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

lead isotopic evidence for an australian source of aeolian dust to antarctica at times over the last 170 000 years abstract systematic analysis of pb sr and nd isotopes of 32 fluvial clay samples 6 km 2 murray darling basin mdb located in semiarid southeastern australia displays similar isotopic values between some mdb clays and dust from several ice core samples from the epica dome c in antarctica close scrutiny of several ratios of the four pb isotopes and in particular 208 pb 207 pb versus 206 pb 207 pb shows that several samples from the darling sub basin of the mdb display similar values for the same isotopes for dome c samples from different ages and more particularly during wet phases in australia marine isotopic stages 5e 3 and 1 the combination of nd and sr isotopic ratios from the same mdb fluvial clays clearly eliminates the murray sub basin and supports the darling sub basin as a potential source of aeolian material to antarctica overall the australian dust supply to antarctica predominantly occurred during interglacial periods the work presented here shows that aerosols generated in southeastern australia can travel to parts of west antarctica and this is supported by atmospheric observations and models in addition evidence of australian dust in antarctic ice cores further implies dust deposition in the southern ocean would have occurred in the past current meteorological observations also imply that the western pacific and indian ocean sector of the southern ocean would frequently receive aeolian dust components originating from southeastern australia

early cambrian ocean anoxia in south china the cause of the most marked changes in the evolution of life which define the first order stratigraphic boundary between the precambrian and the phanerozoic eon remains enigmatic and a highly topical subject of debate a global ocean anoxic event triggered by large scale hydrogen sulphide h 2 s release to surface waters has been suggested by wille et al on the basis of two data sets from south china and oman to explain the fundamental biological changes across the precambrian cambrian pc c boundary here we report a new precise shrimp u pb zircon age of 532 3 0 7 million years myr ago fig 1 for a volcanic ash bed in the critical unit that reflects the ocean anoxic event the lowermost black shale sequence of the niutitang formation in the guizhou province south china this age is significantly younger than the precise pc c boundary age of 542 0 0 3 myr ago approximately 10 myr younger than the extinction of the ediacaran fauna and thus challenging the view of a major ocean anoxic event having been responsible for the major changes in the direction of evolution at the pc c boundary

advection and removal of 210pb and stable pb isotopes in the oceans a general circulation model study abstract natural pb isotope variability in the oceans encodes information about the sources of continental material to the oceans about ocean circulation and about pb removal in order to use this information we must understand the natural cycle of pb in the oceans which is overprinted by large anthropogenic input in this study we use 210 pb which has not been significantly anthropogenically perturbed to investigate oceanic pb geosecs 226 ra and model derived atmospheric fluxes of 210 pb are used to input 210 pb into an ocean general circulation model irreversible scavenging of this 210 pb onto settling biogenic particles and at the seafloor are tuned so that the model replicates the observed pattern of 210 pb in the oceans the best fit model run provides a map of the variability of residence time for pb the global average residence time of pb in this model is 48 yr but there is over an order of magnitude variation between areas of high and low productivity this is expected to enhance provinciality of pb isotope ratios in the oceans because stable pb isotopes are expected to behave in seawater in a similar fashion to 210 pb the pattern of removal of 210 pb derived by the model can be used to investigate the behavior of stable pb isotopes we use a simplified input of pb consisting of five point sources representing major rivers and a disseminated dust input although this simplified input scheme does not allow precise reconstruction of pb concentration and isotopes in the oceans it allows us to answer some first order questions about the behavior of pb as an ocean tracer with a total pb input of 6 3 10 7 mol yr chow t j and patterson c c the occurrence and significance of pb isotopes in pelagic sediments geochim cosmochim acta 26 263 308 1962 the model predicts natural seawater pb concentrations averaging 2 2 pmol kg even in the absence of anthropogenic input the model ocean exhibits a near surface maximum in pb concentration and the model suggests natural pb concentrations in the northern hemisphere an order of magnitude higher than in the southern hemisphere a point source of pb is suggested to dominate the seawater pb inventory close to the source but is reduced to typically less than 10 of the inventory by the time that pb is advected out of the originating ocean this length scale of advection for pb isotope signals confirms their potential as tracers of ocean circulation assuming an 8 dissolution of dust their input to the open ocean are seen to be a significant portion of pb inventory throughout the oceans and make up 50 of the pb inventory in the model s southern ocean finally a preliminary investigation of the response of pb isotope distributions to changes in boundary conditions between glacial and interglacial times illustrates that significant variation in the pb isotopes are expected in some regions even for reasonably small changes in climate conditions

isotopic evidence of contaminant lead in the south atlantic troposphere and surface waters abstract the third intergovernmental oceanographic commission ioc baseline contaminant cruise may june 1996 has established the first lead isotopic compositions in the surface water and the atmosphere of the equatorial and south atlantic ocean these ratios have evidenced both anthropogenic and natural origins of lead along the cruise transect from 33 s to 10 n the isotopic gradients tentatively have been attributed to aeolian as well as surface water advective inputs from a suite of rather local and remote sources to the southern hemisphere relatively low 206pb 207pb ratios x sd were encountered within the south equatorial current between 17 s and 5 s 1 156 0 003 those were bracketed by more radiogenic ratios at higher latitudes in the southern hemisphere 33 s to 23 s within the brazil current and the subtropical gyre 1 163 0 003 and in the northern hemisphere 0 to 10 n 1 165 0 005 the latter were comparable to ratios of surface water in the north atlantic equatorial ocean 1 169 0 006 under a combined contaminant influence of both north american westerlies 1 19 1 20 and european easterlies 1 155 1 165 that predominance of contaminant lead contrasts with the measurable presence of natural lead in surface waters of the equatorial ocean which are attributed to aeolian inputs of saharan dust the ratios of lead in surface waters at higher latitudes in the south atlantic are characteristic of anthropogenic lead aerosols also detected in antarctic ice and could substantiate as well the hypothesized aerosol recycling of lead by sea spray emission in the far southern hemisphere the atmospheric lead isotopic compositions 206pb 207pb in bulk depositions 1 171 0 006 precipitation 1 171 0 006 and aerosols 1 168 0 011 were generally more radiogenic than the surface waters 1 162 0 005 beside a poor representation of a short term atmospheric sampling this difference could reflect a recent evolution in atmospheric lead emissions which have not yet been reflected in oceanic surface waters it may also be due in part to advective lead inputs from surface oceanic circulation of the south equatorial current

evaluation of δ13c chemostratigraphy for intrabasinal correlation vendian strata of northeast siberia integrated sedimentologic stratigraphic and geochemical 13 c 18 o fe mn and sr data from vendian cambrian carbonate ramp deposits of the northeast siberian platform olenek uplift and kharaulakh mountains region are used to constrain primary time dependent oscillations in the carbon isotope record and to evaluate 13 c chemostratigraphy for high resolution intrabasinal correlation the vendian 13 c record of northeast siberia reflects global variations seen elsewhere by displaying in ascending order a strong positive isotopic shift to values near 6 herein named the p interval an intermediate interval of relatively little isotopic change i interval which shows in some sections a monotonic decrease in 13c from 2 at the base to near 0 at the top and a negative excursion to 4 n interval just beneath the vendian cambrian boundary in addition to secular isotopic shifts these strata exhibit local small scale signals related to intrabasinal variations in subsidence erosion and diagenetic alteration e g degradation of organic matter dolomitization and hydrothermal and burial effects these local intrabasinal processes in some cases have modified both the magnitude and form of the primary isotopic excursions which are used as the basis for correlation in all studies carbon isotope profiles provide an important method to evaluate intrabasinal variations in subsidence erosion and stratigraphic completeness these profiles reflect increasing subsidence along the platform to basin transition whereas progressive truncation of isotopic profiles along this trend illustrate pronounced uplift and erosion of ramp strata along unconformity surfaces

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

biogeochemical cycling of dissolved zinc along the geotraces south atlantic transect ga10 at 40 s the biogeochemical cycle of zinc zn in the south atlantic at 40 s was investigated as part of the uk geotraces program to date there is little understanding of the supply of zn an essential requirement for phytoplankton growth to this highly productive region vertical zn profiles displayed nutrient like distributions with distinct gradients associated with the water masses present surface zn concentrations are among the lowest reported for the world s oceans 2 0 97 n 460 our results suggest that the use of a global zn si relationship would lead to an underestimation of dissolved zn in deeper waters of the south atlantic by utilizing si and a new tracer zn our data indicate that the preferential removal of zn in the southern ocean prevented a direct return path for dissolved zn to the surface waters of the south atlantic at 40 s and potentially the thermocline waters of the south atlantic subtropical gyre the importance of zn for phytoplankton growth was evaluated using the zn soluble reactive phosphorus srp relationship we hypothesize that the low zn concentrations in the south atlantic may select for phytoplankton cells with a lower zn requirement in addition a much deeper kink at 500m in the zn srp ratio was observed compared to other oceanic regions key points dissolved zinc biogeochemical cycle investigated in the south atlantic ocean 2014 american geophysical union all rights reserved

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

the origin of decoupled carbonate and organic carbon isotope signatures in the early cambrian ca 542 520 ma yangtze platform abstract the early cambrian ca 542 520 ma strata in south china record two prominent negative carbonate carbon isotope 13ccarb excursions of early nemakit daldynian n d and early tommotian ages across each of these excursions carbonate and organic carbon isotopes 13ccarb and 13corg are strongly decoupled regional correlation across a shelf to basin transect shows lateral heterogeneity of 13corg during the early middle n d but more homogenized 13corg values across the basin during the late n d and tommotian the temporal and lateral variations in 13corg suggest that decoupled 13ccarb and 13corg across the n d 13ccarb excursion were possibly caused by diagenetic alteration of organic matter and or amplification of detrital organic carbon isotope signature in low toc carbonates in contrast decoupled 13ccarb and 13corg of the upper n d and tommotian were likely resulted from chemoautotrophic methanotrophic biomass contribution to toc in organic rich black shale and carbonates the decoupled 13ccarb 13corg pattern from the lower n d strata ca 542 ma shows striking similarities with those from the basal ca 635 ma and upper ca 551 ma doushantuo formation in all three cases decoupled 13ccarb 13corg are seen in organic poor carbonates toc 0 1 and coupled 13ccarb 13corg occur in organic rich black shale and carbonates at the end of the negative 13ccarb excursion these similarities suggest that the shift from decoupled to coupled 13ccarb 13corg has no causal link with the terminal oxidation of a large oceanic doc reservoir given the pervasive anoxia euxinia in ediacaran early cambrian oceans local doc rich environments may have been common but a large oceanic doc reservoir capable of buffering the 13c of marine organic matter requires independent evidence

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

carbonate carbon isotope chemostratigraphy and u pb zircon geochronology of the liuchapo formation in south china constraints on the ediacaran cambrian boundary in deep water sequences abstract the ediacaran cambrian transition was one of the most significant intervals in geological history witnessing the origin of the metazoans and major environmental changes establishing a precise chronostratigraphic framework for the ediacaran cambrian transition has great significance for understanding the geological and evolutionary processes during this transition an integrated study on carbonate carbon isotopes and u pb zircon dating was conducted within the liuchapo formation in the sifangjing section in northeastern guizhou province south china to recognize the ediacaran cambrian boundary in slope facies of the yangtze block a substantial negative carbonate carbon isotope excursion was recognized within the lower part of the liuchapo formation moreover a weighted mean u pb zircon age of 540 7 3 8 6 6 ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion the carbon isotope and age dating results indicate that the ediacaran cambrian boundary within the sifangjing section should be placed in the lower part of the liuchapo formation additionally in the sifangjing section a distribution of horodyskia minor extends up to the basal cambrian while the last appearance datum lad of palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the liuchapo formation this relationship indicates that the lad of the palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the ediacaran cambrian boundary successions in slope and deep water basin settings of the yangtze block

impact of anthropogenic pb and ocean circulation on the recent distribution of pb isotopes in the indian ocean abstract pb and pb isotope ratios in the modern ocean have been altered significantly by anthropogenic pb inputs over the past century most studies of anthropogenic pb in the ocean have focused on the north atlantic and north pacific oceans and the impact of anthropogenic pb inputs to the indian ocean and processes controlling the distribution of pb in the indian ocean are poorly known this study presents the pb and pb isotopic composition 206 pb 207 pb 208 pb 207 pb of 11 deep stations from the indian ocean japanese geotraces cruise kh 09 5 from the bay of bengal and arabian sea to the southern ocean 62 s the pb isotope ratios of the indian ocean range 1 140 1 190 for 206 pb 207 pb and 2 417 2 468 for 208 pb 207 pb with lower ratios appearing in the shallow waters of the northern indian ocean and higher ratios appearing in the deep layers of the southern ocean this result agrees with a previous study on pb concentrations echegoyen et al 2014 showing that the indian ocean particularly its northern part is largely perturbed by anthropogenic pb inputs 206 pb 207 pb and 208 pb 207 pb of the indian sector southern ocean are still lower than natural pb showing this region was also affected by anthropogenic pb anomalously low or high 206 pb 207 pb and 208 pb 207 pb were observed in the thermocline and shallow waters of the southern indian ocean and the arabian sea which are ascribed to water mass distribution e g subantarctic mode water and evolving pb isotope ratios of this region as dominant anthropogenic pb sources change 206 pb 207 pb and 208 pb 207 pb in the bay of bengal are higher than those in the arabian sea which might be the result of the anthropogenic pb inputs from different provenance or seawater exchanging pb isotopes with natural particles derived from rivers and or sediments at the basin boundaries

contrasting multiproxy reconstructions of surface ocean hydrography in the agulhas corridor and implications for the agulhas leakage during the last 345 000 years planktonic 18o and mg ca derived sea surface temperature sst records from the agulhas corridor off south africa display a progressive increase of sst during glacial periods of the last three climatic cycles the sst increases of up to 4 c coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites mg ca derived sst maximizes during glacial maxima and glacial terminations to values about 2 5 c above full interglacial sst the paired planktonic 18o and mg ca derived sst records yield glacial seawater 18o anomalies of up to 0 8 indicating measurably higher surface salinities during these periods the sst pattern along our record is markedly different from a u37k derived sst record at a nearby core location in the agulhas corridor that displays sst maxima only during glacial terminations possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of sst contrasts during glacials in association with seasonal changes of agulhas water transports and lateral shifts of the agulhas retroflection the different sst reconstructions derived from u37k and mg ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the agulhas current and interocean salt leakage is not as straightforward as previously suggested

the double spike toolbox the double spike technique is a well established method for correcting for instrumental mass fractionation in mass spectrometry the precision of the technique is controlled by the choices of double spike composition and the proportions in which the double spike and sample are mixed to make these choices easier we provide software the double spike toolbox for calculating optimal double spikes which are chosen purely on the basis of minimising error propagation in addition we provide cocktail lists of optimal double spikes for all 33 elements that have 4 or more naturally occurring isotopes using some sensible default parameters as examples we discuss the application of the software to fe pb and ca isotopes

behavior of osmium at the freshwater saltwater interface based on ganga derived sediments from the estuarine zone 1 leaching experiments performed on several sediments of the ganga river suggest that between 10 and 20 of the osmium is in an easily exchangeable position analyses of sediments from two estuarine rivers the pussur and the lower meghna reveal no enrichment of os in the saltwater freshwater mixing zone relative to ganga sediments of similar al2o3 sio2 ratio suggesting that osmium is not significantly trapped in this estuary however a significant decrease of the 187os 188os ratio is observed in the pussur sediments relative to the ganga composition these latter are derived entirely from the ganga or from erosion of the ganga paleodelta and thus would be expected to have similar os isotopic compositions nd isotopic results from the pussur are indistinguishable from those of the ganga while the sr isotopic results are at the lower end of the ganga range confirming the absence of a major source difference between ganga and pussur sediments it thus seems unlikely that the difference in os isotopic signature can be entirely explained by a change in provenance suggesting instead that the os compositions have been modified our results show that the less radiogenic os compositions of the pussur sediments cannot result simply from desorption of radiogenic os or from scavenging of river or seawater os instead the decrease of the 187os 188os ratio could imply a complex exchange between dissolved os derived partly from seawater and os in the leachable fraction of sediments this mechanism could therefore constitute both a source and a sink for seawater osmium and may significantly influence the osmium marine budget

the influence of bays on adjusted sea level over adjacent shelves with application to the labrador shelf we examine how low frequency variations in adjusted sea level over a continental shelf are influenced by an inland sea connected to the shelf through a strait an analytical model shows that free continental shelf waves propagating by the mouth of the strait are strongly modified at a period corresponding to a helmholtz like resonance of the inland sea and strait also near this period atmospheric pressure variations over the inland sea result in relatively strong flow through the strait and the resulting cross isobath flow over the exterior shelf efficiently generates continental shelf waves in the region forward of the strait calculations using a fully nonlinear numerical model with more realistic although still idealized topography verify the predictions of the simpler analytical model we apply this theory to the hudson bay labrador shelf system where we find that this mechanism of shelf wave generation strongly influences the shelf response in the energetic meteorological band 2 6 days data from nain labrador are analyzed using multiple linear regression models and lend further support to the theory

marine biogeochemical cycling during the early cambrian constrained by a nitrogen and organic carbon isotope study of the xiaotan section south china the precambrian cambrian boundary is claimed as one of the most crucial biological breakthroughs on our planet when changes in chemical and physical conditions together with key biological innovations helped to trigger a biodiversity explosion the yangtze platform south china mainly characterized by continuous and unaltered successions of this age is ideally suited to high resolution palaeomarine investigations of this event in this study 15n and 13corg records from xiaotan section yunnan sw china were investigated in order to provide insight into variations in primary productivity ecological developments and marine environment the ediacaran early cambrian xiaotan section is characterized by relatively high sedimentation rates and variable lithologies carbonates cherts phosphorites sandstones and siltstones that alternate through nearly 600 meters thickness organic carbon isotope values vary between 36 and 21 tightly following and helping to complete published 13ccarb trends the base of the cambrian is characterized in this section by a significant drop from 25 to 35 mirroring the 13ccarb fall observed at this and other sections worldwide higher in the section in the dahai member values increase to 20 again demonstrating communication between doc and dic pools during the early cambrian on 105 106 year time scales from the base of the overlying shiyantou formation 13corg values remain around 30 until the end of the section testifying to an interval of more modest change in dic 13c that would be consistent with biostratigraphic correlations nitrogen isotope values vary independently from carbon isotope trends exhibiting several major 15n cycles with values fluctuating between 9 and 1 robust trends in 15n within the dahai member testify to changes in the ratio between nitrogen fixation and denitrification possibly reflecting fluctuations in the water column chemocline as 13c values reached their global acme up section nitrogen isotope values show dampened cyclicity with values remaining between 0 and 5 indicating establishment of an equilibrium state in marine biogeochemistry and nutrient cycles the overall variability in 15n closely resembles that of recent marine sediments while the observed cyclicity is defined by several samples in all cases these observations argue for good preservation of original isotopic signatures which bodes well for future n isotope studies of the precambrian cambrian boundary

new u pb zircon ages of the ediacaran cambrian boundary strata in south china the ediacaran cambrian transition is a critical interval marking drastic biological oceanic and geochemical co evolutions in geological history but it is poorly constrained geochronologically in south china we here present two new sets of sims u pb zircon ages from ediacaran cambrian boundary strata dengying liuchapo and niutitang formations deposited in the slope basin environments of carbonate platforms two weighted mean u pb ages of 542 1 5 0 ma and 542 6 3 7 ma in the basal and mid upper liuchapo formation respectively in slope and basinal settings provide the first direct age set for the ediacaran cambrian boundary in south china another two u pb ages of 524 2 5 1 ma and 522 3 3 7 ma from the base of the overlying niutitang formation indicate that this widespread unit in south china was deposited about 20 ma after the onset of the cambrian

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

role of oceanic circulation on contaminant lead distribution in the south atlantic abstract both the relatively high lead concentrations and their characteristic anthropogenic isotopic compositions attest to the widespread contamination of industrial lead in the western equatorial and south atlantic ocean spatial gradients in those isotopic signatures evidence the conservative lateral transport of lead in oceanic water masses while the discrete isotopic signatures in deep oceanic waters substantiate the complementary hypothesis that the release of lead from settling particles is relatively small on a decadal time scale specifically the relatively low radiogenic lead e g 206pb 207pb 1 148 0 009 in the lower north atlantic deep water l nadw south of 10 north is primarily attributed to us industrial lead emitted in the northern hemisphere prior to 1965 and the more radiogenic lead e g 206pb 207pb 1 180 0 006 in the upper north atlantic deep water u nadw is primarily attributed to subsequent industrial lead emissions in that hemisphere in contrast the relatively radiogenic lead e g 206pb 207pb 1 186 0 007 in the antarctic bottom water aabw seemingly reflects a mixture of natural and anthropogenic lead sources within the southern hemisphere and its isotopic dissimilarity with that e g 206pb 207pb 1 159 0 002 of antarctic intermediate water aaiw and the aabw may be due to differences in either their aeolian or water mass inputs

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

petrology and geochemistry of chert on the marginal zone of yangtze platform western hunan south china during the ediacaran cambrian transition the ediacaran cambrian transition was one of the most critical intervals in earth history during this interval widespread chert was precipitated commonly as a stratal wedge in carbonates along the southern margin of the yangtze platform south china the chert wedge passes into a full chert succession further basinward to the south east four lithotypes of chert are identified across the marginal zone in western hunan mounded vein brecciated and bedded chert the mounded chert is characterized by irregular to digitiform internal fabrics generally with abundant original vesicles and or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals the host chert or matrix of these mounds is dominated by amorphous cryptocrystalline silica commonly disseminated with pyrite the vein chert with minor quartz locally generally cross cuts the overlying dolostone and chert horizons and terminates under the mounded and or bedded chert bodies the brecciated chert commonly occurs as splayed intrusions or funnel shaped wedges and cross cuts the topmost dolostones the bedded chert the most common type generally is thin to medium bedded and laminated locally it is composed of amorphous silica with minor amounts of black lumps microthermometry of fluid inclusions from vein and void lining minerals mainly quartz and barite revealed homogenization temperatures from 120 to 180 c for the trapped primary fluids compositionally these chert deposits generally are pure with sio2 92 wt and only minor fe2o3 and al2o3 contents most of which show positive europium anomalies in rare earth element patterns especially for the mounded chert all these data suggest that the marginal zone chert deposits resulted from a low temperature silica rich hydrothermal system in which the mounded chert was precipitated around the releasing vents i e as silica chimneys the vein and splayed brecciated chert however was formed along the syndepositional fault fracture conduits that linked downward while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor these petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation rapid tectonodepositional and oceanic changes during the ediacaran cambrian transition in south china

lead and aluminum in atlantic surface waters 50 n to 50 s reflecting anthropogenic and natural sources in the eolian transport lead and aluminum were measured with a 40 100 km resolution in surface water on two transects across the atlantic ocean one in may 1990 from cape town to the north sea the other in november 1990 from the north sea to the strait of magellan samples were drawn 14 m below surface at normal speed from a 2 m long snorkel system mounted on the bottom of the ship directly into a clean room area in the tropics both pb and al show maximum concentrations in the intertropical convergence zone itcz correlated with each other and with minimum salinities indicating wet deposition as their common source even in this area characterized by large inputs of mineral aerosols the pb al ratio shows that the major source of soluble lead 95 is anthropogenic at higher latitudes al is low throughout 10 20 nmol kg whereas enhanced pb values show the anthropogenic inputs off south africa northern argentina and especially western europe very low pb and especially al concentrations in the upwelling areas associated with the canary and benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition and of the adhering reactive trace metals

tracing the agulhas leakage with lead isotopes the transport of warm and salty waters from the indian ocean to the south atlantic by the agulhas current constitutes a key return route of the meridional overturning circulation despite the importance of the agulhas leakage on interoceanic exchange its role on biogeochemical cycles is poorly documented here we present the first lead pb concentration and isotope data for surface seawater collected during the geotraces cruise d357 in the agulhas current system lead in surface waters of the cape basin is described by three distinct end members the south african coast open south atlantic seawater and indian ocean seawater the latter stands out in its pb isotopic composition and can be tracked within two distinct agulhas rings high pb concentrations in the agulhas rings further corroborate an indian ocean provenance of waters and suggest that the agulhas leakage represents a major conduit not only for heat but also for trace metals

terreneuvian small shelly faunas of east yunnan south china and their biostratigraphic implications the study discusses the detailed composition of terreneuvian small shelly fossil ssf assemblages of eastern yunnan province meishucun xianfeng and huize regions the described sections represent shallow water deposits of the yangtze platform that include a number of stratigraphical hiati the reported ssf assemblages can be assigned to the regional ssf biozones i iii anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone zones ii and iii are slightly redefined based on new data two subzones of zone ii are proposed here namely annelitellus yangtzensis obtusoconus honorabilis subzone and maikhanella cambriana oelandiella korobkovi subzone claviconchella qianyii gen et sp nov and bubiites simplex gen et sp nov are reported here we also provide a critical revision of the ssf distribution for the well known meishucun section the correlation scheme for east yunnan documents the extent and duration of stratigraphical hiati the distribution of ssfs and the lithological characterization indicate three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification this prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata considering the complexity of the terreneuvian earth history as well as the uniqueness of ssf an integration of sedimentology geochemistry and paleontology is needed for future ssf study

germanium silicon of the ediacaran cambrian laobao cherts implications for the bedded chert formation and paleoenvironment interpretations sedimentary strata of the terminal ediacaran 635 542 ma to early cambrian 542 488 ma laobao liuchapo bedded cherts in the south china block include the ediacaran oxidation event and the cambrian explosion understanding the origin and depositional environment of the bedded cherts may provide insight into how the earth s surface environment changed between the proterozoic and phanerozoic we measured major and trace element compositions and ge si ratios of the laobao cherts from northern guangxi province the laobao cherts were deposited in the deep basinal environment of the south china block we show that the composition of the laobao cherts is determined by a mixture of four components quartz clay carbonate and pyrite iron oxide the quartz component is the dominant component of the laobao cherts the maximum estimated ge si of the quartz component is between 0 4 and 0 5 mol mol which is close to the ge si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids these ge si systematics suggest that normal seawater rather than mid ocean ridge hydrothermal fluids is the primary si source for the laobao cherts the ge si of the clay component varies between 1 and 10 mol mol which is comparable to the ge si of typical marine clays but 10 100 times lower than that of chert nodules from early ediacaran beds the doushantuo formation predating the terminal ediacaran laobao cherts studied here our observations indicate that the clay component ge si ratio decreased from the early ediacaran to the late ediacaran we speculate that high ge si ratios in clays reflect the preferential chelation of ge by dissolved organic compounds adsorbed onto clays if so this suggests that the decrease in ge si ratio of the clay component in the ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the ediacaran cambrian transition consistent with oxidation of the oceans during the late ediacaran finally the seawater origin of the laobao cherts also suggests that replacement of carbonate may not be the primary cause for bedded chert formation instead direct precipitation from seawater or early diagenetic silicification of calcareous sediments perhaps due to the emergence of si accumulation bacteria may have been responsible for the bedded laobao liuchapo chert formation in south china block