Jusqu’à ces dernières années, la chronologie des œuvres pariétales préhistoriques reposait surtout sur la méthode du carbone 14 par spectrométrie de masse par accélérateur, permettant de dater directement les dessins réalisées avec du charbon de bois (Arnold et al., 1987, Valladas et al., 2001). Pour les représentations non réalisées avec du charbon (oxyde de fer, gravures …), nous nous sommes intéressés à la datation des voiles de calcite recouvrant ces œuvres, ou à celle de leur support, afin de déterminer des bornes chronologiques « terminus ante ou post quem » pour leur réalisation.
Le travail méthodologique mis en œuvre a montré la nécessité de  réaliser des datations croisées en utilisant à la fois la méthode uranium-thorium (ou 230Th/234U) et celle du 14C sur ces dépôts carbonatés, afin de déterminer de possibles « ouvertures du système géochimique » ou au contraire pour valider les âges obtenus. Cette méthodologie a été appliquée à des œuvres de la grotte de Nerja dans le sud de l’Espagne, mais aussi à des œuvres des Montagnes du Huashan, dans le Sud de la Chine (voir figure 1).
A Nerja, nous avons déterminé que des marques rouges non figuratives sont plus anciennes que 25 000 ans et peuvent être associées avec une phase d’occupation ancienne connue de la grotte (entre 39,035 et 25,555 cal BP). La datation de voiles de calcites sur et sous les peintures des montagnes du Huashan a quant à elle permis de contraindre leur âge entre 1856 ± 16 and 1728 ± 41 ans BP, soit entre les années 25 à 220 de notre ère.

 

Références :

Valladas H, Pons-Branchu E., Dumoulin JP, Quiles A., Medina-Alcaide MA ; Sanchidrain JL. (2017) U/Th and C-14 cross dating of parietal calcite deposits: application to Nerja cave (Andalusia, Spain) and future perspectives. Radiocarbon  59 (6). 1955-1967. Doi:10.1017/RDC.2017.120
Shao Q., Pons-Branchu E.,  Zhu QP., Wei Wang W, Valladas H, Fontugne.M. (2017). High precision U/Th dating of the rock paintings at Mt. Huashan, Guangxi, southern China. Quaternary research, 88 (1) 1-13. Doi: 10.1017/qua.2017.24
Sanchidrián JL, Valladas H, Medina - Alcaide MA., Pons-Branchu E., Quiles A (2017) New perspectives for 14C dating of parietal markings using CaCO3 thin layers: an example in Nerja cave (Spain). Journal of Archaeological Science reports 12. pp 74-80. Doi:10.1016/j.jasrep.2017.01.028
Pons-Branchu E., Bourrillon R., Conkey M., Fontugne M., Fritz C., Gárate D., Quiles A., Rivero O, Sauvet G., Tosello G., Valladas H., White R. (2014). U-series dating of carbonate formations overlying Paleolithic art: interest and limitations. Bulletin de la Société préhistorique française, Tome 111, numéro 2, avril-juin 2014, p. 211-224. Doi: 10.3406/bspf.2014.14395

Arnold, M., E. Bard, P. Maurice & J.C. Duplessy. 1987. 14C dating with the Gif-sur-Yvette Tandetron accelerator: status report. Nuclear Instruments and Methods in Physics Research B29: 120-123.
Valladas H., Clottes J., Geneste J-M., Garcia M. A., Arnold M., Cachier H., Tisnérat-Laborde N., “Evolution of prehistoric cave art”. Nature 413, 4 October 2001, p. 479.

Soils are the major component of the terrestrial ecosystem and the largest organic carbon reservoir on Earth. However, they are a nonrenewable natural resource and especially reactive to human disturbance and climate change. Despite its importance, soil carbon dynamics is an important source of uncertainty for future climate predictions and there is a growing need for more precise information to better understand the mechanisms controlling soil carbon dynamics and better constrain Earth system models. The aim of our work is to compare soil organic carbon stocks given by different global and regional databases that already exist. We calculated global and regional soil carbon stocks at 1 m depth given by three existing databases (SoilGrids, the Harmonized World Soil Database, and the Northern Circumpolar Soil Carbon Database). We observed that total stocks predicted by each product differ greatly: it is estimated to be around 3,400 Pg by SoilGrids and is about 2,500 Pg according to Harmonized World Soil Database. This difference is marked in particular for boreal regions where differences can be related to high disparities in soil organic carbon concentration. Differences in other regions are more limited and may be related to differences in bulk density estimates. Finally, evaluation of the three data sets versus ground truth data shows that (i) there is a significant difference in spatial patterns between ground truth data and compared data sets and that (ii) data sets underestimate by more than 40% the soil organic carbon stock compared to field data.

Référence : Tifafi M., Guenet B., Hatté C., 2018. Large difference in global and regional total soil carbon stock estimates on SoilGrids, HWSD, and NCSCD: Intercomparison and evaluation based on field data from USA, England, Wales and FranceGlobal Biogeochemical Cycles 32, 42-56. Doi : 10.1002/2017GB005678

Thèse UVSQ ED129 et projet ANR DedyCAS

Quantification of paleoprecipitation during the Last Glacial is a key element to reconstruct palaeoclimates. Recently, fossil calcite granules have been identified in loess sequences with high contents in specific horizons. In this study, we explored for the first time the potential of this new bio-indicator as a climatic proxy for precipitation in western Europe during the Last Glacial. We extracted 30 granules from eleven samples belonging to three tundra gleys and two brown soils from the Nussloch loess sequence previously dated between 50 and 20 ka. Stable carbon isotope measurements were performed on each granule and duplicated. Throughout the studied section, d13C values range from -15.4 to -10.3‰ for tundra gleys and from -14.9 to -9.5‰ for brown soils. By taking into account the fractionation factor between the carbon ingested by the earthworm and the carbon output of the granules, the d13C values of these granules reflect the composition of the C3 plant vegetation cover. Thus, we estimated the d13C of the plants with a mean value of -24.3 ± 0.9‰ for tundra gleys and -24.1 ± 0.9‰ for brown soils, which are in agreement with values obtained from organic matter preserved in sediments. Palaeoprecipitation range over both tundra gley horizons and brown soils were estimated at about 333 [159-574] mm/yr by using an empirical relationship determined between present-day plant leaf isotopic discrimination and the mean annual precipitation. This original preliminary study highlights the potential of earthworm calcite granule d13C measurements as a new proxy for paleoprecipitation during the Last Glacial interstadials in continental environments.

Référence : Prud’homme C., Lécuyer C., Antoine P., Hatté C., Moine O., Fourel F., Amiot R., Martineau F., Rousseau D.-D., 2018. d13C signal of earthworm calcite granules: A new proxy for palaeoprecipitation reconstructions during the Last Glacial in western Europe. Quaternary Science Reviews 179, 158-166. Doi: 10.1016/j.quascirev.2017.11.017

Financé par ANR ACTES

Actu-terre-snowball_F-1.docx (120 Ko)

Quinze instruments de musique de l’Égypte ancienne ont été datés par le Laboratoire de mesure du carbone 14, en collaboration avec l’Institut français d’archéologie orientale du Caire et le CNRS (HiSoMA, UMR 5189). Ces instruments de musiques composent, parmi d’autres objets, la nouvelle exposition du Louvre-Lens « Musiques ! Échos de l’Antiquité  », un voyage passionnant à la découverte des musiques de l’Antiquité. .

Voir attaché

Contacts : LMC14 / LSCE-UMR 8212 : Lucile Beck et Emmanuelle Delqué-Količ ; IFAO :

A. Quiles ; CNRS UMR 5189 HiSoMA:

Sibylle Emerit (commissaire de l’exposition); musée du Louvre, département des Antiquités égyptiennes:

Hélène Guichard (commissaire de l’exposition)

http://www.snoeckpublishers.be/usite/snoeckpub_frbe/index.asp?p=914&c=T6&i=621

COMMUNIQUE_LMC14_v6b.docx (159 Ko)

Harpe14C.jpg

COMMUNIQUE_LMC14_v6.docx

Abstract: The transformation of snow into ice is a complex phenomenon which is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas-ice age difference is essential to document the phasing between CO₂ and temperature changes especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ¹⁵N of air measured in ice cores.

All firn densification models applied to deglaciations show a large disagreement with δ¹⁵N measurements in several sites of East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ¹⁵N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model-data mismatch for the gas trapping depth evolution over the last deglaciation at coldest sites of East Antarctica  while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ¹⁵N evolution  during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in coldest conditions. unless threshold effects are taken into account.

C. Bréant, P. Martinerie, A. Orsi, L. Arnaud and A. Landais

Reference :  Clim. Past, 13, 833-853, 2017, doi:10.5194/cp-13-833-2017

A 22.4 m-long shallow firn core was extracted during the 2006/2007 field season from coastal Adélie Land. Annual layer counting based on sub-annual analyses of δ¹⁸O and major chemical components was combined with 5 reference years associated with nuclear tests and non-retreat of summer sea ice to build the initial ice core chronology (1946-2006), stressing uncertain counting for 8 years. We focus here on the resulting δ¹⁸O and accumulation records. With an average value of 21.8±6.9 cm w.e. y^-1, local accumulation shows multi-decadal variations peaking in the 1980s, but no long-term trend. Similar results are obtained for δ¹⁸O, also characterized by a remarkably low and variable amplitude of the seasonal cycle. The ice core records are compared with regional records: temperature, stake area accumulation measurements, and variations in sea ice extent, and outputs from two models nudged to ERA atmospheric reanalyses: the high resolution atmospheric general circulation model (AGCM) including stable water isotopes ECHAM5-wiso and the regional atmospheric model MAR. A significant linear correlation is identified between decadal variations in δ¹⁸O and regional temperature. No significant relationship appears with regional sea-ice extent. A weak and significant correlation appears with Dumont d’Urville wind speed, increasing after 1979. The model-data comparison highlights the inadequacy of ECHAM5-wiso simulations prior to 1979, possibly due to the lack of data assimilation to constrain atmospheric reanalyses. Systematic biases are identified in the ECHAM5-wiso simulation, such as an over-estimation of the mean accumulation rate and its inter-annual variability, a strong cold bias, and an under-estimation of the mean δ¹⁸O value and its inter-annual variability. As a result, relationships between simulated δ¹⁸O and temperature are weaker than observed. Such systematic precipitation and temperature biases are not displayed by MAR, suggesting that the model resolution plays a key role

along the Antarctic ice sheet coastal topography.  Inter-annual variations in ECHAM5-wiso temperature and precipitation accurately capture signals from meteorological data and stake observations, and are used to refine the initial ice core chronology within 2 years. After this adjustment, remarkable positive (negative) δ¹⁸O anomalies are identified in the ice core record and the ECHAM5-wiso simulation, respectively in 1986 and 2002 (1998-99). Despite uncertainties associated with post-deposition processes and signal-to-noise issues in one single coastal ice core record, we conclude that the S1C1 core can correctly capture major annual anomalies in δ¹⁸O as well as multi-decadal variations. These findings highlight the importance of improving the network of coastal high resolution ice core records, and stress the skills and limitations of atmospheric models for accumulation and δ¹⁸O in coastal Antarctic areas, particularly important for the overall East Antarctic ice sheet mass balance.

Authors : S. Goursaud, V. Masson-Delmotte, V. Favier, S. Preunkert, M. Fily, H. Gallée, et al

Reference :  The Cryosphere, 11, 343-362, 2017, doi.org/10.5194/tc-11-343-2017

En datant par le ¹⁴C, les granules de vers de terre retrouvées dans une séquence de loess, une équipe pluridisciplinaire de chercheurs a permis de donner, pour la première fois, un cadre chronologique à toutes les phases de redoux de la dernière période glaciaire.

Alors que les événements de Dansgaard-Oeschger (succession de réchauffement (interstade)- refroidissement (stade) au cours de la dernière période glaciaire) ont été reconnus dans les carottes de glace et plusieurs carottes de sédiments marins, leur systématique présence et leur datation précise étaient encore à révéler sur le continent. C'est maintenant chose faite !  La séquence de loess de Nussloch (vallée du Rhin) était connue depuis plusieurs décennies comme l'enregistrement le plus complet de ces alternances climatiques du glaciaire, avec les phases de réchauffement caractérisées par des pseudo-sols, les gleys de toundra. Pendant les interstades, le développement des vers de terre s'est traduit par la présence d'excrétat carbonaté, les "granules". Tous les gleys ont été datés par datation ¹⁴C sur les granules. Tous les interstades enregistrés dans les glaces ont trouvé leur pendant sur le continent dans les gleys de Nussloch. Quelques horizons faiblement exprimés du Dernier Maximum Glaciaire se retrouvent même sans interstade contemporain au Groenland. Ces résultats révèlent la haute sensibilité des environnements loessiques aux changements climatiques glaciaires et une dynamique climatique plus complexe aux moyennes qu’aux hautes latitudes entre -27 000 et -20 000 ans. En perspective, cette étude ouvre les portes de reconsttitution des gradients paléoenvironnementaux régionaux, voire continentaux, propres à chaque fluctuation climatique glaciaire.

Toute la variabilité climatique du dernier glaciaire -  Moine

Coordination : Vaiedelich S., Hatté C.
Projet Ile de France – Domaine d’Intérêt Majeur "Patrimoine et Matériaux"

DatIM ambitionne de lever les verrous scientifiques liés au positionnement chronologique de l'instrumentarium en ajoutant la datation 14C à la palette d'approches classiquement utilisées. Au-delà de la poursuite de la construction d’une histoire de l’usage musical et des pratiques d’entretiens, de réparation ou de restaurations qui sont adressées à l’instrument de musique, elles consolideront l’émergence de concerts historiquement documentés, favorisant la valorisation des collections muséales ou privées. DatIM s'attachera à construire une chronologie autour de 3 corpus d'importance: 1- l'archet du XVIIème siècle et ses pratiques successives, 2- le clavecin et les questions de positionnement relatif dans le temps des éléments de caisse, de jeu et de piètements, 3- des luths emblématiques des XVI et XVIIème siècle et l'authenticité de leur barrage.
DatIM combine les expertises de 4 entités, 2 acteurs publics et 2 acteurs privés, et l'émergence d'une nouvelle génération d'appareils de mesure du 14C qui permet de travailler sur quelques 10µg de carbone (contre 1mg classiquement). Le croisement des expertises s'entend depuis la caractérisation in situ de l'échantillon, son prélèvement, la définition des contaminants potentiels et l'intégration de tous les indices chronologiques disponibles, relatifs et absolus, muséaux et physiques pour définir le cadre temporel de la vie des instruments. DatIM implique la muséologie, la caractérisation des matériaux, la chimie, la mesure physique et les statistiques bayesiennes. Au-delà des valorisations classiques sous forme d'articles ou de communications à destination des communautés 14C, muséale et de facture instrumentale, DatIM s'implique également dans la communication vers les professionnels de la facture instrumentale et les experts liés à ces objet anciens ainsi que vers le grand public, notamment dans le cadre des actions sur Paris-Saclay.

Contact : Christine Hatté

The eruption of Samalas in Indonesia in 1257 ranks among the largest sulfur-rich eruptions of the Common Era with sulfur deposition in ice cores reaching twice the volume of the Tambora eruption in 1815. Sedimentological analyses of deposits confirm the exceptional size of the event, which had both an eruption magnitude and a  7volcanic explosivity index.

During the Samalas eruption, more than 40 km³ of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km. However, the climatic response to the Samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of Northern Hemisphere summers than inferred from tree-ring-based temperature reconstructions.

Here, we draw on historical archives, ice-core data and tree-ring records to reconstruct the spatial and temporal climate response to the Samalas eruption. We find that 1258 and 1259 experienced some of the coldest Northern Hemisphere summers of the past millennium. However, cooling across the Northern Hemisphere was spatially heterogeneous. Western Europe, Siberia and Japan experienced strong cooling, coinciding with warmer-than-average conditions over Alaska and northern Canada. We suggest that in North America, volcanic radiative forcing was modulated by a positive phase of the El Niño–Southern Oscillation. Contemporary records attest to severe famines in England and Japan, but these began prior to the eruption. We conclude that the Samalas eruption aggravated existing crises, but did not trigger the famines.

Authors : Guillet S., Corona C. , Stoffel M., Khodri M. Lavigne F., Ortega P., Eckert N., Dkengne Sielenou P., Daux V.,…, Masson-Delmotte V.,…

 References :  Nature Geosciences 10, 123-128, 2017

Objectives: Stable isotope data provide insight into the reconstruction of ancient human diet. However, cooking may alter the original stable isotope compositions of food due to losses and modifications of biochemical and water components.

Methods: To address this issue, carbon, nitrogen and oxygen isotope ratios were measured on meat aliquots sampled from various animals such as pork, beef, duck and chicken, and also from the flesh of fishes such as salmon, European seabass, European pilchard, sole, gilt-head bream, and tuna. For each specimen, three pieces were cooked according to the three most commonly-known cooking practices: boiling, frying and roasting on a barbecue.

Results: Our data show that cooking produced isotopic shifts up to 1.8‰, 3.5‰ and 5.2‰ for δ¹³C, δ¹⁵N and δ¹⁸O values, respectively. Such variations between raw and cooked food are much greater than previously estimated in the literature; they are more sensitive to the type of food rather than to the cooking process itself, except in the case of boiling.

Conclusions: Reconstructions of paleodietary may thus suffer slight bias in cases of populations with undiversified diets that are restrained towards a specific raw or cooked product, or using a specific cooking mode. In cases of oxygen isotope compositions from skeletal remains (bones, teeth), they not only constitute a valuable proxy for reconstructing past climatic conditions, but they could also be used to improve our knowledge of past human diet.

Authors : Royer A., Daux V., Fourel F., Lécuyer C.

Reference : American Journal of Physical Anthropology , In Press, 2017

Abstract: The Arctic is among the fastest warming regions on Earth, but it is also one with limited spatial coverage of multi-decadal instrumental surface air temperature measurements. Consequently, atmospheric reanalyses are relatively unconstrained in this region, resulting in a large spread of estimated 30-year recent warming trends, which limits their use to investigate the mechanisms responsible for this trend.

Here, we present a surface temperature reconstruction over 1982-2011 at NEEM (51^∘ W, 77^∘ N), in North Greenland, based on the inversion of borehole temperature and inert gas isotope data. We find that NEEM has warmed by 2.7±0.33∘C over the past 30 years, from the long-term 1900-1970 average of -28.55±0.29^∘C. The warming trend is principally caused by an increase in downward longwave heat flux. Atmospheric reanalyses underestimate this trend by 17%, underlining the need for more in situ observations to validate reanalyses.

Authors : Anais J. Orsi, Kenji Kawamura, Valérie Masson-Delmotte, Xavier Fettweis, Jason E.Box, Dorthe Dahl-Jensen, Gary D. Clow, Amaelle Landais, Jeffrey P. Severinghaus

Reference :  Geophysical Research Letters, doi: 10.1002/2016gl072212, 2017

Abstract: Using  new  high-resolution ¹⁰Be  measurements in  the  NGRIP,  EDML  and  Vostok  ice  cores,  together  with previously  published  data  from  EDC,  we  present  an  improved synchronization between Greenland and Antarctic ice cores during the Laschamp geomagnetic excursion ∼41 kyr ago. We estimate the precision of this synchronization to be ± 20 years, an order of magnitude better than previous work.

La mesure des isotopes de l’eau dans des carottes de neige courtes est un outil primordial pour étudier la variabilité climatique récente en Antarctique. Encore faut-il pouvoir interpréter de façon quantitative ce signal en termes de variations de température. C’est dans ce but que Camille Bréant et Alexandra Touzeau sont parties en Antarctique prélever des échantillons et effectuer des mesures isotopiques. Les deux jeunes femmes étaient chacune à des endroits diamétralement opposés de l’Antarctique (cf carte) : Camille Bréant a déployé un analyseur de spectroscopie laser pour mesurer en continu la composition isotopique de la vapeur sur le site côtier de Dumont d’Urville pendant qu’Alexandra Touzeau a participé à la campagne Kohnen 2016-2017 et a effectué des traverses de plusieurs centaines de kilomètres sur la partie Atlantique du plateau Est-Antarctique pour récolter plus de 40 carottes de neige superficielles de 1 à 200 m chacune.

Abstract: Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (dD or d¹⁸O) in ice cores are often taken as reference for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rate. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs.

We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data:

1-            The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meter depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs d¹⁸O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (~ 0.7-0.8 ‰.°C^-1 for d¹⁸O vs temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46 ‰.°C^-1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer.

2-            Post-deposition effects linked to exchanges between the snow surface and the atmospheric

water vapor lead to an evolution of d¹⁸O in the surface snow even in the absence of any precipitation event. This evolution preserves the positive correlation between d¹⁸O of snow and surface temperature but is associated with a much slower d¹⁸O vs temperature slope than the slope observed in the seasonal precipitation.

3-            Post-deposition effects clearly limit the archiving of high resolution (seasonal) climatic variability in the polar snow but we suggest that sites with an accumulation rate of the order of 40 kg.m^-2.yr^-1 may record a seasonal cycle at shallow depth. .

Authors  : A. Landais, M. Casado, F. Prié, O. Magand, L. Arnaud, A. Ekaykin et al.

Reference :  Comptes-Rendus Geosciences, accepté

Immigration and mobility in the mediaeval and post-mediaeval periods in Norway has, up until now, mainly been discussed on the basis of historical sources. This paper presents the results of stable oxygen isotope (d¹⁸O) analyses of the 1^st and 3^rd molars from 95 individuals from mediaeval and post-mediaeval Trondheim, as well as new information about the d¹⁸O composition in the precipitation and drinking water in Trondheim. Through these analyses, the authors have attempted to shed light on the age of migrating individuals and directions of the migrations, investigate temporal changes with regard to migration, as well as making suggestions regarding the proportion of immigrants to locals in the population.

Used alone, the isotopic compositions of O and H in ice give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. Recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. The signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. We look at the relationship between isotopes and tempera-ture, using results from 3 traverses across Antarctica. We take advantage of these measures to see how 2nd-order parameters (d-excess, ¹⁷O-excess) are related to δ¹⁸O. d-excess increases in the interior of the continent, due to the distillation process, whereas ¹⁷O-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. The slope of the δ¹⁸O vs. temperatu-re relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The 2nd-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation is complicated by local temperature effects in East Antarctica. We then check if the same relationships between δ¹⁸O and 2nd-order parameters are found in the snow from four snow pits. While the d-excess remains opposed to δ¹⁸O in most snow pits, the ¹⁷O-excess is no longer positively correlated to δ¹⁸O and even shows anti-correlation to δ¹⁸O at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.

Authors : A.    Touzeau, A. Landais, B. Stenni, R. Uemura et al.

ref. : The Cryosphere, Vol. 10, pages 837-852.

The production of hydrogen by serpentinization in ultramafic-hosted hydrothermal systems is simulated by coupling thermodynamic and dynamic modeling in the framework of a thermo-hydraulic single-pass model where a high-temperature hydrothermal fluid moves preferentially through a main canal of high permeability. The alteration of ultramafic rocks is modeled with a first-order kinetic formulation, wherein the serpentinization rate coefficient, K_r, takes the form: K_r = A exp(-α(T-T₀)²). In this formulation, α determines the temperature range of the reaction and T₀ is the temperature at which the serpentinization rate reaches its maximum. This model is applied to the Rainbow hydrothermal system, which is situated on the Mid-Atlantic Ridge, and characterized by a high temperature, a high mass flux, and a very high hydrogen concentration. The results show that a first-order kinetic law gives a useful representation of the kinetics of serpentinization. The estimated value for the parameter A in the temperature-dependent formulation of the serpentinization rate coefficient lies in the range (1–5)x10^-11 s^-1. This effective parameter is several orders of magnitude lower than the values obtained from small grain-size experiments, but in agreement with other published modeling studies of natural systems. Numerical simulations show that the venting site is able to produce the observed high concentration of hydrogen during the whole continuous lifetime of the Rainbow site.

 Human occupation in Europe strongly fluctuated over the Quaternary. Archaeological records suggest an intermittent human occupation in Western Europe between 900 and 500 ka, especially in the north of Europe at latitude higher than 45°N. On the opposite, southern Europe, more stable from a palaeoenvironmental point of view, was occupied continuously. This period is followed by a more widespread and dense occupation over the last 450 ka. In parallel, the last 900 ka are characterized by global climatic oscillations and display shifts between glacial/drier and interglacial/wetter periods that modulate the general repartition of fauna and flora. The pacing of these climatic periods is well recorded in numerous palaeoclimatic archives that provide global as well as regional information concerning past climatic and environmental changes. A transition is observed from 1.25 Ma until up to 450 ka (Mid-Pleistocene Revolution) with a change of the dominant periodicity of climate cycles from 41ka to 100 ka in the absence of substantial change in orbital forcing. After 450 ka, the amplitude between glacials and interglacials increases. The change in periodicity since 450 ka corresponds to a change in the density of human occupations as well as the Acheulean technoculture expansion in Europe. There is a general perception that these climatic and environmental oscillations have played a role in human occupation and his morphological evolution. For instance, temperate environments might have favored permanent occupations or occupations over larger territories with long periods dominated by dry meadows and steppes and followed by the expansion of broadleaf deciduous and confireous forests. Testing this hypothesis for the period encompassing 900 to 500 ka is a challenge because of the lack of a common chronological framework between climatic/environmental archives and sites of human occupation, but also because archaeological records are only snapshots of cultural and morphological changes of hominins.

Authors : AM.-H. Moncel, A.Landais, V. Lebreton, N. Combourieu-Nebout, S. Nomade, L. Bazin

Ref. : Quaternary International, dx.doi.org/10.1016/j.quaint.2016.09.065.

  Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ¹⁸O_calc and δ¹³C_calc) are regularly used to reconstruct paleoenvironmental conditions. The δ¹⁸O_calc values mainly reflect the oxygen isotope composition of the waters ingested by birds (δ¹⁸O_w), which in turn are controlled by local climatic parameters (air temperature, local humidity), whereas the δ¹³C_calc value provides information on birds foraging environment as well as local relative humidity. However, the interpretation of δ¹⁸O_calc values of fossil eggshells is limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids and drinking water have not been determined yet. For this purpose, eggshells, albumen and drinking water of extant birds have been sampled and analyzed for their oxygen and carbon isotope compositions. Enrichments in ¹⁸O relative to ¹⁶O between body fluids and drinking water of +2.2±0.4 ‰ for semi-aquatic birds and of +4.1 ±0.5‰ for terrestrial birds are observed. Using our dataset and published values, two empirical equations relating the δ¹⁸O_calc value of eggshell calcite to the δ¹⁸O_w value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to two cases of fossil eggshells from Lanzarote, Canary Islands, in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene of Valle Grande. Both δ¹⁸O_calc and δ¹³C_calc of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater with a δ¹⁸O_w value -0.6±0.3‰. In the case of the Pliocene giant bird, low δ¹³C_calc values of eggshells point to a terrestrial lifestyle and the δ¹⁸O_calc values allowed us to calculate an ingested local freshwater δ¹⁸O_w value of -2.8±0.3‰.  This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental (marine or freshwater) or climatic (local air temperatures, precipitations) conditions.

Authors : N. Lazzerini , C. Lécuyer, R. Amiot, D. Angst, E. Buffetaut, F.  Fourel , V. Daux  et al.

Ref. :  Sci. Nature 103:81

This study is the first presenting annually resolved chronologies of both δ¹⁸O and δ¹³C in Nothofagus pumilio and Fitzroya cupressoides trees from Northern Patagonia. Interannual variability in δ¹⁸O and δ¹³C was assessed over the period 1952-2011. Based on these chronologies, we determined the primary climatic controls on stable isotopes and tree physiological responses to changes in atmospheric CO₂ concentrations (c_a), temperature and humidity. Changes in specific intrinsic water use efficiency (iWUE) were inferred from variations in δ¹³C whereas the effects of CO₂ increase on stomatal conductance were explored using δ¹⁸O. Over the 60-year period, iWUE increased significantly (by ca. 25%) in coincidence with the rise of c_a. The two species appear to have different strategies of leaf gas-exchange. Whereas iWUE variations were likely driven by both stomatal conductance and photo-synthetic assimilation rates in Fc, they were largely related to stomatal conductance in Np. After removing the low-frequency trends related to increasing c_a, significant relation-ships between δ¹³C and summer temperatures were recorded for both species.  However, δ¹³C variations in Fc were more strongly influenced by summer temperatures than in Np Our results advocate for an indirect effect of summer temperatures on stable isotope ratios, which are mostly influenced by sunlight radiation in Fc and relative humidity/soil moisture in Np. δ¹³C variations in Fc were spatially correlated to a large area south of 35°S in southern South America. These promising results encourage the use of δ¹³C variations in Fc for reconstructing past variations in temperature and large-scale circulation indexes such as the Southern Annular Mode.

Authors : A. Lavergne, V. Daux V., R. Villalba , M. Pierre, M. Stievenard, A. Srur

Au cours des 40 dernières années, la recherche sur les carottes de glace a produit des résultats de référence pour l’évolution de la température polaire et de la composition atmosphérique au cours des 800 000 dernières années sur les échelles de temps orbitales et millénaires. Plus récemment, des progrès ont été faits dans la datation cohérente des carottes de glace en intégrant des marqueurs stratigraphiques et une méthode d’analyse bayésienne. Ces progrès permettent de compiler facilement les différents enregistrements issus des carottes de glace. Les avancées récentes dans l’analyse et la datation des carottes de glace ont permis de mieux documenter le déphasage entre augmentation de température et augmentation de concentration de dioxyde de carbone dans l’atmosphère. Lors des deux dernières déglaciations, il est maintenant établi que les augmentations initiales de concentration atmosphérique en dioxyde de carbone et température antarctique sont synchrones à ± 200 ans. Les mesures à haute résolution dans les carottes de glace et les efforts de datation relative entre Groenland et Antarctique permettent d’étudier les processus à l’œuvre lors de la variabilité millénaire de la dernière période glaciaire. En plus du phénomène de bascule bipolaire, il a été mis en évidence récemment une variabilité climatique régionale en Antarctique lors de ces événements millénaires.

Enfin, les carottes de glace apportent aussi des informations pertinentes pour l’étude du système couplé climat – calotte de glace dans un contexte de température plus élevée. Les reconstructions récentes du dernier interglaciaire à partir des carottes de glace groenlandaises indiquent en effet une température d’environ 8°C plus élevée qu’à l’actuel au Groenland.

Author : A. Landais

Ref. : Quaternaire, Vol. 27, pages 197-212.

As part of its ongoing project on repositories for high-activity, long-lived radioactive waste, a 2000 m deep borehole was drilled by the French Nuclear Waste Agency (ANDRA) in the layered structure of alternating aquifers and aquitards of the Eastern Paris Basin. Among the information retrieved from this borehole, the vertical distribution of chloride in porewaters showed that, in addition to vertical diffusion, lateral advection in the aquifers plays a major part in transporting chlorine away from the study area. Helium concentrations were also measured in porewaters along the borehole. Because the helium input function is different from that of chlorine, it represents an excellent alternative tracer to further constrain transport characteristics. We applied an advection–diffusion model to the helium profiles with the appropriate source term for ⁴He based on U–Th measured concentrations of uranium and thorium. ⁴⁰Ar/³⁶Ar data, which were available along the whole sequence, were also simulated. The modelled and measured ⁴He profiles were in good agreement, indicating that the transport parameters used for the chlorine simulations were robust. ⁴⁰Ar/³⁶Ar simulations also gave coherent results and confirmed that most of the radiogenic ⁴⁰Ar remained trapped in the rocks (primarily in clays and feldspars).

 Authors : P. Jean-Baptiste, B. Lavielle, E. Fourré, T. Smith, M. Pagel

Ref : Geological Society Special Publications 443.

In palaeoclimate reconstructions, the combination of proxy records measured in different climate archives is challenging because of the uncertainties associated with each proxy, but it can also help reduce some of these uncertainties. Here, we present a novel approach to combine speleothem and tree ring proxies for a drought reconstruction of the last 640 years: a fluid inclusion δ¹⁸O record from a stalagmite from Villars Cave (southwest France) and a tree ring cellulose δ¹⁸O record of Quercus spp. from the nearby Angoulême area. The δ¹⁸O of the fluid inclusions is taken as an estimate of the δ¹⁸O of the trees’ source water. Then, the cellulose and source water δ¹⁸O are used to calculate the leaf water isotopic enrichment, as well as relative humidity, which is the dominant controlling factor of this enrichment.

This article presents a reconstruction of summer droughts in France based on annually resolved, absolutely dated chronologies of oxygen isotope ratios (δ¹⁸O) in tree ring cellulose from Quercus spp. Samples were taken from living trees and timber wood from historic buildings at two sites: Fontainebleau (48°23’ N, 2°40’ E; 1326–2000 CE) and Angoulême (45°44’ N, 0°18’ E; 1360–2004 CE). Cellulose δ¹⁸O from these sites proved to be a good proxy of summer climate, as the trees were sensitive to temperature and moisture availability. However, offsets in average δ¹⁸O values between tree cohorts necessitated a correction before joining them to the final chronologies. Using the corrected δ¹⁸O chronologies, we developed models based on linear regression to reconstruct drought, expressed by the standardized precipitation evapotranspiration index (SPEI). The significant correlations between the SPEI and cellulose δ¹⁸O (r=0.70), as well as the verification of the models by independent data support the validity of these reconstructions. At both sites, recent decades are characterized by increasing drought. Fontainebleau displays dominantly wetter conditions during earlier centuries, whereas the current drought intensity is not unprecedented in the Angoulême record. While the δ¹⁸O chronologies at the two studied sites are highly correlated during the 19th and 20th centuries, there is a significant decrease in the correlation coefficient between 1600 and 1800 CE, which indicates either a weaker climate sensitivity of the tree ring proxies during this period, or a more heterogeneous climate in the north and the south of France. Future studies of tree ring isotope networks might reveal if the seasonality and spatial patterns of past droughts can explain this decoupling.

 Authors : I. Labuhn, V. Daux, O. Girardclos, M. Stievenard, M. Pierre, V. Masson-Delmotte

Ref. : Climate of the Past, 12, 1101–1117.

Very little is known about Neanderthal cultures, particularly early ones. Other than lithic implements and exceptional bone tools, very few artefacts have been preserved. While those that do remain include red and black pigments and burial sites, these indications of modernity are extremely sparse and few have been precisely dated, thus greatly limiting our knowledge of these predecessors of modern humans. Here we report the dating of annular constructions made of broken stalagmites found deep in Bruniquel Cave in southwest France. The regular geometry of the stalagmite circles, the arrangement of broken stalagmites and several traces of fire demonstrate the anthropogenic origin of these constructions. Uranium-series dating of stalagmite regrowths on the structures and on burnt bone, combined with the dating of stalagmite tips in the structures, give a reliable and replicated age of 176.5 thousand years (±2.1 thousand years), making these edifices among the oldest known well-dated constructions made by humans. Their presence at 336 metres from the entrance of the cave indicates that humans from this period had already mastered the underground environment, which can be considered a major step in human modernity. The attribution of the Bruniquel constructions to early Neanderthals is unprecedented in two ways. First, it reveals the appropriation of a deep karst space (including lighting) by a pre-modern human species. Second, it concerns elaborate constructions that have never been reported before, made with hundreds of partially calibrated, broken stalagmites (speleofacts) that appear to have been deliberately moved and placed in their current locations, along with the presence of several intentionally heated zones. Our results therefore suggest that the Neanderthal group responsible for these constructions had a level of social organization that was more complex than previously thought for this hominid species.

Authors : J. Jaubert, S. Verheyden, D. Genty, M. Soulier, Hai Cheng, D. Blamart et al.

ref : Nature, Vol. 534, pp. 111-115

In this article, we present a first synthesis of the chronology of Cussac Cave (Dordogne, SW France). This deep cavern (1.6 km), discovered in 2000, is very well preserved (e.g. intact floors) and thus favorable to research, especially given its rare association of parietal art and human remains, deposited in at least three locations. The scientific team working since 2009 presents here a first diachronic reconstruction of the natural (geological, biological) and anthropogenic (cultural, spiritual) elements relevant to the sectors of the cave accessible for study.

In addition to the nuclear dating methods commonly used in karst contexts and decorated sites (U–Th and ¹⁴C for speleothems, ¹⁴C-AMS for organic materials, bone and charcoal), we drew upon other disciplines to determine the relative chronology of the events that occurred in the cave: geosciences (karstology, sedimentary geology, geoarchaeology), biological anthropology, paleontology, zooarchaeology, anthracology, ichnology, lithic and osseous technology, and of course, the study of parietal art. Their integrated study enabled us to define a coherent and global chronological framework. The results confirm that bears frequented the cavity several times before any human incursions. Humans later ventured into the cave after it had already undergone several phases of karstogenesis, collapse, sedimentation, erosion and concretion formation. The nuclear methods and relative dating methods employed concur in favor of the hypothesis of human incursions only during the Middle Gravettian period, approximately 28–29,000 cal BP, to carry out spiritual, graphic and sepulchral activities. After the cave was abandoned by Gravettian people, some final sedimentary and biological events occurred (partial flooding, concretion formation, presence of mesofauna and microfauna, etc.), but were insufficient to significantly modify the decorated and sepulchral sanctuary. Later human frequentations (Late Glacial, Late Magdalenian, Late Neolithic) are quantitatively anecdotal and, most importantly, were limited to the cave porch and vestibular areas, which were sealed-off from the internal zone by rockfall debris and Late Glacial or Holocene concretion formations

Authors : J. Jaubert, D. Genty, H.Valladas, P. Courtaud, C. Ferrier, V. Feruglio…

ref. : Quaternary International (Available online 12 April 2016)

Past climate is an important benchmark to assess the ability of climate models to simulate key processes and feedback. Model–data comparisons can help to constrain the uncertainties associated with transfer functions. We have put together a global database of proxy records of oxygen (d¹⁸O), hydrogen (dD) and carbon (d¹³C) stable isotopes from different archives: ocean and lake sediments, corals, ice cores, speleothems and tree-ring cellulose. Source records were obtained from the georeferenced PANGAEA and NOAA libraries, complemented by additional data obtained from a literature survey. About 3000 source records were screened for chronological information and temporal resolution of proxy records. Altogether, this database consists of hundreds of dated d¹⁸O, d¹³C and dD records in a standardized simple text format, comple-mented with a metadata Excel catalog. This compilation effort highlights the need to homogenize and structure the format of datasets and chronological information as well as enhance the distribution of published datasets that are currently highly fragmented and scattered. In the last part, we illustrate the type of application allowed by our database by comparing several key periods highly investigated by the paleoclimate community. We focus on records spanning the past 200 years, the mid-Holocene (MH, 5.5–6.5 ka; calendar kiloyears before 1950), the Last Glacial Maximum (LGM, 19– 23 ka), and those spanning the last interglacial period (LIG, 115–130 ka). Basic statistics have been applied to characterize anomalies between these different periods. Most changes from the MH to present day and from LIG to MH appear statistically insignificant. Significant global differences are reported from LGM to MH with regional discrepancies in signals from different archives and complex patterns.

Pour l’instant, l’application de la théorie des valeurs extrêmes était limitée aux systèmes qui décrivent la dynamique d’un point dans le temps. Ce cadre est utile pour étudier des phénomènes physiques localisés comme par exemple les extrêmes de température atmosphérique mesurés à un endroit spécifique. Cependant, il n’existe pas de théorie pour étudier la dynamique chaotique des systèmes spatialement étendus, ce qui est pertinent pour modéliser plusieurs extrêmes géophysiques comme les tempêtes extratropicales étendues sur une surface des plusieurs milliers de Km. Etant donné que la dynamique détermine la récurrence des observations, nous avons étudié plusieurs classes des systèmes d’un point de vue théorique et numérique, en déterminant les conditions nécessaires pour l’application de la théorie des valeurs extrêmes quand la dynamique est perturbé avec du bruit stochastique [1]. Ce cadre est pertinent aux applications géophysiques ou la turbulence à petite échelle ainsi que l’incertitude sur les mesures jouent le rôle du bruit.  Nous avons transformés ces théorèmes mathématiques en outils numériques qui nous ont permit de caractériser les récurrences des champs de pression atmosphérique de 1948 jusqu'au aujourd'hui [2]. Cet étude démontre que les extrêmes géophysiques sont origines par des extrêmes des systèmes dynamiques. Les métriques des systèmes dynamiques nous permettent de déterminer la rareté et la prédictibilité des champs de circulation atmosphérique  avant  de faire un modèle de prévision météorologique. L’analyse d’un champ journalier demande seulement un second sur un ordinateur portable. Les résultats pour l’Atlantique du Nord sont  régulièrement
mise à jour a cet adresse.

[1] Valerio Lucarini, Davide Faranda, Ana Cristina Gomes Monteiro Moreira de Freitas,Jorge Miguel Milhazes de Freitas, Mark Holland, Tobias Kuna, Matthew Nicol, Mike Todd, Sandro Vaienti. Book: Extremes and Recurrence in Dynamical Systems. ISBN 978-1-118-63219-2, 312 pages, Wiley, 2016.

[2] Davide Faranda, Gabriele Messori and Pascal Yiou. Dynamical proxies of North Atlantic predictability and extremes. Scientific Reports, 7-41278, 2017.

Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000 years. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (~400 ka ago) were globally strong (warm), while MIS 13a (~500 ka ago) was cool at many locations. A step change in strength of interglacials at 450 ka is apparent only in atmospheric CO₂ and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid nonlinear reactions of ice volume, CO₂, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10–30 ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.

Authors : A. Berger, A. Landais, … V. Masson-Delmotte et al.

Ref. : Reviews of Geophysics, Vol. 54 Reviews of Geophysics, Vol. 54

During the austral summer 2016-17, an infrared spectrometer monitoring water stable isotopes in the vapour has been deployed by Camille Bréant from LSCE (Laboratoire des Sciences du Climat et de l’Environnement, Paris, France) at the coastal station of Dumont d’Urville in East Antarctica (see Fig. 1). This campaign has provided continuous measurements of isotopic composition of the water vapour for 40 days, showing important diurnal cycles (up to 5‰ in δ¹⁸O) which differs from all other coastal records from Polar Regions (see Fig. 2). Important precipitation events are also imprinted in the records.  

Storms and tsunamis, which may seriously endanger  human  society,  are  amongst  the  most  devastating  marine catastrophes that can occur in coastal areas. Many such events are known  and have been reported  for the Mediterranean, a region where high-frequency occurrences of these extreme events coincides with some of the most densely populated coastal areas in the world. In a sediment core from the Mar Menor (SE Spain), we discovered eight coarse-grained layers which document marine incursions during periods of intense  storm  activity  or  tsunami  events.  Based  on  radiocarbon dating, these extreme events occurred around 5250, 4000,  3600,  3010,  2300,  1350,  650,  and  80  years  cal BP. No comparable events have been observed during the 20thand  21st  centuries.  The  results  indicate  little  likelihood  ofa  tsunami  origin  for  these  coarse-grained  layers,  although historical tsunami events are recorded in this region. These periods  of  surge  events  seem  to  coincide  with  the  coldest periods  in  Europe  during  the  late  Holocene,  suggesting  acontrol  by  a  climatic  mechanism  for  periods  of  increased storm activity. Spectral analyses performed on the sand percentage  revealed  four  major  periodicities  of  1228±327, 732±80, 562±58, and 319±16 years.

Very little is known about Neanderthal cultures1, particularly early ones. Other than lithic implements and exceptional bone tools2, very few artefacts have been preserved. While those that do remain include red and black pigments3 and burial sites4, these indications of modernity are extremely sparse and few have been precisely dated, thus greatly limiting our knowledge of these predecessors of modern humans5. Here we report the dating of annular constructions made of broken stalagmites found deep in Bruniquel Cave in southwest France. The regular geometry of the stalagmite circles, the arrangement of broken stalagmites and several traces of fire demonstrate the anthropogenic origin of these constructions. Uranium-series dating of stalagmite regrowths on the structures and on burnt bone, combined with the dating of stalagmite tips in the structures, give a reliable and replicated age of 176.5 thousand years (±2.1 thousand years), making these edifices among the oldest known well-dated constructions made by humans. Their presence at 336 metres from the entrance of the cave indicates that humans from this period had already mastered the underground environment, which can be considered a major step in human modernity.

Human occupation in Europe strongly fluctuated over the Quaternary. Archaeological records suggest an intermittent human occupation in Western Europe between 900 and 500 ka, especially in the north of Europe at latitude higher than 45°N. On the opposite, southern Europe, more stable from a palaeoenvironmental point of view, was occupied continuously. This period is followed by a more widespread and dense occupation over the last 450 ka. In parallel, the last 900 ka are characterized by global climatic oscillations and display shifts between glacial/drier and interglacial/wetter periods that modulate the general repartition of fauna and flora. The pacing of these climatic periods is well recorded in numerous palaeoclimatic archives that provide global as well as regional information concerning past climatic and environmental changes. A transition is observed from 1.25 Ma until up to 450 ka (Mid-Pleistocene Revolution) with a change of the dominant periodicity of climate cycles from 41ka to 100 ka in the absence of substantial change in orbital forcing. After 450 ka, the amplitude between glacials and interglacials increases. The change in periodicity since 450 ka corresponds to a change in the density of human occupations as well as the Acheulean technoculture expansion in Europe. There is a general perception that these climatic and environmental oscillations have played a role in human occupation and his morphological evolution. For instance, temperate environments might have favored permanent occupations or occupations over larger territories with long periods dominated by dry meadows and steppes and followed by the expansion of broadleaf deciduous and confireous forests. Testing this hypothesis for the period encompassing 900 to 500 ka is a challenge because of the lack of a common chronological framework between climatic/environmental archives and sites of human occupation, but also because archaeological records are only snapshots of cultural and morphological changes of hominins.

M-H.Moncel, A.Landais, V.Lebreton, N.Combourieu-Nebout

Reference :  Quaternary International, dx.doi.org/10.1016/j.quaint.2016.09.065, 2016

Abstract The soil memory recorded in paleosols of loess-paleosol sequences is an important contributor to our understanding of past climatic conditions. Molecular proxies based on the organic matter preserved in paleosols form an essential part of this record, but the long-term preservation of SOM is poorly understood, especially for sediment traps and slope profiles. This paper addresses the composition of organic material from the Early Weichselian A-horizons of the Rocourt paleosol, a major paleostratigraphic marker for the Eemian and Early Weichselian in Western Europe. NaOH-extractable organic matter from an exceptionally thick Rocourt profile in the Kesselt Quarry (Belgian Loess Belt) was analyzed by pyrolysis-Gas Chromatography/Mass Spectrometry (pyrolysis-GC/MS) and the results evaluated against paleopedological data. The molecular composition of the organic matter at Kesselt was compared with reference samples from two nearby quarries (including the type locality at Veldwezelt-Hezerwater), and to a sample from the contemporary Nussloch sequence in Germany. The SOM composition found at the four sites indicated a large content of microbial matter and was dominated by carbohydrates and N compounds, many of which were not reported before from SOM pyrolysates. Differences in the molecular composition between samples, both within profiles and between sites, coincided with differences in landscape position (slope-shoulder-plateau) and fossil redox conditions (surface gleys). Samples form drier and more upland situations contained more burnt material, while samples from slope profiles and surface gleys contained even more microbial material, in particular chitin. Results therefore suggest that the admixture of microbial SOM is considerable in loess-paleosols and that differences in edaphic conditions (in particular slope position and soil moisture) and occurrence of wildfires are important for the long-term preservation of SOM. These should therefore be considered when interpreting biogeochemical proxies.

K.Vancampenhout , J.Schellekens , J.Slaets , C. Hatté , P. Buurman

 (2016) Quaternary International 418, 105-115.

PURPOSE Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified.

MATERIALS AND METHODS In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on ¹³⁷Cs, ²¹⁰Pb(xs), and meteoric ¹⁰Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusionadvection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including ¹³C and ¹⁴C isotopes) and of the 0–2-μm particles with the data.

RESULTS AND DISCUSSION We showed that (i) the model satisfactorily reproduces the organic carbon, ¹³C, and ¹⁴C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies.

As part of its ongoing project on repositories for high-activity, long-lived radioactive waste, a 2000 m deep borehole was drilled by the French Nuclear Waste Agency (ANDRA) in the layered structure of alternating aquifers and aquitards of the Eastern Paris Basin. Among the information retrieved from this borehole, the vertical distribution of chloride in porewaters showed that, in addition to vertical diffusion, lateral advection in the aquifers plays a major part in transporting chlorine away from the study area. Helium concentrations were also measured in porewaters along the borehole. Because the helium input function is different from that of chlorine, it represents an excellent alternative tracer to further constrain transport characteristics. We applied an advection–diffusion model to the helium profiles with the appropriate source term for ⁴He based on U–Th measured concentrations of uranium and thorium. ⁴⁰Ar/³⁶Ar data, which were available along the whole sequence, were also simulated. The modelled and measured ⁴He profiles were in good agreement, indicating that the transport parameters used for the chlorine simulations were robust. ⁴⁰Ar/³⁶Ar simulations also gave coherent results and confirmed that most of the radiogenic ⁴⁰Ar remained trapped in the rocks (primarily in clays and feldspars).

P. Jean-Baptiste, B. Lavielle, E. Fourré, T. Smith, M. Pagel

Geological Society Special Publications 443, (2016) 2017

RATIONALE: Compound-specific stable carbon isotope analysis by GC/C/IRMS is widely used in studies of environmental or biological functioning. In the case of derivatized molecules, a calibration might be required due to added non-analyte carbon and in some cases non-stoichiometric recovery by the mass spectrometer.

METHODS: Two biological materials of known isotopic composition were produced by microbial cell cultures on either ¹³C-labelled glucose or non-labelled glucose as sole source of carbon. Subsequent hydrolyzed amino acids were derivatized as tert-butyldimethylsilyl (tBDMSi) derivatives and analyzed by GC/C/IRMS. The ¹³C-enrichment measurements were used as a direct calibration to calculate the original ¹³C/¹²Cratios of individual amino acids.We tested this calibration on both known and unknown samples.

RESULTS: For the main proteinogenic amino acids we could determine the number of non-analyte added carbon atoms and assess the non-stoichiometrical recovery of tBDMSi carbon atoms, due to their incomplete oxidation in the combustion step of GC/C/IRMS. The calibration enabled the determination of the natural abundances (d¹³C values) of amino acids with an average accuracy of ±1.1‰.

Loess–paleosol sequences in the Vojvodina region in the southeastern Carpathian Basin have been intensively studied to obtain a high-resolution stratigraphical framework for the Upper Pleistocene in this part of Europe. In these studies, millennial-scale sedimentation variations in the Upper Pleniglacial have been coupled to the Greenland Ice dust record, indicating that the rapid climate variability characterizing the North Atlantic and Greenland areas, is reflected in the loess deposits at the southern edge of the European loess belt. Rapid variations were recently also reported for the stable isotopic composition of organic matter in the Surduk loess-paleosol sequence, located in the Vojvodina region, andwere interpreted as episodes of increased C4-vegetation over the last glacial period. Based on potential coinciding changes in oceanic and atmospheric circulation patterns, these episodes were attributed to plant moisture stress rather than by fluctuations in temperature, although exclusive proof has not yet been provided. Herewe report a high-resolution record of continental air temperature and precipitation over the past 40,000 years based on soil bacterial lipid signatures preserved in the Surduk loess–paleosol sequence.

The Nussloch loess–palaeosol sequence (Rhine Valley, Germany) is considered to be one of the most complete records of the last glacial period in Western Europe due to its very high sedimentation rate and its good chronological control. This sequence is therefore a good framework in which to develop new proxies for palaeoenvironmental reconstructions. In this study, we explore, for the first time, the potential of earthworm calcite granules as a new bio-indicator and climatic proxy of absolute air and soil temperature in the context of Last Glacial loess. These granules are composed of rhomboedric calcite crystals, organized in a radial crystalline structure. As these granules are individually generated by earthworms at a relative fast rate, they are expected to record intra-annual variations in the available sources of oxygen: percolating waters of meteoric origin. We extracted thirty earthworm calcite granules from 11 of 5 cm layers thick from tundra gley and brown soil horizons previously, dated at 45 to 23ka.

Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow.

Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for one month in December-January 2014-2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading to this isotopic composition.

Mathieu Casado,  Amaelle Landais  , Valérie Masson-Delmotte, Christophe Genthon,  Erik Kerstel, Samir Kassi, Laurent Arnaud, Ghislain Picard, Frederic Prie, Olivier Cattani, Hans-Christian Steen-Larsen, Etienne Vignon, Peter Cermak

Atmospheric Chemistry and Physics, Vol. 16, pages 8521-8538, 20163

Abstract: Au cours des 40 dernières années, la recherche sur les carottes de glace a produit des résultats de référence pour l’évolution de la température polaire et de la composition atmosphérique au cours des 800 000 dernières années sur les échelles de temps orbitales et millénaires. Plus récemment, des progrès ont été faits dans la datation cohérente des carottes de glace en intégrant des marqueurs stratigraphiques et une méthode d’analyse bayésienne. Ces progrès permettent de compiler facilement les différents enregistrements issus des carottes de glace. Les avancées récentes dans l’analyse et la datation des carottes de glace ont permis de mieux documenter le déphasage entre augmentation de température et augmentation de concentration de dioxyde de carbone dans l’atmosphère. Lors des deux dernières déglaciations, il est maintenant établi que les augmentations initiales de concentration atmosphérique en dioxyde de carbone et température antarctique sont synchrones à ± 200 ans. Les mesures à haute résolution dans les carottes de glace et les efforts de datation relative entre Groenland et Antarctique permettent d’étudier les processus à l’œuvre lors de la variabilité millénaire de la dernière période glaciaire.

Abstract: Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using δ¹⁸O_atm, δO₂⁄N₂ and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of δO₂∕N₂ and δ18Oatm data encompassing Marine Isotopic Stage (MIS) 5 (between 100 and 160 ka) and the oldest part (340–800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of δO₂∕N₂ and δ¹⁸O_atm records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights some site-specific δO₂∕N₂ variations. Such an observation, the evidence of a 100 ka periodicity in the δO₂∕N₂ signal and the difficulty to identify extrema and mid-slopes in δO₂∕N₂ increase the uncertainty associated with the use of δO₂∕N₂ as an orbital tuning tool, now calculated to be 3–4 ka. When combining records of δ¹⁸O_atm and δO₂∕N₂ from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (∼ 400 ka, ∼ 720–800 ka). Our data set reveals a time-varying offset between δO₂∕N₂ and δ¹⁸O_atm records over the last 800 ka that we interpret as variations in the lagged response of δ¹⁸O_atm to precession. The largest offsets are identified during Terminations II, MIS 8

Abstract: The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process.