balancing rare earth element distributions in the northwestern mediterranean sea abstract elemental concentrations of rare earth elements ree and isotopic compositions of neodymium end have been measured in three water column profiles in the north western mediterranean sea clear enrichments of ree are observed when comparing to adjacent atlantic waters suggesting ree inputs along the circulation in this area for the first time relative proportions of external sources including submarine groundwater discharges sgd have been quantified for the studied area atmospheric deposition is estimated to be the most important external source for all the ree with an average contribution of 44 followed by diffusion from porewaters which provide a 30 dissolved riverine fluxes account for 11 sgd for 10 and dissolution of remobilized surface sediments the remaining 6 mass balances accounting for seawater transport and identified external sources have been delineated for the three main water masses modified atlantic waters levantine intermediate waters and western mediterranean deep waters they show that the balances of ree in this area are dominated by seawater mass mixing superimposed on this hydrography ree vertical profiles are affected by external sources and biogeochemical cycling dissolved ree are correctly balanced in deep waters whereas substantial missing fluxes are identified in the surface and intermediate water masses additional net lree outputs and hree inputs are required in the surface waters while net output fluxes for all the ree are missing at intermediate waters the most likely process suggested here is an active reversible scavenging consistent with a stronger adsorption of lree compared to hree in the particular case of the redox sensitive cerium the most plausible mechanism to explain the net output missing fluxes is ce 3 removal by particle scavenging via oxidation to insoluble ce 4 estimated ce oxidation rates of 0 33 d 1 in surface waters agree well with previously published values exchange fluxes derived from the isotopic nd mass balance indicate higher nd scavenging in surface compared to intermediate waters

sulfate minerals control dissolved rare earth element flux and nd isotope signature of buoyant hydrothermal plume emso azores 37 n mid atlantic ridge abstract while hydrothermal vents are now thought to be a major source of dissolved iron to the oceans they have always been considered to be a sink for the dissolved rare earth elements drees however true dissolved ree observations in hydrothermal plumes are still lacking here we report for the first time the dree concentrations and neodymium isotopic compositions dend of buoyant hydrothermal fluids at lucky strike mid atlantic ridge we find that 27 to 62 of total hydrothermal drees are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation after this initial loss all drees behave quasi conservatively within the buoyant plume dissolved phase end dend in the evolving plume are identical to black smoker dend of 9 0 and contrast radically with dend of the local deep water mass at 12 0 plume dend as low as 6 6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater dend signature we find based on the first plume dree observations that hydrothermal plumes are in fact a source of dree to the north atlantic deep water precipitation dissolution processes of hydrothermally derived minerals i e sulfates in the buoyant plume and fe oxy hydroxide in the non buoyant plume will likely affect the fate of other trace metals and their isotopic composition

element geochemistry and neodymium isotope systematics of the neoarchean banded iron formations in the qingyuan greenstone belt north china craton abstract pure marine chemical sediments such as banded iron formations bif are excellent archives of ancient seawater and may also provide constraints on the coeval hydrosphere atmosphere system however on the bases of interpreted depositional settings it has long been argued that algoma type bif merely recorded the intrabasinal volcanic or hydrothermal conditions here we couple systematic major and trace elements data with samarium sm neodymium nd isotopic analyses of 2 56 ga old algoma type bifs and associated schists from different stratigraphic horizons of the qingyuan greenstone belt qgb in the north china craton ncc to characterize the source and depositional environment over a short period 30 ma meanwhile we also compare our results with data for other archean to paleoproterozoic superior and algoma type bifs especially those near contemporaneous counterparts in the ncc to further evaluate the reliability of qgb bifs as proxies for the neoarchean seawater low al2o3

constraining erosional input and deep water formation in the north atlantic using nd isotopes many marine radiogenic isotope records show both spatial and temporal variations reflecting both the degree of mixing of distinct sources in the oceans and changes in the distribution of chemical weathering on the continents however changes in weathering and transport processes may themselves affect the composition of radiogenic isotopes released into seawater the provenance of physically weathered material in the labrador sea constrained through the use of ar ar ages of individual detrital minerals has been used to estimate the relative contributions of chemically weathered terranes releasing radiogenic isotopes into the labrador sea a simple box model approach for balancing observed nd isotope variations has been used to constrain the relative importance of localised input in the labrador sea and the subsequent mixing of labrador sea water into north atlantic deep water the long term pattern of erosion and deep water formation around the north atlantic seems to have been a relatively stable feature since 1 5 ma although there has been a dramatic shift in the nature of physical and chemical weathering affecting the release of hf and pb isotopes the modelled nd isotopes imply a relative decrease in water mass advection into the labrador sea between 2 4 and 1 5 ma accompanied by a decrease in the rate of overturning possibly caused by an increased freshwater input into the labrador sea

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

the large scale evolution of neodymium isotopic composition in the global modern and holocene ocean revealed from seawater and archive data neodymium isotopic compositions 143nd 144nd or end have been used as a tracer of water masses and lithogenic inputs to the ocean to further evaluate the faithfulness of this tracer we have updated a global seawater end database and combined it with hydrography parameters temperature salinity nutrients and oxygen concentrations carbon isotopic ratio and radiocarbon of dissolved inorganic carbon archive end data are also compiled for leachates foraminiferal tests deep sea corals and fish teeth debris from the holocene period 10 000 years at water depths 1500 m property property plots show clear correlations between seawater end and the other variables suggesting that large scale water mass mixing is a primary control of deepwater end distribution at 200 m basin scale seawater t s end diagrams demonstrate the isotopic evolution of different water masses seawater and archive end values are compared using property property plots and t s end diagrams archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the pacific both positive and negative offsets exist in the northern north atlantic applying multiple regression analysis to deep 1500 m seawater data we established empirical equations that predict the main large scale deepwater end trends from hydrography parameters large offsets from the predicted values are interpreted as a sign of significant local regional influence dominant continental influence on seawater and archive end is observed mainly within 1000 km from the continents generally seawater and archive end values form gradual latitudinal trend in the atlantic and pacific at depths 600 m consistent with the idea that nd isotopes help distinguish between northern southern sourced water contributions at intermediate and deep water depths

silicon isotope fractionation during nutrient utilization in the north pacific the distribution of silicon in the north pacific is controlled by the utilization of silicic acid by diatoms a process that fractionates silicon si isotopic compositions silicon isotope variations are presented for six water column profiles from the surface mixed layer down to the deep waters of the north pacific ocean although the observed si isotopic variations display an apparently simple inverse relationship with dissolved nutrient concentrations in fact they reflect mixing of surface waters undergoing active si isotope fractionation and deep waters with more uniform concentrations and isotope compositions samples from the surface of the subtropical gyre have the lowest dissolved si concentrations and heaviest si isotope compositions of marine waters measured thus far fractionation in the surface waters follows a typical rayleigh type distillation curve for a closed surface water reservoir resulting from stratification of the surface layer in the subarctic region in contrast an open system prevails within the subtropical gyre where there is significant recycling of silicic acid in the upper water column and lateral transport of silicon within surface currents for deep waters the si isotope composition distinguishes between the northern north pacific deep water npdw and the southerly derived bottom water the relatively light si isotope compositions measured from waters within the subarctic gyre provides evidence for isolation of the nutrient pool in the north pacific

water mass transformation in the barents sea inferred from radiogenic neodymium isotopes rare earth elements and stable oxygen isotopes abstract nearly half the inflow of warm and saline atlantic water aw to the arctic ocean is substantially cooled and freshened in the barents sea which is therefore considered a key region for water mass transformation in the arctic mediterranean am numerous studies have focused on this transformation and the increasing influence of aw on arctic climate and biodiversity yet geochemical investigations of these processes have been scarce using the first comprehensive data set of the distributions of dissolved radiogenic neodymium nd isotopes expressed as nd rare earth elements ree and stable oxygen isotope 18o compositions from this region we are able to constrain the transport and transformation of aw in the barents sea and to investigate which processes change the chemical composition of the water masses beyond what is expected from circulation and mixing inflowing aw and norwegian coastal water ncw both exhibit distinctly unradiogenic nd signatures of 12 4 and 14 5 respectively whereas cold and dense polar water pw has considerably more radiogenic nd signatures reaching up to 8 1 locally formed barents sea atlantic water bsaw and barents sea arctic atlantic water bsaaw are encountered in the northeastern barents sea and have intermediate nd values resulting from admixture of pw containing small amounts of riverine freshwater from the ob 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

new constraints on the sources and behavior of neodymium and hafnium in seawater from pacific ocean ferromanganese crusts the behavior of dissolved hf in the marine environment is not well understood due to the lack of direct seawater measurements of hf isotopes and the limited number of hf isotope time series obtained from ferromanganese crusts in order to place better constraints on input sources and develop further applications a combined nd hf isotope time series study of five pacific ferromanganese crusts was carried out the samples cover the past 38 myr and their locations range from sites at the margin of the ocean to remote areas sites from previously unstudied north and south pacific areas and water depths corresponding to deep and bottom waters for most of the samples a broad coupling of nd and hf isotopes is observed in the equatorial pacific end and ehf both decrease with water depth similarly end and ehf both increase from the south to the north pacific these data indicate that the hf isotopic composition is in general terms a suitable tracer for ocean circulation since inflow and progressive admixture of bottom water is clearly identifiable the time series data indicate that inputs and outputs have been balanced throughout much of the late cenozoic a simple box model can constrain the relative importance of potential input sources to the north pacific assuming steady state the model implies significant contributions of radiogenic nd and hf from young circum pacific arcs and a subordinate role of dust inputs from the asian continent for the dissolved nd and hf budget of the north pacific some changes in ocean circulation that are clearly recognizable in nd isotopes do not appear to be reflected by hf isotopic compositions at two locations within the pacific ocean a decoupling of nd and hf isotopes is found indicating limited potential for hf isotopes as a stand alone oceanographic tracer and providing evidence of additional local processes that govern the hf isotopic composition of deep water masses in the case of the southwest pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of antarctic glaciation

nd isotope composition of conodonts an accurate proxy of sea level fluctuations abstract analyses of the nd isotope composition of conodonts from the anti atlas morocco the montagne noire france and the rhenohercynian domain germany provide insight into the temporal and lateral variations in seawater geochemistry in the western part of the variscan sea during the late devonian most of the isotopic excursions accurately record changes in sea level the end values decreased during regression phases when erosion accelerated supply of unradiogenic nd from old continental sources a rise in sea level generated a positive shift in end values due to input of more radiogenic oceanic water into the seawater reservoir of the shelf areas the method has great potential for sea level research paleoceanography and correlation because sea level changes can be precisely recognized even in successions with uniform monotonous lithologies however it has a significant limitation being valid only in epeiric seas and shelf areas we have used the nd isotope record to reconstruct the eustatic sea level changes in late frasnian early famennian time the onset of the organic rich kellwasser units coincides with negative trends in end values this accords with oxygen deficiency at the sea bottom being initiated by short term regressive events which in turn would be consistent with cooling periods of glacial origin as previous authors have suggested

neodymium isotope evolution of nw tethyan upper ocean waters throughout the cretaceous neodymium isotope compositions of twenty four fish teeth nineteen from the nw tethys and five from different locations within the tethys are interpreted to reflect the evolution of tethyan upper ocean water composition during the cretaceous and used to track changes in erosional inputs to the nw tethys and in oceanic circulation throughout the cretaceous the rather high end up to 7 6 of the nw tethyan upper ocean waters recorded from the late berriasian to the early aptian and the absence of negative excursions during this interval support the presence of a permanent westward flowing tethys circumglobal current tcc this implies that temperature variations during this time period inferred from the oxygen isotope analysis of fish tooth enamel were not driven by changes in surface oceanic currents but rather by global climatic changes the results presented here represent a significant advance over previously published cretaceous seawater nd isotope records our newly acquired data now allow the identification of two stages of low end values in the nw tethys during the early albian middle albian interval down to 10 and the santonian early campanian down to 11 4 which alternate with two stages of higher end values up to 9 during the late albian turonian interval and the maastrichtian used in conjunction with the oxygen isotope record the fluctuations of end values can be related to major climatic oceanographic and tectonic events that appeared in the western tethyan domain d 2005 elsevier b v all rights reserved

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

the isotopic composition of neodymium in the north pacific abstract we have determined the isotopic composition of neodymium in two water column profiles in the western north pacific and in bottom waters from three other locations in the north pacific the vertical profiles reveal that the water column is stratified with respect to isotopic composition mid depths associated with pacific deep water are uniform having nd 0 3 shallow waters are variable but deep waters are less radiogenic having md 0 4 4 to 5 in the western basin the more negative bottom waters in the western north pacific provide evidence for the advective transport of rare earth elements from antarctic sources to this region bottom waters in the eastern north pacific are more radiogenic nd 0 3 3 to 3 8 indicating very little transport of ree from antarctic sources to this basin overall the isotopic composition of nd in pacific bottom waters appears to be conservative when compared to the silica distribution in spite of evidence for nd removal the findings are generally compatible with other parameters such as temperature salinity and nutrient distributions the presence of nd isotopic signatures associated with antarctic sources in these waters provides evidence for a small component of rare earth elements of north atlantic origin in the bottom waters of the north pacific this is the first tracer evidence to corroborate the suggestion of reid and lynn 1971 that some of the temperature and salinity properties of the deep waters of the north pacific originated in the norwegian and greenland seas

rare earth element distributions in the west pacific trace element sources and conservative vs non conservative behavior abstract recent studies suggest that transport and water mass mixing may play a dominant role in controlling the distribution of dissolved rare earth element concentrations ree at least in parts of the north and south atlantic and the pacific southern ocean here we report vertically and spatially high resolution profiles of dissolved ree concentrations ree along a nw se transect in the west pacific and examine the processes affecting the ree distributions in this area surface water ree patterns reveal sources of trace element te input near south korea and in the tropical equatorial west pacific positive europium anomalies and middle ree enrichments in surface and subsurface waters are indicative of te input from volcanic islands and fingerprint in detail small scale equatorial zonal eastward transport of tes to the iron limited tropical east pacific the low ree of north and south pacific tropical waters and antarctic intermediate water are a long range i e preformed laterally advected signal whereas increasing ree with depth within north pacific intermediate water result from release from particles optimum multiparameter analysis of deep to bottom waters indicates a dominant control of lateral transport and mixing on ree at the depth of lower circumpolar deep water 3000 m water depth 75 100 explained by water mass mixing allowing the northward tracing of lcdw to 28 n in the northwest pacific in contrast scavenging in the hydrothermal plumes of the lau basin and tonga fiji area at 1500 2000 m water depth leads to ree deficits 40 60 removal and marked ree fractionation in the tropical west pacific overall our data provide evidence for active trace element input both near south korea and papua new guinea and for a strong lateral transport component in the distribution of dissolved rees in large parts of the west pacific

changes in pacific ocean circulation following the miocene onset of permanent antarctic ice cover we integrate micropaleontological and geochemical records benthic stable isotopes neodymium isotopes benthic foraminiferal abundances and xrf scanner derived elemental data from well dated pacific ocean successions 15 12 7 ma to monitor circulation changes during the middle miocene transition into a colder climate mode with permanent antarctic ice cover together with previously published records our results show improvement in deep water ventilation and strengthening of the meridional overturning circulation following major ice expansion at 13 9 ma neodymium isotope data reveal however that the provenance of intermediate and deep water masses did not change markedly between 15 and 12 7 ma we attribute the increased 13c gradient between pacific deep and intermediate water masses between 13 6 and 12 7 ma to more vigorous entrainment of pacific central water into the wind driven ocean circulation due to enhanced production of intermediate and deep waters in the southern ocean prominent 100 kyr ventilation cycles after 13 9 ma reveal that the deep pacific remained poorly ventilated during warmer intervals at high eccentricity whereas colder periods low eccentricity were characterized by a more vigorous meridional overturning circulation with enhanced carbonate preservation the long term 13c decline in pacific intermediate and deep water sites between 13 5 and 12 7 ma reflects a global trend probably related to a re adjustment response of the global carbon cycle following the last 400 kyr carbon maximum cm6 of the monterey excursion

rare earth element geochemistry of laminated diatom mats from tropical west pacific evidence for more reducing bottomwaters and higher primary productivity during the last glacial maximum rare earth elements ree along with selected major and trace elements were measured in laminated ethmodiscus rex diatom mats and associated sediments diatomaceous clay and pelagic clay in two sediment cores collected from the parece vela basin of the eastern philippine sea ree distributions are characterized by strong enrichment of middle ree mree and heavy ree hree over light ree lree and slight enrichment of mree over hree this distribution pattern suggests that ree compositions of the laminated e rex diatom mats were not the product of e rex blooms an inference also supported by the fact that ti normalized ree concentrations are not clearly different from those in the diatomaceous clay and pelagic clay comparison of ree patterns with the vertical distribution of authigenic phases in the sediment indicates that lree were dominantly associated with detrital materials whereas mree and hree were selectively enriched by mn oxyhydroxides and authigenic phosphates in the pelagic clay a weak negative ce anomaly cannot be linked to oxic depositional conditions but instead is attributed to the retention of a negative ce anomaly associated with authigenic phosphates in the laminated e rex diatom mats a weak positive ce anomaly is consistent with depositional sulfidic anoxic conditions and is interpreted to represent enhanced scavenging of reduced aqueous ce3 by barite in a strongly reducing environment moreover variably negative to positive ce anomalies in the diatomaceous clay may reflect the concurrent operation of the two processes controlling ce accumulation in the laminated e rex diatom mats and pelagic clay the study cores show a ubiquitous positive eu anomaly owing to the presence of volcanic materials the smaller eu anomaly in the laminated e rex diatom mats and diatomaceous clay relative to that in the pelagic clay may be attributed to the release of reduced eu2 from mineral phases to the sediment pore water under strongly reducing conditions previous studies have shown that the advection of lower circumpolar water lcpw strengthened during the last glacial maximum lgm which should have resulted in better ventilation of the deep eastern philippine sea evidence presented here for more reducing bottomwater conditions during the laminated e rex diatom mats formation implicates elevated primary productivity and enhanced organic sinking fluxes as primary controls on redox changes in the eastern philippine sea during the lgm enhanced primary productivity and more reducing bottomwaters during the laminated e rex diatom mats deposition resulted in a larger respired carbon pool in the deep eastern philippine sea which may have been part of a larger scale modulation of atmospheric co2 variation during pleistocene glacial interglacial cycles by deep ocean carbon storage c 2011 elsevier b v all rights reserved

the origin of the pacific equatorial 13 c water abstract examination of the vertical distributions of temperature salinity oxygen and nutrient salts in the thermostad of the equatorial 13 c water in the eastern pacific ocean indicates that local vertical mixing is unimportant in creating the thermostad and the characteristics of the 13 c water maps are presented that show the oceanwide distributions of depth geostrophic flow salinity oxygen phosphate silica and nitrate on the 160 cl t 1 isanosteric surface which nearly coincides with the core of the 13 c water the maps suggest that the original characteristics of the 13 c water are acquired in the surface and thermocline layers to the northeast of new zealand and in the tasman sea by winter convection and vertical mixing the acquired characteristics are advected to the thermostad in the eastern pacific via a long route starting from the source region the flow is first eastward in high latitudes and then returns westward in low latitudes around the anticyclonic subtropical gyre of the sout

isotopic composition of neodymium in waters from the drake passage the isotopic composition of neodymium has been determined in seawaters from the drake passage the antarctic circumpolar current which controls interocean mixing flows through this passage the parameter e nd 0 which is a function of the ratio of neodymium 143 to neodymium 144 is found to be uniform with depth at two stations with a value which is intermediate between the values for the atlantic and the pacific and indicates that the antarctic circumpolar current consists of about 70 percent atlantic water cold bottom water from a site in the south central pacific has the neodymium isotopic signature of the waters in the drake passage by using a box model to describe the exchange of water between the southern ocean and the ocean basins to the north together with the isotopic results an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the pacific and the southern ocean concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth these results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo oceanographic studies

diagnostic model of the three dimensional circulation in the upper equatorial pacific ocean abstract to investigate the processes that maintain the large scale annual average thermal structure of the equatorial pacific the three dimensional ocean circulation for a large area is determined from a diagnostic model applied to repeated meridional hydrographic sections along 150 w and 11o w from 5 n to 5 s geostrophic balances are used to determine velocity profiles from 0 to 500 db across the boundaries of the region zonal velocities across 150 w and 110 w at approximately 1 lattitude intervals from 5 n to 5 s and meridional velocities across 5 n and 5 s averaged over the zonal distance between 150 w and 110 w poleward wind driven flows across 5 n and 5 s based on climatological zonal wind stress are added to the geostrophic velocities in the mixed layers to achieve overall mass conservation the reference dynamic height field at 500 db is adjusted at four of the 21 stations by about 1 dyn cm horizontal nondivergence is used to determine meridional velocities between 0 75 and 5 latitudes

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

nd isotopic structure of the pacific ocean 70 30 ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world the oceanic meridional overturning circulation moc is a crucial component of the climate system impacting heat and nutrient transport and global carbon cycling past greenhouse climate intervals present a paradox because their weak equator to pole temperature gradients imply a weaker moc yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients to investigate the mode of moc that operated during the early cenozoic we compare new nd isotope data with nd tracer enabled numerical ocean circulation and coupled climate model simulations assimilation of new nd isotope data from south pacific deep sea drilling project and ocean drilling program sites 323 463 596 865 and 869 with previously published data confirm the hypothesized moc characterized by vigorous sinking in the south and north pacific 70 to 30 ma compilation of all pacific nd isotope data indicates vigorous distinct and separate overturning circulations in each basin until 40 ma simulations consistently reproduce south pacific and north pacific deep convection over a broad range of conditions but cases using strong deep ocean vertical mixing produced the best data model match strong mixing potentially resulting from enhanced abyssal tidal dissipation greater interaction of wind driven internal wave activity with submarine plateaus or higher than modern values of the geothermal heat flux enable models to achieve enhanced moc circulation rates with resulting nd isotope distributions consistent with the proxy data the consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

neodymium isotopes and concentrations in caribbean seawater tracing water mass mixing and continental input in a semi enclosed ocean basin we present the first full water column nd isotope end and concentration data for caribbean seawater as well as for stations close to the orinoco river mouth and in the florida straits the surface inflow into the southeastern caribbean via the guyana current is characterized by an endsignature of 10 9 which is a consequence of the mixing of relatively unradiogenic endsignatures 13 6 supplied by the orinoco river with contributions from the amazon river 10 despite the proximity to land sub surface and intermediate waters within the caribbean largely retain the endsignatures of their source water masses in the atlantic in contrast the deep waters of the caribbean show endsignatures at least 3 endunits more radiogenic than the inflowing upper north atlantic deep water unadw a endshift from 13 to 9 7 can be explained by addition of radiogenic nd to the deep caribbean through weathering inputs from land however in order to balance such large shifts in endwith at the same time modest increases in nd concentrations nd must also be removed from seawater within the basin it is suggested that the long residence time of deep waters in the caribbean allows significant interaction of seawater with sinking particles and seafloor sediments resulting in more radiogenic values these findings have implications for the use of endas a proxy for paleocirculation in restricted basins in which the residence times of the deep waters are long

environmental magnetism of pleistocene sediments in the north pacific and ontong java plateau temporal variations of detrital and biogenic components 1 an environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the pacific ocean using sediment cores of pleistocene age the proportion of interacting i to noninteracting n i single domain components was estimated from first order reversal curve diagrams and the proportion of middle m to low l coercivity components was determined from decomposition of isothermal remanent magnetization irm acquisition curves the i and m components are interpreted to be carried by terrigenous maghemite while the n i and l components represent biogenic magnetite an inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility arm to saturation irm sirm and the i n i ratio was confirmed for sediments across wide expanses in the pacific ocean this implies that arm sirm can be used to estimate the relative abundances of biogenic and terrigenous components in sediments in the north pacific the relative abundance of the i and m components increases in glacial periods variations of arm sirm and s ratio s 0 1t resemble each other and decrease in the same time intervals these variations reflect increases of terrigenous input in glacial periods as eolian dust on the ontong java plateau in the western equatorial pacific on the other hand minima in arm sirm and s 0 1t occur at glacial to interglacial transitions and the relative abundance of the i and m components increases in these periods terrigenous material in this region is considered to be transported mainly from the new guinea and solomon islands by the equatorial undercurrent the higher proportion of the terrigenous component at glacial to interglacial transitions is coeval with carbonate preservation maxima reported from the ontong java plateau suggesting a linkage between the two

holocene shifts in sub surface water circulation of the north east atlantic inferred from nd isotopic composition in cold water corals abstract variations of the sub polar gyre spg and the sub tropical gyre stg circulation during the holocene are believed to be related to regional and global climate over this time period to improve our understanding of these phenomena we provide new constraints on variations in surface circulation patterns using neodymium isotopes end on precisely u th dated coral fragments of l pertusa the fragments were retrieved from two sediment cores taken from cold water coral cwc mounds at 127 134 m water depth in the mingulay reef complex located on the western british continental shelf the results have been combined with end analyzed on seawater samples from two stations located on the continental shelf and margin in order to establish whether end is a reliable proxy of the ocean circulation variations and notably of the relative contribution of water originating from the spg and stg end values in cwcs from the mingulay reef complex range from 14 5 0 4 to 11 8 0 3 highlighting two major variations unradiogenic end values 14 5 0 4 indicate a higher contribution of water from the spg around 2 8 ka conversely more radiogenic values at 3 4 ka 11 8 0 3 point to a declining spg strength accompanied by stronger northward penetration of stg water along the western european margin transported by the shelf edge current sec and or cooler and fresher waters from the interior seas the eastward extension of the spg at 2 8 ka is associated with lower 14c reservoir age 200 yrs compared to periods associated with a higher contribution of stg waters this indicates that 14c reservoir ages are mainly a function of vertical mixing of the sub surface of the ocean as stronger vertical ventilation is not associated with a higher proportion of local radiogenic surface water we hypothesize it could represent vertical ventilation in the north eastern atlantic active spg is associated with a better ventilation of the water masses within the spg and warmer climatic conditions in northern europe and in the eastern norwegian sea linked to an intensification of the surface limb of the amoc

nd isotopic constraints on the origin of suspended particles in the atlantic sector of the southern ocean 1 in the nutrient rich southern ocean fe is a vital constituent controlling the growth of phytoplankton despite much effort the origin and transport of fe to the oceans are not well understood in this study we address the issue with geochemical data and nd isotopic compositions of suspended particle samples collected from 1997 to 1999 in the south atlantic sector of the southern ocean al th and rare earth element ree concentrations as well as 143nd 144nd isotopic ratios in acetic acid leached particle samples representing the lithogenic fraction delineate three major sources 1 patagonia and the antarctic peninsula provide material with nd 4 that is transported toward the east with the polar and subpolar front jets 2 the south african shelf although its influence is limited by the circumpolar circulation and wind direction can account for material with nd of 12 to 14 adjacent to south africa and 3 east antarctica provides material with nd of 10 to 15 to the eastern weddell sea and adjacent antarctic circumpolar current for this region we interpret the nd isotopic evidence in combination with oceanographic atmospheric constraints as evidence for supply of significant amounts of terrigenous detritus by icebergs

contrasting geochemical cycling of hafnium and neodymium in the central baltic sea the central baltic sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages this allows the investigation of water mass mixing using radiogenic isotope compositions of nd and hf as well as their geochemical cycling across varying redox conditions in the water column in this study we present the distribution of nd and hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central baltic sea onboard the rv oceania as a part of the international geotraces program the results obtained indicate that nd isotopes effectively trace the mixing between more radiogenic saline waters from the south and unradiogenic fresh waters from the north which helps to understand the reliability of nd isotopes as water mass tracer in the open ocean in surface waters nd shows higher concentrations and less radiogenic isotope compositions at the northern stations which are progressively diluted and become more radiogenic to the south consistent with the counterclockwise circulation pattern of central baltic sea surface waters in contrast to the variable nd concentrations hf shows much less variability at the gotland deep station the nd concentrations of the euxinic waters are higher by a factor 10 than those of the overlying oxygen depleted waters whereas hf only shows small concentration variations this indicates faster removal of hf from the water column than nd moreover the dissolved hf isotope signatures document great variability but no consistent mixing trends our explanation is that hf has a lower residence time than nd and also that the hf isotope signatures of the sources are highly heterogeneous which is attributed to their differing magmatic and tectonic histories as well as incongruent post glacial weathering around the central baltic sea

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

south atlantic intermediate water advances into the north east atlantic with reduced atlantic meridional overturning circulation during the last glacial period the nd isotopic composition end of seawater and cold water coral cwc samples from the gulf of cadiz and the alboran sea at a depth of 280 827 m were investigated in order to constrain middepth water mass dynamics within the gulf of cadiz over the past 40 ka end of glacial and holocene cwc from the alboran sea and the northern gulf of cadiz reveals relatively constant values 8 6 to 9 0 and 9 5 to 10 4 respectively such values are similar to those of the surrounding present day middepth waters from the mediterranean outflow water mow end 9 4 and mediterranean sea water msw end 9 9 in contrast glacial end values for cwc collected at thermocline depth 550 827 m in the southern gulf of cadiz display a higher average value 8 9 0 4 compared to the present day value 11 7 0 3 this implies a higher relative contribution of water masses of mediterranean msw or south atlantic origin east antarctic intermediate water eaaiw our study has produced the first evidence of significant radiogenic end values 8 at 19 23 24 and 27 ka which are coeval with increasing iceberg discharges and a weakening of atlantic meridional overturning circulation amoc since mow end values remained stable during the last glacial period it is suggested that these radiogenic end values most likely reflect an enhanced northward propagation of glacial eaaiw into the eastern atlantic basin

the effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern cascadia accretionary margin analytical challenges in obtaining high quality measurements of rare earth elements rees from small pore fluid volumes have limited the application of rees as deep fluid geochemical tracers using a recently developed analytical technique we analyzed rees from pore fluids collected from sites u1325 and u1329 drilled on the northern cascadia margin during the integrated ocean drilling program iodp expedition 311 to investigate the ree behavior during diagenesis and their utility as tracers of deep fluid migration these sites were selected because they represent contrasting settings on an accretionary margin a ponded basin at the toe of the margin and the landward tofino basin near the shelf s edge ree concentrations of pore fluid in the methanogenic zone at sites u1325 and u1329 correlate positively with concentrations of dissolved organic carbon doc and alkalinity fractionations across the ree series are driven by preferential complexation of the heavy rees simultaneous enrichment of diagenetic indicators doc and alkalinity and of rees in particular the heavy elements ho to lu suggests that the heavy rees are released during particulate organic carbon poc degradation and are subsequently chelated by doc ree concentrations are greater at site u1325 a site where shorter residence times of poc in sulfate bearing redox zones may enhance ree burial efficiency within sulfidic and methanogenic sediment zones where ree release ensues cross plots of la concentrations versus cl li and sr delineate a distinct field for the deep fluids z 75 mbsf at site u1329 and indicate the presence of a fluid not observed at the other sites drilled on the cascadia margin changes in ree patterns the presence of a positive eu anomaly and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous crescent terrane located east of the drilled transect

tectonic processes in papua new guinea and past productivity in the eastern equatorial pacific ocean phytoplankton growth in the eastern equatorial pacific ocean today accounts for about half of the new production the fraction of primary production fuelled by externally supplied nutrients in the global ocean the recent demonstration that an inadequate supply of iron limits primary production in this region1 supports earlier speculation that in the past fluctuations in the atmospheric deposition of iron bearing dust may have driven large changes in productivity2 but we argue here that only small 2 nm increases in the iron concentration in source waters of the upwelling equatorial undercurrent are needed to fuel intense diatom production across the entire eastern equatorial pacific ocean episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island arc region of papua new guinea which has experienced intensive volcanic erosional and seismic activity over the past 16 million years cycles of plankton productivity recorded in eastern equatorial pacific sediments may therefore reflect the influence of tectonic processes in the papua new guinea region superimposed on the effects of global climate forcing

neodymium concentration and isotopic composition distributions in the southwestern indian ocean and the indian sector of the southern ocean abstract neodymium concentration and isotopic composition profiles were determined for two stations in the crozet basin in the southwestern indian ocean and one station in the indian sector of the southern ocean the station located in the northern part of the crozet basin showed very similar nd concentrations sio2 and dissolved oxygen profiles to those previously reported for the closest station in the madagascar basin however the station in the northern part of the crozet basin and the previously studied station in the madagascar basin exhibited clearly different nd isotopic values at water depths of approximately 400 m which was attributed to a strong influence of the agulhas return current on the crozet basin station and or a large contribution of the south equatorial current to the madagascar basin the nd isotopic profile at er 14 in the indian sector of the southern ocean was similar to those of stations in the atlantic sector of the southern ocean at depths above 2000 m conversely variable nd isotopic compositions were observed in the indian and atlantic sectors of the southern ocean at depths below 2000 m suggesting the importance of local nd to determination of the nd isotopic composition of deeper depths the pb isotopic compositions which are strongly controlled by anthropogenic pb showed different features in vertical profile from nd isotopic compositions at all stations the nd isotopic composition profiles of stations from the crozet basin showed a clear peak corresponding to antarctic intermediate water whereas a clear peak corresponding to subantarctic mode water was observed for pb isotopic vertical profiles a combined nd and pb isotopic composition study of seawater may clarify the contribution of natural and anthropogenic sources to pb in the ocean 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

towards explaining the nd paradox using reversible scavenging in an ocean general circulation model abstract the isotopic composition of the rare earth element neodymium nd has the potential to serve as water mass tracer because it is naturally tagged by continental sources with distinct ages and lithologies however in order to understand the limitations of this approach we need to know more about the physical and biogeochemical processes controlling the distribution of nd in the modern ocean for example nd isotope ratios behave quasi conservatively while concentrations in the water column generally increase with depth showing a broadly nutrient like behaviour we define this decoupling of nd concentrations and isotopic compositions as the nd paradox for the first time we model nd concentrations and isotopic compositions simultaneously and address the hypothesis that the nd paradox can be explained by a combination of lateral advection and reversible scavenging we impose a reversible scavenging model of nd removal from the ocean on the ocean circulation fields from the mit general circulation model using the transport matrix method we conclude that reversible scavenging is an active and important component in the cycling of nd in the ocean in the absence of an adequate alternative explanation reversible scavenging should be considered a necessary component in explaining the nd paradox

sea surface chlorophyll signature in the tropical pacific during eastern and central pacific enso events 1 recent analyses of physical measurements show the existence of a central pacific type of el nino cpen with a sea surface temperature warming pattern distinct from that of the classical eastern pacific el nino epen in this study we analyze the surface chlorophyll signature of el nino southern oscillation enso using monthly maps of satellite derived chlorophyll anomalies between september 1997 and december 2010 we identify five typical enso structures the first structure describes the lonely 1997 1998 epen of the period the second and third represent la nina the fourth illustrates intermediate conditions and the fifth characterizes cpen during the 1997 1998 epen a large eastward shift of the oligotrophic warm pool and a reduction of equatorial upwelling result in negative chlorophyll anomalies east of 170 e between 10 s and 10 n during the four cpen events a reduced eastward shift yields negative chlorophyll anomalies in the equatorial band within about 160 e and 160 w only westward surface current in the central basin limits the expansion of the anomaly core negative chlorophyll anomalies that extend eastward from the equatorial anomaly core probably result from reduced upward iron fluxes linked to the deepening of the equatorial undercurrent during la nina the westward expansion of the equatorial upwelling results in positive chlorophyll anomalies west of the date line away from the equatorial band advection of oligotrophic warm pool waters by enhanced eastward countercurrents drives negative anomalies within 8 10 n and toward the marquesas islands during cpen while reduced countercurrents lead to positive chlorophyll anomaly during la nina

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

plate tectonics radiogenic isotopic tracers and paleoceanography the case of the manganese crusts in the pacific abstract hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean isotopic compositions of long life radiogenic isotopes that are dissolved in the ocean such as nd and pb are mixtures of different erosion products continents volcanics arcs ridges etc transported by oceanic currents or winds isotopic studies on mn crusts are thus potential paleogeographic and paleoceanographic tracers however global paleogeography can drastically evolve over the period of growth of crust as well as the latitude longitude and water depth of the mn crust thus each crust sampled a succession of geographic sites related to its spatial evolution through time for this reason valid information about the past ocean isotopic composition can only be extracted from mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each mn crust we followed this approach for six hydrogenous mn crusts from the pacific ocean that have recorded pb and nd isotopic signals for the past 80 myr the evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the pacific plate and surrounding continents of the hot spots and ridges as well as the paths of the six crusts the differences and similarities between the pb and nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers the nd isotopes are strongly influenced by the exchange between indian and pacific waters specifically by the progressive closure of the indonesian gateway the closed central pacific characteristics are defined from the extrapolation of the isotopic trend this highlights the important role played by erosion of volcanic arcs in the nd isotopic value of seawater our approach also stresses the influence of local volcanic activity ridges or active hot spot for lead isotopes

an efficient method for computing green s functions for a layered half space at large epicentral distances nowadays with the dramatic increase in computational ability the dis crete wavenumber integration method dwim see e g bouchon and aki 1977 bouchon 1979 1981 has been one of the most favorable techniques of computing the synthetic seismograms for a layered half space because of its simplicity accuracy and fair efficiency for some cases particularly for the case of the near field however it becomes less efficient for the case of far field that is at large epicentral distances and the larger the epicentral distance is the less efficient dwim will be in this study we propose an efficient numerical wavenumber integration method the self adaptive filon s integration method safim to compute efficiently the dynamic green s functions for a layered half space at large epicentral distances this new integration technique is build upon the particular fifth order filon s integration scheme apsel 1979 apsel and luco 1983 and the principle of the self adaptive simpson inte gration technique by using numerical examples we demonstrate that safim is not only accurate but also very efficient for large epicentral distances according to our study we find that at a relatively short epicentral distance r 500 km the classical dwim is more efficient than safim at a medium range of epicentral distance 500 kmr 1200 km both methods have similar efficiency at large epicentral dis tance r 1200 km however safim is significantly more efficient than dwim and the larger the epicentral distance is the more efficient safim will be for in stance when r 2000 km safim only needs about 1 3 of the computation time of dwim therefore this new integration method is expected to be very useful in com puting synthetic seismograms at large epicentral distances

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

expansion of the southern california oxygen minimum zone during the early to mid holocene due to reduced ventilation of the northeast pacific abstract oceanic deoxygenation observed since the 1950s has drawn increasing concern as dissolved oxygen do regulates marine biodiversity and biogeochemical cycles yet the do time series from direct instrumental measurements is insufficiently long several decades to constrain the centennial to millennial variability here we present redox sensitive metal re u and mo records from santa barbara basin sbb california to reconstruct subsurface do through the holocene significantly higher authigenic metal fluxes and coherent benthic foraminifera faunal responses along a published depth transect reveal vertical expansion and intensification of the southern california oxygen minimum zone omz prior to 6 ka comparison with post industrial trace metal records suggests low oxygen conditions were more extreme during early to mid holocene mh highlighting the magnitude of omz variability in the absence of anthropogenic influences inconsistencies between authigenic metal fluxes and local oxygen control indicate a remote weakening of the north pacific intermediate water npiw formation prior to the mh reduced ventilation of the mid depth north pacific is supported by state of the art earth system model simulations with realistic mh 6 ka forcing highlighting the importance of brine rejection during sea ice formation in changing the buoyancy of npiw and its basin wide influences on north pacific omz evidence from holocene marine lake records and model simulations further suggests a southward intertropical convergence zone itcz migration and a consequent deepening of the aleutian low al towards late holocene which favors more sea ice brine rejection thus mid depth ventilation in the north pacific was closely associated with atmospheric circulation during the holocene

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

rare earth elements and nd isotopes as tracers of modern ocean circulation in the central mediterranean sea abstract seawater rare earth element ree concentrations and nd isotopic composition end are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater however their measurements are basically lacking in the mediterranean sea water column this study analyzes 9 seawater stations around the central mediterranean sea to clarify the relative importance of external sources vertical biogeochemical processes and lateral water mass transport in controlling ree and end distributions concentrations of ree do not show nutrient like profiles with depth likely indicative of relatively young waters with limited accumulation of remineralized ree light ree lree present a non conservative behavior which largely peak at surface waters and rapidly decrease with depth the negative correlation of surface lree enrichment with offshore distance highlights the influence of continental input from the western italian coast to the tyrrhenian surface waters in contrast to other regions with reported boundary exchange this process does not modify the end values here on the other side distributions of dissolved heavy ree hree and end display a conservative behavior that can be explained by mixing of western maw and wmdw and eastern liw and emdw originated waters we test this hypothesis with an optimum multi parameter analysis ompa including hree and end parameters even though the limited data set consistent results of water mass fractions are obtained for the four main water masses although with some particularities while liw takes on major importance when considering hree in the model emdw fractions are preferentially detected with end this latter finding implies a noticeable deep water flux across the sicily strait into the western mediterranean that was not clearly evidenced before

tracing water mass mixing and continental inputs in the southeastern atlantic ocean with dissolved neodymium isotopes abstract in contrast to the vigorous deep ocean circulation system of the north and southwestern atlantic ocean no systematically sampled datasets of dissolved radiogenic neodymium nd isotope signatures exist to trace water mass mixing and provenance for the more restricted and less well ventilated angola basin and the cape basin in the southeastern atlantic ocean where important parts of the return flow of the atlantic meridional overturning circulation are generated here to improve our understanding of water mass mixing and provenance we present the first full water column nd isotope expressed as end values and concentration data for a section across the western angola basin from 3 to 30 s along the zero meridian and along an e w section across the northern cape basin at 30 s sampled during geotraces cruise ga08 compared with the southwestern atlantic basin we find overall less radiogenic end signatures reaching 17 6 in the uppermost 200 m of the angola and cape basins in the western angola basin these signatures are the consequence of the admixture of a coastal plume originating near 13 s and carrying an unradiogenic nd signal that likely resulted from the dissolution of fe mn coatings of particles formed in river estuaries or near the west african coast the highly unradiogenic nd isotope signatures in the upper water column of the northern cape basin in contrast originate from old archean terrains of southern africa and are introduced into the mozambique channel via rivers like the limpopo and zambezi these signatures allow tracing the advection of shallow waters via the agulhas and benguela currents into the southeastern atlantic ocean the nd isotope compositions of the deep water masses in both basins primarily reflect conservative water mass mixing with the only exception being the central angola basin where the signatures are significantly overprinted by terrestrial inputs bottom waters of the cape basin show excess nd concentrations of up to 6 pmol kg 20 originating from resuspended bottom sediments and or dissolution of dust but without significantly changing the isotopic composition of the waters due to similar end values of particles and bottom waters ranging between 9 6 and 10 5 given that bottom waters within the cape basin today are enriched in nd non conservative nd isotopic effects may have been resolvable under past glacial boundary conditions when bottom waters were more radiogenic

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

dissolved rare earth elements distribution in the solomon sea abstract trace elements and isotopes teis were measured as part of the geotraces pandora cruise july august 2012 r v l atalante among them rare earth elements rees as pertinent tracers of land ocean inputs and water mass transformations this work discusses results of 19 dissolved ree dree profiles measured using a trispike method in the coral sea and inside and at the exits of the solomon sea a semi enclosed sea with complex topography and straits overall drees except the insoluble ce show nutrient like profiles i e depleted at the surface and enriched at depth illustrative nd concentrations range from 5 pmol kg at the surface to 25 pmol kg at 5000 m depth however local dree enrichments are observed mostly in the straits indispensable solomon and vitiaz straits and along the island coasts a box model allows calculating and discussing the fate of the drees in the different water layers flowing through the solomon sea finally subtle variations revealed by la ce eu anomalies and the normalized light versus heavy ree ratio expressed as ndn ybn allows the identification of specific mechanisms affecting the distribution of the different drees the positive eu anomaly observed in the surface layers reflects the basaltic origin of external inputs consistent with the intensive weathering and or volcanic activity affecting the surrounding islands these data also confirm that the distributions of heavy drees like yb are better correlated to the dsi concentrations than that of the other rees 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

hawaiian imprint on dissolved nd and ra isotopes and rare earth elements in the central north pacific local survey and seasonal variability abstract dissolved neodymium isotopes 143nd 144nd expressed as end and rare earth elements rees have the potential to trace the provenance of lithogenic material as well as water masses the central north pacific is poorly investigated with respect to its nd isotope signature and ree cycling and little is known about the contributions of volcanic islands such as hawaii relative to dust input from asian deserts to the surface water ree budgets here we present dissolved nd isotope and ree data along with long lived radium isotope activities from hawaii ocean time series station aloha and coastal waters from oahu sampled for a geotraces process study in february 2011 the data are supplemented with seasonal samples from aloha our results show a clear influence of the hawaiian islands on the coastal ocean and surface waters at aloha during february expressed by higher surface water ra activities radiogenic surface end end 1 4 to 1 0 and elevated eu anomalies eu eu 1 3 seasonal cycles of asian dust deposition most likely contribute to the seasonal end variability of surface waters at aloha as suggested by more negative end and the lack of eu anomalies in summer neodymium isotopes in the intermediate and deep water column at aloha trace typical north pacific water masses such as north pacific intermediate water and north pacific deep water we suggest that a radiogenic end excursion in 1000 2000 m water depth observed in various north pacific profiles is controlled by advection of a modified upper circumpolar deep water or north equatorial pacific intermediate water we further present an updated average end signature of 3 5 0 5 for north pacific deep water and show that ree patterns of deep waters at aloha are dominantly controlled by vertical processes

143nd 144nd in pacific ferromanganese encrustations and nodules abstract 143 nd 144 nd ratios have been measured in fe mn encrustations and nodules taken from a wide area of the pacific and over a large depth range over much of the pacific e nd 0 values fall between 2 5 and 5 0 similar to values for nd presently dissolved at mid depth in the pacific deposits forming within the realm of antarctic bottom water aabw are distinctly less radiogenic e nd 0 6 0 to 7 5 and appear to have sampled nd both from ambient aabw e nd 0 8 5 and from higher in the water column e nd 0 0 3 to 4 5 samples drilled from 50 to 65 mm within one crust are chemically and isotopically distinct from surface layers of the same crust the isotope values suggest that the mid depth pacific may have previously exhibited a less radiogenic nd isotope signal than that presently observed

maghemite to magnetite reduction across the fe redox boundary in a sediment core from the ontong java plateau influence on relative palaeointensity estimation and environmental magnetic application summary during reduction diagenesis production of dissolved fe2 by reduction of ferric oxide starts at the fe redox boundary the associated magnetic property changes may influence palaeomagnetic and environmental magnetic records of marine sediments however this has not been evaluated thoroughly in this study using a gravity core from the ontong java plateau we document in detail rock magnetic changes across the fe redox boundary and investigate their influence on relative palaeointensity estimation and on a magnetic proxy for the proportion of terrigenous biogenic magnetic minerals the magnetic mineral assemblage above the fe redox boundary is characterized by a component with a mean coercivity of 100 mt in isothermal remanent magnetization irm component analyses and low s ratios s 0 1t low temperature irm measurements and mossbauer spectroscopy indicate that the degree of maghemitization is higher above the fe redox boundary from these observations we conclude that reduction of maghemite to magnetite occurs at the fe redox boundary and we infer that a maghemite skin on magnetic grains is lost across the boundary relative palaeointensity variations obtained by normalizing nrm intensity with sirm agree well with regional and global palaeointensity stacks which suggests that relative palaeointensity estimation is not significantly affected by the fe redox boundary temporal variations of the ratio of anhysteretic remanent magnetization susceptibility and saturation irm arm sirm coincide with the regional pattern across the ontong java plateau it is also possible to estimate variations in the proportion of terrigenous to biogenic components using the arm sirm ratio across the fe redox boundary

equatorial currents in the pacific ocean 1992 1997 a medium resolution ocean general circulation model of the tropical pacific ocean is used to explore current structure and variability on the equator for the period from 1992 to 1997 the model assimilates surface and subsurface temperature data from expendable bathythermographs and the tropical ocean global atmosphere tropical atmosphere ocean toga tao moorings and altimetry data from the topex poseidon satellite currents from the model are compared with current observations from the toga tao moorings at 110 w 140 w and 165 e since current data are not assimilated these data provide an independent verification of the model results the comparison shows that the model produces accurate currents over a wide range of spatial and temporal scales in particular the model correctly resolves temporal variability from instability waves with periods of less than a month to interannual changes with periods of several years the model results are used to explore zonal velocity changes associated with the onset of the 1997 1998 el nino southern oscillation enso event the event began with a series of equatorial kelvin waves which were excited by westerly wind bursts in the western pacific and propagated to the eastern pacific the passage of these waves is associated with an initial strengthening of the equatorial undercurrent euc followed by a rapid shutdown of the euc the weakening of the undercurrent during enso is consistent with previous descriptions and results from the collapse of the easterly trade winds in the western pacific

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

nd isotopic composition of water masses and dilution of the mediterranean outflow along the southwest european margin nd isotopic compositions epsilon nd of seawater profiles and deep sea corals collected off the coast of iberia and from the bay of biscay were measured 1 to constrain the nd isotopic composition of water masses along the southwest european margin 2 to track the mediterranean outflow water mow during its northward propagation and 3 to establish hydrological changes during the last 1500 years the eastern north atlantic central water enacw is characterized by nd isotopic composition of around 12 0 mediterranean sea water msw is collected from 800 and 1200 m depth and is characterized by epsilon nd values ranging from 10 9 off the coast of iberia to 11 6 in the bay of biscay these epsilon nd results suggest a strong dilution of the pure mow at the strait of gibraltar epsilon nd 9 4 of approximately 40 and 30 along its northward circulation pathway essentially with a contribution from enacw at around 2000 m depth epsilon nd water profiles display the occurrence of a nonradiogenic water mass epsilon nd 13 originating from the labrador sea labrador sea water fossil deep sea corals dated between 84 and 1500 years display nd isotopic compositions that vary moderately from present day seawater values suggesting a weaker influence of mow in the formation of msw during the dark ages and the little ice age these recent cold events seem to be associated with a reduction in the northward penetration of msw which may result from a greater eastward extension of the middepth subpolar gyre and or a reduction of msw formation likely tied to a variation in deep mediterranean water production

iron sources and dissolved particulate interactions in the seawater of the western equatorial pacific iron isotope perspectives this work presents iron isotope data in the western equatorial pacific marine aerosols and top core margin sediments display a slightly heavy fe isotopic composition 56 fe of 0 33 0 11 2sd and 0 14 0 07 respectively samples reflecting the influence of papua new guinea runoff sepik river and rabaul volcano water are characterized by crustal values in seawater fe is mainly supplied in the particulate form and is found with a 56 fe between a0 49 and 0 34 0 07 the particulate fe seems to be brought mainly by runoff and transported across continental shelves and slopes aerosols are suspected to enrich the surface vitiaz strait waters while hydrothermal activity likely enriched new ireland waters dissolved fe isotopic ratios are found between a0 03 and 0 53 0 07 they are almost systematically heavier than the corresponding particulate fe and the difference between the signature of both phases is similar for most samples with 56 fe dfe pfe 0 27 0 25 2sd this is interpreted as an equilibrium isotopic fractionation revealing exchange fluxes between both phases the dissolved phase being heavier than the particles suggests that the exchanges result in a net nonreductive release of dissolved fe this process seems to be locally significantly more intense than fe reductive dissolution documented along reducing margins it may therefore constitute a very significant iron source to the ocean thereby influencing the actual estimation of the iron residence time and sinks the underlying processes could also apply to other elements

limits on conservative behavior of nd isotopes in seawater assessed from analysis of fish teeth from pacific core tops abstract neodymium nd isotopes have become an accepted water mass tracer for paleoceanographic reconstructions however high rates of radiogenic nd input from volcanic islands arcs in the western equatorial pacific wep and the subarctic north pacific sanp can significantly alter the isotopic composition of ambient seawaters leading to questions about the conservative nature of nd isotopes in the pacific here we present the first comprehensive study of nd isotopes preserved in core top fossil fish teeth debris from 31 sites in the pacific to define the vertical and horizontal distributions of seawater nd isotopes and to test the reliability of nd isotopes as a water mass tracer in the pacific we found that nd isotopic values of northward flowing lower circumpolar deep water lcdw are significantly modified in the western central equatorial pacific and the sanp as a result of local radiogenic inputs from young circum pacific island arcs consequently modified lcdw with 5 end is created in the central equatorial pacific while recirculated north pacific deep water npdw acquires a radiogenic nd isotope value 2 end in the sanp nd isotopic ratios of fish teeth debris in the central north pacific plotted against salinity or phosphate concentration from the overlying bottom water produce a mixing envelope between modified lcdw and npdw indicating that these nd isotopic values represent the southern and northern sourced end member values for the central north pacific and that mixing of these water masses defines vertical profiles of nd isotopes in this region in the eastern equatorial pacific eep three water masses modified lcdw npdwsanp and npdwwestern pacific combine to produce nd isotopic values that reflect this conservative mixture therefore nd isotopes behave as a conservative water mass tracer in the central north pacific and the eep but high rates of lithogenic inputs from young circum pacific island arcs compromise the conservative behavior of nd isotopes in the wep and sanp

rare earth element behavior during groundwater seawater mixing along the kona coast of hawaii abstract groundwater and seawater samples were collected from nearshore wells and offshore along the kona coast of the big island of hawaii to investigate rare earth element ree behavior in local subterranean estuaries previous investigations showed that submarine groundwater discharge sgd is the predominant flux of terrestrial waters to the coastal ocean along the arid kona coast of hawaii groundwater and seawater samples were filtered through 0 45 m and 0 02 m pore size filters to evaluate the importance of colloidal and soluble i e truly dissolved ionic species and or low molecular weight lmw colloids fractions of the rees in the local subterranean estuaries mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility wwtf proximal to the kaloko hanokohau national historic park and more pristine groundwater from a well constructed in a lava tube at kiholo bay were conducted with local seawater to study the effect of solution composition i e ph salinity on the concentrations and fractionation behavior of the rees as groundwater mixes with seawater in kona coast subterranean estuaries the mixed waters were also filtered through 0 45 or 0 02 m filters to ascertain the behavior of colloidal and soluble fractions of the rees across the salinity gradient in each mixing experiment concentrations of the rees were statistically identical two tailed student t test 95 confidence between the sequentially filtered sample aliquots indicating that the rees occur as dissolved ionic species and or lmw colloids in kona coast groundwaters the mixing experiments revealed that the rees are released to solution from suspended particles or colloids when kona coast groundwater waters mix with local seawater the order of release that accompanies increasing ph and salinity follows light ree lree middle ree mree heavy ree hree release of rees in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each ree that occurs in solution as dicarbonato complexes i e ln co3 2 as ph increases across the salinity gradient input normalized ree patterns of kona coast groundwater and coastal seawater are nearly identical and relatively flat compared to north pacific seawater indicating that sgd is the chief source of these trace elements to the ocean along the kona coast additionally ree concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open ocean seawater values from the north pacific further demonstrating the importance of sgd fluxes of rees to these coastal waters taken together these observations indicate that large scale removal of rees which characterizes the behavior of rees in the low salinity reaches of many surface estuaries is not a feature of the subterranean estuary along the kona coast a large positive gadolinium gd anomaly characterizes groundwater from the vicinity of the wwtf the positive gd anomaly can be traced to the coastal ocean providing further evidence of the impact of sgd on the coastal waters estimates of the sgd fluxes of the rees to the coastal ocean along the kona coast i e 1 3 2 6 mmol nd day 1 are similar to recent estimates of sgd fluxes of rees along florida s east coast and to rhode island sound all of which points to the importance of sgd as significant flux of rees to the coastal ocean

the neodymium isotopic composition of waters masses in the eastern pacific sector of the southern ocean the antarctic circumpolar current is one of the key components of ocean circulation and a knowledge of its isotopic composition is essential to the use of neodymium nd isotopes to trace circulation now and in the past here we present 57 new analyses of the nd isotopic composition of the water column in the eastern pacific sector of the southern ocean documenting both the variation in three dimensions as well as the controls on that variability nd isotopic data for the middle of the water column demonstrate the homogeneity of circumpolar deep water cdw at an end value of 8 7 0 1 this homogeneity reflects the large nd inventory in the acc flow and the degree to which this large inventory buffers the nd characteristics of the acc against extra oceanic inputs from the continents either via dust from the atmosphere or through dissolved and particulate material from the adjacent continents cdw upwells onto the amundsen sea shelf and even here its nd isotopic properties are close to conserved in the middle of the water column end 8 0 0 2 at 600 m at the top and bottom of the shelf water column however the nd isotopic and concentration characteristics are strongly modified to end as high as 4 5 all the shelf water column data obtained here are consistent with net addition of nd to bottom and surface waters with a contrasting isotopic composition that is matched by local sediment end 1 to 2 followed by conservative mixing of that water into intermediate levels mixing with this shelf composition also leads to significant modification of open ocean surface water nd isotopic shift around 1 epsilon unit in the acc as it flows eastwards modification of open ocean bottom waters by interaction with sediment is more subtle but there is marked non conservative removal of nd accompanied by significant changes in isotopic composition in waters within 10 m of the seabed the new data demonstrate the conservativity of nd in the middle water column especially for such large volume flows as the acc though boundary exchange type processes are clearly important in this region and their imprint on both the shelf and open ocean surface water is significant there is no observable impact on the main core of cdw this finding augurs well for the use of nd isotopes as a conservative water mass tracer now and in the past for example these data suggest that the only likely control on the temporal variability of southern component deep water exported northwards into the atlantic through the last glacial cycle is variations in the input of north atlantic deep water in the atlantic sector on the other hand the data also suggest caution in the use of sedimentary archives of bottom water nd as records of deep water nd isotopic characteristics given the dramatic modification of bottom waters on the shelf and the more subtly non conservative behaviour in the open ocean bottom water that are both suggestive of modification of the nd characteristics of bottom waters by sediment

neodymium isotopic characterization of ross sea bottom water and its advection through the southern south pacific since the inception of the international geotraces program studies investigating the distribution of trace elements and their isotopes in the global ocean have significantly increased in spite of this large scale effort the distribution of neodymium isotopes 143nd 144nd end and concentrations nd in the high latitude south pacific is still understudied specifically north of the antarctic polar front apf here we report dissolved nd isotopes and concentrations from 11 vertical water column profiles from the south pacific between south america and new zealand and across the antarctic frontal system results confirm that ross sea bottom water rsbw is represented by an endvalue of 7 and for the first time show that these nd characteristics can be traced into the southeast pacific until progressive mixing with ambient lower circumpolar deep water lcdw dilutes this signal north of the apf that is endbehaves conservatively in rsbw opening a path for studies of past rsbw behavior neodymium concentrations show low surface concentrations and a linear increase with depth north of the apf south of the apf surface nd is high and increases with depth but remains almost constant below 1000m this vertical and spatial nd pattern follows the southward shoaling density surfaces of the southern ocean and hence suggests supply of nd to the upper ocean through upwelling of nd rich deep water low particle abundance due to reduced opal production and seasonal sea ice cover likely contributes to the maintenance of the high upper ocean nd south of the apf this suggests a dominant lateral transport component on nd and a reduced vertical control on nd concentrations in the south pacific south of the apf

on the relationship between nd isotopic composition and ocean overturning circulation in idealized freshwater discharge events using a cost efficient climate model the effect of changes in overturning circulation on neodymium isotopic composition nd is systematically examined for the first time idealized sequences of abrupt climate changes are induced by the application of periodic freshwater fluxes to the north atlantic na and the southern ocean so thus mainly affecting either the formation of north atlantic deep water nadw or antarctic bottom water aabw variations in nd reflect weakening and strengthening of the formation of nadw and aabw changes in ndof end members are relatively small relationships between nd and the strength of nadw or aabw are more pronounced for aabw than for nadw atlantic patterns of variations in nd systematically differ between na and so experiments additionally the signature of changes in nd in the atlantic and the pacific is alike in na but opposite in so experiments discrimination between na and so experiments is therefore possible based on the atlantic pattern of variations in nd and the contrariwise behavior of nd in the atlantic and the pacific in further experiments we examined the effect of variations in magnitudes of particle export fluxes within the examined range and although settling particles represent the only sink of nd their effects on nd are relatively small our results confirm the large potential of nd as a paleocirculation tracer but also indicate its limitations of quantitative reconstructions of changes in the atlantic meridional ocean circulation

fingerprinting northeast atlantic water masses using neodymium isotopes dissolved neodymium nd isotopic composition expressed as end has been analysed for 82 seawater samples collected from 13 stations stretching from the alboran sea to the iceland basin the distribution of the end values of water masses was thus investigated for the first time along the western european margin in order to explore whether the water masses flowing in the eastern subpolar and subtropical atlantic reveal distinct isotopic patterns the modified atlantic water maw in the alboran sea displays end values between 9 2 0 2 and 8 9 0 2 that are significantly more radiogenic than those reported in previous studies 10 8 0 2 to 9 7 0 2 suggesting temporal variations in the nd isotopic composition of the water that enters the mediterranean sea from the strait of gibraltar the end value of the underlying modified winter intermediate water wiw has been established for the first time 9 8 0 3 and is compatible with a nd signature acquired from the sinking of maw in the northwestern mediterranean sea within the gulf of cadiz southern mediterranean sea water msw 10 6 0 2 differs slightly from the northern msw 9 9 0 4 owing to a significant contribution of modified east antarctic intermediate water eaaiw 10 9 0 2 in the northeast atlantic the north atlantic current surface water located in the inter gyre region north of 46 n displays end values of between 14 0 0 3 and 15 1 0 3 reflecting the subpolar gyre signature along the western european margin end values of surface water decrease toward the north from 10 4 1 6 to 13 7 1 0 in agreement with the gradual mixing between subtropical and subpolar water at intermediate depth end values decrease from 9 9 0 4 within the gulf of cadiz to 12 1 0 3 within the porcupine seabight indicating a strong dilution of the msw with subpolar water within the rockall trough and the iceland basin the more negative end values at mid depth 13 5 0 3 indicate that the msw has no influence even during periods of low nao index water masses deeper than 1200 m in the northeast atlantic are clearly influenced by the less radiogenic labrador sea water lsw 13 2 0 3 and 14 5 0 3 that mixes locally end between 10 3 0 2 and 11 3 0 3 in the iceland basin with the iceland scotland overflow water isow

the concentration and isotopic composition of diffusible nd in fresh and marine waters abstract variations in the nd isotopic composition of ocean water through time recorded in marine deposits are suggested to document changes in erosional input and ocean circulation thus characterization of the dissolved nd component in seawater is important but few attempts have been made to directly measure truly dissolved nd here we report nd data obtained using the technique of diffusive gradients in thin films dgt designed to measure in situ diffusible labile trace metals in aqueous solutions the method samples free ions and possibly very small complexes the concentration and isotopic composition of nd in fresh brackish and seawater have been determined with dgt analyzed with thermal ionization mass spectrometry and compared with filtered and bulk water samples concentrations measured in water samples and with dgt show that the relative amount of diffusible nd increases with salinity from being about 10 in the fresh water to 42 in seawater at each sampled site the isotopic composition of nd in the water shows a similar isotopic composition within errors with nd sampled using the dgt method these results indicate that there is a complete exchange between the particulate colloidal fraction and the truly dissolved phase therefore our findings suggest that solute nd reflects both the isotopic composition of the marine sediments and the bulk water

dissolved rare earth elements tracing lithogenic inputs over the kerguelen plateau southern ocean abstract dissolved rare earth elements rees were measured in the water masses upstream from and over the kerguelen plateau indian sector of the southern ocean upstream from the plateau the ree profiles were consistent with published data from the southern and indian oceans over the plateau a one box model yields a lithogenic nd flux from the dissolution of lithogenic material of 89 20 t nd y 1 and a corresponding dissolved iron input larger than 100 000 t fe y 1 however despite evidence of this significant lithogenic input dissolved fe is strongly depleted in the upper layers contrasting with the enriched ree concentrations this contrast stresses the different behaviours of ree and iron in the surface waters and the fact that strong fertilization does not imply dissolved fe replete waters

southern ocean source of 14 c depleted carbon in the north pacific ocean during the last deglaciation radiocarbon depleted carbon dioxide was released to the atmosphere at the end of the last glacial period but its source remains controversial neodymium isotope records of deglacial intermediate water circulation in the eastern north pacific ocean from fish teeth support a southern ocean source

evolution of the neodymium isotopic signature of neritic seawater on a northwestern pacific margin new constrains on possible end members for the composition of deep water masses in the late cretaceous ocean the neodymium nd isotope composition of fish remains has beenwidely used to track past changes in oceanic circulation although the number of published nd isotope data for the cretaceous has markedly increased in the last years no consensus has been reached on the structure of the oceanic circulation and its evolution during the late cretaceous yet this period is characterised bymajor geodynamical and climatic changes andmarked by the disappearance of global oceanic anoxic events inwhich changes in oceanic circulation modesmay have played a significant role in this study we present the first record of nd isotopic composition of fish remains from continental margin environments on the northwestern pacific margin yezo group in the hokkaid area northern japan for the late cretaceous period this record interpreted in terms of nd isotopic composition of local neritic seafloor seawater is characterised by relatively radiogenic nd isotope compositions and presents variations of several e units from the turonian to the campanian ranging from 5 5 to 0 5 e units although most values remain in the 1 to 3 range conversely the local detrital fraction remains more constant and around 4 e units on the studied interval this new set of seawater nd data contains some of the most radiogenic values for the cretaceous published yet the more radiogenic seawater nd isotope values compared to that of the sediments points to an input of radiogenic seawater in the studied area by surface currents during the late cretaceous similarly to the modern configuration these radiogenic waters could have been conveyed in the studied area by a southward current comparable to the modern oyashio current bathing the hokkaid area our data are then consistent with the presence in the northern pacific of highly radiogenic seawater and support the northern and northwestern pacific as a possible radiogenic source for the deep parts of the basin as such this work represents a first step toward a better characterisation of the various end members that could have contributed to the nd isotopic signature of the deep water masses filling the cretaceous oceans

seasonal variations in dissolved neodymium isotope composition in the bay of bengal abstract constraining the dissolved neodymium nd cycle in the ocean is paramount for using nd isotopic composition e nd as a tracer to reconstruct deep sea paleocirculations or continental weathering on different time scales dissolved end has been measured in seawater samples from six hydrological stations collected along 89 e north south transect in the bay of bengal bob in order to assess the impact of seasonal freshwater and sediment discharges from the continental river systems seawater samples collected in this study during june 2012 reveal more radiogenic end a difference of 2 epsilon units for the upper 2000 m and 0 5 epsilon unit below 2000 m and 3 8 pmol kg lower nd concentrations than the reported values of nearby seawater samples collected in november 2008 these observations are most plausibly explained by a seasonal variations in dissolved nd concentrations and end in the bob induced by seasonal variations in the freshwater and sediment discharges from the ganges brahmaputra g b river system however we cannot entirely exclude the possibility of spatial differences given that the water stations collected in this study are not exactly the same positions collected in november 2008 a two box model suggests 1 the particulate nd inputs from the g b river system mainly control the seasonal shift of end observed in the bob seawater and 2 a very rapid nd exchange exists between lithogenic particles and seawater at least on the scale of a few months seasonal changes in seawater end may also occur in other marginal seas and in the outflows of major rivers and these need to be taken into account when using the end proxy in the ocean

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved

holocene history and environmental reconstruction of a hercynian mire and surrounding mountain landscape based on multiple proxies abstract we discovered the first peat section covering the entire holocene in the hrub jesenik mountains representing an island of unique alpine vegetation whose history may display transitional features between the hercynian and carpathian regions we analysed pollen plant macrofossils more abundant in bottom layers testate amoebae more abundant in upper layers peat stratigraphy and chemistry we found that the landscape development indeed differed from other hercynian mountains located westward this is represented by pinus cembra and larix during the pleistocene holocene transition the early expansion of spruce around 10 450 cal yr bp and survival of larix during the climatic optimum the early holocene climatic fluctuations are traced in our profile by species compositions of both the mire and surrounding forests the mire started to develop as a calcium rich percolation fen with some species recently considered to be postglacial relicts meesia triquetra betula nana shifted into ombrotrophy around 7450 cal yr bp by autogenic succession and changed into a pauperised nutrient enriched spruce woodland due to modern forestry activities we therefore concluded that its recent vegetation is not a product of natural processes from a methodological viewpoint we demonstrated how using multiple biotic proxies and extensive training sets in transfer functions may overcome taphonomic problems

separating biogeochemical cycling of neodymium from water mass mixing in the eastern north atlantic abstract the radiogenic neodymium nd isotope ratio 143nd 144nd expressed in e nd is being used as a tracer in paleo and modern ocean circulation however the mechanisms controlling input distribution and internal cycling are far from understood for example globally nd concentration nd commonly follows patterns of nutrient tracers generally increasing with depth below the thermocline while e nd tends to reflect the water masses which has often been referred to as the nd paradox here we present dissolved nd isotopes and concentrations at unprecedented vertical and spatial resolution from the eastern part of the us geotraces north atlantic zonal transect gulf of cadiz mauritanian shelf cape verde islands the nd of all samples ranges from 12 3 to 36 7 pmol kg with lowest nd usually found within the layer of highest chlorophyll a levels chl max suggesting removal through scavenging the nd isotope compositions range between e nd 13 4 and 9 9 with lower values at the surface within the extension of the saharan dust plume and a benthic nepheloid layer bnl less negative values are found in oligotrophic surface waters mediterranean outflow water mow and near the cape verde islands overall water mass mixing derived from e nd is best visible at the strait of gibraltar where mow enters the atlantic ocean most of the sub thermocline e nd varies within a small range with poor water mass distinction due to the dominance of north atlantic deep water high surface nd associated with more negative e nd is interpreted to be the result of dust deposition and dissolution local nd maxima with no apparent change in e nd compared to ambient seawater observed within a zone of minimum oxygen concentration omz at 500 m depth off mauritania suggest minor input of lithogenic nd but a rather high contribution through desorption of previously scavenged nd that is saharan dust in this area has only a minor influence on the isotope composition of water below the uppermost surface layer the low e nd values and elevated nd within the bnl on the other hand indicate release from detrital material our new high resolution dataset gives valuable insights into the nd distribution near continental margins influenced by high atmospheric inputs and changing oxygen conditions we show how vertical and lateral processes overlap to produce the observed nd distribution bringing us forward in understanding the nd paradox