abrupt changes in antarctic intermediate water circulation over the past 25 000 years the formation and circulation of antarctic intermediate water has varied over glacial interglacial timescales a neodymium record from the atlantic ocean basin suggests that changes in circulation may have been driven by changes both in antarctic intermediate water formation in the southern ocean and in the strength of north atlantic meridional overturning

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

ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

the hafnium neodymium isotopic composition of atlantic seawater the first full water column hafnium isotopic compositions of atlantic seawater have been obtained at seven locations from the labrador sea to the drake passage despite subpicomolar concentrations in seawater a precision of the hf isotopic measurements of 03 epsilon hf units was achieved an overall epsilon hf range between 3 1 in the labrador sea and 4 4 in antarctic bottom water was determined the distribution of which broadly reflects continental weathering inputs within particular water column profiles significant differences of up to 4 epsilon hf units occur combined with nd isotope data of the same samples it is evident that the hf isotopic composition of seawater is too radiogenic for a given nd isotopic composition and that the largest difference between expected and measured hf isotopic compositions in seawater occurs near the oldest continental crust in the labrador sea this corroborates the previous proposition which was mainly based on ferromanganese crust data that the hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly to some extent by hydrothermal contributions hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years which is significantly shorter than previously assumed the hf isotopic composition of past seawater can therefore serve as a proxy for short distance basin scale mixing processes and the regime and intensity of nearby continental weathering processes c 2009 elsevier b v all rights reserved

pliocene and quaternary depositional model of the algarve margin contourite drifts gulf of cadiz sw iberia seismic architecture tectonic control and paleoceanographic insights abstract the contourite drifts off southwest iberia that formed as a result of the interaction of the mediterranean outflow water mow with the continental middle slope were studied in the algarve margin using multichannel reflection seismic lines oil wells piston cores and a bathymetric compilation of four datasets the seismostratigraphic interpretation of a dense array of oil industry seismic and stratigraphic correlation allowed the identification of five seismic units of early pliocene through holocene in the faro and albufeira drifts and four correlative seismic units in the lagos and sagres drifts and three in the portimao drift a three phased evolutionary model for the contourite formation is proposed firstly a precursory phase of pliocene age made up of sheeted drifts represents an initial phase of deposition under bottom current activity that is correlated with the first stages of an enhanced mow at about 3 5 ma secondly the building up phase of early pleistocene age is related to a strengthening of the mow close to the onset of the northern hemisphere glaciations at about 2 6 ma during which were deposited low mounded drifts thirdly the growing phase from middle pleistocene through holocene suggests the presence of a stronger mow since the beginning of the middle pleistocene transition at about 1 3 1 0 ma accounting for the deposition of mounded drifts and formation of the alvares cabral moat seismostratigraphic interpretation and isochron maps allowed for the establishment of the main oceanographic climatic morphologic and tectonic factors that controlled the drifts deposition i the pliocene and quaternary mow circulation forced by climate changes ii the sea bottom topography inherited from the late miocene mainly shaped by the portimao lagos and bartolomeu dias canyons system iii the interaction between along slope and down slope processes since the pliocene and iv pliocene quaternary fault activity and diapirism

nd and sr isotope compositions of different phases of surface sediments in the south pacific extraction of seawater signatures boundary exchange and detrital dust provenance the radiogenic isotope composition of neodymium nd and strontium sr are useful tools to investigate present and past oceanic circulation or input of terrigenous material we present nd and sr isotope compositions extracted from different sedimentary phases including early diagenetic fe mn coatings unclean foraminiferal shells fossil fish teeth and detritus of marine surface sediments core tops covering the entire midlatitude south pacific comparison of detrital nd isotope compositions to deep water values from the same locations suggests that boundary exchange has little influence on the nd isotope composition of western south pacific seawater concentrations of rare earth elements ree and al ca ratios of unclean planktonic foraminifera suggest that this phase is a reliable recorder of seawater nd isotope composition the signatures obtained from fish teeth and nondecarbonated leachates of bulk sediment fe mn oxyhydroxide coatings also agree with unclean foraminifera direct comparison of nd isotope compositions extracted using these methods with seawater nd isotope compositions is complicated by the low accumulation rates yielding radiocarbon ages of up to 24 kyr thus mixing the signal of different ocean circulation modes this suggests that different past seawater nd isotope compositions have been integrated in authigenic sediments from regions with low sedimentation rates combined detrital nd and sr isotope signatures indicate a dominant role of the westerly winds transporting lithogenic material from south new zealand and southeastern australia to the open south pacific the proportion of this material decreases toward the east where supply from the andes increases and contributions from antarctica cannot be ruled out

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

transport estimates at the western section of the strait of gibraltar a combined experimental and numerical modeling study 1 three yearlong time series of acoustic doppler current profiler adcp observations at a single station in espartel sill strait of gibraltar were used to compute an outflow of q2 0 82 sv through the main channel the cross strait structure of the velocity field or the outflow through a secondary channel north of the submarine ridge of majuan in espartel section is not captured by observations so that an improved version of a numerical model cepom has been used to fill the observational gap previously the model performance has been checked against historical data sets by comparing harmonic constants of the main diurnal and semidiurnal constituents from observed and modeled data at different sites of the strait considering the great complexity of tidal dynamics in the area the comparison is quite satisfactory and validates the model to infer the exchange at longer timescales using a climatological april in the simulation extracting a single station from the model at the same position as the monitoring station and processing the data similarly the model gives an outflow through the southern channel 13 higher than observations the inclusion of the cross strait structure of velocity reduces the computed outflow through the southern channel whereas the contribution of the northern channel brings the total outflow close to that computed using a single station 5 smaller if the same correction is applied to observations the total outflow would reduce to q2 0 78 sv the paper also assesses the importance of eddy fluxes to the total outflow their contribution being negligible 5

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

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

decadal changes in the mid depth water mass dynamic of the northeastern atlantic margin bay of biscay the lithium magnesium li mg molar ratios radiocarbon measurements d 14 c and nd isotopic composition end of the aragonite skeleton of a branching cold water coral cwc species madrepora oculata collected alive in the bay of biscay at 691 m water depth were investigated to reconstruct a robust record of the mid depth water mass dynamics between 1950 and 1990 ad temperature estimates based on the skeletons li mg molar ratios reveal small decadal changes of about 1 1 ca t thermocline depth synchronous to and of similar amplitude as surface temperature anomalies d 14 c

two circulation regimes of the mediterranean outflow revealed by lagrangian measurements the eurofloat experiment was a joint initiative to examine the large scale spreading of mediterranean water mw and labrador sea water in the northeast north atlantic rafos float data from the southern mw portion of the eurofloat experiment have been examined in conjunction with historical float data in order to calculate quasi eulerian means in an effort to separate and quantify the constituents of the spreading of the mw tongue east of the mid atlantic ridge while recent studies focussed chiefly on the role of meddies in the shaping of the mw tongue this analysis also examines the tongue s second constituent that is the background non meddy advective and diffusive flow the results suggest the existence of two regimes approximately to the north and south of the 36 n parallel i e the latitude of the gulf of cadiz which are distinguished by different types of dominant spreading mechanisms for mw to the south of the gulf of cadiz the background flow shows an incoherent and weak mean whereas the mean velocity of the salt enhanced meddies is strong and to the southwest in contrast to the north of 36 n the mean velocity of the meddies seems to be less pronounced and the background flow is shown to be a major component in the northwestward spreading of the mw tongue the two regimes are separated by the azores current which previously has been hypothesized to act as a dynamic barrier to the southward advective spreading of the background regime which the meddies are able to penetrate because of their high kinetic energy overall the meddies are calculated to contribute to approximately half of the total salinity anomaly flux

late glacial to recent paleoenvironmental changes in the gulf of cadiz and formation of sandy contourite layers planktonic foraminifera and coccoliths were analyzed from six gravity cores obtained on a deep terrace located on the upper continental slope of the gulf of cadiz between 400 and 700 m water depth the lithology of these cores consists mainly of muds with some interbedded sandy or silty foraminifer rich layers that have been reported as contourites originated by the action of the mediterranean outflowing waters mow sweeping the sea bottom today after the last glacial characterized by muddy sedimentation sandy contourites start to deposit in the gulf of cadiz during the bolling allerod 14 11 14c kyr bp climatic optimum this trend was broken during the younger dryas 11 10 14c kyr bp and started again after the end of the younger dryas this pattern is recorded in most of the cores by a single sandy contourite layer formed during the first deglaciation stage bolling allerod time and a sandy contourite interval that initiates immediately after the end of the younger dryas during the second stage of the deglaciation and continues during the holocene the stratigraphy and climatic reconstruction was based on the evolution of the calcareous plankton assemblages during the last climatic transition from the last glacial to the recent holocene the sharp reduction of sinistral n pachyderma along with the reduction of g quinqueloba mark the base of bolling allerod time this is also related to a prominent peak of the subtropical species g sacculifer and g ruber the younger dryas is identified by a reduction in abundance of the subtropical species that again increase just after this period the second step of deglaciation is marked by a sharp decrease in the relative abundance of dextrally coiled n pachyderma in previous papers the sequence of sandy contourites has been related to sea level rise greater gibraltar sill depth and enhanced energy of the mow in this work we suggest that the individual sand layer episodes are condensed layers originating during times of rapid warming and relative sea level rise within the last deglaciation during these times the coastline migrated more rapidly landward and the terrigenous input decreased as it began to be trapped on land and on the shelf resulting in a major drop in sedimentation rate on the upper continental slope in times of low sedimentation rate the particles would have a longer residence time within the upper mixed layer of the near surface sediment and therefore the energy of currents would act longer producing a more efficient winnowing of the sediment at the same time more generations of benthic organisms would rework the mixed layer favoring this winnowing

influence of the mediterranean outflow on the isotopic composition of neodymium in waters of the north atlantic the isotopic composition of neodymium in the water column of the eastern north atlantic near the strait of gibraltar has been determined for several depths the data show that the mediterranean outflow results in a significant shift in e nd 0 toward more radiogenic values of 143 nd 144 nd in the water column at a 1000 m depth this corresponds to a depth in the neighborhood of the salinity maximum associated with the mediterranean outflow the core of the mediterranean outflow gives e nd 0 9 8 as compared to e nd 0 12 in overlying and underlying waters demonstrating that the mediterranean waters are distinct from the atlantic from mixing considerations we estimate that pure mediterranean waters have e nd 0 6 possible sources of this relatively radiogenic nd could be from drainage of young continental terranes or the injection of remobilized nd from deep sea sediments that have a young radiogenic volcanic component new data from a depth profile in the western atlantic is presented comparison of nd data for the eastern north atlantic with that for the western north atlantic shows fundamental differences in the water column structures for e nd 0 while both regions show a pronounced maximum in e nd 0 the western basin maximum occurs at the near surface rather than at 1000 m in addition deep waters of the eastern basin are found to be more radiogenic than the western basin these differences indicate several sources of isotopically distinct nd in the north atlantic the deep waters of the north atlantic 1000 m have the lowest values of e nd 0 measured in the oceans we believe that the source of these low e nd 0 values which we associate with north atlantic deep water is either from freshwater drainage off the precambrian shields of north america and asia into the arctic ocean or from the injection of older continentally derived ree from deep sea sediments sm and nd concentrations are found to increase with depth and e nd 0 changes with depth indicating both vertical and lateral transport processes from different sources this suggests a surface source of nd and injection of ree into the water column from deep sea sediments or large scale bottom currents with high ree concentrations

no change in the neodymium isotope composition of deep water exported from the north atlantic on glacial interglacial time scales quantifying past circulation is a vital part of testing our understanding of the modern and future climate system the isotopic composition of neodymium nd in marine precipitates has considerable promise as a recorder of past circulation patterns but its robust application requires knowledge of the end member compositions in order to correctly deconvolute a downstream signal we show here using in situ high temporal resolution analyses of ferro manganese crusts from the north atlantic that the nd isotopic composition of deep water during times of much more extensive northern hemisphere ice cover was no different than the modern day interglacial value this result is surprising but greatly simplifies the use of nd isotopes as tracers of the strength and patterns of circulation in the atlantic in the past

synchronous deglacial overturning and water mass source changes understanding changes in ocean circulation during the last deglaciation is crucial to unraveling the dynamics of glacial interglacial and millennial climate shifts we used neodymium isotope measurements on postdepositional iron manganese oxide coatings precipitated on planktonic foraminifera to reconstruct changes in the bottom water source of the deep western north atlantic at the bermuda rise comparison of our deep water source record with overturning strength proxies shows that both the deep water mass source and the overturning rate shifted rapidly and synchronously during the last deglacial transition in contrast any freshwater perturbation caused by heinrich event 1 could have only affected shallow overturning these findings show how changes in upper ocean overturning associated with millennial scale events differ from those associated with whole ocean deglacial climate events

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

the contribution of geochemistry to ancient harbor geoarcheology the example of ostia antica abstract once trapped in ancient harbor basins sediments form environmental archives that have been widely studied by geoarcheologists in recent decades especially to help reconstruct fluvio marine landscapes of the last millennia in some cases classic environmental markers cannot be used for this purpose either because of their scarcity in the sedimentary deposits or because analytical costs limit the resolution that can be achieved in order to remedy these shortcomings and to complement the more commonly used proxies elemental and isotopic geochemistry has been added to the geoarcheological toolkit here we show how to read the evolution of the paleo environmental dynamics in the water column of ostia antica rome s first maritime harbor using the geochemical and isotopic record of a 3000 year old sediment core drilled in the ancient harbor basin a comparison of the results obtained from ostia antica with those of other ancient mediterranean harbors reveals the nature of the main environmental processes operating during the formation of sedimentary deposits in harbor basins from this comparative approach it appears that the respective weight of each control factor is dependent on the coastal geomorphological context of the sites where the harbors were established since the discovery of the harbor of ostia antica in 2014 this method has provided the means for the first time to identify two distinct harbor basin regimes an initial marine dominated regime from the middle of the 4th c bc to the 3rd c bc and a later freshwater dominated regime up to the 2nd c bc more generally we observe the effects of the dynamics of the deltaic progradation of the tiber which very early on was subject to a hydro climatic component on the processes of alluviation of the harbor basin additionally and also for the first time in harbor geoarcheology pb isotope compositions measured specifically on uncontaminated sediments demonstrate their utility for both identifying the geological sources of the sediments of the tiber delta and discriminating finer from larger particles the present study further provides an opportunity to test the validity of two hypotheses recently put forward 1 that a series of three tsunamis is recorded in the harbor silts and 2 that an initial lagoon type harbor was constructed at ostia antica which later evolved into a fluvial harbor neither of these hypotheses are supported by the present data

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

a major and long term pliocene intensification of the mediterranean outflow 3 5 3 3 ma ago largely continuous millennial scale records of benthic delta o 18 mg ca based temperature and salinity variations in bottom waters were obtained from deep sea drilling project dsdp site 548 east atlantic continental margin near ireland 1250 m water depth for the period 3 7 3 0 ma ago high epsilon nd values of 10 7 to 9 show that this site monitored changes in mediterranean outflow water mow throughout the mid pliocene bottom water variability at ocean drilling progam odp site 978 alboran sea 1930 m water depth provides a complementary record of mow composition near its west mediterranean source both sites show a singular and persistent rise in bottom water salinities by 0 7 1 4 psu and in densities by similar to 1 kg m 3 from 3 5 to 3 3 ma ago which is matched by an similar to 3 degrees c increase in bottom water temperature at site 548 this event suggests the onset of strongly enhanced deep water convection in the mediterranean sea and a related increase in mow flow as a result of major aridification in the mediterranean source region in harmony with model suggestions the enhanced mow flow has possibly intensified upper north atlantic deep water formation

indian ocean circulation and productivity during the last glacial cycle abstract the indian ocean is an important part of the global thermohaline circulation system receiving deep waters sourced from the southern ocean and being the location of upwelling and surface ocean current flow which returns warm and salty waters to the atlantic it is also an ideal location to reconstruct the link between thermohaline circulation and deep water nutrient contents no mixing occurs between major deep water masses along flow paths within the indian ocean so changes in water mass provenance reflect changes in deep ocean circulation while nutrient contents reflect addition and dissolution of organic matter we present neodymium nd and carbon c isotope records from an equatorial indian ocean core sk129 cr2 spanning the last 150 kyr the nd isotope record shows that an increased proportion of north atlantic deep water nadw reached the indian ocean during interglacials marine isotope stages mis 1 and 5 and a reduced proportion during glacials mis 2 4 and 6 and also that changes occurred during mis 3 the magnitude and timing of deglacial and some mis 3 variability is very similar to those in the rc11 83 tno57 21 south atlantic deep cape basin nd isotope record piotrowski et al 2005 since the deep cape basin is oceanographically upstream of the indian ocean from a deep water circulation perspective the nd isotopes suggest that atlantic meridional overturning circulation changes were effectively propagated from the southeastern atlantic into the central indian ocean via the southern ocean comparison of the nd and c isotope records shows that deep ocean circulation was decoupled from nutrient content changes on glacial interglacial timescales in particular suggesting higher productivity during mis 5 increased equatorial productivity during mis 5 is supported by benthic infaunal epifaunal foraminiferal 13 c gradients as well as benthic foraminiferal 13 c gradients along deep water flow concurrent warming indicated by planktonic foraminiferal mg ca during mis 5 at the site is consistent with changing thermocline temperature and may indicate a link to surface ocean hydrographic changes

contourite drift molded by deep mediterranean outflow since its inception in early pliocene time the deep mediterranean outflow has eroded and sculptured the southern iberian margin the 50 km long 300 m thick faro drift constructed by this powerful bottom current has been the subject of detailed study sandy silty and muddy contourite facies can be clearly characterized and a distinctive vertical arrangement or sequence of these facies can be related to hydrodynamic fluctuation these results are important for the identification of ancient contourites the reconstruction of paleocirculation patterns and documentation of the effects of quaternary climates on the mediterranean outflow

reactivity of neodymium carriers in deep sea sediments implications for boundary exchange and paleoceanography the dissolved neodymium nd isotopic distribution in the deep oceans is determined by continental weathering inputs water mass advection and boundary exchange between particulate and dissolved fractions reconstructions of past nd isotopic variability may therefore provide evidence on temporal changes in continental weathering inputs and or ocean circulation patterns over a range of timescales however such an approach is limited by uncertainty in the mechanisms and importance of the boundary exchange process and the challenge in reliably recovering past seawater nd isotopic composition end from deep sea sediments this study addresses these questions by investigating the processes involved in particulate solution interactions and their impact on nd isotopes a better understanding of boundary exchange also has wider implications for the oceanic cycling and budgets of other particle reactive elements sequential acid reductive leaching experiments at ph 2 5 on deep sea sediments from the western indian ocean enable us to investigate natural boundary exchange processes over a timescale appropriate to laboratory experiments we provide evidence that both the dissolution of solid phases and exchange processes influence the end of leachates which suggests that both processes may contribute to boundary exchange we use major element and rare earth element ree data to investigate the pools of nd that are accessed and demonstrate that sediment leachate end values cannot always be explained by admixture between an authigenic component and the bulk detrital component for example in core wind 24b acid reductive leaching generates end values between 11 and 6 as a function of solution solid ratios and leaching times whereas the authigenic components have end 11 and the bulk detrital component has end 15 we infer that leaching in the mascarene basin accesses authigenic components and a minor radiogenic volcanic component that is more reactive than madagascan derived clays the preferential mobilisation of such a minor component demonstrates that the nd released by boundary exchange could often have a significantly different end composition than the bulk detrital sediment these experiments further demonstrate certain limitations on the use of acid reductive leaching to extract the end composition of the authigenic fraction of bulk deep sea sediments for example the detrital component may contain a reactive fraction which is also acid extractible while the incongruent nature of this dissolution suggests that it is often inappropriate to use the bulk detrital sediment elemental chemistry and or end composition when assessing possible detrital contamination of leachates based on the highly systematic controls observed and evidence from ree patterns on the phases extracted we suggest two approaches that lead to the most reliable extraction of the authigenic end component and good agreement with foraminiferal based approaches either i leaching of sediments without a prior decarbonation step or ii the use of short leaching times and low solution solid ratios throughout

correlation of sea level curves for the lower silurian of the bruce peninsula and lake timiskaming district ontario paleobathymetric interpretation of strata from the bruce peninsula and lake timiskaming district of ontario shows strong correlations with data from the michigan upper peninsula and ontario s manitoulin island three to four cycles of fluctuating sea level occurred during early silurian llandoverian time throughout much of the northern great lakes area and involved the highly regular replacement of ostracode vermiform coral algal and pentamerid communities by one another although exposure is more limited than on manitoulin island or the michigan upper peninsula important clues regarding early silurian geography are found in strata of the bruce peninsula and lake timiskaming district continued thinning of stratigraphic units and an increased incidence of disconformities from north to south on the bruce peninsula suggest the episodic rise of the algonquin arch farther to the south and west contrary to earlier paleogeographic reconstructions the patterns of community changeovers preserved in the si

late quaternary turbidite emplacement on the horseshoe abyssal plain iberian margin abstract the horseshoe abyssal plain hap is located on the iberian margin at approximately 4800 m water depth and is confined within topographic elevations with a relief of about 3000 m with the exception of gorringe bank which rises to only 20 m below sealevel the plain is built up by an alternation of turbidites of the order of meter thick beds numbered h2 h3 h8 and h13 contrasting with sets of thinner beds of the order of decimeters thick h4 5 6 7 and h9 10 11 12 and pelagites centimeters in thickness an intensive study of eight piston cores using visual observation color and thickness relative stratigraphic position of units magnetic susceptibility logs calcium carbonate content and mineralogy of turbid te bases concludes in a bed by bed correlation of all individual turbidites the major source of terrigenous material feeding the hap is the sao vicente canyon which incises the portuguese shelf while minor sources are the surrounding seamounts the elongate geometry of the abyssal plain with its single dominant source of sediments produced laterally continuous deposits from both large and small flows these covered the entire 356 km length of the plain grain size analysis of the four thickest turbidites h2 h3 h8 and h9 demonstrates only slight downcurrent fining and vertical grading expressed best in the ratio of coarse silt to fine silt plus clay a small amount of sand is carried the length of the plain the thicker units all show the same pattern of thickness with a maximum in the middle of the plain around a topographic constriction and bend this is most plausibly explained as due to reduction in flow speed of an initially supercritical flow causing enhanced deposition some of the beds appear to have a double coarse layer in the base which may indicate partial reflection of flows from the side of the basin it is suggested by application of equations for flow behavior that both thick 3 m and thin 0 3 m beds are due to supercritical flows a few tens of meters high however the thick beds resulted from high concentration flows cv 4 by volume whereas thinner beds require low concentration cv 1 to run out over the full length of the basin the stratigraphy is tied into the dated oceanic pelagic record by analysis of foraminifera in the pelagic layers above the turbidites and through recognition of two heinrich layers h 1 and h 2 ages 14 3 and 21 ka the resulting age framework shows higher turbidite frequency in the glacial 2 7 kyr than interglacial holocene 1 0 kyr this also gives higher mass flux during the glacial emplacement of turbidites cannot be clearly related to sea level changes but may well be due to seismic activity however one of the largest earthquakes in human experience lisbon in 1755 triggered only a thin turbidite invalidating the term seismite for thick turbidites

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

neoglacial change in deep water exchange and increase of sea ice transport through eastern fram strait evidence from radiogenic isotopes sediment core msm5 5 712 from the west spitsbergen continental margin has been investigated at high resolution for its seawater derived neodymium nd and lead pb isotope compositions stored in ferromanganese oxyhydroxide coatings of the sediment particles to reconstruct holocene changes in the sources and mixing of bottom waters passing the site the radiogenic isotope data are used in combination with a multitude of proxy indicators for the climatic and oceanographic development of the eastern fram strait during the past 8500 years to calibrate the downcore data seawater and core top samples from the area were analysed for their radiogenic isotope compositions core top leachates reveal relatively high more radiogenic nd isotope compositions between end 9 7 and 9 1 which are higher than present day seawater end in eastern fram strait 12 6 to 10 5 and indicate that the seawater values have only been established very recently the core top data agree well with the downcore signatures within the uppermost 40 cm of the sediment core end 9 1 to 8 8 indicating a reduced inflow of waters from the nordic seas concurrent with cool conditions and a south eastward shift of the marginal ice zone after ca 2 8 cal ka bp late holocene high sea ice abundances in eastern fram strait are coeval with the well known neoglacial trend in the northern north atlantic region in contrast warmer conditions of the late early to mid holocene were accompanied by lower less radiogenic end signatures of the bottom waters indicating an increased admixture from the nordic seas 10 6 to 10 1 a shift to significantly more radiogenic end signatures of the detrital material also occurred at 3 cal ka bp and was accompanied by a marked increase in supply of fine grained ice rafted material irf from the arctic ocean to the core site the most likely source areas for this radiogenic material are the shallow arctic shelves in particular the kara sea shelf the evolution of the pb isotope compositions of past seawater was dominated by local signatures characterized by high 208 207 206pb 204pb values during the warm early and mid holocene periods related to enhanced chemical weathering on svalbard and high glacial and riverine input derived from young granitic more radiogenic material to the west spitsbergen margin at 3 cal ka bp both detrital and seawater pb isotope data changed towards more kara sea like signatures

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

sediment failures and flows in the gulf of cadiz eastern atlantic several types of sediment failures in the gulf of cadiz were observed using multibeam bathymetry acoustic imagery and high resolution seismic these instabilities are mainly sediment failures and flows their width and length vary from 1 to more than 10 km the failures are mainly related to high sedimentation rates particularly in places where the mediterranean outflow water mow spills over such as channel bends and the outer side of the giant contourite levee steep slopes are also a trigger for failure at the continental shelf slope transition on valley sides on canyon flanks and on the sides of bathymetric highs other mass movements are related to fluid escape mud volcanoes and earthquakes in areas where the mow flows along the seafloor the constant shearing and related erosion can add to the overall stresses the frequency of failures can be estimated using the deposits resulting of their distal transformations into turbidites

the seawater neodymium and lead isotope record of the final stages of central american seaway closure the shoaling and final closure of the central american seaway cas resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of atlantic meridional overturning circulation amoc the exact timing of cas closure is key to interpreting its importance here we present a reconstruction of deep and intermediate water nd and pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial pacific ocean drilling program odp site 1241 and the caribbean odp sites 998 999 and 1000 covering the final stages of cas closure between 5 6 and 2 2 ma the data for the pacific site indicate no significant atlantic caribbean influence over this entire period the caribbean sites show a continuous trend to less radiogenic nd isotope compositions during the pliocene consistent with an enhancement of upper north atlantic deep water unadw inflow and a strengthening of the amoc superimposed onto this long term trend shorter term changes of intermediate caribbean nd isotope signatures approached more unadw like values during intervals when published reconstructions of seawater salinity suggested complete closure of the cas the data imply that significant deep water exchange with the pacific essentially stopped by 7 ma and that shallow exchange which still occurred at least periodically until approximately 2 5 ma may have been linked to the strength of the amoc but did not have any direct effect on the intermediate and deep caribbean nd isotope signatures through mixing with pacific waters

closure of the central american isthmus and its effect on deep water formation in the north atlantic modern ocean thermohaline driven circulation influences global climate by transporting heat to high latitudes1 2 and by affecting the exchange of co2 between ocean and atmosphere3 north atlantic deep water nadw plays a key role in this circulation and quaternary climate cycles have been linked to changes in nadw flow4 general circulation model simulations indicate that before closure some 3 4 million years ago of the central american isthmus the narrow strip of land linking north and south america the direct flow of low salinity water from the pacific to the atlantic ocean would have led to a smaller nadw flow5 6 sedimentation patterns7 and nutrient proxies8 11 support these model results by indicating an increase in nadw flow around the time of isthmus closure but these records do not allow changes in different nadw sources to be distinguished and the overall effect of closure on global ocean circulation is poorly known here we present nd pb and sr isotope records preserved by a hydrogenous ferromanganese crust from the nadw flow path in the western north atlantic ocean these records indicate that the isotopic signal associated with nadw strengthened around 3 4 million years ago showing that deep water that formed in the labrador sea made a gradually increasing contribution to nadw flow these data taken together with those from the central pacific ocean12 indicate an increased nadw flow since isthmus closure and suggest that the closure established today s general pattern of ocean circulation

spatial and temporal evolution of lead isotope ratios in the north atlantic ocean between 1981 and 1989 29 68 w in the early 1980s 206 pb 207 pb ratios in the north african basin averaged 1 193 0 005 1 s similar radiogenic ratios within the level of analytical precision average 0 29 were found in the labrador and iceland basins 1 198 0 006 and in the norwegian sea 1 196 0 008 these radiogenic mixed layer signatures along with atmospheric global lead emission patterns suggest that most north atlantic lead in the early 1980s was derived from north american leaded gasoline samples in the east iberian basin near portugal and france showed lower 206 pb 207 pb ratios between 1 167 and 1 182 indicating a significant influence of less radiogenic atmospheric lead transported from europe and possibly the influence of the rio tinto acid mine drainage very close to shore in the gulf of cadiz pb across the entire north atlantic basin ranged between 54 and 145 pmol kg with the lowest values 54 74 pmol kg found at high latitudes 65 n in the late 1980s surface waters in the western subtropical north atlantic north american basin sargasso sea 47 w and in the eastern subtropical north atlantic north african basin central iberian basin 53 these elemental and isotopic results demonstrate the strongly variable isotopic and elemental signatures of north american and european lead throughout the north atlantic ocean frequently dominated by high 206 pb 207 pb and pb north

trace fossils as a paleoceanographic tool evidence from late quaternary sediments of the southwestern iberian margin biogenic structures in late quaternary sediments from the southwestern iberian continental slope were studied by using x ray images from two cores from 580 and 1750 m water depth eight different ichnocoenoses were observed indistinct bioturbation planolites dominated thalassinoides dominated chondrites dominated planolites and thalassinoides dominated pyritized microburrows such as trichichnus and mycellia dominated chondrites trichichnus and mycellia dominated and zoophycos variations of the ichnocoenoses within the cores show a striking correlation with climatically induced changes in the hydrographical regime i e current strength and bathymetric position of the mediterranean outflow water mow comparison of the response of the ichnocoenoses to changes in bottom water conditions and substrate between the two cores studied indicate that bottom water oxygenation and enrichment of particulate organic matter at the base of the mow layer are the primary factors controlling the ichnocoenoses the traces even recorded short term climatic changes such as the younger dryas cold event the spatial and temporal distribution patterns are in good agreement with earlier models of the mow history which gives reason to see a refinement of trace fossils as a complementary tool for paleoceanographical studies

high resolution stratigraphy of the mediterranean outflow contourite system in the gulf of cadiz during the late pleistocene the impact of heinrich events abstract a detailed high resolution stratigraphic analysis of the mediterranean outflow contourite system at the continental slope of the gulf of cadiz has been carried out through the correlation between a dense network of seismic reflection profiles sparker airgun 3 75 khz and parametric echosounder topas calypso giant piston and standard gravity cores from such correlation we determine a stacking pattern constituted by four main seismic units a d that are internally structured into ten subunits each subunit shows a single sequence formed by transparent seismic facies at the base to smooth parallel reflectors of moderate to high amplitude facies at the top being well correlated in the cores with a coarsening upward sequence the latest pleistocene holocene deposits form glacial interglacial depositional sequences related to cycles with a frequency range below the milankovitch band that corresponds to millennial timescale climatic changes such as dansgaard oeschger 1 5 ka and bond cycles 10 15 ka oxygen isotope records of planktonic foraminifera and the occurrence of ice rafted debris ird in the most recent contourite subunits show clear evidence of the influence of the north atlantic climatic conditions especially the climatic heinrich events h in the slope sedimentation of the gulf of cadiz and then in the circulation of the mediterranean outflow water mow the coarser contourite deposits are mostly associated with the last glacial maximum younger dryas and heinrich events on the central area of the middle slope during globally cooler conditions the mow was denser so that it was more active in deeper areas than today on the other hand during warm periods the mow became less dense favoring an increased intensity of the mow on the distal area of the upper slope therefore spatial and vertical fluctuations of the mow contourite system are strongly affected by global climate and oceanographic changes being clearly influenced by iceberg discharges and probably also by the resumption of thermohaline circulation in the north atlantic ocean during ice melting periods

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

hydrographic conditions along the western iberian margin during marine isotope stage 2 the surface water hydrography along the western iberian margin as part of the north atlantic s eastern boundary upwelling system consists of a complex seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions such as during marine isotope stage mis 2 and how north atlantic meltwater events especially heinrich events affected them to help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern iberian margin md95 2040 md95 2041 md99 2336 and md99 2339 the records reveals that with the exception of the heinrich events and greenland stadial gs 4 hydrographic conditions along the western iberian margin were not much different from the present during the last glacial maximum lgm subtropical surface and subsurface waters penetrated poleward to at least 40 6 n site md95 2040 export productivity was in general high on the western margin during the lgm and low in the central gulf of cadiz in agreement with the modern situation during the heinrich events and gs 4 on the other hand productivity was high in the gulf of cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling heinrich event 1 had the strongest impact on the hydrography and productivity off iberia and was the only period when subarctic surface waters were recorded in the central gulf of cadiz south of lisbon 39 n the impact of the other heinrich events was diminished and not all of them led to a significant cooling in the surface waters thus climatic impacts of heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

lateglacial and holocene palaeohydrology in the western mediterranean region the lake estanya record ne spain abstract the multi proxy analysis of sediment cores recovered in karstic lake estanya 42 02 n 0 32 e 670 m a s l ne spain located in the transitional area between the humid pyrenees and the semi arid central ebro basin provides the first high resolution continuous sedimentary record in the region extending back the last 21 000 years the integration of sedimentary facies elemental and isotopical geochemistry and biogenic silica together with a robust age model based on 17 ams radiocarbon dates enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation arid conditions represented by shallow lake levels predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum 21 18 cal kyrs bp and the lateglacial reaching their maximum intensity during the period 18 14 5 cal kyrs bp including heinrich event 1 and the younger dryas 12 9 11 6 cal kyrs bp less saline conditions characterized the 14 5 12 6 cal kyrs bp period suggesting higher effective moisture during the bolling allerod the onset of more humid conditions started at 9 4 cal kyrs indicating a delayed hydrological response to the onset of the holocene which is also documented in several sites of the mediterranean basin higher although fluctuating holocene lake levels were punctuated by a mid holocene arid period between 4 8 and 4 0 cal kyrs bp a major lake level rise occurred at 1 2 cal kyrs bp conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop occurring around 800 cal yrs bp which coincides with the medieval climate anomaly the main hydrological stages in lake estanya are in phase with most western mediterranean and north atlantic continental and marine records but our results also show similarities with other iberian and northern african reconstructions emphasizing peculiarities of palaeohydrological evolution of the iberian peninsula during the last deglaciation

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

an improved method for extracting marine sediment fractions and its application to sr and nd isotopic analysis the radiogenic isotopic composition of both detrital and fe mn fractions in marine sediments can be used in paleoceanography to infer changes of bottom water circulation we have examined various chemical techniques for the analysis of sr and nd isotope ratios in these fractions and present a robust method that can be used to separate both the fe mn oxides and the detrital fraction from a marine sediment sample for isotopic analysis our sequential leaching procedure involves the use of 10 acetic acid followed by 1 m hydroxylamine hydrochloride in 25 acetic acid to remove the carbonate component and the fe mn oxide fraction respectively the applicability of our chemical procedure is illustrated with examples from a marine sediment core raised from the northern cape basin southeast atlantic ocean

deglacial upslope shift of ne atlantic intermediate waters controlled slope erosion and cold water coral mound formation porcupine seabight irish margin abstract turbulent bottom currents significantly influence the formation of cold water coral mounds and sedimentation processes on continental slopes combining records from coral mounds and adjacent slope sediments therefore provide an unprecedented palaeo archive to understand past variations of intermediate water mass dynamics here we present coral ages from coral mounds of the belgica province porcupine seabight ne atlantic which indicate a non synchronous holocene re activation in mound formation suggested by a temporal offset of 2 7 kyr between the deep start 11 3 ka bp at 950 m depth and shallow start 8 6 ka bp at 700 m depth mounds a similar depth dependent pattern is revealed in the slope sediments close to these mounds that become progressively younger from 22 1 ka bp at 990 m to 12 2 ka bp at 740 m depth based on core top ages we suggest that the observed changes are the consequence of enhanced bottom water hydrodynamics caused by internal waves associated to the re invigoration of the mediterranean outflow water mow and the development of a transition zone tz between the mow and the overlying eastern north atlantic water enaw which established during the last deglacial these highly energetic conditions induced erosion adjacent to the belgica mounds and supported the re initiation of mound formation by increasing food and sediment fluxes the striking depth dependent patterns are likely linked to a shift of the enaw mow tz moving the level of maximum energy 250 m upslope since the onset of the last deglaciation

reduced admixture of north atlantic deep water to the deep central south pacific during the last two glacial periods the south pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the atlantic ocean the southern ocean and the pacific basin are exchanged here we reconstruct the deep water circulation of the central south pacific for the last two glacial cycles from 240 000 years ago to the holocene based on radiogenic neodymium nd and lead pb isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the east pacific rise the records show small but consistent glacial interglacial changes in all three isotopic systems with interglacial average values of 5 8 and 18 757 for end and 206pb 204pb respectively whereas glacial averages are 5 3 and 18 744 comparison of this variability of circumpolar deep water cdw to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of north atlantic deep water to cdw during cold stages the absolute values and amplitudes of the benthic 13c variations are essentially indistinguishable from other records of the southern hemisphere and confirm that the low central south pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies in addition the combined detrital nd and strontium 87sr 86sr isotope signatures imply that australian and new zealand dust has remained the principal contributor of lithogenic material to the central south pacific

contourites of the gulf of cadiz a high resolution record of the paleocirculation of the mediterranean outflow water during the last 50 000 years the mediterranean outflow water mow paleocirculation during the last 50 000 years has been inferred from the grain size distribution of contourite beds in core md99 2341 from the gulf of cadiz southern iberian margin atlantic ocean three main contourite facies are described their vertical succession defines two contourite sequences that reveal past variations of the mow bottom current velocity a comparison of contourite sequences and the planktonic 18o record of core md99 2341 with the 18o record from greenland ice core gisp2 show a close correlation of sea surface water conditions and deep sea contouritic sedimentation in the gulf of cadiz with northern hemisphere climate variability on millennial timescales a high mow velocity prevailed during dansgaard oeschger stadials heinrich events and the younger dryas cold climatic interval the mow velocity was comparatively low during the warm dansgaard oeschger interstadials bolling allerod and the early holocene rapid sea level fluctuations on the order of 35 m during marine oxygen isotope stage 3 are considered to have exerted limiting controls on the mow volume transport and thus positively modulated the mow behaviour during the last 50 kyr

flow and solute transport monitoring in the karst aquifer in sw slovenia the role of the unsaturated zone in the karst aquifer hydraulic behaviour was brought into focus in these studies of the catchment of the hubelj spring sw slovenia the variations of natural tracers in precipitation and in groundwater during a summer storm event made it possible to trace local flow and solute transport in the observed aquifer the results produced data on the aquifer recharge storage and discharge processes as well as on mechanisms that affected them which reflects a karst groundwater dynamics also at a regional scale they point out the significance of effects of the fast preferential flow epiflow that is the main factor controlling solute contaminant transport towards the aquifer saturated zone numerous arguments indicate that the karst aquifer flow and solute transport mechanisms depend on the hydraulic behaviour of the epikarst zone

a boundary exchange influence on deglacial neodymium isotope records from the deep western indian ocean the use of neodymium nd isotopes to reconstruct past water mass mixing relies upon the quasi conservative behaviour of this tracer whereas recent studies in the modern oceans have suggested that boundary exchange involving the addition of nd from ocean margin sediments may be an important process in the nd cycle here we suggest that the relative importance of water mass advection versus boundary exchange can be assessed where the deep western boundary current in the indian ocean flows past the madagascan continental margin a potential source of highly unradiogenic nd foraminiferal coatings and bulk sediment reductive leachates are used to reconstruct bottom water nd isotopic composition end in 8 holocene age coretops with excellent agreement between the two methods these data record spatial variability of 4 end units along the flow path of circumpolar deep water end 8 8 in the deep southern inflow upstream of madagascar which evolves towards end 11 5 offshore northern madagascar whereas end 7 3 where deep water re circulates in the eastern mascarene basin this variability is attributed to boundary exchange and together with measurements of detrital sediment end an isotope mass balance suggests a deep water residence time for nd of 400 yr along the madagascan margin considering deglacial changes a core in the deep inflow upstream of madagascar records end changes that agree with previous reconstructions of the circumpolar deep water composition in the southern ocean consistent with a control by water mass advection and perhaps indicating a longer residence time for nd in the open ocean away from local sediment inputs in contrast sites along the madagascan margin record offset end values and reduced glacial interglacial variability underlining the importance of detecting boundary exchange before inferring water mass source changes from nd isotope records the extent of madagascan boundary exchange appears to be unchanged between the holocene and late glacial periods while a consistent shift towards more radiogenic end values at all sites in the late glacial compared to the holocene may represent a muted signal of a change in water mass source or composition

late quaternary variability of mediterranean outflow water from radiogenic nd and pb isotopes mediterranean outflow water mow is characterised by higher temperatures and salinities than other ambient water masses mow spreads at water depths between 500 and 1500 m in the eastern north atlantic and has been a source of salinity for the atlantic meridional overturning circulation in the north atlantic we used high resolution nd and pb isotope records of past ambient seawater obtained from authigenic ferromanganese coatings of sediments in three gravity cores at 577 1745 and 1974 m water depth in the gulf of cadiz and along the portuguese margin complemented by a selection of surface sediments to reconstruct the extent and pathways of mowover the past 23 000 years the surface and downcore nd isotope data from all water depths exhibit only a very small variability close to the present day composition of mowbut do not reflect the present day nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station in contrast the pb isotope records show significant and systematic variations which provide evidence for a significantly different pattern of the mow pathways between 20 000 and 12 000 years ago compared with the subsequent period of time

temporal stability of the neodymium isotope signature of the holocene to glacial north atlantic the neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales unlike nutrient proxies such as 13 c or cd ca nd isotopes are not thought to be altered in any significant way by biological processes and thus they can serve as a quasi conservative water mass tracer however the application of nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the north atlantic end member through time here we present the first results of nd isotopes measured in u th dated deep sea corals from the new england seamounts in the northwest atlantic ocean our data are consistent with the conclusion that the nd isotopic composition of north atlantic deep and intermediate water has remained nearly constant through the last glacial cycle the results address long standing concerns that there may have been significant changes in the nd isotopic composition of the north atlantic end member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

climatically driven changes in sediment supply on the sw iberian shelf since the last glacial maximum the assemblages of marine sediments on the sw iberian shelf have been controlled by contributions from distinct sources which have varied in response to environmental changes since the last glacial maximum lgm the rapid decadal scale mediterranean overturning circulation permits mixing of suspended particles from the entire mediterranean sea they are entrained into the suspended particulate matter spm carried by mediterranean outflow water mow which enters the eastern north atlantic through the strait of gibraltar and spreads at intermediate depths in the gulf of cadiz and along the portuguese continental margin other major sediment sources that have contributed to the characteristics and budget of spm along the flow path of mow on the sw iberian shelf are north african dust and river transported particles from the iberian peninsula to reconstruct climate and circulation driven changes in the supply of sediments over the past 23 000 cal yr b p radiogenic nd sr and pb isotope records of the clay size sediment fraction were obtained from one gravity core in the gulf of cadiz 577 m water depth and from two gravity cores on the portuguese shelf 1745 m 1974 m water depth these records are supplemented by time series analyses of clay mineral abundances from the same set of samples contrary to expectations the transition from the lgm to the holocene was not accompanied by strong changes in sediment provenance or transport whereas heinrich event 1 h1 and the african humid period ahp were marked by significantly different isotopic signatures reflecting changes in source contributions caused by supply of ice rafted material originating from the north american craton during h1 and diminished supply of saharan dust during the ahp the data also reveal that the timing of variations in the clay mineral abundances was decoupled from that of the radiogenic isotope signatures

glacial rapid variability in deep water temperature and δ18o from the western mediterranean sea abstract deep water temperatures dwts from the western mediterranean sea are reconstructed for the last 50 ka based on the analysis of mg ca ratios in benthic foraminifera from core md95 2043 collected in the alboran sea the exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the dansgaard oeschger d o rapid climatic variability the applicability of mg ca thermometry in the western mediterranean deep water mass wmdw is first tested by the analysis of different benthic species in a collection of mediterranean core tops the results indicate the need of a readjustment of the existing cibicidoides spp calibrations in order to reconstruct present western mediterranean dwt values 12 7 c different physiological effects in the mg uptake between the c pachydermus living in different regions could account for this offset in the mediterranean samples consequently the obtained dwt record still has many uncertainties in absolute terms but trends provide valuable information on past changes in wmdw conditions the dwt record shows significant oscillations in relation to the d o cycles colder values occurred during the time of d o stadials and warmer ones during d o interstadials surprisingly the coldest dwts occurred during the time of heinrich event 4 he4 and not during the last glacial maximum lgm when dwts were mostly warm these and other particular features of the dwt reconstruction mimic changes in the vegetation from the eastern mediterranean indicating the control of the mediterranean climate on the dwt record paired analyses of mg ca and 18 occ calcite 18 o provide the opportunity to reconstruct deep water 18 o 18 odw and past salinities and hence changes in past wmdw density due to the large error associated with these calculations they can only be discussed in terms of relative changes between different intervals the results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early holocene in relation to the 18 odw conditions present today densest wmdw were formed during most of marine isotopic stage mis 2 and during the d o stadials not associated with hes while lightest wmdw dominated during d o interstadials the 18 odw record shows a d o variability pattern likely controlled by changes in the composition and intensity of the local run off and also to changes in the 18 ow signal of the atlantic inflow changes in the residence time of the mediterranean waters governed by the global sea level are also considered to exert an important role governing mediterranean 18 ow and salinity particularly during mis 2 overall our results are consistent with the formation of dense wmdw during d o stadials and even denser during most of mis 2

evidence for enhanced mediterranean thermohaline circulation during rapid climatic coolings molecular biomarkers c37 alkenones n nonacosane and n hexacosanol and toc are used together with benthic 18o and 13c data to document the hydrographic response of the western mediterranean sea to rapid climatic variability these proxies are recorded in core md 95 2043 alboran sea affording the study of the dansgaard oeschger d o and heinrich he variability during the last glacial period the results suggest that rapid changes in the western mediterranean thermohaline circulation occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation occurred during cold intervals he and d o stadials probably driven by a strengthening of north westerly wind over the north western mediterranean sea in contrast decreased intensity of the thermohaline circulation is detected during warm intervals d o interstadials which led to low oxygenated deep water masses and better preservation of the organic matter in the sediment

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

retreat of the laurentide ice sheet tracked by the isotopic composition of pb in western north atlantic seawater during termination 1 during the last glacial maximum much of north america was covered by the laurentide ice sheet its melting during termination 1 led to systematic changes in proglacial lake formation continental runoff and possibly north atlantic meridional overturning circulation the accompanying change in chemical weathering rates in the interior of north america throughout the deglaciation resulted in a pronounced change in seawater pb isotope composition in the western north atlantic ocean here we present the first high resolution records of seawater pb isotope variations of north atlantic deep water extracted from authigenic fe mn oxyhydroxides in three sediment cores 51ggc 1790 m depth 31ggc 3410 m depth 12jpc 4250 m depth from the blake ridge off florida these data reveal a striking excursion from relatively unradiogenic 206pb 204pb as low as 18 93 towards highly radiogenic pb isotope compositions that was initiated during the bolling allerod interstadial and was most pronounced in both intermediate and deep waters during and after the younger dryas 206pb 204pb as high as 19 38 at 8 8 ka in 4250 m this pattern is interpreted to be a direct function of increased inflow of continent derived radiogenic pb into the western north atlantic supplied through chemical weathering of north american rocks that had been eroded and freshly exposed during the preceding glacial cycle these sediment derived data are complemented by new laser ablation pb isotope data from a ferromanganese crust from the blake plateau at 850 m water depth which show only small glacial interglacial pb isotope variations of the florida current 206pb 204pb between 19 07 and 19 16 the lack of change in the blake plateau record at the same time as the radiogenic excursion in the deeper sediments supports a northern origin of the pulse of radiogenic pb after the younger dryas the deep western north atlantic has experienced a persistent highly radiogenic pb supply that was most pronounced during the first half of the holocene and still lasts until today

stable runoff and weathering fluxes into the oceans over quaternary climate cycles the effect of glacial interglacial cycles on surface weathering rates has been unclear a beryllium based proxy for weathering shows minimal variations in the input of silicate weathering products to the oceans for the past two million years

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

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

campanian maastrichtian ocean circulation in the tropical pacific the pacific ocean is the largest water body on earth and circulation in the pacific contributed significantly to climate evolution in the latest cretaceous the culmination of a period of long term cooling here we present new high resolution late campanian to maastrichtian benthic and planktic foraminiferal stable isotope data and a neodymium nd isotope record obtained from sedimentary ferromanganese oxide coatings of ocean drilling program hole 1210b from the tropical pacific ocean shatsky rise these new records resolve 13 million years in the latest cretaceous providing insights into changes in surface and bottom water temperatures and source regions of deep to intermediate waters covering the carbon isotope excursions of the campanian maastrichtian boundary event cmbe and the mid maastrichtian event mme our new benthic foraminiferal 18o and nd isotope records together with published nd isotope data show markedly parallel trends across the studied interval over a broad range of bathyal to abyssal water depths interpreted to reflect changes in the intensity of deep ocean circulation in the tropical pacific in particular we observe a three million year long period of cooler conditions in the early maastrichtian 72 5 to 69 5 ma when a concomitant change toward less radiogenic seawater nd isotope signatures probably marks a period of enhanced admixture and northward flow of deep waters with southern ocean provenance we suggest this change to have been triggered by intensified formation and convection of deep waters in the high southern latitudes a process that weakened during the mme 69 5 to 68 5 ma the early maastrichtian cold interval is closely related to the negative and positive carbon isotope trends of the cmbe and mme the millions of years long duration of these carbon cycle perturbations suggests a tectonic forcing of climatic cooling possibly related to changes in ocean basin geometry and bathymetry

mediterranean outflow strengthening during northern hemisphere coolings a salt source for the glacial atlantic abstract high resolution grain size and magnetic susceptibility records from the eastern gulf of cadiz site md99 2339 1170 m water depth reveal contourites formed by the mediterranean outflow mow during the last 47 kyr bp oscillations in the mow s intensity occurred in phase with greenland temperature variations with a stronger outflow during northern hemisphere coolings such as dansgaard oeschger stadials heinrich events and the younger dryas benthic 13c data implies the western mediterranean deep water as one of the main sources feeding the outflow current while differential changes in the properties of the mediterranean source and entrained north atlantic central water largely control the mow s strength detailed studies for heinrich events 1 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern gulf of cadiz while incursions of icebergs and subpolar surface water were not favorable for the mow s intensification as the mow was strong when the atlantic s thermohaline circulation thc was weakened the heat and salt injected by the mow into the intermediate north atlantic waters might have preconditioned the thc to switch from the stadial to the interstadial mode

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

world map of nd isotopes in sea floor ferromanganese deposits the nd isotopic compositions of hydrogenous ferromanganese encrustations and nodules largely reflect those of the overlying seawater integrated over the few millions of years over which they grow available nd isotope data on ocean floor hydrogenous deposits suggest control by nd from particulates blown from the continents and released by volcanic activity associated with subduction zones and midocean ridges the regional nd isotope variations display a marked similarity to the broad patterns of present day deep ocean circulation suggesting that the particulates that are the sources of oceanic nd travel along with water masses despite rapid 10 100 ka perturbations during glacial periods the long term patterns of water mass movements and oceanic fluxes of particulates have remained essentially stable over the last few million years

impact of iceberg melting on mediterranean thermohaline circulation during heinrich events down core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopes in international marine past global changes study images core md99 2343 in order to study the interactions between climate change in the northern hemisphere and the western mediterranean thermohaline circulation at times of heinrich events he our results confirm the antiphase correlation between enhanced north atlantic deep water formation and low ventilation in the mediterranean however this study reveals that this antiphase relationship in deepwater formation between the north atlantic and mediterranean was interrupted during times of he when the injection of large volumes of water from melting icebergs reached the entrance to the mediterranean these events which lasted less than 1000 years are represented by pronounced decreases in both planktonic d18o and benthic d13c signals lower salinities of mediterranean surface water resulted in a slowdown of western mediterranean deepwater overturn even though cold sea surface temperatures and drier climate should have resulted in enhanced deepwater formation

new constraints on the pb and nd isotopic evolution of ne atlantic water masses 1 time series of lead pb and neodymium nd isotope compositions were measured on three ferromanganese crusts recording the evolution of ne atlantic water masses over the past 15 ma the crusts are distributed along a depth profile 700 4600 m comprising the present day depths of mediterranean outflow water and north east atlantic deep water a pronounced increase of the 206pb 204pb in the two deeper crusts starting at 4 ma and a decrease in 143nd 144nd in all three crusts took place between 6 4 ma and the present these patterns are similar to isotope time series in the western north atlantic basin and are consistent with efficient mixing between the two basins however the changes occurred 1 3 ma earlier in the eastern basin indicating that the northeastern atlantic led the major change in pb and nd isotope composition probably due to a direct supply of labrador seawater via a northern route the pb isotope evolution during the pliocene pleistocene can generally be explained by mixing between two end members corresponding to mediterranean outflow water and north east atlantic deep water but external sources such as saharan dust are likely to have played a role as well the pb isotope composition of the shallowest crust that grew within the present day mediterranean outflow water does not show significant pb isotope changes indicating that it was controlled by the same pb sources throughout the past 15 ma

glacial to interglacial changes in the settling depth of the mediterranean outflow plume we present micropalaeontological and grain size records for a set of sediment cores from the gulf of cadiz southwest spain that reflect changes in the position and strength of the mediterranean outflow mo current the cores sample a sediment drift the gil eanes drift that is positioned lower on the slope in the gulf of cadiz than the position of the main current today the data indicate that the drift is of glacial age and that the glacial mo current was positioned lower on the slope than today but also that it was active over a considerably reduced area of the slope we argue that this observation is consistent with physical constraints on the gibraltar exchange and on the likely settling and spreading behavior of the mo plume along the iberian margin under glacial environmental and sea level conditions the deeper settling of the mo is likely to have influenced the formation of glacial north atlantic intermediate water and also may have exerted indirect influence on the formation of glacial north atlantic deep water

changes in silicate utilisation and upwelling intensity off peru since the last glacial maximum insights from silicon and neodymium isotopes we combine the stable silicon isotope composition 30si of diatoms and the radiogenic neodymium isotope compositions end of past seawater extracted from the authigenic fraction of the sediments mn fe coatings of particles and benthic foraminifers as well as the radiogenic isotope compositions nd sr of the detrital material itself to reconstruct silicic acid utilisation water mass mixing and upwelling intensity from the same marine sediments in the peruvian upwelling region during the past 20 000 years additionally the sedimentary signals were compared to the water column isotope compositions along the peruvian shelf the dissolved end in the water column ranges from 5 7 to 0 6 the corresponding end signatures of the coatings and the benthic foraminifers of the surface sediments range from 4 5 to 1 8 and from 2 5 to 2 2 respectively the detrital end 87sr 86sr signatures range from 6 3 to 0 0 70508 0 71049 all phases show a trend from more radiogenic end values in the north towards less radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology the end signatures of the coatings extracted from sediment core so147 106kl located in the present day centre of coastal upwelling near 12 s have been essentially constant 1 5 throughout the past 20 000 years while the detrital end 87sr 86sr varied between values of 0 7 0 70620 during the last glacial and 4 5 0 70849 during the late holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling the 30si signature of both total biogenic opal 30siopal and of hand picked diatoms 30sidiatom ranged from 0 3 last glacial to 1 4 late holocene confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms our combined bsio2 mar 30siopal and detrital radiogenic isotope results demonstrate that the strongest el nino southern oscillation conditions off peru of the past 20 ka have prevailed during the past 5 ka

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

neodymium isotopic composition of the mediterranean outflow and the eastern north atlantic the neodymium concentration and isotopic composition of the mediterranean outflow in the strait of gibraltar has been directly determined the outflow has a dissolved nd concentration of 23 pmoles kg with nd 0 9 4 these results are in clear disagreement with previous values inferred for the mediterranean this concentration and nd 0 do not sharply contrast with north atlantic deep water nadw values and can produce isotopic anomalies no larger than 1 unit in the north atlantic a new profile in the eastern north atlantic does not exhibit an nd 0 anomaly at the depth of the mediterranean water core in accordance with the above inferences while concentrations and nd 0 at this site indicate that nd is conservative in the deep eastern north atlantic a previously reported nd 0 anomaly in the eastern north atlantic originally associated with the mediterranean outflow has a different source the direct contribution of the mediterranean outflow to the nadw nd budget is small 10 of the high latitude sources however the outflow plus entrained water supply 30 of the total nd associated with northern latitude deep water sources concentrations of dissolved nd in the outflow are enriched compared to the atlantic inflow which has 16 pmoles kg with nd 0 11 8 the principal source of the excess dissolved nd is inferred to be partial dissolution of detrital particles simple mass balance calculations suggest that 0 6 of the nd associated with detrital river transported sediments and or 3 5 of the nd associated with eolian particles delivered to the mediterranean is mobilized during passage into the marine environment if general these mobilization efficiencies imply that the dissolution of detrital particles is a significant source of dissolved nd and other rare earth elements in seawater

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

tectonically driven changes in the indian ocean circulation over the last 25 ma neodymium isotope evidence abstract changes in ancient oceanic current patterns have been strongly influenced by plate tectonics particularly by the opening or closing of gateways between different oceans such modifications of oceanic circulation have important consequences on climate we studied the nd seawater isotopic composition of indian and pacific ocean cores using nd isotopes which are good paleo oceanographic tracers we focused on the past 25 ma which are marked by the closure of the indonesian gateway as well as the mediterranean connection we show that a strong westerly oceanic surface current which we refer to the miocene indian ocean equatorial jet miojet linked the eastern and western indian ocean from 14 ma to 3 ma and infer that this major change in oceanic circulation probably induced important variations of global climate

southernmost evidence of large european ice sheet derived freshwater discharges during the heinrich stadials of the last glacial period galician interior basin northwest iberian continental margin abstract reconstruction of circum atlantic ice sheet motion and instabilities is crucial to understanding the mechanisms that triggered and or enhanced abrupt climate changes using enviromagnetic and geochemical data we provide a continuous and well dated record of the evolution of glacial interglacial sedimentation on the northwest iberian margin during the last glacial period covering the last six heinrich stadials the record shows european sediments that were related to meltwater pre events during the initial stages of hs1 hs2 and hs4 that corroborate the channel river depositional history the record also includes ird from the laurentide ice sheet and the european ice sheet during the final stages of these stadials i e heinrich events therefore this study provides insight into one of the potential forcing mechanisms for heinrich events and by inference for heinrich stadials