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This paper proposes a biostratigraphic framework for the last 50 kyr in the contourite depositional system (CDS) of the Gulf of Cadiz with a solid and independent age control, and tests the reliability of faunal-based analyses in a bottom current-dominated environment related to high current velocities. The distribution of planktonic foraminifera and pteropods has been studied in twenty-two piston cores of the Holocene and Late Pleistocene age from the Gulf of Cadiz. A detailed correlation between the cores has been made possible by a large radiocarbon and isotopic data set and a high degree of similarity of frequency changes within several species by coiling direction changes of Globorotalia truncatulinoides and Globorotalia hirsuta and by occurrences of the polar species Neogloboquadrina pachyderma and Limacina retroversa. Occurrences of these polar species are clearly related to paleoclimatic oscillations and reflect rapidly changing surface water conditions in the Gulf of Cadiz during the latest Pleistocene that have been observed regardless of sedimentation rates and sedimentary environments (contouritic drifts vs slope without bottom current influence).

Fifteen Iberian margin sediment cores, distributed between 43°12′N and 35°53′N, have been used to reconstruct spatial and temporal (sub)surface circulation along the Iberian margin since the Last Glacial period. Time-slice maps of planktonic foraminiferal derived summer sea surface temperature (SST) and export productivity (Pexp) were established for specific time intervals within the last 35 ky: the Holocene (Recent and last 8 ky), Younger Dryas (YD), Heinrich Stadials (HS) 1, 2a, 2b, 3, and the Last Glacial Maximum (LGM). The SST during the Holocene shows the same latitudinal gradient along the western Iberian margin as present-day with cold but productive areas that reflect the influence of coastal upwelling centers. The LGM appears as a slightly less warm, but more productive period relative to the Holocene and present-day conditions, suggesting that sea-level minima forced a westward displacement of the coastal upwelling centers possibly accompanied by a strengthening of northward winds. During the YD, a longitudinal thermal front is depicted at 10°W, with cold polar waters offshore and warmer subtropical waters inshore, suggesting that the subtropical Paleo-Iberian Poleward Current more likely flowed at a more inshore location masking the local SST signal and amplitude of variation. A substantial cooling and drop in productivity is observed during all HS, in particular HS1 and HS3, reflecting the penetration of icebergs-derived meltwater. These most extreme southward extensions of very cold waters define a strong SST gradient that marks a possible Paleo-Azores Front. Higher production south of this front was likely fed by frontal nutrient advection.

The direct comparison between marine and terrestrial data from the NW Iberian margin, core MD03-2697, allows us to accurately evaluate, without chronological ambiguity, the vegetation response to North Atlantic climate events across the last deglaciation. Comparison of MD03-2697 data with other marine and terrestrial records from a vast area stretching from the Azores to western (W) France, Iberia and its margin, the W Mediterranean and NW Africa reveals the importance of enhanced winter North Atlantic westerlies episodes in driving a heterogeneous regional climatic signal during particular events of the last deglaciation. Heinrich Stadial 1 (HS1)/Oldest Dryas is a complex event marked by three synchronous main phases (a: extremely cold/relatively wet; b: cool/dry; c: relatively warmer/increasing moisture availability) in regions directly influenced by the North Atlantic while it is characterized by a single phase (cold and dry) in most inland and high altitude areas. Changes in the strength and position of North Atlantic westerlies could explain the variability in moisture during HS1 from W Pyrenees to W Mediterranean. The Bolling-Allerod (B-A) event is marked by a synchronous progressive increase of ocean and atmospheric temperatures and precipitation from the Bolling to the Allerod in W Iberia and W Pyrenees contrasting with the Greenland temperature pattern. Mid-to high latitudes thermal contrast and the gradual strengthening of the Atlantic Meridional Overturning Circulation (AMOC) triggered the continuing enhancement of westerlies, and moisture, along this period.Finally, the Younger Dryas (YD) Stadial is characterized by a land-ocean synchronous returning cold conditions (but not so cold as HS1) and, although dry conditions persisted during this period, extreme winter precipitation occurrences might have affected the most coastal areas of north and central W Iberia and Pyrenees. In contrast, dry conditions persisted during the YD in the western Mediterranean regions. The westerlies migrated further north following the displacement of the Polar Front during the deglaciation precluding the input of moisture in the W Mediterranean region, which persisted very dry during the YD Stadial. (C) 2016 Published by Elsevier Ltd. MAR/LA00015/2014; ANR-05-BLAN0310-01; ANR 2011 BSH3 0005

The direct sea–land correlation applied to core MD99-2331 retrieved from the north-western Iberian margin shows a two-phase pattern within Heinrich events 4, 2 and 1 in the ocean and in the adjacent landmasses. Changes between wet/cold and dry/cool conditions in the Iberian Peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the Atlantic Meridional Overturning Circulation. Here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the MD99-2331 record and other available palaeoclimate sequences from the North Atlantic region (18–75°N and 0–75°W). The climatic asymmetry observed between mid- and subtropical eastern North Atlantic latitudes (wet/dry) and the Blake Outer Ridge (dry/wet) during H4, H2 and H1 can be explained by changes in the position of the Atlantic jet-stream. During the first phase of H4, H2 and H1 the Atlantic jet-stream was located further south following the southward displacement of the oceanic thermal front as far south as 35°–37°N. On the contrary, during the second phase of H4, H2 and H1 the jet-stream was located further north following the northward displacement of this thermal front as far north as 42°N. From the atmospheric point of view, these two phases are reminiscent of the present-day negative and positive prevailing modes of the North Atlantic Oscillation (NAO), respectively, but high-resolution studies of additional North Atlantic key sites and climate simulations are needed to confirm the hypothesis of a NAO-like mechanism operating on millennial timescales.

Using analysis of marines cores from the Bay of Biscay as a basis, a system of different episodes of the Upper Pleistocene and the Holocene in the area of the Bay is presented. These episodes are characterized by several sedimentological and micropaleontological observations and particularly by the analysis of the coiling ratio of a few species of planktonic foraminifera. From the cores it is thus possible to determine the Holocene, the Wurmian with its four glacial and three interglacial stages, and, at the base of the last glacial stage, the Riss-Wurm interglacial or its upper level.

The Mediterranean outflow water (MOW) paleocirculation during the last 50,000 years has been inferred from the grain-size distribution of contourite beds in core MD99-2341 from the Gulf of Cadiz (Southern Iberian Margin–Atlantic Ocean). Three main contourite facies are described. Their vertical succession defines two contourite sequences that reveal past variations of the MOW bottom-current velocity. A comparison of contourite sequences and the planktonic δ18O record of core MD99-2341 with the δ18O record from Greenland Ice Core GISP2 show a close correlation of sea-surface water conditions and deep-sea contouritic sedimentation in the Gulf of Cadiz with Northern Hemisphere climate variability on millennial timescales. A high MOW velocity prevailed during Dansgaard-Oeschger stadials, Heinrich events and the Younger Dryas cold climatic interval. The MOW velocity was comparatively low during the warm Dansgaard-Oeschger interstadials, Bolling-Allerod and the Early Holocene. Rapid sea-level fluctuations on the order of 35 m during Marine Oxygen Isotope Stage 3 are considered to have exerted limiting controls on the MOW volume transport and thus positively modulated the MOW behaviour during the last 50 kyr.

Very few sediment records allow addressing the paleoceanographic changes that took place on orbital and/or sub-Milankovitch time scales in the South–West Atlantic. Here, a set of sediment cores located across a deep channel-levee system in the South Brazilian basin (3700–3900 m depth) is used to infer the sediment dynamics that prevailed on this system during the late Quaternary and to relate this pattern to climate changes. The spatial distribution of deposits (changes in mineralogy, texture, structure, and sedimentation rate according to the morphology) indicates bulk of sediment supplies is distributed on the Sao Tome system by bottom advective processes. The silty–sandy layers, originate undoubtedly from turbidity currents whereas the fine-grained muds and oozes, that form the major part of the deposits, are controlled by deep geostrophic currents. In addition to variations forced by the orbital cycles, (more turbidites, less carbonates and higher sedimentation rate during glacials) the sediment records (chiefly the CaCO 3 record) document outstanding higher frequency regional changes in sedimentation. According to the location of the cores at the present day interface between NADW and AABW, we infer that changes in sedimentation are related to pulses of AABW versus NADW production. These changes, commonly marked by asymmetric carbonate pattern of about 10 kyr, suggest that the relative influence of NADW versus AABW followed, throughout the last 190 kyr, a repetitive sequence of progressive increase and sharp decrease. The rather sharp shut down observed during the late glacial could be associated to Heinrich events, when NADW production stopped, but similar events are also well expressed during MIS 5, MIS 6 and at the end of MIS 7.

The direct land–sea–ice correlation, performed in the north-western Iberian margin core MD01-2447, shows that Marine Isotope Stage 7 (MIS 7) is marked by an alternation of five warm and cold periods. This climatic variability is, in general, synchronously detected in marine and terrestrial realms by our record. Termination III is marked by three cold episodes. The last one interrupts the forest development in north-western Iberia related to the deglacial climatic amelioration. It begins in the middle of Termination III but the maximal cold conditions occur at the beginning of low ice volume conditions. MIS 7 is characterised by three periods of very low ice volume, associated with marine and continental high temperatures in and off north-western Iberia. The correlation of our record with ODP site 980 shows that the climatic variability detected in the north-western Iberian region has also an imprint in northern North Atlantic. It also highlights that most of the cold periods are associated with iceberg discharges in the North Atlantic. The comparison of the north-western Iberian margin sequence with the long European pollen records has allowed refining the correlation of the marine and continental stratigraphy for MIS 7.

The Marine Isotope Stage 11 interglacial, centred at similar to 400 ka, appears to be the best candidate for understanding climatic changes in the context of low insolation forcing such as that of our present interglacial. Direct correlation between terrestrial (pollen) and marine climatic indicators and ice volume proxy from deep-sea core MD01-2447 (off northwestern Iberia) shows for the first time the phase relationship between southwestern European vegetation, sea surface temperatures in the northeastern Atlantic mid-latitudes and ice volume during MIS 11. A warmest 32,000 years-long period and three following warm/cold cycles occurred synchronously on land and ocean. The end of the warmest period sees the glacial inception which coincides with the replacement of warm deciduous forest by conifer (pine-fir) expansion in northwestern Iberia and, consequently, with the southward migration of the tree line in high latitudes in response to declining summer insolation. As weak insolation changes alone cannot account for ice growth, the associated vegetation changes must now be considered as a potential major feedback mechanism for glaciation initiation during MIS 11. (c) 2005 Elsevier Ltd. All rights reserved.

High-resolution terrestrial (pollen) and marine (planktic and benthic isotopes, coarse fraction, and N. pachyderma (s)) analyses have been performed in the Marine Isotope Stage (MIS) 5 interval of IMAGES core MD99-2331 retrieved in the northwestern Iberian margin. This study shows the occurrence of a Zeifen Interstadial/Stadial succession on land and in the ocean during the first part of MIS 5e. In northwestern Iberia, the Eemian is marked from 126 to 122 ka by the development of deciduous Quercus forest at the same time as Mediterranean forest colonised southern Iberia, and deciduous Quercus-Corylus forest occupied northernmost European regions. From 121 to 115 ka Carpinus betulus forest developed in NW Iberia indicating a winter cooling by 2degreesC on land and an increase in annual precipitation by 100-200 min along with a Sea Surface Temperature (SST) decreasing trend off Iberia. A similar cooling has been documented at the same time in northern Germany (52degreesN) by the replacement of deciduous forest by coniferous (Abies-Picea) formations, implying a southward displacement of the deciduous tree line between similar to60degreesN and 50degreesN as early as 120 ka. The southward migration of the tree line between 72degreesN and 58degreesN simulated by the Earth Model of Intermediate Complexity MoBidiC from 122 and 120 ka and considered as a major process to initiate the last glaciation is, therefore, compatible with data. Between 115 and 110 ka, the substantial ice accumulation in northern high latitudes (MIS 5e/5d transition) was synchronous with successive drops, C26 and C25, in northeastern Atlantic SST. In northwestern Iberia Abies-Pinus trees developed at the expense of Quercus-Carpinus forest. A tundra-like environment occupied northern Germany, marking the end of the interglacial in northwestern Europe at 115 ka, and boreal forest likely colonised northeastern France. The first displacement of the vegetation belts at 121 ka was enhanced at 115 ka indicating an amplification of the vegetation and climate gradients in northeastern Atlantic and European borderlands probably related with the well-developed ice caps at that time. The comparison between the general trend in the estimated and simulated MoBidiC winter and summer temperatures for latitudes between 35 and 45degreesN, shows that both follow quite straightforwardly the precession signal although the simulated and reconstructed temperatures agree better in the South than North of 40degreesN. Annual precipitation is exhibiting opposite trend in the data and in the model. This contradiction is likely the fact that the zonal climate simulated by the model may not accurately represent the regional climate features, as reconstructed from the pollen. (C) 2004 Elsevier B.V All rights reserved.

The structure of the A/Z = 3 nucleus 15B has been investigated using the in-beam $\gamma$ -spectroscopy technique with a fragmentation reaction of a 36S beam on a 9Be target at 77.5 ${\rm MeV}\cdot A$ . The fragments were identified and selected by their energy loss and time of flight using the SPEG spectrograph. $\gamma$ -ray energies and intensities have been measured in coincidence with the projectile-like fragments. From this information as well as from the $\gamma\gamma$ -coincidence relationships a level scheme is proposed for 15B up to the neutron separation energy. The experimental results have been interpreted using shell model calculations in the psd valence space. Effects of the weakly bound nature of the valence neutrons have been observed.

A precise assessment of the hydrological changes in the northern Atlantic Ocean throughout the last climatic cycle stands as one of the key priorities for understanding the mechanisms of global climate change. A high resolution micropalaeontological study of a sediment core (MD95-2015) retrieved from the South Icelandic Basin, allows us to infer patterns of North Atlantic surface hydrological changes during the present (Holocene) and the ultimate (Marine Isotopic Stage 5) Interglacial periods. The downcore distribution of organic-walled dinoflagellate cysts (dinocysts) is used, in conjunction with additional proxies (sediment magnetic susceptibility, CaCO3, stables isotopes and planktic foraminifer assemblages) to identify climatic instabilities of various amplitudes. These events are mostly characterised by prominent changes in relative abundance of the dinocysts Spiniferites mirabilis and Operculodinium centrocarpum, whose maximum values are thought to trace sea-surface temperature peaks at the core site. Two hypsithermal periods are identified on this basis, between 126 and 120 kyr BP and from 9.2 to 5.7 cal kyr BP (∼8–5 14C kyr BP), respectively. Some discrepancies between the micropalaeontological tracers used are discussed here in the light of their qualitative and quantitative (transfer functions) ecological interpretation.

The Gulf of Cadiz, west of the Strait of Gibraltar, is the site of water exchange between the Atlantic Ocean and the Mediterranean where many palaeoceanographic studies have taken place over the last several decades. Based on 21 cores from three cruises, oxygen isotope curves, 139 radiocarbon dates, and microfaunal analyses, this work presents and discusses the main bioevents used as detailed biostratigraphic points in this area for the late Quaternary. Those bioevents, such as well-known cold events (Younger Dryas, Heinrich events) or bioevents occurring during the Holocene, are essentially based on planktonic foraminifer species and/or coiling ratio and the point occurrences of pteropod species. The large and extensive data set allows us to discuss ages and the spatial validity of such bioevents.

Theories explaining the origin of the abrupt, massive discharges of ice-rafted detritus (IRD) into the glacial North Atlantic (the Heinrich layers (HLs)) generally point to the Laurentide ice sheet as the sole source of these events, until it was found that the IRDs also originated from Icelandic and European ice sheets [Bond and Lotti, 1995; Snoeckx er al., 1999; Grousset et al., 2000]. This apparent contradiction must be reconciled as it raises fundamental questions about the mechanism(s) of HL origin. We have analyzed two similar to 12 cm thick HLs in an ultrahigh-resolution mode (1-2 century intervals) in a mid-Atlantic ridge piston core. The delta O-18 record (N. pachyderma left coiling) reveals strong excursions induced by the melting of the icebergs; these excursions are associated with a strong decrease in the amount of planktic foraminifers and with a 30 degreesC cooling of the surface waters. Counts of coarse detrital grains reveal that IRD are deposited according to a typical sequence (I) volcanic glass, (2) quartz and feldspars, (3) detrital carbonate, that implies a chronology in the melting of the differentpan-Atlantic ice sheets. Sr and Nd isotopic composition confirm that in both Heinrich layers H1 and H2, "precursor" IRD came from first Europe/Iceland, followed then by Laurentide-derived IRD. An internal cyclicity can be identified: during H1 and H2, about four to six major, abrupt discharges occurred roughly on a century timescale. The delta C-13 and delta N-15 records reveal that dominant inputs of continent-derived organic matter are associated with IRD within the HLs, hiding the plankton productivity signal.

High spin states in ${}^{193}\mathrm{Tl}$ have been populated by the ${}^{181}\mathrm{Ta}{(}^{16}\mathrm{O},6n)$ reaction at 110 MeV and \ensuremath{\gamma}-ray spectroscopy was performed using the EUROGAM II array. In addition to the two known superdeformed (SD) bands, three new superdeformed bands have been identified. The dynamic moments of inertia of two of these new bands display a sudden and opposite change of slope and two of them have identical transition energies within 2 keV. The behavior of their dynamic moments of inertia and their \ensuremath{\gamma} transitions allowed us to propose configurations for the proton orbitals involved around the SD shell closure $Z=80.$ The intrinsic proton states identified are the two signature partners of the $[411]1/2$ and the negative signature of the $[651]1/2$ orbitals. Their properties are compared to the predictions of two theoretical calculations.

A Coulomb excitation experiment has been performed in order to study the subshell closure atN = 40 for neutron-rich nuclei. This subshell effect is thought to be enhanced when largeN/Z ratios are encountered. Therefore, theZ = 2868Ni is of particular interest in order to test this behaviour. Some experimental information is already available for68Ni at low excitation energy: a 0+ 2 isomer, a 2+ state and a long-lived 5- state. The high energy of the 2+ state suggests the shell closure though its reduced transition probabilityB(E2) has never been mesured. The nuclei68Ni,70,72Zn,76Ge have been produced in the fragmentation of a86Kr beam at 60 MeV/A. The selection of these secondary beams has been performed by LISE3 spectrometer at GANIL. Performances of the detector system “Château de Cristal” and preliminary results on reduced transition probabilitiesB(E2) are presented and discussed.

The nucleus195Pb has been populated with the184W+16O reaction at 113 MeV. Two dipole γ-ray cascades have been observed using the EUROGAM spectrometer. A comprehensive level scheme related to these structures has been established. Multiparticle configurations are attributed to these high-spin structures from detailed comparison with the neighbouring nuclei,193Hg,194Pb and195Tl. Band crossings due to i13/2 neutron pair breaking are observed in195Pb at about the same frequencies as in the isotone193Hg.

Recent data from the EUROGAM array have revealed dipole transitions linking signature partner superdeformed bands in 194Tl and 195Tl nuclei. Measurements of the decay branching ratios, taken together with the average quadrupole moment of the neighboring superdeformed nuclei, enable the absolute M1 strengths to be determined. From these data and using the strong coupling model, we find that two SD bands in 195Tl are due to the 81st proton being in the [642]5/2+ orbital and four from the six SD bands in 194Tl correspond to a configuration where the intrinsic spins of the single proton and single neutron are aligned.

Dipole transitions linking the superdeformed Yrast signature-partner bands in 195Tl have been observed using the EUROGAM 1 spectrometer. From the measurements of the photon decay branching ratios, taken together with the average quadrupole moment measured in neighbouring superdeformed nuclei, we find that the two signature partner superdeformed bands involve the excitation of the 81 st proton into the i 13 2 Ω= 5 2 intruder orbital

A new superdeformed band is reported in 193Hg which has properties that are consistent with it being based on the unfavoured N = 7 (π, α) = (−, +12) intruder orbital. The signature splitting at hω = 200 keV of this intruder orbital and its favoured (−, −12) partner is estimated to be 160±30 keV, which is in agreement with cranked mean field calculations. This band completes the set of low-lying quasi-neutron orbitals predicted to be at the N = 113 superdeformed Fermi-surface. The previously known superdeformed bands in 193Hg have been extended to higher rotational frequencies, hω ⩾ 0.40 MeV.

International audience; We attempt to quantify the 14C difference between the atmosphere and the North Atlantic surface during a prominent climatic period of the last deglaciation, the Younger Dryas event (YD). Our working hypothesis is that the North Atlantic may have experienced a measurable change in 14C reservoir age due to large changes of the polar front position and variations in the mode and rate of North Atlantic Deep Water (NADW) production.We dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere-sea surface 14C gradient. We selected terrestrial vegetal macrofossils and planktonic foraminifera (Neogloboquadrina pachyderma left coiling) mixed with the same volcanic tephra (the Vedde Ash Bed) which occurred during the YD and which can be recognized in North European lake sediments and North Atlantic deep-sea sediments. Based on AMS ages from two Norwegian sites, we obtained about 10,300 yr BP for the ‘atmospheric’ 14C age of the volcanic eruption. Foraminifera from four North Atlantic deep-sea cores selected for their high sedimentation rates ( > 10 cm kyr−1) were dated by AMS (21 samples). For each core the raw 14C ages assigned to the ash layer peak is significantly older than the 14C age obtained on land. Part of this discrepancy is due to bioturbation, which is shown by numerical modelling. Nevertheless, after correction of a bioturbation bias, the mean 14C age obtained on the planktonic foraminifera is still about 11,000–11,100 yr BP. The atmosphere-sea surface 14C difference was roughly 700–800 yr during the YD, whereas today it is 400–500 yr. A reduced advection of surface waters to the North Atlantic and the presence of sea ice are identified as potential causes of the high 14C reservoir age during the YD.

The complete spectrum of [gamma] rays following the decay of superdeformed (SD) states in [sup 192]Hg has been extracted. The spectrum, which comprises a quasicontinuous component and sharp lines, reveals the decay mechanism and defines the excitation energies of the SD band. The decay of SD states results from the coupling between a cold, ordered SD system with a hot, chaotic one with normal deformation.

Two regular dipole gamma -ray cascades have been observed in 194Pb. A comprehensive level scheme related to these structures has been built and first members of rotational bands built on K=8 and K=11 two-proton oblate states have been identified. From the excitation energies, spin values, behaviours of the moments of inertia and alignments, and from the comparison with the isotone 192Hg, multiparticle configurations can be attributed to three high-spin structures of 194Pb built respectively on the 4966 keV, 4334 keV and 6198 keV levels: ( pi 9/2(505) pi 13/2(606))(vi13/2)2, ( pi 9/2(505) pi 13/2(606))(vf5/2vi13/2), ( pi 9/2(505) pi 13/2(606)) (vf5/2(vi13/2)3). Within this interpretation, the regular dipole bands correspond to the presence of two or three i13/2 decoupled neutrons.

Dipole transitions linking signature partner superdeformed bands in 193Hg have been observed. Measurements of the photon decay branching ratios, taken together with the average superdeformed quadrupole moment measured in neighboring nuclei, enable the absolute M1 strengths to be determined. From these data, using the strong coupling model, we find (gK-gR)K/Q0=-0.14±0.01 (e b)−1, gK=-0.65±0.14 with Ω=2.8±0.8. These data are consistent with the superdeformed neutron orbital being [512]5/2− as predicted by cranked Woods-Saxon calculations.

International audience; A comparison of the deglaciation •5180 r•ord of northeastern Atlantic core SU 81-18 with that calculated by adding the •5180 changes due to sea surface temperature and ice volume variations shows that planktonic foraminifera have also recorded seawater •5180 changes due to salinity (local advection and evaporation-precipitation (E-P)) changes. Using a simple ocean box model of meltwater dilution during the deglaciation, we show that sea surface salinity covaried with temperature. Despite the injection of meltwater associated with the climate warming, sea surface salinity was high when sea surface water was warm and low during cold events. This implies that the combined effect of local E-P changes and northward advection of saline subtropical water were the main factor responsible for the surface water salinity variations in the northeastern Atlantic Ocean during the last 18,000 years. INTRODUCTION Pleistocene glacial-interglacial oscillations resulted in large variations of surface water temperature, continental ice volume, and sea level [Emiliani, 1955; CLIMAP Project Members, 1976; 1981; Fairbanks, 1989]. According to a theory developed by Milankovitch [ 1930], insolation changes due to variations of the position of the Earth on its orbit around the Sun trigger •Centre des Faibles Radioactivit[s, Laboratoire mixte Centre National d'Etudes Spatiales-Commissiariat •t l'Energie Atomique

High spin states of189Au were populated via the174Yb (19F, 4n reaction at 86, 90, 95 and 100 MeV beam energies. The study of the relative population of oblate and prolate structures shows a striking disappearance of the prolate band relative to the oblate ones as the beam energy goes from 86 to 100 MeV.

A subset of the Eurogam array has been used to investigate the decay out of the superdeformed (SD) band in 194Pb. Two new band members and a new decay pattern into the low lying states at normal deformation (ND) have been established for this band. In the level scheme at normal deformation, the linking transitions between the previously known floating ΔI = 1 sequence and the lower states have been established for the first time. In this talk we will also report on the preliminary results of the search for the linking transitions between the SD and ND states in 192Hg with the fully operational EUROGAM array.

Paleohydrological changes in the area of the southern part of the Mozambique channel were studied on the basis of isotopic and microfaunal analysis and radiocarbon dating (on planktonic microfauna) of a Quaternary core spanning the last 25,000 years. The results permit tracing the history of changes in the environment and paleohydrology since the last glacial phase: strong oxygenation of the intermediate waters during the Dryas, greater than at present during the last glacial stage, slight oxygenation of the same waters during Termination lb and the base of the Holocene. The effect of influx of fresh water from the Zambezi River during the lower Holocene is evident.

The 99−105Tc isotopes have been produced at high spin as fission fragments following the fusion reaction 37Cl(170 MeV) + 176Yb and studied with the Euroball3 array. The high-spin structures of 103Tc have been identified for the first time. From the systematics of the yrast states of 97−105Tc, the location of individual proton states can be analyzed as a function of the neutron number.

International audience; A set of numerical equations is developed to estimate past sea surface temperatures (SST) from fossil Antarctic diatoms. These equations take into account both the biogeographic distribution and experimentally derived silica dissolution. The data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments. Factor analysis of 166 samples (124 Holocene core top and 42 artificial samples) resolved four factors. Three of these factors depend on the water mass distribution (one Subantarctic and two Antarctic assemblages); factor 4 corresponds to a “dissolution assemblage”. Inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of SST over a wide range of biosiliceous dissolution. A transfer function (DTF 166/34/4) is derived from the distribution of these factors versus summer SST. Its standard error is ± 1°C in the −1 to +10 °C summer temperature range. This transfer function is used to estimate SST changes in two southern ocean cores (43°S and 55°S) which cover the last climatic cycle. The time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios. The reconstructed SST records present strong analogies with the air temperature record over Antarctica at the Vostok site, derived from changes in the isotopic ratio of the ice. This similarity may be used to compare the oceanic isotope stratigraphy and the Vostok time scale derived from ice flow model. The oceanic time scale, if taken at face value, would indicate that large changes in ice accumulation rates occurred between warm and cold periods.

The distribution of terrigenous and carbonate absolute accumulation rates in the northeastern Atlantic during the last climatic cycle shows that climate and sediment accumulation are closely coupled, either directly or through oceanic circulation and eustatic variation. The strong contrast between the glacial and Holocene flux distribution is related to oceanic circulation changes: either surface circulation which governs both the ice-rafting supply and the planktonic biogenic production, or, more particularly, deep circulations via the reinitiation of the Iceland-Scotland overflow. Glacial erosion and the low sea-level stand enhance the terrigenous supply, but the Holocene deep circulation reinforcement leads to important material reworking. As a consequence, an almost constant average sediment flux is obtained (4g· −2 ·ky −1 during the Holocene, compared to 4.7 g·cm −2 ·ky −1 during the glacial period). During the Holocene period, the notable increase in mean carbonate flux (from 1.5 to 3 g·cm −2 ·ky −1 ) is associated with carbonate biogenic production, but the carbonate flux distribution shows the influence of redistributive agents. On margins, fluxes do not simply decrease from continental sources to the oceanic basin. Eustatic drops leads to a shift in the areas of preferential accumulation from the upper to the lower slope. During the deglacial warming period, the fluxes are respectively an average of two and three times higher than during the Holocene and the glacial periods. Their importance highlights the major impact of rapid climatic changes. Finally, local conditions — the location of terrigenous sources and the presence of contour currents — are among the many factors which will modify the trends observed on a global scale.

The distribution of planktic foraminiferal δ18O over the North Atlantic Ocean has been interpreted by Duplessy et al. (1991, 1992) in terms of the distribution of surface water salinity during the last glacial maximum (LGM) and the Younger Dryas (YD). We present here the implications of this surface salinity distribution for changes in deep convection during these periods. Temperature/salinity/density diagrams of the water column have been constructed using the plancktic and benthic foraminifera δ18O values together with sea surface temperature estimates obtained by using micropaleontological transfer functions. The precision of these reconstructions is limited by the remaining uncertainties in the two basic assumptions upon which the methods are based: — the sea surface temperature reconstruction by CLIMAP are valid within the statistical uncertainties; — the water salinity/δ18O relationship is well constrained for surface and intermediate ocean waters. A significant difference between the modern and the reconstructed glacial water structure is observed. During the LGM, the modern relatively warm and salty Norwegian Sea surface water and the North Atlantic Deep Water (NADW) were replaced by low salinity surface water in the northern Atlantic Ocean and the Norwegian Sea and cold deep water (0–1°C). However, surface water salinity in the central North Atlantic Ocean (52–54°N., 25–40°W.) was sufficiently high to permit deep water convection as a source of North Atlantic intermediate and deep waters. Open ocean convection at the northern limit of the subtropical surface waters (around 40°N.) may have contributed to the ventilation of the intermediate waters. The waters deeper than 2000 m were the result of mixing between poorly-oxygenated southern waters and well-ventilated North Atlantic deep waters. A similar reconstruction for the cold YD period indicates that the modern type of circulation, with warm and ventilated NADW, was largely in operation and that the hydrologic pattern was different from that prevailing during the LGM.

[1] Three highly resolved pollen and sea surface temperature records from the Iberian margin (36–42°N) reveal the local evolution of vegetation and climate associated with the rapid climatic variability of marine isotope stage 3. The comparison of the climate at these midlatitudes with δD and d excess from Greenland ice cores shows that the north-south climatic gradient underwent strong variations during the long Greenland Interstadials (GIs) 8 and 12. After the Northern Hemispheric rapid warming at the Greenland Stadial (GS)-GI transition, the trend during the first part of the GI is a Greenland cooling and an Iberian warming. This increase of the North Atlantic climatic gradient led to moisture transportation to Greenland from midlatitudes (lightest d excess) and to a drying episode in Iberia. The subsequent temperature decrease in Greenland and Iberia associated with the precipitation increase in the latter region occurred when the major source of Greenland precipitation shifted to lower latitudes (d excess increase).

Lateral transport of fine-grained organic carbon particles can complicate the interpretation of paleoclimate records based on organic proxies. Here we investigated the effect of lateral transport on newly developed temperature and soil organic matter proxies, TEX86 and BIT index, respectively, in core MD88–769 recovered from the South East Indian Ridge. Our results show that TEX86 and BIT records in comparison to diatom and foraminifera records were representative for more local climate changes while alkenones and n-alkanes originated from distant areas by oceanic and atmospheric transport, respectively. This suggests that TEX86 and BIT paleoclimate records are primarily influenced by local conditions and less subjected to long-distance lateral transport than other organic proxies in the Southern Ocean.

High resolution multiproxy analysis (microcharcoal, pollen, organic carbon, Neogloboquadrina pachyderma (s), ice rafted debris) of the deep-sea record MD04-2845 (Bay of Biscay) provides new insights for understanding mechanisms of fire regime variability of the last glacial period in western France. Fire regime of western France closely follows Dansgaard–Oeschger climatic variability and presents the same pattern than that of southwestern Iberia, namely low fire regime associated with open vegetation during stadials including Heinrich events, and high fire regime associated with open forest during interstadials. This supports a regional climatic control on fire regime for western Europe through fuel availability for the last glacial period. Additionally, each of Heinrich events 6, 5 and 4 is characterised by three episodes of fire regime, with a high regime bracketed by lower fire regime episodes, related to vegetational succession and complex environmental condition changes.

High-spin states have been studied in 101Tc produced as a fission fragment in the reaction 176Yb +28Si at 145 MeV. Gamma rays were detected with the EUROGAM2 array. The level scheme of 101Tc has been extended up to 4.2 MeV excitation energy and several band structures are observed. Configurations are assigned to two new bands on the basis of their behaviour and of cranked Hartree-Fock-Bogolyubov calculations.

The structure of N19-22 nuclei was investigated by means of in-beam gamma-ray spectroscopic technique using fragmentation reactions of both stable and radioactive beams. Based on particle-gamma and particle-gamma gamma coincidence data, level schemes are constructed for the neutron-rich nitrogen nuclei. The experimental results are compared with shell model calculations. The strength of the N=14 and Z=8 shell closures and the weakening of the shell model interaction WBT are discussed.

We present a new high-resolution marine pollen record from NW Iberian margin sediments (core MD03-2697) covering the interval between 340 000 and 270 000 years ago, a time period centred on Marine Isotope Stage (MIS) 9 and characterized by particular baseline climate states. This study enables the documentation of vegetation changes in the north-western Iberian Peninsula and therefore the terrestrial climatic variability at orbital and in particular at millennial scales during MIS 9, directly on a marine stratigraphy. Suborbital vegetation changes in NW Iberia in response to cool/cold events are detected throughout the studied interval even during MIS 9e ice volume minimum. However, they appear more frequent and of higher amplitude during the 30 000 years following the MIS 9e interglacial period and during the MIS 9a-8 transition, which correspond to intervals of an intermediate to high ice volume and mainly periods of ice growth. Each suborbital cold event detected in NW Iberia has a counterpart in the Southern Iberian margin SST record. High to moderate amplitude cold episodes detected on land and in the ocean appear to be related to changes in deep water circulation and probably to iceberg discharges at least during MIS 9d, the mid-MIS 9c cold event and MIS 9b. This work provides therefore additional evidence of pervasive millennial-scale climatic variability in the North Atlantic borderlands throughout past climatic cycles of the Late Pleistocene, regardless of glacial state. However, ice volume might have an indirect influence on the amplitude of the millennial climatic changes in Southern Europe.

Sea surface temperature and oxygen isotopic records from two well-dated Indian Ocean cores covering the last deglaciation show the occurrence of two periods of increased salinity along the route of warm surface water transport from the Indian to the Atlantic Ocean, one between 18 and 14.5 ka and the other during the Younger Dryas. Our results imply that during these periods, salt accumulated in the tropical Atlantic, creating favorable conditions for an abrupt resumption of the thermohaline circulation and abrupt northern hemisphere warming. Furthermore, we suggest that the observed pattern of millennial climate variability during the last glacial and deglaciation resulted from the interaction between the relatively slow rhythm of expansion and decay of the northern hemisphere ice sheets, and El Nino–Southern Oscillation variability, through changes in the position of the Intertropical Convergence Zone. This interaction generated an oscillator with millennial time response that operated at times of sufficient northern hemisphere ice sheets extent.

The comparison between modern terrestrial and marine pollen signals in and off western Iberia shows that marine pollen assemblages give an integrated image of the regional vegetation colonising the adjacent continent. Present-day Mediterranean and Atlantic forest communities of Iberia are well discriminated by south and north marine pollen spectra, respectively. Results from Total Pollen Concentration together with recognized conceptual models of fine particle dynamics in the Iberian margin have allowed us to establish the present-day pattern of pollen dispersion in this region. The 25 000 year-long record of continental (pollen) and marine ( δ 18 O of Globigerina bulloides , Ice-rafted detritus—IRD and Neogloboquadrina pachyderma s.) proxies, from the Galician margin composite core (MD99-2331 and MD03-2697), show that vegetation cover in north-western Iberia has responded contemporaneously to the climate variability of the North-Atlantic. The vegetation response to the well known North Atlantic Heinrich events 2 and 1 (H2 and H1) is however complex and characterised by two vegetation phases at low and mid-altitudes of north-western Iberia. The beginning of each Heinrich event is marked on land by an important pine forest reduction and the expansion of heathers which are synchronous with the heaviest planktic δ 18 O values and the maxima of N. pachyderma (s.) suggesting that these first phases were cold and wet. Pinus forest expansion characterising the second phase of each Heinrich event indicates a less cold episode associated, during H1, with an increase of dryness as suggested by the development of semi-desert associations. The comparison of our Galician margin multi-proxy record with several pollen sequences from in and off Iberia allows us to demonstrate that H1 event is the marine equivalent of the Oldest Dryas on the continent. The occurrence of temperate trees during the last glacial maximum (LGM) and the rapid expansion of deciduous Quercus during the Bolling-Allerod period in our Galician margin composite sequence show that not only the southern but also north-western Iberia was a refugium zone for deciduous trees during the last glacial period, especially at low and mid-altitude zones. Furthermore, the comparison between southern and northern marine and terrestrial sequences allows us to confirm that vegetation responded to the Bolling-Allerod warming, the Younger Dryas cold event and the Holocene more quickly in low and mid-altitudes of north-western Iberia and in the south than in the high altitude northern region most likely as the result of the higher density of refugia for temperate trees in these zones during the LGM.

Understanding the recent formation of a sedimentary system such as a deep-sea turbidite system (DSTS) requires an accurate stratigraphic control on deposits. Due to the important terrigeneous input which disrupts the sedimentary record, DSTS is an environment where stratigraphic control is difficult to assess. Most of the time, traditional stratigraphic tools are not accurate enough. This has led to a rather limited number of studies concerning stratigraphy in DSTS. In this study, we examine several hemipelagic long piston cores collected from the Nile DSTS (eastern Mediterranean), in order to understand the recent evolution of the complex sedimentary system in this area. The first aim of this study is to show how to obtain a reliable timeframe in DSTS. Indeed, we provided a detailed ecostratigraphical scheme based on planktonic foraminiferal distribution, oxygen isotope records and lithostratigraphy (sapropels and tephra) of three cores where the sedimentation is least disturbed. We have identified 29 foraminiferal ecozones during the last 250,000 years BP, with an approximately 2000-year time resolution. The time span of each ecozone was constrained by the oxygen isotope record, 14 C AMS radiometric data, tephrochronology and the sapropel chronology. These high-resolution ecostratigraphical time subdivisions have been applied in discontinuous mixed hemipelagic/turbiditic sequences of a levee record. This example shows how to date gravity events, formation and time periods of sedimentary accumulations.

The last five isotopic interglacials (marine isotope stages 11, 9, 7, 5 and 1) were investigated in Iberian margin deep-sea cores, using terrestrial (pollen) and marine (planktic foraminifera assemblages, benthic and planktic oxygen isotopes) climatic indicators. This work shows that the climatic variability detected on the continent is contemporaneously recorded in the ocean, but temperature changes are not in phase with ice volume variations. The comparison of the different marine isotope stages highlights a common pattern within these stages. They are characterized by three major climatic cycles, related to orbital cyclicity, on which suborbital climatic fluctuations are superimposed. Particularly, suborbital events interrupt the deglacial warming associated with Terminations IV to I and the second major warm period of each isotopic interglacial as well as the transitions towards glacial marine isotope stages. MIS 7 displays a short first warm period (8kyr) followed by a striking cold and dry period succeeded by a new strong warmth. In contrast, MIS 11 presents the longest period (31kyr) of the last 450000 years.

It has been proposed that tropical events could have participated in the triggering of the classic, high-latitude, iceberg-discharge Heinrich events (HE). We explore low-latitude Heinrich events equivalents at high resolution, in a piston core recovered from the tropical north-western African margin. They are characterized by an increase of total dust, lacustrine diatoms and fibrous lacustrine clay minerals. Thus, low-latitude events clearly reflect severe aridity events that occurred over Africa at the Saharan latitudes, probably induced by southward shifts of the Inter Tropical Convergence Zone. At a first approximation, it seems that there is more likely synchronicity between the high-latitude Heinrich Events (HEs) and low-latitude events (LLE), rather than asynchronous behaviours.

Paleoenvironmentat records in Europe describing paleofires extending back to the Last Interglacial have so far been unavailable. Here, we present paleofire results from the combined petrographic and automated image analysis of microcharcoal particles preserved in marine core MD95-2042 retrieved Off Southwestern Iberia and covering the last climatic cycle. The variability of inicrocharcoal concentrations reveals that the variability of fire emissions is mainly imprinted by the 23 000 yr precessional cycle. A focus on the Last Glacial Period further shows that paleofires follow the variability of Dansgaard-Oeschger oscillation and Heinrich events and, therefore, parallel the variability of atmospheric temperatures over Greenland detected in ice cores. There is no evidence for fire increase related to human activity. The variability of fire emission by-products for the Last Glacial Period is interpreted in terms of changes in biomass availability. Low fire activity is associated with periods of drought which saw the development of semi-desert vegetation that characterised stadial periods. Fire activity increased during wetter interstadials, related to the development of open Mediterranean forests with more woody fuel availability. (c) 2007 Elsevier Ltd. All rights reserved.

Spin and parity values of the states of two dipole bands in 194Pb have been determined from internal conversion and linear polarisation measurements. The multiparticle configurations assigned previously to these dipole bands are discussed within these results.

The high-spin normally deformed and superdeformed states of ${}^{194}\mathrm{Hg}$ have been populated in an exit channel of the ${}^{16}{\mathrm{O}+}^{186}\mathrm{W}$ reaction at 110 MeV bombarding energy. The Doppler shift analysis of the energies of the \ensuremath{\gamma} transitions de-exciting both normally deformed and superdeformed states in ${}^{194}\mathrm{Hg}$ indicates a lower recoil velocity of the ${}^{194}\mathrm{Hg}$ nucleus compared to that of the ${}^{196}\mathrm{Pb}$ nucleus obtained from the $6n$ exit channel of the complete-fusion compound nucleus. This suggests that incomplete fusion plays the main role in the population of normally deformed and superdeformed states of ${}^{194}\mathrm{Hg}$ in this reaction.

Nuclear structure of the neutron rich {sup 25-29}Ne nuclei has been investigated through the in-beam {gamma}-ray spectroscopy technique using fragmentation reactions of both stable and radioactive beams. Level schemes have been deduced for these Ne isotopes. In order to examine the importance of intruder fp configurations, they are compared to shell model calculations performed either in the restricted sd or in the larger sdpf valence space. The {sup 25,26}Ne and {sup 27}Ne nuclei were found to be in agreement with the sd shell model calculations, whereas {sup 28}Ne exhibits signatures of the intruder fp shell contribution.

The hydrological impact of the massive iceberg discharges during Heinrich events has been quantified for Heinrich 4 about 37 kyr ago. This event took place in a context of relatively stable orbital forcing and global ice volume. In this article, we propose to quantify the hydrological impact of the Heinrich event 1 which occurred at about 16 kyr BP. This time period is particularly interesting because orbital forcing was strong and it marks the onset of the last deglaciation. The results obtained here show that Heinrich event 1 has a larger isotopic amplitude than Heinrich event 4 when considering the cores located near the melting source. Concerning surface circulation, the northward progression of the North Atlantic Drift is affected only by Heinrich event 4, possibly because of the latitudinal extension of the melting area during this event., L’impact hydrologique des décharges massives d’icebergs liées aux événements de Heinrich a été quantifié pour l’événement de Heinrich 4, datant d’environ 37 ka BP, dans un contexte de relative stabilité des paramètres orbitaux et du volume global de glace. Dans cette note, nous proposons de quantifier l’impact hydrologique de l’événement de Heinrich 1, il y a 16 ka BP, qui s’est déroulé au début de la dernière déglaciation, sous des conditions de forçage orbital très différent. Les résultats montrent que l’amplitude isotopique de l’événement de Heinrich 1 est plus grande que celle de l’événement de Heinrich 4, lorsqu’on se place à proximité des sources de fonte. En revanche, la dérive nord-atlantique n’est affectée que pendant l’événement de Heinrich 4, vraisemblablement à cause de la disposition latitudinale de la langue de fonte pendant cet événement.