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International audience; The Holocene is commonly referred to as a period of relatively stable climate conditions. It is however affected by a climate anomaly 8.2 kyr ago, postulated to be the result of weakened Meridional Overturning Circulation (MOC) triggered by a freshwater outburst. This time period offers then a good opportunity to study the relationship between intermediate water masses renewal and hydrology. We have focused our work on core MD95-2037 (37°05,23 N ; 32°01,87 W, 2100 m) located in the subtropical North Atlantic gyre, on the eastern side of the mid-Atlantic ridge. Age model has been constrained using 14C AMS measurements on planctonic foraminifera, and the studied time interval is restricted between 3 and 11 kyr. Reconstructed Sea Surface Temperature (SST), and the benthic oxygen and carbon isotopes at this site remained stable during the studied period. In order to reconstruct intermediate water mass hydrology, we used Mg/Ca of benthic foraminifera as a representation of deep water temperature. Mg/Ca measurements were performed on a single benthic species C. wuellerstorfi and a linear temperature calibration has been established from published and new core-top data. In-situ deep water temperature is 3.7°C, and is within temperature range where carbonate chemistry of ambient deep water is expected to have an increasing effect on the processes controlling the incorporation of Mg during shell growth. We show a gradual increase of benthic Mg/Ca from 11 kyr, reaching a maximum during the abrupt cold climate anomaly at 8.2 kyr. From this time the benthic Mg/Ca is steadily then decreasing towards core-top value. Using the comparison of Mg/Ca-Temperature signal with the dynamic tracer 231Pa/230Th record from the same core we show the synchrony between a decrease of the renewal rate of the intermediate water masse and change in intermediate water hydrology connected with the climate anomaly 8.2 kyr ago. However, whereas intermediate overturning seems to be drastically affected, going from a "Glacial mode" characterized with important renewal rate of intermediate water masses to the "modern mode", with slower intermediate renewal rate, hydrology appears only temporarily disturbed.

We present high-resolution records of upper ocean temperatures derived from Mg/Ca ratios of surface-dwelling Globigerina bulloides and subsurface-dwelling Neogloboquadrina pachyderma sinistral and the relative abundance of N. pachyderma sinistral for the period 55-8 ka BP from NE Atlantic sediment core MD01-2461. Millennial-scale temporal variability and longer-term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 (MIS 3) to the last glacial maximum (LGM). The correspondence of all temperature proxies and convergence of paired oxygen isotope (delta O-18) records from both planktonic species implies a breakdown in the thermocline and year-round mixing of the upper water column through the LGM, perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum-North Atlantic ice sheets. Millennial-scale divergence in surface and subsurface temperatures and delta O-18 across the last glacial correspond to meltwater release and the development of a strong halocline associated with both Heinrich (H) events and instabilities of the NW European ice sheet. During such episodes, G. bulloides Mg/Ca appears to record ambient, even warming summer sea surface temperatures across H events while the other proxies record maximum cooling.

The Mg and Sr content of ostracod valves have been used to reconstruct past temperature and salinity, and their stable isotopes have been used to reveal aspects of marine, lake and estuary hydrology. However, significant uncertainties surround ostracod calcification processes, the incorporation mechanisms of trace elements, and the sensitivity of proxy tracers to complex confounding factors. The valves of most ostracods are composed of micron-scale crystalline grains embedded in an organic matrix. The fine-scale geochemistry of these structures, and the nature of the influence of biological mineralisation processes on valve chemistry, remain poorly constrained. We have performed sub-micron resolution X-ray microscopy of a marine Krithe ostracod valve, and determined the chemical coordination of Mg, and the distribution of Mg, Na and S throughout the crystal-organic valve structure. These trace elements display systematic sub-micron-scale compositional variations within the mineral grains and inter-granular matrix of the valve ultrastructure. These patterns imply that Krithe biomineralisation processes significantly modulate trace element incorporation at the sub-micron scale. Thus Krithe chemical composition is likely to be decoupled to some extent from the water in which they calcified. Most importantly, Mg K-edge Near-Edge X-Ray Absorption Fine Structure (NEXAFS) spectra, and the coincidence of high-Mg regions with S-rich organic layers reveal that Mg is not primarily hosted in the calcite structure in the valve. Our results highlight the need to understand the processes that drive this fine-scale chemical heterogeneity and their influence on connections between the external environment and valve geochemistry, if ostracods are to be used as sources of paleoenvironmental proxies.

It has long since been noted that minor element (Me) partitioning into biogenic carbonates is sometimes different from Me partitioning into inorganically precipitated carbonates. The prime example is the partitioning coefficient, which might be lower or even higher than the one of inorganically precipitated carbonate. Such a difference is usually termed "vital effect" and is seen as indicative of a biologically modified minor element partitioning. Over the last three decades interest in conceptual biomineralization models compatible with minor element and isotope fractionation has been steadily increasing. However, inferring features of a biomineralization mechanism from Me partitioning is complicated, because not all partitioning coefficients show vital effects in every calcium carbonate producing organism. Moreover, the partitioning coefficient is not the only aspect of Me partitioning. Other aspects include polymorph specificity and rate dependence. Patellogastropod limpets are ideally suited for analysing Me partitioning in terms of biomineralization models, because they feature both aragonitic and calcitic shell parts, so that polymorph specificity can be tested. In this study, polymorph-specific partitioning of the minor elements Mg, Li, B, Sr, and U into shells of the patellogastropod limpet Patella caerulea from within and outside a CO2 vent site at Ischia (Italy) was investigated by means of LA-ICP-MS. The partitioning coefficients of U, B, Mg, and Sr (in aragonite) differed from the respective inorganic ones, while the partitioning coefficients of Li and Sr (in calcite) fell within the range of published values for inorganically precipitated carbonates. Polymorph specificity of Me partitioning was explicable in terms of inorganic precipitation in the case of Sr and Mg, but not Li and B. Seawater carbon chemistry did not have the effect on B partitioning that was expected on the basis of data on inorganic precipitates and foraminifera. Carbon chemistry did affect Mg (in aragonite) and Li, but only the effect on Mg was explicable in terms of calcification rate. On the one hand, these results show that Me partitioning in P. caerulea is incompatible with a direct precipitation of shell calcium carbonate from the extrapallial fluid. On the other hand, our results are compatible with precipitation from a microenvironment formed by the mantle. Such a microenvironment was proposed based on data other than Me partitioning. This is the first study which systematically employs a multi-element, multi-aspect approach to test the compatibility of Me partitioning with different conceptual biomineralization models.

The isotopic composition of carbon, δ¹³C, in seawater is used in reconstructions of ocean circulation, marine productivity, air-sea gas exchange, and biosphere carbon storage. here, a synthesis of δ¹³C measurements taken from foraminifera in marine sediment cores over the last 150 000 years is presented. The dataset comprises previously published and unpublished data from benthic and planktonic records throughout the global ocean. Data are placed on a common δ¹⁸ O age scale and filtered to remove timescales shorter than 6 kyr. Error estimates account for the resolution and scatter of the original data, and uncertainty in the relationship between δ¹³C of calcite and of dissolved inorganic carbon (DIC) in seawater. This will assist comparison with δ¹³C of DIC output from models, which can be further improved using model outputs such as temperature, DIC concentration, and alkalinity to improve estimates of fractionation during calcite formation. High global deep ocean δ¹³C, indicating isotopically heavy carbon, is obtained during Marine Isotope Stages (MIS), 1, 3, 5a, 5c and 5e, and low δ¹³C during MIS 2, 4, and 6, which are temperature minima, with larger amplitude variability in the Atlantic Ocean than the Pacific Ocean. This is likely to result from changes in biosphere carbon storage, modulated by changes in ocean circulation, productivity, and air-sea gas exchange. The North Atlantic vertical δ¹³C gradient is greater during temperature minima than temperature maxima, attributed to changes in the spatial extent of Atlantic source waters. There are insufficient data from shallower than 2500 m to obtain a coherent pattern in other ocean basins. The data synthesis indicates that basin-scale δ¹³C during the last interglacial (MIS 5e) is not clearly distinguishable from the Holocene (MIS 1) or from MIS 5a and 5c, despite significant differences in ice volume and atmospheric CO₂ concentration during these intervals. Similarly, MIS 6 is only distinguishable from MIS 2 or 4 due to globally lower δ¹³C values both in benthic and planktonic data. This result is obtained despite individual records showing differences between these intervals, indicating that care must be used in interpreting large scale signals from a small number of records.

An increase in whole ocean alkalinity during glacial periods could account, in part, for the drawdown of atmospheric CO2 into the ocean. Such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity. We present evidence, based on downcore measurements of benthic foraminiferal B/Ca and Mg/Ca from a core in the Weddell Sea, that the deep ocean carbonate ion concentration, [CO32-], was elevated by ∼25 μmol/ kg during each glacial period of the last 800 kyr. The heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the Atlantic and Pacific by the changing ventilation and chemistry of Weddell Sea waters. These waters are more corrosive than interglacial northern sourced waters but not as undersaturated as interglacial southern sourced waters. Our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification. The Weddell records display low [CO32-] during deglaciations and peak interglacial warmth, coincident with maxima in percent CaCO3 in the Atlantic and Pacific oceans. Should the burial rate of alkalinity in the more alkaline glacial deep waters outstrip the rate of alkalinity supply, then pelagic carbonate production by the coccolithophores at the end of the glacial maximum could drive a decrease in ocean [CO32-] and act to trigger the deglacial rise in pCO2. Copyright 2010 by the American Geophysical Union.

Understanding the interaction between climate and biotic evolution is crucial for deciphering the sensitivity of life. An enigmatic global mass extinction occurred in the deep oceans during the Mid Pleistocene, with a loss of over 100 species (20%) of sea floor calcareous foraminifera. An evolutionarily conservative group, benthic foraminifera often comprise >50% of benthic eukaryote biomass on the deep ocean floor. Here, we test extinction hypotheses (temperature, corrosiveness, productivity) in the Tasman Sea, using geochemistry and micropalaeontology, and find evidence from several globally distributed sites for a change in phytoplankton food source as the extinction cause. Coccolithophore evolution may have enhanced the seasonal ‘bloom’ nature of primary productivity and fundamentally shifted it towards a more intra-annually variable state at ~0.8 Ma. Our results highlight seasonality as a potential new consideration for Mid-Pleistocene global biogeochemical climate models, and imply that deep sea biota may be sensitive to future changes in productivity.

The shallow water benthic foraminifera Ammonia aomoriensis and Amphistegina lessonii were grown at different seawater Sr/Ca and the test Sr/Ca ratio was determined by Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry. A. aomoriensis test Sr/Ca is positively correlated with seawater Sr/Ca. The linear regression has a slope of 0.17, representing the overall Sr partitioning coefficient KDSr. The slope remains unchanged, if seawater Ca concentration is changed in order to change the seawater Sr/Ca. In the case of A. lessonii, the slopes of the linear regressions representing KDSr differ from one another i.e., 0.16 if the Sr concentration is changed and 0.32 if the Ca level is changed. This difference in KDSr can be explained by the, relative to A. aomoriensis, high Mg content of A. lessonii (ca. 40 mmol/mol), distorting the calcite lattice and weakening the discrimination against Sr. The Mg content of A. aomoriensis is too low (ca. 4 mmol/mol) to observe the influence on Sr partitioning. All data are compatible with a recently developed model for minor element partitioning in foraminifera (Nehrke et al., 2013; Mewes et al., 2015a). On the whole, our data confirm the model (applicability of the model to Sr and dependence of the calcite Sr/Ca on seawater Sr/Ca, as opposed to seawater Sr concentration), and improve our understanding of the model (influence of calcite Mg/Ca on Sr partitioning).

Two new boreholes provide the first direct evidence of the age of the Australian Great Barrier Reef. An inner shelf sequence (total depth, 86 m; basal age = 210 ± 40 ka) comprises a dominantly siliciclastic unit (thickness 52–86 m), overlain by four carbonate units (total thickness 0–34 m). A shelf-edge and slope sequence (total depth 210 m) reveals three major sections: (1) a lower section of resedimented flows deposited on a lower slope, (2) a mid-section including intervals of corals, rhodoliths, and calcarenites with low- angle graded laminae, and (3) an upper section of four shelf- margin coral-reef units separated by karst surfaces bearing paleosols. Sr isotope and magnetostratigraphic data indicate that the central Great Barrier Reef is relatively young (post Bruhnes-Matuyama boundary time), and our best estimate for the onset of reef growth on the outer barrier system is ca. 600 ± 280 ka. This date suggests that reef initiation may have been related to the onset of full eccentricity-dominated glacio-eustatic sea-level oscillation as inferred from large-amplitude “saw-tooth? 100 k.y. ?18O cycles (after marine isotope stage 17), rather than to some regional environmental parameter. A major question raised by our study is whether reef margins globally display a similar growth history. The possibility of a global reef initiation event has important implications for basin to shelf partitioning of CaCO3, atmospheric carbon dioxide levels, and global temperature change during Quaternary time.

The isotopic composition of carbon, δ13C, in seawater is used in reconstructions of ocean circulation, marine productivity, air-sea gas exchange, and biosphere carbon storage. Here, a synthesis of δ13C measurements taken from foraminifera in marine sediment cores over the last 150 000 years is presented. The dataset comprises previously published and unpublished data from benthic and planktonic records throughout the global ocean. Data are placed on a common δ18O age scale suitable for examining orbital timescale variability but not millennial events, which are removed by a 10 ka filter. Error estimates account for the resolution and scatter of the original data, and uncertainty in the relationship between δ13C of calcite and of dissolved inorganic carbon (DIC) in seawater. This will assist comparison with δ13C of DIC output from models, which can be further improved using model outputs such as temperature, DIC concentration, and alkalinity to improve estimates of fractionation during calcite formation.\ud \ud High global deep ocean δ13C, indicating isotopically heavy carbon, is obtained during Marine Isotope Stages (MIS) 1, 3, 5a, c and e, and low δ13C during MIS 2, 4 and 6, which are temperature minima, with larger amplitude variability in the Atlantic Ocean than the Pacific Ocean. This is likely to result from changes in biosphere carbon storage, modulated by changes in ocean circulation, productivity, and air-sea gas exchange. The North Atlantic vertical δ13C gradient is greater during temperature minima than temperature maxima, attributed to changes in the spatial extent of Atlantic source waters. There are insufficient data from shallower than 2500 m to obtain a coherent pattern in other ocean basins. The data synthesis indicates that basin-scale δ13C during the last interglacial (MIS 5e) is not clearly distinguishable from the Holocene (MIS 1) or from MIS 5a and 5c, despite significant differences in ice volume and atmospheric CO2 concentration during these intervals. Similarly, MIS 6 is only distinguishable from MIS 2 or 4 due to globally lower δ13C values both in benthic and planktonic data. This result is obtained despite individual records showing differences between these intervals, indicating that care must be used in interpreting large scale signals from a small number of records.

Millennial-scale records of planktonic foraminiferal Mg/Ca, bulk sediment U37 K′, and planktonic foraminiferal δ 18O are presented across the last two deglaciations in sediment core NIOP929 from the Arabian Sea. Mg/Ca-derived temperature variability during the penultimate and last deglacial periods falls within the range of modern day Arabian Sea temperatures, which are influenced by monsoon-driven upwelling. The U37 K′-derived temperatures in MIS 5e are similar to modern intermonsoon values and are on average 3.5°C higher than the Mg/Ca temperatures in the same period. MIS 5e U37 K′ and Mg/Ca temperatures are 1.5°C warmer than during the Holocene, while the U37 K′-Mg/Ca temperature difference was about twice as large during MIS 5e. This is surprising as, nowadays, both proxy carriers have a very similar seasonal and depth distribution. Partial explanations for the MIS 5e U37 K′-Mg/Ca temperature offset include carbonate dissolution, the change in dominant alkenone-producing species, and possibly lateral advection of alkenone-bearing material and a change in seasonal or depth distribution of proxy carriers. Our findings suggest that (1) Mg/Ca of G. ruber documents seawater temperature in the same way during both studied deglaciations as in the present, with respect to, e.g., season and depth, and (2) U37 K′-based temperatures from MIS 5 (or older) represent neither upwelling SST nor annual average SST (as it does in the present and the Holocene) but a higher temperature, despite alkenone production mainly occurring in the upwelling season. Further we report that at the onset of the deglacial warming, the Mg/Ca record leads the U37 K′ record by 4 ka, of which a maximum of 2 ka may be explained by postdepositional processes. Deglacial warming in both temperature records leads the deglacial decrease in the δ 18O profile, and Mg/Ca-based temperature returns to lower values before δ 18O has reached minimum interglacial values. This indicates a substantial lead in Arabian Sea warming relative to global ice melting.

We present high-resolution records of upper ocean temperatures derived from Mg/Ca ratios of surface-dwelling Globigerina bulloides and subsurface-dwelling Neogloboquadrina pachyderma sinistral and the relative abundance of N. pachyderma sinistral for the period 55–8 ka BP from NE Atlantic sediment core MD01-2461. Millennial-scale temporal variability and longer-term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 (MIS 3) to the last glacial maximum (LGM). The correspondence of all temperature proxies and convergence of paired oxygen isotope (δ 18O) records from both planktonic species implies a breakdown in the thermocline and year-round mixing of the upper water column through the LGM, perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum–North Atlantic ice sheets. Millennial-scale divergence in surface and subsurface temperatures and δ 18O across the last glacial correspond to meltwater release and the development of a strong halocline associated with both Heinrich (H) events and instabilities of the NW European ice sheet. During such episodes, G. bulloides Mg/Ca appears to record ambient, even warming summer sea surface temperatures across H events while the other proxies record maximum cooling.

In this study we present a sea surface temperature (SST) record from the western Arabian Sea for the last 20,000 years. We produced centennial-scale δ

Variations in the near-bottom flow speed of Iceland-Scotland Overflow Water (ISOW) are documented in a 230-year-long deep-sea sediment record from the eastern flank of Reykjanes Ridge in the subpolar North Atlantic at (sub)decadal time scales. For recent decades, the ISOW palaeocurrent reconstructions show similarities with observational hydrographic data. Furthermore, recent ISOW flow changes fall mostly within the range of its variability of the past 230 years. The record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar North Atlantic with the North Atlantic Oscillation (NAO) index, with more (less) vigorous ISOW flow during negative (positive) phases of the NAO. Our results suggest that the changes in ISOW vigor are largely controlled by the transport and characteristics of Labrador Sea Water rather than variations in the overflow itself, with implications for the meridional overturning of the Atlantic Ocean and climate.

In core top samples in the Nordic Seas, Mg/Ca ratios of N. pachyderma ( sin.) are generally consistent with previous high-latitude calibration data but do not reflect the modern calcification temperature gradient from 2 degrees C in the northwest to 8 degrees C in the southeast. This is because Mg/Ca ratios in foraminiferal shells from the central Nordic Seas are similar to 0.4 mmol/mol higher than expected from calibrations of Nurnberg ( 1995) and Elderfield and Ganssen ( 2000). The enhanced Mg/Ca ratios are observed in an area with low sedimentation rates (< similar to 5 cm/kyr). Possible factors that may cause this include bioturbation, Holocene variability in old core tops, dissolution, pore water chemistry, occurrence of volcanic ash, and other natural variability. The enhanced foraminiferal Mg/Ca ratios in areas of the Nordic Seas and the northern North Atlantic may also be linked with secondary factors related to the presence of fresher and colder water masses, possibly combined with pore water chemistry in low-sedimentation areas differing from high-sedimentation areas.

We present evidence that the characteristic chemical signature (based on coupled benthic foraminiferal Cd/Ca and δ13C) of Antarctic Intermediate waters (AAIW) penetrated throughout the intermediate depths of the Atlantic basin to the high-latitude North Atlantic during the abrupt cooling events of the last deglaciation: Heinrich 1 and the Younger Dryas. AAIW may play the dynamic counterpart to the ''bipolar seesaw'' when near-freezing salty bottom waters from the Antarctic (AABW) sluggishly ventilate the deep ocean. Our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters (NADW) and fresh southern sourced waters (AABW and AAIW). Further, the glacial ocean may be susceptible to the more finely balanced relative densities of NADW and AAIW, due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for NADW collapse via a negative salinity feedback. The unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters. Copyright 2005 by the American Geophysical Union.

The variability in Mg/Ca and Sr/Ca within individual tests and chambers of tests, and samples consisting of differing numbers of individuals, was determined for Globigerina bulloides and Globorotalia truncatulinoides in a North Atlantic core top sample (52.918°N 16.917°W'). The variability in Mg/Ca and Sr/Ca within individual tests and chambers was determined by electron microprobe, and samples consisting of variable sample size were measured using inductively coupled plasma optical emission spectrometer (ICP-OES). Large compositional heterogeneity was found within individual chambers, and within the test as a whole, of the two species and the presence of regions with up to ∼10 mmol/mol Mg/Ca, especially in G. bulloides. Mean Mg/Ca decreases in successive chambers of G. bulloides (especially the 300-355 μm fraction) and is accompanied by decreasing variance but is not statistical significant. Sr/Ca is much more homogeneously distributed, with a normal distribution, and shows no differences from chamber to chamber. The variability of Mg/Ca and Sr/Ca decreases with increasing sample size, from single to five to twenty tests per sample, approximately as for a normal distribution, with greater variability for G. bulloides than for G. truncatulinoides, equivalent to uncertainties in temperature (n = 20) of 1.1 °C and 0.7°C for the two species within the whole of the sediment mixed layer. Copyright 2005 by the American Geophysical Union.

Sr/Ca in planktonic foraminifera recovered from the water column over 0-800 m along a meridional transect in the North Atlantic Ocean from 30° to 60°N were compared with data from core-top samples on the same transect and with in situ temperatures determined from water column CTD profiles. Species belonging to the globorotaliid genus show significant variability in Sr/Ca from place to place, whereas non-globorotaliid species show no significant variability. This variability for the globorotaliid species in core-top samples has already been shown to covary with calcification temperature derived from δ

The use of liquid and solid standards for foraminiferal Mg/Ca and Sr/Ca determinations and interlaboratory calibration has been investigated. Preparation of single element standard solutions from primary solid standard material enables the preparation of mixed standard solutions with Mg/Ca and Sr/Ca ratios of known accuracy to better than 0.1%. We also investigated commercial reference materials to determine whether existing carbonate standards could be used as reference material for Mg/Ca determinations in foraminiferal calcite. We propose that, in the absence of a pure calcium carbonate standard certified for Mg/Ca, ECRM 752-1, a limestone CRM containing Mg/Ca within the range of typical foraminifera, is a suitable solid standard for interlaboratory calibration. Replicate Mg/Ca determinations showed that, provided silicate phases are removed by centrifugation, this material is homogenous within the precision of daily instrumental Mg/Ca determinations over a range of sample weights from 10 to 1000 mg, taken from two separate bottles of ECRM 752-1. Results gave an average value of Mg/Ca = 3.75 mmol/mol (0.015 s.d., 0.41% r.s.d.) on 118 determinations from the two bottles.

The oceans cover over two-thirds of the Earth’s surface. They play a vital role in global biogeochemical cycles, contribute enormously to the planet’s biodiversity and provide a livelihood for millions of people. (...)

International audience; [1] Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of +/- 0.2 degreesC and +/- 0.5 degreesC, respectively. The analysis of foraminifera suggests an interlaboratory variance of about +/-8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about +/- 2 - 3 degreesC. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about +/- 1 - 2 degreesC) and a bias (about 1 degreesC) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

Records of planktonic foraminiferal shell weights for Globigerina bulloides, covering Termination I from four proximal sites at waters depths from 1150 to 4045 m in the northeast Atlantic, demonstrate the influence of dissolution superimposed upon initial shell weight variability. Records of shell weight, unaffected by dissolution, may be used as a reference for interpreting deeper records in terms of preservation history. Combining records of planktonic shell weight (and benthic δ13C) from shallow and deep sites suggests that maximum oceanic stratification and incursion of southern sourced deep waters in the North Atlantic occurred at about 18–20 ka, defining the glacial mode of Atlantic circulation. Reduced stratification and enhanced preservation in deeper waters reflect conditions during Heinrich event 1. A state similar to the modern mode of Atlantic circulation was attained by about 10 ka.

Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2–3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1–2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

Paired measurements of Mg/Ca and delta(18)O(cc) (calcite delta(18)O) in benthic foraminifera from a deep-sea core recovered on the Iberian Margin (MD99-2334K; 37degrees 48'N, 10degrees10'W; 3,146 m) have been performed in parallel with planktonic delta(18)O(cc) analyses and counts of ice-rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic delta(18)O(cc) allows the proxy records from MD99-2334K to be placed confidently on the GISP2 time-scale. This correlation is further corroborated by AMS C-14-dates. Benthic Mg/Ca measurements in MD99-2334K permit the reconstruction of past deep-water temperature (T-dw) changes since -34 cal. ka BP (calendar kiloyears before present). Using these T-dw estimates and parallel benthic delta(18)O(cc) measurements, a record of deepwater delta(18)O (delta(18)O(dw)) has been calculated. Results indicate greatly reduced T-dw in the deep Northeast Atlantic during the last glaciation until -15 cal. ka BP, when T-dw warmed abruptly to near-modern values in parallel with the onset of the Bolling-Allerod interstadial. Subsequently, Tdw reverted to cold glacial values between -13.4 and -11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice-rafting event. Similar millennial-scale T-dw changes also occurred during the last glaciation. Indeed, throughout the last -34 cal. ka, millennial delta(18)O(dw) and T-dw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower T-dw and delta(18)O(dw) conditions occurred. In general, millennial T-dw and delta(18)O(dw) variations recorded in MD99-2334K describe an alternation between colder, low-delta(18)O(dw) and warmer, high delta(18)O(dw) conditions, which suggests the changing local dominance of northern-sourced North Atlantic Deep Water (NADW) versus southern-sourced Antarctic Bottom Water (AABW). The observed similarity of the T-dw and GISP2 delta(18)O(ice) records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low-delta(18)O(dw) AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic delta(18)O(cc) signal since -34 cal. ka BP.

Paleoceanographic reconstructions from the North Atlantic indicate massive ice breakouts from East Greenland near the onset of cold Dansgaard-Oeschger (D-O) stadials. In contrast to these coolings in the North Atlantic area, a new sea-surface temperature record reveals concomitant warm spells in the northern North Pacific. A sensitivity experiment with an atmospheric general circulation model is used to test the potential impact of sea-surface warmings by 3.5C in the North Pacific, on top of otherwise cold stadial climate conditions, on the precipitation regime over the Northern Hemisphere ice sheets. The model predicts a maximum response over East Greenland and the Greenland Sea, where a 40% increase in net annual snow accumulation occurs. This remote effect of North Pacific warm spells on the East Greenland snow-accumulation rate may play an important role in generating D-O cycles by rebuilding the ice lost during ice breakouts. In addition, the increased precipitation over the Greenland Sea may help to sustain the D-O stadial climate state.

Rev. Soc. Geol. España, 12(1), ano 1999 Lithostratigraphy, main biostratigraphic events (first and last ocurrence), 87Sr/86Sr as well as KlAr isotopic ages, are presented for the Lower Tagus basin (LTB) Miocene (Lisboa and Peninsula de Setubal regions). Eight depositional sequences (DS) delimited by regional disconformities related with transgressive surfaces are defined. The main features of the Depositional Sequences are as follows: Depositional sequence (DS) A (Aquitanian). Biostratigraphy (Biost.): Small mammals from Km 10: MN2 (MN3?); ostracoda: Aquitanian fauna. Isotopic age (IA): glauconites (KlAr) values between 19 and 24 Ma. 87Sr/86Sr ages from the glauconite levels: 22.3 (+0.4-0.7) Ma. Lower and upper boundaries not well established. DS BO (Lower Burdigalian). Biost.: foraminifera - Fa Globigerinoides altiaperturus (NS); mammals - Fa Brachyodus intermedius (MN3); ostracoda - La Hemicyprideis helvetica and Pokomyella lusitanica at the LTB. IA (87Sr/86Sr): Foz da Fonte -19.S (±0.2) Ma, Penedo Sui (base) - 20.0(±0.4)Ma; Almada (top) - 18.3 (+0.-0.2) Ma. Mammal sites: Av. do Uruguai - 21.S( +O.S- 0.3) Ma; Univ. Cat6lica - 20.S (+0.3-0.2) Ma. DS Bl (Middle Burdigalian). Biost.: foraminifera - Catapsydrax unicavus and Globigerinoides altiaperturus (N6); mammals - Fa Gomphotherium, La of Brachyodus (MN4); ostracoda -La Ruggieria (R.) micheliniana, Cnestocythere truncata, Pokomiella minor and Triebelina raripila. fA (87Sr/86Sr) Foz da Fonte - 19.7 (+0.3-0.2) to 18.S (+0.2-0.S) Ma. DS B2 (Upper Burdigalian). Biost.: mammals -Fa Bunolistriodon and Megacricetodon primitivus (MN4); ostracoda - La Miocyprideisfortisensis. IA (87Sr/86Sr): Penedo Norte 17.7 (+0.7-0.S) Ma; 17.8 (+0.7- O.S) Ma. DS Ll (Upper Burdigalian and Langhian). Biost.: foraminifera - Fa Praeorbulina (N8); mammals - Fa (upper part) Hispanotherium and Megacricetodon collongensis, La M. primitivus (MNS); ostracoda - Fa Pterigocythereis (P.) siveteri and Loxoconcha (L.) ducasseae. IA (87Sr/86Sr): Penedo Norte 17.3 (+0.6-0.5) Ma. DS SI (Upper Langhian and Serravallian). Biost.: foraminiferaFa Orbulina suturalis, O. universa and Globorotalia cf. menardii; ostracoda -Fa Aurila (u.) oblonga, Ruggieria (R.) nuda, R. tetraptera tetraptera, Nomurocythereis seminulum, Pterygocythereis (P.) jonesi y Olinfalunia costata. IA (87Sr/86Sr): Chelas 14.7 (+ 1.S-0.S) Ma, Almada (Brielas ) (lower part) - 14.0 (±0.4 ) Ma, Penedo (upper part) 12.S (+ 1.0-2.0) Ma. DS S2? (Upper Serravallian) is poorly characterized due to strong condensation (Foz da Fonte-Rib. Lage) and poor outcrops (Lisbon region). Biost.: foraminifera - La Globigerinoides subquadratus (top). DS Tl (Tortonian). Biost.: foraminifera - La Globorotalia mayeri (lower part), Fa Neogloboquadrina acostaensis (upper part); ostracoda - Fa Aurila (U.) zbyszewskii, Celtia quadridentada and Cyheretta (C.) simplex. IA: Penedo Norte: KlAr- 1O.9S±0.2S Ma; 87Sr/86Sr - 11.3 (+ 1.7-2.8) Ma; Almada (Foz de Rego) - 8.3 (+ 1.9-3.3) Ma; Fonte da Telha S.2 (+3.1-1.2) Ma.

Second Congress R.C.A.N.S., Salamanca, pp.37-55

The isotopic composition of carbon, δ13C, in seawater is used in reconstructions of ocean circulation, marine productivity, air-sea gas exchange, and biosphere carbon storage. Here, a synthesis of δ13C measurements taken from foraminifera in marine sediment cores over the last 150 000 years is presented. The dataset comprises previously published and unpublished data from benthic and planktonic records throughout the global ocean. Data are placed on a common δ18O age scale suitable for examining orbital timescale variability but not millennial events, which are removed by a 10 ka filter. Error estimates account for the resolution and scatter of the original data, and uncertainty in the relationship between δ13C of calcite and of dissolved inorganic carbon (DIC) in seawater. This will assist comparison with δ13C of DIC output from models, which can be further improved using model outputs such as temperature, DIC concentration, and alkalinity to improve estimates of fractionation during calcite formation. High global deep ocean δ13C, indicating isotopically heavy carbon, is obtained during Marine Isotope Stages (MIS) 1, 3, 5a, c and e, and low δ13C during MIS 2, 4 and 6, which are temperature minima, with larger amplitude variability in the Atlantic Ocean than the Pacific Ocean. This is likely to result from changes in biosphere carbon storage, modulated by changes in ocean circulation, productivity, and air-sea gas exchange. The North Atlantic vertical δ13C gradient is greater during temperature minima than temperature maxima, attributed to changes in the spatial extent of Atlantic source waters. There are insufficient data from shallower than 2500m to obtain a coherent pattern in other ocean basins. The data synthesis indicates that basin-scale δ13C during the last interglacial (MIS 5e) is not clearly distinguishable from the Holocene (MIS 1) or from MIS 5a and 5c, despite significant differences in ice volume and atmospheric CO 2 concentration during these intervals. Similarly, MIS 6 is only distinguishable from MIS 2 or 4 due to globally lower δ13C values both in benthic and planktonic data. This result is obtained despite individual records showing differences between these intervals, indicating that care must be used in interpreting large scale signals from a small number of records. © Author(s) 2010.

This Discussion Meeting Issue of the Philosophical Transactions A had its genesis in a Discussion Meeting of the Royal Society which took place on 10–11 October 2011. The Discussion Meeting, entitled ‘Warm climates of the past: a lesson for the future?’, brought together 16 eminent international speakers from the field of palaeoclimate, and was attended by over 280 scientists and members of the public. Many of the speakers have contributed to the papers compiled in this Discussion Meeting Issue. The papers summarize the talks at the meeting, and present further or related work. This Discussion Meeting Issue asks to what extent information gleaned from the study of past climates can aid our understanding of future climate change. Climate change is currently an issue at the forefront of environmental science, and also has important sociological and political implications. Most future predictions are carried out by complex numerical models; however, these models cannot be rigorously tested for scenarios outside of the modern, without making use of past climate data. Furthermore, past climate data can inform our understanding of how the Earth system operates, and can provide important contextual information related to environmental change. All past time periods can be useful in this context; here, we focus on past climates that were warmer than the modern climate, as these are likely to be the most similar to the future. This introductory paper is not meant as a comprehensive overview of all work in this field. Instead, it gives an introduction to the important issues therein, using the papers in this Discussion Meeting Issue, and other works from all the Discussion Meeting speakers, as exemplars of the various ways in which past climates can inform projections of future climate. Furthermore, we present new work that uses a palaeo constraint to quantitatively inform projections of future equilibrium ice sheet change.

A synthesis about the Neogene and Quaternary of Algarve (Southern Portugal) is presented. New isotopic 87Sr/86Sr ages as well as biostratigraphic data about the Miocene deposits allow to present a new stratigraphic frame for the previously characterized units. The Lagos-Portimão Formation corresponds to deposits of temperate carbonate platform sedimentological type, developed during a long time span (Lower Burdigalian to Upper Serravallian). A major change in sedimentation conditions (carbonate to siliciclastic environments) occurred in the Lower Tortonian with the deposition of yellowish sands. Spongoliths rich in microfossils are represented in Algarve inland. Their age is not well established; calcareous nannofossils indicate the CN5a zone (Upper Serravallian) while foraminifera point out at least Nl6 zone (Lower Tortonian). In the Upper Tortonian, the sedimentation is widespread in Eastern Algarve, related with the Guadalquivir Basin infill. The deposits begin with detrital limestones, locally very rich in Heterostegina, passing to fossiliferous conglomerates and siltstones (Cacela Formation). Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±0.17 Ma. However, glauconites may be reworked from older deposits (Cacela Formation). The Galvana Conglomerate could be related to Pliocene deposits are not well characterized. Olhos de Água sands, with a thin marine intercalation rich in marine vertebrates (fishes, a crocodile, cetaceans, sirenians), may be Upper Pliocene; however, the vertebrates point out to a Serravallian to Tortonian age. 87Sr/86Sr ages on oysters from above the level with vertebrates point out to 3.0(+2.5-1.0) Ma. Similar sand deposits occur at Morgadinho (Luz de Tavira). These sands are overlain by marls, lignite clays, lacustrine limestones and a silty calcareous crust. A small mammals association indicate an age span between Upper Pliocene and Lower Middle Pleistocene (MN17-MN20). A Biharian mammal fauna (Lower Pleistocene) was collected at Algoz in similar deposits. In the present state of knowledge, Morgadinho and Algoz deposits may be correlative.

Paired measurements of Mg/Ca and δ18Occ (calcite δ18O) in benthic foraminifera from a deep-sea core recovered on the Iberian Margin (MD99-2334K; 37°48′N, 10°10′W; 3,146 m) have been performed in parallel with planktonic δ18Occ analyses and counts of ice-rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic δ18Occ allows the proxy records from MD99-2334K to be placed confidently on the GISP2 time-scale. This correlation is further corroborated by AMS 14C-dates. Benthic Mg/Ca measurements in MD99-2334K permit the reconstruction of past deep-water temperature (Tdw) changes since ∼34 cal. ka BP (calendar kiloyears before present). Using these Tdw estimates and parallel benthic δ18Occ measurements, a record of deep-water δ18O (δ18Odw) has been calculated. Results indicate greatly reduced Tdw in the deep Northeast Atlantic during the last glaciation until ∼15 cal. ka BP, when Tdw warmed abruptly to near-modern values in parallel with the onset of the Bølling-Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ∼13.4 and ∼11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice-rafting event. Similar millennial-scale Tdw changes also occurred during the last glaciation. Indeed, throughout the last ∼34 cal. ka, millennial δ18Odw and Tdw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower Tdw and δ18Odw conditions occurred. In general, millennial Tdw and δ18Odw variations recorded in MD99-2334K describe an alternation between colder, low-δ18Odw and warmer, high δ18Odw conditions, which suggests the changing local dominance of northern-sourced North Atlantic Deep Water (NADW) versus southern-sourced Antarctic Bottom Water (AABW). The observed similarity of the Tdw and GISP2 δ18Oice records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low-δ18Odw AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic δ18Occ signal since ∼34 cal. ka BP.