eastern mediterranean surface water nd during eemian sapropel s5 monitoring northerly mid latitude versus southerly sub tropical freshwater contributions abstract a well developed sapropel s5 was deposited in the eastern mediterranean during the last interglacial eemian 124 119 ka freshwater contributions to the basin at this time can be traced using the isotopic composition of nd in planktonic foraminifera this enables differentiation between radiogenic sources to the south under the influence of the african monsoon and unradiogenic sources to the north relating to the mid latitude westerlies here we compare new nd data from a core in the southeast aegean sea with published data from the ionian and levantine seas shifts towards more radiogenic nd in the lower and middle parts of sapropel s5 are most pronounced in the ionian sea record with nd and 18og ruber co varying more closely here than in the levantine and aegean seas this is consistent with a freshwater source proximal to the ionian sea site likely indicating a substantial reactivation of rivers flowing northward from the central saharan watershed the lack during s5 deposition of a noticeable shift towards more unradiogenic nd in the aegean record would exclude a large influx of water from the northern borders of the eastern mediterranean during sapropel deposition these findings support a scenario whereby the last interglacial eastern mediterranean was influenced strongly by the remote effects of an intensified african monsoon with more local precipitation in the northern borders contributing relatively little to the sea surface composition

first nd isotope record of mediterranean atlantic water exchange through the moroccan rifian corridor during the messinian salinity crisis we present the first neodymium isotope reconstruction of mediterranean atlantic water exchange through the moroccan rifian corridor 8 5 ma this covers the late miocene messinian salinity crisis msc a period when progressive tectonic restriction of the mediterranean atlantic seaways resulted in extreme basin wide mediterranean salinity fluctuations the rifian corridor was one of these seaways and until now relatively poor age constraints existed for the timing of corridor closure due to the impact of uplift and erosion on the sedimentary record the bottom water nd isotope record from the continuous bou regreg valley succession in northwest morocco allows us to explore corridor connectivity with the atlantic data from the interior and mediterranean edge of the rifian corridor respectively the taza guercif and melilla basins northern morocco provide new information on corridor shallowing and the provenance of water flowing through the seaway as a result we can constrain the age of rifian corridor closure to 6 64 6 44 ma we also find no evidence of the siphoning of atlantic waters through the seaway 7 20 6 58 ma our results cannot exclude the possibility that at times during the messinian salinity crisis mediterranean outflow water reached the atlantic

neodymium isotopes in benthic foraminifera core top systematics and a down core record from the neogene south atlantic abstract records of the past neodymium nd isotope composition of the deep ocean can resolve ambiguities in the interpretation of other tracers we present the first nd isotope data for sedimentary benthic foraminifera comparison of the nd of core top foraminifera from a depth transect on the cape basin side of the walvis ridge to published seawater data and to the modern dissolved sio2 nd trend of the deep atlantic suggests that benthic foraminifera represent a reliable archive of the deep water nd isotope composition neodymium isotope values of benthic foraminifera from odp site 1264a angola basin side of the walvis ridge from the last 8 ma agree with fe mn oxide coatings from the same samples and are also broadly consistent with existing fish teeth data for the deep south atlantic yielding confidence in the preservation of the marine nd isotope signal in all these archives the marine origin of the nd in the coatings is confirmed by their marine sr isotope values these important results allow application of the technique to down core samples the new nd datasets along with ancillary cd ca and nd ca ratios from the same foraminiferal samples are interpreted in the context of debates on the neogene history of north atlantic deep water nadw export to the south atlantic in general the nd and 13c records are closely correlated over the past 4 5 ma the nd isotope data suggest strong nadw export from 8 to 5 ma consistent with one interpretation of published 13c gradients where the nd record differs from the nutrient based records changes in the pre formed 13c or cd ca of southern derived deep water might account for the difference maximum nadw export for the entire record is suggested by all proxies at 3 5 4 ma chemical conditions from 3 to 1 ma are totally different showing on average the lowest nadw export of the record modern day values again imply nadw export that is about as strong as at any stage over the past 8 ma

planktonic foraminiferal depth habitat and δ18o calibrations plankton tow results from the atlantic sector of the southern ocean varies by several orders of magnitude across a large gradient in sea surface temperature and other hydrographic features demonstrating high sensitivity of foraminiferal populations to regional differences in water properties the depth of maximum abundance for key species such as globigerina bulloides and neogloboquadrina pachyderma is not constant from station to station the pattern suggests that their abundance and shell chemistry are tied to density horizons or other conditions such as food availability that become more sharply defined with depth in the northern subantarctic the consistent observation of globorotalia inflata and globoratalia truncatulinoides as relatively deep dwelling species confirms their utility as indicators of upper thermocline properties in d 18 o all species are observed to be isotopically lighter than predicted from water properties but the species specific offset is fairly uniform at all stations these observations define the utility of multispecies d 18 o for reconstructing temperature and density stratification from past surface oceans index terms 4267 oceanography general paleoceanography 4572 oceanography physical upper ocean processes 4870 oceanography biological and chemical stable isotopes 3030 marine geology and geophysics micropaleontology keywords stratification d 18 o

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

variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

records of the nd isotope composition of seawater from the bay of bengal implications for the impact of northern hemisphere cooling on itcz movement abstract this study presents a record of planktonic foraminiferal neodymium isotopic gradients along a north south transect in the bay of bengal during time slices of late holocene and last glacial maximum lgm age together with a record of planktonic foraminiferal variation in the northern bay of bengal 15 n over the last 195 ky in late holocene core top planktonic foraminifera the north south end gradient rises from nonradiogenic values of 12 at 20 n to 10 at 5 n in parallel with the modern surface salinity gradient controlled by discharge of himalayan rivers in the northern bay during the lgm end increased throughout the bay the contrast between northernmost and southernmost sites decreased and maximum end values of 6 5 occurred between 12 and 15 n a small part of the shift to higher mean end throughout the bay during the glacial may arise from a uniform increase in deposition of far field dust from arabian and persian gulf regions however the spatial pattern of end variation between lgm and late holocene also suggests a shift from modern dominance of nonradiogenic nd sources from the ganges brahmaputra basin to lgm dominance of more radiogenic nd sources from arakan coastal rivers over the last 195 ky at 15 n the most radiogenic end values of 7 occur at glacial maxima and the most nonradiogenic values of 11 occur during interglacials end values are highly correlated with glacial interglacial variations in planktonic foraminiferal 18o in this record shifts in river sources from the more northerly ganges brahmaputra watershed to the more southerly arakan coastal river systems respond dominantly to inter tropical convergence zone itcz movement driven by northern hemisphere cooling during 100 ky glacial interglacial cycles with a small component of variation on precessional timescales the nonlinear correlation of end with ice volume suggests that itcz movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume these data add support to recent general circulation models of itcz response to northern hemisphere ice sheets which simulate decreased glacial precipitation in the ganges brahmaputra basin and increased glacial precipitation in the southern arakan coastal basin

rare earth elements in the mediterranean sea and mixing in the mediterranean outflow abstract mediterranean surface waters contain elevated levels of the rare earth elements compared to similar nutrient depleted open ocean waters application of a flux balance model shows that the mediterranean is a net sink for ce and a net source for the other ree the abundance pattern of the excess ree required for mass balance is enriched in heavy ree and has a negative ce anomaly this supports a marine possibly coastal source for the ree although the magnitudes of the fluxes involved are consistent with aeolian input an aeolian source would require large scale removal of ce and the light ree within the mediterranean sea a mixing model to compute trace metal anomalies in the mediterranean outflow predicts the observed ree concentrations well this implies that ce behaves conservatively in outflow waters over the calculated one month period for mediterranean water to reach the study site application to other trace metals gives good agreement for al cd and mn

microscale neodymium distribution in sedimentary planktonic foraminiferal tests and associated mineral phases neodymium isotopic ratios recorded in calcareous foraminiferal tests shells and associated authigenic minerals were used to trace past water masses although the origin of preserved nd signals is still a matter of debate we determined for the first time the microscale nd distribution in two planktonic foraminifera species globigerinoides ruber and neogloboquadrina dutertrei and coexisting authigenic minerals from two selected time slices 15 6 and 129 kyr of a marine sediment core in the panama basin elemental mapping of nd ca fe mn and si was performed using nanosims ion probe and electron probe microanalysis epma on uncleaned tests together with scanning electron microscopy sem imagery epma and sem images revealed the presence of fe rich framboidal minerals inside test pores and inner chambers particularly in the old samples the young sample presented fe and mn rich patches on the inner test wall the nd intensity in fe mn rich patches and in some framboids was much higher than in foraminiferal calcite where the nd distribution was randomly heterogeneous with no systematic features such as an ontogenic nd rich layer or species specific differences the relationship between nd fe and mn confirmed a significant role of fe mn oxides as a nd carrier the high nd enrichment in some framboids could be explained by nd adsorption onto oxidized surface of fe sulfides particles rather than direct incorporation since the authigenic precipitates are major nd carrier phases the nd isotopic signals in sedimentary foraminiferal tests likely reflect bottom pore water values rather than surface water ones

neodymium isotopic composition in foraminifera and authigenic phases of the south china sea sediments implications for the hydrology of the north pacific ocean over the past 25 kyr end and normalized rare earth elements ree patterns of benthic and planktonic foraminifera and fe mn coatings precipitated on sediments have been investigated for the south china sea scs to 1 assess the reliability of the extraction of past seawater end in the scs and to 2 reconstruct past hydrological changes during the last 25 kyr reductively cleaned mono specific planktonic foraminifera globigerinoides ruber and mixed benthic foraminifera in core top sediments from 1500 to 2400 m display similar end values to those of the modern pacific deep water pdw end of 3 9 to 4 4 furthermore the end of the reductive cleaning solutions shows similar end values to ones obtained on cleaned foraminifera combined with paas normalized ree patterns these results confirm that the oxidative and reductive cleaning procedure applied to foraminifera does not totally remove all of the fe mn coatings and that end values yielded by cleaned planktonic foraminifera retain the end imprint of the bottom and or pore water end values obtained from a leaching procedure carried out on the bulk non decarbonated sediments are comparable to the end values of the modern pdw whereas a similar leaching procedure applied to decarbonated sediments reveals a bias due to contamination with nd deriving from lithogenic particles in core md05 2904 seawater end reconstructed from planktonic foraminifera indicates that the last glacial period is characterized by lower end 5 2 0 2 to 6 4 0 3 than the late holocene 4 1 0 2 assuming that nd input from river does not change strongly the end of the pdw of the northern scs these end variations suggest a higher relative proportions of southern sourced water in the deep water of the western subtropical pacific ocean during the last glacial period

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

effects of temperature on mg ca in neogloboquadrinid shells determined by live culturing 1 new culturing protocols allowed the development of a mg ca temperature calibration equation for neogloboquadrina pachyderma d when cultured between 9 c and 19 2 c mg ca in n pachyderma d shell calcite exhibits a clear dependence on temperature shell calcite mg ca increased exponentially with temperature mg ca 0 51 0 15 0 23 exp 0 10 0 02 t limited data suggest n dutertrei exhibit similar elemental temperature relationships to n pachyderma d we applied the temperature relationship established by culturing to mg ca in neogloboquadrinid shells collected using plankton tows compared to measured sst the calculated temperatures were within 2 c for mg ca 95 ci multiple samples from single tows generally had calculated temperatures that ranged from near surface values to temperatures consistent with calcification depths down to 70 m our work indicates that mg ca temperature calibration equations for temperate and polar foraminiferal species have a similar exponential constant but a higher pre exponential constant than those for surface dwelling tropical species therefore accurate paleotemperature reconstructions from temperate and polar species require the use of an equation distinct from those used for tropical species

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

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

reservoir rock chemo mechanical alteration quantified by triaxial tests and implications to fracture reactivation abstract co 2 injection into geological formations shifts the geochemical equilibrium between the minerals and resident brine the induced mineral brine co 2 reactions can alter the reservoir rock strength and deformational behavior which subsequently affects co 2 storage mechanical integrity this study attempts to investigate quantitatively the effect of mineral cement and particle dissolution through numerical modeling and validation of triaxial tests performed on unaltered and geologically altered entrada sandstone we utilize a numerical model that couples the discrete element method dem and the bonded particle model bpm to perform simulations of triaxial tests on synthetic rocks that mimic tested rock samples under various confining stresses numerical results in agreement with experimental evidence show that both cement and particle dissolution significantly contribute to rock weakening in sandstone samples with carbonate hematite cements and pore filling carbonate sensitivity analyses show that the brittleness of dem numerical samples is mostly conditioned by the cement bond size among all cement microscopic parameters an alteration path that mimics the mineral dissolution under subsurface boundary conditions leads to 1 vertical compaction and horizontal stress relaxation in the reservoir rock and 2 transfer of stresses to adjacent strata that results in bond breakage and potentially natural fracture reactivation at a large scale

northern hemisphere climate control of the bengali rivers discharge during the past 4 ma abstract nd isotopes are useful tracers for paleoceanography due to the short nd residence time in seawater and the large differences between the isotopic signatures of various geological reservoirs therefore nd variations reflect the geological history of individual oceanic basins using a differential dissolution technique which extracts nd isotopes of seawater trapped in mno2 coatings and carbonates in marine sediment we measured almost two hundred samples from odp sites 758 and 757 in the northern bay of bengal covering the last 4 ma for the first time we have shown a covariation between nd and 18o over at least the last 800 ka we also show that from 4 ma to 2 6 ma nd is almost constant and starts to fluctuate at 2 6 ma when northern glaciations increased from 2 6 ma to 1 ma the fluctuation period is close to 40 ka while from 1 ma to present it is dominantly 100 ka we attribute these findings to mixing between himalayan river water that ultimately originates as indian summer monsoon rain and normal bay of bengal seawater previous studies on seawater using nd 18o analyzed on planktonic foraminifera and sedimentary data can be integrated into this model a simple quantitative binary mixing model suggests that the summer monsoon rain was more intense during interglacial than glacial periods during last glacial episode the monsoon trajectory was deviated to the east at a large scale the indian monsoon is fully controlled by the variations in northern hemisphere climate but with a complex response function to this forcing our study clearly establishes the large potential of nd isotope data to evaluate the hydrological river regime during the quaternary and its relationship with climate fluctuations particularly when the sediment archive is sampled close to sediment sources

manganese and iron in indian ocean waters abstract the first vertical profiles of dissolved mn and fe for the nw indian ocean are reported the area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters the dissolved fe profile exhibits a maximum 5 1 nm in the oxygen minimum zone with low values both in surface waters 0 3 nm and deep waters around 1 nm mn concentrations in the surface waters are elevated 2 0 4 3 nm and decrease rapidly in an offshore direction below the first 25 m concentrations decrease dramatically 0 5 1 3 nm indicating removal by oxidation and particle scavenging further down various mn maxima are observed which can be related to hydrographic features sigma 1 1 intermediate water originating from the red sea lost its dissolved o2 while flowing northward along the omani coast and exhibits a strong mn maximum 4 6 6 5 nm coincident with the deep o2 minimum 2 2 at the two inshore stations in the gulf of oman this is overlain by relatively modest mn maxima 2 7 nm related to arabian gulf overflow water 3 3 finally the strong mn maxima 4 4 5 6 nm in the oxygen minimum zone at the two offshore stations are related to yet another watermass below these various maxima concentrations decrease gradually to values as low as 90 pm at 2000 meters depth towards the seafloor concentrations increase again leading to a modest bottom water maximum 0 7 1 5 nm the overall vertical distributions of mn and fe are strikingly similar also in actual concentrations to those previously reported for the eastern equatorial pacific an area also characterized by an extensive o2 minimum zone

dissolved manganese in the north atlantic ocean 0 35 n abstract dissolved manganese was measured in samples taken from vertical profiles at 13 stations between 0 and 35 n in the atlantic ocean concentrations of dissolved manganese were highest in the surface waters 1 10 to 3 17 nmol l and decreased rapidly over the top few hundred metres to generally low less than 0 5 nmol l and uniform levels for the remainder of the water column highest concentrations in surface waters occurred in latitudes which have particularly high loadings of atmospheric dust of saharan origins and it is suggested that eolian inputs are the most significant source of manganese to the upper water column in this area in the sections of profiles affected by advection of mediterranean water the concentrations of dissolved manganese were similar to those found generally for the atlantic water masses and are consistent with recent data for the mediterranean the generally low concentrations in deep water indicate that in the areas studied there are no major influences of advection of dissolved manganese from sources on the slope or the mid ocean ridge

neodymium isotopes in planktonic foraminifera a record of the response of continental weathering and ocean circulation rates to climate change the neodymium nd isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka here we present the first nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative reductive techniques the data along with mn ca ratios suggest that cleaned foraminifera provide a reliable record of nd in seawater and hold out the prospect of using nd in foraminifera to examine changes in seawater that accompany glacial interglacial climatic cycles the principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic fe mn coatings these contain large amounts of nd and other trace elements but can be cleaned off using highly reducing reagents mn ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range 10 100 mol mol that has yielded success in studies of transition elements in forams mass balance modelling suggests that for residual mn ca ratios 100 mol mol nd added to the foram in the coating will never shift the measured nd isotope composition significantly away from the seawater value acquired by the foram test in the water column additionally nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids finally core top planktonic foraminifera for two sites have nd isotope compositions that are identical to local surface seawater the data we present here for labrador sea forams over the past 2 5 m y are interpreted in terms of changes in the seawater isotopic composition the data show a pronounced shift from end values of 12 to 19 in the period 2 5 1 5 ma this change is interpreted to result from the initiation of northern hemisphere glaciation and the increased derivation of labrador sea nd via ice rafting from archaean terranes in central canada in combination with stable isotope and foraminiferal relative species abundance data the new nd data are consistent with the surface hydrography of the labrador sea being dominated by a fluctuating balance between cold polar waters containing unradiogenic nd and warm subtropical waters containing more radiogenic nd the major change in labrador sea nd that is observed in the past 2 5 ma can on its own account for the change in the nd isotope composition of north atlantic deep water over the same time period

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

neodymium in modern foraminifera from the indian ocean implications for the use of foraminiferal nd isotope compositions in paleo oceanography abstract the use of the nd isotope composition of planktic foraminifera as a proxy for sea surface water is based on the assumption that nd is incorporated during initial calcification and preserved after foraminifera death subsequent transport through the water column and storage in the sediment pile to test this assumption nd concentrations are reported from foraminiferal tests collected from 20 to 3045 m depth multinets and sediment traps from offshore somalia and in the somali basin of the indian ocean nd partition coefficients calculated for two species globigerinoides ruber and globigerina bulloides sampled in the uppermost water column 100 m are 16 52 the measured nd ca ratio of living foraminifera is 8 nmol mol which is 8 190 times lower than reported in cleaned foraminifera from sediment cores 61 1500 nmol mol moreover the nd content of foraminiferal tests varies markedly within the water column 8 220 nmol mol ca recording a positive correlation with mn content r2 0 91 the observed changes in the nd concentration after foraminiferal death appear to reflect nd addition from deeper in the water column and imply a major disturbance of the primary nd isotope composition formed at the surface the high nd ca reported for cleaned foraminifera from sediment cores are interpreted to be a consequence of current cleaning techniques although cleaning successfully removes organics and secondary mn coatings into solution any released rare earth elements ree are subsequently re adsorbed onto the calcite cleaning removes elements with a 2 valency state into solution e g cd and mn but more reactive elements with higher valency states e g ree3 th4 are re absorbed onto residual carbonate it is concluded that although foraminifera clearly record temporal variations in nd isotope composition the relationship between these variations and changes in the sea surface nd isotope composition has yet to be established unambiguously further work is required to rule out the possibility that the nd in foraminifera represents a mixed signal derived from surface sediments and bottom and pore waters

rare earth element association with foraminifera abstract neodymium isotopes are becoming widely used as a palaeoceanographic tool for reconstructing the source and flow direction of water masses a new method using planktonic foraminifera which have not been chemically cleaned has proven to be a promising means of avoiding contamination of the deep ocean palaeoceanographic signal by detrital material however the exact mechanism by which the nd isotope signal from bottom waters becomes associated with planktonic foraminifera the spatial distribution of rare earth element ree concentrations within the shell and the possible mobility of ree ions during changing redox conditions have not been fully investigated here we present ree concentration and nd isotope data from mixed species of planktonic foraminifera taken from plankton tows sediment traps and a sediment core from the nw atlantic we used multiple geochemical techniques to evaluate how where and when rees become associated with planktonic foraminifera as they settle through the water column reside at the surface and are buried in the sediment analyses of foraminifera shells from plankton tows and sediment traps between 200 and 2938 m water depth indicate that only 20 of their associated nd is biogenically incorporated into the calcite structure the remaining 80 is associated with authigenic metal oxides and organic matter which form in the water column and remain extraneous to the carbonate structure remineralisation of these organic and authigenic phases releases ions back into solution and creates new binding sites allowing the nd isotope ratio to undergo partial equilibration with the ambient seawater as the foraminifera fall through the water column analyses of fossil foraminifera shells from sediment cores show that their ree concentrations increase by up to 10 fold at the sediment water interface and acquire an isotopic signature of bottom water adsorption and complexation of ree3 ions between the inner layers of calcite contributes significantly to elevated ree concentrations in foraminifera the most likely source of ree ions at this stage of enrichment is from bottom waters and from the remineralisation of oxide phases which are in chemical equilibrium with the bottom waters as planktonic foraminifera are buried below the sediment water interface redox sensitive ion concentrations are adjusted within the shells depending on the pore water oxygen concentration the concentration of ions which are passively redox sensitive such as ree3 ions is also controlled to some extent by this process we infer that a the nd isotope signature of bottom water is preserved in planktonic foraminifera and b that it relies on the limited mobility of particle reactive ree3 ions aided in some environments by micron scale precipitation of mnco3 this study indicates that there may be sedimentary environments under which the bottom water nd isotope signature is not preserved by planktonic foraminifera tests to validate other core sites must be carried out before downcore records can be used to interpret palaeoceanographic changes

nd ca ratios in plankton towed and core top foraminifera confirmation of the water column acquisition of nd planktic foraminifera have been used as recorders of the neodymium nd isotopic composition of seawater although there is still controversy over the precise provenance of the nd signal we present an extensive multispecific plankton tow nd ca data set from several geographic locations se atlantic ne atlantic norwegian sea and western mediterranean together with core top samples from the mediterranean region the range of nd ca ratios in plankton towed foraminifera cleaned only of organic material from all regions 0 01 0 7 mol mol is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps with distribution coefficients kd ranging between 4 and 302 for the mediterranean where core top and plankton tow data are both available the range for plankton tows 0 05 0 7 mol mol is essentially identical to that for the core tops 0 1 0 5 mol mol readsorption of nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process we find a relationship between manganese mn and nd in plankton tow samples that is mirrored by a similar correlation in core top samples this relationship suggests that fe mn coatings are of negligible importance to the nd budgets of foraminifera as the nd mn ratio it implies is over an order of magnitude greater than that seen in other fe mn oxide phases rather since both plankton tows and core tops present a similar behavior the nd mn relationship must originate in the upper water column the data are consistent with the acquisition of nd and mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes collectively the results help to explain two abiding puzzles about nd in sedimentary planktic foraminifera their high ree contents and the fact that they record a surface water nd isotopic signal regardless of the cleaning procedure used

new neodymium isotope data quantify nile involvement in mediterranean anoxic episodes the development of widespread anoxic conditions in the deep oceans is evidenced by the accumulation and preservation of organic carbon rich sediments but its precise cause remains controversial the two most popular hypotheses involve 1 circulation induced increased stratification resulting in reduced oxygenation of deep waters or 2 enhanced productivity in the surface ocean increasing the raining down of organic matter and overwhelming the oxic remineralization potential of the deep ocean in the periodic development of deep water anoxia in the pliocene pleistocene mediterranean sea increased riverine runoff has been implicated both as a source for nutrients that fuel enhanced photic zone productivity and a source of a less dense freshwater cap leading to reduced circulation basin wide stagnation and deep water oxygen starvation monsoon driven increases in nile river discharge and increased regional precipitation due to enhanced westerly activity two mechanisms that represent fundamentally different climatic driving forces have both been suggested as causes of the altered freshwater balance here we present data that confirm a distinctive neodymium nd isotope signature for the nile river relative to the eastern mediterranean providing a new tracer of enhanced nile outflow into the mediterranean in the past we further present nd isotope data for planktonic foraminifera that suggest a clear increase in nile discharge during the central intense period of two recent anoxic events our data also suggest however that other regional freshwater sources were more important at the beginning and end of the anoxic events taken at face value the data appear to imply a temporal link between peaks in nile discharge and enhanced westerly activity

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

mg ca in foraminifera from plankton tows evaluation of proxy controls and comparison with core tops abstract calibrations and validations of the mg ca paleothermometer in planktic foraminifera have traditionally been performed by means of core tops sediment trap samples and culture experiments in this study mg ca ratios have been measured in 8 species of planktic foraminifera non globorotaliids globigerina bulloides neogloboquadrina incompta orbulina universa globigerinoides ruber white and g sacculifer and globorotaliids globorotalia inflata g hirsuta and g truncatulinoides collected live from the north atlantic the southeast atlantic the northeast pacific and the norwegian sea mg ca ratios for n incompta o universa g ruber g sacculifer and g truncatulinoides are similar to available north atlantic core top studies and consistent with previous calibration equations in contrast some g bulloides g inflata and g hirsuta mg ca ratios are higher than predicted based on 18 o values and exhibit considerable scatter this elevation may be in part related to the impact of potential isotopic disequilibrium effects on 18 o derived temperatures which the mg ca ratios are compared to another factor that may affect mg ca ratios in some plankton samples is the lack of low mg test components e g final chambers or gametogenic calcite because of the incompleteness of the life cycle at the time of collection n incompta mg ca ratios are correlated with salinity with mg ca changing about 16 per salinity unit suggesting that salinity may have an important influence on mg ca of some species even in non extreme salinity environments this is the first extensive multispecific plankton tow mg ca data set from different oceanographic regions which has been used to test the mg ca temperature proxy in the context of published calibration data highlighting the complex physiological ecological controls on the acquisition of the proxy signal

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

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

extracting foraminiferal seawater nd isotope signatures from bulk deep sea sediment by chemical leaching the seawater radiogenic neodymium 143nd 144nd isotope signature is an invaluable tool for the reconstruction of past deep water provenance sedimentary foraminifera or fish teeth are among the most reliable archives known for nd isotope based reconstructions of past seawater as the distribution and preservation of these archives are limited the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative this method however implies the risk of generating artefacts due to the possible release of non seawater derived nd during the extraction procedure here we revisit and further investigate the reliability of the extraction of seawater derived nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid reductive mix solutions repeated application of such stepwise leaching procedures to different non decarbonated sediments from distinct settings across the deep atlantic ocean shows pronounced elemental and nd isotope trends during the leaching process in the laboratory our results show that seawater nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series during chemical extraction the carbonates effectively work as a buffer preventing acid induced mobilisation of fe oxides and volcanogenic material once this buffer is consumed potentially present volcanogenic phases are considerably attacked leading to shifts in the extracted nd isotope signal of up to 12 epsilon units such volcanogenic phases are a significant source of contaminant nd reflected by markedly elevated al nd signatures we consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments which is simple to use provides excellent agreement with data obtained from uncleaned foraminifera and can be easily screened for contamination

climate driven glacial interglacial variations in the osmium isotope composition of seawater recorded by planktic foraminifera abstract this study presents osmium os isotope and elemental data for cleaned planktic foraminifera authigenic fe mn oxyhydroxides and pelagic carbonate host sediments from odp site 758 in the southernmost reaches of the bay of bengal the os in the bulk sediments appears to be dominantly hydrogeneous sourced by carbonate and fe mn oxyhydroxide but variations in this particular core are controlled by the presence of volcanic ash fe mn oxyhydroxide leachates of the bulk sediments from holocene samples also yield an os isotope composition close to that of seawater but the record diverges from that of foraminifera at a depth corresponding to the oxic post oxic boundary suggesting diagenetic mobilization of os at depths below this holocene planktic foraminifera cleaned using oxidative reductive techniques also give os isotope compositions indistinguishable from modern seawater but the record obtained for the past 150 kyr shows strong covaraitions of 187 os 188 os with both the local and global oxygen isotope record with less radiogenic os isotope compositions during glacial intervals these results indicate that foraminifera provide a robust record of seawater os isotope compositions and comparison of the data obtained here with records from the other major oceans demonstrate global changes in 187 os 188 os over this time interval while the covariation with oxygen isotopes suggest a process controlling the os isotope composition that is in phase with global climate cycles global excursions to relatively unradiogenic 187 os 188 os during glacial intervals are consistent with decreased input of radiogenic continental material reflecting cooler temperatures and reduced continental runoff modelling indicates that the shift to unradiogenic values during glacial intervals could be caused by an 30 decrease in the global river flux with an 5 change in river composition if the residence time of os in the oceans is 5 ka then the post glacial recovery to present day seawater values is consistent with a corresponding increase in the river flux of around 30 however if the residence time of os is closer to 40 ka as is suggested by the global river flux then this demands either significant changes in both the riverine os flux and composition of around 40 and 30 respectively that closely follow the oxygen isotope record or else a short lived post glacial pulse of weathering some 75 greater than the steady state flux in either case these results clearly indicate that climatic changes affect both the flux and composition of weathered material delivered to the oceans on glacial interglacial timescales

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

interlaboratory comparison study of mg ca and sr ca measurements in planktonic foraminifera for paleoceanographic research thirteen laboratories from the usa and europe participated in an intercomparison study of mg ca and sr ca measurements in foraminifera the study included five planktonic species from surface sediments from different geographical regions and water depths each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples analysis of solutions of known mg ca and sr ca ratios showed that the intralaboratory instrumental precision is better than 0 5 for both mg ca and sr ca measurements regardless whether icp oes or icp ms is used the interlaboratory precision on the analysis of standard solutions was about 1 5 and 0 9 for mg ca and sr ca measurements respectively these are equivalent to mg ca based temperature repeatability and reproducibility on the analysis of solutions of 0 2 c and 0 5 c respectively the analysis of foraminifera suggests an interlaboratory variance of about 8 rsd for mg ca measurements which translates to reproducibility of about 2 3 c the relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability about 1 2 c and a bias about 1 c due to the application of different cleaning methods by different laboratories improving the consistency of cleaning methods among laboratories will therefore likely lead to better reproducibility even more importantly the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility

neodymium isotopes in the mediterranean sea comparison between seawater and sediment signals nine depth profiles of dissolved nd concentrations and isotopic ratios epsilon nd were obtained in the levantine basin the ionian the aegean the alboran seas and the strait of gibraltar thirteen core top sediments and nile river particle samples were also analyzed leached with 1 n hcl acetic acid or hydroxylamine hydrochloride the seawater epsilon nd values become more radiogenic during the eastward circulation in the mediterranean sea the relationship between salinity and the seawater epsilon nd shows that the nd isotopic signature is more conservative than salinity in the mediterranean sea the water mass with the highest epsilon nd 4 8 is found at about 200 m in the easternmost levantine basin the average epsilon nd value for deep waters is 7 0 in the eastern basin 2 5 epsilon units higher than in the western basin by examining the sensitivity of seawater epsilon nd to nd inputs from the nile we conclude that the most significant radiogenic nd source is partially dissolved nile river particles the nd flux from the nile river water has a minor influence on the mediterranean seawater end except for the easternmost levantine basin the leachate epsilon nd values are consistent with the seawater values in the easternmost levantine basin the leachate end values obtained with hcl leaching are systematically higher than the seawater values the relationship between leachate and residual epsilon nd values indicates that the hcl leaching partially dissolves lithogenic nd so the dissolution of nile river particles is the cause of the observed shift some end values obtained with hydroxylamine hydrochloride leaching are higher than those obtained with hcl leaching although the reason for this shift is not clear sr 87 sr 86 successfully detects the presence of a nonmarine component in the leachate our results suggest that leaching performance may vary with the mineralogy of marine sediments at least in the case of the mediterranean sea copyright c 2004 elsevier ltd

epithermal precious metal mineralization in a strike slip corridor the san dimas district durango mexico the san dimas district durango mexico was investigated to define the structural control of epithermal ag au mineralization and to unravel the tectonic history of the area three distinct deformational events have been identified deformational event d 1 is characterized by the formation of subvertical east west to east north east west southwest trending tension gashes and hybrid extensional shear fractures that were caused by the ongoing but weakened compression due to subduction west of mexico during the early oligocene changing stress conditions during deformational event d 2 developed north south trending right lateral strike slip faults with accompanying secondary structures forming a complex pattern of a transtensional corridor the structures of both d 1 and d 2 are hosted by the lower volcanic group and the underlying piaxtla intrusive rocks and they carry low sulfidation epithermal silver gold mineralization subsequent extension on reactivated north south trending strike slip faults and northwest southeast trending normal faults established basin and range type tectonics through both the oligocene and miocene the transition from compression to extension is documented by this strike slip corridor which was established during the late oligocene

the potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past dissolved rare earth element ree concentration data from intermediate and deep seawater form an array characterized by higher middle ree enrichments mree mree in the north atlantic and a progressive increase in heavy to light ree ratios hree lree as water masses age the rees in foraminifera are fractionated towards higher mree mree and lower hree lree relative to seawater calculations based on a scavenging model show that the ree patterns in uncleaned core top foraminifera resemble those adsorbed onto calcite particulate organic material and hydrous ferric oxides but the full extent of the ree fractionation measured in foraminifera was not reproduced by the model however differences in the hree lree mree mree ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater ree distribution under oxic conditions the hree lree and mree mree compositions of uncleaned foraminifera at the sediment seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth in suboxic sedimentary environments all uncleaned foraminiferal ree concentrations are elevated relative to core top values indicating addition of rees from pore waters the hree lree ratio is highest when sedimentation rates were greatest lippold et al 2009 and when high fe ca ratios in the uncleaned foraminifera indicate that fe was mobile in sediments that have not experienced suboxic conditions during burial uncleaned foraminifera preserve the seawater signal taken up at the sediment seawater interface and are therefore suggested to be a suitable archive of changes in the ree signal of past bottom waters this article is protected by copyright all rights reserved

assessment of seawater nd isotope signatures extracted from foraminiferal shells and authigenic phases of gulf of guinea sediments the radiogenic neodymium nd isotope composition of foraminiferal shells provides a powerful archive to investigate past changes in sources and mixing of water masses however seawater nd isotope ratios extracted from foraminiferal shells can be biased by contaminant phases such as organic matter silicates or ferromanganese coatings the removal of which requires rigorous multiple step cleaning of the samples here we investigate the efficiency of flow through and batch cleaning methods to extract seawater nd isotope compositions from planktonic foraminifera in a shelf setting in the gulf of guinea that is strongly influenced by riverine sediment inputs nd isotope analyses of reductively and oxidatively cleaned mono specific planktonic foraminiferal samples and reductively cleaned mixed benthic foraminifera were complemented by analyses of non reductively cleaned mono specific planktonic foraminiferal samples fe mn coatings of de carbonated bulk sediment leachates and the residual detrital fraction of the same sediment al ca and mn ca ratios of fully cleaned foraminiferal samples reveal indistinguishable levels of cleaning efficiency between the batch and the flow through methods and the nd isotope compositions obtained from application of both methods are identical within error furthermore non reductively cleaned foraminiferal samples have the same nd isotope composition as reductively cleaned foraminifera at our study sites close to the niger river mouth the nd isotope composition of the foraminifera agree with the seawater nd isotope composition of nearby stations based on the combined extracted nd isotope signatures and element to calcium ratios as well as rare earth element distribution patterns we infer that the planktonic foraminiferal nd isotope signatures reflect bottom water pore water signatures the isotopic composition of the bulk de carbonated sediment leachates fe mn coatings differs significantly from the foraminiferal data at this site and probably reflects particles that acquired their ferromanganese pre formed pre formed ferromanganese coatings in nearby rivers therefore in such river influenced shelf settings foraminiferal shells should be used to obtain unbiased bottom seawater signatures

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