater samples display an inverse relationship between dissolved cd contents and isotope compositions which range from e114 110cd 3 0 5 for cd rich waters 0 8 1 0 nmol kg to e114 110cd 38 6 for surface water with a cd concentration of only 0 003 nmol kg all e114 110cd data are reported relative to the jmc cd munster standard this suggests that the cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake of dissolved seawater cd by phytoplankton a few samples do not follow this trend as they exhibit extremely low cd contents 0 008 nmol kg and nearly un fractionated cd isotope compositions such complexities which are not revealed by concentration data alone require that the cd distribution at the respective sites was affected by additional processes such as water mass mixing atmospheric inputs of cd and or adsorption uniform isotope compositions of e114 110cd 3 3 0 5 1 s d were determined for seawater from 900 m depth despite of cd concentrations that display the expected increase along the global deep water pathway from the atlantic 0 3 nmol kg to the pacific ocean 0 9 nmol kg this indicates that the biomass which is remineralized in the deeper ocean is also characterized by a very constant cd isotope composition this observation is in accord with the interpretation that the cd distribution in surface waters is primarily governed by rayleigh fractionation during near quantitative uptake of dissolved seawater cd

determination of the copper isotope composition of seawater revisited a case study from the mediterranean sea abstract a new technique for the determination of dissolved copper isotope composition 65cu of seawater was applied to examine copper sources and internal cycling in the mediterranean sea along the geotraces ga04n transect a succession of chelating resin with nitrilotriacetic acid functional groups and strong base anion exchange resin together with optimization of the multi collector inductively coupled plasma mass spectrometry set up allowed to isolate copper from seawater matrix and to measure the 65cu 63cu ratios in seawater with an external precision of 0 06 2 s d this method was first applied for inter comparison measurements to surface and deep waters sampled at the bermuda atlantic time series station bats in the north atlantic ocean during the geotraces intercalibration cruise 1 disparities in 65cu reported here and in the literature over these samples showed a need to investigate whether a new inter comparison sample should be decided upon or whether the use of uv oxidation can also affect the measurement of 65cu we also measured total dissolved cu concentration dcu t and 65cu for 12 stations in the mediterranean sea the 65cu distribution showed significant variations in the euphotic zone at the chl a maximum and at bottom depths copper isotope ratios ranged from 0 21 to 0 76 0 06 2 s d yielding an average of 0 51 0 20 2 s d n 96 for the mediterranean sea a strong zonation between natural aerosol deposition to the south and anthropogenic aerosol deposition to the north was seen in the sample set dulaquais et al 2017 gerringa et al 2017 rolison et al 2015 natural dust deposits seemed to draw 65cu toward lower values and deeper in the euphotic zone whereas the impact of anthropogenic aerosols seemed restricted to an increase in dcu t at the chl a maximum 65cu showed significant increase which we attributed to scavenging on and or uptake by phytoplankton the isotope signature of cu sources to the mediterranean sea was also investigated and we inferred a significant source of isotopically heavy cu in the gibraltar area potentially originating from a release of cu sulfide leached in the mining area of southern spain i e iberian pyrite belt in rivers and transported to the mediterranean sea in surface by seasonal water mass circulation conversely marine sediments appear to be a source of isotopically light cu to deep waters this study provides new hints on the use of copper isotopes to study sources and sinks of cu in seawater this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

three dimensional numerical modeling of mixing at river confluences lateral mixing of a pollutant is considered as a slow process that is usually complete within 100 300 river widths recent studies on flow dynamics at river confluences revealed that lateral mixing can be markedly enhanced when the tributary channel is shallower than the main channel this study uses a three dimensional model to examine mixing processes immediately downstream of confluences as well as further downstream in the mainstream simulations are presented for a concordant and discordant laboratory junction and a field confluence for a low and a high flow condition the decrease in standard deviation at a cross section of a tracer over a distance of 5 channel widths is 30 for discordant beds but only 10 for concordant beds in the laboratory simulation at the natural site bed discordance is more important at the low flow than at the high flow with corresponding decreases in the standard deviation of 31 and 18 over 3 5 channel widths mixing is completed after a distance of 25 and 37 channel widths for the low and high flow conditions respectively further downstream mixing is mainly affected by planform curvature of the channel

how earth s atmosphere evolved to an oxic state a status report the evolution of the earth s atmosphere is essentially the story of atmospheric oxygen virtually every realm of the earth sciences biology geology geochemistry oceanography and atmospheric science is needed to piece together an understanding of the history of oxygen over the past decade new data from these fields has shown that there were two significant increases in atmospheric o2 levels at around 2 4 2 3 and 0 8 0 6 billion years ago respectively throughout earth history oceanic sulfate concentrations appear to have increased in accord with greater o2 levels while levels of methane a strong greenhouse gas may have inversely mirrored o2 both oxic transitions occurred in eras characterized by bsnowball earthq events and significant disturbances in the carbon cycle perhaps associated with increases in o2 and losses of methane to understand what controlled the oxygenation of the atmosphere it is necessary to determine how o2 is consumed on geologic time scales through reaction with reductants released from the earth s crust and mantle there was apparently a long delay between the appearance of oxygenic photosynthesis and oxygenation of the atmosphere and a plausible explanation is that excess reductants scavenged photosynthetic o2 from the early atmosphere however a quantitative understanding of how and why o2 became abundant on our reducing planet is still lacking thus the study of the early atmosphere remains a frontier field with much to be discovered d 2005 elsevier b v all rights reserved

cu isotopes and concentrations during weathering of black shale of the marcellus formation huntingdon county pennsylvania usa abstract the complex weathering processes which govern the production of soil from bedrock have proven difficult to understand for many lithologies weathering of black shale is of particular interest because it releases organic carbon and heavy metals as solutes and therefore impacts the health of terrestrial and aquatic ecosystems to understand black shale weathering a geochemical survey was initiated for soils developed on shales of the marcellus formation at a zero order catchment at a satellite site of the susquehanna shale hills critical zone observatory located in jackson corner pennsylvania this formation is an organic and metal rich carbonaceous shale that underlies much of new york pennsylvania ohio and west virginia in this paper we focus on the effects of weathering on variations of cu isotopes in the shale cu concentration data for soil were normalized using ti concentrations to document the mobility of cu relative to bedrock at both the ridgetop and valley floor depletion profiles for cu are documented in the soils the cu in the soils is depleted in 65 cu average 65 cu 0 5 0 2 compared to the parent material average 65 cu 0 03 0 15 consistent with loss of cu from soils the pore waters contain 10 ppb cu on average and are enriched in the heavy isotope average value 65 cu 1 14 0 44 rayleigh fractionation models using the concentration and isotope data of the soils are consistent with pyrite weathering and loss of cu from the ridgetop but downslope transport and cu re precipitation at the valley floor

native cu from the oceanic crust isotopic insights into native metal origin abstract ocean drilling has revealed that although a minor mineral phase native cu ubiquitously occurs in the oceanic crust cu isotope systematics for native cu from a set of occurrences from volcanic basement and sediment cover of the oceanic crust drilled at several sites in the pacific atlantic and indian oceans constrains the sources of cu and processes that produced cu0 we propose that both hydrothermally released cu and seawater were the sources of cu at these sites phase stability diagrams suggest that cu0 precipitation is favored only under strictly anoxic but not sulfidic conditions at circum neutral ph even at low temperature in the basaltic basement dissolution of primary igneous and potentially hydrothermal cu sulfides leads to cu0 precipitation along veins the restricted cu isotope variations 65cu 0 02 0 19 similar to host volcanic rocks suggest that cu0 precipitation occurred under conditions where cu species were dominant precluding cu redox fractionation in contrast the cu isotope variations observed in the cu0 from sedimentary layers yield larger cu isotope fractionation 65cu 0 41 0 95 suggesting that cu0 precipitation involved redox processes during the diagenesis with potentially seawater as the primary cu source we interpret that native cu precipitation in the basaltic basement is a result of low temperature 20 65 c hydrothermal processes under anoxic but not h2s rich conditions consistent with positive 65cu signatures the sediment cover receives major cu contribution from hydrogenous i e seawater sources although hydrothermal contribution from plume fallout cannot be entirely discarded in this case disseminated hydrogenous and or hydrothermal cu might be diagenetically remobilized and reprecipitated as cu0 in reducing microenvironment

entrainment and turbulence in saline underflow in lake ogawara under certain tidal conditions a saline underflow originating in the pacific ocean moves into lake ogawara japan the underflow consists of a uniform saline bottom layer that is slightly warmer than the ambient and an interfacial shear layer in which the velocity and density are decreased within the experimental area the underflow is confined to a channel approximately 1 km wide and is essentially two dimensional the underflow had a bulk richardson number defined in terms of the mean properties between 1 and 2 the rate of entrainment into the bottom layer was calculated using two distinct methods the first method used the change in the maximum salinity of the underflow measured at two stations along the path of the underflow to infer the amount of ambient water entrained the second method made direct measurements of vertical mass fluxes with a profiler the agreement between the two methods was excellent the measured entrainment coefficients were consistent with the derived entrainment law the turbulent structure of the flow was mapped for a 3 h quasi steady period of the flow turbulence is predominantly generated on the bottom boundary and is transported vertically to the density interface where it leads to mixing

fate of particulate copper and zinc isotopes at the solimoes negro river confluence amazon basin brazil abstract the behaviour and fate of copper cu and zinc zn at river confluences is poorly understood although chemical and physical processes during mixing of compositionally different tributaries might condition metal availability and fluxes to the ocean to identify and quantify the effect of such processes in river mixing zones particulate cu and zn isotope signatures 65cuspm and 66znspm were measured along cross sections and vertical profiles at the largest river confluence in the world the encontro das aguas mixing zone of the amazon river where the organic rich negro river meets the sediment rich solimoes river the negro river suspended sediments with highly variable cu and zn concentrations as well as 65cuspm and 66znspm are mostly influenced by organic matter and by the lateritic cover of the watershed the solimoes river suspended sediments more homogeneous in cu and zn concentration and isotope composition across the river section reflect the signature of weathered silicate rich sediments derived from the andes the solimoes river supplies the majority of the suspended cu and zn to the amazon river and despite important flux losses across the confluence 35 for cu and 27 for zn 65cuspm and 66znspm show a conservative behaviour during the mixing in the dissolved load cu concentrations and 65cudiss mostly supplied by the solimoes river behave conservatively whereas zn derived mainly from the negro river suffers an important loss 58 that can be attributed to zn adsorption onto the suspended sediments from the solimoes river this transfer does not induce a significant 66znspm shift in the amazon river suspended sediments therefore cu and zn isotope ratios in the suspended sediments behave conservatively through this confluence which mixes two very chemically contrasted rivers our findings thus suggest that the riverine isotopic information on the sources of particulate cu and zn is preserved during tributary mixing

heavy nickel isotope compositions in rivers and the oceans abstract nickel is a biologically active trace metal whose dissolved concentration depth profiles in the ocean show nutrient like behaviour if the pronounced removal of nickel from the dissolved phase in the surface ocean and its return in the deep is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers one of the principal sources of nickel to the oceans the dissolved phase of rivers exhibits substantial variability in both ni concentration and 60 ni from 2 2 to 35 nmol kg 1 and 0 29 to 1 34 respectively the most striking result from the nickel isotope analyses of rivers is that they are substantially heavier by up to 1 for 60 ni than the range for silicate rocks on the continents a finding that is analogous to that for other transition metal isotope systems if the data presented here are close to representative of the global riverine flux they suggest an annual input of ni to the oceans of 3 6 10 8 moles and a discharge and concentration weighted 60 ni average of 0 80 the relationship between ni isotopes and concentrations shows similarities with those for other transition metal isotope systems where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates either in the weathering environment or during transport in stark contrast to the rivers the dataset for seawater is very homogeneous with 2sd of the entire dataset being only twice the analytical reproducibility the second main feature is that seawater is distinctly heavier in ni isotopes than rivers the average 60 ni is 1 44 0 15 2sd and only 2 of the 29 seawater analyses have a ni isotopic composition that is lighter than the heaviest river the lack of an isotopic shift associated with the drawdown of nickel concentrations in the surface ocean suggests that the cycling of nickel between the surface and deep ocean is not associated with a pronounced isotopic fractionation the isotopic data also present a mass balance problem the main output of nickel from the oceans sorption to fe mn oxides appears to be similar in isotopic composition to the dissolved phase yet the riverine input is lighter than the dissolved pool this observation either requires other inputs that are isotopically heavy or an output that is isotopically light further large inputs over and above the dissolved riverine source appear to be required by what we know of the elemental budget but the isotopic mass balance suggests that such an input needs to be isotopically much heavier than both the riverine dissolved load and the lithogenic isotopic composition of nickel