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Through the discharge of pollutants, urbanization and industrial activities impact all the compartments of the environment and the ecosystems. Consequently, metal pollution of soils and atmosphere has become a significant problem in urban areas.In the Dunkirk agglomeration (Northern France), the construction of a large seaport during the 20th century was accompanied by the installation of several metallurgical industries. Dust emissions resulting from their production and storage activities are mainly composed of atmospheric particles of soot, aluminosilicates, silica, calcium or iron. These industrial particles can be associated with specific minor and trace elements : Cr, Cu, K, Mg, Mn, Na, Pb, Ti, Zn or Cl. The composition and the size of the particles determine their fate after emission and influence their toxicity. This study focuses on sedimentable particles (>20 µm) that cannot penetrate deeply into the respiratory system but can be ingested, especially by children. Due to its location (1 to 2 km South-West of major industries), the city of Gravelines is particularly exposed to dust deposition during North-East windy and dry events.Among the studies conducted on particles emitted in the Dunkirk area, none was focused on soil matrices. Therefore, the question of the long-term fate of their deposition remains open : what is the influence of these dusts on the chemical quality of the soils of Gravelines ? Which areas of the city of Gravelines are the most affected by metal contamination (potentially associated with dust) ?Pedological and chemical parameters of topsoils (the first 5 cm) sampled in the city of Gravelines were, first, characterized with the aim to interpret their reactivity to metal inputs. Then, the trace metal concentrations of topsoils and collected dust samples were determined by inductively coupled plasma-mass spectrometry (ICP–MS) to (1) map the areas contaminated by trace metals, (2) assess the levels of environmental pollution, (3) quantitatively characterize the metals associated with dust fallout, and (4) highlight the specific influence of industrial dusts on the potential soil contamination in Gravelines. The first results on the metal contents measured in the topsoil samples of Gravelines rather reflect a diffuse metallic contamination. The study of the entire topsoil samples may be questioned because of the dilution of the "dust" signal by the soil matrix. The relative youth of the large seaport of Dunkirk (between 30 and 40 years old), as well as the probable re-mobilization of dust by the winds, may partly explain the moderate contamination measured in soils of Gravelines. However, our results show higher levels of contamination (for some specific metals) and a significant Pollution Load Index (PLI) in the soils located near dust emission sources. Moreover, the combined mapping of metal contents and soil parameters allows the identification of possible differences in metal behavior depending on the nature of the matrix considered. This latter aspect will be discussed in particular according to the use of soils and vegetation (e.g. proximity of the vegetable gardens), in order to highlight areas requiring special attention from an ecotoxicological point of view.

International audience; Recent culture studies of living coccolithophores have established a biogeochemical framework for the use of the geochemical compositions of their calcite biominerals as proxies in palaeoceanography. Yet, questions remain regarding the transferability of such experimental data to fossil coccoliths. Here we analysed the carbon and oxygen isotopic composition of Miocene coccoliths to assess the suitability of such data for reconstructing the past environment. We found that the oxygen isotopic compositions of the relatively small Noelaerhabdaceae coccoliths gathered in the 3-5 μm fractions appear to be a suitable material to derive temperatures after a correction for a constant vital offset of 0.8‰. The interpretation of the isotopic signal of the relatively large Coccolithales coccoliths (5-8 μm fractions) is more complex, but supports results from cultures. The expression of the carbon and oxygen vital effect in coccoliths appears to be limited during the so-called Miocene Climate Optimum (MCO), a period of relatively elevated atmospheric pCO2. Subsequently, during the Miocene Climatic Transition (MCT; ~14 Ma), which saw a decline in pCO2, large carbon and oxygen vital effects were expressed in coccolith calcite. This phenomenon predates the postulated “Late Miocene Threshold” by approximately 4 Ma, and cannot be reconciled as a temporally-synchronous nor localised feature. Furthermore, we observed a statistically significant correlation between the oxygen and carbon offsets of the small relative to large coccoliths (hence, the vital effect per se) that is likely linked to variations in atmospheric CO2. This biogeochemical correlation further supports a forcing of the environment on the cellular physiology (growth rate and utilisation of intracellular carbon) and ultimately the magnitude of isotopic vital effects in fossil coccoliths.

The mechanisms governing the development of deep-sea fans is a matter of debate and their understanding at Milankovitch and millenial time-scales is challenged by complex architectures and the lack of material suitable for establishing reliable chronostratigraphies. Based on a detailed investigation of the emplacement of channel-levee-lobe systems and their successive bifurcations and seaward-landward migrations (Picot et al., 2016), we present for the last 210 ka a detailed chronostratigraphic framework of the migration pattern based mainly on radiocarcarbon dating of channels and lobes abandonment or initiation. The comparison of architectural cycles to proxies of external factors (sea-level and climate) suggest that sea-level changes have minor impacts on the architectural evolution of the Congo Fan. In contrast, comparison with climate and environmental proxies (West African monsoon, pollen grain assemblages, Kaolinite/Smectite) evidences a major impact on the timing of the development of the architectural pattern, at least for the last 38 kyr. A general scheme of the growth pattern of the Congo Fan in link with climate evolution is proposed: the stacking pattern of the Congo Fan responds to humidity/aridity cycles that generate successive progradation and retrogradation of avulsion points. These climate changes are under the control of the West African monsoon which, by controlling the rainfall and vegetation on the watershed, ultimately impacts the composition and volume of the sediment source and the transport capacity of gravity flow generated in the canyon and flowing in the turbiditic channels.

Despite their omnipresence in pelagic carbonate sediments, the coccoliths, the calcite biominerals produced by the coccolithophores, have historically been under-exploited in palaeoenvironmental studies. This is due, in part, to their small size (2-20 microns), which makes them difficult to isolate from other particles, and to the large differences in isotopic composition existing between coccolith calcite and equilibrium conditions. This so-called “vital effect” complicates the use of coccolith geochemistry to derive paleoclimatic signals with confidence. Recent studies from cultured and fossil coccoliths have shown that the oxygen and carbon isotopic compositions of the coccoliths are particularly sensitive to the availability of CO2 in the environment, upon which the coccolithophores rely for their photosynthetic activity. Therefore, our approach here is to test whether the coccolith geochemistry can be used as a novel proxy for surface ocean and atmospheric CO2 concentrations.In this study, different size fractions of coccoliths were extracted from carbonate sediments of site MD95-2037 in the Northern Atlantic Ocean and run for isotopic analysis. Using calibrations between coccolith vital effects and seawater [CO2] from culture studies, we present a seawater [CO2] curve for site MD95-2037 across Termination II (130 kyrs). The curve was in turn translated into atmospheric pCO2 estimates taking into account changes in ancillary parameters (such as temperature). Coccolith-derived CO2 concentrations yield comparable values, both for the absolute numbers and trends, to the record from Vostok ice cores. This coherency is confirmed by a 80 ppm-shift in pCO2 concentrations in the North Atlantic between glacial and interglacial times reconstructed from the coccolith record.Altogether, these datasets confirms that coccolith geochemistry can indeed be used to reconstruct past changes in [CO2]sw. Perspectives for this study include providing the scientific community with a new record of pCO2 for periods extending beyond the Vostok record, in particular the Mid-Pleistocene Transition, where a decrease in global pCO2 has been put forward to explain the shift from 41 kyr- to 100 kyr-cycles in glacial-interglacial cycles.

International audience

International audience; Coccolithophores have been extensively studied to understand the environmental control on calcification in a key biological group influencing the alkalinity of seawater. Previous studies have established that bulk calcification scales with cell division rates under a wide range of pH conditions. Yet, the fine scale ultrastructural changes of the coccoliths and therefore the pH-sensitive underlying mechanisms altering biomineralization of the coccoliths remain largely under-constrained. Using circularly polarized light and high-resolution microscopy, we have generated mass estimates of cultured Gephyrocapsa oceanica coccoliths grown in media with pH values ranging from 7.4 to 9.0. These mass estimates representing a bulk calcification response were related to the morphological changes within the coccoliths. From optimal (pH 8.6) down to pH 7.4 conditions, we have observed that impaired cell growth and lower calcite quota are accompanied by a 35% decrease in mean coccolith mass. The data further show that seawater acidification does not homogenously affect calcification of the coccoliths, as a clear decrease of the breadth of the tube (a structure surrounding the central area of the coccoliths) was detected, whereas all other ultrastructural components were far less impacted. We discuss this specific sensitivity to acidification as the possible consequence of the altered interaction of the acidic polysaccharides used for biomineralization and ambient concentration of protons released by calcification that substantially modify the growth patterns, the morphology, and ultimately the mass of the coccoliths.

The present work examines the relationship between pH-induced changes in growth and stable isotopic composition of coccolith calcite in two coccolithophore species with a geological perspective. These species (Gephyrocapsa oceanica and Coccolithus pelagicus) with differing physiologies and vital effects possess a growth optimum corresponding to average pH of surface seawater in the geological period during their first known occurrence. The “ancestral” C. pelagicus has much wider pH tolerance in terms of growth rates than the more recently evolved G. oceanica. Diminished growth rates are explained by the challenge of proton translocation into the extracellular environment at low pH and enhanced aqueous CO2 limitation at high pH. Reducing the cell dynamics in this way leads to a lower degree of oxygen isotopic disequilibrium in G. oceanica. In contrast, the slower growing species C. pelagicus, which typically precipitates near-equilibrium calcite, does not show any modulation of oxygen isotope signals with changing pH. Overall, carbon and oxygen isotope compositions are best explained by the degree of utilization of the internal dissolved inorganic carbon (DIC) pool and the dynamics of isotopic reequilibration inside the cell. Thus, the “carbonate ion effect” may not apply to coccolithophores. This difference with foraminifera can be traced to different modes of DIC incorporation into these two distinct biomineralizing organisms. From a geological perspective, these findings have implications for refining the use of oxygen isotopes to infer more reliable sea surface temperatures (SSTs) from fossil carbonates and contribute to a better understanding of how climate-relevant parameters are recorded in the sedimentary archive.

Reconstruction of sea surface temperatures from the oxygen isotope composition (δ18O) of calcite biominerals synthesised in the mesopelagic zone of the oceans requires knowledge of the δ18O of seawater and constraints on the magnitude of biological 18O∕16O fractionation (the so-called vital effect). In the palaeoceanography community, seawater δ18O and salinity are unduly treated as a common parameter owing to their strong covariation both geographically and in the geological register. If the former parameter has arguably no notable influence on the biogeochemistry of marine calcifiers, salinity potentially does. However, how salinity per se and the effect of osmotic adjustment can modulate the biogeochemistry, and in turn, the expression of the vital effect in calcite biomineral such as the coccoliths remains undocumented. In this culture-based study of coccolithophores (Haptophyta) belonging to the Noelaerhabdaceae family, we kept temperature and seawater δ18O constant, and measured basic physiological parameters (growth rate and cell size), and the isotope composition (18O∕16O and 13C∕12C) of coccoliths grown under a range of salinity, between 29 and 39. Ultimately, the overarching aim of this biogeochemical study is to refine the accuracy of palaeotemperature estimates using fossil coccoliths. We found that despite significant physiological changes in the coccolithophores, varying salinity does not modulate biological fractionation of oxygen isotopes. This observation contrasts with previous in vitro manipulations of temperature and carbonate chemistry that led to substantial changes in the expression of the vital effect. As such, salinity does not affect temperature estimation from coccolith-bearing pelagic sequences deposited during periods of change in ice volume, especially at the highest latitudes, or in coastal regions. By contrast, the carbon isotope composition of the coccoliths is influenced by a growth rate mediated control of salinity with implications for deriving productivity indices from pelagic carbonate.

In this study we investigate the temperature dependence of oxygen isotope ratios preserved in calcite formed by the dinoflagellate Thoracosphaera heimii, focusing primarily on the development of a geological proxy. Geochemical analysis of the calcite shells produced by this species represents a valuable proxy for reconstructing environmental conditions in the intermediate photic zone. Calibration is based on isotopic analysis from culture experiments performed in very dilute batch conditions, as well as from near-monospecific T. heimii assemblages separated from core top sediments. Results are similar for both approaches and indicate that T. heimii shells have oxygen isotope compositions close to equilibrium values predicted for inorganic calcite precipitation. This calibration of the isotopic composition of dinoflagellate calcite indicates that monospecific assemblages of T. heimii can be used to unravel paleotemperatures in the intermediate photic zone by applying isotopic transfer functions for equilibrium calcite. In culture, however, a δ 18 O offset of A1‰ is observed at temperatures

Three macroalgal species belonging to Chlorophyta (Ulva rigida), Rhodophyta (Ellisolandia elongata) and Phaeophyceae (Heterokontophyta; Cystoseira tamariscifolia), natu- rally growing at the same shore level and representing 3 morpho-functional groups, were exposed to short-term changes in temperature under different carbon and nitrogen regimes. Experiments were conducted in outdoor tanks at 4 combinations of carbon and nitrogen levels under reduced solar radiation. In vivo chl a fluorescence parameters and pigment contents were monitored to assess diurnal physiological responses and potential for recovery. Strong fluctuations in chl a flu- orescence parameters, but not in chl a content, were observed in response to diurnal variation in solar radiation and light climate within the tanks; sensitivity varied between algal species and, in some cases, depended on the carbon and nitrogen regime. Nitrogen uptake was similarly high in U. rigida and E. elongata and lowest in C. tamariscifolia. In U. rigida and E. elongata, chl a con- centrations decreased after high-carbon treatments. Effective photosystem II quantum efficiency was reduced in all species at noon, and lowest in C. tamariscifolia. The results highlight the com- plexity of physiological short-term acclimations which were most likely linked to biochemical changes at the cellular level. Long-term experiments are required in future for more comprehen- sive investigation of the observed interactive effects of the different environmental parameters.

The geochemical events (negative shifts in δ13C and δ18O, and Mn peak) associated with the “Schistes carton” of Quercy (SW France) do not appear to be due only to lithological variations and a differential diagenesis. They correspond to the Lower Toarcian global event and seem to be connected to a destabilization phase of gas hydrates. During its oxidation by seawater, the release of methane gas with a very low carbon isotopic ratio (− 60%) led to the production of CO2 and carbonates with a negative δ13C. The consumption of oxygen in the seawater resulted in conditions that were first dysoxic and then anoxic. The reduction of burrowing and bioturbation associated with this oxidation resulted in the laminated appearance of the “Schistes carton”. The decrease in the oxygen content led to a decrease in MnO2 microparticles present in the water column and sediments. This created a complementary source of Mn2+ that was incorporated into the carbonates produced during this event. Furthermore, an increase in the average seawater temperature (δ18O) appears associated with this event. Finally, the apparent diachronism of geochemical events in the Boreal and the Tethyan realms is discussed.

Coccolithophorid algae, particularly Emiliania huxleyi, are prolific biomineralisers that, under many conditions, dominate communities of marine eukaryotic plankton. Their ability to photosynthesise and form calcified scales (coccoliths) has placed them in a unique position in the global carbon cycle. Contrasting reports have been made with regards to the response of E. huxleyi to ocean acidification. Therefore, there is a pressing need to further determine the fate of this key organism in a rising CO2 world. In this paper, we investigate the phenotype of newly isolated, genetically diverse, strains of E. huxleyi from UK Ocean Acidification Research Programme (UKOA) cruises around the British Isles, the Arctic, and the Southern Ocean. We find a continuum of diversity amongst the physiological and photosynthetic parameters of different strains of E. huxleyi morphotype A under uniform, ambient conditions imposed in the laboratory. This physiology is best explained by adaptation to carbonate chemistry in the former habitat rather than being prescribed by genetic fingerprints such as the coccolithophore morphology motif (CMM). To a first order, the photosynthetic capacity of each strain is a function of both aqueous CO2 availability, and calcification rate, suggestive of a link between carbon concentrating ability and calcification. The calcification rate of each strain is related linearly to the natural environmental [CO32−] at the site of isolation, but a few exceptional strains display low calcification rates at the highest [CO32−] when calcification is limited by low CO2 availability and/or a lack of a carbon concentrating mechanism. We present O2-electrode measurements alongside coccolith oxygen isotopic composition and the uronic acid content (UAC) of the coccolith associated polysaccharide (CAP), that act as indirect tools to show the differing carbon concentrating ability of the strains. The environmental selection revealed amongst our recently isolated strain collection points to the future outcompetition of the slow growing morphotypes B/C and R (which also lack a carbon concentrating mechanism) by more rapidly photosynthesising, and lightly calcified strains of morphotype A but with their rate of calcification highly dependent on the surface ocean saturation state. The mechanism of E. huxleyi response to carbonate chemistry in the modern ocean appears to be selection from a continuum of phenotype.

Despite a growing body of work that uses diatom δ 30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ 30Si. Once the correct size fraction is selected (generally 2-20μm), diatom δ 30Si shows a strong negative correlation with surface water silicic acid concentration (R 2=0.92), highly supportive of the qualitative use of diatom δ 30Si as a proxy for silicic acid utilisation. The core top diatom δ 30Si matches well with mixed layer filtered diatom δ 30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ 30Si in sediments from the Southern Ocean. However, the core top diatom δ 30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ 30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ 30Si. © 2012.

The glacial/interglacial cycles of the Pleistocene were first recognised by variations in the oxygen isotopic composition of planktonic foraminifera from cores in the Caribbean Sea. Since this pioneering work by Emiliani, this proxy has been extensively applied to a variety of carbonate biominerals over the entirety of the Meso-Cenozoic. However, palaeoceanographic studies have overwhelmingly focused on foraminifera compared to other calcifying microorganism fossils, such as the coccoliths. In this study, I revisit coccolith stable isotopic data obtained from the classic P6304-4 core in light of recent developments in the biogeochemistry of coccolithophores. In particular, I show that the coccolith stable isotope record of the last 13 Marine Isotope Stages (∼480 kyrs) is significantly biased by large vital effects. The magnitude of coccolith carbon and oxygen isotope vital effects is not uniform, but shows remarkable co-variance with the Vostok CO2 ice record. During periods of relatively elevated CO2 (interstadials), the expression of the vital effect is relatively small, whereas it can as high as +3‰ for the oxygen isotopes during glacial stadials, which I argue is a result of enhanced CO2 limitation of coccolithophores. Using this paradigm, I propose that coccolithophore vital effects are not a complicating factor, but rather the signal of interest. As the magnitude of the coccolith vital effect is shown to scale with pCO2, coccolith carbon and oxygen isotopes may be used in conjunction with foraminifera data to reconstruct and refine aqueous CO2 concentrations in the past.

By recreating a range of geologically relevant concentrations of dissolved inorganic carbon (DIC) in the laboratory, we demonstrate that the magnitude of the vital effects in both carbon and oxygen isotopes of coccolith calcite of multiple species relates to ambient DIC concentration. Under high DIC levels, all the examined coccoliths exhibit significantly reduced isotopic offsets from inorganic calcite compared to the substantial vital effects expressed at low (preindustrial and present-day) DIC concentrations. The supply of carbon to the cell exerts a primary control on biological fractionation in coccolith calcite via the modulation of coccolithophore growth rate, cell size and carbon utilisation by photosynthesis and calcification, altogether accounting for the observed interspecific differences between coccolith species. These laboratory observations support the recent hypothesis from field observations that the appearance of interspecific vital effect in coccolithophores coincides with the long-term Neogene decline of atmospheric CO2 concentrations and bring further valuable constraints by demonstrating a convergence of all examined species towards inorganic values at high pCO2 regimes. This study provides palaeoceanographers with a biogeochemical framework that can be utilised to further develop the use of calcareous nannofossils in palaeoceanography to derive sea surface temperature and pCO2 levels, especially during periods of relatively elevated pCO2 concentrations, as they prevailed during most of the Meso-Cenozoic.

Coccoliths contribute significantly to pelagic sediments formed over the last 200 million years, yet their geochemistry has been largely overlooked as a potential record of palaeoenvironmental information. Recently developed techniques have enabled successful extraction of coccolith-dominated sediment fractions. However, the reliability of palaeoenvironmental interpretations that can be drawn from coccolith analyses is still confounded by a poor understanding of the “vital effect” – the physiological component of the isotopic composition of biominerals. Here we demonstrate that oxygen isotope composition in core-top coccoliths is not only set by the temperature and isotopic composition of seawater, but appears to be controlled to first order by the environmental factors regulating algal growth rate. Partial registration of the isotopic signature of assimilated CO2 (with a heavy isotopic composition relative to other dissolved inorganic carbon species) is confirmed to be the dominant mechanism behind the vital effect recorded in the Noelaerhabdaceae coccoliths. Our data point towards a strong role of growth irradiance on expression of the 18O and 13C vital effects, ranging from limited (near equilibrium composition) in low light regimes to 3% offset in oxygen isotopes at higher growth irradiances, such as those found under light-saturated conditions typically imposed in laboratory cultures. This highlights the importance of considering environmental controls when translating oxygen isotope composition of coccoliths into temperature estimates. Furthermore, our calibration suggests that the alkenone-based CO2 palaeobarometer proxy may be refined by combining paired organic/calcite measurements during the Cenozoic.

Short-term effects of increasing pCO(2); 380 ppm (LC) vs. 700 ppm (HC); at different nitrogen levels; 5 mu M nitrate (LN) vs. 50 mu M (HN); on the contents of protein, mycosporine-like amino acids (MAAs), phenolic compounds and total fatty acids, antioxidant activity, calcification and C: N ratios were analyzed in 3 eulittoral Mediterranean macroalgae with different bio-optical characteristics and carbon assimilation efficiencies: Cystoseira tamariscifolia (Heterokontophyta), Ulva rigida (Chlorophyta) and Ellisolandia elongata (Rhodophyta). After acclimation to different pCO(2) and nitrogen conditions for 6 d, the algae were subjected to a 4 degrees C temperature increase for 3 d. Increasing temperature and pCO(2) produced alterations in the biochemical composition of the 3 macroalgae. Short-term variations of protein levels were observed in U. rigida, with clearly decreased values in the HCLN treatment. In C. tamariscifolia, protein decreased after the temperature increase but only under LC. The interaction of temperature and N affected phenolic compounds only in U. rigida and the content of MAAs in E. elongata. The functional patterns of the 3 macroalgae in response to the pCO(2), nitrogen and temperature regimes may be explained in terms of their bio-optical characteristics and antioxidant activity. The vulnerability and acclimation of the 3 species to the expected variations of climate change factors are discussed.

Coccolithophore biominerals, the coccoliths, represent an important part of the Meso-Cenozoic sedimentary archive. Geochemical analyses of coccoliths can be used to unravel climatic fluctuations in the oceanic realm, but such reconstructions are complicated due to the problem of the "vital effect". This concept refers to the modulation in the record of the physico-chemistry of seawater in calcite due to algal physiology. For decades, it was thought that the magnitude of the vital effect was species-specific and constant for a given species. Recent studies aiming at a mechanistic understanding of these processes point towards a plastic and environmental-dependent interplay between the physiology of coccolithophores and isotopic composition in coccolith calcite. This "mobilis in mobili" relationship opens the door to the possibility to explore the vital effects as palaeoenvironmental proxies undertaking an interspecies approach. New physiological parameters, such as the quantification of calcification rates, pH, and calcium and carbon pools in the coccolith vesicle would further help geologists to constrain the vital effect. Emerging "non-traditional" isotope systems will also contribute to refine the transfer functions between coccolith geochemistry, vital effect, and palaeoenvironments.

In this study, we show that there are independent controls of 18O/16O and 13C/12C fractionation in coccolithophore and dinoflagellate calcite due to the contrasting kinetics of each isotope system. We demonstrate that the direction and magnitude of the oxygen isotope fractionation with respect to equilibrium is related to the balance between calcification rate and the replenishment of the internal pool of dissolved inorganic carbon (DIC). As such, in fast growing cells, such as those of Emiliania huxleyi and Gephyrocapsa oceanica (forming the so-called "heavy group"), calcification of the internal carbon pool occurs faster than complete isotopic re-adjustment of the internal DIC pool with H2O molecules. Hence, coccoliths reflect the heavy oxygen isotope signature of the CO2 overprinting the whole DIC pool. Conversely, in large and slow growing cells, such as Coccolithus pelagicus ssp. braarudii, complete re-equilibration is achieved due to limited influx of CO2 leading to coccoliths that are precipitated in conditions close to isotopic equilibrium ("equilibrium group"). Species exhibiting the most negative oxygen isotope composition, such as Calcidiscus leptoporus ("light group"), precipitate coccolith under increased pH in the coccolith vesicle, as previously documented by the "carbonate ion effect". We suggest that, for the carbon isotope system, any observed deviation from isotopic equilibrium is only "apparent", as the carbon isotopic composition in coccolith calcite is controlled by a Rayleigh fractionation originating from preferential incorporation of 12C into organic matter. Therefore, species with low PIC/POC ratios as E. huxleyi and G. oceanica are shifted towards positive carbon isotope values as a result of predominant carbon fixation into the organic matter. By contrast, cells with higher PIC/POC as C. braarudii and C. leptoporus maintain, to some extent, the original negative isotopic composition of the CO2. The calcareous dinoflagellate Thoracosphaera heimii exhibits different behaviour for both isotopic systems, in particular with respect to its very negative carbon isotope composition, owing to coeval intra and extracellular biomineralisation in this group. In this study, we also investigate the sensitivity of 18O/16O fractionation to varying ambient oxygen isotope composition of the medium for inorganic, coccolithophore, and dinoflagellate calcite precipitated under controlled laboratory conditions. The varying responses of different taxa to increased oxygen isotope composition of the growth medium may point to a potential bias in sea surface temperature reconstructions that are based on the oxygen isotopic compositions of sedimentary calcite, especially during times of changing seawater oxygen isotopic composition. Overall, this study represent an important step towards establishing a mechanistic understanding of the "vital effect" in coccolith and dinoflagellate calcite, and provides valuable information for interpreting the geochemistry of the calcareous nannofossils in the sedimentary record, at both monospecific and interspecies levels.

In order to understand the significance of worldwide deposition of black shale facies in the Early Toarcian (~ 183 Ma), considerable attention has been drawn to this Early Jurassic sub-Stage over the last three decades. The discovery of a pronounced negative carbon isotope excursion (CIE) within the black shales disrupting the generally positive trend in carbon isotopes has stimulated many studies, particularly with a view to establish the local vs. global nature of this major geochemical phenomenon. Here we document the sedimentological and chemostratigraphic evolution of a proximal environment in the Luxembourgian sedimentary area, the so-called Gutland. At Bascharage, Lower Toarcian sediments record the isotopic signature of the Early Toarcian Oceanic Anoxic Event (OAE) by a pronounced positive trend that testifies for widespread anoxia. The expression of the carbon isotope perturbation in this section however, is unusual compared to adjacent NW European sections. A first −7 ‰ negative CIE, whose onset is recorded at the top of the tenuicostatum zone, can be assigned to the well-documented and potentially global T-CIE with confidence using the well-constrained ammonite biostratigraphic framework for this section. In this interval, facies contain only a limited amount of carbonate as a result of intense detrital supply in such a proximal and shallow environment. Stratigraphically higher in the section, the serpentinum zone records a subsequent CIE (−6 ‰) that is expressed by four negative steps, each being accompanied by positive shifts in the oxygen isotopic composition of carbonate. The preservation state of coccoliths and calcareous dinoflagellates in the second CIE is excellent and comparable to that observed in under- and overlying strata, so this cannot be an artefact of diagenesis. Considering the nature of this record, and the lack of such a pronounced event in the serpentinum zone in coeval sections in Europe, we hypothesise that this second CIE was caused by local factors. The geochemical record of carbonate with a relatively light carbon and relatively heavy oxygen isotopic composition is compatible with the so-called Küspert model, by which a CIE can be explained by an influx of 12C-rich and cold waters due to upwelling bottom water masses. With the ongoing effort of high-resolution studies of the Meso-Cenozoic eras, further CIEs are likely to be found, but it has to be remembered that their (global) significance can only be determined via an integrated sedimentological, mineralogical, micropalaeontological and geochemical approach.

Lower Toarcian strata (Lower Jurassic) have been extensively studied with a view to understanding the oceanographic, climatic and biological processes that drove the Earth's system into an Oceanic Anoxic Event (OAE). For this time period, the evolution of the European marine seaways is now relatively well constrained owing to multiple geochemical studies, but investigations regarding climatic trends in the continental realm remain sparse. In the present study, we test the clay mineralogy as a continental climate-sensitive proxy in the well-documented Sancerre core (southern Paris Basin). We compare variations in the kaolinite content with p CO 2 fluctuations (derived from paired carbon isotopes; ∆ 13 C = δ 13 C carb − δ 13 C org ), taking advantage of the detailed chemostratigraphic, palaeoenvironmental and sequence stratigraphy frameworks established for this core material. The results indicate a substantial decrease in kaolinite abundance at the end of the Pliensbachian, which is compatible with a long-term diminution in continental weathering and an inferred temperature decrease. The early Toarcian, prior to the carbon cycle perturbation and deposition of black shale facies, remained relatively cold with minima in both the proportion of kaolinite and reconstructed p CO 2 . The mineralogical and geochemical responses across the prominent negative carbon isotope excursion (CIE) itself are not univocal. The first of four steps that compose the negative limb of the CIE at Sancerre is associated with decreased kaolinite and p CO 2 , and increased carbonate oxygen isotope ratios. Taken together, these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition. Conversely, the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in Yorkshire, providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the CIE. Relaxation in the intensity of continental weathering, as suggested by resumed low kaolinite abundance is seen immediately after the cessation of CO 2 input (after the fourth step of the CIE). The interval spanning the upper portion of the early Toarcian and the middle Toarcian records a subsequent long-term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment. Continued greenhouse conditions, even after the recovery from the carbon isotope perturbation and “regional” black shale deposition, are likely related to sustained CO 2 emission by Karoo–Ferrar volcanism through the considered interval.

The controls on stable Sr isotope fractionation into the calcite produced by the coccolithophore species Emiliania huxleyi , Coccolithus pelagicus spp. braarudii and Gephyrocapsa oceanica are investigated . Each species has been cultured under controlled laboratory conditions at a range of temperatures (10–25 °C) to test the potential of δ 88/86 Sr as a proxy for growth rate and/or sea surface temperature. Coccolithophores are one of the most abundant pelagic calcifiers; since Sr substitutes to some degree for Ca in their calcite coccoliths, coccolithophores represent a significant output of Sr from seawater, potentially influencing the δ 88/86 Sr mass balance in the modern oceans. The coccoliths are investigated for their δ 88/86 Sr, Sr/Ca, and δ 18 O measured as function of temperature. As temperature is increased all species show a negative stable Sr isotopic fractionation, related to a temperature controlled growth rate. We infer the shift of δ 88/86 Sr to lighter values as indicative of a kinetic control on the isotope fractionation, revealing the potential of δ 88/86 Sr as a proxy for growth rate, which in these experiments is primarily dictated by temperature. The results from these experiments indicate that coccolithophore calcite incorporates Sr with a very light δ 88/86 Sr isotope composition as low as ∼0‰.

One of the most elusive aspects of the Toarcian oceanic anoxic event (T-OAE) is the paradox between carbon isotopes that indicate intense global primary productivity and organic carbon burial at a global scale, and the delayed expression of anoxia in Europe. During the earliest Toarcian, no black shales were deposited in the European epicontinental seaways, and most organic carbon enrichment of the sediments postdated the end of the overarching positive trend in the carbon isotopes that characterises the T-OAE. In the present study, we have attempted to establish a sequence stratigraphic framework for Early Toarcian deposits recovered from a core drilled in the Paris Basin using a combination of mineralogical (quartz and clay relative abundance) and geochemical (Si, Zr, Ti and Al) measurements. Combined with the evolution in redox sensitive elements (Fe, V and Mo), the data suggest that expression of anoxia was hampered in European epicontinental seas during most of the T-OAE (defined by the positive carbon isotope trend) due to insufficient water depth that prevented stratification of the water column. Only the first stratigraphic occurrence of black shales in Europe corresponds to the "global" event. This interval is characterised by >10% Total Organic Carbon (TOC) content that contains relatively low concentration of molybdenum compared to subsequent black shale horizons. Additionally, this first black shale occurrence is coeval with the record of the major negative Carbon Isotope Excursion (CIE), likely corresponding to a period of transient greenhouse intensification likely due to massive injection of carbon into the atmosphere–ocean system. As a response to enhanced weathering and riverine run-off, increased fresh water supply to the basin may have promoted the development of full anoxic conditions through haline stratification of the water column. In contrast, post T-OAE black shales during the serpentinum and bifrons Zones were restricted to epicontinental seas (higher Mo to TOC ratios) during a period of relative high sea level, and carbon isotopes returning to pre-T-OAE values. Comparing palaeoredox proxies with the inferred sequence stratigraphy for Sancerre suggests that episodes of short-term organic carbon enrichment were primarily driven by third-order sea level changes. These black shales exhibit remarkably well-expressed higher-frequency cyclicities in the oxygen availability in the water column whose nature has still to be determined through cyclostratigraphic analysis.

Reconstructions of seawater temperature based on measurement of oxygen isotopes in carbonates mostly derive from analyses of bulk sediment samples or manually picked foraminifera. The temperature dependence of 18 O fractionation in biogenic calcite was first established in the 1950s and the objective of the present study is to re-evaluate this temperature dependence in coccolith calcite with a view to developing a robust proxy for reconstructing “vital effect”-free δ 18 O values. Coccoliths, the micron-sized calcite scales produced by haptophyte algae that inhabit surface mixed-layer waters, are a dominant component of pelagic sediments. Despite their small size, recent methodological developments allow species-specific separation (and thus isotopic analysis) of coccoliths from bulk sediments. This is especially the case for Calcidiscus spp. coccoliths that are relatively easy to separate out from other sedimentary carbonate grains including other coccolith taxa. Three strains of coccolithophores belonging to the genus Calcidiscus and characterised by distinct cell and coccolith diameters were grown in the laboratory under controlled temperature conditions over a range from 15 to 26 °C. The linear relationship that relates 18 O fractionation to the temperature of calcification is here calibrated by the equation: T [°C] = –5.83 × (δ 18 O Calcidiscus – δ 18 O medium ) + 4.83 ( r = 0.98). The slope of the regression is offset of ∼–1.1‰ from that of equilibrium calcite. This offset corresponds to the physiologically induced isotopic effect or “vital effect”. The direction of fractionation towards light isotopic values is coherent with previous reports, but the intensity of fractionation in our dilute batch cultures was significantly closer to equilibrium compared to previously reported offset values. No significant isotopic difference was found between the three Calcidiscus coccolithophores, ruling out a control of the cell geometry on oxygen isotope fractionation within species of this genus. This also indicates that our culture calibration may be applied to all Calcidiscus coccoliths found in the sediment. We compared the culture calibration to δ 18 O measured from near-monogeneric Calcidiscus fractions separated out from core top sediments. We found concordant 18 O fractionation factors for the core top calibration with a good linear coefficient ( r = 0.94). The near-monogeneric Calcidiscus assemblages seem, however, to record slightly heaviest δ 18 O values compared to the data of culture study. This discrepancy may be due to a possible seasonality effect on the production of Calcidiscus coccoliths. The uncertainty of the calibration is of similar magnitude to those of other proxies used for SST reconstruction, such as foraminiferal δ 18 O or the alkenone undersaturation index. This confirms that coccoliths can be used as a complementary or alternative substrate to foraminiferal shells for isotopic analyses. Comparing δ 18 O of coccoliths to these other SST proxies, or developing an interspecific comparison of coccolith geochemistry may give insights into the carbonate chemistry of seawater through key periods of the geological record.

International audience; In the Toarcian (Early Jurassic; ~183 Myr ago), the ocean-atmosphere system was subject to one of the larg- est perturbations of the carbon cycle in the last 250 Myr known as the Toarcian Oceanic Anoxic Event (T- OAE). This event was accompanied by a -6‰ negative carbon-isotope excursion (CIE) caused by massive injection of isotopically light carbon into the ocean-atmosphere system, possibly from destabilisation of gas hydrates. This study reveals the pacing and sequence of events leading up to the CIE and to widespread de position of organic-rich sediments. The very high-resolution isotopic record from exceptionally well- preserved carbonate and organic matter from the Paris Basin enables recognition of increased CO2 levels ~130 kyr in advance of the major negative CIE. An accelerated increase in the pCO2 is registered ~25 kyr be- fore the onset of this negative excursion and was so rapid and so intense that it led to a water column under-saturated with respect to calcium carbonate in the Paris Basin. Undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface-dwelling calcifiers. These environ- mental perturbations, representing precursor phases of CO2 injection, predate the first step towards relative- ly light carbon-isotope in carbonate and organic matter and are tentatively attributed to Karoo-Ferrar magmatism. This negative shift was registered slightly earlier in terrestrial carbon than marine carbonate. Subsequent global warming is credited with liberating isotopically light carbon, and ultimately fostered an- oxia in the Paris Basin: the response of these cumulative inputs of carbon to the Earth system. Isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative CIE, suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation, ~45 kyr after the first step of the CIE. This re- establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon.

[1] The Early Toarcian was characterized by two large perturbations to the carbon cycle: a positive trend associated with increased organic matter burial and ocean anoxia, and a pronounced negative carbon isotope excursion (CIE). We contrast the geochemical evolution in the carbonate phases of two successions: one from the Paris Basin (Sancerre core, comprising black shales), the other from the Lusitanian Basin (Peniche section with very minor lithological expression of bottom water anoxia). Our aim was to identify whether these carbon cycle perturbations were related, and differentiate between the common (global) versus regional expressions of the biogeochemical response and ocean chemistry. Our results highlight contrasts in timing of different phases of anoxia in both locations through the widely documented negative CIE. Widespread anoxic conditions were not a necessary prerequisite for generating a pronounced CIE, as required by the recycling (so-called “Kuspert”) model. The production of carbonate simultaneously dropped during the δ13C negative shift in both locations, likely in response to lowered seawater saturation rate induced by substantial absorption of CO2 from the atmosphere. The recovery interval was accompanied by a rapid reestablishment of seawater alkalinity, and primary and carbonate productivity in epicontinental seas, as evidenced by high δ13C and Sr/Ca, in contrast with the more open ocean regime in the Lusitanian Basin. Our results confirm that parallels can be draw between the ocean productivity response and feedback during the Toarcian CIE and the PETM. Both events are characterized by ocean acidification and reduced pelagic calcification followed by a peak in nearshore coccolith productivity, which could have helped the recovery from the perturbation.

The causes of the pronounced negative excursion in carbon-isotope values that was recorded during the Early Toarcian Oceanic Anoxic Event (T-OAE) are still under debate, particularly with regard to the local versus global pattern of the excursion, and the extent to which recorded signals are under a diagenetic control. In this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a Toarcian section recovered from the Sancerre-Couy borehole, southern Paris Basin. Beyond the recognition of a - 6‰ δ13C excursion in the bulk carbonate content, our data also demonstrate that biogenic particles (such as coccoliths) and inorganic grains precipitated as early diagenetic phases (including dolomite) both record the excursion with the same magnitude. Although several black shales occur through the Paris Basin Toarcian section, it is only that associated with the onset of the OAE that coincides with a large negative carbon-isotope excursion. Taken together these observations indicate that during this event, the entire water column was characterized by homogeneous carbon-isotope values; such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re-mineralized organic carbon (cf. "the Küspert model"), since this would have required a strong vertical gradient in the water column. Additionally, the Paris Basin data show that the decrease in carbonate δ13C values during the OAE occurred in several discrete steps (each of some - 2‰), as has previously been found for organic carbon substrates in other European sections. The stepped nature of the isotopic profile, which is part of a stratigraphic signature previously ascribed to Milankovitch forcing, is compatible with regular pulsed input of light carbon into the whole atmosphere-ocean system from a climatically sensitive source such as gas hydrate, or from thermal methanogenesis of organic-rich sediments in the Karoo-Ferrar large igneous province. Contrasts in the amplitude of the negative carbon-isotope excursion on a regional scale remain an important unexplained aspect of the Toarcian record. © 2008 Elsevier B.V. All rights reserved.

International audience; A protocol is described for separating sub‐20 lm‐sized particles contained in sedimentary rocks into size fractions. Geochemical data from manually isolated foraminifera are commonly used in the interpretation of marine palaeoenvironments; problems associated with the isolation of calcareous nannofossils hampers their geochemical exploitation. However, geochemistry performed on calcareous nannofossil monotaxic assemblages should provide more meaningful data sets than those generated from the highly heterogeneous bulk carbonate. This protocol is based on cascade filtering steps, using polycarbonate membranes with well‐calibrated pores. Strong ultrasonic treatment can further be applied to selectively reduce the size of particles for greater enrichment. Obtained residues frequently comprise near‐monotaxic nannofossil assemblages. The application of this technique, which can be achieved within less than 2 days, has provided distinct fractions of coccoliths, calcareous dinoflagellate shells and also diagenetic monocrystals. This protocol is designed for application in reconstructing the history of water‐column physicochemistry and diagenesis. It also has the potential to provide insights into the biogeochemistry of calcareousnannoplankton, including vital effects.

International audience; The carbonate clumped isotope (or Δ47) thermometer relies on the temperature dependence of the abundance of 13C18O16O22- ion groups within the mineral lattice. This proxy shows tremendous promise to reconstruct past sea surface temperatures (SSTs), but requires calibration of the relationship between Δ47 and calcification temperatures. Specifically, it is important to determine whether biologically-driven fractionation (the so-called “vital effect”) overprints Δ47 values, as reported in some biominerals such as the foraminifera and the coccoliths for the carbon and oxygen isotope systems. Despite their abundance in the pelagic environment, coccolithophores have not been comprehensively investigated to test the reliability of coccolith Δ47-inferred temperatures. In this study, we cultured three geologically-relevant coccolith species (Emiliania huxleyi, Coccolithus pelagicus, and Calcidiscus leptoporus) at controlled temperatures between 7 and 25 ± 0.2 °C. Other variables such as pCO2, pH, alkalinity, nutrient concentrations and salinity were kept constant at mean present-day oceanic conditions. Although cultured coccoliths exhibit substantial species-specific oxygen and carbon isotope vital effects, we found that their Δ47 composition follows a statistically indistinguishable relationship with 1/T2 for all three species, indicating a lack of interspecific vital effects in coccoliths. Further, the Δ47 composition of coccolith calcite is identical to inorganic calcite precipitated at the same temperature, indicating an overall absence of clumped isotope vital effect in coccolith biominerals. From a paleoceanographic perspective, this study indicates that the Δ47 values of sedimentary coccoliths – even from highly diverse / mixed assemblages – can be analyzed to reconstruct SSTs with confidence, as such temperature estimates are not biased by taxonomic content or changing interspecies vital effects through time.

Among the major obstacles in constraining paleoclimates for periods of “greenhouse” type is the poor preservation state of the sedimentary archive, and the existence of limits for each of the different applied geochemical markers. These obstacles lead to great uncertainties on the values and distribution of sea surface temperatures (SSTs) and atmospheric CO2 concentrations. Therefore, the mechanisms that brought the Earth’s system from a “greenhouse” to an “icehouse” regime throughout the Paleogene are not well constrained. In this thesis, we reconstructed the thermal evolution of the superficial ocean and the evolution of atmospheric pCO2 during the Paleogene from the isotopic signal (δ18O and ∆13C) of the fossilized carbonate exoskeleton of coccolithophores: coccoliths. Our data reveal a global cooling of surface waters from the Early to the Middle Eocene. During the Late Eocene and across the Eocene-Oligocene transition, values for pCO2 decrease, and cooling at high latitudes continues, allowing for the set up of an ice sheet in Antarctic, while the tropical belt warms. This change in the distribution of heat fluxes at the Earth’s surface during this period is synchronous to the deepening of the Drake Passage and to the set up of a vigorous Antarctic Circumpolar Current. These results thus highlight the driving role of changing oceanic circulations for climate dynamics during this transition. This thesis also proves the existence of important latitudinal thermal gradients throughout the Paleogene. The hypothesis of a homogeneous distribution of SSTs between the Equator and the poles, which prevails in the literature but remains hard to modelise, can thus be rejected.; Un obstacle majeur à la caractérisation des paléoclimats en période de type « greenhouse » tient à la mauvaise préservation des archives sédimentaires et à des limites dans les calibrations des marqueurs géochimiques utilisés. Ces limitations entrainent de grandes incertitudes sur les valeurs et la répartition des températures des eaux de surface (SSTs) et des concentrations en CO2 atmosphérique. Les mécanismes qui ont fait basculer le système Terre d’un régime de type greenhouse à icehouse au cours du Paléogène restent donc encore mal contraints. Dans cette thèse, l’évolution thermique de l'océan superficiel et les pCO2 atmosphériques au cours du Paléogène ont étés estimées à partir du signal isotopique (δ18O et ∆13C) des exosquelettes carbonatés des coccolithophoridés : les coccolithes. Les données montrent un refroidissement global des SSTs de l’Eocène inférieur à moyen. A l’Eocène supérieur et au travers de la transition Eocène-Oligocène, les pCO2 diminuent et le refroidissement des hautes latitudes se poursuit, induisant la mise en glace de l’Antarctique, tandis que la ceinture tropicale se réchauffe. Ce bouleversement dans la répartition des flux de chaleur à la surface de la Terre est synchrone de la mise en place d’un courant circumpolaire antarctique plus vigoureux. Ces résultats mettent donc en évidence le rôle moteur des changements de circulations océaniques dans la dynamique climatique de cette transition. De plus, cette thèse prouve également l’existence de gradients thermiques latitudinaux importants tout au long du Paléogène. L'hypothèse d'une répartition homogène des SSTs entre l’équateur et les pôles, si difficile à modéliser peut être écartée.

Among the major obstacles in constraining paleoclimates for periods of “greenhouse” type is the poor preservation state of the sedimentary archive, and the existence of limits for each of the different applied geochemical markers. These obstacles lead to great uncertainties on the values and distribution of sea surface temperatures (SSTs) and atmospheric CO2 concentrations. Therefore, the mechanisms that brought the Earth’s system from a “greenhouse” to an “icehouse” regime throughout the Paleogene are not well constrained. In this thesis, we reconstructed the thermal evolution of the superficial ocean and the evolution of atmospheric pCO2 during the Paleogene from the isotopic signal (δ18O and ∆13C) of the fossilized carbonate exoskeleton of coccolithophores: coccoliths. Our data reveal a global cooling of surface waters from the Early to the Middle Eocene. During the Late Eocene and across the Eocene-Oligocene transition, values for pCO2 decrease, and cooling at high latitudes continues, allowing for the set up of an ice sheet in Antarctic, while the tropical belt warms. This change in the distribution of heat fluxes at the Earth’s surface during this period is synchronous to the deepening of the Drake Passage and to the set up of a vigorous Antarctic Circumpolar Current. These results thus highlight the driving role of changing oceanic circulations for climate dynamics during this transition. This thesis also proves the existence of important latitudinal thermal gradients throughout the Paleogene. The hypothesis of a homogeneous distribution of SSTs between the Equator and the poles, which prevails in the literature but remains hard to modelise, can thus be rejected.; Un obstacle majeur à la caractérisation des paléoclimats en période de type « greenhouse » tient à la mauvaise préservation des archives sédimentaires et à des limites dans les calibrations des marqueurs géochimiques utilisés. Ces limitations entrainent de grandes incertitudes sur les valeurs et la répartition des températures des eaux de surface (SSTs) et des concentrations en CO2 atmosphérique. Les mécanismes qui ont fait basculer le système Terre d’un régime de type greenhouse à icehouse au cours du Paléogène restent donc encore mal contraints. Dans cette thèse, l’évolution thermique de l'océan superficiel et les pCO2 atmosphériques au cours du Paléogène ont étés estimées à partir du signal isotopique (δ18O et ∆13C) des exosquelettes carbonatés des coccolithophoridés : les coccolithes. Les données montrent un refroidissement global des SSTs de l’Eocène inférieur à moyen. A l’Eocène supérieur et au travers de la transition Eocène-Oligocène, les pCO2 diminuent et le refroidissement des hautes latitudes se poursuit, induisant la mise en glace de l’Antarctique, tandis que la ceinture tropicale se réchauffe. Ce bouleversement dans la répartition des flux de chaleur à la surface de la Terre est synchrone de la mise en place d’un courant circumpolaire antarctique plus vigoureux. Ces résultats mettent donc en évidence le rôle moteur des changements de circulations océaniques dans la dynamique climatique de cette transition. De plus, cette thèse prouve également l’existence de gradients thermiques latitudinaux importants tout au long du Paléogène. L'hypothèse d'une répartition homogène des SSTs entre l’équateur et les pôles, si difficile à modéliser peut être écartée.