revisiting the rare earth elements in foraminiferal tests are the rare earth elements rees in foraminifera a valuable proxy for use in paleoceanographic and climate change studies in order to investigate this we attempted a comprehensive study of rees in planktonic and benthic foraminifera several different cleaning protocols were tested although the hydroxylamine used to clean all foraminifera in this study removes an unidentified source of ree contamination it seems to remobilize metal oxides that are otherwise unaffected in flow through dissolution the calculated ree distribution coefficients kd ree s are between 100 and 500 for both planktonic and benthic foraminifera these kds are high compared to other elements in biogenic calcite but can be explained through a general model of element incorporation during foraminiferal calcification from data taken from eight core tops in the southeast pacific we conclude that the rees in planktonic foraminifera are indeed useful as a proxy for upper ocean water mass and mixed layer biogenic productivity alternatively the rees in benthic foraminifera are useful as a proxy for carbon flux to the sea floor these proxies should be robust down core unless the sediments have undergone anoxic diagenesis which stabilizes fe carbonate thus overprinting the primary ree signature however it is clear from ree distributions in foraminiferal tests if anoxic conditions have occurred

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

neodymium isotopes in seawater from the barents sea and fram strait arctic atlantic gateways abstract the neodymium concentration c nd and isotopic composition e nd in seawater have been determined in the water column at five sites in the barents sea fram strait area where most of the water exchange between the arctic ocean and the north atlantic takes place in the main arctic ocean inflow branch across the barents sea the concentration and isotopic composition c nd 15 5 pmol kg and e nd 10 8 are similar to those reported for the northeastern nordic seas which is consistent with this region being a source area for the arctic inflow due to the addition of nd from svalbard shelf sediments the c nd in the surface waters above 150 m in the fram strait inflow branch is higher by a factor of 2 and the e nd is shifted to lower values 11 8 in the stratified nansen basin where cold low salinity water overlies warmer atlantic water the c nd and e nd do not vary with the vertical temperature salinity structure but are essentially constant and similar to those of the atlantic inflow throughout the entire water column down to 3700 m depth which indicates that the nd is to a large extent of atlantic origin compared to the atlantic inflow water the nd in the major arctic ocean outflow the fram strait show higher c nd in the surface waters above 150 m and a higher e nd 9 8 throughout the entire water column down to 1300 m depth sources for the more radiogenic nd isotopic composition in deep water of the fram strait outflow most likely involve boundary exchange with sediments on the shelf and slope as the water passes along the canadian archipelago river water is a possible source in the surface water but it also seems likely that pacific water nd modified by interactions on the shelf is an important component in the fram strait surface outflow changes in the relative proportions of inflow of river water and flow of pacific water through the arctic ocean could thus influence the isotopic composition of nd in the north atlantic

trace metal distributions within a sitka eddy in the northern gulf of alaska in the northern gulf of alaska mesoscale anticyclonic eddies have been implicated as a mechanism of the cross shelf exchange of iron fe replete coastal waters with fe deplete subarctic alaskan gyre waters based on existing hydrography and macronutrient distributions a sitka eddy sampled during august 2007 is divided into a surface eddy core a shallow subsurface eddy core and a deeper subsurface eddy core the distributions of aluminum al manganese mn and fe in the eddy are examined and compared to distributions at shelf stations similar to where the eddy formed as well as basin stations representative of the fe limited subarctic alaskan gyre relative to basin stations dissolved and particulate al and dissolved mn were elevated in eddy core waters reactive fe concentrations within the shallow subsurface eddy core were nearly seven times greater than reactive fe concentrations at similar densities at the basin stations this shallow subsurface eddy core is likely mixed into the euphotic zone during storm induced mixing as well as mixing during isopycnal relaxation as an eddy dies out the flux of reactive fe to surface waters from the shallow subsurface core of eddies in the gulf of alaska is a significant source compared to both remote and local atmospheric dust deposition it is hypothesized that fe supply from eddies in the eastern gulf of alaska shifts the core of the high nutrient lower than expected chlorophyll water farther west in conjunction with an eddy desert in that same region

southern ocean control of silicon stable isotope distribution in the deep atlantic ocean the fractionation of silicon si stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon delta si 30 dissolved in seawater a sensitive tracer of the oceanic biogeochemical si cycle we present a high precision dataset that characterizes the delta si 30 distribution in the deep atlantic ocean from denmark strait to drake passage documenting strong meridional and smaller but resolvable vertical delta si 30 gradients we show that these gradients are related to the two sources of deep and bottom waters in the atlantic ocean waters of north atlantic and nordic origin carry a high delta 30 sisignature of 1 7 parts per thousand into the deep atlantic while antarctic bottom water transports si with a low delta si 30 value of around 1 2 parts per thousand the deep atlantic delta si 30 distribution is thus governed by the quasi conservative mixing of si from these two isotopically distinct sources this disparity in si isotope composition between the north atlantic and southern ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate delta n 15 no3 we infer that the meridional delta si 30 gradient derives from the transport of the high delta si 30 signature of southern ocean intermediate mode waters into the north atlantic by the upper return path of the meridional overturning circulation moc the basin scale deep atlantic delta si 30 gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes which fractionates si isotopes between the abyssal and intermediate mode waters formed in the southern ocean

rare earth element fluxes and geochemical budget in the eastern equatorial pacific rare earth element ree patterns and flux measurements of sediment traps sediments and nodules from the eastern tropical pacific demonstrate the dominance of ree supply to the sea floor by particle settling quantitative partitioning of the particle flux reveals that biogenic debris is the major ree carrier in shallow depths however the labile particles are surpassed in importance by alumino silicate particles at greater depths regeneration of biogenic associated ree appears responsible for la ce variations in the particle flux with depth and provides the primary source of ree accreted by nodules

spatial distribution of dissolved neodymium and end in the bay of bengal role of particulate matter and mixing of water masses abstract the concentration and isotope composition of dissolved nd have been measured in the water column along an 87 e transect gio1 section of international geotraces program in the bay of bengal bob to investigate the effect of water mass mixing and nd release from particulate matter in determining these properties the concentration of nd in surface waters of the bob shows a north south decreasing non linear trend 46 to 22 pmol kg with salinity whereas its depth profiles typically show a high value in surface waters a minimum 15 to 23 pmol kg in the shallow subsurface 50 200 m followed by a gradual increase with depth the nd concentration of bob waters is generally higher than that in nearby oceanic basins on the other hand the e nd values in the bob are less radiogenic compared to those reported for other regions of the global oceans except baffin bay the north atlantic subpolar gyre and the niger delta margin and show a greater variation in the upper water column surface waters of the southernmost profile 6 n show a more radiogenic e nd value 8 which decreases to 15 in the northernmost profile 20 n close to the values for dissolved and particulate phases of the ganga brahmaputra g b rivers this latitudinal trend is most likely a result of variations in mixing proportion between the more radiogenic indonesian throughflow surface waters iw and unradiogenic bob low salinity water the former s signature being more clearly discernible in surface waters of the two southernmost profiles 6 n and 8 5 n attempts to balance the nd budget in the water column based on an inversion model suggest that in addition to water masses other source s is required the strength of which is estimated to vary from 1 to 65 of the measured nd concentration the calculations also show that the e nd of this additional source s has to be in the range of 16 2 typical of g b river sediments these observations coupled with the north south distribution of dissolved nd and e nd indicate that this additional source is release from particulate phases supplied by the g b river system the calculations also bring out the presence of hot spots of nd release excess nd near the sediment water interface along the northern slope of the bay indicating supply of nd from continental margin sediments this study underscores the significant role of dissolved particulate nd from the ganga brahmaputra river system in contributing to the dissolved nd budget of the global oceans

the estuarine chemistry of rare earth elements comparison of the amazon fly sepik and the gulf of papua systems abstract a comparison of the amazon fly gulf of papua and sepik river systems has shown that there are two distinct processes operating on dissolved rare earth elements ree in estuaries large scale salt induced coagulation in the low salinity region and small to extensive release in the mid to high salinity region fractionation of the ree occurs during both removal and release the order of removal follows lree mree hree and the order of release follows hree mree lree where l m and h refer to light middle and heavy ree respectively hence estuarine reactions can modify the relative abundance of dissolved ree reaching the oceans operating in tandem the removal and release lead to the preferential removal of the lree and the preferential release of hree during estuarine mixing this combination in turn results in an effective river water flux river flux after modifications by estuarine chemistry which is evolved toward the ree composition of seawater which has a heavy ree enriched composition when normalized against the ree composition of rivers or the earth s continental crust the increase of dissolved ree in the mid to high salinity waters of the amazon and fly estuaries suggests a sediment and or suspended sediment source the lack of ree increases in the sepik river estuary strengthens this explanation as the mixing zone of this estuary is located over a deep shelf where there is little physical contact between bottom sediment and estuarine waters in marked contrast the amazon and fly estuaries are dominated by the active resuspension and deposition of bottom sediments the resupply of ree accompanied by fractionation may result from ree carbonate complexation during the reaction of seawater with suspended particles and or bottom sediment estuarine and shelf sediments may be important sources of dissolved nd to the oceans thereby helping to maintain the inter ocean differences in the nd isotopic composition of seawater by reducing the residence time of nd in the oceans

balancing the global oceanic neodymium budget evaluating the role of groundwater the distinctly different end 0 values of the atlantic indian and pacific oceans requires that the residence time of nd in the ocean i e nd be on the order of or less than the ocean mixing time of 500 1500 yr however estimates of nd based on river influxes range from 4000 to 15 000 yr thus exceeding the ocean mixing time in order to reconcile the oceanic nd budget and lower the residence time by roughly a factor of 10 an additional as yet unidentified and hence missing nd flux to the ocean is necessary dissolution of materials deposited on continental margins has previously been proposed as a source of the missing flux in this contribution submarine groundwater discharge sgd is examined as a possible source of the missing nd flux neodymium concentrations n 730 and end 0 values n 58 for groundwaters were obtained from the literature in order to establish representative groundwater values mean groundwater nd concentrations and end 0 values were used along with recent estimates of the terrestrial freshwater component of sgd 6 of river discharge on a global basis to test whether groundwater discharge to the coastal oceans could account for the missing flux employing mean nd concentrations of the compiled data base i e 31 8 nmol kg for all 730 analyses and 11 3 nmol kg for 141 groundwater samples from a coastal aquifer the global terrestrialderived sgd flux of nd is estimated to range between 2 9 10 7 and 8 1 10 7 mol yr these estimates are of the same order of magnitude and within a factor of 2 of the missing nd flux i e 5 4 10 7 mol yr applying the sgd nd flux estimates the global average end 0 of sgd is predicted to be 9 1 which is similar to our estimate for the missing nd flux 9 2 and in agreement with the mean s d end 0 measured in groundwaters i e end 0 8 9 4 2 the similarities in the estimated sgd nd flux and corresponding end 0 values to the magnitude and isotope composition of the missing nd flux are compelling and suggest that discharge of groundwater to the oceans could account for the missing nd flux future investigations should focus on quantifying the nd concentrations and isotope compositions of groundwater from coastal aquifers from a variety of coastal settings as well as the important geochemical reactions that effect nd concentrations in subterranean estuaries in order to better constrain contributions of sgd to the oceanic nd budget

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

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

a rare earth element signature of bacteria in natural waters abstract this study shows that rare earth element ree distribution patterns between bacteria and water for five different bacterial strains bacillus subtilis escherichia coli alcaligenes faecalis shewanella putrefaciens and pseudomonas fluorescens exhibit a steep increase in the heavy ree hree part of the distribution pattern and a weak peak around the middle ree mree part though the ree patterns for b subtilis and e coli were already reported in our previous paper takahashi y ch tellier x hattori k h kato k fortin d 2005 adsorption of rare earth elements onto bacterial cell walls and its implication for ree sorption onto natural microbial mats chem geol 219 53 67 the present results clearly show that the characteristic ree pattern is commonly observed for various bacterial species in addition similar ree patterns were observed for bioflims containing neutrophilic iron oxidizers and other bacteria formed in a groundwater discharge area in the budo pond in hiroshima japan suggesting that the ree distribution pattern found in the laboratory experiments was reproduced in naturally occurring bacteria in fresh waters in addition the ree pattern characterized by a maximum at mree and an increase at hree was also observed in fe oxyhydroxide precipitates formed below the same biofilm which contained bacterial remnants these results show that the presence of bacteria in natural fe oxyhydroxides and possibly in other natural minerals can be reflected in the shape of ree patterns such results could potentially be extended to geological materials such as banded iron formation bif and used to discuss the effect of microbial activity on the formation of bif although there are still many problems related to the extrapolation of the results obtained for fe oxyhydroxides in modern water systems to bif such as abiotic processes and post depositional alteration of the ree patterns our study suggests that the ree pattern can be used as another tool to assess the role of bacteria in mineral formation in natural waters

surface roughness imaging of currents shows divergence and strain in the wind direction images of sea surface roughness for example obtained by synthetic aperture radars sar or by radiometers viewing areas in and around the sun glitter at times provide clear observations of meso and submesoscale oceanic features interacting with the surface wind waves particular deformation properties of surface currents are responsible for those manifestations ignoring other sources of surface roughness variations the authors limit their discussion to the mean square slope mss variability this study confirms that vortical currents and currents with shear in the wind direction shall not be expressed in surface roughness images only divergent currents or currents with no divergence but strained in the wind direction can exhibit surfaceroughnesssignatures morespecifically nondivergentcurrentsmightbetracedwitha458sensitivityto the wind direction a simple method is proposed in order to interpret high resolution roughness images where roughness variations are proportional to u x 1 a y y a linear combination of the along wind and crosswind current gradients the polarization parameter a depends upon the sensor look direction and the directional properties of the surface waves selected by the sensor the use of multiple look directions or possible acquisitions with different wind directions shall thus help to retrieve surface currents from surface roughness observations

the distribution of neodymium isotopes and concentrations in the eastern equatorial pacific water mass advection versus particle exchange the radiogenic isotope composition of the rare earth element ree neodymium nd is a powerful water mass proxy for present and past ocean circulation the processes controlling the nd budget of the global ocean are not quantitatively understood and in particular source and sink mechanisms are still under debate in this study we present the first full water column data set of dissolved nd isotope compositions and nd concentrations for the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omz is located this region is of particular interest for understanding the biogeochemical cycling of rees because anoxic conditions may lead to release of rees from the shelf whereas high particle densities and fluxes potentially remove the rees from the water column data were obtained between 1 40 n and 16 s along a nearshore and an offshore transect near surface zonal current bands such as the equatorial undercurrent euc and the subsurface countercurrent sscc which are supplying oxygen rich water to the omz are characterized by radiogenic nd isotope signatures end 2 surface waters in the northernmost part of the study area are even more radiogenic end 3 most likely due to release of nd from volcanogenic material deep and bottom waters at the southernmost offshore station 14 s are clearly controlled by advection of water masses with less radiogenic signatures end 7 originating from the southern ocean towards the equator however the deep waters show a clear trend towards more radiogenic values of up to end 2 the northernmost station located in the panama basin shows highly radiogenic nd isotope signatures in the entire water column which indicates that particle scavenging downward transport and release processes play an important role this is supported by relatively low nd concentrations in deep waters 3000 6000 m in the eep 20 pmol kg compared to locations in the northern and central pacific 40 60 pmol kg which suggests enhanced removal of nd in the eep

the sedimentary flux of dissolved rare earth elements to the ocean abstract we determined pore fluid rare earth element ree concentrations in near surface sediments retrieved from the continental margin off oregon and california usa these sites represent shelf to slope settings which lie above within and below the oxygen minimum zone of the northeast pacific the sediments are characterized by varying degrees of net iron reduction with pore fluids from the shelf sites being generally ferruginous and the slope sediments having less pronounced iron reduction zones that originate deeper in the sediment package ree concentrations show maxima in shallow upper 2 10 cm subsurface pore fluids across all sites with concentrations that rise more than two orders of magnitude higher than seawater these pore fluid enrichments highlight the importance of a sedimentary source of rees to the ocean s water column here we use our measurements to estimate the diffusive flux of nd out of ocean sediments resulting in a global flux between 18 and 110 10 6 mol nd yr 1 while we do assume that our pore fluid profiles as well as the very limited data previously published are representative of a wide array of ocean environments this calculated flux can account for the modeled missing nd source flux 76 10 6 mol nd yr 1 in global budgets arsouze et al 2009 pore fluid normalized ree patterns show distinct variation in the middle ree and heavy ree enrichments with sediment depth and amongst sites these patterns show that the heavy ree enrichment of pore fluids at our deep slope site 3000 m water depth is closest to the heavy ree enrichment of seawater this observation supports the view that ree cycling within the upper ten centimeters of deep sea marine sediments as opposed to shallower continental shelf and slope sediments plays a significant role in controlling the integrated global ree flux from the pore fluids and consequently the broad scale ree pattern in seawater

the distribution of neodymium isotopes in arctic ocean basins nd concentration and isotope data have been obtained for the canada amundsen and makarov basins of the arctic ocean a pattern of high nd concentrations up to 58 pm at shallow depths is seen throughout the arctic and is distinct from that generally seen in other oceans where surface waters are relatively depleted a range of isotopic variations across the arctic and within individual depth profiles reflects the different sources of waters the dominant source of water and so nd is the atlantic ocean with lesser contributions from the pacific and arctic rivers radiogenic isotope nd signatures up to epsilon nd 6 5 can be traced in pacific water flowing into the canada basin waters from rivers draining older terrains provide very unradiogenic nd down to epsilon nd 14 2 that can be traced in surface waters across much of the eurasian basin a distinct feature of the arctic is the general influence of the shelves on the nd concentrations of waters flowing into the basins either from the pacific across the chukchi sea or from across the extensive siberian shelves water shelf interaction results in an increase in nd concentration without significant changes in salinity in essentially all waters in the arctic through processes that are not yet well understood in estuarine regions other processes modify the nd signal of freshwater components supplied into the arctic basin and possibly also contribute to sedimentary nd that may be subsequently involved in sediment water interactions mixing relationships indicate that in estuaries nd is removed from major river waters to different degrees deep waters in the arctic are higher in nd than the inflowing atlantic waters apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins these enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the makarov basin epsilon nd similar to 10 5 but have created distinctive nd isotope signatures that were found near the margin of the canada basin with epsilon nd similar to 9 0 the deep waters of the amundsen basin are also distinct from the atlantic waters with epsilon nd 12 3 indicating that there has been limited inflow from the adjacent makarov basin through the lomonosov ridge c 2009 elsevier ltd all rights reserved

exhumation of serpentinized peridotite in the northern manila subduction zone inferred from forward gravity modeling the taiwan integrated geodynamic research program taiger collected two wide angle and reflection seismic transects across the northern manila subduction zone that provide constraints on the seismic velocity structure of the crust two dimensional gravity modeling along these two transects shows a significant relatively high density 3 12 and 3 02 g cm3 in the fore arc region at the interface between the subducting eurasian plate and the accretionary prism in front of the luzon arc on the overriding philippine sea plate the anomalous density in this zone is higher than that in the fore arc crust and the accretionary prism but lower than that in mantle numerous geophysical and geological data together with numerical models have indicated that serpentinization of the fore arc mantle is both expected and observed serpentinization of mantle rocks can dramatically reduce their seismic velocity and therefore their seismic velocity in a density to velocity conversion therefore the source of the high density material could be serpentinized fore arc mantle with serpentinization caused by the dehydration of the subducting eurasian plate we interpret that positive buoyancy combined with weak plate coupling forces in the northern manila subduction zone is resulting in this serpentinized fore arc mantle peridotite being exhumed

a synoptic survey of young mesoscale eddies in the eastern gulf of alaska eddies in the gulf of alaska are important sources of coastal water and associated nutrients iron and biota to the high nutrient low chlorophyll central gulf of alaska three primary eddy formation regions along the eastern boundary of the gulf have been identified from south to north haida sitka and yakutat in the spring of 2005 three eddies one of each type were sampled soon after their formation the subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water the sitka and yakutat core waters also exhibited a subsurface temperature maximum mesothermal water coincident in depth with the iron maximum suggesting that eddies may play a role in the formation of temperature inversions observed throughout the gulf of alaska the data suggest different formation regions with the yakutat eddy forming in shallow shelf water with riverine input while the sitka and haida eddies appear to form in deeper water

composition of rare earth elements in settling particles collected in the highly productive north pacific ocean and bering sea implications for siliceous matter dissolution kinetics and formation of two ree enriched phases abstract settling particles were sampled monthly for 1 year using an automated time series sediment trap positioned at similar depths at two sites of high diatomaceous productivity in the north pacific ocean and bering sea the particles were analyzed for rare earth elements rees by inductively coupled plasma mass spectrometry icp ms with and without chemical treatment of the bulk samples to isolate siliceous fractions the ree composition of the bulk samples is explained largely by the contribution of two distinct components i carbonate with a higher ree concentration a negative ce anomaly and lighter ree lree enrichment ii opal with a lower ree concentration a weaker negative ce anomaly and heavier ree hree enrichment the siliceous fractions of settling particles are characterized by high si al ratios 30 190 reflecting high diatom productivity at the studied sites the la al ratio of the siliceous fraction is close to that of the upper crust but the lu al and lu la ratios are significantly higher than those of the upper crust or airborne particles indicating the presence of excess hrees in the siliceous fraction diatoms are believed to be important carriers of hrees the ce anomaly eu anomaly slope of the ree pattern and ree of the siliceous fraction vary exponentially with decreasing total mass flux they can be well reproduced according to the differential dissolution kinetics of elements in the order of ce

the geochemistry of rare earth elements in the amazon river estuary abstract the estuarine geochemistry of rare earth elements rees was studied using samples collected in the amazon river estuary from the amasseds amazon shelf sediment study cruise of august 1989 extensive removal of dissolved 0 22 m filtered trivalent rees from river water occurs in the low 0 6 salinity region removal by the salt induced coagulation of river colloids leads to fractionation among the ree iii series the order of removal is light rees middle rees heavy rees there also is the enhanced removal of ce relative to trivalent la and nd in the low salinity 0 6 zone and in the zone of high biological activity this is the first field observation of strong ce removal associated with coagulation of river colloids and biological productivity the argument is made that the decrease in the ce anomaly across a biological front is caused by biologically mediated oxidation of ce iii to ce iv coagulation of river colloids and biologically mediated oxidation of ce iii lead to fractionation of ree iii and redox modification of ce these processes result in the ree composition becoming fractionated relative to the amazon river water and crust and more evolved toward the ree composition of the oceans this study implies that reactions in estuaries play significant yet poorly understood roles in controlling the ree composition and ce anomaly of the oceans

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

deep dissolved iron profiles in the eastern north atlantic in relation to water masses concentrations of dissolved iron dfe 0 2 m were determined at two stations in the biscay abyssal plain north east atlantic in march 2002 dfe concentrations in the surface layer 0 23 0 34 nm were typical of winter conditions in this area at 1000 m dfe concentrations increased to 0 62 0 86 nm this feature is consistent with the production of dfe by remineralization of the biogenic material however at this depth mediterranean outflow water mow could be an additional source of dfe below 2500 m dfe concentrations were constant 0 75 0 04 nm an interesting feature of the profiles was the intermediate maximum of dfe 1 19 1 12 nm around 2000 m associated with the labrador sea water lsw we suggest that the iron enrichment of lsw occurred when this water mass reached the continental margin likely in the vicinity of the goban plateau vertical distributions were highly dependent on water masses encountered

the geochemistry of rare earth elements in the seasonally anoxic water column and porewaters of chesapeake bay a twelve cruise time series study of a seasonally anoxic basin in chesapeake bay was carried out between february 1988 and february 1989 data from filtered bottom water and upper 0 1 cm porewater samples are presented this is the first study in which time series measurements have been employed to understand the low temperature geochemistry of rare earth elements rees the focus is on the coupling between redox reduction oxidation variations and ree cycling fractionation of trivalent rees and development of cerium anomalies the time series results demonstrate that rees have large seasonal cycles in both the water column and porewaters in response to the development of anoxia in the spring and reoxygenation in the fall the transition from oxic to suboxic to anoxic conditions results in the release of rees into the upper porewaters and bottom waters the release of rees and fe are coincident in the bottom waters while the release of rees lags fe by approximately 50 days in the upper porewaters this decoupling is explained in terms of a redox front which moves upward from the sediments to bottom waters during the development of seasonal anoxia the release of rees to the upper porewaters and bottom water are accompanied by 1 1 fractionation across the trivalent ree series and by 2 2 the preferential input of ce relative to its trivalent only ree neighbors ree iii fractionation is such that the relative rate of release increases from lu to la light ree middleree heavyree during reoxygenation removal of dissolved rees occurs from both the water column and upper porewaters and follows the same relative rates lree mree hree cerium removal occurs faster than its neighbor ree iii indicating a rapid oxidation of ce iii to ce iv

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

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 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

biogeochemical implications from dissolved rare earth element and nd isotope distributions in the gulf of alaska dissolved rare earth element ree concentrations and nd isotope compositions were measured for surface waters and full water column profiles of the gulf of alaska goa and compared to water mass properties and circulation in order to better understand the mechanisms controlling the input and transport of rees in the ocean the rees display a typical open ocean range of concentrations i e la 12 66 pm lu 0 2 2 5 pm and depth distributions i e surface ocean depletion and enrichment with water depth nd isotope signatures are highly radiogenic as expected for the north pacific margin ranging from 3 8 to 0 2 epsilon nd the most radiogenic values were found in the coastal waters but also in the cores of eddies indicating efficient export of rees from the margins and across the mixed layer this is the first time that distinct nd isotope distributions in near surface waters can be directly assigned to offshore eddy transport a distinct mid depth similar to 2200 m nd isotope signal was found that most likely reflects advection of a water mass that formed through past down welling in the northern pacific subsurface nd isotope compositions appear to behave conservatively and can be explained through a ree distribution model proposed here this model is based on multivariate analysis of the rees and invokes two distinct pools of dissolved rees a passive pool complexed by carbonate ions and a bio reactive pool that is microbially manipulated the latter pool is only significant in the upper water column and most likely reflects the indirect effects of microbial cycling of iron our model of the open ocean ree distribution contributes to explaining the conservative nature of nd isotopes and provides a mechanism linking surface ocean and pore water ree dynamics

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

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

modeling the distribution of nd isotopes in the oceans using an ocean general circulation model nd isotopic compositions of authigenic phases in marine archives are increasingly used as a tracer of past changes in ocean circulation such applications assume that water masses are tagged with distinct nd isotope compositions in source regions and that away from these regions the nd isotope ratios observed in deep waters mainly reflect water mass mixing however the degree to which the simple assumption of quasi conservative mixing reflects the complicated reality of general circulation in the oceans is not well understood here we present numerical simulations of the nd isotope distribution in seawater using an offline ocean general circulation model ogcm treating the nd isotopic composition of seawater as a conservative tracer nd isotope data from modern surface waters are used to generate an interpolated map of nd isotope compositions for the entire surface ocean this map is treated as a fixed surface boundary condition that is propagated into the interior ocean by the advective diffusive transport of the ocean model until a steady state is reached this treatment of nd isotopes was chosen because it mimics the behavior of well known and well understood conservative tracers such as potential temperature and salinity the model results for all non surface grid points are then compared to published data this simple approach produces nd isotope estimates for north atlantic deep water that are consistent with observations but produces values lower than observed in the deep pacific and southern oceans indicating the need for a source of radiogenic nd directly to the deep pacific ocean sensitivity tests show this to be a robust result by fixing the return flow of the pacific ocean to the southern ocean with nd isotope ratios that are consistent with modern observations the model results are brought into close agreement with a majority of the available data with the addition of a deep pacific source of radiogenic nd more than half of the simulated values from the interior ocean fall within one e unit of the corresponding observations our results thus indicate that the deep pacific ocean requires a source of radiogenic nd in addition to inputs to the surface ocean and that when the deep waters of the north atlantic and north pacific are set with realistic values a majority of intermediate areas are consistent with quasi conservative mixing of these two end members

hafnium and neodymium isotopes in surface waters of the eastern atlantic ocean implications for sources and inputs of trace metals to the ocean we present hafnium hf and neodymium nd isotopic compositions and concentrations in surface waters of the eastern atlantic ocean between the coast of spain and south africa these data are complemented by hf and nd isotopic and concentration data as well as rare earth element ree concentrations in saharan dust hafnium concentrations range between a maximum of 0 52 pmol kg in the area of the canary islands and a minimum value of 0 08 pmol kg in the southern angola basin neodymium concentrations also show a local maximum in the area of the canary islands 26 pmol kg but are even higher between 20n and 4n reaching maximum concentrations of 35 pmol kg these elevated concentrations provide evidence of inputs from weathering of the canary islands and from the partial dissolution of dust from the sahara sahel region the inputs from ocean island weathering are also reflected in radiogenic hf and nd isotopes the hf isotopic compositions of dust samples themselves are highly variable ranging between ehf 20 and 0 6 the combined hf and nd isotopic compositions of dust plot close to the terrestrial array during periods of appreciable dust load in the atmosphere during low atmospheric dust loading combined hf and nd isotopic compositions similar to seawater are observed most of the variability can be explained in terms of variable degrees of zircon loss from the dust samples which in turn is linked to sorting during atmospheric transport to the eastern atlantic ocean and possibly presorting by sedimentary redistribution on the continent in addition increasing relative proportions of radiogenic clay minerals with decreasing grain size may contribute to the radiogenic hf isotopic compositions observed while the nd isotopic composition in the surface ocean reflects the nd isotopic composition of the saharan dust adjacent to the sahara sahel region the release of hf from that dust appears to be incongruent and results in surface ocean hf isotopic compositions which are 10 ehf more radiogenic than the bulk dust radiogenic hf appears to be released from clays and possibly from trace apatite rare earth element patterns of dust samples indicate the presence of apatite but provide no evidence for ferromanganese grain coatings suggesting that such coatings are insignificant in the release of hf and nd from saharan dust to the surface ocean the nd isotopic composition of the surface waters becomes less radiogenic south of the equator most likely reflecting the release of nd from congo river sediments the release of hf from saharan dust and the congo river sediments however does not produce distinct hf isotopic signatures in the surface ocean implying that the mobile fraction of hf integrated over large continental areas is isotopically uniform the hf isotopic uniformity in the surface ocean means that the limited variability in deep water isotopic compositions is consistent with a short deep water residence time and reflects homogenous continental inputs rather than efficient deep water homogenization

online preconcentration icp ms analysis of rare earth elements in seawater the rare earth elements rees with their systematically varying properties are powerful tracers of continental inputs particle scavenging intensity and the oxidation state of seawater however their generally low pmol kg concentrations in seawater and fractionation potential during chemical treatment makes them difficult to measure here we report a technique using an automated preconcentration system which efficiently separates seawater matrix elements and elutes the preconcentrated sample directly into the spray chamber of an icp ms instrument the commercially available seafast system elemental scientific inc makes use of a resin with ethylenediaminetriacetic acid and iminodiacetic acid functional groups to preconcentrate rees and other metals while anions and alkali and alkaline earth cations are washed out repeated measurements of seawater from 2000 m water depth in the southern ocean allows the external precision 2 of the technique to be estimated at 23 for all rees and 15 for most comparison of nd concentrations with isotope dilution measurements for 69 samples demonstrates that the two techniques generally agree within 15 accuracy was found to be good for all rees by using a five point standard addition analysis of one sample and comparing measurements of mine water reference materials diluted with a nacl matrix with recommended values in the literature this makes the online preconcentration icp ms technique advantageous for the minimal sample preparation required and the relatively small sample volume consumed 7 ml thus enabling large data sets for the rees in seawater to be rapidly acquired

modelling nd isotopes with a coarse resolution ocean circulation model sensitivities to model parameters and source sink distributions the neodymium nd isotopic composition nd of seawater is a quasi conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies here we present a comprehensive approach for the simulation of the two neodymium isotopes 143nd and 144nd using the bern3d model a low resolution ocean model the high computational efficiency of the bern3d model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of nd concentrations and nd to the parametrisation of sources and sinks previous studies have been restricted in doing so either by the chosen approach or by computational costs our study thus presents the most comprehensive survey of the marine nd cycle to date our model simulates both nd concentrations as well as nd in good agreement with observations nd covaries with salinity thus underlining its potential as a water mass proxy results confirm that the continental margins are required as a nd source to simulate nd concentrations and nd consistent with observations we estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects nd only to a small extent on the other hand the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both nd concentrations and nd furthermore despite their small contribution we find dust and rivers to be important components of the nd cycle in additional experiments we systematically varied the diapycnal diffusivity as well as the atlantic to pacific freshwater flux to explore the sensitivity of nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation these experiments reveal that nd concentrations and nd are comparatively little affected by variations in diapycnal diffusivity and the atlantic to pacific freshwater flux in contrast an adequate representation of nd sources and sinks is crucial to simulate nd concentrations and nd consistent with observations the good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of nd in further model studies

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties