radiogenic nd isotope labeling of the northern ne atlantic during mis 2 paleoceanographic reconstructions rely on chemical proxies which are controlled by physical chemical and biological marine parameters the accurate interpretation of proxy records relies on the integrity of proxy environmental relationships through time and under changing conditions in this study we closely examine paleo controls on authigenic nd isotope records from five cores in the northern ne atlantic approximating a depth transect allowing spatial and temporal relationships to be reconstructed we compare our nd isotope records with other paleocirculation proxies and consider the sedimentalogical controls on nd isotope signals by comparing ice rafted detritus lithology and counts detrital sediment chemistry and redox sensitive element concentrations measured on foraminifera authigenic coatings with this suite of geochemical and sedimentalogical data we show that nd isotope records in the northern ne atlantic were labeled by radiogenic sediments however this modification did not occur in the pore waters of each core but instead likely reflects changes in the nd isotopic composition of deep waters caused by the input of ice rafted sediment during heinrich events and the last glacial maximum this study has implications for understanding how localized changes in the nd isotope signal can set a watermass end member composition decoupling chemical proxy circulation relationships locally but providing a signal which can be potentially traced along the deep water flowpath such scenarios must be considered in future interpretations of glacial nd isotope records taken from within the ice rafted detritus belt and downstream along watermass flowpaths

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

abyssal origin for the early holocene pulse of unradiogenic neodymium isotopes in atlantic seawater the neodymium isotopic composition of authigenic phases of deep sea sediment cores can be interpreted as reflecting past changes in water mass mixing proportions if end member water mass compositions are constrained through time here we present three new records spanning 2480 to 4360 m depth in the north atlantic ocean that show seawater nd isotope values in the early to mid holocene that are more radiogenic than values from the abyssal northwest atlantic this finding indicates that that the end member composition of north atlantic deep water was more stable within its core than it was at abyssal depths the spatial distribution of the unradiogenic neodymium isotope values observed in the north atlantic suggests a bottom source and therefore that they were unlikely to have been due to the production of intermediate depth labrador sea water we infer that the unradiogenic authigenic nd isotope values were most likely derived from a pulse of poorly chemically weathered detrital material that was deposited into the labrador sea following laurentide ice sheet retreat in the early holocene this unradiogenic sediment released neodymium into the bottom waters yielding an unradiogenic seawater signal that was advected southward at abyssal depths and attenuated as it vertically mixed upward in the water column to shallower depths the southward dispersion of these unradiogenic seawater values traces deep water advection however the exact values observed at the most abyssal sites cannot be interpreted as proportionate to the strength of deep water production without improved constraints on end member changes

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

evolution of the central nordic seas over the last 20 thousand years the deep and surface water paleoceanographic evolution of the central nordic seas over the last 20 thousand years was reconstructed using various micropaleontological isotopic and lithological proxy data these show a high spatial and temporal complexity of the oceanic circulation when compared with other records from the region during early deglaciation a collapse of ice sheets surrounding the nordic seas released large amounts of freshwater that affected both the surface and bottom water circulation and significantly contributed to heinrich stadial 1 during the younger dryas the central nordic seas were affected by a last major freshwater plume which probably originated from the arctic ocean when major ice rafting had ceased around 11ka subsurface temperatures started to rise however atlantic water advection and subsurface temperatures reached their maximum in the central nordic seas later than along the eastern continental margin that spatio temporal offset is explained by a gradual re routing and westward expansion of the atlantic water flow during times when the greenland sea gyre system became more steadily established in the greenland basin the holocene thermal maximum ended c 5 5ka and time coeveal with an increase in sea ice export from the arctic in the lofoten basin the cooling occurred later after 4ka and together with a weakening of the overturning processes the neoglacial cooling was reached c 3ka together with low solar irradiance expanding sea ice and a slight decrease in deep convection at c 2ka subsurface temperatures began to rise again due to an increasing influence of atlantic waters

neodymium associated with foraminiferal carbonate as a recorder of seawater isotopic signatures neodymium isotopic ratios in marine environments have been used as a tracer of water masses and exchange processes between dissolved and particulate phases the interest in this tracer has been growing with improvement of our knowledge on its chemical behaviour in the modern ocean and the identification of sedimentary phases that preserve past seawater epsilon nd values in the last few decades the nd isotopic composition measured on fe mn crusts sediment leachates bulk carbonate fraction corals and fish teeth have been increasingly interpreted in the context of understanding the role of the ocean in paleoclimate changes in particular calcareous foraminiferal tests shells have acquired increasing attention as an archive of seawater nd isotopic signatures because it allows continuous high resolution records to be measured and directly compared to other proxies including stable isotopes and trace metals the main challenge of interpreting the nd isotopic composition of foraminifera is determining the origin of the nd preserved within them in this review we present an overview of methodological progress including that of bulk foraminifera and microanalyses within foraminiferal tests as well as geochemical meaning of extracted nd concentrations and isotopic compositions the growing body of evidence suggests that nd isotopic signatures of sedimentary planktonic foraminifera correspond to bottom water values rather than surface water ones the nd rich phases associated with sedimentary foraminifera are adhesive nano scale particles of mn and fe oxides and hydroxides and mn rich carbonates formed within layers of foraminiferal calcite mechanical cleaning to remove clay minerals is likely to be sufficient in most cases to reconstruct past bottom water circulations unresolved issues include the potential influence of pore water nd on epsilon nd values extracted from sedimentary foraminiferal tests under different sedimentalogical and oceanographic conditions c 2013 elsevier ltd all rights reserved

the resilience and sensitivity of northeast atlantic deep water end to overprinting by detrital fluxes over the past 30 000 years abstract the neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing for its accurate application knowledge about the origin and preservation of nd in sedimentary archives is crucial recently concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer given potential nd fluxes from sediments into bottom waters abbott et al 2015a and inferred relabelling of ocean waters by settling detrital material roberts and piotrowski 2015 consequently a decoupling of water mass provenance and proxy variations may arise we investigate the mobility of nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the northeast atlantic the constructed records from sediment leachates span extreme nd isotope variations including volcanic end 0 and laurentian end 27 sources we find that nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis thereby overprinting any archived bottom water nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals however we do not observe any definite indication of diffusive vertical migration of nd into adjacent layers furthermore bottom water nd isotope signatures were not modified to a measurable degree by any potential benthic flux of nd during the deposition of these detrital sediment layers consequently the nd isotope composition of the pelagic glacial northeast atlantic water masses were resilient to such episodic large detrital fluxes apart from extreme local sedimentation events we confirm the presence of detritally overprinted deep waters north of 47 n during the peak glacial from comparison of northeast atlantic depth transects we furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced atlantic meridional overturning circulation and elevated ice rafting overall our study demonstrates that a thorough evaluation of the proportion of nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of nd isotopes as a water mass tracer

weathering versus circulation controlled changes in radiogenic isotope tracer composition of the labrador sea and north atlantic deep water geological reconstructions and general circulation models suggest that the onset of both northern hemisphere glaciation 2 7 myr ago and convection of labrador sea water lsw were caused by the closure of the panama gateway 4 5 myr ago time series data that have been obtained from studies of ferromanganese crusts from the northwestern atlantic suggest that radiogenic isotopes of intermediate ocean residence time pb and nd can serve as suitable tracers to reconstruct these events however it has been unclear until now as to whether the changes that have been observed in isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering in this paper we adopt a box model approach to demonstrate that the shifts in radiogenic isotope compositions are unlikely to be due to changes in convection in lsw but can be explained in terms of increases of erosion levels due to the glaciation of greenland and canada furthermore we provide experimental evidence for the incongruent release of a labile fraction of strongly radiogenic pb and nonradiogenic nd from continental detritus eroding into the labrador sea this can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in radiogenic pb should provide such a rich supply of radiogenic pb to the oceans an important general conclusion is that the compositions of radiogenic isotopes in seawater are not always a reflection of their continental sources perhaps more importantly the transition from chemical weathering to mechanical erosion is likely to result in significant variations in radiogenic tracers in seawater

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

early stage weathering systematics of pb and nd isotopes derived from a high alpine holocene lake sediment record highlights deglacial chemical weathering monitored by adsorbed isotopic and elemental signals resilience of authigenic geochemical signals towards variable lake redox conditions pronounced early deglacial weathering of labile accessory minerals remarkably congruent uranogenic and reduced thorogenic pb isotope release anthropogenic atmospherically deposited pb pollution since over 2000 years abstract radiogenic pb and nd isotopes are well established tools in paleoceanographic science tracing ambient climate and continental runoff to the oceans down to sub millennial timescales particularly in case of pb isotopes a clear climate dependency of continental isotopic runoff on glacial interglacial transitions has been observed pb isotopes were reported to be released incongruently during initial chemical weathering this incongruent release implies that pb isotopic runoff compositions differ from the bulk catchment pb isotopic signal yet only little is known about the processes leading to the incongruent release and the timescales of weathering on the continents in this study we targeted the adsorbed trace metal signature in sediments from a swiss high alpine lake that have accumulated since the retreat of the large alpine ice domes during the last deglaciation to investigate initial pb and nd isotope weathering processes in a granitic environment additionally selected adsorbed element concentrations and ratios were analysed to complement the isotopic physico chemical weathering information the integrity of the presented isotope records is supported by further investigation into the lake environment e g oxic anoxic conditions and its potential influence on the isotopic record the pb isotope records during the early lake phase witnessed high amplitude isotopic fluctuations linked to the initial chemical weathering of fine glacial substrate this finding is also supported by the lithology of the core and rapidly decreasing adsorbed th and u concentrations following this early lake phase the majority of the holocene traced congruent release of 207pb 204pb and 206pb 204pb and a significant depletion of 208pb 204pb in the adsorbed phase these findings corroborate earlier suggestions of more effective weathering of uranogenic minerals yet also call for the presence of more weathering resistant thorogenic minerals in the lake catchment the latest 2 2 ka of the record are significantly overprinted by anthropogenic pb deposition coinciding with the rise and fall of the roman empire finally our data suggest that nd isotopes are equally affected by incongruent weathering during the initial deglacial weathering processes albeit at smaller magnitude than seen for pb isotopes

ventilation history of nordic seas overflows during the last de glacial period revealed by species specific benthic foraminiferal 14c dates formation of deep water in the high latitude north atlantic is important for the global meridional ocean circulation and its variability in the past may have played an important role in regional and global climate change here we study ocean circulation associated with the last de glacial period using water column radiocarbon age reconstructions in the faroe shetland channel southeastern norwegian sea and from the iceland basin central north atlantic the presence of tephra layer faroe marine ash zone ii dated to 26 7 ka enables us to determine that the middepth 1179 m water depth and shallow subsurface reservoir ages were 1500 and 1100 14c years respectively older during the late glacial period compared to modern suggesting substantial suppression of the overturning circulation in the nordic seas during the late last glacial maximum and the onset of deglaciation 20 18 ka nordic seas overflow was weak but active during the early deglaciation 17 5 14 5 ka our data reveal large differences between 14c ventilation ages that are derived from dating different benthic foraminiferal species pyrgo and other miliolid species yield ventilation ages 6000 14c years while all other species reveal ventilation ages 2000 14c years these data either suggest subcentennial regional circulation changes or that miliolid based 14c ages are biased due to taphonomic or vital processes implications of each interpretation are discussed regardless of this enigma the onset of the bolling allerod interstadial 14 5 ka is clearly marked by an increase in middepth nordic seas ventilation and the renewal of a stronger overflow

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

glacial freshwater discharge events recorded by authigenic neodymium isotopes in sediments from the mendeleev ridge western arctic ocean the freshwater budget of the arctic ocean is a key component governing the deep water formation in the north atlantic and the global climate system we analyzed the isotopic composition of neodymium end in authigenic phases of marine sediments on the mendeleev ridge in the western arctic ocean spanning an estimated time interval from present to about 75 ka bp this continuous record was used to reconstruct the end of the polar deep water pdw and changes in freshwater sources to the pdw through time three deviations in end from a long term average of 10 2 were identified at estimated 46 51 35 39 and 13 21 ka bp the estimated 46 51 ka bp event can be traced to bursting of ice dammed lakes accompanying the collapse of the barents kara ice sheet which would have released radiogenic nd to the eastern arctic ocean the cyclonic surface circulation in the eastern arctic ocean must have been stronger than at present for the event to be recorded on the mendeleev ridge for the 35 39 and 13 21 ka bp events it is likely that the laurentide ice sheet lis supplied the unradiogenic freshwater the configuration of the anticyclonic circulation in the western arctic was probably similar to today or expanded eastward our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the arctic ocean the effect on the formation of nadw was probably minor

flushing of the deep pacific ocean and the deglacial rise of atmospheric co 2 concentrations during the last deglaciation 19 000 9 000 years ago atmospheric co2 increased by about 80 ppm understanding the mechanisms responsible for this change is a central theme of palaeoclimatology relevant for predicting future co2 transfers in a warming world deglacial co2 rise hypothetically tapped an accumulated deep pacific carbon reservoir but the processes remain elusive as they are underconstrained by existing tracers here we report high resolution authigenic neodymium isotope data in north pacific sediment cores and infer abyssal pacific overturning weaker than today during the last glacial maximum but intermittently stronger during steps of deglacial co2 rise radiocarbon evidence suggestive of relatively old deglacial deep pacific water is reinterpreted here as an increase in preformed 14c age of subsurface waters sourced near antarctica consistent with movement of aged carbon out of the deep ocean and release of co2 to the atmosphere during the abyssal flushing events the timing of neodymium isotope changes suggests that deglacial acceleration of pacific abyssal circulation tracked southern hemisphere warming sea ice retreat and increase of mean ocean temperature the inferred magnitude of circulation changes is consistent with deep pacific flushing as a significant and perhaps dominant control of the deglacial rise of atmospheric co2

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

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

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

grain size separation and sediment mixing in arctic ocean sediments evidence from the strontium isotope systematic the 87 rb 86 sr and 87 sr 86 sr ratios of laptev sea sediments of arctic ocean sediments and of suspended particulate matter spm from siberian rivers lena and khatanga form pseudo isochrons due to grain size separation processes which are referred to as lena mixing envelope lme and as flood basalt envelope fbe at the land ocean transition the reduction of the particle velocity causes a deposition of coarser grained material and the contact with saline water enhances a precipitation of finer grained material the coarse grained material is enriched in sr showing less radiogenic 87 sr 86 sr ratios whereas fine grained material is depleted in sr relative to rb showing more radiogenic 87 sr 86 sr ratios the experimentally determined spread of the 87 rb 86 sr and 87 sr 86 sr ratios as a function of grain size in one sediment sample is on the same order as the natural spread of the 87 sr 86 sr ratios observed in all samples from the arctic ocean chemical index of alteration cia for the lena river spm tend to confirm previous observations that chemical alteration is negligible in the arctic environment thus these pseudo isochrons reflect an average age and the average isotope composition in the river drainage area calculated apparent ages from the fbe reflect the age of the siberian flood basalt of about 220 ma and the initial ratio of 0 707 1 reflects their mantle origin the age calculated from the lme of about 125 ma reflects accidentally the jurassic and cretaceous age of the sediments drained by the lena river and the initial ratio of 0 714 1 reflects the crustal origin of their source rocks comparison of geographical locations reveals that all samples from the eastern laptev sea east of 120 degrees e fall along the lme whereas all samples from the western laptev sea west of 120 degrees e fall between lme and fbe mixing calculations based on 143 nd 144 nd measurements not influenced by grain size show that about 75 of the western laptev sea sediments originate from the lena drainage area whereas about 25 of the sediments are delivered from the siberian flood basalt province sediments from the central arctic ocean are isotopically related to the lena drainage area and the siberian flood basalt province however sediments from the arctic ocean margins close to novaya semlya greenland the fram strait and svalbard originate from sources not yet identified c 1999 elsevier science b v all rights reserved

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

combining meteorites and missions to explore mars laboratory studies of meteorites and robotic exploration of mars reveal scant atmosphere no evidence of plate tectonics past evidence for abundant water and a protracted igneous evolution despite indirect hints direct evidence of a martian origin came with the discovery of trapped atmospheric gases in one meteorite since then the study of martian meteorites and findings from missions have been linked although the meteorite source locations are unknown impact ejection modeling and spectral mapping of mars suggest derivation from small craters in terrains of amazonian to hesperian age whereas most martian meteorites are young 4 5 ga and formation of enriched and depleted reservoirs however the history inferred from martian meteorites conflicts with results from recent mars missions calling into doubt whether the igneous histor y inferred from the meteorites is applicable to mars as a whole allan hills 84001 dates to 4 09 ga and contains fluid deposited carbonates accompanying debate about the mechanism and temperature of origin of the carbonates came several features suggestive of past microbial life in the carbonates although highly disputed the suggestion spurred interest in habitable extreme environments on earth and throughout the solar system a flotilla of subsequent spacecraft has redefined mars from a volcanic planet to a hydrologically active planet that may have harbored life understanding the history and habitability of mars depends on understanding the coupling of the atmosphere surface and subsurface sample return that brings back direct evidence from these diverse reservoirs is essential

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

ice sheet driven weathering input and water mass mixing in the nordic seas during the last 25 000 years abstract neodymium nd isotopes are a powerful proxy tool for reconstructing past changes in water mass mixing but reliable application of this proxy requires constraints on past changes of source water compositions a key region of the global deep water circulation system are the nordic seas which provide dense waters fundamental for the formation of north atlantic deep water nadw yet the nd isotope evolution of past deep waters in the nordic seas is so far poorly constrained here we present the first reconstructions of seawater nd isotope compositions extracted from marine sediments at two locations in the central and northern nordic seas covering the period from the last glacial to the present further insights into past changes in sediment provenance weathering inputs and water mass mixing are provided by complementary seawater and detrital strontium sr and lead pb isotope compositions our new data reveal that changes in source and magnitude of weathering inputs from the scandinavian and svalbard barents ice sheets sis and sbis respectively controlled the nd and pb isotope composition of the nordic seas deep waters during the last glacial period during the last glacial maximum lgm deep waters showed distinctly unradiogenic nd and radiogenic pb isotope signatures most likely driven by weathering inputs of the sbis in contrast the deglaciation was characterized by enhanced sbis ice dynamics and or meltwater release delivering sediments from the distal eurasian shelves to the norwegian sea pulses of volcanogenic sediment supply changed the deep water nd isotope composition during heinrich stadials 1 2 and the bolling period as such the glacial deglacial nd and pb isotope evolution was markedly different in the nordic seas the north atlantic and the arctic oceans respectively during the holocene pb isotopes indicate synchronized weathering fluxes around the north atlantic whereas the influence of local weathering input on the nd isotope evolution of the deep nordic seas ceased instead the holocene nd isotope signal has been driven by the strength of the advection convection of water masses in the study area these new constraints on changes in the nordic seas provide important endmember information for nd isotope based reconstructions of nadw export downstream in the atlantic ocean

plio pleistocene evolution of water mass exchange and erosional input at the atlantic arctic gateway water mass exchange between the arctic ocean and the norwegian greenland seas has played an important role for the atlantic thermohaline circulation and northern hemisphere climate we reconstruct past water mass mixing and erosional inputs from the radiogenic isotope compositions of neodymium nd lead pb and strontium sr at ocean drilling program site 911 leg 151 from 906 m water depth on yermak plateau in the fram strait over the past 5 2 myr the isotopic compositions of past bottom waters were extracted from authigenic oxyhydroxide coatings of the bulk sediments neodymium isotope signatures obtained from surface sediments agree well with present day deepwater end signature of 11 0 0 2 prior to 2 7 ma the nd and pb isotope compositions of the bottom waters only show small variations indicative of a consistent influence of atlantic waters since the major intensification of the northern hemisphere glaciation at 2 7 ma the seawater nd isotope composition has varied more pronouncedly due to changes in weathering inputs related to the waxing and waning of the ice sheets on svalbard the barents sea and the eurasian shelf due to changes in water mass exchange and due to the increasing supply of ice rafted debris ird originating from the arctic ocean the seawater pb isotope record also exhibits a higher short term variability after 2 7 ma but there is also a trend toward more radiogenic values which reflects a combination of changes in input sources and enhanced incongruent weathering inputs of pb released from freshly eroded old continental rocks

geochemical response of the mid depth northeast atlantic ocean to freshwater input during heinrich events 1 to 4 heinrich events are intervals of rapid iceberg sourced freshwater release to the high latitude north atlantic ocean that punctuate late pleistocene glacials delivery of fresh water to the main north atlantic sites of deep water formation during heinrich events may result in major disruption to the atlantic meridional overturning circulation amoc however the simple concept of an amoc shutdown in response to each freshwater input has recently been shown to be overly simplistic here we present a new multi proxy dataset spanning the last 41 000 years that resolves four heinrich events at a classic mid depth north atlantic drill site employing four independent geochemical tracers of water mass properties boron calcium carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates we also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast north atlantic our data reveal distinct geochemical signatures for each heinrich event suggesting that the sites of fresh water delivery and or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released at no time during the last 41 kyr was the mid depth northeast north atlantic dominantly ventilated by southern sourced water instead we document persistent ventilation by glacial north atlantic intermediate water gnaiw albeit with variable properties signifying changes in supply from multiple contributing northern sources

the impact of sedimentary coatings on the diagenetic nd flux because ocean circulation impacts global heat transport understanding the relationship between deep ocean circulation and climate is important for predicting the ocean s role in climate change a common approach to reconstruct ocean circulation patterns employs the neodymium isotope compositions of authigenic phases recovered from marine sediments in this approach mild chemical extractions of these phases is thought to yield information regarding the end of the bottom waters that are in contact with the underlying sediment package however recent pore fluid studies present evidence for neodymium cycling within the upper portions of the marine sediment package that drives a significant benthic flux of neodymium to the ocean this internal sedimentary cycling has the potential to obfuscate any relationship between the neodymium signature recovered from the authigenic coating and the overlying neodymium signature of the seawater for this manuscript we present sedimentary leach results from three sites on the oregon margin in the northeast pacific ocean our goal is to examine the potential mechanisms controlling the exchange of nd between the sedimentary package and the overlying water column as well as the relationship between the end composition of authigenic sedimentary coatings and that of the pore fluid in our comparison of the neodymium concentrations and isotope compositions from the total sediment sediment leachates and pore fluid we find that the leachable components account for about half of the total solid phase nd therefore representing a significant reservoir of reactive nd within the sediment package based on these and other data we propose that sediment diagenesis determines the end of the pore fluid which in turn controls the end of the bottom water consistent with this notion despite having 1 to 2 orders of magnitude greater nd concentration than the bottom water the pore fluid is still 0 001 of the total nd reservoir in the upper sediment column therefore the pore fluid reservoir is too small to maintain a unique signature and instead must be controlled by the larger reservoir of nd in the reactive coatings in addition to achieve mass balance we find it necessary to invoke a cryptic radiogenic end of 10 trace mineral source of neodymium within the upper sediment column at our sites when present this cryptic trace metal results in more radiogenic pore fluid

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

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

consistently dated records from the greenland grip gisp2 and ngrip ice cores for the past 104 ka reveal regional millennial scale δ18o gradients with possible heinrich event imprint abstract we present a synchronization of the ngrip grip and gisp2 ice cores onto a master chronology extending back to 104 ka before present providing a consistent chronological framework for these three greenland records the synchronization aligns distinct peaks in volcanic proxy records and other impurity records chemo stratigraphic matching and assumes that these layers of elevated impurity content represent the same instantaneous event in the past at all three sites more than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash tephra tie points using the reference horizons we transfer the widely used greenland ice core chronology gicc05modelext to the two summit cores grip and gisp2 furthermore we provide gas chronologies for the summit cores that are consistent with the gicc05modelext timescale by utilizing both existing and new gas data ch4 concentration and 15n of n2 we infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was 10 greater at summit compared to at ngrip the 18o temperature proxy records from ngrip grip and gisp2 are generally very similar and display synchronous behaviour at climate transitions the 18o differences between summit and ngrip however changed slowly over the last glacial interglacial cycle and also underwent abrupt millennial to centennial scale variations we suggest that this observed latitudinal 18o gradient in greenland during the glacial period is the result of 1 relatively higher degree of precipitation with a pacific signature at ngrip 2 increased summer bias in precipitation at summit and 3 enhanced rayleigh distillation due to an increased source to site distance and a potentially larger source to site temperature gradient we propose that these processes are governed by changes in the north american ice sheet nais volume and north atlantic sea ice extent and or sea surface temperatures sst on orbital timescales and that changing sea ice extent and ssts are the driving mechanisms on shorter timescales finally we observe that maxima in the summit ngrip 18o difference are roughly coincident with prominent heinrich events this suggests that the climatic reorganization that takes place during stadials with heinrich events possibly driven by a southward expansion of sea ice and low ssts in the north atlantic are recorded in the ice core records

bottoms up sedimentary control of the deep north pacific ocean s end signature the ability to reconstruct past ocean currents is essential for determining ocean circulation9s role in global heat transport and climate change our understanding of the relationship between circulation and climate in the past allows us to predict the impact of future climate driven circulation changes one proposed tracer of past ocean circulation is the neodymium isotope composition e nd of ancient water masses however ambiguities in what governs the e nd distribution in the modern ocean hamper interpretations of this tracer here we present e nd values for marine pore fluids sediments and the overlying water column for three sites in the north pacific we find that ocean bottom water e nd e nd bw in the northeast pacific lies between the value expected for the water mass 3 3 and the measured e nd of sediment pore fluid e nd pw 1 8 moreover e nd pw resembles the e nd of the sediment combined these findings are consistent with recent assessments that sediment pore fluids may be a major source of rare earth elements to the ocean and suggest that the benthic flux of nd from pore fluids exerts the primary control over the deep ocean distribution of e nd

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

the origin of norwegian sea deep water a nearly homogeneous water mass the norwegian sea deep water is found below 2000 m depth in the norwegian and lofoten basins of the norwegian sea recent observations indicate that this water is a mixture of relatively cold and fresh greenland sea deep water with warmer saltier eurasian basin deep water from the arctic ocean we have found this mixture along the western and southern periphery of the greenland sea near the level where the pressure compensated densities of the parent water masses are equal the along isopycnal mixing produces a remarkably uniform water mass which can be traced only a short distance away from its entry into the norwegian sea through gaps in the mid ocean ridge north of jan mayen island direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

ocean circulation and freshwater pathways in the arctic mediterranean based on a combined nd isotope ree and oxygen isotope section across fram strait the water masses passing the fram strait are mainly responsible for the exchange of heat and freshwater between the nordic seas and the arctic ocean the arctic mediterranean am disentangling their exact sources distribution and mixing however is complex this work provides new insights based on a detailed geochemical tracer inventory including dissolved nd isotope end rare earth element ree and stable oxygen isotope 18o data along a full water depth section across fram strait we find that nd isotope and ree distributions in the open am primarily reflect lateral advection of water masses and their mixing seawater particle interactions exert important control only above the shelf regions as observed above the ne greenland shelf advection of northward flowing warm atlantic water aw is clearly reflected by an end signature of 11 7 and a nd concentration nd of 16 pmol kg in the upper 500 m of the eastern and central fram strait freshening and cooling of the aw on its way trough the am are accompanied by a continuous change towards more radiogenic end signatures e g 10 4 of dense arctic atlantic water this mainly reflects mixing with intermediate waters but also admixture of dense kara sea waters and pacific derived waters the more radiogenic end signatures of the intermediate and deep waters reaching 9 5 are mainly acquired in the sw nordic seas through exchange with basaltic formations of iceland and se greenland inputs of nd from svalbard are not observed and surface waters and nd on the svalbard shelf originate from the barents sea shallow southward flowing arctic derived waters 200 m form the core of the east greenland current above the greenland slope and can be traced by their relatively radiogenic end reaching 8 8 and elevated nd 21 to 29 pmol kg these properties are used together with 18o and standard hydrographic tracers to define the proportions of pacific derived 30 based on nd isotopes and atlantic derived waters as well as of river waters 8 shallow waters 150 m on the ne greenland shelf share some characteristics of arctic derived waters but exhibit less radiogenic end values reaching 12 4 and higher nd up to 38 pmol kg in the upper 100 m this suggests local addition of greenland freshwater of up to 6 in addition to these observations this study shows that the pronounced gradients in end signatures and ree characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the am

a multiproxy reconstruction of the evolution of deep and surface waters in the subarctic nordic seas over the last 30 000yr on the basis of various lithological mircopaleontological and isotopic proxy records covering the last 30 000 calendar years cal kyr the paleoenvironmental evolution of the deep and surface water circulation in the subarctic nordic seas was reconstructed for a climate interval characterized by intensive ice sheet growth and subsequent decay on the surrounding land masses the data reveal considerable temporal changes in the type of thermohaline circulation open water convection prevailed in the early record providing moisture for the fennoscandian barents ice sheets to grow until they reached the shelf break at 26 cal kyr and started to deliver high amounts of ice rafted debris ird into the ocean via melting icebergs low epibenthic 18o values and small sized subpolar foraminifera observed after 26 cal kyr may implicate that advection of atlantic water into the nordic seas occurred at the subsurface until 15 cal kyr although modern like surface and deep water conditions first developed at 13 5 cal kyr thermohaline circulation remained unstable switching between a subsurface and surface advection of atlantic water until 10 cal kyr when ird deposition and major input of meltwater ceased during this time two depletions in epibenthic 13c are recognized just before and after the younger dryas indicating a notable reduction in convectional processes despite an intermittent cooling at 8 cal kyr warmest surface conditions existed in the central nordic seas between 10 and 6 cal kyr however already after 7 cal kyr the present day situation gradually evolved verified by a strong water mass exchange with the arctic ocean and an intensifying deep convection as well as surface temperature decrease in the central nordic seas this process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal kyr and eventually to today s steep east west surface temperature gradient the time discrepancy between intensive vertical convection after 5 cal kyr but warmest surface temperatures already between 10 and 6 cal kyr strongly implicates that widespread postglacial surface warming in the nordic seas was not directly linked to the rates in deep water formation

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

neodymium isotopic composition of deep sea corals from the ne atlantic implications for past hydrological changes during the holocene the nd isotopic composition of deep sea corals lophelia pertusa and madrepora oculata located on the rockall bank at a depth of 747 m was investigated to reconstruct past hydrological changes of the north atlantic the coral 3nd values ranged from 15 4 to 11 9 and demonstrate strong and systematic changes during the holocene most likely reflecting changes in seawater 3nd the 3nd record displays a general trend with a small decrease from 14 1 to 15 2 during the time interval from 9400 to 6000 yrs followed by an abrupt increase in 3nd towards more radiogenic 3nd values ranging from 13 9 to 11 9 these variations imply strong changes in the relative proportions of upper intermediate waters originating in the subtropical and subpolar atlantic which are characterised today by 3nd of 10 4 11 5 and 15 respectively therefore we suggest that the 3nd of reef frameworks forming deep sea corals reveals strong evidence of systematic mid holocene changes in mid depth subpolar gyre circulation a wider eastward extension of the subpolar gyre induced by stronger westerlies and a less intense deepwater formation in the labrador sea occurred during the early mid holocene supposedly larger amounts of freshwater from the subpolar gyre were carried eastward underneath the nordic seas similar to today a freshening of the subpolar gyre may have been offset by a reinforcement of the nac and higher salinities of water masses contributing to the nordic inflow beyond 6000 yrs a weakening of the subpolar gyre triggered an extension of saline subtropical water masses to the eastern north atlantic increasing the potential for labrador sea deep convection and reducing the contribution of subpolar atlantic waters to the basin scale re circulation at the upper intermediate depth and to the nordic seas inflow such modifications could have affected deep water convective activity in the northern hemisphere through a redistribution of freshwater from the early holocene melting of northern hemisphere ice sheets

experimental evidence for mineral controlled release of radiogenic nd hf and pb isotopes from granitic rocks during progressive chemical weathering the role of accessory minerals in the incongruent release of hf and pb during continental weathering and its implications for the generation of distinct seawater isotope compositions is subject of debate while it has been suggested that radiogenic hf and pb isotope signatures released during the dissolution of rocks are controlled by the relative abundances of minerals with distinct isotope compositions and differences in their resistance to dissolution there has not been a comprehensive experimental investigation of these processes to date we carried out systematic sequential leaching experiments on fresh and partly weathered granitic rock samples as well as separated zircons from the central aar granite in switzerland combined with major and rare earth element concentrations our new quantitative experimental data reveal systematic preferential release of radiogenic nd hf and pb isotopes primarily controlled by dissolution characteristics of the host rock s easily dissolvable accessory and major minerals in particular apatite and sphene during weak chemical weathering moreover pb isotope signatures of incipient weathering conditions contrary to expectations indicate initial congruent release of pb from freshly exposed mineral surfaces that becomes subsequently incongruent during more advanced chemical weathering stages as well as enhanced physical weathering conditions the dissolution of major minerals i e feldspars becomes dominant for nd and pb isotope signatures whereas hf isotopes are still dominated by contributions from highly radiogenic accessories additional leaching experiments of zircon separates were performed to test the specific role of zircons for hf isotope compositions of riverine runoff it is demonstrated that zircon is more efficiently dissolved when physical weathering is enhanced this increased hf release originating from partial dissolution of zircons however is quantitatively not sufficient to explain less radiogenic hf isotope signatures in seawater during episodes of enhanced mechanical erosion alone moreover the observed addition of hf from the more congruent dissolution of the zircon free fractions of the parent rock due to enhanced physical weathering indicate that these minerals also play an important role in controlling hf isotope signatures released under deglacial conditions

pb isotopes and geochemical monitoring of arctic sedimentary supplies and water mass export through fram strait since the last glacial maximum 1 elemental and pb isotope measurements were performed on leachates and residues from surface sediments and two 50 cm cores mc04 and mc16 collected along a ne sw transect through fram strait geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the strait 1 the easternmost edge of the strait 2 the eastern part of the strait off the svalbard margins and 3 the western part of the strait influenced by supplies from svalbard the nordic seas with possible contributions from northwestern siberian margins and sea ice and water outflow from the arctic respectively core mc16 in the third domain beneath the outflowing arctic waters spans the last glacial maximum present interval sediments from this core were leached to obtain detrital residues and exchangeable leachates fractions detrital supplies to core mc16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in arctic sedimentary sources detrital 206pb 204pb and 208pb 206pb ratios illustrate two mixing trends trends a and b corresponding to the pre and post younger dryas yd intervals respectively these trends represent binary mixtures with a common end member canadian margins and either a siberian trend a or greenland trend b margin end member the yd is marked by an isotopic excursion toward the canadian end member suggesting a very active beaufort gyre possibly triggered by massive drainage of the laurentide ice sheet pb isotope compositions of leachates thought to represent the signature of the overlying water masses define a unique linear trend coincident with trend a this suggests that water masses acquired their signature through exchange with particulate fluxes along the canadian and siberian continental margins

authigenic pb isotopes from the laurentian fan changes in chemical weathering and patterns of north american freshwater runoff during the last deglaciation climate dependent chemical weathering trends have a strong impact on the dissolved pb isotopic composition of continental runoff during glacial terminations so that this tracer can be used to reconstruct the impact of the north american deglaciation on aspects of freshwater runoff and ocean chemistry here we present authigenic fe mn oxyhydroxide derived pb isotope records from lower laurentian fan sediments that trace the local deglacial continental runoff signal through the gulf of st lawrence we use these records to investigate changes in the pb isotopic composition of the north american runoff and their relationship to deglacial processes the new pb isotope records are very similar to those from the subtropical deep nw atlantic locations though the new data are at higher resolution and exhibit much greater amplitudes of change due to their laurentide ice sheet proximal setting unradiogenic compositions 206pb 204pb as low as 18 8 at 18 5 ka during the latest glacial change towards highly radiogenic compositions during the early holocene 206pb 204pb 20 1 at 11 2 ka late holocene 206pb 204pb values return to intermediate values around 206pb 204pb 19 6 these new data support previous inferences that the pb isotopic composition of the deep atlantic is controlled during deglaciation by changes in the pattern and intensity of continental chemical weathering in more detail the most significant change in the entire pb isotope record starts at 12 5 ka and lasts until about 11 ka this observation of strong pb isotopic changes across a climatically cold period in the north atlantic region suggests that at this location pb isotopic compositions recorded in deep marine authigenic fe mn oxyhydroxides not only trace deglacial changes in chemical weathering intensity but also highly depend on major freshwater runoff routes in interior north america our data suggest a gradual opening of the eastward freshwater runoff route in the course of the younger dryas

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

influence of brine formation on arctic ocean circulation over the past 15 million years the early oceanographic history of the arctic ocean is important in regulating and responding to climatic changes however constraints on its oceanographic history preceding the quaternary the past 1 8 myr have become available only recently because of the difficulties associated with obtaining continuous sediment records in such a hostile setting here we use the neodymium isotope compositions of two sediment cores recovered near the north pole to reconstruct over the past approx15 myr the sources contributing to arctic intermediate water a water mass found today at depths of 200 to 1 500 m we interpret high neodymium ratios for the period between 15 and 2 myr ago and for the glacial periods thereafter as indicative of weathering input from the siberian putoranan basalts into the arctic ocean arctic intermediate water was then derived from brine formation in the eurasian shelf regions with only a limited contribution of intermediate water from the north atlantic in contrast the modern circulation pattern with relatively high contributions of north atlantic intermediate water and negligible input from brine formation exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 myr we suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes