abrupt changes in deep atlantic circulation during the transition to full glacial conditions 1 six ocean drilling program odp sites in the northwest atlantic have been used to investigate kinematic and chemical changes in the western boundary undercurrent wbuc during the development of full glacial conditions across the marine isotope stage 5a 4 boundary 70 000 years ago sortable silt mean grain size ss measurements are employed to examine changes in near bottom flow speeds together with carbon isotopes measured in benthic foraminifera and planktic foraminiferal fragmentation as proxies for changes in water mass chemistry a depth transect of cores spanning 1 8 4 6 km depth allows changes in both the strength and depth of the wbuc to be constrained across millennial scale events ss measurements reveal that the flow speed structure of the wbuc during warm intervals interstadials was comparable to modern holocene conditions however significant differences are observed during cold intervals with higher relative flow speeds inferred for the shallow component of the wbuc 2 km depth during all cold stadial intervals including heinrich stadial 6 and a substantial weakening of the deep component 3 4 km during full glacial conditions our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation involving glacial north atlantic intermediate water that was quantitatively distinct from preceding cold stadial events furthermore our chemical proxy data show that the physical response of the wbuc during the last glacial inception was probably coupled to basin wide changes in the water mass composition of the deep northwest atlantic

the evolution of climatically driven weathering inputs into the western arctic ocean since the late miocene radiogenic isotope evidence highlights seawater hf nd pb isotopic evolution in the deep arctic ocean of the past 7 myr climatically driven changes in weathering inputs since 4 ma north american laurentide ice sheet runoff controlled the isotopic budget in the canada basin more congruent hf release due to glacial weathering conditions past arctic ocean water masses show larger isotopic differences than today abstract we present the first continuous records of dissolved radiogenic neodymium hafnium and lead isotope compositions of deep waters in the western arctic ocean spanning the time from the late miocene to the present the data were obtained from three hydrogenetic ferromanganese fe mn crusts recovered from seamounts along the northernmost edge of the northwind ridge in the canada basin from water depths of 2200 2400 and 3600 m dating the crusts using cosmogenic 10be documents undisturbed present day growth surfaces and yields growth rates between 27 and 2 2 mm myr the nd hf isotope time series of the three crusts show similar evolutions from endend ehf ehf of 8 5 4 in the oldest parts to 11 5 4 at the surfaces and a pronounced trend to less radiogenic values starting at 4 ma this coincided with a trend of the pb isotope evolution towards more radiogenic 206pb 204pb 207pb 204pb and 208pb 204pb it is inferred that climatically controlled changes in weathering regime and sediment transport along the north american continent were responsible for the major change of the radiogenic isotope composition of the arctic deep water adw in the canada basin based on these records we conclude that weathering inputs from the north american continent linked to enhanced glacial conditions started to increase and to influence the radiogenic isotope composition of adw 4 million years ago and were further intensified at 1 ma these new time series differ markedly from the radiogenic isotope evolution of arctic intermediate water recorded on the lomonosov ridge and suggest that much larger isotopic differences between the water masses of the arctic ocean than today prevailed in the past

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

north atlantic versus southern ocean contributions to a deglacial surge in deep ocean ventilation past glacial interglacial climate transitions were accompanied by millennial scale pulses in atmospheric co2 that are widely thought to have resulted from the release of co2 via the southern ocean however direct proxy evidence for a southern ocean role in regulating past ocean atmosphere co2 exchange is scarce here we use combined radiocarbon and neodymium isotope measurements from the last deglaciation to confirm greatly enhanced overturning and or air sea exchange rates relative to today in particular during the bolling allerod warm interval we show that this deglacial pulse in ocean ventilation was not driven by the north atlantic overturning alone and must have involved an increase in the ventilation of southern sourced deep waters our results thus confirm the removal of a physical and or dynamical barrier to effective air sea co2 exchange in the southern ocean during deglaciation and highlight the antarctic region as a key locus for global climate carbon cycle feedbacks

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

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

boundary scavenging at the east atlantic margin does not negate use of 231pa 230th to trace atlantic overturning abstract the 231 pa 230 th method is a promising tool to reconstruct ocean circulation over the past glacial interglacial cycle however marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of atlantic meridional overturning circulation amoc by influencing the fractionation between the in situ produced 231 pa and 230 th in ocean water here we present 231 pa 230 th down core profiles from high particle flux areas off namibia and senegal covering the past 35 ka the 231 pa 230 th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses our results show that sedimentary 231 pa 230 th in the eastern atlantic margin is linked to particle flux but controlled primarily by the mode of the amoc our data suggest that during the past 30 ka the high productivity eastern margin was not capable of importing and storing significant amounts of 231 pa from the open ocean consequently the applicability of the 231 pa 230 th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231 pa sink

evolution of the deep atlantic water masses since the last glacial maximum based on a transient run of ncar ccsm3 during the last deglaciation from approximately 21 to 11 thousand years ago the high latitudes of the atlantic ocean underwent major changes besides the continuous warming the polar and subpolar ocean surface received a large amount of meltwater from the retracting ice sheets these changes in temperature and salinity affected deep waters such as the antarctic bottom water aabw and the north atlantic deep water nadw which are formed in the southern ocean and in the northern north atlantic respectively in this study we present the evolution of the physical properties and distribution of the aabw and the nadw since the last glacial maximum using the results of a transient simulation with ncar ccsm3 in this particular model scenario with a schematic freshwater forcing we find that modern nadw with its characteristic salinity maximum at depth was absent in the beginning of the deglaciation while its intermediate version glacial north atlantic intermediate water gnaiw was being formed gnaiw was a cold and relatively fresh water mass that dominated intermediate depths between 60 and 20 n at this time most of the deep and abyssal atlantic basin was dominated by aabw within the onset of the bolling allerod period at nearly 15 thousand years ago ka gnaiw expanded southwards when the simulated meridional overturning circulation overshoots the transition between gnaiw and nadw ocurred after that when aabw was fresh enough to allow nadw to sink deeper in the water column when the nadw appears 11 ka aabw retracts and is constrained to lie near the bottom

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

comparison of methods to determine q in shallow marine sediments from vertical reflection seismograms four methods for the determination of q in marine sediments are compared two traditional methods i e the risetime and the spectral ratio method and two newly established ones the spectrum modeling and the wavelet modeling method in the latter one q and the reflection time t are determined simultaneously which gives a much better accuracy for t than reading it from the seismogram the risetime and the spectral ratio methods are used for obtaining q directly from the data the principle of the modeling methods is to calculate the effect of absorption and dispersion on a reference wavelet or its spectrum for various values of q and the best fit between the observed and the calculated data leads to the optimum result numerical tests on synthetic data show that a precision of more than 25 for data containing noise or superposed arrivals can hardly be achieved in any case wavelet modeling is the superior method application to data from a vertical reflection profile in the baltic sea yields q in the range of 15 100 for different layers which is to be expected in the sedimentary environment of this area

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

influence of ocean circulation and benthic exchange on deep northwest atlantic nd isotope records during the past 30 000 years neodymium nd isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance to better constrain the controls of water mass provenance and nonconservative effects on the archived nd isotope signal we present a new depth transect of nd isotope reconstructions from the blake bahama outer ridge along the north american continental margin covering the past 30 ka we investigated five sediment cores that lie directly within the main flow path of the deep western boundary current a major advection route of north atlantic deep water we found offsets between core tops and seawater nd isotopic compositions that are observed elsewhere in the northwest atlantic a possible explanation for this is the earlier suggested redistribution of sediment by nepheloid layers at intermediate as well as abyssal depths transporting material downslope and along the continental margin these processes potentially contributed to nd isotope excursions recorded in northwest atlantic sediment cores during the bolling allerod and early holocene an atlantic wide comparison of nd isotope records shows that the early holocene excursions had an additional contribution from conservative advection of unradiogenic dissolved nd nevertheless the trends of the nd isotope records are in general agreement with previous reconstructions of water mass provenance from the entire atlantic and also reveal millennial scale changes during the last deglaciation in temporal high resolution which have rarely been reported before further the new records confirm that during cold periods the northwest atlantic was bathed by an increased contribution of southern sourced water

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

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

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

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

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

stable isotope genealogy of meteorites one of the oldest problems in meteoritics is that of taxonomically grouping samples in recent years the use of isotopes particularly oxygen isotopes has proved very successful in this respect other light element systematics potentially can perform the same function for example nitrogen in iron meteorites and nitrogen and carbon in ureilites and snc meteorites these measurements will serve to extend and augment existing classification schemes and provide clues to the nature of meteorite parent bodies they can also aid in the recognition of the isotopic signatures relating to inaccessible regions of the earth

the influence of particle composition and particle flux on scavenging of th pa and be in the ocean we have examined the relative affinity of th pa and be for sorption from seawater onto particles of variable composition opal carbonate lithogenic particles and organic carbon nuclide concentrations in particles collected from time series sediment traps were normalized by the dissolved nuclide concentration in the overlying water column in order to compute partition coefficients under conditions spanning a wide range of particle flux and particle composition our results suggest that the affinity of particles for pa and be increases with their increasing opal content and decreasing carbonate content while the affinity of particles for th increases with increasing carbonate content and decreases with increasing opal content we find no correlation between the aluminosilicate content of particles and their affinity for scavenging of any of these elements extrapolating to a pure caco3 end member the partition coefficient for th 9 0 106 g g 1 is 40 times greater than for pa and roughly 100 times greater than for be whereas for a pure opal end member the partition coefficient for th 3 9 105 g g 1 is slightly less than that for pa and be partition coefficients decrease with increasing particle flux in open ocean settings but not in an ocean margin region this kinetic effect reflects the increasing contribution of unaltered surface material reaching the sediment traps as particle flux increases the degree of fractionation between pa and th and between be and th depends on the opal carbonate rain ratio these results challenge the use of sedimentary 231pa 230th and 10be 230th ratios as simple proxies of particle flux however the strong dependence of nuclide scavenging on the opal carbonate rain ratio may provide a needed tool for reconstructing past changes in planktonic community composition

widespread and synchronous change in deep ocean circulation in the north and south atlantic during the late cretaceous modern thermohaline circulation plays a role in latitudinal heat transport and in deep ocean ventilation yet ocean circulation may have functioned differently during past periods of extreme warmth such as the cretaceous the late cretaceous 100 65 ma was an important period in the evolution of the north atlantic ocean characterized by opening ocean gateways long term climatic cooling and the cessation of intermittent periods of anoxia oceanic anoxic events oaes however how these phenomena relate to deep water circulation is unclear we use a proxy for deep water mass composition neodymium isotopes end to show that at north atlantic odp site 1276 deep waters shifted in the early campanian 78 83 ma from end values of 7 to values of 9 consistent with a change in the style of deep ocean circulation but 10 myr after a change in bottom water oxygenation conditions a similar but more poorly dated trend exists in end data from dsdp site 386 the campanian end transition observed in the north atlantic records is also seen in the south atlantic and proto indian ocean implying a widespread and synchronous change in deep ocean circulation although a unique explanation does not exist for the change at present we favor an interpretation that invokes late cretaceous climatic cooling as a driver for the formation of southern component water which flowed northward from the southern ocean and into the north atlantic and proto indian oceans

changes in pacific ocean circulation following the miocene onset of permanent antarctic ice cover we integrate micropaleontological and geochemical records benthic stable isotopes neodymium isotopes benthic foraminiferal abundances and xrf scanner derived elemental data from well dated pacific ocean successions 15 12 7 ma to monitor circulation changes during the middle miocene transition into a colder climate mode with permanent antarctic ice cover together with previously published records our results show improvement in deep water ventilation and strengthening of the meridional overturning circulation following major ice expansion at 13 9 ma neodymium isotope data reveal however that the provenance of intermediate and deep water masses did not change markedly between 15 and 12 7 ma we attribute the increased 13c gradient between pacific deep and intermediate water masses between 13 6 and 12 7 ma to more vigorous entrainment of pacific central water into the wind driven ocean circulation due to enhanced production of intermediate and deep waters in the southern ocean prominent 100 kyr ventilation cycles after 13 9 ma reveal that the deep pacific remained poorly ventilated during warmer intervals at high eccentricity whereas colder periods low eccentricity were characterized by a more vigorous meridional overturning circulation with enhanced carbonate preservation the long term 13c decline in pacific intermediate and deep water sites between 13 5 and 12 7 ma reflects a global trend probably related to a re adjustment response of the global carbon cycle following the last 400 kyr carbon maximum cm6 of the monterey excursion

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

how well would modern day oceanic property distributions be known with paleoceanographic like observations author s gebbie g streletz gj spero hj abstract 2016 american geophysical union all rights reserved compilations of paleoceanographic observations for the deep sea now contain a few hundred points along the oceanic margins mid ocean ridges and bathymetric highs where seawater conditions are indirectly recorded in the chemistry of buried benthic foraminiferal shells here we design an idealized experiment to test our predictive ability to reconstruct modern day seawater properties by considering paleoceanographic like data we attempt to reconstruct the known modern day global distributions by using a state estimation method that combines a kinematic tracer transport model with observations that have paleoceanographic characteristics when a modern like suite of observations practical salinity seawater 18o 13cdic po4 no3 and o2 is used from the sparse paleolocations the state estimate is consistent with the withheld data at all depths below 1500 m suggesting that the observational sparsity can be overcome physical features such as the interbasin gradients in deep 13cdic and the vertical structure of atlantic 13cdic are accurately reconstructed the state estimation method extracts useful information from the pointwise observations to infer distributions at the largest oceanic scales at least 10 000 km horizontally and 1500 m vertically and outperforms a standard optimal interpolation technique even though neither dynamical constraints nor constraints from surface boundary fluxes are used when the sparse observations are more realistically restricted to the paleoceanographic proxy observations of 13c 18o and cd ca however the large scale property distributions are no longer recovered coherently at least three more water mass tracers are likely needed at the core sites in order to accurately reconstruct the large scale property distributions of the last glacial maximum

changes in northeast atlantic hydrology during termination 1 insights from celtic margin s benthic foraminifera abstract using benthic foraminiferal based proxies in sediments from the celtic margin we provide a well dated record across the last deglaciation of the channel river dynamics and its potential impact on the hydrology of intermediate water masses along the european margin our results describe three main periods 1 during the last glacial maximum and before 21 ka bp the predominance of meso oligotrophic species suggests well oxygenated water masses after 21 ka bp increasing proportions of eutrophic species related to enhanced riverine supply occurs concomitantly with early warming in greenland air temperatures 2 a thick laminated deposit occurring during a 1500 years long period of seasonal melting of the european ice sheet eis is associated with early heinrich stadial 1 period 18 2 16 7 ka bp the benthic proxies describe low salinity episodes cold temperatures severe dysoxia and eutrophic conditions on the sea floor perhaps evidence for cascading of turbid meltwaters 3 during late hs1 16 7 14 7 ka bp conditions on the celtic margin s seafloor changed drastically and faunas indicate oligotrophic conditions as a result of the ceasing of eis meltwater discharges while surface waters were cold due to laurentide ice sheet lis icebergs releases increasing benthic mg ca ratios reveal a progressive warming of intermediate water masses whereas oxygen proxies indicate overall well oxygenated conditions in addition to the well known effect of eis meltwaters on surface waters in the celtic margin our benthic record documents a pronounced impact on intermediate water depths during hs1 which coincided with major amoc disruptions

deglacial diatom productivity and surface ocean properties over the bermuda rise northeast sargasso sea 1 diatom assemblages document surface hydrographic changes over the bermuda rise between 19 2 and 14 5 ka subtropical diatom species and chaetoceros resting spores dominate the flora as in north atlantic productive regions today from 16 9 to 14 6 ka brackish and fresh water diatoms are common and their contribution is generally coupled with total diatom abundance this same interval also contains rare grains of ice rafted debris coupling between those proxies suggests that successive discharge of icebergs might have stimulated productivity during heinrich event 1 h1 iceberg migration to the subtropics likely created an isolated environment involving turbulent mixing upwelled water and nutrient rich meltwater supporting diatom productivity in an otherwise oligotrophic setting in addition the occurrence of mode water eddies likely brought silica rich waters of southern ocean origin to the euphotic zone the persistence of lower salinity surface water beyond the last ice rafting suggests continued injection of fresh water by cold core rings and advection around the subtropical gyre these results indicate that opal productivity may have biased estimates of meridional overturning based on 231pa 230th ratios in bermuda rise sediments during h1

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

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

a poisoned chalice deep sea sediments often carry information about past temperatures in the upper ocean directly above their location but as mccave cautions in this perspective interpretation of the sediments can be complicated by deep sea processes for example material transported laterally in the deep ocean may distort the upper ocean signal in the sediments a report by ohkouchi illustrates such processes at bermuda rise the study yields a detailed understanding of deep sea sediment transport processes aiding the interpretation of sediment records at this site and sounding a warning for others

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

early holocene laurentide ice sheet deglaciation causes cooling in the high latitude southern hemisphere through oceanic teleconnection the impact of the early holocene laurentide ice sheet lis deglaciation on the climate at southern hemisphere high latitudes is studied in three transient simulations performed with a global climate model of the coupled atmosphere ocean vegetation system considering the lis deglaciation we quantify separately the impacts of the background meltwater fluxes and the changes in topography and surface albedo in our model the meltwater input into the north atlantic results in a substantial weakening of the atlantic meridional overturning circulation associated with absence of deep convection in the labrador sea northward ocean heat transport by the atlantic ocean is reduced by 28 this weakened ocean circulation leads to cooler north atlantic deep water nadw upwelling of this cool nadw in the southern ocean results in reduced surface temperatures by 1 degrees c to 2 degrees c here between 9 and 7 ka compared to an experiment without lis deglaciation poleward of the polar front zone this advective teleconnection between the southern and northern hemispheres overwhelms the effect of the classical bipolar seesaw mechanism these results provide an explanation for the relatively cold climatic conditions between 9 and 7 ka reconstructed in several proxy records from southern hemisphere high latitudes such as antarctic ice cores

oceanic forcing of penultimate deglacial and last interglacial sea level rise sea level histories during the two most recent deglacial interglacial intervals show substantial differences1 3 despite both periods undergoing similar changes in global mean temperature4 5 and forcing from greenhouse gases6 although the last interglaciation lig experienced stronger boreal summer insolation forcing than the present interglaciation7 understanding why lig global mean sea level may have been six to nine metres higher than today has proven particularly challenging2 extensive areas of polar ice sheets were grounded below sea level during both glacial and interglacial periods with grounding lines and fringing ice shelves extending onto continental shelves8 this suggests that oceanic forcing by subsurface warming may also have contributed to ice sheet loss9 12 analogous to ongoing changes in the antarctic13 14 and greenland15 ice sheets such forcing would have been especially effective during glacial periods when the atlantic meridional overturning circulation amoc experienced large variations on millennial timescales16 with a reduction of the amoc causing subsurface warming throughout much of the atlantic basin9 12 17 here we show that greater subsurface warming induced by the longer period of reduced amoc during the penultimate deglaciation can explain the more rapid sea level rise compared with the last deglaciation this greater forcing also contributed to excess loss from the greenland and antarctic ice sheets during the lig causing global mean sea level to rise at least four metres above modern levels when accounting for the combined influences of penultimate and lig deglaciation on glacial isostatic adjustment this excess loss of polar ice during the lig can explain much of the relative sea level recorded by fossil coral reefs and speleothems at intermediate and far field sites a reduction in the strength of the atlantic meridional overturning circulation initiated during the penultimate deglaciation led to excess polar ice losses contributing to higher sea levels during the last interglacial period

nd isotopic structure of the pacific ocean 70 30 ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world the oceanic meridional overturning circulation moc is a crucial component of the climate system impacting heat and nutrient transport and global carbon cycling past greenhouse climate intervals present a paradox because their weak equator to pole temperature gradients imply a weaker moc yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients to investigate the mode of moc that operated during the early cenozoic we compare new nd isotope data with nd tracer enabled numerical ocean circulation and coupled climate model simulations assimilation of new nd isotope data from south pacific deep sea drilling project and ocean drilling program sites 323 463 596 865 and 869 with previously published data confirm the hypothesized moc characterized by vigorous sinking in the south and north pacific 70 to 30 ma compilation of all pacific nd isotope data indicates vigorous distinct and separate overturning circulations in each basin until 40 ma simulations consistently reproduce south pacific and north pacific deep convection over a broad range of conditions but cases using strong deep ocean vertical mixing produced the best data model match strong mixing potentially resulting from enhanced abyssal tidal dissipation greater interaction of wind driven internal wave activity with submarine plateaus or higher than modern values of the geothermal heat flux enable models to achieve enhanced moc circulation rates with resulting nd isotope distributions consistent with the proxy data the consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

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

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

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

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

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

incursions of southern sourced water into the deep north atlantic during late pliocene glacial intensification the circulation and internal structure of the oceans exert a strong influence on earth s climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss circulation change particularly in the atlantic ocean is widely suggested to have been instrumental in the intensification of northern hemisphere glaciation when large ice sheets first developed on north america and eurasia during the late pliocene approximately 2 7 million years ago yet the mechanistic link and cause effect relationship between ocean circulation and glaciation are debated here we present new records of north atlantic ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the last glacial to holocene 35 5 thousand years ago and the late pliocene to earliest pleistocene 3 3 2 4 million years ago our data show no secular change instead we document major southern sourced water incursions into the deep north atlantic during prominent glacials from 2 7 million years ago our results suggest that atlantic circulation acts as a positive feedback rather than as an underlying cause of late pliocene northern hemisphere glaciation we propose that once surface southern ocean stratification and or extensive sea ice cover was established cold stage expansions of southern sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean helping to increase the amplitude of glacial cycles

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

thermohaline circulation crisis and impacts during the mid pleistocene transition the mid pleistocene transition mpt marked a fundamental change in glacial interglacial periodicity when it increased from 41 thousand year to 100 thousand year cycles and developed higher amplitude climate variability without substantial changes in the milankovitch forcing here we document by using nd isotopes a major disruption of the ocean thermohaline circulation thc system during the mpt between marine isotope stages miss 25 and 21 at 950 to 860 thousand years ago which effectively marks the first 100 thousand year cycle including an exceptional weakening through a critical interglacial mis 23 at 900 thousand years ago its recovery into the post mpt 100 thousand year world is characterized by continued weak glacial thc the mpt ocean circulation crisis facilitated the coeval drawdown of atmospheric co2 and high latitude ice sheet growth generating the conditions that stabilized 100 thousand year cycles

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

more reducing bottom water redox conditions during the last glacial maximum in the southern challenger deep mariana trench western pacific driven by enhanced productivity abstract the modern southern mariana trench is characterized by oligotrophic surface waters resulting in low primary productivity and well oxygenated bottom waters this study investigates changes in the redox conditions of bottom waters in the southern mariana trench during the last glacial maximum lgm and their potential causes we measured major trace and rare earth elements ree in three gravity cores gc03 gc04 and gc05 and one box core bc11 retrieved from the southern challenger deep at water depths from 5289 to 7118 m the upper sediment layers of both gc05 and bc11 are dominated by valve fragments of the giant diatom ethmodiscus rex forming laminated diatom mats ldms 14c ams dates of bulk organic matter show that the ldms accumulated between 18 4 and 21 8 kyr b p corresponding to the lgm modest enrichments of u and mo along with weak or absent ce anomalies in the ldm point to suboxic conditions during the lgm in contrast non ldm samples exhibit little to no enrichment of redox sensitive elements as well as negative ce anomalies indicating deposition under oxic bottom water conditions the ce anomalies are considered valid proxies for bottom water redox conditions because ree signatures were acquired in the early diagenetic environment as indicated by strong p ree correlations and middle ree enrichment associated with early diagenetic cycling of fe mn oxyhydroxides in the sediment column followed by capture of the ree signal by biogenic and or authigenic apatite we postulate that the more reducing bottom water conditions during the lgm were linked to increased primary productivity induced by enhanced asian dust input as shown in earlier studies the increased primary productivity associated with ethmodiscus rex blooms in the eastern philippine sea played a significant role in capturing atmospheric co2 during the lgm consequently the magnitude of atmospheric co2 sequestration by giant diatom blooms during the lgm may have been greater than previously envisaged

evolution of the stable carbon isotope composition of atmospheric co2 over the last glacial cycle we present new c measurements of atmospheric co covering the last glacial interglacial cycle complementing previous records covering terminations i and ii most prominent in the new record is a significant depletion in c atm of 0 5 occurring during marine isotope stage mis 4 followed by an enrichment of the same magnitude at the beginning of mis 3 such a significant excursion in the record is otherwise only observed at glacial terminations suggesting that similar processes were at play such as changing sea surface temperatures changes in marine biological export in the southern ocean so due to variations in aeolian iron fluxes changes in the atlantic meridional overturning circulation upwelling of deep water in the so and long term trends in terrestrial carbon storage based on previous modeling studies we propose constraints on some of these processes during specific time intervals the decrease in c atm at the end of mis 4 starting approximately 64 kyr b p was accompanied by increasing co this period is also marked by a decrease in aeolian iron flux to the so followed by an increase in so upwelling during heinrich event 6 indicating that it is likely that a large amount of c depleted carbon was transferred to the deep oceans previously i e at the onset of mis 4 apart from the upwelling event at the end of mis 4 and potentially smaller events during heinrich events in mis 3 upwelling of deep water in the so remained reduced until the last glacial termination whereupon a second pulse of isotopically light carbon was released into the atmosphere

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

evolution of antarctic intermediate water during the plio pleistocene and implications for global climate evidence from the south atlantic abstract formed in the southern ocean antarctic intermediate water aaiw plays a fundamental role in the modern climate system as an important sink for atmospheric co2 and as a mid depth conduit supplying nutrient rich waters to subtropical and tropical upwelling regions during the transition from warm pliocene greenhouse conditions to pleistocene icehouse conditions around 3 ma model simulations suggest dramatic circulation changes in the southern ocean aaiw formation region due to cooling and expanded sea ice cover around antarctica however the history and properties of aaiw over this time period are still poorly understood here we trace aaiw source water provenance temperature and salinity changes over the last 4 myr using nd isotopes of fe mn oxyhydroxide encrusted foraminifera benthic foraminiferal mg ca and stable isotopes from southwest atlantic dsdp site 516 our results show that modern aaiw properties emerged gradually over the last 3 myr as evidenced by gradual cooling 6 c and freshening of intermediate waters over this same interval end values decrease and diverge away from those of pacific sourced waters and converge on values of present day circumpolar deep water cdw these observations are in accordance with model simulations indicating increased deep vertical mixing at the polar front associated with sea ice extension these modified aaiw source waters penetrated increasingly northward into the atlantic at intermediate depths enhancing nutrient supply and contributing to surface cooling along subtropical coastal upwelling sites these circulation changes may have facilitated ocean co2 storage providing a positive feedback amplifying global cooling and intensification of northern hemisphere glaciation

greenland temperature response to climate forcing during the last deglaciation greenland ice core water isotopic composition 18 o provides detailed evidence for abrupt climate changes but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns we investigate greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean atmosphere climate model contrary to the traditional 18 o interpretation the younger dryas period was 4 5 2 c warmer than the oldest dryas due to increased carbon dioxide forcing and summer insolation the magnitude of abrupt temperature changes is larger in central greenland 9 to 14 c than in the northwest 5 to 9 c fingerprinting a north atlantic origin simulated changes in temperature seasonality closely track changes in the atlantic overturning strength and support the hypothesis that abrupt climate change is mostly a winter phenomenon

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

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

did north atlantic overturning halt 17 000 years ago models indicate that a complete shutdown of deep and intermediate water production is a possible consequence of extreme climate conditions in the northern north atlantic and the high ratio of 231pa to 230th on bermuda rise is evidence that this might have happened 17 ka during heinrich event 1 h1 however new radiocarbon data from bivalves that lived at 4 6 km on the bermuda rise during h1 lead to a different conclusion the bivalve data do indeed indicate ventilation of the deep western north atlantic was suppressed during h1 but not as much as it was during the last glacial maximum we propose that high diatom flux to the bermuda rise during h1 is at least in part responsible for increased 231pa 230th at that time although we cannot say for sure why opal production was so high in a gyre center location at that time increased leakage of silica rich waters from the southern ocean to the north atlantic is one possibility

multi proxy reconstruction of sea surface and subsurface temperatures in the western south atlantic over the last 75 kyr abstract millennial scale oscillations are known to be important in the climatic evolution of the atlantic basin but which internal processes originates these oscillations are still uncertain in this study we investigated how the greenland and antarctic climates affect the sw atlantic through basin wide oceanographic features such as the nadw formation and the agulhas leakage we reconstructed sea surface and subsurface temperatures sst and subt using three lipid based biomarker proxies uk 37 tex86 and ldi indexes from a sediment core nap 63 1 retrieved from the sw atlantic slope 24 8 s 44 3 w this location allowed us to evaluate the temperature oscillations of the brazil current without any terrigenous or upwelling derived biases both tex86 based and ldi based estimates represent the mean annual sst while the uk 37 based estimates represent the subt around 30 m water depth the periods with the most well mixed water column were observed during intervals of cooling orbital trends due to the time required to transfer the surface cooling to the subsurface the temperature reconstructions showed a general colder mis 3 when compared to the mis 4 they also showed evidence of a late response to deglaciation with its onset in the sw atlantic occurring in the middle of the last glacial maximum based on these reconstructions the nap 63 1 sst orbital scale trend seems to be linked to the antarctic climate influenced by local insolation changes these temperature records also presented a clear millennial periodicity around 8 kyr on this timescale the millennial oscillations in the sw atlantic s sst are likely linked to the nadw formation

limits on conservative behavior of nd isotopes in seawater assessed from analysis of fish teeth from pacific core tops abstract neodymium nd isotopes have become an accepted water mass tracer for paleoceanographic reconstructions however high rates of radiogenic nd input from volcanic islands arcs in the western equatorial pacific wep and the subarctic north pacific sanp can significantly alter the isotopic composition of ambient seawaters leading to questions about the conservative nature of nd isotopes in the pacific here we present the first comprehensive study of nd isotopes preserved in core top fossil fish teeth debris from 31 sites in the pacific to define the vertical and horizontal distributions of seawater nd isotopes and to test the reliability of nd isotopes as a water mass tracer in the pacific we found that nd isotopic values of northward flowing lower circumpolar deep water lcdw are significantly modified in the western central equatorial pacific and the sanp as a result of local radiogenic inputs from young circum pacific island arcs consequently modified lcdw with 5 end is created in the central equatorial pacific while recirculated north pacific deep water npdw acquires a radiogenic nd isotope value 2 end in the sanp nd isotopic ratios of fish teeth debris in the central north pacific plotted against salinity or phosphate concentration from the overlying bottom water produce a mixing envelope between modified lcdw and npdw indicating that these nd isotopic values represent the southern and northern sourced end member values for the central north pacific and that mixing of these water masses defines vertical profiles of nd isotopes in this region in the eastern equatorial pacific eep three water masses modified lcdw npdwsanp and npdwwestern pacific combine to produce nd isotopic values that reflect this conservative mixture therefore nd isotopes behave as a conservative water mass tracer in the central north pacific and the eep but high rates of lithogenic inputs from young circum pacific island arcs compromise the conservative behavior of nd isotopes in the wep and sanp

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

the neodymium isotopic composition of waters masses in the eastern pacific sector of the southern ocean the antarctic circumpolar current is one of the key components of ocean circulation and a knowledge of its isotopic composition is essential to the use of neodymium nd isotopes to trace circulation now and in the past here we present 57 new analyses of the nd isotopic composition of the water column in the eastern pacific sector of the southern ocean documenting both the variation in three dimensions as well as the controls on that variability nd isotopic data for the middle of the water column demonstrate the homogeneity of circumpolar deep water cdw at an end value of 8 7 0 1 this homogeneity reflects the large nd inventory in the acc flow and the degree to which this large inventory buffers the nd characteristics of the acc against extra oceanic inputs from the continents either via dust from the atmosphere or through dissolved and particulate material from the adjacent continents cdw upwells onto the amundsen sea shelf and even here its nd isotopic properties are close to conserved in the middle of the water column end 8 0 0 2 at 600 m at the top and bottom of the shelf water column however the nd isotopic and concentration characteristics are strongly modified to end as high as 4 5 all the shelf water column data obtained here are consistent with net addition of nd to bottom and surface waters with a contrasting isotopic composition that is matched by local sediment end 1 to 2 followed by conservative mixing of that water into intermediate levels mixing with this shelf composition also leads to significant modification of open ocean surface water nd isotopic shift around 1 epsilon unit in the acc as it flows eastwards modification of open ocean bottom waters by interaction with sediment is more subtle but there is marked non conservative removal of nd accompanied by significant changes in isotopic composition in waters within 10 m of the seabed the new data demonstrate the conservativity of nd in the middle water column especially for such large volume flows as the acc though boundary exchange type processes are clearly important in this region and their imprint on both the shelf and open ocean surface water is significant there is no observable impact on the main core of cdw this finding augurs well for the use of nd isotopes as a conservative water mass tracer now and in the past for example these data suggest that the only likely control on the temporal variability of southern component deep water exported northwards into the atlantic through the last glacial cycle is variations in the input of north atlantic deep water in the atlantic sector on the other hand the data also suggest caution in the use of sedimentary archives of bottom water nd as records of deep water nd isotopic characteristics given the dramatic modification of bottom waters on the shelf and the more subtly non conservative behaviour in the open ocean bottom water that are both suggestive of modification of the nd characteristics of bottom waters by sediment

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

bathyal records of enhanced silicate erosion and weathering on the exposed luzon shelf during glacial lowstands and their significance for atmospheric co2 sink abstract we present a new high resolution multiproxy data set of mass accumulation rates sr nd isotopes as well as major and trace elements for the siliciclastic sediment fraction from international marine global change study core md06 3052 located on the continental slope of the western philippine sea we integrate our new data with published grain sizes and sea surface temperatures from the same core as well as with equatorial pacific sea level and east asian summer monsoon precipitation in order to constrain at high resolution changes in physical erosion and chemical weathering intensities on luzon and sediment source to sink processes we assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric co2 since 156 kyr bp sr nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on luzon 68 100 with a lesser contribution from asian dust 0 32 different indices indicate that stronger physical erosion and chemical weathering occurred during marine isotope stage mis 6 130 156 kyr bp as well as in the latter stage of mis 3 and mis 2 14 40 kyr bp the large sea level lowstands and associated significant exposure of continental shelf in the western philippine sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf furthermore we notice the relatively good coherence between chemical weathering intensities on luzon and global atmospheric co2 concentrations over these cold intervals we suggest that strengthening of chemical weathering of silicates on luzon and other tropical arcs within 20 of the equator during the quaternary glacial sea level lowstands may significantly contribute to the lowering of atmospheric co2 concentrations during ice ages we estimate that a significant fraction up to 16 i e 8 ppmv of all atmospheric co2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only 1 of the exorheic drainage area worldwide

on the relationship between nd isotopic composition and ocean overturning circulation in idealized freshwater discharge events using a cost efficient climate model the effect of changes in overturning circulation on neodymium isotopic composition nd is systematically examined for the first time idealized sequences of abrupt climate changes are induced by the application of periodic freshwater fluxes to the north atlantic na and the southern ocean so thus mainly affecting either the formation of north atlantic deep water nadw or antarctic bottom water aabw variations in nd reflect weakening and strengthening of the formation of nadw and aabw changes in ndof end members are relatively small relationships between nd and the strength of nadw or aabw are more pronounced for aabw than for nadw atlantic patterns of variations in nd systematically differ between na and so experiments additionally the signature of changes in nd in the atlantic and the pacific is alike in na but opposite in so experiments discrimination between na and so experiments is therefore possible based on the atlantic pattern of variations in nd and the contrariwise behavior of nd in the atlantic and the pacific in further experiments we examined the effect of variations in magnitudes of particle export fluxes within the examined range and although settling particles represent the only sink of nd their effects on nd are relatively small our results confirm the large potential of nd as a paleocirculation tracer but also indicate its limitations of quantitative reconstructions of changes in the atlantic meridional ocean circulation

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

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

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

antarctic intermediate water penetration into the northern indian ocean during the last deglaciation abstract the two stage increase in atmospheric carbon dioxide co2 and the associated decrease in radiocarbon 14c during the last deglaciation are thought to have been linked to enhanced southern ocean upwelling and the rapid release of sequestered 14c depleted co2 antarctic intermediate water aaiw originating from the southern ocean reflects variations in the southern ocean and crucially mirrors the chemical signature of upwelling deep water however the penetration of aaiw into the northern indian ocean and its relationship with deglacial climate changes have not been thoroughly elucidated to date here we present the neodymium isotopic composition e nd of mixed planktonic foraminifera from core md77 176 from an intermediate depth in the northern indian ocean to reconstruct the past evolution of intermediate water during deglaciation the e nd record in the northern indian ocean displays two pulse like shifts towards more radiogenic southern ocean values during the deglaciation and these shifts coincide with excursions in 14 c and e nd records in the pacific and atlantic oceans these results suggest invasion of aaiw into the northern hemisphere oceans associated with enhanced southern ocean ventilation during deglaciation our new e nd record strongly supports the close linkage of aaiw propagation and atmospheric co2 rise through southern ocean ventilation during deglaciation

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

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

constraining the variability of the atlantic meridional overturning circulation during the holocene there is a converging body of evidence supporting a measurable slowdown of the atlantic meridional overturning circulation amoc as climate warms and northern hemisphere ice sheets inexorably shrink within this context we assess the variability of the amoc during the holocene based on a marine sediment core retrieved from the deep northwest atlantic which sensitively recorded large scale deglacial transitions in deep water circulation while there is a diffuse notion of holocene variability in labrador and nordic seas overturning we report a largely invariable deep water circulation for the last 11 000 years even during the meltwater pulse associated with the 8 2 ka event sensitivity tests along with high resolution 231pa 230th data constrain the duration and the magnitude of possible holocene amoc variations the generally constant baseline during the holocene suggests attenuated natural variability of the large scale amoc on submillennial timescales and calls for compensating effects involving the upstream components of north atlantic deep water

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

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

deep atlantic ocean carbon storage and the rise of 100 000 year glacial cycles over the past three million years earth s climate oscillated between warmer interglacials with reduced terrestrial ice volume and cooler glacials with expanded polar ice sheets these climate cycles as reflected in benthic foraminiferal oxygen isotopes transitioned from dominantly 41 kyr to 100 kyr periodicities during the mid pleistocene 1 250 to 700 kyr ago ka because orbital forcing did not shift at this time the ultimate cause of this mid pleistocene transition remains enigmatic here we present foraminiferal trace element b ca cd ca and nd isotope data that demonstrate a close linkage between atlantic ocean meridional overturning circulation and deep ocean carbon storage across the mid pleistocene transition specifically between 950 and 900 ka carbonate ion saturation decreased by 30 mol kg 1 and phosphate concentration increased by 0 5 mol kg 1 coincident with a 20 reduction of north atlantic deep water contribution to the abyssal south atlantic these results demonstrate that the glacial deep atlantic carbon inventory increased by approximately 50 gt during the transition to 100 kyr glacial cycles we suggest that the coincidence of our observations with evidence for increased terrestrial ice volume reflects how weaker overturning circulation and southern ocean biogeochemical feedbacks facilitated deep ocean carbon storage which lowered the atmospheric partial pressure of co2 and thereby enabled expanded terrestrial ice volume at the mid pleistocene transition deep atlantic carbon storage increased and the meriodional overturning circulation weakened at the mid pleistocene transition to 100 000 year glacial interglacial cycles according to analyses of foraminifera trace elements and nd isotopes