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The 87Sr/86Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and mid-Oligocene to mid-Miocene features the most rapid rates of increase in the 87Sr/86Sr of the Cenozoic. Because previous records of the 87Sr/86Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambigiously distinguish m.y. scale variations in the rate of 87Sr/86Sr change from variations in sedimentation rate. In this study, we produce the first 87Sr/86Sr results from an Oligocene to early Miocene site with a precise age model derived orbital tuning of high resolution benthic δ18O, at the Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in 87Sr/86Sr, as well as periods of relative stasis. These changes can be directly compared with the high resolution benthic δ18O in the same site. We find slowing of the rate of 87Sr/86Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the Mid-Oligocene Glacial Interval, and a rapid steeping in the 87Sr/86Sr increase coincides with the benthic δ18O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock, and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctic. We additionally generate the first 87Sr/86Sr data from ODP Site 1168 and International Ocean Discovery Program (IODP) Site 1406 during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere mid-latitude sites, and to better estimate the duration of early Miocene hiatus and condensed sedimentation.

The global overturning ocean circulation plays a key role in global climate by distributing heat around the Earth and by triggering or amplifying major climate changes. Neodymium (Nd) isotopes are widely used to trace present-day and past ocean circulation changes; however, their value as a circulation tracer has been increasingly challenged by studies that have focused on processes that can modify seawater Nd isotope ratios (for example, seawater interaction with particles, pore water fluxes from sediments). The Southwest Atlantic represents an excellent test bed for investigating the integrity of Nd isotopes as an ocean circulation tracer, as it includes the major Atlantic northern and southern hemisphere-sourced end-member water masses associated with the global overturning ocean circulation, Antarctic Intermediate Water , North Atlantic Deep Water , and Antarctic Bottom Water (AAIW, NADW, and AABW, respectively) and potential regional sources of Nd that could impact that integrity. This study reports Nd isotope data on the GEOTRACES GA02 Southwest Atlantic Meridional Transect, spanning the equator to ∼50°S. Below the pycnocline , substantial non-conservative behavior is observed only in samples dominated by AAIW in the northern portion of the transect (∼25°S to the equator); this appears to reflect addition of Nd from the cratons of South America or Africa from above the pycnocline. This effect is not observed at depths directly below dominated by NADW. Otherwise, Nd isotopes behave as a near-conservative water mass tracer along the transect, with 48% of samples within analytical error of the predicted value from water mass mixing, and 84% within 0.9 εNd -units (∼3 times the analytical error), thus confirming its potential at most depths and locations in the Southwest Atlantic to reconstruct past ocean circulation changes.

The causes of the Mid-Pleistocene Transition, the shift from ∼41-ky to 100-ky interglacial–glacial cycles and more intense ice ages, remain intensely debated, as this fundamental change occurred between ∼1,250 and 650 ka without substantial changes in astronomical climate forcings. Recent studies disagree about the relative importance of events and processes in the Northern and Southern Hemispheres, as well as whether the shift occurred gradually over several interglacial–glacial cycles or abruptly at ∼900 ka. We address these issues using a north-to-south reconstruction of the Atlantic arm of the global meridional overturning ocean circulation, a primary means for distributing heat around the globe, using neodymium (Nd) isotopes. Results reveal a period of intense erosion affecting the cratonic shields surrounding the North Atlantic between Marine Isotope Stages (MIS) 27 and 25 (∼980 and 950 ka), reflected by unusually low Nd isotope ratios in deep North Atlantic seawater. This episode preceded a major ocean circulation weakening between MIS 25 and 21 (950 and 860 ka) that coincided with the first ∼100-ky-long interglacial–glacial onset of Northern Hemisphere glaciation at around 2.4 to 2.8 Ma. The data point to a Northern Hemisphere–sourced initiation for the transition, possibly induced through regolith loss and increased exposure of the crystalline bedrock, which would lead to increased friction, enabling larger ice sheets that are characteristic of the 100-ky interglacial–glacial cycles.

espanolEste estudio investiga el origen sedimentario de los materiales depositados por el rio Amazonas durante los ultimos 30 kyr BP y reconstruye el patron de precipitacion del area fuente. Para ello, se han utilizado quince muestras de un registro sedimentario marino ubicado en el margen de la Guayana Francesa y se han analizado los isotopos de Neodimio (Nd) y de Estroncio (Sr). Los resultados (Sr: 0.71385±0.00166; eNd: -11.67±0.55) sugieren que la zona del Amazonas occidental es la fuente principal del material terrigeno, y apuntan a la cuenca del rio Solimoes como el origen mas probable. Asi mismo, el analisis paleoclimatico de la zona refuerza esta conclusion, exhibiendo condiciones continentales humedas para los Heinrich Stadials 1 y 2 en comparacion con el Ultimo Maximo Glacial, asi como para el Ultimo Maximo Glacial en comparacion con el Holoceno temprano EnglishThis study investigates the sedimentary origin of materials deposited by the Amazon River over the last 30 kyr BP and reconstructs the precipitation pattern of the source area at the time of the erosion. For this purpose, fifteen samples of a down-core sediment record from the French Guiana margin have been used to analyse neodymium (Nd) and strontium (Sr) isotope ratios. The sample results (Sr: 0.71385±0.00166; eNd: -11.67±0.55) suggest that the western Amazon basin catchment area is the main source of the terrigenous material, and point to the Solimoes river basin as the most probable origin. This study also discusses the strong coherence between the registered millennial events and the atmospheric settings of the region, which indicate humid land conditions for the Heinrich Stadials 1 and 2 compared to the Last Glacial Maximum, and during the Last Glacial Maximum compared to the early Holocene.

A high resolution study of calcareous nannofossils has been performed on samples from the Sapropel S1interval deposited in the North Ionian Sea, with the aim to assess the paleoenvironmental changes in the photic zone during this crucial interval in Mediterranean circulation. Calcareous nannofossil data have been integrated with planktonic foraminiferal data recently published from which the paleoclimatic curve has been constructed. Placoliths (namely Emiliania huxleyi) and Florisphaera profunda distributions, along with that of planktonic foraminifer Globigerinoides ruber white, evidence that, after a progressive weakening of surface water mixing, a deep chlorophyll maximum developed just prior to the sapropel deposition. We suggest that these changes took place as a response to enhanced precipitation conditions and riverine discharge as testified by increasing trend of reworked coccoliths and the occurrence of lower salinity taxon Braarudosphaera bigelowii. Calcareous nannofossils also point out that the oceanographic (water column stratification, reduced bottom water ventilation) and biogeochemical (increased primary production) processes that occurred during the S1 formation were particularly dominant during the earliest part of the older S1 warm phase (S1a). Our results support than some re-ventilation events of the shallow depth of studied site (665 m) occurred to some extent, particularly during the final phases of S1a. The distribution of holococcoliths, more abundant during the cold interruption phase S1i, seems confirm that the preservation of these tiny and delicate coccoliths, highly susceptible to dissolution, is enhanced under seafloor re-ventilation conditions. Finally, we tentatively suggest that preservation also plays a significant role in the distribution of the warm upper photic zone taxa, particularly during the warm S1b interval.

In the eastern Mediterranean Sea, the early Holocene was characterized by major climatic and oceanographic changes that led to the formation of the last sapropel (S1) between 10.8 and 6.1 kyr cal. BP. These hydrographic changes might have altered the water exchange between the eastern and western Mediterranean sub-basins through the Strait of Sicily, but the existing evidences are inconclusive. In the present study we show new evidence from sediment core NDT-6-2016 located at the western flank of the Sicily channel, a key location to monitor the surface/intermediate water exchange between the two Mediterranean sub-basins. We perform paleo-hydrographic reconstructions based on planktic foraminifera ecology for the last 15 kyr cal. BP, including the S1 deposition interval. In addition, δ18O measurements in both Globigerina bulloides and Globigerinoides ruber and also major elements analyses in bulk sediment are presented. Our results show that significant changes in surface water properties occurred in W-Sicily characterized by a strong contrast in the seasonal hydrographic conditions during the S1 interval. This study proposes that the oceanographic changes in the eastern Mediterranean associated with the surface freshening promoted by the African monsoon likely triggered a restricted water exchange through the Strait of Sicily. This situation led to limited influence of the surface Atlantic waters into the studied area that favored the development of intense summer stratification and vertical winter mixing. This situation changed at about 7 kyr cal. BP when a decrease in the summer stratification probably reflected the influence of the eastward path of the surface Atlantic Waters. This situation would suggest a reinforcement of the water exchange through the Strait of Sicily that marked the end of the extreme conditions that prevailed in the eastern Mediterranean during the S1 formation.

The rare earth elements (REEs) are widely used as geochemical tracers in the earth, planetary, and ocean sciences. Inductively coupled plasma‐mass spectrometry (ICP‐MS) has become the method of choice to analyze REE concentrations because it can rapidly measure the entire REE spectrum at the same time. This Technical Report presents a user‐friendly "REE Calculation Workbook" in Microsoft Excel to be used for calculating REE abundances in samples equilibrated with a multielement REE spike. This Workbook can be conveniently used to calculate REE concentrations in natural samples for spiked and unspiked elements measured by ICP‐MS. For the spiked elements, their concentrations are calculated using isotope dilution equations. Using these spiked elements as references, concentrations of the four mono‐isotopic REE elements, and other REE elements that are treated as mono‐isotopic elements (in our case, La and Lu), can be calculated. The REE Workbook can be easily set up for use with different REE spikes. Evaluation of our analytical quality using a quadrupole ICP‐MS on 10‐ml‐sized seawater samples shows that our analyses are comparable to high‐precision thermal ionization mass spectrometry (TIMS) studies, with much less time spent processing and analyzing, and with the added advantages of determining mono‐isotopic elements. An important result is the clear demonstration of enrichments in Gd and Er compared to neighboring elements in seawater samples. In addition, we compare and evaluate commonly used reference standards BCR‐1, Post‐Archean Australian Shale (PAAS), and North American Shale Composite (NASC).

High-resolution paleoceanographic reconstruction of surface water properties during the most recent Sapropel event (S1) has been carried out by means of quantitative analyses of planktonic foraminiferal assemblages, planktonic foraminiferal oxygen isotopes (δ18O) and XRF elemental data from a 655 m depth core recovered in the North Ionian Sea. The results show that the S1 interval presents two distinctive warm phases (S1a and S1b), separated by a cold interruption event (S1i). High resolution faunal and geochemical analyses allow to identify two sub-phases within S1a interval, the oldest one has similar characteristics to S1b interval while the youngest sub-phase has less stratified surface waters with relatively lower nutrient content. The high abundance of Globigerinoides ruber white variety opposite to the low percentages of Neogloboquadrina pachyderma during the pre-S1 phase suggests that the onset of surface waters stratification occurred prior to the beginning of Sapropel deposition, acting as a pre-conditioning phase. Paleo-productivity proxies indicate that the deposition of S1 initiated after an increase in nutrient content, potentially related to increased fluvial inputs. Based on the integrated ecological interpretation of our records we argue that S1a and S1b are characterized as warm, stratified and nutrient rich surface waters in the Ionian Sea, while proxies related to oxygen content indicate dysoxic deep waters linked to a combination of the high nutrient content and stratified water column. The S1 interruption phase is characterized by the entrance of colder waters that caused mixing of the stratified water column and re-ventilation of the deep dysoxic waters.

The formation of North Atlantic Deep Water (NADW) in the North Atlantic is an important modulator of the climate system, as it drives the global termohaline circulation, responsible for the distribution of heat, salts and nutrients across the oceans. ODP Site 1063 (4584 m), on the deep Bermuda Rise, is located in the mixing zone between NADW and Antarctic Bottom Water (AABW) and appears to be a good location to study how ocean circulation and climate interconnect. Here we present a new record based on Nd isotope ratios that covers ~1 Ma at that Site. Our data shows Nd isotope ratios during parts of interglacials that are much lower than present day NADW. These results are coherent with recent published studies on the last interglacial–glacial cycle that show that the deep North Atlantic Nd isotope ratios are also lower than NADW during the early interglacial. However, Nd isotope values from the shallower DSDP Site 607 (3427 m), within the core of NADW, have remained similar to modern NADW during interglacials over the same time interval. Site 607 is thought to represent the deep North Atlantic, as shown by an Atlantic meriodional transect that displays Nd isotopes ratios for glacial and interglacial maxima over the last ~1 Ma. We suggest that Nd isotope ratios at Site 1063 do not fully represent the North Atlantic endmember of the AMOC during interglacials, but regional or local processes. However, glacial values at Site 1063 fitting those of Site 607 suggest that Nd isotope ratios represent, indeed, water mass mixing during glacial periods. The low Nd-isotope ratios in the deep Bermuda Rise during interglacials would be the result of particle-seawater exchange derived from the arrival of freshly ground, poorly weathered bedrock from the Canadian shield to the North Atlantic during major ice sheet retreats, such as deglaciations as well as stadial-to-interstadial transitions. Consequently, a deep, regionally constrained layer of seawater is tagged with this extreme Nd isotope signature that is not representative of the AMOC. We suggest that a benthic nepheloid layer, whose development is driven by a deep-recirculating gyre system regulated by the interaction between the northward flowing Gulf Stream and the southward flowing deep western boundary current, facilitates the periodical masking of the deep Atlantic Nd isotope signature at Site 1063. The intermittence of the masking allows for a speculation on how the deep-recirculating gyre system might have changed over the last ~1 Ma glacial-to-interglacial cycles.

The Mid-Pleistocene Transition (MPT, ~1.3-0.7 Ma) is one of the most drastic climatic transition in the recent climatic history of our planet. During this transition, glacial-interglacial variability shifted from 41- to 100-ka cycles, without notable changes in the orbital forcing. Internal forcing mechanisms in Earth’s climate likely shifted the system towards particularly more extreme glacial periods. A decrease in the atmospheric CO₂ contemporary to a severe weakening of the Atlantic deep-ocean circulation around 900 ky suggests that weakened deep-ocean circulation facilitated the capture of CO₂ into the deep ocean and thus contributed to the switch towards more intense and longer glacial periods. ODP Site 668B, in the deep eastern equatorial Atlantic, has been previously used to reconstruct the atmospheric CO₂ evolution across the MPT using boron isotopes in surface dwelling foraminifera. Here we present new high resolution proxies from the same site covering the last 2 Ma. In particular, benthic foraminifera stable isotopes and trace elements (B/Ca, Mg/Ca, Cd/Ca), as well as Nd isotope data (εNd) from Fe-Mn encrusted foraminifera shells. Using the newly improved chronology based on benthic foraminifera stable isotopes we show that our new εNd data covaries substantially with the atmospheric pCO₂ data and shows a glacial-interglacial variability through the entire record, with εNd values matching typical glacial-interglacial range values in the North-Atlantic basin (~-11 to ~-14). Between ~1 to 2 Ma, when the 41-ka-cycles were dominant, εNd data also covaries with carbonate ion saturation index (ΔCO₃²-) as derived from the new B/Ca data, Bottom Water Temperatures (BWT, Mg/Ca) and, with deep ocean nutrient content (phosphate derived from Cd/Ca). Results indicate a higher fraction of warmer, less corrosive and nutrient-poor northern-sourced waters (higher BWT, higher ΔCO32-, lower Cd/Ca, lower εNd) reaching the deep-equatorial Atlantic during interglacial periods compared to glacial periods. Interestingly, this covariation does not stand after ~0.9Ma. Even though εNd and BWT data suggest an increased contribution of southern-sourced waters to the site during glacial periods after 0.9Ma, as shown by a gradual decrease in glacial BWT (>1°C) and increasing glacial εNd values (~1ε units), both B/Ca and Cd/Ca show a distinctive low frequency variability superimposed to the glacial-interglacial variability. These oscillations can be interpreted as infiltrations and/or overflows of southern-sourced waters across the mid-ocean ridge into the SE Atlantic basin that do not completely follow glacial-interglacial periodicity. We propose that bathymetrical constrains exert a control on the chemistry of the deep waters in the deep eastern equatorial Atlantic with potential impacts on global climate. Partially isolated sub-basins such as the SE Atlantic could have effectively acted as carbon reservoirs over longer time scales than glacial-interglacial changes.

Severe changes in the western Mediterranean (WMed) thermohaline circulation occurred during the last major glacial-interglacial transition, mostly due to oceanographic and atmospheric re-adjustments. Changes in water column stratification or deep water convection are controlled by the evaporation-precipitation balance of the basin but also by temperature and the intensity of local winds.A general freshening of the inflowing Atlantic waters through the Strait of Gibraltar during the central phase of the Heinrich Stadial (HS) 1 due to the intense iceberg melting favoured increased water column stratification in the WMed and reduced deep convection, as observed by synchronous depletions in both the benthic δ13C and grain-size signals from a location close to the deep convection source. Post-glacial sea level rise further enhanced stratification of the WMed, with minimum deep convection achieved at a later time, and leading to the formation of the last Organic Rich Layer (ORL) in the Alboran Sea. These stratified conditions in the surface WMed were also favoured by more stable atmospheric conditions related to summer insolation maxima.The integrated study of benthic foraminifera assemblages and TOC records from three sediment cores distributed between 900 m to 2400 m water depths in the basin corroborate the deterioration of deep water ventilation conditions during this period but also provide a first glimpse on an earlier re-ventilation of the intermediate layer. However, the Deep Western Mediterranean Waters did not re-ventilated until the early Holocene, when deep water convection in the Gulf of Lion was resumed by a major cold event with intensified north-westerly winds.We review these key changes in the western Mediterranean thermohaline system by means of neodymium isotopic ratios (εNd) measurements on Fe-Mn encrusted planktonic foraminifera from 4 sediment cores covering a depth profile from 650 mwd to 2400 mwd. Neodymium isotope ratios are used here as a conservative water mass mixing proxy thus allowing to investigate changes of the western Mediterranean thermohaline circulation during the last 22 kyr. Validation of Fe-Mn encrusted foraminifera εNd as tracer of deep water masses in the Mediterranean has been carried out by means of analysis in core-top samples from depths representing main Mediterranean water masses and comparison with published seawater εNd values.Our results show a quite homogeneous εNd signal for intermediate and deep waters during the end of the last glacial period, prior to the deposition of the ORL, likely suggesting a very well homogenized water column. However, significant differences can be observed between the deepest record and those of intermediate depths during the ORL time interval and the early Holocene (14-6 kyr), pointing to important changes in the western Mediterranean thermohaline circulation and likely suggesting different waters mass sources for deep and intermediate levels.

VII International Symposium on Marine Sciences (ISMS 2020), 1-3 July 2020 (Barcelona).-- 2 pages, Mediterranean Outflow Water (MOW) actsas a net source of salt and heat into North Atlantic intermediate depths that ultimately contributes to the Atlantic Meridional Overturning Circulation, and it has been hypothesised that MOW variability might influence global climate. Although several studies have documented major glacial-interglacial changes in deep- and intermediate Mediterranean circulation patterns, littleisknown about associated impacts on MOW properties, in particular its residence time and geochemical signature. Using cold-water coral sets from along the pre- and MOW-path from the Alboran Seato the northern Galician Bank weaimto identify changes in both the ventilation state of the watermasses flowing out of the Mediterranean and the distribution of coral growth through paired Uranium-series and AMS radiocarbon ages complemented by trace element measurements in benthic foraminifera. Our results show a particular spatio-temporal coral distribution with glacial presence only at the deepest sites of the Gulf of Cadiz (~1000m), followed by ~300m Western Mediterranean (WMed) coral appearance across the deglaciation/mid Holocene (14-4kyr), to end with a proliferation at the Strait of Gibraltar and Galicia Bank from ~6kyr towards the present. We hypothesise 1) that ~300m WMed area might have been bathed in Atlantic waters inflow during the glacial due tosea-level drop, returning to Levantine Intermediate Water influence over the deglaciation, and 2) that MOW reached deeper areas outside of the Mediterranean Seain the Gulf of Cadiz during the glacial. Regarding the reservoir age, a little ~300yr change is observed at the WMedat 150-450m when corals appear at the Bølling-Allerød, but in synchrony with significant changes in hydrographical parameters. Overall, our results suggest a watermass reorganization at the surface-intermediate layer of the WMed during the deglaciation/early Holocene, that need to be further explored through Nd isotope analysis and trace elements beyond the deglaciation

12 pages, 6 figures, 2 tables, supplementary material https://doi.org/10.1016/j.pocean.2020.102340, Seawater rare earth element (REE) concentrations and Nd isotopic composition (εNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and εNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the εNd values here. On the other side, distributions of dissolved heavy REE (HREE) and εNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and εNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW takes on major importance when considering HREE in the model, EMDW fractions are preferentially detected with εNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before, This research has been financially supported by the TIMED Project funded by the European Commission (ERC Consolidator Grant to I. Cacho; ID: 683237). The authors thank financial support from the CHIMERA Project (CTM2016-75411-R), Generalitat de Catalunya-Grups de Recerca Consolidats (2017 SGR 315) and the Project of Strategic Interest NextData PNR 2011-2013 (www.nextdataproject.it). [...]. E. Garcia-Solsona acknowledges support from a post-doctoral fellowship (FPDI-2013-15660) and L.D. Pena from the Ramón y Cajal program (MINECO, Spain). I. Cacho thanks the ICREA-Academia programme from the Generalitat de Catalunya. J.N. Pérez-Asensio has been funded by a Beatriu de Pinós postdoctoral fellowship from AGAUR (Generalitat de Catalunya) and the European Commission (Marie Curie-COFUND), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

We thank the constructive comments of three anonymous reviewers that substantially improved this manuscript. JNPA has been funded by a Postdoctoral fellowship Beatriu de Pinós funded by the AGAUR from the Generalitat de Catalunya and the European Union through the Marie Curie-COFUND actions. LDP acknowledges support from the Ramón y Cajal program (MINECO, Spain), JF from the Serra Húnter Programme (Generalitat de Catalunya) and IC from the ICREA-Academia program from the Generalitat de Catalunya. We are indebted to Albert Català and Montse Guart (University of Barcelona), and Joaquim Perona and Regina Roca (CCiT-UB) for their support with the laboratory work., Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2019.106075., The accumulation of an Organic Rich Layer (ORL) during the last deglaciation in the Alboran Sea (western Mediterranean Sea) and its link to changes in deep and intermediate water circulation are here investigated. Benthic foraminiferal assemblages and the shallow infaunal foraminifer Uvigerina peregrina δ13C record support the establishment of sustained high organic matter fluxes, and thus eutrophic conditions at the sea floor, during the late phase of the ORL (Younger Dryas to early Holocene periods). Since organic matter fluxes were lower (mesotrophic conditions) during the Bølling-Allerød period, they cannot be solely responsible for the ORL initiation. Geochemical, sedimentological and micropalaeontological proxies support a major weakening of the deep-water convection in the Gulf of Lion as the main driver for the development of poorly-ventilated conditions from intermediate depths (946 m) to the deep western Mediterranean basin that promoted the beginning of the ORL deposition. Nevertheless, a better ventilation at intermediate depths was established during the late ORL, while the deep basin remained poorly ventilated. We propose that our data reflect the arrival of a new better-ventilated intermediate water mass analogue to the current Levantine Intermediate Water (LIW) and/or a new intermediate water mass from the Gulf of Lion. The ultimate source of this water mass needs to be further explored but chronologies of the changes recorded here indicate that intermediate and deep ventilation phases were decoupled between the western and eastern Mediterranean basins during the deglaciation and early-middle Holocene., This work was funded by the projects TIMED (Call ref: ERC-CoG-2015; proposal number 683237) of the European Research Council (Consolidator Grants), CHIMERA (CTM2016-75411-R), CGL2015-66835-P and RTI2018-099489-B-I00 of the Ministerio de Economía y Competitividad of Spain. The Research Group GRC Geociències Marines (2017 SGR 315) of the Generalitat de Catalunya is also acknowledged, as well as the Research Groups RNM-178 and RNM-190 (Junta de Andalucía).

Dissolved rare earth element ([REE]) and neodymium isotopic (eNd) data from the US GEOTRACES Eastern Equatorial Pacific Transect (EPZT) are presented. These data are compared to watermass distributions ( Peters et al., 2018 ), particulate data ( Lam et al., 2018 ) and carbonate species data ( Bates, 2018 ) to evaluate present theories of REE and eNd geochemistry, given that the Pacific has been notably intractable in relation to these ideas ( Jones et al., 2008 ). The [REEs] have typical depth profile distributions (e.g., [La] ranges from ∼5 to 15 pmol/kg in the surface, increasing with depth to values of ∼40 pmol/kg), as does eNd (ranging from ∼-1 to -6 eNd; similar to previous Pacific data). However, despite the unsurprising nature of these data, several apparent inconsistencies with respect to current models for REE/eNd geochemistry arise. These are: (1) While eNd remarkably maintains watermass distribution information, there is a significant (+1.4 eNd) offset in the data compared to published end-member compositions, indicating a strong but largely consistent non-conservative component; (2) Reversible scavenging seems an unlikely mechanism for redistribution of [REE] and eNd in the water column; (3) There does not appear to be any correlation of [REE] to carbonate ion concentration, and; (4) There are indications of influence from a benthic flux, but the evidence is ambiguous.

The global ocean overturning circulation is a major means of distributing heat around the Earth, and an important trigger or amplifier of climate change. This study presents a 1.5-Myr-long neodymium (Nd) isotope record of Deep Sea Drilling Project Site 607, in the core of present-day North Atlantic Deep Water (NADW), the water mass that drives the overturning circulation and its Atlantic end-member (Broecker, 1991; Gordon, 1991), in order to document its composition through time. This time interval is marked by major changes in fundamental aspects of the Earth's climate, including the Mid-Pleistocene Transition (MPT) from ∼41-kyr to ∼100-kyr interglacial-glacial cycles and more intense glacials. The new record, mainly focusing on interglacial and glacial peaks, shows a pattern that mimics the record of benthic foraminiferal δ18O (Lisiecki and Raymo, 2005) in that the magnitude of interglacial-glacial Nd isotope shifts were smaller in the 41-kyr world than in the 100-kyr world. During the “900 ka event” (Clark et al., 2006), between ∼960 and 860 ka, marking the first 100-kyr interglacial-glacial cycle, the Nd isotope ratios shift abruptly to higher values, consistent with increased incursion of Southern Ocean water masses into the deep North Atlantic. This pattern was previously observed in the South Atlantic over the same time interval and interpreted as a weakened presence of NADW signal that reflected a period of disrupted deep ocean overturning circulation, termed the “MPT-AMOC crisis” (Pena and Goldstein, 2014). The Site 607 data support this interpretation and show the effects to be basin-wide. Following the disruption, an enhanced southern-sourced Nd isotope signature remained for ∼200 kyr during the period of “lukewarm interglacials” (Howe and Piotrowski, 2017; Jaccard et al., 2013), consistent with weaker overturning circulation. With the exception of this “MPT-AMOC crisis and recovery” interval, the Nd isotope ratios during interglacial peaks have been similar to present-day NADW, indicating similar interglacial North Atlantic ocean circulation dynamics both before and after the MPT. This contrasts with the pattern during glacial periods of the 100-kyr world, during which Nd isotopes have continued to follow the pattern of the 900-kyr event indicating a strong southern water mass signal, interpreted as intensified incursions of Southern Ocean water into the deep North Atlantic and consistent with a generally weaker overturning circulation during glacials.

Paleoclimatic evolution of the last 140 ka (Marine Isotopic Stages MIS 1 to MIS 5) in the South Bay of Biscay has been studied by considering microfossil changes in sediment samples of deep core PP10-17. This core was retrieved at 2882 m water depth (mwd) in the Landas Plateau and is formed by 1792 cm of clay-silt continuously deposited sediment. For this study, a total of 114 samples have been examined, yielding approximately 60 thousands of specimens of foraminifers (181 benthic species, BF) and ostracods (70 spp.). Reconstruction of the benthic response is based on the main foraminifer and ostracod species by considering their oxic/anoxic character as well as other ecological features of the assemblages. Detailed quantification of microfossils (planktonic and benthic foraminifers, ostracods) together with grain size analyses and magnetic susceptibility of the sediments allow us to characterize many of the climatic events registered in this core. Based on a robust chronostratigraphy by correlation with reference core MD95-2002 and Greenland ice core records (GICC05modelext), we are able to characterize a detailed response of benthic environments to cooling/warming, oxygen-content and productivity cycles in the region. MIS 5 has been characterized by oscillations of the planktonic/benthic foraminifer ratio (Oceanity index, OI; 60–90%); this index was higher (90–100%) and stable through the MIS 4–MIS 3 intervals. We found BF species indicators of different climatic-related events. Thus, MIS 5a, c, e interstadials are evidenced by Bulimina gibba and B. aculeata while the stadials MIS 5b, d are shown by the occurrence of Melonis pompilioides. Heinrich events, with massive iceberg discharges into the N Atlantic Ocean, are indicated by presence of Globobulimina affinis, particularly during the MIS 4 to MIS 2 interval. The beginning of MIS 4 is indicated by the appearance of new species of BF and an increase of Cassidulina laevigata. Krithe spp. and C. laevigata are good indicators of the LGM (Last Glacial Maximum, 19–23 ka) when the OI decreased. Other cooling periods (e.g. Younger Dryas, YD, around 12–13 ka) are shown as well by an increase of M. pompilioides, similar to that of the MIS 5d stadial. The Holocene (11.5 ka to present) is marked by an increase in the oceanity index, disappearance of cold-water indicators and the occurrence of Uvigerina peregrina. A shallow infaunal microhabitat of benthics foraminifers (Cibicides, Cassidulina, Uvigerina) and ostracods (Krithe, Argilloecia) has been linked to favorable bottom conditions, with oxic to slightly suboxic conditions (high diversity and equitability of assemblages) reflecting an active Atlantic Meridional Overturning Circulation (AMOC) during many D/O interstadials. The opposite conditions were established for deep infaunal BF (Bulimina, Globobulimina) where the strong dysoxic bottom conditions are indicative of poor ventilation produced by a reduction or shutdown of the AMOC during Heinrich stadials.

Rare earth elements (REEs) are used as tracers for oceanic trace element cycling. However, the low (picomolar level) dissolved REE concentrations and time-consuming methods have so far hindered their extensive use in marine studies. This study reports the first application of the automated seaFAST-pico system (Elemental Scientific Inc.) in offline mode and using multi-element isotope dilution inductively coupled plasma-mass spectrometry (ID ICP-MS) for the robust and rapid pre-concentration, purification, and analysis of dissolved REEs from small volumes of seawater (11–12 mL). Accuracy of our new method is checked with replicates of GEOTRACES intercalibration seawater from BATS (Bermuda Atlantic Time Series, North Atlantic) at 15 m and 2000 m water depths. Our results show excellent agreement (within the analytical uncertainty, 2σ SD) with the published intercalibrated values from the GEOTRACES intercalibration study. Replicates of GEOTRACES intercalibration seawater from SAFe at 3000 m water depth (Sampling and Analysis of Iron, North Pacific) indicate a procedural long-term error of ≤ 3.9% 2σ RSD for all REEs, except for Ce and Gd. An international intercomparison from 4 labs using SAFe 3000 m seawater aliquots, 2 of which also use the seaFAST-pico system in offline mode, and different pre-concentration, purification, and analytical methods shows excellent agreement between REE concentrations within 7% (2σ RSD) (except for Ce 71%, Gd 14%, Lu 12%). This is comparable to the agreement obtained for the BATS 15 m and 2000 m samples by six different labs for the international GEOTRACES intercalibration study (van de Flierdt et al., 2012). The REE intercomparison values of SAFe 3000 m (i.e., the average of the values from the 4 labs) in this study agree within the analytical uncertainties (2σ SD) with published REE values of deep seawater from nearby stations. Our international intercomparison provides the first REE intercomparison values for the GEOTRACES intercalibration station SAFe at 3000 m, and establishes the first reference seawater REE values for quality control of future REE studies in the Pacific Ocean as SAFe will remain a GEOTRACES baseline, and hence intercalibration station, for cruises in the North Pacific. Our method is easy to adopt and enables the extensive use of REEs, thereby opening the way to build a global seawater REE data set.

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 µmol kg−1 and phosphate concentration increased by 0.5 µmol 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.

17 pages, 6 figures, 1 table, supporting information https://dx.doi.org/10.1002/2015PA002883, data will be available at the Scientific Earth Drilling Information Service (http://sedis.iodp.org), Pangaea website (http://www.pangaea.de), and NOAA Paleoclimatology (https://www.ncdc.noaa.gov/data-access/paleoclimatology-data)

The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González., National Science Foundation (U.S.) (Grant OCE-0608600), National Science Foundation (U.S.) (Grant OCE0938349), National Science Foundation (U.S.) (Grant OCE-1243377), National Science Foundation (U.S.) (Grant OCE-1546580)

Circulating between different cycles Around a million years ago, large-scale ocean circulation changed dramatically during the switch from ∼41,000- to ∼100,000-year long glacial cycles. Pena and Goldstein analyzed the isotopic composition of neodymium in marine sediments from the South Atlantic. The results suggest how the contributions of deep water from northern and southern sources varied across the transition. The boundary between the two glacial states appears to have been marked by a dramatic weakening, perhaps even a shutdown, of deep-water currents. Science , this issue p. 318

The planktonic foraminifera Globorotalia menardii, absent in the Atlantic Ocean during the last glacial period, reappeared during the Holocene. As it was present in the Indian Ocean during glacial time, its reappearance might be thought to have been connected to rejuvenation of conveyor circulation. But, as first shown by Glenn Jones and confirmed here, it was a significant contributor to the Atlantic's foraminifer population only after 7000 years ago.

13 pages, 6 figures, 2 tables, supplementary data https://doi.org/10.1016/j.epsl.2013.02.028, The Southern Ocean is increasingly recognized as a key player in the general ocean thermohaline circulation and the global climate system during glacial-interglacial transitions. In particular, the advection of Southern Ocean intermediate waters (SOIW), like Antarctic Intermediate Water and Sub-Antarctic Mode Water, to the Eastern Equatorial Pacific (EEP), through a so-called >oceanic tunnelling> mechanism, is an important means for rapid transfer of climatic signals (such as heat, fresh water, salt, and chemical species) from high-to-low latitudes. However, information on how intermediate water advection rates changed in the past, and particularly during deglaciations, is fragmentary. We present new results for Nd isotopes (εNd) in cleaned foraminifera shells (Neogloboquadrina dutertrei) for the last 30kyr at ODP Site 1240 in the EEP. N. dutertrei preferentially dwells in the lower thermocline, at the core of the Equatorial Undercurrent (EUC), and the εNd variability over time provides a record of the changes in the εNd of the EUC. Through mixing models we show that the EUC record is primarily controlled by changes in the volume transport of intermediate waters and not by Southern Ocean εNd changes. Southern Ocean signals in the EUC are stronger during colder intervals (Younger Dryas, last glacial maximum and Heinrich stadials 1 and 2), in agreement with tropical Atlantic intermediate water records. In addition, covariations between N. dutertrei δ13C, molecular biomarkers, and diatom productivity at Site 1240 confirm the intermediate water route as an important mechanism for the transfer of climate signals from high-to-low latitudes. Changes in the SOIW chemistry during the deglaciation are likely linked to the upwelling of 'old' deep waters in the Southern Ocean and subsequent export as intermediate waters, which are coeval with the atmospheric CO2 rise. Moreover, a comparison of multiple proxy records for the last 30kyr indicates a latitudinal shift and/or a change in the convection depth of intermediate waters in the Southern Ocean prior to the onset of the deglaciation. © 2013 Elsevier B.V., L.D.P., S.L.G. and S.R.H. acknowledge support from US National Science Foundation (NSF) Grant OCE-10-31198, and the LDEO Climate Center. E.C., C.P., and I.C. acknowledge funding from the Spanish Ministerio de Ciencia e Innovación through Grants CTM2006-01957/MAR and CTM2009-08849/MAR, from Generalitat de Catalunya (Catalan Government) through Grant 2009SGR142 and a Ramón y Cajal Contract (to E.C.). I.C. also thanks the Spanish GRACCIE CONSOLIDER (CSD2007-00067). S.L.G. acknowledges support from the Storke Endowment of the Columbia University Department of Earth and Environmental Sciences. L.D.P. was partly supported by a LDEO Postdoctoral Fellowship. This research used samples provided by the Ocean Drilling Program (ODP), which is sponsored by the US NSF and participating countries under management of Joint Oceanographic Institutions (JOI). This is LDEO Contribution number 7673

One of the key activities during the initial phase of the international GEOTRACES program was an extensive international intercalibration effort, to ensure that results for a range of trace elements and isotopes (TEIs) from different cruises and from different laboratories can be compared in a meaningful way. Here we present the results from the intercalibration efforts on neodymium isotopes and rare earth elements in seawater and marine particles. Fifteen different laboratories reported results for dissolved 143Nd/144Nd ratios in seawater at three different locations (BATS 15 m, BATS 2000 m, SAFe 3000 m), with an overall agreement within 47 to 57 ppm (2σ standard deviation of the mean). A similar agreement was found for analyses of an unknown pure Nd standard solution carried out by 13 laboratories (56 ppm), indicating that mass spectrometry is the main variable in achieving accurate and precise Nd isotope ratios. Overall, this result is very satisfactory, as the achieved precision is a factor of 40 better than the range of Nd isotopic compositions observed in the global ocean. Intercalibration for dissolved rare earth element concentrations (REEs) by six laboratories for two water depths at BATS yielded a reproducibility of 15% or better for all REE except Ce, which seems to be the most blank-sensitive REE. Neodymium concentrations from 12 laboratories show an agreement within 9%, reflecting the best currently possible reproducibility. Results for Nd isotopic compositions and REE concentrations on marine particles are inconclusive, and should be revisited in the future.

Millennial to multi-centennial benthic foraminiferal stable isotope, sortable silt mean grain size ( SS ― ) and benthic foraminiferal Cd/Ca records are presented for core MD96-2080 from 2488 m water depth at the western Agulhas Bank Slope off South Africa. The data demonstrate the interplay between Northern and Southern Component Waters as the Atlantic Meridional Overturning Circulation (MOC) shifted between glacial and interglacial modes. During early phases of Marine Isotope Stages (MIS) 6 and 8, the Atlantic MOC was little different from its interglacial mode. Benthic foraminiferal δ13C modulation during these stages can be explained by mean-ocean δ13C changes, while, only subtle benthic foraminiferal Cd/Ca increases indicate a continued influence of Northern Component Waters (NCW). Later glacial stages are characterized by a progressive incursion of nutrient-enriched waters presumably a mixture of Upper and Lower Southern Component Waters (SCW). Maximum SS ― values during late glacial ventilation minima suggest increased near-bottom flow speeds. The combined ventilation and flow-speed pattern indicates an enhanced influence of SCW, most likely linked with a northward migration of the Antarctic Circumpolar Current (ACC) which progressively decreased the influence of NCW at site MD96-2080. Peak-maximum seawater Cd concentrations (Cdsw, derived from benthic foraminiferal Cd/Ca) overlap in time with increased deposition of ice-rafted debris (IRD) in the North Atlantic and plot outside the δ13C/Cdsw field in the South Atlantic. The anomalies conceivably are the South Atlantic equivalents of peak Cdsw maxima associated with Heinrich-type events in the North Atlantic and reflect a substantially reduced Atlantic MOC.

Marine Isotope Stage 3 (MIS 3, 59.4–27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard–Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard–Oeschger stadials.

16 pages, 8 figures, 1 table, A multiproxy study of the sedimentary record carried out on gravity core CGPL00-1 retrieved from the outer Galician continental shelf (NW of Spain) has allowed us to establish the main climate fluctuations affecting the region during the Upper Holocene. Grain size, TOC, C/N ratio, biogenic opal and planktonic foraminifera are the main analysed parameters. Lithology and grain size distribution lead to identify two sedimentary sequences: a lower half mainly composed by glauconitic sand and a muddy upper half. A chronology has been established based on three AMS radiocarbon ages, 907 cal. BC, 898 cal. BC and 1399 AD, and the aforementioned sedimentary sequences. The obtained radiocarbon ages are the first dated sediment samples for the Galician continental shelf. Geochemical markers show different trends in both sequences: low and/or fluctuating values in the sandy sequence and high and relatively constant values in the upper muddy sequence. The whole sandy interval is interpreted to be a nearly instantaneous deposit from a distal storm ebb current. The muddy interval was deposited in a stable and low-energy marine environment, similar to that found on the present outer shelf. The shift from a storm-dominated shelf to a low-energy environment took place synchronous with the Subboreal/Subatlantic transition, when an increase in storminess appears related to climatic instability. Transitional planktonic foraminiferal assemblage dominates the whole record, although a change to more abundant cold water species at 1420 AD, may relate to an intense upwelling pulse, probably reinforced by colder atmospheric temperatures during the Little Ice Age (LIA). Despite the presence of an upwelling regime since 1420 AD, lesser amount of opal has accumulated in the outer shelf due to enhanced offshore transport and stronger remineralization, This work was funded by REN2000-1102 MAR, PGIDT00MAR30103PR and PGIDT00PXI30105PR Projects

5 pages, 2 figures, supporting information www.pnas.org/lookup/suppl/doi:10.1073/pnas.1009761108/-/DCSupplemental, Understanding oceanic processes, both physical and biological, that control atmospheric CO2 is vital for predicting their influence during the past and into the future. The Eastern Equatorial Pacific (EEP) is thought to have exerted a strong control over glacial/interglacial CO2 variations through its link to circulation and nutrient-related changes in the Southern Ocean, the primary region of the world oceans where CO2-enriched deep water is upwelled to the surface ocean and comes into contact with the atmosphere. Here we present a multiproxy record of surface ocean productivity, dust inputs, and thermocline conditions for the EEP over the last 40,000 y. This allows us to detect changes in phytoplankton productivity and composition associated with increases in equatorial upwelling intensity and influence of Si-rich waters of sub-Antarctic origin. Our evidence indicates that diatoms outcompeted coccolithophores at times when the influence of Si-rich Southern Ocean intermediate waters was greatest. This shift from calcareous to noncalcareous phytoplankton would cause a lowering in atmospheric CO2 through a reduced carbonate pump, as hypothesized by the Silicic Acid Leakage Hypothesis. However, this change does not seem to have been crucial in controlling atmospheric CO2, as it took place during the deglaciation, when atmospheric CO2 concentrations had already started to rise. Instead, the concomitant intensification of Antarctic upwelling brought large quantities of deep CO2-rich waters to the ocean surface. This process very likely dominated any biologically mediated CO2 sequestration and probably accounts for most of the deglacial rise in atmospheric CO2, We thank Robert Anderson, Thomas Marchitto, and Gisela Winckler for kindly providing data. E.C., C.P., and I.C. acknowledge funding from the Spanish Ministerio de Ciencia e Innovación through Grants CTM2006-01957/MAR and CTM2009-08849/MAR, and a Ramón y Cajal Contract (to E.C.). L.D.P. acknowledges support from National Science Foundation Grant OCE-10-31198. G.A.L. published with permission of Geoscience Australia. This is a contribution from the Marine Biogeochemistry and Global Change research group, funded by Generalitat de Catalunya (Catalan Government) through Grant 2009SGR142

Planktonic δ18O and Mg/Ca-derived sea surface temperature (SST) records from the Agulhas Corridor off South Africa display a progressive increase of SST during glacial periods of the last three climatic cycles. The SST increases of up to 4°C coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites. Mg/Ca-derived SST maximizes during glacial maxima and glacial Terminations to values about 2.5°C above full-interglacial SST. The paired planktonic δ18O and Mg/Ca-derived SST records yield glacial seawater δ18O anomalies of up to 0.8‰, indicating measurably higher surface salinities during these periods. The SST pattern along our record is markedly different from a U37K′-derived SST record at a nearby core location in the Agulhas Corridor that displays SST maxima only during glacial Terminations. Possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of SST contrasts during glacials in association with seasonal changes of Agulhas water transports and lateral shifts of the Agulhas retroflection. The different SST reconstructions derived from U37K′ and Mg/Ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the Agulhas Current and interocean salt leakage is not as straightforward as previously suggested.

High resolution benthic foraminiferal stable isotopes (δ18O, δ13C) and molecular biomarkers in the sediments are used here to infer rapid climatic changes for the last 8200 years in the Ría de Muros (NW Iberian Margin). Benthic foraminiferal δ18O and δ13C potentially register migrations in the position of the hydrographic front formed between two different intermediate water masses: Eastern North Atlantic Central Water of subpolar origin (ENACWsp) and subtropical origin (ENACWst). The molecular biomarkers in the sediment show a strong coupling between continental organic matter inputs and negative δ13C values in benthic foraminifera. The rapid centennial and millennial events registered in these records have been compared with two well known North Atlantic Holocene records from the subtropical Atlantic sea surface temperatures (SST) anomalies off Cape Blanc, NW Africa and the subpolar Atlantic (Hematite Stained Grains percentage, subpolar North Atlantic). Comparison supports a strong link between high- and low-latitude climatic perturbations at centennial–millennial time scales during the Holocene. Spectral analyses also points to a pole-to-equator propagation of the so-called 1500 yr cycles. Our results demonstrate that during the Holocene, the NW Iberian Margin has undergone a series of rapid events which are likely triggered at high latitudes in the North Atlantic and are rapidly propagated towards lower latitudes. Conceivably, the propagation of these rapid climatic changes involves a shift in atmospheric and oceanic circulatory systems., The authors acknowledge to the EU project HOLSMEER: Holocene Shallow Marine Environments of Europe (EVK2-CT-2000-00060) for providing samples and financial support, GRACCIE (Consolider-Ingenio, CDS 2007-00067); CONTOURIBER (CTM 2008-06399-C04-01/MAR) y Proxecto 08MDS036000PR (Xunta de Galicia). L.P. and P.D. also thank the EU Acces to Research Infrastructures Paleostudies Program (Geosciences Faculty, Bremen University, Germany) for providing us with analytical facilities, and to F. Lamy for all the help provided. L.P. acknowledges a fellowship from the Comer Abrupt Climate Change Foundation (USA). Thoughtful comments and discussion provided by P.G. Mortyn are greatly thanked. Also thanks to Antje Volker and an anonymous reviewer for very insightful comments that helped to improve the quality of this paper. This is LDEO contribution 7352.

[1] The Eastern Equatorial Pacific (EEP) is a high nutrient–low chlorophyll region of the ocean. Downcore nitrogen isotope records from the EEP have been previously interpreted as a direct reflection of changes in nutrient consumption. However, the observed changes in sedimentary δ15N since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron-to-nitrate ratio of the surface waters. Rather, downcore N isotope records in the EEP strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary δ15N records along the western margin of the Americas. This similarity is attributed to the overprinting of the N isotopic composition of nitrate in the EEP through the advection of nitrate westward from the margins in the subsurface. A local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary δ15N records of denitrification changes from two new EEP δ15N records (TR163-22 and ODP Site 1240). The denitrification records used are from 1) the Central American margin (ODP Site 1242) and 2) the South American margin (GeoB7139-2). The degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11–13 ka, and finally it increases into the Holocene. The derived EEP nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand. The influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the Southern Ocean and the release of sequestered CO2 and nutrient-rich, O2 poor waters from the deep ocean. This has important implications for understanding the glacial-interglacial scale variation in intermediate water suboxia and water column denitrification.

The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere(1). Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean(2,3) could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments(4,5), but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown(6,7). Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.

An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to 6 mmol/mol) were circulated with a dissolution protocol for analysis. Participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories. Statistical analysis was performed in accordance with the International Standardization Organization standard 5725, which is based on the analysis of variance (ANOVA) technique. Repeatability (RSDr%), an indicator of intralaboratory precision, for Mg/Ca determinations in solutions after centrifuging increased with decreasing Mg/Ca, ranging from 0.78% at Mg/Ca = 5.56 mmol/mol to 1.15% at Mg/Ca = 0.79 mmol/mol. Reproducibility (RSDR%), an indicator of the interlaboratory method precision, for Mg/Ca determinations in centrifuged solutions was noticeably worse than repeatability, ranging from 4.5% at Mg/Ca = 5.56 mmol/mol to 8.7% at Mg/Ca = 0.79 mmol/mol. Results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility. Additionally, the study confirmed the suitability of these solid standards as reference materials for foraminiferal Mg/Ca (and Sr/Ca) determinations, provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases.

Interannual-decadal variability in the equatorial Pacific El Nino–Southern Oscillation (ENSO) induces climate changes at global scale, but its potential influence during past global climate change is not yet well constrained. New high-resolution eastern equatorial Pacific proxy records of thermocline conditions present new evidence of strong orbital control in ENSO-like variability over the last 275,000 years. Recurrent intervals of saltier thermocline waters are associated with the dominance of La Nina–like conditions during glacial terminations, coinciding with periods of low precession and high obliquity. The parallel dominance of δ 13C-depleted waters supports the advection of Antarctic origin waters toward the tropical thermocline. This “oceanic tunneling” is proposed to have reinforced orbitally induced changes in ENSO-like variability, composing a complex high- and low-latitude feedback during glacial terminations.

High resolution benthic foraminiferal oxygen and carbon stable isotopes (?18O, ?13C) from core EUGC-3B are used here to infer rapid climatic changes for the last 8500 yr in the Ría de Muros (NW Iberian Margin). Benthic foraminiferal ?18O and ?13C potentially register migrations in the position of the hydrographic front formed between two different intermediate water masses: Eastern North Atlantic Central Water of subpolar origin (ENACWsp), and subtropical origin (ENACWsp). The isotopic records have been compared with two well established North Atlantic marine Holocene paleoceanographic records from low (Sea Surface Temperatures anomalies off Cape Blanc, NW Africa) and high latitudes (Hematite Stained Grains percentage, subpolar North Atlantic). This comparison clearly demonstrates that there is a strong link between high- and low-latitude climatic perturbations at centennial-millennial time scales during the Holocene. Spectral analyses also points at a pole-to-equator propagation of the so-called 1500 yr cycles. Our results demonstrate that during the Holocene, the NW Iberian Margin has undergone a series of cold episodes which are likely triggered at high latitudes in the North Atlantic and are rapidly propagated towards lower latitudes. Conceivably, the propagation of these rapid climatic changes involves a shift of atmospheric and oceanic circulatory systems and so a migration of the hydrographical fronts and water masses all along the North Atlantic area.

13 pages, 6 figures, 2 tables., The Tagus Prodelta (W Portugal) and the Muros Ría (NW Spain) are areas of high deposition rates registering high-resolution palaeoclimatic records for western Iberia. We compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature (sea surface temperatures and oxygen isotopes), continental input (grain size, iron and magnetic susceptibility) and productivity (inorganic and organic carbon, carbon isotopes, benthic foraminifera and diatoms). Biogeochemical changes in the Tagus Prodelta reflect widely recognized North Atlantic climatic periods encompassing the Roman Period (AD 0-350), the Dark Ages (AD 400-700), the ‘Mediaeval Warm Period’ (MWP; AD 800-1200) and the ‘Little Ice Age’ (LIA; AD 1300-1750). The atmospheric North Atlantic Oscillation (NAO) drives the Tagus Prodelta multidecadal, long-term variability in precipitation-river input during cold periods (negative NAO) and marine upwelling during warmer periods (positive NAO), a scheme that is reversed in the Galician region. The Muros Ría shows only local hydrodynamics until AD 1150, including a ‘suboxic’ event in the inner Ría around AD 500-700. Since AD 1150 Atlantic warm upwelled waters have ventilated the outer Ría but only reach the inner Ría at AD 1750. The twentieth-century records are also interpreted as a reflex of the inverse NAO mode in both areas, resulting in amplification of the LIA biogeochemical water conditions. Centennial-scale solar activity appears to be another important forcing mechanism (or the only one, if solar activity drives the NAO and ‘Bond-cycles’) behind changes in the hydrography of the Tagus Prodelta, and primary production, bottom ventilation and organic carbon degradation in the Muros Ría., We are grateful to participants and crews of Discovery 249, Poseidon PALEO 1, and B/O Mytilus cruises, and for laboratory technical assistance in grain size, LECO, isotopes, foraminifera and diatoms at the INETI-Laboratory of Marine Geology. Thanks to C. Kissel for the magnetic susceptibility measurements in Gif-sur-Yvette, to M. Siegl for isotope measurements and the ARI-Program at the University of Bremen, to E. Salgueiro and 5. Vaqueiro for XRF measurements at the Bremen Core Repository, to J. Heinemeier for helpful discussions during the construction of age models, to A. Ferreira for critical data discussion and A. Voelker for comments on the manuscript. The comments of an anonymous reviewer helped to improve the final version of this paper. Financial support was provided by EU project HOLSMEER (EVK2-CT-2000-00060). T. Rodrigues was supported by the Fundação para a Ciéncia e Tecnologia, INGMAR project.

[1] The geochemical composition of foraminifera shells from an Ocean Drilling Program site in the Panama Basin has been analyzed by several analytical techniques (LA-ICP-MS, ICP-MS, XRD, SEM, EDX) in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions. LA-ICP-MS results on uncleaned tests indicate the presence of MnMg-rich contaminant phases at the inner surfaces of the foraminiferal shells (which have Mn/Ca ratios up to 400 mmol mol 1 and Mg/Ca ratios up to 50 mmol mol 1 ). We have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included. The analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high Mn values are associated with at least two different contaminant phases, of which only one is linked to high Mg values. XRD analysis further reveals that the Mn-Mg-rich phase is the Ca-Mn-Mg carbonate kutnahorite (Ca(Mn, Mg)(CO3)2). Our results demonstrate that the presence of kutnahorite-like minerals can bias Mg/Ca ratios toward higher values (by 7–36%) and lead to significant overestimation of past seawater temperatures (by 0.9 up to 6.2� C, in the case of these Panama Basin samples). Components: 11,867 words, 13 figures, 3 tables.