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

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

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

rootless shield and perched lava pond collapses at kīlauea volcano hawai i effusion rate is a primary measurement used to judge the expected advance rate length and hazard potential of lava flows at basaltic volcanoes the rapid draining of lava stored in rootless shields and perched ponds can produce lava flows with much higher local effusion rates and advance velocities than would be expected based on the effusion rate at the vent for several months in 2007 2008 lava stored in a series of perched ponds and rootless shields on k lauea volcano hawai i was released episodically to produce fast moving a lava flows several of these lava flows approached royal gardens subdivision and threatened the safety of remaining residents using time lapse image measurements we show that the initial time averaged discharge rate for one collapse triggered lava flow was approximately eight times greater than the effusion rate at the vent though short lived the collapse triggered a lava flows had average advance rates approximately 45 times greater than that of the p hoehoe flow field from which they were sourced the high advance rates of the collapse triggered lava flows demonstrates that recognition of lava accumulating in ponds and shields which may be stored in a cryptic manner is vital for accurately assessing short term hazards at basaltic volcanoes

neodymium isotope constraints on chemical weathering and past glacial activity in svalbard abstract neodymium nd isotopes in leached authigenic components of marine sediments have been increasingly used as a tracer of past ocean water masses despite the general assumption that the nd isotopic composition of solutes released during chemical weathering fingerprints the source rocks on continents preferential dissolution of easily dissolvable phases may result in significant deviations in nd isotopic composition between the solutes and the source rocks with potential implications for the utility of nd isotopes in paleoenvironmental studies here we present the nd isotopic compositions of leached and detrital fractions separated from bedrock and marine sediment samples from the svalbard archipelago our goal is to further understand the behaviour of nd isotopes during chemical weathering in glacial catchments and evaluate how glacier fluctuations and associated weathering congruency may have affected the export of dissolved nd isotope signatures to seawater our results confirm that terrestrial weathering on svalbard causes considerable nd isotopic decoupling between the leached and detrital fractions of fjord sediments end resulting from the preferential dissolution of marine precipitates in glaciated catchments dominated by sedimentary rocks we also show that the degree of nd isotopic decoupling has fluctuated in response to climate variability on svalbard during the holocene which is also as suggested by the occurrence of generally higher end values during periods of glacier advances in sediment cores retrieved from two different fjords dicksonfjorden and woodfjorden we posit that the high end values can be ascribed to incongruent chemical weathering of fresh rock flour produced by glacial abrasion this finding suggests that the degree of nd isotopic decoupling could be used as a new proxy for tracing glacial fluctuations and associated glacier derived nutrient inputs to the marine realm

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

rare earth elements and neodymium isotopes in sedimentary organic matter abstract we report rare earth element ree and neodymium nd isotope data for the organic fraction of sediments collected from various depositional environments i e rivers n 25 estuaries n 18 open ocean settings n 15 and cold seeps n 12 sedimentary organic matter som was extracted using a mixed hydrogen peroxide nitric acid solution 20 h2o2 0 02 m hno3 after removal of carbonate and oxy hydroxide phases with dilute hydrochloric acid 0 25 m hcl a series of experimental tests indicate that extraction of sedimentary organic compounds using h2o2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates however this contamination is expected to be minor for ree because measured concentrations in h2o2 leachates are about two orders of magnitude higher than in the above mentioned phases the mean ree concentrations determined in the h2o2 leachates for samples from rivers estuaries coastal seas and open ocean settings yield relatively similar levels with ree 109 86 ppm mean s n 58 the organic fractions leached from cold seep sediments display even higher concentration levels 285 150 ppm mean s n 12 the h2o2 leachates for most sediments exhibit remarkably similar shale normalized ree patterns all characterized by a mid ree enrichment compared to the other ree this suggests that the distribution of ree in leached sedimentary organic phases is controlled primarily by biogeochemical processes rather than by the composition of the source from which they derive e g pore river or sea water the nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions in contrast the som extracted from marine sediments display end values that typically range between the end signatures for terrestrial organic matter inferred from the analysis of the sedimentary detrital fractions and marine organic matter inferred from the analysis of local surface seawater a notable exception is the case of organic matter om fractions leached from cold seep sediment samples which sometimes exhibit end values markedly different from both terrigenous and surface seawater signatures this suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes recycling pore water ree characterized by a distinct isotopic composition overall our results confirm that organic matter probably plays an important role in the oceanic ree budget through direct scavenging and remineralization within the water column both the high ree abundances and the shape of shale normalized patterns for leached som also suggest that om degradation in sub surface marine sediments during early diagenesis could control to a large extent the distribution of ree in pore waters benthic fluxes of organic bound ree could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins neodymium isotopes could provide useful information for tracing the origin terrestrial versus marine and geographical provenance of organic matter with potential applications in paleoceanography in particular future studies should further investigate the potential of nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation

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

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

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

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

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

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

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

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

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

nd and pb isotopes in atlantic and pacific water masses before and after closure of the panama gateway two nd and pb isotope time series of hydrogenous ferromanganese crusts one from the tehuantepec ridge in the deep eastern equatorial pacific and the other from blake plateau in the shallow northwestern atlantic which cover the past 7 8 m y show no variations coincident with the final closure of the panama gateway estimated as ca 3 5 ma the record of the atlantic crust located in the present day gulf stream shows a shift in isotope composition from ca 8 to 5 ma that is explained by a diminishing supply of pacific water it is argued that the major restriction of water mass exchange through the panama gateway occurred before 5 ma and thus cannot serve as a direct cause of the onset of northern hemisphere glaciation the absence of a significant signature in the isotope records from the pacific crust suggests that the volume of water exchanged with the atlantic through shallow archipelagic straits of the gateway during the 3 4 m y prior to closure was too small to influence the radiogenic isotope composition of pacific deep water

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

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

testing the extraction of past seawater nd isotopic composition from north atlantic deep sea sediments and foraminifera neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components including fish teeth ferromanganese oxides extracted by acid reductive leaching cleaned foraminifera and foraminifera with fe mn oxide coatings here we compare nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera as well as from oxidatively reductively cleaned foraminiferal shells from sediment cores in the north atlantic sedimentary volcanic ash contributes a significant fraction of the nd when the ferro manganese fe mn oxide coatings are leached from bulk sediments reductive leachates of marine sediments from north atlantic core tops near iceland or directly downstream from iceland scotland overflow waters record nd values that are significantly higher than seawater indicating that volcanic material is easily leached by acid reductive methods the nd values from sites more distal to iceland are similar to modern seawater values showing little contamination from iceland derived volcanogenic material in all comparisons core top planktonic foraminifera nd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the nd isotopic signature of deep north atlantic water masses

in search of the 31 march 1761 earthquake and tsunami source earthquake catalogs for the iberian peninsula report three strong magnitude events in the eighteenth century 27 december 1722 1 november 1755 and 31 march 1761 these events have magnitudes greater than 7 and generated tsunamis that damaged the portuguese coasts however their source areas are controversial because of the lack of detailed and coherent historical descriptions the 31 march 1761 earthquake was felt in lisbon at noon alarming the inhabitants and throwing down ruins of the past 1 november 1755 earthquake according to several sources the earthquake was followed by a tsunami that was observed as far as cornwall united kingdom cork ireland and barbados caribbean the portuguese catalogs locate this event on the horseshoe abyssal plain south of gorringe bank and attribute a magnitude of 7 5 the caribbean tsunami catalog lander et al 2002 locates the event further north 37 n 10 w and estimates of its epicenter intensity as ix in this study we present a reappraisal of the available historical reports concerning the 1761 event a revision of the macroseismic intensities along iberia and the tsunami observations along the western portuguese and galicia coasts england ireland and the west indies with this dataset we use backward raytracing techniques to discuss the location of the event and its integration with one of the major tsunami generation areas in the western portuguese margin we conclude that the 31 march 1761 earthquake took place at 12 01 a m lisbon time its epicenter was located about 34 5 n 13 w and had a tsunami magnitude close to 8 5 online material felt reports from the 31 march 1761 earthquake

foraminiferal end in the deep north western subtropical pacific ocean tracing changes in weathering input over the last 30 000 years abstract this study focuses on the neodymium isotopic composition end of mixed planktonic foraminifera species in sediment cores collected on the north western margin of the south china sea scs and in the western equatorial pacific the aim was to identify temporal changes in the end of the upper circumpolar deep water ucdw during its northward penetration in the western subtropical pacific and to re evaluate the significance of deep water end changes at the northern margin of the scs over the past 25 kyr the past seawater end record derived from sediments of the subtropical western pacific displays a narrow range from 2 9 0 3 to 1 6 0 4 this suggests that the end of the ucdw is greatly modified during its northward penetration through the process of boundary exchange along the western volcanic margin of the south pacific and that the unradiogenic end signature of the ucdw observed in the south pacific about 6 has not been propagated beyond the equatorial pacific at least not over the last 25 kyr seawater end values obtained from the northern scs display large variations with values that are lower 6 8 0 3 to 5 6 0 2 for the last glacial period than for the late holocene 5 7 0 3 to 4 1 0 2 such glacial end cannot be attributed to a higher proportion of southern sourced water ssw as end values of the ucdw in the equatorial western pacific are more radiogenic than those observed in the scs the evolution of the seawater end values of the northern scs during the last glacial period and the last climatic transition is coeval with variations in the contribution of sediments from the pearl river the low sea level stand of the last glacial period resulted in a more proximal position of the pearl river mouth relative to core md05 2904 which a higher input of freshwater and in particular detrital sedimentary particles originating from the pearl river that partially dissolved during sinking led to a decrease in the seawater end along the north western margin of the scs enhanced rainfalls associated with intensified monsoon and more frequent typhoon activities during the early holocene climatic optimum from 9 to 7 cal kyr bp are linked to a decrease in sea surface salinity lower 18o values of planktonic foraminifera and a decrease in end values 6 2 0 3 induced by lithogenic nd input from pronounced freshwater and sediment discharge from distal rivers

seawater carbonate ion δ13c systematics and application to glacial interglacial north atlantic ocean circulation seawater carbonate ion and 13c are affected by many processes including biology air sea exchange alkalinity change and mixing between different water masses study of modern ocean data shows that deep ocean carbonate ion and 13c of dissolved inorganic carbon can be used together as useful tracers for deep water mass reconstructions in the past we present records of deep water carbonate ion concentration co32 changes of the north atlantic ocean water column since the last glacial quantitatively reconstructed using benthic foraminiferal boron calcium b ca ratios records from six cores over 1 to 4 km reveal that the carbonate chemistry of the glacial north atlantic was more stratified than the modern ocean with higher co32 by 20 30 mol kg 1 at 1 2 km and lower co32 by 20 mol kg 1 at sites deeper than 3 5 km producing an 800 m glacial shoaling of calcite saturation horizon comparison with benthic foraminiferal 13c and var epsilonnd of fe mn oxide leachates shows that the deep glacial waters with low co32 are consistent with a southern ocean source while those with high co32 but distinct 13c chemistry were supplied by two endemic sources one being the norwegian greenland sea ngs our carbonate ion results suggest that the glacial boundary between north and south sourced deep waters is at 2 8 km significantly deeper than 2 3 km estimated from benthic foraminiferal 13c weakened surface compensation inflow to the ngs promoted cooling and continental ice growth at north high latitude and a deeper boundary may reduce atmospheric co2 sequestration in the deep atlantic implying a greater role of other parts of the ocean

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

dynamic intermediate ocean circulation in the north atlantic during heinrich stadial 1 a radiocarbon and neodymium isotope perspective the last deglaciation was characterised by a series of millennial scale climate events that have been linked to deep ocean variability while often implied in interpretations few direct constraints exist on circulation changes at mid depths here we provide new constraints on the variability of deglacial mid depth circulation using combined radiocarbon and neodymium isotopes in 24 north atlantic deep sea corals their aragonite skeletons have been dated by uranium series providing absolute ages and the resolution to record centennial scale changes while transects spanning the lifetime of a single coral allow sub centennial tracer reconstruction our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid depth water column 1 7 2 5 km on timescales of less than 100 years during the latter half of heinrich stadial 1 the neodymium isotopic variability 14 5 to 11 0 ranges from the composition of the modern northern sourced waters towards more radiogenic compositions that suggest the presence of a greater southern sourced component at some times however in detail simple two component mixing between well ventilated northern sourced and radiocarbon depleted southern sourced water masses cannot explain all our data instead corals from 15 0 ka and 15 8 ka may record variability between southern sourced intermediate waters and radiocarbon depleted northern sourced waters unless there was a major shift in the neodymium isotopic composition of the northern endmember in order to explain the rapid shift towards the most depleted radiocarbon values at 15 4 ka we suggest a different mixing scenario involving either radiocarbon depleted deep water from the greenland iceland norwegian seas or a southern sourced deep water mass since these mid depth changes preceded the bolling allerod warming and were apparently unaccompanied by changes in the deep atlantic they may indicate an important role for the intermediate ocean in the early deglacial climate evolution

ocean ventilation and sedimentation since the glacial maximum at 3 km in the western north atlantic 1 stable isotope sedimentological and radiocarbon data from cores at 3 km water depth on the blake ridge western subtropical north atlantic reveal the history of deep water ventilation since the last glacial maximum lgm bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment but the sand flux mostly foraminifera was nearly identical at a given time this suggests that the rain rate of foraminifera mostly planktonic was constant that transport of foraminifera was negligible and that current controlled differences in clay and silt transport drive bulk accumulation in two of the cores flux peaks in the benthic foraminifera cibicidoides and uvigerina peregrina occurred during the younger dryas yd cold event and at 18 2 19 6 21 1 25 0 and 28 1 ka radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was 1000 years during the yd and for older events it was as great as 2000 years these results contrast with holocene ventilation which was 500 years and 700 years at 1500 years and 7100 years before present respectively

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

reconstructing seawater circulation on the moroccan shelf of gondwana during the late devonian evidence from nd isotope composition of conodonts 1 the nd isotope composition of conodonts is used for the first time as a paleoceanographic proxy to reconstruct seawater circulation conodonts from two stratigraphic levels in the eastern anti atlas the lower part of the frasnian zone 11 base of the kellwasser facies and the boundary interval of the uppermost crepida rhomboidea zones top of the kellwasser facies were selected for reconstruction of seawater circulation on the moroccan shelf of gondwana during late devonian times the recognized lateral variations in nd values are in very good agreement with current related sedimentary features they provide evidence for communication of the moroccan shelf with the rheic ocean to the southwest and with the variscan sea to the north in the frasnian the general seawater flow was directed from the southwest to the east and was influenced by a local riverine input of low radiogenic nd from the south the west african craton and or the pan african ougarta belt and from the northwest the precambrian basement of the anti atlas the combined set of nd isotopic records and directional data from the middle famennian reveals a circulation pattern different from that of the frasnian it was dominated by a general westward flow with a countercurrent in the central tafilalt area the establishment of a new circulation system during the famennian suggests essential changes in paleogeography of the western part of the variscan realm

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

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

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

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

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

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

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

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

oscillating glacial northern and southern deep water formation from combined neodymium and carbon isotopes abstract while ocean circulation is driven by the formation of deep water in the north atlantic and the circum antarctic the role of southern sourced deep water formation in climate change is poorly understood here we address the balance of northern and southern sourced waters in the south atlantic through the last glacial period using neodymium isotope ratios of authigenic ferromanganese oxides in thirteen deep sea cores from throughout the south atlantic the data indicate that northern sourced water did not reach the southern ocean during the late glacial and was replaced by southern derived intermediate and deep waters the high resolution neodymium isotope record 300 yr sample spacing from two spliced deep cape basin sites indicates that over the last glacial period northern sourced water mass export to the southern ocean was stronger during the major greenland millennial warming intervals and southern hemisphere cool periods and particularly during the major interstadials 8 12 and 14 northern sourced water mass export was weaker during greenland stadials and reached minima during heinrich events the benthic foraminiferal carbon isotopes in the same cape basin core reflect a partial control by southern hemisphere climate changes and indicate that deep water formation and ventilation occurred in the southern ocean during major greenland cooling intervals stadials together neodymium isotopes and benthic carbon isotopes provide new information about water mass sourcing and circulation in deep southern ocean waters during rapid glacial climate changes combining carbon and neodymium isotopes can be used to monitor the relative proportion of northern and southern sourced waters in the cape basin to gain insight into the processes which control the carbon isotopic composition of deep waters in this study we show that deep water formation and circulation was more important than biological productivity and nutrient regeneration changes for controlling the carbon isotope chemistry of antarctic bottom water during millennial scale glacial climate cycles this observation also lends support to the hypothesis that ocean circulation is linked to interhemispheric climate changes on short timescales and that ventilation in the glacial ocean rapidly switched between the northern and southern hemisphere on millennial timescales

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

reorganization of the upper ocean circulation in the mid holocene in the northeastern atlantic a micropaleontological investigation was conducted on two sediment cores from the reykjanes ridge rr core lo09 14 59 12 30 n 31 05 94 w and the faroe shetland channel fsc core hm03 133 25 60 06 55 n 06 04 18 w to document hydrographical changes of the north atlantic current nac during the holocene dinocyst and coccolith assemblages were analyzed and quantitative reconstructions of sea surface temperatures ssts and sea surface salinities ssss were conducted based on dinocyst assemblages both proxies suggest a major reorganization of surface circulation patterns in the northeastern north atlantic between 7 and 5 4 ka bp at both sites ssss before 6 5 7 ka bp were lower than during the mid late holocene suggesting dispersal of meltwater through the nac long term trends of ssts however show higher than present summer ssts on the rr from 9 3 to 6 ka bp and lower than present ssts in the fsc until ca 5 4 ka bp the contrasted sst trends at the two sites suggest that decreasing summer

influence of the amazon river on the nd isotope composition of deep water in the western equatorial atlantic during the oligocene miocene transition highlights records of seawater endend are highly unradiogenic across the omt at ceara rise strong influence of amazon particulate nd on seawater endend at ceara rise point sourced riverine nd influences seawater far from continental shelf regional sedimentary nd flux can be confused with water mass mixing signals abstract dissolved and particulate neodymium nd are mainly supplied to the oceans via rivers dust and release from marine sediments along continental margins this process together with the short oceanic residence time of nd gives rise to pronounced spatial gradients in oceanic 143nd 144nd ratios endend however we do not yet have a good understanding of the extent to which the influence of riverine point source nd supply can be distinguished from changes in mixing between different water masses in the marine geological record this gap in knowledge is important to fill because there is growing awareness that major global climate transitions may be associated not only with changes in large scale ocean water mass mixing but also with important changes in continental hydroclimate and weathering here we present endend data for fossilised fish teeth planktonic foraminifera and the fe mn oxyhydroxide and detrital fractions of sediments recovered from ocean drilling project odp site 926 on ceara rise situated approximately 800 km from the mouth of the river amazon our records span the mi 1 glaciation event during the oligocene miocene transition omt 23 ma we compare our endend records with data for ambient deep atlantic northern and southern component waters to assess the influence of particulate input from the amazon river on nd in ancient deep waters at this site endend values for all of our fish teeth foraminifera and fe mn oxyhydroxide samples are extremely unradiogenic end 15end 15 much lower than the endend for deep waters of modern or oligocene miocene age from the north atlantic end 10end 10 and south atlantic end 8end 8 this finding suggests that partial dissolution of detrital particulate material from the amazon end 18end 18 strongly influences the endend values of deep waters at ceara rise across the omt we conclude that terrestrially derived inputs of nd can affect endend values of deep water many hundreds of kilometres from source our results both underscore the need for care in reconstructing changes in large scale oceanic water mass mixing using sites proximal to major rivers and highlight the potential of these marine archives for tracing changes in continental hydroclimate and weathering

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

hafnium and neodymium isotope variations in ne atlantic seawater the 176hf 177hf ratio of seawater is measured directly with 143nd 144nd in a composite vertical profile in the ne atlantic the value of hf of intermediate and deep water exhibits little variation and averages 1 0 0 8 surface water shows a wider range 5 7 to 3 3 while intermediate and deep water samples plot on or close to the seawater hf nd isotope array defined by ferromanganese deposits near surface seawater samples plot between the seawater and terrestrial rock hf nd arrays it is likely that the shallow water variability in hf arises from a short residence time of hf in surface water and isotopically heterogeneous inputs the difference between surface and intermediate deep water hf may be maintained by the release of surface scavenged hf at depth from a subset of sinking particles the composition of end at middepths reflects overlying surface water and water advected along isopycnals from areas where they outcrop in winter uniform hf values below 1000 m suggest the residence time of hf may be longer than that of nd the radiogenic isotopic composition of seawater hf relative to nd and terrestrial rocks suggests that minerals with high lu hf ratios may be preferentially weathered providing a source of radiogenic hf to the oceans

subpolar mode water formation traced by neodymium isotopic composition 1 the formation of subpolar mode water spmw is documented by combining neodymium isotopic composition nd ic as a conservative tracer with salinity temperature and o2 concentration nd ic reveals a more pronounced eastward extension of the labrador current particularly its subarctic intermediate water component than the other parameters nd ic also suggests that waters flowing through the denmark strait do not significantly contribute to the spmw formation a two end member mixing involving subarctic intermediate water and maybe ultimately labrador current water and north atlantic central water is proposed to explain spmw formation these results provide important insight into the processes controlling the nd ic in the north atlantic subpolar gyre which could provide a means for reconstructing the northward extension of the gulf stream in the past

millennial scale propagation of atlantic deep waters to the glacial southern ocean the compilation of changes in the magnetic properties at various sites distributed along the path of the deepwater mass in north atlantic shows large amplitude short term fluctuations reflecting changes in the strength of the north atlantic deep water nadw these changes which suggest a two mode deep glacial circulation dynamic are perfectly concurrent with air temperature changes over greenland they also share a similar pattern with those reported in the nd isotope ratios from the deep cape basin during the same time period greenland interstadials were accompanied by increased flow speed of nadw and relatively more nadw reaching the southern ocean while during greenland stadials and heinrich events both the north atlantic flow speed of nadw and its presence in the south atlantic were reduced it is demonstrated that both proxies are tracing the same water mass and their reliability for monitoring changes in the deepwater circulation is therefore clearly established after using the climatically independent geomagnetic assisted stratigraphy to put the northern and southern hemisphere records on the same age scale the south atlantic record appears to lag changes in north atlantic flow speeds by approximately 860 220 years during the most prominent and best defined cycles interstadials 12 and 8 although future work is needed this significant offset provides a first observation and tentative quantification of the time needed for glacial northern component water to mix downward and to flow from the north to the south atlantic

neodymium isotopic study of baffin bay water sources of ree from very old terranes water samples were collected from baffin bay and surrounding areas in order to evaluate this region as a potential source of nd from old continental material to atlantic water the isotopic data ranged from e nd 0 9 0 to 26 with most of the data around e nd 0 20 compared with values of north atlantic deep water nadw with e nd 0 13 5 the concentration of nd in baffin bay waters was as high as 6 10 12 g g compared with 2 5 10 12 g g for nadw the combination of low e nd and high nd concentration indicates that baffin bay may be a significant source of nd from very old crustal material a simple box model was used to evaluate the contribution to the nd budget of nadw and it was concluded that a substantial fraction of the nd from ancient crustal sources that is required to maintain the isotopic composition of nadw could be supplied by baffin bay outflow

north atlantic deep water export to the southern ocean over the past 14 myr evidence from nd and pb isotopes in ferromanganese crusts the intensity of north atlantic deep water nadw production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate here we present a new approach to reconstruct the overall strength of nadw export from the north atlantic to the southern ocean over the past 14 myr applying the deep water nd and pb isotope composition as recorded by ferromanganese crusts and nodules we present the first long term nd and pb isotope time series for deep southern ocean water masses which are compared with previously published time series for nadw from the nw atlantic ocean these data suggest a continuous and strong export of nadw or a precursor of it into the southern ocean between 14 and 3 ma an increasing difference in nd and pb isotope compositions between the nw atlantic and the southern ocean over the past 3 myr gives evidence for a progressive overall reduction of nadw export since the onset of northern hemisphere glaciation nhg the nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37 depending on location

southern ocean evidence for reduced export of north atlantic deep water during heinrich event 1 deep sea corals form unique high resolution archives of ocean circulation that can be dated using the decay of uranium to thorium they are abundant in the southern ocean and can provide unprecedented insights into ocean circulation and ocean chemistry on sub millennial time scales in areas where application of traditional paleoceanographic proxies is difficult here we present the first coupled neodymium nd isotope and radiocarbon data from deep sea corals in the drake passage southern ocean adding new constraints on ocean circulation during the last heinrich event h1 16 7 ka the modern day drake passage water column is homogeneous with respect to nd isotopes expressed in epsilon units nd its isotopic value of close to 9 is largely controlled by the mixture of north atlantic deep water and pacific deep water the aragonite of modern drake passage corals reflects this water column value whereas a fossil coral from h1 is significantly higher at 6 4 0 4 we interpret this 2 5 unit shift as a reduction in the influence of north atlantic sourced nd in the southern ocean during h1 this interpretation is supported by a series of radiocarbon analyses on the same sample and is consistent with a twofold or greater reduction in export of north atlantic waters from the atlantic basin combining analyses of radiocarbon and nd isotopes on u series dated deep sea coral skeletons holds great potential for quantification of past ocean ventilation rates

north atlantic deep water and climate variability during the younger dryas cold period the younger dryas the last large millennial scale climate oscillation 12 9 11 6 ka has been widely attributed to a massive meltwater discharge event that disrupted ocean circulation and plunged the circum north atlantic back into a near glacial state low resolution deep water reconstructions indicate lower north atlantic deep water nadw production during the younger dryas though the 14 c record requires some deep water production herein we reconstruct deep water mass variations using a southern gardar drift sediment core with an expanded younger dryas section we show that southern sourced water invaded the deep north atlantic to start the younger dryas but was replaced by nadw within 500 yr southern sourced waters briefly reappeared at the end of the younger dryas these deep water reorganizations to start and end the younger dryas suggest that increased meltwater fluxes were limited temporally and focused on regions where deep water convection occurred during the deglaciation

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

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

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